Deformation in the blueschists of the Greater Antilles: subduction versus collision processes

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ABSTRACTS

415

Deformation in the blueschists of the Greater Antilles: subduction versus collision processes * G. Draper ~ep~rtrn~~t of Geoiogy Fi~r~da International (Received

University, Miami, FL 33199, USA

November

27,1989)

Abstract In the Greater occur in several

Antilles, tectonic

Cretaceous blueschists settings and exhibit a

variety of deformation states, allowing the region to be used as a test case to formulate a preliminary model for the relation of blueschist deformation

to processes

(or less dramatic continental

of subduction

docking)

and collision

with buoyant

deformation

states occur in

Bahama

platform.

to the Late Cretaceous Antilles arc with the

Samana

probably

represents

of meta-igneous

a

some

blocks, into

these

coherent

blueschist-greenschist

fabrics terranes

transition

rocks that are moderately deformed. Planar tectonite fabrics dominate and strain is not parhigh.

Part

fractured,

and

fracturing

related

metamorphic

The rocks of both areas have undergone multiphase deformation which produced tectonite fabrics and tight to isoclinal folds. The Escambray related Greater

In

of the terrane

this is possibly

The blueschists

coherent metasedimentary terranes in central Cuba (Escambray) and eastern Hispaniola (Samana).

rocks are clearly collision of the

fabrics.

may be tightly folded. The melanges protrude

ticularly

oceanic,

or arc material.

The most complex

tectonite

is pervasively

due

to hydraulic

to rapid exhumation. of Jamaica

L-S

fabrics,

exhibit which

distinct become

synmore

planar as the terrane grades into the greenschist facies. The linear component of the fabric appears to be parallel to the trend of the subduction zone in which they formed-a feature also observed in the Sanbagawa Belt of Japan. The origin of this feature

is problematic,

transcurrent

movement

but

may

be

following

related

collision

to or

fragment of the Bahama platform which underplated the Hispaniola part of the Greater Antilles

docking

arc in the Early Tertiary. Undeformed blueschists occur as tectonic blocks in protrusive serpentinite melanges in the

the Greater Antilles blueschists is suggested. During the early stages of subduction, deformation in

with buoyant

A model to explain

ocean crust. the deformation

features

of

Rio San Juan Complex of north-central Hispaniola (and possibly in Oriente, eastern Cuba). The blocks are thought to represent fragments of the hanging wall of the subduction zone, which were cooled

the subduction zone was absent or limited to the footwall. The undeformed rocks in the hanging wall were later incorporated into rising serpentinite

during the initial stages of subduction and incorporated into rising serpentinite diapirs. A later serpentinite melange protrudes the earlier body and contains blueschists blocks with S-L or L-S

blueschists is produced when buoyant crust is introduced into the subduction zone, in the form of oceanic plateaus or seamounts (? Jamaica) or continental material (Samana, Escambray). Deformation is probably concentrated in the footwall of the subduction, and is only found in the hanging wall when fragments of the downgoing plate are detached to underplate the hanging wall. If minor

* Supported 8306148

by National

Science

and EAR 8509452.

Elsevier Science Publishers

B.V.

Foundation

grants

EAR

diapirs

(Rio

San Juan,

Oriente).

Deformation

of

416

topograhic highs of the downgoing plate are detached and accreted in this manner during normal subduction, they may then be sampled by later serpentinite diapirs (Rio San Juan). Rapid uplift

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ABSTRACTS

and consequent unloading following cessation of subduction (especially if caused by the introduction of buoyant material) may produce extensive hydraulic fracturing.