Sub-ophiolite metamorphic rocks in the Tungku area, Lahad Datu, eastern Sabah, Malaysia: origin and tectonic significance

Abstract

Sub-ophiolite metamorphic rocks (garnet amphibolites) found as clasts in late Early Miocene to late Middle Miocene melange formed at high pressures and temperatures are interpreted as derived from a metamorphic sole underlying the Darvel Bay Ophiolite Complex, formed during subduction of ocean crust and the emplacement of the ophiolite complex in Sabah. Mineral chemistry and bulk rock geochemistry of the garnet amphibolites show that they are MORB tholeiites and represent oceanic crustal materials. These rocks were metamorphosed as pyroxene granulites and garnet amphibolites at high temperatures and pressures characteristic of upper mantle and were deformed and recrystallised with mylonitic textures in the amphibolite facies. A KlAr age of 76 ± 21 Ma obtained from garnet amphibolite during the present study coincides with the Late Cretaceous-Palaeogene age of subduction beneath the Darvel Bay Ophiolite inferred from the stratigraphic evidence.