Early cretaceous (pre-Albian) radiolarians from blocks in Ayer Complex melange, eastern Sabah, Malaysia, with comments on their regional tectonic significance and the origins of enveloping melanges

Abstract

Radiolarians provide age constraints for chert blocks occurring in a Miocene mudstone matrix melange located between Lahad Datu and the Segama River in eastern Sabah. Chert samples have yielded a moderately well-preserved radiolarian fauna of Early Cretaceous (?pre-Albian) age. This age is notably older than basement oceanic rocks in the nearby Sulu and Celebes seas. Tectonic reconstructions indicate that the Chert-Spilite Formation of eastern Sabah, from which the blocks were most probably derived, may represent fragments of early Pacific ocean seafloor. These blocks were incorporated into mud-matrix melange which developed during Early Miocene NW-directed collision and overthrusting of the Sulu volcanic arc onto thinned continental crust rifted from South China. Diapiric ascent of muds overpressured during this collision occurred in response to extensional relaxation and rifting in the Sulu Sea.