Early Cretaceous tectonic events implied in the time‐lag between the age of radiolarian chert and its metamorphic basement in the Bantimala area, South Sulawesi, Indonesia

Abstract

The Bantimala Complex of South Sulawesi consists mainly of mklange, chert, basalt, ultramafic rocks and high pressure type metamorphic rocks. Well-preserved radiolarians were extracted from 10 samples of chert, and K-Ar age dating was done for muscovite from five samples of schist of the Bantimala Complex. The radiolarian assemblage from chert is assigned middle Cretaceous (late Albian-early Cenomanian) age, while the K-Ar age data from schist range from 132 Ma to 114 Ma except for one sample with rare muscovite. The radiolarian chert is unconformably underlain by schist in the Bantimala Complex. The stratigraphic relationship and the time lag of these two kinds of age data from chert and underlying schist suggest short-time tectonic events immediately followed by a quick waning tectonism in this region during the Albian-Cenomanian transgression.

Prograde and retrograde evolution of eclogites from the Bantimala Complex in South Sulawesi, Indonesia

“…K-Ar phengite datings of the eclogites and garnetglaucophane rocks from the Bantimala Complex yielded ages ranging from 113 ± 6 to 137 ± 3 Ma, interpreted as exhumation ages (Wakita et al, 1994Parkinson et al, 1998).…”

“…Hatched areas represent the inferred P-T conditions for the oceanic crust beneath present-day NE Japan (cold) and SW Japan (warm) subduction zones (Peacock and Wang, 1999). kinson et al, 1998) and Bantimala Complexes (113-137 Ma: Wakita et al, 1994Wakita et al, , 1996Parkinson et al, 1998). As a consequence, there are two possibilities for the subduction system in these complexes: (1) the Bantimala and Luk Ulo Complexes might be derived from different subduction complexes, similar to the NE and SW Japan subduction system, or (2) the Bantimala and Luk Ulo Complexes are derived from a single subduction system, as proposed by Hamilton (1979), Parkinson et al (1998), and Kadarusman et al (2007), and experienced metamorphic evolution as a result of increasing/decreasing geothermal gradients during continuous subduction.…”

“…1b). The Bantimala Complex is a tectonic stack of slices mainly consisting of various sedimentary rocks, ultramafic rocks, metabasites, and metapelites with ages ranging from Jurassic to middle Cretaceous (Sukamto, 1982;Wakita et al, 1994Wakita et al, , 1996Miyazaki et al, 1996;Parkinson et al, 1998). The metamorphic rocks mainly occur within a mélange unit.…”

“…This was deduced from the common occurrence of high-pressure metamorphic rocks, an accretionary complex, mélange unit, serpentinite in the two complexes, along with relatively similar ranges of Cretaceous K-Ar ages [113-137 Ma for Bantimala Complex (Wakita et al, 1994Parkinson et al, 1998); 110-124 Ma for Luk Ulo Complex (Ketner et al, 1976;Miyazaki et al, 1998;Parkinson et al, 1998)]. …”

“…1a). The study area (South Sulawesi) predominantly comprises sandstone, shale, chert, basalt, dunite, lherzolite, serpentinite, and various metamorphic rocks ranging from low grade to eclogite-facies conditions (Sukamto, 1982;Wakita et al, 1994Wakita et al, , 1996Miyazaki et al, 1996;Parkinson et al, 1998) (Fig. 1b).…”