On the structure and tectonic evolution of the Taku Schists and their surrounding units, Kelantan, NE Malaysia
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Structural field-data collected in the Taku Schists and surrounding units in the state of Kelantan, NE Malaysia, indicate a structure of an asymmetric, doubly plunging anticline, with a steeply dipping eastern flank. The contact with the surrounding sediments in the southeast was found to be mylonitic, indicating severe shearing along the contact zone. Stretching lineations developed throughout the Taku Schists, show a dominant plunge direction of 130E. Kinematic indicators show that the tectonic movement is dominantly top down to southeast. The results are used to construct a comprehensive tectonic evolution of the Taku Schists. The protoliths of the schists are Early to Middle Permian deposits, accumulated on the fore-arc of the Sukhothai volcanic arc. They are affected by regional contractional event, D1, during the Triassic collision of the Sibumasu Terrane and the Sukhothai Arc. The D1-structures are the pervasive foliation fabric S1 and regional thrust faulting. The D1-event is synchronous with the metamorphic event M1, which is burial metamorphism in amphibolite facies. In Cretaceous times, the Stong Complex intrudes in the crust as a result of decompression melting. Crustal thinning causing decompression is related to slab rollback of the oceanic slab subducted during the Triassic collision. During the Late Cretaceous, subduction of the Australian plate along the Sunda margin ceases for a short period of time due to continental collision with a micro-continental plate. Resumed subduction causes N-S oriented contraction, folding the S1 foliation fabric in open folds with E-W oriented axial planar strike (D2). Eocene dextral transtension moves the East Malaya Block to the southeast, and causes localised exhumation (D3). The Taku Schists are exhumed as a result of the localised exhumation, along the detachment plane in the southeast. The driving mechanism is most consistent with simple shear models for metamorphic core complexes. This model explains the doubly plunging anticlinal geometry of the foliation fabric S1, the consistent stretching lineations with top down to southeast kinematics, the mylonitic zone along the southeast border of the Taku Schists, the parallelism between fold hinges throughout the Taku Schists and the stretching lineations, and the similarity between kinematics of young normal faults and of the stretching lineations. The Stong Complex shows localised deformation structures with parallel stretching lineations and shear sense kinematics to those observed in the Taku Schists. These structures are resultant of the same transtensional deformation event, D3. The exhumation mechanism for the Stong Complex is therefore the same as for the Taku Schists: most consistent with the simple shear model for metamorphic core complexes.