1.b.fases deformaci+ôn
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GEOLOGA ARGENTINA - 2014
1. Conceptos y Nomenclatura Tectnica y Geotectnica
1.B. Fases de deformacin y su relacin temporal con el
emplazamiento de intrusiones gneas, los eventos metamrficos y las
secuencias volcano-sedimentarias.
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FASES TECTNICAS / FASES METAMRFICAS / FASES MAGMTICAS
GEOLOGA ARGENTINA - 2014
SON FASES (tambin llamados EVENTOS) DENTRO DE UN CICLO
OROGNICO, DONDE OCURRE DEFORMACIN TECTNICA,
METAMORFISMO O MAGMATISMO
LAS TRES FASES PUEDEN OCURRIR SIMULTNEAMENTE
O GUARDAR RELACIONES DIACRNICAS
INTRUSIONES PRE / SIN / POST-TECTNICAS
INTRUSIONES PRE / SIN / POST-METAMRFICAS
METAMORFISMO PRE / SIN / POST-TECTNICO CON RESPECTO A
ALGUNA FASE DE DEFORMACIN
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FASES TECTNICAS EN TERRENOS METAMRFICOS E GNEO-
METAMRFICOS
GEOLOGA ARGENTINA - 2014
Durante el desarrollo de un Ciclo Orognico, las Fases de
Deformacin (D1, D2,) guardan relacin con Eventos Intrusivos (I1, I2,) y Metamrficos (M1, M2,).
En estos terrenos esta relacin puede ser establecida mediante
criterios de sobreimpresin (overprinting) de fbricas y estructuras.
De esta manera pueden ser separados grupos de estructuras y
relacionar su formacin con los eventos gneos y metamrficos.
Los Eventos Metamrficos son episodios de metamorfismo
caracterizados por cambios (progrado y retrogrado) en las
asociaciones mineralgicas en un volumen de roca.
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In most deformed rocks, structures with different style and orientation and
minerals, which represent different metamorphic grades, overprint each other.
This means that equilibrium is generally not attained at each stage: mineral
assemblages representative of different metamorphic conditions may be
frozen in at different stages during burial and uplift.
GEOLOGA ARGENTINA - 2014
Schematic diagram of a biotite foliation (horizontal), a chlorite foliation (inclined)
and a brittle fault.
The sequence of over-printing relations is: biotite foliation-chlorite foliation-fault.
The three structures may represent different deformation phases since they
overprint each other, have different orientation and represent probably different
metamorphic conditions
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GEOLOGA ARGENTINA - 2014
1. Overprinting relations may be
produced by a single
deformation phase
2. Subsequent deformation
phases do not necessarily
produce overprinting relations
Passchier & Trouw (1995)
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GEOLOGA ARGENTINA - 2014
3. Only the relative age of deformation phases can be established
Passchier & Trouw (1995)
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GEOLOGA ARGENTINA - 2014
Fases de deformacin y su relacin
temporal con el desarrollo de las
secuencias volcano-sedimentarias.
Establecido el rgimen tectnico
asociado al desarrollo de la cuenca,
las relaciones temporales se
establecen en base a relaciones de
discordancias (angulares,
progresivas,..), la geometra de los
estratos, etc.
Se utilizan los prefijos PRE / SIN /
POST en relacin a la estructura o
rgimen que controla la depositacin
(ej. Pre-Rift, Sin-Rift, Post-Rift; Sin-
Inversin, Post-Inversin)
Modelo conceptual de Inversin de
un hemigraben por reactivacin de la
falla que limita el depocentro
sedimentario
(Bally,1984).
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GEOLOGA ARGENTINA - 2014
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GEOLOGA ARGENTINA - 2014
The slaty cleavage (S1) may be
spaced or continuous, but is
generally not a crenulation cleavage
as analysed under normal
microscopic amplification. However,
if analysed by SEM, it may show
crenulation cleavage features, folding
a bedding-parallel foliation of
diagenetic origin.
A common sequence of events in slate and schist belts may serve to
illustrate how the analysis of overprinting relations works (Passchier &
Trouw, 1995)
In the long limbs the angle between
S1 and S0 may become so small that
it is not visible any more in the field
or even in thin sections.
During a first deformation phase (D1),
a penetrative slaty cleavage is
developed at varying angles with
bedding, according to the position in
large D1 folds that are commonly
asymmetric.
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GEOLOGA ARGENTINA - 2014
A second phase of deformation (D2) commonly produces a crenulation
cleavage, folding S1 and S0.
Various stages or morphologies may be present depending on the
intensity of deformation and according to grain growth in response to
metamorphic circumstances.
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GEOLOGA ARGENTINA - 2014
The main problem of this analysis is to establish how to correlate
foliations from one thin section to another, from one outcrop to another,
or even from one analysed area to another.
A third phase of deformation may be recognised by folding of the S2
crenulation cleavage. This may in some cases result in interesting
structures, since according to their orientation certain limbs may be
refolded and others straightened out later phases of deformation may be
recognised in a similar way by overprinting (folding) of earlier foliations.
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GEOLOGA ARGENTINA - 2014
Estratificacin S0, pretectnica; clivaje S1 sintectnico y sinmetamrfico;
Granito pre? Sintectnico?; pre? Sinmetamrfico?
Foliacin de Plano Axial
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GEOLOGA ARGENTINA - 2014
Estratificacin S0, pretectnica; clivaje S1 sintectnico y sinmetamrfico;
Foliacin de Plano Axial REFRACCIN DEL CLIVAJE
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