Studi Karakteristik Batuan Metamorf di Perbukitan Jiwo Barat, Bayat, Kabupaten Klaten, Jawa Tengah

Abstract

The outcrops, which are found in Bayat Complex, consist of Igneous Rocks, Sedimentary and Metamorphic, with ranges of age are from Pre – Tertiary until Neogen. This is may cause of various question about history of geology and tectonic setting of research area. Therefore, this research is majored to know the characteristic of metamorphic rock, including character in the field and microscopic one that will be used to estimate tectonic history that happened in research area.This research has purpose to know the relation between metamorphic rock and other kind of rock around, and the microscopic condition of metamorphic rock including texture, structure, and mineralogy. The characteristic is used as a base in determining metamorphic facies and estimating rock origin, to know petrogenesis of metamorphic rock which later be used to interprets the tectonic history of research area.This research is conducted by using survey and descriptive method. Survey method is done with field investigation at research area, which aims to know geological condition, such as lithology, structure of geology, stratigraphy and geomorphology. Descriptive method is done by describe and interpret the characteristic of metamorphic rock which in research area, to know the process of geology that having an effect on. The next job is analyzing the obtained data by using method of mapping and petrography. The result of this research is that metamorphic rock inclusive into group of low metamorphic degree (low grade), marked by muscovite - chlorite schist, chlorite schist, and phyllite. According to classification of Miyashiro (1973), group of this metamorphic rock inclusive into Greenschist facies, marked by attendance of muscovite, chlorite and quartz minerals. According to model compiled by Winkler (1986), representing modification from Miyashiro (1973), this facies was formed at temperature with range from 300° - 400 C and at pressure 0,2 - 0,5 GPa or equal to 2×108 - 5×108 kg/ms2. Based on mineral content of muscovite - chlorite schist, estimated that this rock has through a retrograde metamorphism, marked by attendance of muscovite and chlorite representing recristalization of biotit, and plagioclase minerals. The protolith of metamorphic rock in research area is rock with continent origin characteristic such as siltstone and claystone, in addition, most of the igneous rock that found has intermediate composition until felsic, and the sedimentary rock shows an inner shelf sedimentary environment. Thereby, can be interpreted that rock group in research area represent convergent complex distinguish continent origin which formed by effect of collision between Eurasia Continental Plate and Microcontinent of East Java at Latest Cretaceous.