FASIES METAMORFISME BASEMENT FORMASI TARAP, KOMPLEK GARBA, BUKIT SITULANGLANG, DESA LUBAR, OGAN KOMERING ULU SELATAN, SUMATERA SELATAN
Abstract
ABSTRAK: Komplek Garba merupakan salah satu produk subduksi Mesozoikum antara Blok Woyla sebagai bagian dari kerak samudera dan West Sumatra Block sebagai bagian dari blok kontinental. Lokasi penelitian terletak di Bukit Situlanglang yang merupakan bagian timur dari Komplek Garba, Desa Lubar, Sumatera Selatan. Produk subduksi lampau menyebabkan tersingkapnya salah satu formasi batuan Pra Tersier berupa batuan metamorf berumur Paleozoikum yang berasal dari West Sumatra Block. Tujuan penelitian yaitu mengidentifikasi karakteristik dan fasies metamorfisme Komplek Garba. Metode yang digunakan berupa pemetaan geologi menunjukkan adanya peningkatan derajat metamorfisme dari timur ke barat hilir sungai Tara, Bungin, dan Air Celau ke arah hulu yang cenderung meningkat ke arah Bukit Situlanglang yang tersusun oleh rijang. Berdasarkan hasil analisis petrografi menunjukkan derajat metamorfsme rendah-sedang seperti batuan filit klorit, filit aktinolit, sekis epidot, sekis hornblend, sekis grafit, sekis klorit, dan sekis muskovit. Batuan di daerah telitian menunjukkan protolith yang berasal dari batuan pelitik, batuan beku mafik, dan ortho-rock. Selain metamorfisme regional, juga ditemukan marmer dan kuarsit yang menunjukkan pengaruh tektonik berupa sesar yang terlihat berupa deformasi pada mineral kuarsa sebagai hasil dari metamorfisme kontak. Fasies di daerah telitian disimpulkan berupa Fasies Greenschist, Epidote-Amphibolite, dan Amphibolite sehingga keterbentukan batuan metamorf menunjukkan pengaruh tektonik yang dominan dipengaruhi oleh kerak kontinental berupa kolisi antara West Sumatra Block dan East Sumatra Block. Namun, kehadiran protolith berupa batuan mafik menunjukkan adanya pengaruh kerak samudera yang berasal dari Woyla Arc.
Kata Kunci: fasies metamorfisme, batuan metamorf, subduksi, batuan basement, Paleozoikum
ABSTRACT: Garba Complex is one of the Mesozoic subduction product between Woyla Block as the part of oceanic crust and West Sumatra Block as the continental crust. The research area located in Situlanglang Hills in the eastern part of Garba, Desa Lubar, South Sumatra. The product of the subduction caused the exposed of one of the Pre Tertiary Formation, the Paleozoic age of metamorphic rocks originated from West Sumatra Block. The purpose of this study is to identify the characteristic, and metamorphic facies of Garba Complex. Based on the geological mapping showed the distribution of the metamorphic rocks that increasing in grade from east to west of downstream of Tara, Bungin, and Air Celau River to upstream relatively increasing towards the Situlanglang Hills (chert member of Garba Formation). Furthermore, from petrography analysis showed the low-moderate grade metamorphism that consist of chlorite phyllite, actinolite phyllite, epidote schist, hornblend schist, graphite schist, chlorite schist, and muscovite schist. The rocks in this study area show the protolith originated from pelitic, mafic rock, and ortho-rock. Beside the regional metamorphism products, there are also found marble and quartzite rocks which show the tectonic product of fault in the form of deformation on quartz minerals as a result of contact metamorphism. The facies in the study area were concluded in the form of Greenschist Facies, Epidote-Amphibolite, and Amphibolite Facies so that the formation of metamorphic rocks showed dominant tectonics affected by continental crust in the form of collisions between West Sumatra Block and East Sumatra Block. However, the presence of protoliths in the form of mafic rocks shows the influence of oceanic crust originating from the Woyla Arc.
Keywords: metamorphic facies, metamorphic rocks, subduction, basement rocks, Paleozoic
