Petrology and Geochemistry of Igneous Rocks in Gunung Badak Complex, Ciletuh Palabuhanratu Geopark, Sukabumi, West Java

Abstract

Gunung Badak Complex is located in Ciletuh Palabuhanratu UNESCO Global Geopark, which preserves significant records of tectonic evolution in Southern West Java. This research aims to characterize igneous rocks and interpret tectonic implications. The methodology includes petrographic analysis, major element geochemical characterization using X-Ray Fluorescence (XRF), and trace elemen and Rare Earth Element (REE) analysis using Inductively Coupled Plasma Mass Spectrometry (ICP-MS) from 8 selected samples. The results identify three distinct rock groups consisting of diorite (SiO₂ 51.5-52.48%), basalt (SiO₂ 50.69-52.52%), and serpentinized peridotite (SiO₂ 40.59%, MgO 34.63%). Diorite and basalt exhibit tholeiitic affinity with low K₂O (0.25-0.69%), Mg# 49.67-58.13, indicating early-stage island arc magmatism. Serpentinized peridotite exhibits residual harzburgite characteristics with Mg# 89.29. Trace element geochemistry shows enrichment of LILE (Cs, Ba, Pb, Sr) relative to HFSE (Nb, Zr), with negative Nb-Ta anomalies and La/Nb ratios of 2.21-3.75 typical of subduction environments. Diorite-basalt displays moderate LREE enrichment ((La/Yb)N 1.38-2.40), while serpentinized peridotite shows LREE depletion ((La/Yb)N 0.54). Dy/Yb ratios (1.20-1.91) indicate magma sources from partial melting of spinel peridotite at depths <50 km. The geodynamic model indicates that serpentinized peridotite originated from lithospheric mantle in a supra-subduction zone (SSZ) environment during Eocene subduction initiation, while diorite and basalt formed during early Miocene island arc magmatism (~22 Ma).