Abstract The Bantimala Complex of South Sulawesi, Indonesia is an assemblage of northeast-dipping tectonically stacked slices. The slices consist mainly of high pressure metamorphic rocks, radiolarian chert, breccia, sandstone and shale, and melange. In order to understand the tectonic evolution of the Bantimala Complex, we have investigated the lithology, age, stratigraphy, structure and relationships of the components. The K-Ar ages of high P-low T metamorphic rocks suggest that an oceanic plate subducted beneath the Sundaland continent during the Late Jurassic or earliest Cretaceous. The subduction ceased during the Albian, and the high pressure schists were exhumed and eroded at the surface before and during the deposition of middle Cretaceous radiolarian chert. The exhumation of the schists was related to the collision of microcontinents derived from Gondwanaland. The Jurassic shallow marine sedimentary rocks in the Bantimala Complex are possibly remnant fragments of the collided microcontinent. Tectonic stacking of the Bantimala Complex was caused by Neogene subduction and collision of another continental fragment further to the east.
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.
To help optimize tsunami warning system in Indonesia, particularly concerning non-seismically inducted tsunamis and at the subnational level, this study employs a qualitative methodology to draw lessons from the Anak Krakatau-induced tsunami on December 22, 2018. A total of 37 community members and 35 government officials in Pandeglang Regency and at the national level participated in in-depth interviews and focus groups discussions. Participants emphasized bureaucratic mismatches and delays, underlining the urgent need for clearer national-subnational communication. The study presents concrete and actionable recommendations for refining warning reception, decision-making, legitimization processes and warning dissemination. Proposed changes such as diversifying information sources and localizing tsunami siren control aim to empower local entities and expedite responses, overall increasing community preparedness for future tsunami threats. By contrasting the experiences and recommendations of affected communities, local government and national-level actors, the study makes a case for improving warning systems based on the past experience and recommendations of the first concerned and first impacted.
Abstract The Bantimala Complex of South Sulawesi consists mainly of mélange, 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 stratigraphie 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.
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