A jadeite–quartz–glaucophane rock from Karangsambung, central Java, Indonesia

Abstract

High‐pressure metamorphic rocks are exposed in Karangsambung area of central Java, Indonesia. They form part of a Cretaceous subduction complex (Luk–Ulo Complex) with fault‐bounded slices of shale, sandstone, chert, basalt, limestone, conglomerate and ultrabasic rocks. The most abundant metamorphic rock type are pelitic schists, which have yielded late Early Cretaceous K–Ar ages. Small amounts of eclogite, glaucophane rock, garnet–amphibolite and jadeite–quartz–glaucophane rock occur as tectonic blocks in sheared serpentinite. Using the jadeite–garnet–glaucophane–phengite–quartz equilibrium, peak pressure and temperature of the jadeite–quartz–glaucophane rock are P = 22 ± 2 kbar and T = 530 ± 40 °C. The estimated P–T conditions indicate that the rock was subducted to ca 80 km depth, and that the overall geothermal gradient was ∼ 7.0 °C/km. This rock type is interpreted to have been generated by the metamorphism of cold oceanic lithosphere subducted to upper mantle depths. The exhumation from the upper mantle to lower or middle crustal depths can be explained by buoyancy forces. The tectonic block is interpreted to be combined with the quartz–mica schists at lower or middle crustal depths.

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

“…At the present stage, only K-Ar ages interpreted as the timing of exhumation were recognized in these complexes, which show similar ranges for the Luk Ulo (110-124 Ma: Ketner et al, 1976;Miyazaki et al, 1998; Par- Figure 13. Compiled P-T conditions of high-pressure metamorphic rocks from the Bantimala and Luk Ulo Complexes.…”

“…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)]. …”

“…The high-pressure metamorphic rocks from the Luk Ulo Complex show lower pressures and temperatures than the Bantimala Complex. Miyazaki et al (1998) estimated the peak condition of jadeite-garnet-quartz-glaucophane rock as 2.2 ± 0.2 GPa at 530 ± 40°C (Fig. 13).…”

Reaction microtextures in jadeitites from the Nishisonogi metamorphic rocks, Kyushu, Japan

“…They described the layers as forming from pre Alpine silicic dykes during the early Alpine high P/T metamorphism. Miyazaki et al (1998) found quartz, glaucophane, phengite, and garnet inclusions in jadeite in a jadeite quartz glaucophane rock forming a tectonic block in serpentinite occurring at Karangsambung in central Java, Indonesia, and estimated the P / T conditions of the metamorphism. Radvanec et al (1998) described a three dimensional image of chemical zoning in a jadeitic pyroxene with quartz, lawsonite, and titanite inclusions occurring in Franciscan quartzose metagraywackes.…”

Subsidence and uplift by slab-related mantle dynamics: a driving mechanism for the Late Cretaceous and Cenozoic evolution of continental SE Asia?

“…5d), are diagnostic of subduction metamorphism . Radiolarian biostratigraphy (Wakita & Munasri 1994) and K -Ar dates on muscovite from quartz-mica schist (124 -110 Ma; Miyazaki et al 1998;Parkinson et al 1998) yield Cretaceous ages for subduction-related rocks. In the Meratus Mountains, SE Borneo, ultramafic rocks (Fig.…”