U-Pb zircon geochronology and geochemistry of Luk Ulo River boulders belong to Late Cretaceous-Paleocene metapsammite and metagranite of Luk Ulo Karangsambung, Central Java, Indonesia.

Abstract

The rock formation of late Cretaceous-Paleocene metapsammite and metagranite found across Luk Ulo Complex indicated boulders with diameter of approximately 1m and rounded shape along Luk Ulo River, Indonesia. However, less research found on geochronology and geochemistry has been conducted in study area, and such rocks require comprehensive understanding of magmatism and tectonic environment of Central Java, Indonesia. Therefore, the main objective of this study is to address the geochemical and geochronological age histories across Central Java, Indonesia, using U-Pb zircon dating technique. Generally, most common types of rocks were observed which composed of hornblende and garnet-bearing metapsammite and metagranite. The geochemical study showed that protolith of rocks with hornblende was identified as Cordilleran granitoid (I-type), which originated from magmatic arc with basaltic differentiation. Furthermore, protolith of rocks containing garnet was categorized as Caledonian granitoid (S-type), which is caused by post-collisional orogeny. The cluster observations of magmatic zircons reveal their magmatic ages, which vary from 67.00 ± 1.2 to 69.10 ± 0.91Ma (late Cretaceous), whereas ages of inherited zircons ranged from 100 ± 5 to 437 ± 13Ma (early Cretaceous to Silurian). Estimated periods of partial melting were found between 100 ± 5Ma and 118 ± 4Ma (early Cretaceous). Comparing the zircon ages of Luk Ulo with the zircon ages from the Sundaland regions reveals that the age distribution patterns are incredibly similar; the peak ages dispersed between the Cretaceous and Triassic periods, as well as Sundaland region was the source of the materials.