The Lubok Antu Melange, Lupar Valley, West Sarawak: a Lower Tertiary subduction complex


Author : Denis N.K. TanPublication : Bulletin of the Geological Society of MalaysiaVolume : 15Page : 31 – 46Year : 1982


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Bulletin of the Geological Society of Malaysia, Volume 15, December 1982, pp. 31 – 46

 

The Lubok Antu Mélange, Lupar Valley, West Sarawak: a Lower Tertiary subduction complex

DENIS N.K. TAN 

Geological Survey of Malaysia, Kuching

 

Abstract: Detailed mapping in the Lupar Valley has resulted in the recognition of a Lower Tertiary mélange here called the Lubok Antu Mélange, and the presence of low-grade regional metamorphic rocks of the prehnite-pumpellyite facies. The Lubok Antu Mélange consists of blocks of Lower Cretaceous radiolarian chert, Upper Cretaceous graywacke and slate, ?Cretaceous and Eocene limestone, calcareous shale, mudstone and sandstone, hornfels, basalt, spilite and gabbro and their metamorphosed equivalents, and serpentinite in a pervasively sheared, dark gray pelitic matrix which, in places, yields fossils of early Tertiary age. It is bounded on the southwest by the Silantek Formation and on the northeast by the Lupar Formation. The metagraywacke, metaconglomerate, metavolcanic rocks and metagabbro, northeast of the Lupar Fault Zone, contain metamorphic mineral assemblages characteristic of the prehnite-pumpellyite facies, indicating low thermal gradient during alteration and, hence, a comparatively high-pressure, low-temperature metamorphism.