sistema de fallas guayape honduras

8/13/2019 Sistema de Fallas Guayape HONDURAS

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0 1 0 0 )KMFig. 3. Major drainages affected by the Guayape fault system

s h o w e d a s e g m e n t o f t h e G F S b u t n o t t h e f u lls t r u c t u r e T h e G F S s h o w n o n E l v i r ' s ( 1 9 7 4 ) g e o l o g i cm a p o f H o n d u r a s i s s c h e m a t i c a n d i s b a s e d o n m a j o rd r a i n a g e p a t t e r n s , t h e m o s t o b v i o u s m a n i f e s t a t i o n o ft h e s y s t e m ( F i g . 3 ). T h i s r e p r e s e n t a t i o n o f t h e G F S i s

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Fig. 4. Sico Valley portion of the Guayape fault system: AC, Agua Caliente; GF, main Guayape fau lt; MK, Mariana k ink; PR, PapaRay s house; S, town of Sico. Known faults are shown as solid lines; probable faults identified from topographic and photo-line amen ts are shown as dashed lines.


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The Guayape fault system, Honduras, Central America 47Guayape fault on his geologic map of Honduras, bu the did not incorporate it into his general geologic mapof Central America.Muehlberger (1976) utilized topographic mapsand available geologic data to define a number oftectonic features, including his cross -Hondu rasCholuteca-Guayape trend. He noted that this trendand several other major fractures that mark theboundaries of tectonic blocks appear to radiate fromthe Gulf of Fonseca. He postulat ed a northwardcomponent of movement on the Chortis block east ofthe Honduras Depression (Fig. 1), resulting in somesinistral slip on the graben-bounding faults of thedepression. This reasoning also implies sinistral slipalong the Guaya pe trend. Sutch's (1979) inter-pretation of the Choluteca-Guayape str uctur e as athrough-going fault zone appears to be based onMueh lberger' s paper. Cur ran (1980, his Fig. 25) alsoshowed the GFS-Choluteca lineament as a through-going feature transecting the isthmus and separatingmajor basement blocks (his Olancho and Moraz~nblocks on the west, from his Mosquitia block on theeast). Curr an suggested that the GFS is at present anormal fault. Burkart and Self (1985) also showedthe GFS-Choluteca lineament as a through-goingfeature, again repeating Elvir's (1974) approximaterepre sentat ion of the fault. They also suggested thatthe Guayape fault has undergone about 50 kilo-meters of sinistral slip, as determined by offsets intopography.More recently, Manton (1987) showed the Gua-yape fault as a sinistral fault, disconnected from theCholu teca fract ure zone. In contras t, Gordon andMuehlberger (1988) viewed the GFS as transectingthe entire isthmus and they presented evidence fordext ral slip. Gordon (1987a) has proposed that theGFS-Choluteca lineament has had a two-phasehistory -- an earlier sinistral phase followed by aneotectonic dextral phase. Gordon (1990) made adetailed s tudy of the GFS and its associated struc-tures in the Catacamas Valley area.This paper is an amplification and modification ofour previous work (Ritchie and Finch, 1984, 1989). Itis based on data collected on a reconnaissance tripmade in 1983, during the course of field work for theGove rnment of Honduras in 1984, 1986, and 1987,and map and aerial photograph interpretation ofthose sections of the GFS that we were unable to visiton the ground.

LOCATION, EXTENT, AND DESCRIPTIONOF THE GUAYAPE FAULT SYSTEMFigu re 2 is a simplified map of the GFS and close-ly related faults and fractures compiled from topo-

graphic maps, aerial photography and reconnais-sance, and field work. In this section we describe theGFS in eight segments, commencing at the northcoast.The northernmost onshore or Sico Valley portionof the GFS (Fig. 4) may be conveniently described in

two segments, the Rio Sico and Sico to Rio Payasegments, extending from the coast to the confluenceof the Rio Paya with the Rio Paulay a, a distance ofabout 55 kin. Access to this part of the GFS is ve rydifficult, and most of the following description is theresult of topographic and photol ineament inte rpr e-tation, supplemented by helicopter reconnaissancemade possible by the Fuer za A~rea Hondurefia.Rio Sico Segment Fig. 4)

The Rio Sico (also known as the Rio Tinto orNegro) enters the Sico Valley from the north east at ahot spring site (Helbig, 1959) known as E1 AguaCaliente. Although this site is an isolated knobseparated by some 2 km from the main topographicfront which forms the no rthea st wall of the SicoValley, it is directly in line with this impressive scarpand may be considered the northernmost point atwhich the main Guayape fault retains a markedtopographic expression. The hot spr ings he re arepresumed to issue from fracture s in the GFS. The RioSico enters the Sico Valley at right angles to thevalley wall, at a point where the valley widens andbecomes less well defined. The Sico's course here isprobably controlled by a cross-fracture.Northwar d from E1 Agua Caliente, the mai n Gua-yape fault can be projected as a weaker topographicand photolineament for 10-11 km, paralleled to thesoutheast (within the valley) by a photolineament ofnearly equal length. Fart her to the north along theprojection of the GFS, the valley is floored with coast-al swamps and jungle-covered alluviated savannahs;however, the last 4 km of the Rio Clau ra to its mouthlie very nearly along this projection, and the rivercourse here may mark the trace of the GFS as itpasses out to sea. Upstream from this nearly s traight4-km segment, the Claura has a typical meanderingpattern that passes within 1.5 km of the modern RioSico. Although the Claura is an insignificant s trea mcompared to the Sico, its delta is bigger than that ofthe larger river and forms the prominent coastalbulge just west of the mouth of the Sico (Figs. 3 and4). The Rio Claura appears to be an abandoned lowerSico stream course - - abandoned as the Sico shifted tothe southeast side of the Sico Valley. This sh ift islikely the result of downdropping of the sou thea stside of the Sico Valley. The beach ridge morphologyof the Claura delta is still p romine ntly visible inaerial photographs, indicating that the delta switch-ing event was relatively recent. Another featu resuggesting relatively recent derangement of theformer drainage system is a small stream that flowsparallel to the upper Claura for over 5 km but in theopposite direction, south westward , to join the Sico.The Rio Sico, after turning to the northeast,gradually approaches the highly irregular southeastside of the valley. Here its course is influenced bybedrock knobs that rise above the otherwise fiatvalley fill. These knobs are probably eroded f aul tblocks in the shatter ed southea st valley wall. Wehave mapped a number of lineam ents here, repre-


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50 R . C . F INCH and A. W. RITCHIEs e n t i n g a t l e a s t t h r e e d i s t i n c t s e t s o f f r a c t u r e s - - o n es e t t r e n d i n g N 4 0 E ( p a r a ll e l t o t h e m a i n G u a y a p ef a u l t ) , o n e t r e n d i n g N 7 7 E , a n d a m i n o r s e t t r e n d i n gN 6oW .

R e c e n t m o v e m e n t w i t h in t h i s c o m p l e x o f f a u l tb l o c k s is i n d i c a te d b y a n a b a n d o n e d m e a n d e r l o op o ft h e R i o S ic o , w h i c h p a s s e s t h r o u g h a s m a l l V - s h a p e dv a l l e y b e t w e e n t w o k n o b s t h a t a r e 2 1 a n d 9 5 m h i g h .T h e m e a n d e r a p p e a r s t o h a v e b e e n a b a n d o n e d d u e t ou p l i f t o f t h e f a u l t b l o ck u n d e r l y i n g t h e k n o b s . P o i n tb a r r i d g e a n d s w a l e t o p o g r a p h y s t i l l e v i d e n t o n t h ei n s i d e o f t h e m e a n d e r s h o w s t h a t t h e a b a n d o n m e n t i sr e c e n t .S i c o t o R i o P a y a S e g m e n t F i g . 4 )

S o u t h w a r d f r o m t h e t o w n o f S i co , t h e S ic o V a l l e yi s d r a i n e d b y th e R i o P a u l a y a , a m a j o r t r i b u t a r y t ot h e R i o S i co . I n t h i s s e g m e n t t h e v a l l e y i s o f m o r eu n i f o r m w i d t h , a v e r a g i n g a b o u t 6 - 7 k m a c r o s s , w i t h ,a s to t h e n o r t h , t h e n o r t h w e s t e r n w a l l b e i n g s h a r p l yd e f i n e d a n d t h e s o u t h e a s t e r n m a r g i n m o r e i rr e g u l a r .F r o m E l A g u a C a l i e n t e t h e v a l l e y w a l l r u n s 1 8 k m i na n e a r l y s t r a i g h t l i n e $ 4 3 - 5 00 W , t h e e s c a r p m e n tg r o w i n g f r o m z e r o r e l i e f j u s t s o u t h w e s t o f E1 A g u aC a l i e n t e k n o b t o g r e a t e r t h a n 3 0 0 m 6 k m t o t h es o u t h w e s t . A n im p r e s s i v e , s h a r p t o p o g r a p h i c s c a r pc h a r a c t e r i z e s t h e n o r t h w e s t w a l l o f t h e S i co V a l le yf o r t h e r e s t o f t h i s s e g m e n t , a n d t h e r e i s n o d o u b t t h a ti t m a r k s t h e m a i n G u a y a p e f au l t . O n l y a v e r y f ewp h o t o l i n e a m e n t s s u g g e s t p a r a l l e l a n d s u b p a r a l l e lf r a c t u r e s i n t h e t e r r a n e l y i n g w e s t o f t h i s e s c a r p m e n t .A t a p o i n t w e c a ll t h e M a r i a n a k i n k , 1 8 k ms o u t h w e s t o f E 1 A g u a C a l i e n t e , t h e S i co v a l l e y w a l l /m a i n G u a y a p e f a u l t m a k e s a s h a r p 3 0 b e n d ( Fi g. 4 ).S o u t h w a r d f r o m t h i s p o i n t t h e v a l l e y w a l l / m a i n f a u l tt r e n d s $ 22 -2 5W q f o r 1 6 k m t o t h e R i o P a y a . T h e t o p o -g r a p h i c e s c a r p m e n t b e c o m e s e v e n m o r e s h a r p l yd e f i n e d i n t h i s s e c t i o n , w i t h r e l i e f u p t o 5 0 0 m . A t t h eM a r i a n a k i n k w e fo u n d n o e v i d e n c e i n th e t o p o -g r a p h y o r p h o t o l i n e a m e n t s t h a t e i t h e r o f t h e c o n -t r a s t i n g m a i n f a u lt t r e n d s e x t e n d s b e y o n d t h e i rj u n c t i o n . A g r o u p o f p h o t o l i n e a m e n t s c r o s s i n g t h eR i o S i co w e s t o f E 1 A g u a C a l i e n t e m a y r e p r e s e n t a no l d c o n t i n u a t i o n o f t h e m o r e n o r t h e r l y t r e n d , b u t t h em o s t r e c e n t a c t i v i t y o n t h e G F S a p p e a r s t o m a k e ac l e a n t re n d c h a n g e a t t h e M a r i a n a k i n k

O u r i n t e r p r e t a t i o n o f t h e S i c o V a l l e y i s t h a t i t i s as t r i k e - s l i p b a s i n ( C h r i s t i e - B l i c k a n d B i d d l e , 1 9 8 5 )c r e a t e d b y p r i m a r i l y d e x t r a l s l ip o n t h e m a i nG u a y a p e f a u l t s o u t h o f t h e M a r i a n a k i n k , n e c e s s i -t a t i n g a p r o m i n e n t c o m p o n e n t o f n o r m a l s l ip o n t h a tp o r t i o n o f t h e f a u l t b e t w e e n t h e k i n k a n d t h e c o a s t( F i g. 4) . T h e n o r t h w e s t w a l l o f t h e v a l l e y , c o n t r o l l e db y t h e m a i n f a u l t , is s h a r p l y d e f i n e d a n d n e a r l yc o n t i n u o u s, w i t h a n a p p a r e n t d o w n t h r o w t o t h es o u t h e a s t . T h e s o u t h e a s t s i d e o f t h e v a l l e y is m o r eb r o k e n u p , a s w o u l d b e e x p e c t e d i n a c o m p l e x o fn o r m a l f a u l t b l o c k s c o ll a p s i n g i n t o t h e o p e n i n g b a s i n .T h e p r e f e re n c e o f t h e R i o P a u l a y a a n d t h e d o w n -s t r e a m p o r t i o n o f t h e R i o Si co fo r th e s o u t h e a s tm a r g i n o f t h e S i c o V a l l e y p r o b a b l y i n d i c a t e s t h a t t h e

s t r u c t u r a l l o w p o i n t is t o w a r d t h i s m a r g i n , a n d i t m a yb e d u e to a c o m p o n e n t o f u p l i f t o n t h e n o r t h w e s t s i d eo f t h e m a i n f a u l t o r t o p r o g r e s s i v e d o w n f a u l t i n g o fb l o c k s a l o n g t h e s o u t h e a s t s i d e a s t h e b a s i n h a sg r o w n .T h e t o p o g r a p h y c h a n g e s c o m p l e t e l y s o u t h o f t h eS i co V a l l e y , w i t h j u n g l e - c o v e r e d m o u n t a i n o u s t e r r a i no n b o t h si d e s o f t h e G F S . A g a i n , a c c e s s p r o b l e m sl i m i t o u r d i s cu s s i o n p r i m a r i l y t o m a p a n d p h o t o i n t e r -p r e t a t i o n , s u p p l e m e n t e d b y s c a t t e r e d h e l i c o p t e r l a n d -i n g i n s p e c t i o n s .R iv P a y a t o P a u l a y a - W a m p u D r a i n a g e D i v i d eS e g m e n t F i g s. 4 a n d 5 )

T h e Ri o P a y a j o in s t h e P a u l a y a j u s t s o u t h o fP a p a R a y ( F ig . 4 ). F r o m h e r e s o u t h w a r d , t h e Si c oV a l l e y c l o s es ra p i d ly . T h e c o u r s e o f t h e l o w e r P a y a ,w h i c h m a y b e f r a c t u r e c o n t r o l l e d , e s s e n t i a l l y m a r k st h e s o u t h e r n t e r m i n u s o f t h e v a l l e y a s a m a j o rt o p o g ra p h ic f e a tu r e . H o w e v e r , t h e m a i n G u a y a p ef a u l t is s t i l l c l e a r l y e x p r e s s e d a s a p r o m i n e n tt o p o g r a p h i c l i n e a m e n t t h a t c o n t i n u e s $ 2 5 W n e a r l yu n b r o k e n f o r 4 0 k m t o t h e l o w d i v i d e s e p a r a t i n g t h eP a u l a y a a n d W a m p f i d r ai n a g e s .S o u t h of w h e r e t h e R i o P a y a c r o s s e s t h e m a i nf a u l t, to p o g r a p h i c a n d p h o t o l i n e a m e n t s t o t h e w e s t o ft h e m a i n t r a c e s u g g e s t t h e p r e s e n c e o f a n o r t h -c o n v e rg i n g f a n o f a t l e a s t f iv e m o r e - n o r t h e a s t e r l y -t r e n d in g s p l a y s o f f t h e m a i n fa u l t . A l t e r n a t i v e l y ,t h e s e f r a c t u r e s c o u l d b e c o n t i n u a t i o n s o f t h e n o r t h -e a s t e r l y - tr e n d i n g f r a c t u r e s t h o u g h t t o c o n t r o l t h el o w e r c o u r s e o f t h e R i o P a y a a n d t h e s o u t h e r n t e r -m i n u s o f t h e S ic o V a l l e y . T o p o g r a p h i c e x p r e s s i o n o ft h e m a i n f a u l t i s s l i g h t l y d i s c o n t i n u o u s i n t h i s z o n e ,b u t q u i c k l y r e g a i n s i t s f i r m e x p r e s s i o n t o c r o s s t h es u c c e e d i n g 1 9 k m a s a s e r i e s o f a l i g n e d ( o f f s e t ? )s t r e a m s e g m e n t s , n a r r o w l i n e a r v a l l e y s , a n d s h u t t e r -r id g e s . S e g m e n t s o f t h e R i o P a u l a y a a n d m a n y o f i t st r i b u t a r i e s f o l l o w t h e m a i n f a u l t t r ac e . T h e u p s t r e a mp o r ti o n s o f t h e C a t a c a m a s - G u a y a b o d r a i n a g e s a p p e a rt o b e o ff s e t s i n i s t r a ll y , b u t t h i s m a y b e o n l y a p p a r e n ti n a s m u c h a s t h e s e s t r e a m s a r e f o r c e d t o f o l lo w a l o n gt h e m a i n f a u l t b y t h e C e r r o P o r t i l lo d e W i l l a n d i t su n n a m e d n o r t h e r n c o n t i n u a t i o n , w h i c h f o r m a k n i f e -e d g e b e d r o c k s h u t t e r r i d g e 1 0 0 -1 5 0 m e t e r s h i g h a n df ou r km long ( F ig . 5 ) .T h r o u g h o u t m o s t o f t h i s s e c t io n t h e t o p o g r a p h y i sv a r i a b l e a n d r u g g e d o n b o t h s i d e s o f t h e m a i n f a u l t .T h e r e s e e m t o b e n o m a j o r d i f f er e n c e s i n t h e g e n e r a le l e v a t i o n s o n o n e s i d e o f t h e f a u l t a s c o m p a r e d t o t h eo t h e r ; h o w e v e r , w h e r e t h e r e a r e d i f f e r e n c e s , t h es o u t h e a s t s i d e i s t h e l o w e r .T h e R i o P a u l a y a f o l lo w s th e m a i n f a u l t f o r o n l y1 6 k m n o r th f r o m t h e P a u l a y a - W a m p 6 d i v i d e .F a r t h e r t o t h e n o rt h i t d i v e r g e s g r a d u a l l y e a s t w a r df ro m t h e m a i n f a u lt u n ti l a t i t s j u n c t i o n w i t h t h eP a y a i t l ie s 4 .5 k m e a s t o f t h e m a i n e s c a r p m e n t . T h eP a u l a y a i n t h i s s e c t i o n i s s o m e w h a t e n t r e n c h e d i n t ot h e f l o o r o f a p o o r l y - d e f i n e d o l d e r v a l l e y u p t o 1 k mw i d e. M u e h l b e r g e r (p e t s . c o m m . , 1 9 8 2 ) h a s i n t e r -p r e t e d s o m e o f t h i s l o w e r to p o g r a p h y a s t h e r e s u l t o f


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T h e G u a y a p e f a u l t s y s t e m , H o n d u r a s , C e n t r a l A m e r i c a 5 1d o w n d r o p p i n g d u e t o s m a l l d e x t r a l p u l l -a p a r t s. T h eo v e r a l l t r e n d o f t h e r i v e r i n t h i s s e c t i o n i s N 3 0 -3 5 E ,a n d i t p r o j e c t s d i r e c t l y i n t o t h e g e n e r a l t r e n d o f t h eP a u l a y a i n t h e S i c o V a l l e y t o t h e n o r t h - - t h a t i s t os a y , th i s s e c t i o n o f t h e P a u l a y a a l i g n s g e n e r a l l y w i t ht h e f a u ~ .c d s o u t h e a s t m a r g i n o f t h e S i c o V a l l e y .R i o W a m p u - R i o T i n t o S e g m e n t F ig . 6 )

T h e R i o T i n t o i s a t r i b u t a r y t o t h e R i o G u a y a p e ,d r a i n i n g t h e s o u t h e r n 4 5 k m o f a m a j o r f a u l t -c o n t r o l l e d v a l l e y t h a t e x t e n d s f o r 7 7 k m N 3 5 E f r o mt h e c o n f l u e n c e o f t h e T i n t o w i t h t h e G u a y a p e n e a r t h ec i t y o f C a t a c a m a s ( F i g s. 6 a n d 7 ). T h i s v a l l e y v a r i e sf r o m 4 to 1 3 k m w i d e . T h e n o r t h e r n p a r t o f t h e v a l l e yi s d r a i n e d b y t h e R i o s W a m p 6 a n d P a u l a y a . A s i n t h ec a s e o f t h e S i c o V a l le y , t h e n o r t h w e s t e r n v a l l e y w a l li s t h e b e t t e r d e f i n e d , w i t h t h e s o u t h e a s t e r n w a l lb e i n g m o r e i r r e g u l a r o r , i n p l a c e s , o b s c u r e . I n t h en o r t h e r n p a r t o f t h e v a l l ey , t h e v a l l e y f lo o r s l o p e st o w a r d t h e s o u t h e a s t a n d i s c o v e r e d w i t h a l l u v i u md e r i v e d p r i m a r i l y f r o m T e r t i a r y t u ft s . T h i s al l u v i a lc o v e r a p p e a r s t o b e th i n , a n d b e d r o c k e x p o s u r e sb e c o m e i n c r ea s i n g l y p r o m i n e n t t o w a r d s t h e s o u t hw h e r e M e s o z o i c c l a s ti c a n d c a r b o n a t e s t r a t a a n d T e r -t i a r y ( ? ) a s h - f l o w a n d a i r - f a l l t u f t s o f t h e C a m p a n t e p ev o l c a n i c r o c k s ( G o r d o n , 1 9 9 0 ) a r e e x p o s e d i n t h ev a l l e y f l o o r. F o r p u r p o s e s o f t h i s d i s c u s s i o n , w e r e f e rt o t h e s o u t h e r n p o r t i o n o f t h i s l o n g f a u l t -c o n t r o l l e dv a l l e y a s t h e T i n t o V a l l e y , a n d t o t h e n o r t h e r np o r t i o n a s t h e C u l m i V a l l e y , a f t e r t h e t o w n o f D u lc eN o m b r e d e C u l m i , t h e o n l y s i z e ab l e t o w n w i t h i n t h i sr e m o t e v a l l e y .

C u l m i V a l le y P o r ti o n o f t h e R i o W a m p u - R i o T i n t oS e g m e n t . T h e h e a d w a t e r s o f t h e P a u l a y a m i n i m a l l yc u t i n t o t h e C u l m i V a l l e y , d r a i n i n g o n l y a b o u t 2 5 k m 2o f t h e n o r t h e r n m o s t p a r t o f t h e v a l l e y , p l u s t h e i m -m e d i a t e l y a d j a c e n t m o u n t a i n s ( F ig . 6 ). T h e P a u l a y a -W a m p f i d r a i n a g e d i v i d e is a l ow , a s y m m e t r i c a l r i d g ew i t h v e r y g e n tl e s l o p es on th e W a m p 6 s i d e b u td r o p p i n g s t e e p l y f o r a b o u t 8 0 m e t e r s o n th e P a u l a y as i d e. C l e a r l y , th e P a u l a y a i s a c t i v e l y p i r a t i n g t r i-b u t a r i e s t h a t f o r m e r l y b e l o n g e d t o t h e W a m p f i . T h i sh e a d w a r d e x t e n s i o n o f t h e P a u l a y a i n to t h e C u l m iV a l l e y h a s t a k e n p l a c e a l o n g t h e m a i n G u a y a p e f a u l tt r a c e .I m m e d i a t e l y s o u t h o f t h e P a u l a y a - W a m p 6 d r ai n -a g e d i v id e , t h e m a i n t r a c e o f t h e G u a y a p e m a k e s ar i g h t - s t e p p i n g t r a n s f e r , w i t h t h e r e s u l t t h a t t h ev a l l e y w a l l a n d m a i n f a u l t t r a c e a r e p o o r l y d e f i n e d f o ra d i s t a n c e o f 5 -6 km . S o u t h w a r d f r o m t h i s s t e p o v e rt h e m a i n t r a c e i s c l e a r l y d e f i n e d f o r 1 5 k m , t o a p o i n tw h e r e a s m a l l l e f t- s t e p p i n g t r a n s f e r o c c u rs . C r e t a -c e o u s l i m e s t o n e a n d T e r t i a r y v o l c a n i c r o c k s a r e e x -p o s e d i n t h e v a l l e y w a l l, j u x t a p o s e d a g a i n s t y o u n g e rt u f f a c e o u s v a l l e y f il l. I m m e d i a t e l y s o u t h o f t h e s h o r t ,l e f t - s t e p p i n g t r a n s f e r , t h e v a l l e y s u d d e n l y n a r r o w sf r o m 1 2 t o 5 k m . T h i s n a r r o w i n g i s d u e i n sm a l l p a r tt o t h e s t e p t o w a r d s t h e v a l l e y m a d e b y t h e m a i n t r a ce ,b u t i t is d u e p r i m a r i l y t o th e o c c u r r e n c e o f a r o u g h l yr e c t a n g u l a r f a u l t b lo c k j u t t i n g o u t f ro m t h e s o u t h e a s t

v a l l e y w a l l. T h i s b l o c k i s c o m p o s e d i n p a r t o f T e r -t i a r y t u f t s .

J u s t n o r t h o f t h e p o i n t w h e r e t h e v a l l e y n a r r o w s ,a n o t h e r l o w d i v i d e c r o s se s t h e v a l l e y f lo o r t o s e p a r a t en o r t h -d r a i n in g t r i b u t a r ie s o f t h e W a m p 6 f r o m s o u t h -d r a i n i n g t r i b u t a r i e s o f t h e T i n t o ( F ig . 6 ). O n c e a g a i n ,t h e W a m p O s id e o f t h e d i v i d e i s c h a r a c t e r i z e d b yg e n t l e s l o p es , w h e r e a s t h e T i n t o s i d e i s s t e e p e r . T h eT i n to t r i b u t a r i e s a r e a c t iv e l y e n c r o a c h i n g h e a d -w a r d l y in t o t h e W a m p f i d r a i n a g e b a s i n . T h i s s i t u a -t io n i s s u r p r i s i n g i n a s m u c h a s th e o v e r a l l g r a d i e n t o ft h e W a m p f i t o i t s c o n f l u e n c e w i t h t h e P a t u c a a t B o c aW a m p 6 ( se e F i g. 3) i s c o n s i d e r a b l y s t e e p e r t h a n t h a to f t h e T i n t o - G u a y a p e - P a t u c a t o B o c a W a m p f l . T h ec a u s e o f t h i s s e e m i n g l y a n o m a l o u s s i t u a t i o n i s t h eb l oc k o f m o u n t a i n s t h r o u g h w h i c h th e W a m p 6 m u s tp a s s a s i t e x i t s t o t h e e a s t f r o m t h e C u l m i V a l l e y .H e r e t h e W a m p 6 f l o w s t h r o u g h a n a r r o w , 3 0 0 - m e t e rd e e p g o r g e c u t i n t o h a r d r o c k s f o r m i n g a t h r e s h o l dt h a t m u s t b e e r o d e d b e f o r e t h e W a m p f i c a n e f f e c t i v e l yc u t in t o t h e C u l m i V a l l e y f l o o r. T h i s t h r e s h o l d e f f e c ti s p ro b a b l y r e s p o n s i b l e f or t h e p o n d i n g o f a l l u v i u m i nt h e n o r t h e r n p a r t o f t h e C u l m i V a l l e y .T h e o r i g in o f t h e w i d e r n o r t h e r n e n d o f t h e C u l m iV a l l e y i s n o t a s r e a d i l y e x p l a i n e d a s t h e S i co V a l l e y .I t c o u l d b e a h i g h l y m o d i f i e d o r c o m p l e x s t r i k e - s l i pb a s i n ( M a n n et al . , 1 9 83 ) p r o d u c e d b y s i n i s t r a l m o t i o no n th e G F S , b u t t h e r e i s no c o n v i n c i n g e v i d e n c e a t t h ep r e s e n t t i m e t o s u p p o r t s u c h a n i n t e r p r e t a t i o n .

T i n t o V a ll ey P o r t io n o f t h e W a m p u - T i n t o S e g -me nt . S o u t h o f t h e W a m p 6 - T i n t o d r a i n a g e d i v id e t h et o p o g r a p h i c e x p r e s s i o n o f t h e G F S c h a n g e s m a r k e d l y( F ig . 7 ). T h e v a l l e y n a r r o w s a n d n e i t h e r t h e n o r t h e r nn o r t h e s o u t h e r n w a l l s f o r m c o n t i n u o u s e s c a r p m e n t s .B e d ro c k e x p o s u r e s , i n c l u d i n g J u r a s s i c - C r e t a c e o u sc l a s t i c s t r a t a , C r e t a c e o u s l i m e s t o n e , a n d T e r t i a r y ( ? )v o l c a n i c r o c k s , b e c o m e m o r e c o m m o n i n t h e v a l l e yf lo o r. A ro a d - m e t a l q u a r r y h a s b e e n o p e n e d i n b r e c -c i a te d l i m e s t o n e d i s p l a y i n g h o r i z o n t a l s l i c k e n s i d e s( X o n F i g . 7 ). N o n e t h e l e s s , n o p a r t i c u l a r f r a c t u r ec a n b e i d e n t if i ed a s t h e m a i n G u a y a p e f a u l t t r a c et h r o u g h t h i s p o r ti o n o f t h e W a m p f i - T i n t o s e g m e n t .A p ro j e c ti o n o f t h e m a i n G F S t r a c e s o u t h w e s t -w a r d f r o m t h e n o r t h w a l l o f t h e C u l m i V a l l e y f a l l sa l o n g t h e a v e r a g e c o u r s e o f t h e R i o T i n t o w h e r e w eh a v e i d e n t i f i e d a s e r i e s o f l e f t - s t e p p i n g e n e c h e l o np h o t o l i n e a m e n t s . W e c o n s i d e r it h i g h l y p r o b a b l e t h a tt h e m a i n G u a y a p e f a u l t z o n e c l o s el y fo l l o w s t h e t h ec o u r s e o f t h e T i n t o t o i ts c o n f l u e n c e w i t h t h e G u a -y a p e , b u t i t is a ls o c le a r t h a t t h e G F S h a s d e v e l o p e d an u m b e r o f s p l a y s t h a t b r e a k o f f i n a m o r e s o u t h -w e s t e r l y t r e n d a t t h e j u n c t i o n o f t h e G F S w i t h t h eC a t a c a m a s s t r u c t u r e .C a t a c a m a s V a l l ey J u n c t i o n F i g . 7 )

T h e s t r u c t u r e o f t h e C a t a c a m a s V a l l e y h a s b e e nd e s c ri b e d b y G o r d o n a n d M u e h l b e r g e r ( 1 98 8 ) a n dG o r d o n ( 19 9 0) . T h e C a t a c a m a s V a l l e y is a m a j o rt o p o g r a p h i c f e a t u r e t h a t e x t e n d s 7 0 k m a l o n g aN 5 5 E a x i s, t e r m i n a t i n g t o t h e n o r t h e a s t a g a i n s t t h e


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5 2 R . C . F IN C H a n d A . W . R IT C H IE

Fig. 6. Culml Valley portion of the Guayape faul t system: DNC town ofDulce Nombre de Culmi; GF main Guayape fault; X road-metal quar ry in brecciated limestone with horizontal slickensides. Known faults are shown as solid lines; probable faults identifi edfrom topographic and photolineaments are shown as dashed lines.

G F S ( F ig . 7 ). I t a v e r a g e s 7 - 8 k m i n w i d t h a n d i sd r a i n e d b y t h e R i o G u a y a p e , w h i c h f lo w s g e n e r a l lya l o n g t h e s o u t h e a s t s i d e o f t h e v a l l e y . T h e r i v e rm e a n d e r s a c r o s s t h i n a l l u v i a l d e p o s i t s w i t h n u m e r -o u s b e d r o c k e x p o s u r e s i n t h e v a l l e y f lo o r .T h e n o r t h w a l l o f t h e v a l l e y , a s p e c t a c u l a r e s c a r p -m e n t r i s i n g o v e r 1 0 0 0 m e t e r s , m a r k s t h e C a t a c a m a sf a u l t. N e a r t h e c it y o f C a t a c a m a s , b a s e m e n t s c h i s tc r o p s o u t f ro m t h e b a s e o f th e e s c a r p m e n t u p t o 3 0 0-3 5 0 m e t e r s a b o v e th e v a l l e y fl o o r. T h e s c h i s t i so v e r l a i n b y a r e l a t i v e l y t h i n s e c t io n o f c l a s ti c s t r a t ab e l o ng i n g t o t h e J u r a s s i c - C r e t a c e o u s H o n d u r a sG r o u p ( D o n n e l l y e t a l . 1 9 9 0 ) , w h i c h a r e i n t u r no v e r l a i n b y C r e t a c e o u s l im e s t o n e . T h e e s c a r p m e n t i s

o f f s et b y s e v e r a l c r o s s - fa u l t s . W i t h i n t h e v a l l e y o nt h e d o w n t h r o w n s id e o f t h e C a t a c a m a s f a u l t , T e r -t ia r y (? } v o l c a n i c u n i t s a r e e x p o s e d .O n t h e so u t h , th e C a t a c a m a s V a l l e y i s b o u n d e db y a b a s e m e n t m a s s i f o f s c h is t, t h r u s t s o u t h e a s t o v e r

a s e ct io n o f H o n d u r a s G r o u p c l a s t i c s t r a t a w h i c hd i f fe r s f r o m t h a t s e e n in th e n o r t h e r n e s c a r p m e n t - -b e i ng m u c h t h i c k e r a n d c o n s i s t i n g m a i n l y o f s h a l e( K o z u c h , 19 8 9 ). A t t h e n o r t h e a s t e n d o f t h i s b l o c k ,T e r t i a ry ( ? ) C a m p a n t e p e t u f t s (G o r d o n , 1 9 90 } e i t h e ro v e r l ie t h e m a s s i f o r a r e b r o u g h t i n t o f a u l t c o n t a c tw i t h i t b y s p l a y s o f t h e G F S .T h e C a t a c a m a s V a l l ey h a s b ee n i n t e r p r e t e d b yG o r d o n ( 1 9 8 7 a) a s a f a u l t w e d g e b a s i n a l o n g a r i g h t -

O . , q ~ ' ~ 0 4

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Fig. 7. Catac amas Valley junction and Rio Tinto portions of the Guayape fault system: CAT city of Catacamas; CF a t a c a m a sfault; CMR Cerro Monte Redondo; GF main Guayape fault; X road-metal quarry in brecciated limestone with horizontalslickensides. Known faults are shown as solid lines; probable faults identified from topographic and photolineaments are shown a sdashed lines


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T h e G u a y a p e f a u l t s y s t e m , H o n d u r a s , C e n t r a l A m e r i c a 5 3l a t e r a l f a u l t i .e . , t h e G F S . T h e g e o m e t r y o f t h ev a l l e y s u g g e s t s t h a t r i g h t - l a t e r a l f a u l t f l a n k b a s i n( M a n n e t a l . , 1 9 9 0 ) i s m o r e a p p r o p r i a t e , c o n s i d e r i n gt h a t t h e C a t a c a m a s f a u l t a p p a r e n t l y t r u n c a t e ss e v e r a l o f t h e m o r e s o u t h w e s t e r l y - t r e n d i n g s p l a y s o fft h e m a i n G F S . A p a i r o f t h e s e t r u n c a t e d s p l a y so u t l i n e a 2 - k m l o n g b r e c c i a t e d f a u l t s l i v e r k n o w n a sC e r r o M o n t e R e d o n d o ( F i g . 7).I n t h e S a n F r a n c i s c o d e B e c e r r a q u a d r a n g l e t ot h e s o u t h w e s t o f C a t a c a m a s , K o z u c h ( 19 8 9) m a p p e d an o r t h - d i p p i n g t h r u s t f a u lt . T h i s p o s t -M i d d l e J u r a s s i ct h r u s t i n d i c a t e s n o r t h - s o u t h c o m p r e s s i o n i n c o m p a t -i b l e w i t h d e x t r a l m o t i o n o n t h e G F S .R i o G u a y a p e S e g m e n t F i g. 7 )

N e a r t h e e a s t e n d o f t h e C a t a c a m a s V a l l e y , t h eR i o G u a y a p e - - f o r w h i c h t h e G F S w a s n a m e d - -t u r n s a b r u p t l y s o u t h e a s t w a r d a s i t r e a c h e s t h e G F S .I t s o o n j o i n s t h e R i o T i n t o a t a T - i n t e r s e c t i o n ( F ig s . 3a n d 7 ) , w h e r e i t t u r n s $ 3 50 W to f lo w a l o n g t h e G F S f o r3 7 k m t o i t s c o n f l u e n c e w i t h t h e R i o G u a y a m b r e ( s e eF i g . 2 ). T h e G u a y a p e c o u r s e f o ll o w s a v a l l e y t h a tv a r i e s f r o m 2 t o 4 k m i n w i d t h , w i t h g e n e r a l l y w e l l -d e f i n e d v a l l e y w a ll s . T h e v a l l e y p r e s u m a b l y f o ll o w sc l o s e ly t h e m a i n G u a y a p e f a u l t t r a ce ; h o w e v e r , n os i n g l e , t h r o u g h - g o i n g t r a c e c a n b e i d e n t i f i e d i n t h i ss e g m e n t . I n s t e a d t h e s y s t e m a p p e a r s t o b e b r o k e n u pi n t o n u m e r o u s s e g m e n t s d i s p e r s e d a c r o s s a z o n e a sm u c h a s t w i c e a s w i d e a s t h e m o d e r n G u a y a p e s t r e a mv a l l e y . O n t h e s o u t h e a s t s i d e o f t h e v a l l e y t h e r e i s ag e n e r a l t e n d e n c y f o r t h e s e g m e n t s t o f o r m a l e f t-s t e p p i n g e n e c h e l o n p a t t e r n , a n d , t o w a r d t h e n o r t he n d o f t h is s e g m e n t , a n o t i c e a b l y a r c u a t e p a t t e r n( c o n c av e t o w a r d t h e G u a y a p e V a l l e y ) is e v id e n t .O n e l i k e l y e x p l a n a t i o n f o r t h e a p p a r e n t d i s p e r s e dn a t u r e o f t h e G F S i n t h i s s e g m e n t i s th e f a c t t h a t t h eb e d r o c k h e r e c o n s i s t s m a i n l y o f a v e r y t h i c k p e l i t ics e c ti o n b e l o n g i n g t o th e A g u a F r i a f o r m a t i o n , a ni n f o rm a l m e m b e r o f t h e J u r a s s i c - C r e t a c e o u s H o n -

d u r a s G r o u p (R i t c h ie a n d F i n c h , 1 98 5 ). W i t h i n t h es h a l y s e c t i o n , m o v e m e n t o n t h e G F S i s s p r e a d o v e rw i d e z o n e s o f d i s t r i b u t e d s h e a r ; f u r t h e r m o r e , l a c k o fm a s s i v e r e s i s t a n t u n i t s o r c o n t r a s t i n g l i t h o l o g i e sr e s u l t s i n p o o r t o p o g r a p h i c e x p r e s s i o n o f t h e s h e a rz one s .R i o G u a y a m b r e S e g m e n t F i g . 8 )

S o u t h w a r d f r om t h e u n i o n o f t h e G u a y a p e a n dG u a y a m b r e t o f o r m t h e R i o P a t u c a ( F ig s . 3 a n d 8 ), t h em a i n f a u l t s o f t h e G F S a r e p r e s u m e d t o b e c l o s e l yr e p r e s e n te d b y t h e c o u r s e o f t h e R i o G u a y a m b r e .H o w e v e r , o n c e a g a i n t h e r e i s n o s in g l e , t h r o u g h -g o i n g t r a c e t h a t c a n b e i d e n t i f i e d a s t h e m a i n f a u l t .T h e c h a r a c t e r o f t h e m a i n z o n e i s g e n e r a l l y s i m i l a r t ot h a t o f t h e G u a y a p e s e g m e n t , w i t h , p e r h a p s , ag r e a t e r v a r i e t y o f s t r a t i g r a p h i c u n i t s i n v o l v e d i n t h ef a u l ti n g . I n ' t h e v i c i n i t y o f t h e v i l l a g e o f E l M a g u e l a rw e m a p p e d s l i c e s o f r e d b e d s a n d l i m e s t o n e b e l o n g i n gt o t h e C r e t a c e o u s V a l l e d e A n g e l e s G r o u p t e c t o n i -c a l ly i n t e r l e a v e d w i t h A g u a F r i a s h a l e a n d s a n d s t o n e(Fig. 8) .A t t he G u a y a p e - G u a y a m b r e j u n c t io n , t h e n o r t h -w e s t v a l le y w a l l f o r m s a n a b r u p t c u s p ( F ig . 8 ). H e r et h e f a u l t t r a c e b o u n d i n g t h e v a l l e y t u r n s f r o mp a r a l l e l t o t h e m a i n G F S t o $ 6 5 0W , f o l l o w s t h i s c o u r s ea p p r o x i m a t e l y 8 k m , t h e n b e g i n s t o c u r v e g e n t l ym o r e t o t h e s o u t h a n d s i m u l t a n e o u s l y b r e a k s u p i n t oa n u m b e r o f l e s s w e l l -d e f i n ed s e g m e n t s . T h e s e l i n e a -m e n t s m a y b e t ra c e d o n a i r p h o t o s a n d t o p o g r a p h i cm a p s a p p r o x i m a t e l y 2 0 k m t o a s e co n d k i n k w h e r et h e t r e n d b e n d s b a c k t o n e a r l y p a r a l l e l t o t h e m a i nG F S - - i .e . , $ 3 5 ~ / . F r o m th i s p o i n t t h e l i n e a m e n t sb e c o m e m o r e o b s c u r e a n d a r e o n l y t e n t a t i v e l y t r a c e -a b l e t o t h e J a m a s t r ~ n V a l l e y a n o t h e r 3 0 k m t o t h es o u th . W e h a v e d e s i g n a t e d t h e s e t h e A z a c u a l p af a u l t s .N o r t h o f t h e s ec o n d k i n k t h e A z a c u a l p a f a u l t ss e p a r a t e t h e h i g h M o n t a f i a d e A z a c u a l p a b l o c k f r o m

--- M T ~ A d e C U Y A M e~ l P A4 -

v 2 2 . ~ . ~ _ I~ K M

, \ . - . . . .

Fig. 8. Guayam bre segment of the Guayape fault system: AF, Azacualpa faults; AZ, town of Azacualpa; EM, town of El Maguelar;VS, town of Villa San ta. Know n faults are show n as solid lines; probable faults identified from topographic and photolineamentsr e shown as dashed lines.


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54 R. C. FINCH and A. W. RITCHIE

' / f ' ,

Z r ~ : .- - . - ~ . ' - ~ ? .x . . \ '

N

\ ,D,,-5

/ - ' , - _ ' :5 - - - - _ _ ' I , ' z

i I

i

I

//_ _ I .. . ~ AF

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A . - - - / ~ . - I i t I ~ i ~ ,/ ~ / ' i , , , 4 ~ // / : j t

t i / I / I I ,~ I / V

l i , W ~ _ _ . . I , ' ~ K M/ ' i ' / P \

10

Fig. 9. Jamastran-E1 Paraiso segment of the Guayape fault system: AF, southern extension of the Azacualpa faults; EC, ElChichicaste; EP, city of El Paraiso; GF, main Guayape faults; PB, Pozo Bendito. Known aults are shown as solid lines; probablefaults identified rom opographic and photolineamentsare shown as dashed lines, ttonduras-Nicaraguaborder indicatedby heavydash-dot line.the low Azacua lpa Valle y (Fig. 8). South of thesecond kink the Azacualpa faults separate the highMontafaa de Cuyam apa from the lower terrai n aroundthe town of Villa Santa. The trend of the Azacualpafaults as they diverge from the main GFS trend isnear ly identical to that of the Cata camas fault, theterrain lying between the Azacualpa faults and theGFS is consistently lower than that to the northwestof the Azacualpa faults, and the most pronounceddevelopmen t of the extensional basin occurs at it snor the rn end where it abut s the GFS. Gordon (1990)interp reted the Azacualpa Valley as a fault wedge ora fault f lank basin analogous to the CatacamasValley basin. We disagree, noting that because thenorthwest escarpment and, therefore, the generatingfault are continuous, the valley represents a dextralrele asin g bend basin (Crowell, 1974). Hot spring semer ging along the north ern portion of the Aza-cualpa faults may hint at their youthfulness.Valle de Jam astr dn- El Paraiso Segment Fig. 9)

The Jamastr~in Valley is a rectangular valleyabout 15 by 13 km, with its long axis parallel to theGFS. The valley is bounded on the n orth west byfaults that are the projected continuation of theAzacualpa faults, and on the southeast by right-stepping en echelon segments of the GFS. Further-more, the topography suggests that the north east andsouth west ends of the valley may also be fau lt-bounded, but this is less certain (Fig. 9).On the basis of a reconnaissance trip in 1983, we(Ritchie and Finch, 1984) suggested that the GFSmakes a right-stepping en echelon connection withthe 165-km-long Chotuteca linea ment in the Valle deJamastrfin-E1 Paraiso region, to form a through-

going system transec ting the entire isthmus. On thebasis of topography , Gordon (1987a) sug geste d t ha tthe Jamastr~n Valley must be a dextral pull-apart,necess i ta ted by dextra l s l ip on r ight-s tepping,overlapping segments of the GFS and Ch olut ecalineament. The results of field work in the area in1984 and 1986 indicate tha t nei the r of thes einte rpret ati ons is correct (Ritchie and Fi nch, 1989).Our field data and map and photo interpretationsdo not support the i nter pret a t io n of the GFS-Choluteca lineament as a through-going feature.Instead, we find that the GFS breaks into a multi-plicity of splay faults and shea r zones represen ted bybands of breccia hundreds of meters thick, p ass ingalong the south east side of the Jama st r~n Valley, andprobably through the valley floor as well, to term-inate finally against a well-developed set of north-west-trending fractures without connecting with theCholutec a lineame nt (Fig. 9). We last see the GFSsome 7 km due west of the ci ty of El Par aiso, where tplaces Jurassic Agua Fria strata against TertiaryPadre Miguel tufts. We find no evidence that faults ofthe Choluteca lineament extend this far northward.Such faults, if they exist, do not appear to break theTertiary volcanic cover in this region as do faults ofthe GFS, and as faults of the C holuteca l ine ame nt dofarther to the south where that feature is betterdeveloped.Our present interpretation is that the GFS-Choluteca lineament does not form a through-goingsys tem, but that the two elements have actedindependently n althou gh possibly in response to thesame tectonic influences. We now view the GFS asterm inat ing in the series of splays developed in theValle de Jamastr~n-E1 Paraiso segment, with themovement being distributed in smaller amounts over


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The Guayape fault system, ttondura s, Central America 55a wider area than elsewhere in the system. TheJam ast r~n Valley appears to be a special case of adextral pull-apart (Crowell, 1974} in which the valleyis not the result of dextral motion on two overlappingsegments of the main fault but rat her of interactionbetween the main GFS and the Azacualpa faultssplays off the GFS. Thus, the Jam astrfi n Valley ismore likely a result of movement on the Azacualpafaults than it is to a relationship with the Cholutecalineament.

NATURE OF THE DISPLACEMENTThe tectonic setting, extreme rectilinearity, andgreat length of the GFS suggest tha t it is a strike-slipfault. This is confirmed by the common occurrence ofhorizontal to sub-horizontal (rakes less th an 30 )slickensides on exposures of discrete fault s and in

zones of shear within the GFS throughout the entirelength visit ed by us. Locally, mesoscopic drag foldswith verti cal axes were also noted (see below). Tha tno pairs of offset features can be une quivoca llyidentified along the GFS suggests that the amoun t ofmoveme nt may be large.As a working prejudice based on the regional tec-tonic pattern, we expected the GFS to prove to be amember of a family of major transcurr ent faultsaffecting the n orthe rn edge of the Chortis block (seeFig. 1): the Motagua, the Jocot~n, the La Ceiba, theAgu~n, the Guayape, and possibly the Patuca faultzone to the east of the GFS. The present sinis tralmovement on the Motagua transform is well docu-mented. Although the GFS has a more northerlytrend than the Motagua and the other faults lyingbetween the GFS and the Motagua, we expected tofind that the GFS exhibited sinistral displacement aswell. Sinistral di splacement has been documented onother N30-40E-trending faults cutting the Chortisblock -- e.g. the faults active during the 1972 Mana-gua earthquake (Brown et al. 1973). However, theManagua faults belong to a group of shorter faultstransverse to the volcanic arc and related to seg-menta tion of the Cocos plate as it is subducted at theMiddle America Trench (Stoiber and Carr, 1973;Carr, 1976; Car t and Stoiber, 1977). It is unli kelythat the much longer GFS, which does not reach thevolcanic arc, is genetically related to these faults.Nevertheless, sinistral slip on these transverse faultssuggests that the N30-35E orientation of the GFSdoes not necessarily require dextral slip, as suggestedby Gordon (1987a). As indi cate d in the followingparag raphs, the eviden ce for the dire ction of dis-placeme nt on the GFS is mixed.Mesoscopic Sl ip Indicators

Much of our mesoscopic st ruct ural data comefrom a major, GFS-related shear zone in the north-east corner of the Jam as trh n Valley in the vicinity ofE1 Chi chi cas te (EC on Fig. 9). Her e we found 33scattered sinistral- and dextral-slip indicators con-

sisting of shear surfaces with associated asymmetricminor folds. A preponderance of dextr al-sl ip indi-cators are associated with steeply-dipping surfacessubparallel to the Guayape trend. Sinistra l indica-tors are more common on surfaces at an angle to thistrend. The sinistral indicators may result from move-ment on complementary or Riedel shears within adextral GFS or may be rotated relic structures froman earlier period of sinis tral motion on the GFS.Cross-cutting relationships are, as might be expected,complex, but it is our observation in the field thatsurfaces associated with dextral indicators cut thoseassociated with sinistral indicators more frequentlytha n the opposite. However, a count of cross- cutti ngrelationships of lineaments on Fig. 2 reveals no pre-ference one way or the other (Carson and Ritchie,1991). In addition , 29 slip indicators were mea sur edon an east-northeast-trending GFS splay fault on theother side of the Jamastrgm Valley at Pozo Bendito(PB on Fig. 9). The patt ern of move ment indi cate d bythese data is similar to that at E1 Chichicaste but,interest ingly enough, 12 of the indicators impl y nor-mal movement on the splay. Such normal movemen t,if real, would be consistent with more recen t de xtralmovement on the GFS. Mesoscopic structura l dat afrom other parts of the GFS are scarce, principall y asa re sult of poor exposure.Ev i de nc e for S i n i s t ra l S l i p

Burk art and Self (1985) suggested th at the GFSwas a sinis tral faul t with about 50 km of displace-ment, based on offsets in topog raphy. The topogra-phic offset referred to is the appa rent displa cement ofthe headwaters of the Guayape and Guay ambr estre am sy stems (Ritchie and Finc h, 1984) (Fig. 10).In the present-day drainage patterns (Figs. 3 and10) the Guayape flows from its headwa ters genera llynortheastward, toward the Caribbean coast, until itnears its junction with the Tinto. Here the rivermakes a nearly 180 turn, away from the coast, tofollow the GFS for 37 km until it meets the Guay-ambre to form the Rio Patuca. Helbig (1959) conclu-ded that the Guayape once drained northeastwardalong the present course of the Tinto, to exit to theCaribbean via either the present Paulaya or Wampt]Valleys. tie viewed the turn ing of the Guay ape backto the southwest as an effect of uplift and blockage ofthe Tinto (then Guayape) Valley by eruptive rocks.We think it hardly likely that the Guayape everflowed to the Caribbean via the Paulaya (whichappears to have only recently pirated its way into theCulmi Valley area). However, a Gua yap e-W amp ~drainage seems much more plausible, with sinistralmovement on the GFS as the cause of its disruption.Today the Rio Wampfi exits the Culmi Valley-Guayape fau lt zone at a point 47 km fro m theGuayape-Tinto confluence. Upstream from its exitcanyon, the headwaters of the Wamph encompass anarea of only 640 km 2, whereas the Guayape drain agebasin up stream from its junction with the Tintocovers some 8140 km ~ (Fig. 10). This discr epanc y in


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T h e G u a y a p e f a u l t s y s t e m , H o n d u r a s , C e n t r a l A m e r i c a 5 7d i m i n i s h t h e e f f e ct s o f t h e e a r l i e r s i n i s t r a l m o v e m e n t ;t h e r e f o r e t h e p r o p o s e d 5 0 k m o f s i n i s t r a l d i s p l a c e -m e n t i n t h e e a r l y p h a s e w o u l d b e a m i n i m u m f i gu r e .A d d i t i o n a l , b u t w e a k , e v i d e n c e f a v o r i n g l a r g e -s c a l e s i n i s t r a l d i s p l a c e m e n t o n t h e G F S i s t h e d i s -t r i b u t i o n o f t h e A g u a F r i a s t r a t a a s c u r r e n t l y k n o w n( R i t c h i e a n d F i n c h , 1 9 8 5 ). T h i s t h i c k u n i t o f t h eH o n d u r a s G r o u p i s b e s t k n o w n i n th e a r e a l y i n g t ot h e w e s t o f t h e J a m a s t r ~ n V a l l e y a n d i n t h e A z a -c u a l p a a r e a. F a r t h e r n o r t h , in t h e C a t a c a m a s V a l l e y ,o n l y a t h in s e c t i o n o f H o n d u r a s G r o u p s t r a t a o c c u r sa l o n g t h e C a t a c a m a s f a u l t o n t h e n o r t h w e s t s i d e o ft h e G F S , w h e r e a s o n t h e s o u t h e a s t s i d e w i d e s p r e a de x p o s u r e s o f A g u a F r i a s h a l e i n d i c a t e a t h i c k s e c t i o nh e r e . T h i s t h i c k s e c t i o n o f A g u a F r i a m a y b e a n o f f s etc o n t i n u a t i o n o f t h e t h i c k A g u a F r i a d e p o s i t s in t h eJ a m a s t r 6 n - A z a c u a l p a r e g io n . O n t h e o t h e r h a n d ,t h i s m a y r e f l e c t o u r l a c k o f k n o w l e d g e o f t h e A g u aF r i a , w h i c h h a s n e v e r b e e n s u b j e c t e d t o re g i o n a lm a p p i n g o r f a c ie s a n a l y s i s .I t i s a l s o i n t h e C a t a c a m a s a r e a t h a t K o z u c h( 19 89 } m a p p e d a t h r u s t f a u l t w h o s e m o t i o n i n d i c a t e sn o r t h - s o u t h c o m p r e s s i o n . T h e a g e o f t h e p e s t- M i d d l eJ u r a s s i c t h r u s t i n g i s p o o r l y c o n s t r a i n e d , b u t i t s o r i en -t a t i o n i s c o m p a t i b l e w i t h s i n i s t r a l s l i p on t h e G F Sa n d i n c o m p a t i b l e w i t h d e x t r a l s l ip .E v i d e n c e f o r D e x t r a l S l i p

T h e e v i d e n c e f or d e x t r a l d i s p l a c e m e n t o n th e G F Sc o n s i s t s p r i m a r i l y o f t h e l a r g e - s c al e t o p o g r a p h i cf e a t u r e s b e s t e x p l a i n e d a s d e x t r a l s t r i k e -s l i p b a s i n s :t h e S i c o, C a t a c a m a s , a n d A z a c u a l p a v a l l e y s a n d , p o s -s i b l y , t h e J a m a s t r 6 n V a l l e y . A d d i t i o n a l ly , G o r d o n sa n a l y s i s o f f a u l t s l ip d a t a i n t h e C a t a c a m a s V a l l e ya r e a ( G o r d o n , p e r s . c o m m . , 1 9 8 7 ) i n d i c a t e s d e x t r a ls l ip , a s d o s o m e o f o u r s l ip i n d i c a t o r s f r o m t h e J a m -a s t r~ m a r e a .

F o l l o w i n g a l e s s c o n v i n c i n g l i n e o f r e a s o n i n g , w eb e l i e v e t h a t r i g h t - s t e p p i n g en eche l on s e g m e n t s a r em o r e l i k e l y t o d e v e l o p in a d e x t r a l s l ip r e g i m e t h a n a sa r e s u l t o f s i n i s t r a l s l ip . A l t h o u g h o c c u r r e n c e s o fb o t h l ef t - a n d r i g h t - s t e p p i n g s e g m e n t s c a n b e s e e na l o n g t h e l e n g t h o f t h e G F S , r i g h t - s t e p p i n g o v e r l a p sa r e m o r e c o m m o n t h a n l e f t - s t e p p i n g o v e r l a p s a l o n gt h e f a u l t t r a c e s t h a t a r e t h e m o r e o b v i o u s a n d l i k e l yy o u n g e r f r a ct u r e s i n t h e s y s t e m e.g. , s e g m e n t s a l on gt h e s o u t h e a s t s i de o f t h e J a m a s t r ~ n V a l le y , w h ic h w ei n t e r p r e t a s t h e m a i n G u a y a p e t r a c e i n th i s a re a }.T w o - S t a g e M o v e m e n t H i s to r y

T a k e n a l t o g e t h e r , t h e e v i d e n c e p r e s e n t l y a v a i l -a b l e , b o t h m e s o c o p i c a n d l a r g e - s c a le , s u g g e s t s t h a tt h e G F S h a s h a d a n e a r l y h i s t o r y o f s i n i s t r a l d i s -p l a c e m e n t , f o l l o w e d b y m o r e r e c e n t d e x t r a l s l ip , a sf i r s t s u g g e s t e d b y G o r d o n ( 1 98 7 a} . T h e e a r l i e r p h a s er e s u l t e d i n a m i n i m u m o f 5 0 k m d i s p l a c e m e n t ; t h ea m o u n t o f d i s p l a c e m e n t i n t h e m o r e r e c e n t d e x t r a lp h a s e i s u n k n o w n b u t w o u l d h a v e t o h a v e b e e n l e s st h a n t h a t o f t h e e a r l i e r p h a s e i n o r d e r t o p r e s e r v e a n yo f t h e s i n i s t r a l o f f s e t.SAES~4:I 2 E

H o w e v e r , a p ro b l em w i t h a n y i n t e r p r e t a t i o nw h i c h a r g u e s f or 50 k m o f s i n i s tr a l m o v e m e n t o n t h eG F S i s t h e d i f fi c u l t y o f t e r m i n a t i n g a f a u l t w i t h t h a tm u c h m o v e m e n t i n th e m a s s o f s p l a y a n d c r o s s - f a u lt si n t h e J a m a s t r ~ n -E 1 P a r a i s o a r ea . P e r h a p s d u r i n g a ne a r l i e r p h a s e o f s i n i s t r a l m o v e m e n t , t h e G F S d i d s te po v e r t o c o n n e c t w i t h t h e C h o l u t e c a l i n e a m e n t , a ss u g g e s t e d b y M u e h l b e r g e r (1 97 6 }. S u c h a n e a r l i e rc o n n e c ti o n , n o w c o v e r ed b y T e r t i a r y v o l c a n i c r o c k sl it tl e d i s t u r b e d b y t h e s m a l l e r d e x t r a l m o v e m e n t ,w o u l d s o lv e t h e p r o b le m o f t e r m i n a t i n g t h e m o v e -m e a t on t h e G F S a n d r e m a i n c o m p a t i b l e w i t h o u ro b s e r v a t i o n t h a t t h e r e i s n o w n o e v i d e n c e f o r a c o n -n e c t i o n b e t w e e n t h e t w o s t r u c t u r e s .

A G E O F T H E G U A Y A P E F A U L T S Y S T E MT h e G F S c u t s v i r t u a l l y th e e n t i r e s t r a t i g r a p h i c

s e c ti o n o f H o n d u r a s , f ro m P a l eo z o ic ( ?) b a s e m e n ts c h i s t t o T e r t i a r y v o l c a n i c ro c k s . A t t h e p r e s e n t t h e r ea r e n o d a t a t o c o n s t r a i n t h e i n i t i a t i o n o f f a u l t i n g .I n t h e J a m a s t r ~ n - E 1 P a r a i s o r e g i o n , f a u l t s o f t h eG F S p l a c e t u f t s o f t h e P a d r e M i g u e l G r o u p a g a i n s tA g u a F r i a s ha l e . T h e t u f t s h a v e b e e n w i d e l y d a t e d i nc e n t r a l H o n d u r a s a s M i o - P l i o c e n e ( W i l l i a m s a n d M c -B i r n e y , 1 9 6 9 ; C u r r a n , 1 9 8 0 ; M c D o w e l l , p e r s . c o m m . ,1 98 6} ; t h e A g u a F r i a c l a s t i c s t r a t a h a v e b e e n d a t e d a sM i d d le J u r a s s i c u s i n g b o t h a m m o n i t e s a n d p l a n t r e-m a i n s ( R i t c h i e a n d F i n c h , 1 98 5 ). I n t h e C a t a c a m a s -C u l m i r e g i o n t h e s y s t e m c u t s t h r o u g h v o l c a n i c r o c k sb e l i e v e d t o b e o f T e r t i a r y a g e ( G o r d o n , 1 9 9 0} . I t i sl ik e l y th a t t h e G F S o r i g in a t e d a s t h e C a r i b b e a n p l a t ee v o lv e d i n T e r t i a r y ti m e . T h e s i n is t r a l m o v e m e n tm a y h a v e o r i g i n a t e d i n r e s p o n s e t o s t r e s s e s r e l a t e d t ot h e C a r i b b e a n - N o r t h A m e r i c a n p l a t e b o u n d a r y a t a ne a r l i e r t i m e w h e n t h e G F S w a s a t a n a p p r o p r i a t eo r i e n t a ti o n . G o r d o n ( 19 8 7a } h a s p r o p o s e d t h a t t h ed e x t r a l p h a s e o f a c t i v i t y o n t h e G F S i s n e o t e c t o n i c .M u c h o f t h e d i s c u s s io n r e g a r d i n g t h e h i s t o r y o ft h e G F S a n d it s r e l a ti o n s h i p t o t h e N O A M - C A R I Bb o u n d a r y ( G o r d o n , 1 9 8 7 a , b , 1 9 9 0 } h a s b e e n s p e c u l a -t i v e a n d c o n t r a d i ct o r y . T h i s s p e c u l a t i o n r e s u l t s , t o al a rg e d e g re e , f ro m a l a c k o f u n d e r s t a n d i n g o f t h en a t u r e o f t h e r e l at i o n s h i p b e t w e e n t h e G F S a n d t h ep l a t e b o u n d a r y . I n d e e d , M a n n et al . ( 1 9 9 0 } d o n o ti n c l u d e t h e G F S i n t h e i r l i s t o f f a u l t s i n c l u d e d i n t h ep l a t e b o u n d a r y z o n e. W i t h o u t s o m e k n o w l e d g e o f t h ei n t er a c ti o n b e t w e e n t h e G F S a n d t h e N O A M - C A R I Bb o u n d a r y , a n y a t t e m p t a t p l a c e m e n t o f t h e G F S i n ar e g i o n a l t e c t o n i c p i c t u r e i s n e c e s s a r i l y s p e c u l a t i v e .N u m e r o u s f e a t u r e s s u p p o r t t h e p r o p o s a l t h a tn e o t e c t o n i c m o v e m e n t h a s t a k e n p l a c e o n t h e G F S .T h e e x t r e m e c r i s p n e s s o f t h e t o p o g r a p h i c e x p r e s s i o no f t h e m a i n G u a y a p e t h r o u g h o u t m u c h o f i t s l e n g t he.g. , t h e C e r r o P o r t i ll o d e W i l l s h u t t e r r i d g e ( s e eF i g . 5 ) , a n d t h e m o d e r n t e c t o n i c b a s i n s d e v e l o p e d a se x t e n s i o n a l f e a t u r e s a l o n g t h e G F S a r g u e f o r r e c e n t ,i f n o t c u r r e n t , a c t i v i t y o n th e f a u l t s y s t e m . T h eC l a u r e d S i c o d e l t a s w i t c h a n d b l o c k - f a u l t i n g - i n d u c e dm e a n d e r a b a n d o n m e n t a l o n g t h e R io S i c o a r e b e s te x p l a i n e d b y r e c e n t a c t iv i t y a l o n g th e G F S . I n t h e


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58 R. C. FINCH and A. W. RITCHIEAzacualpa area we found two outcrops of semi-consolidated, poorly-sorted gravel beds that havebeen rotated to near vertical. These beds crop out inan area dominantly floored with Agua Fria strata ,but we believe the gravel beds to be of Tert iar y age(probably late Terti ary), tectonically interleaved withthe Agua Fria by movement on the GFS. The rela-tively poor integra tion of drainage networks in the LaColonia region may indicate di srupt ion of olderdrain ages by relat ively recent move ment on the GFS.Hot springs, commonly associated with youn g faults,are known to occur in four places along the GFS;however, fracture-controlled hot springs are exceed-ingly common in Honduras (Finch, 1986) and cannotbe considered proof of anything more than the factthat the fractures facilitate the movement of thermalwaters. Althou gh some epicentral locations plotnear, and possibly along the GFS (Sutch, 1979), nomodern seismic activity can be definitely attributedto movement on this system.In spite of numerous indications of relativelyrecent activity on the GFS, at no place could we findany certain displacement of Quaternary features.Multipl e levels of str eam terrac es are well developedalong the Rio Guayambre. Such terrace levels andterra ce fr onts migh t be expected to show the effects ofmodern movement on the GFS, as do the terracesalong the Rio E1 Tambor in the Motagua fault zone(Bosc, 1971; Schwartz e t a l . 1979), but we could notfind any examples of offset or disrupted terracesalong the GFS. Other than the young exten siona lbasins th emselves, all indicators of recent activity onthe GFS occur on the nor theast ern h alf of the system- - e . g . the Portillo de Will shutterridge and recentdrainage changes in the Paulaya and Claura/Sieorivers. This can be explained as a sout hwest warddying out of slip on the GFS proper as movement isaccommodated by the series of extensional basins. Itcould also indicate th at activity on the GFS is indeedrela ted to the NOAM-CARIB bounda ry in some way.If the GFS were still active today it would be ex-pected to be associated with historical seismic events.Sutch (1979, her Fig. 18) shows four epicenters forshallow focus earthquakes recorded between 1898and 1978 that appear to be spatially related to theGFS. She noted (p. 58) tha t info rmati on rega rdingindividual faults cannot be extrapola ted due toinsufficient data. Historically, Honduras has beensufficiently free of seismic damage tha t little efforthas been expended in seismic studies within therepublic. From presently available data it is notpossible to say with certainty that activity continueson the GFS.In sum, the GFS is probably a Tertiary featurethat has undergone an early sinistral slip phase,followed by a neotectonic dextral phase. Motion onthe GFS appears to be greatly reduced in Holocenetime but likely has continued to some degree on thenorthea stern portion of the feature.

CONCLUSIONSThe Guayape faul t sy ste m (GFS) t ren ds N30 -35E across the Chortis block of the Caribbean Platefor approximately 290 km from the vicinity of the cityof E1 Parais o to the Carib bean coast. We find noevidence that the GFS connects with the Cholutecalineament or that the GFS continues beyond ElParaiso in any form.Large-scale tectonic features associated with theGFS, extensional basins in particular , indi cate a dex-tral sense of movement for the fault system. How-ever, offset stream dr ainage fe atures suggest a mini-mum of 50 km of sinistral offset. From th e ap paren trelative ages of these and other features, it appearsthat the GFS has had a two-stage movement history,with the dextral movement being the more recent. Inany case, motion on the GFS has diminished duringthe Holocene.The sinistral movement is likely Tertiary andmay have occurred at a time when the orientation ofthe Chortis block aligned the proto-GFS with thesinistral Caribbean-North American plate boundary.Rotation of the Chortis block into its pre sent orienta-tion has placed the GFS in an orie ntat ion more n earl ycomplementary to the sinistral NOAM-CARIB plateboundary, which could explain the neotectonic dex-tral movement on the syste m as proposed by Gordon(1987a,b). However, an arg um en t that the N30-35Eorientati on of the GFS necessitates a dext ral sense ofmovement is contraindicated by the sinistral move-

ment observed on faults of that orientati on duri ng the1972 Managua, Nicaragua, earthquake (Brown e t a l .1973) and by the sinistral displacement on arcsegmentation faults transverse to the Middle Ameri-can volcanic arc (Stoiber and Carr, 1973; Carr, 1976;Ca rt and Stoiber, 1977). Precise plac eme nt of t hGFS in a regional tectonic picture await s furt her d ataon the nature of the interaction offshore of the GFSand the NOAM-CARIB plate boundary.

Acknowledgements We g r a te f u ll y a c k n o w l e d g e t h e i n v a l u a b l es u p p o r t o f t h e D i r e c c i 6 n G e n e r a l d e M i n a s e H i d r o c a r b u r o e , , heI n s t i t u t o G e o g r ~ f i co N a c i o n a l , a n d F u e r z a A 6 r e a H o n d u r e f i a o f t h eR e p u b l ic o f H o n d u r a s , a n d t h e s u p p o r t o f o u r o w n i n s t i t u t i o n s ,T e n n e s s e e T e c h n o l o g i c a l U n i v e r s i t y a n d t h e C o l l e g e o f C h a r l e s t o n .I n a d d i t i o n , w e e x p r e s s o u r s p e c i a l a p p r e c i a t i o n t o W . R . M u e h l -b e r g e r o f t h e U n i v e r s i t y o f T e x a s a t A u s t i n , w i t h o u t w h o s e l o n gt e r m s u p p o r t a n d m a n y v a l u a b l e s u g g e s t i o n s t h i s p a p e r w o u l d n o th a v e b e e n w r i t t e n .


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Resumen--El sistema de fallas del Guayape {GFS) es la estructura mas larga y continua en Honduras yuno de los mayores ele mentos tectbnicos en el bloque Chortis de la plata Caribe. Sin embargo, este siste made fallas ha sido ignorado en la mayoria de estudios tect6nicos realizados en esa regi6n, debido,apar ente ment e, a la falta de datos detallados sobre la localizaci0n, dimensi6n y naturaleza del sistema. Esteestudio intenta proporcionar esta informaci6n faltante. E1 GFS es una franja compleja de fallas que v ariadesde 2 has ta 25 km en ancho, con rumbo N30-35E y una longitud de 290 km. Se exti ende desde la front erade Honduras con Nicaragua, cerca de El Paraiso, hasta la costa del Caribe en las proximidades de ladesemboc adura del Rio Sico. Perfiles de reflexi6n sismica sugieren que el GFS se extiende a la plataf ormacontinental. Mapeo geol6gico en el campo e interpreta cion de fotografias a~reas indica n que el ver daderoGFS desaparece en una zona de bifurcaciones Csplay faults }, las que son intersect adas por otro siste ma defallas en la regi6n comprendida entre el Valle de Jam ast ran y E1 Paraiso. En esta ar ea, el GFS no presen taninguna conexi6n en echelon que muestre continuidad con el lineamiento de Choluteca al suroeste. La m~sobvia manifestaci6n del GFS es un alineamiento de segmentos largos de los rios Guayambre, Guayape,Tinto, Paulaya y Sico. La longitud y rectitud del GFS indican que 6ste es un sist ema de fallas de trans -currencia, lo cual es confirmado en el campo por la abundancia de slickensides horizontales, pliegues dearr ast re con ejes verticales, ~shutterridges y otras estruc turas tipicas en zonas de fallas de transc urre nciacomo cuencas de origen extensional engendradas por desplazamiento lateral. Adicio nalmen te, falla ssubsidiar ias de car~cter ~dip-slip son comunes, como debe esperarse, princi palmen te asoci ada s a la scuencas de origen extensional. Desplazamientos lateral es de m~ts de 50 km de cauces de rios, indicadoresmesosc6picos de direcci6n del movimiento, la distribuci6n regional de una lutita que es un miem bro delGrupo Honduras, y consideraciones tect6nico-regionales sugieren un de splazamie nto latera l izquierdo en elGFS. Pot otto lado, tres, o posiblemente cuatro, cuencas recientes originadas por movimiento trans curr entede desplazam iento latera l derecho y la prevalencia de indicadores mesosc6picos de direccibn de mo vimientode car~cter lateral derecho sugieren un desplazamiento lateral derecho en el GFS. Una hi storia de des-lizamiento horizontal en dos etapas es indicada, con una fase de movimient o horizontal lateral izquierdo demt~s de 50 km, seguida pot una fase de movimiento horizontal lateral derecho de menor despla zamiento. ElGFS intersec ta formaciones tan recientes como las tobas del Grupo Padre Miguel del Mioceno y gra vas delTerciario(?) mas recientes. La topografla angular del GFS en varia s localidades y la edad apar ent eme ntereciente de las cuencas de origen extensional, indican que el GFS es joven. Aunque fu entes ter male s encuatro localidades y dispersa informaci6n sismica podrian set indicadores de activ idad rec ient e en elsistema , no existe evidencia convincente que asegure la misma. La edad del sistema es desconocida. Sinembargo, la fase de movimiento lateral izquierdo coincide con el movimiento lateral izquierdo del bloqueChortis, a lo largo de la falla Motagua-Swan (limite entre las placas NOAM-CARIB) durante el Terciario.Una continuaci6n del movimiento del bloque Chortis a lo largo del limite de placas pudo haber rotado elbloque hacia una posici6n favorable par a el inicio del movimiento lateral derecho.

sistema de fallas guayape honduras

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