1.B.FASES DEFORMACI+ôN

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.

FASES TECTNICAS / FASES METAMRFICAS / FASES MAGMTICAS


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

FASES TECTNICAS EN TERRENOS METAMRFICOS E GNEO-

METAMRFICOS


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.

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.


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


1. Overprinting relations may be

produced by a single

deformation phase

2. Subsequent deformation

phases do not necessarily

produce overprinting relations

Passchier & Trouw (1995)


3. Only the relative age of deformation phases can be established

Passchier & Trouw (1995)


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).


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.


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.


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.


Estratificacin S0, pretectnica; clivaje S1 sintectnico y sinmetamrfico;

Granito pre? Sintectnico?; pre? Sinmetamrfico?

Foliacin de Plano Axial


Estratificacin S0, pretectnica; clivaje S1 sintectnico y sinmetamrfico;

Foliacin de Plano Axial REFRACCIN DEL CLIVAJE

1.B.FASES DEFORMACI+ôN

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