MORPHOMETRIC, PETROGRAPHY, AND GEOCHEMISTRY ANALYSIS OF PILLOW LAVA IN KARANGSAMBUNG: IMPLICATION FOR TECTONIC SETTING KARANGSAMBUNG

• Main Author: Gunarsih, Dina
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/45697
• Institution: Institut Teknologi Bandung

Karangsambung has a distinct dimension of pillow lavas outcrop located in Kali Muncar, Kali Mandala and Kali Susu. Pillow size indicates the original condition under which the pillows formed. These pillows are interpreted as having the same tectonic setting, but disparate slope and depth affected on pillows dimension. This research aims to understand the formational condition of pillow lavas and its implication for tectonic setting in Karangsambung, assuming the pillow outcrop is as same as its origin. The number of data used in this research is 222 data of pillows size. The number of samples analyzed by petrography is 20 rocks. Major and trace element geochemistry of six samples of rock are analyzed by using X-Ray Fluorescence (XRF), whereas rare earth element of three samples is analyzed by Inductively Coupled Plasma – Optical Emission Spectrometry (ICP-OES). Further, cooling time and relative viscosity of 12 samples and cooling rate of six samples are determined by using Crystal Size Distribution method. Based on geochemistry and petrography, these lavas have tholeiitic magma affinity related to mid-oceanic ridge tectonic setting. Kali Muncar has perfect pillows shape, 1,89 mean ratio width and length, a little interpillow matrix abundance, and 11 % - 27% phenocryst abundance. Cooling time of its crystal is 9,7 to 10,3 months, 7,90 x 10-10 K/s to 9,09 x 10-10 K/s cooling rate, and 1,49 to 1,99 relative viscosity. Kali Susu has unperfect and flat pillows shape, 1,51 mean ratio width and length, and more abundant of interpillow matrix than Kali Muncar pillows. Phenocryst abundance of rock sample in Kali Susu is 10% to 14%, 5,1 to 10,3 months of cooling time, 33,10 x 10-10 K/s to 36,42 x 10-10 K/s cooling rate, and 1,44 to 1,60 relative viscosity. Further, Kali Mandala has very unperfect and flat pillows shape, 1,02 mean ratio width and length, and the most abundant of interpillow matrix. Phenocryst abundance of rock sample is 22% to 30%, 11,7 to 12 months of cooling time, 1,76 x 10-10 K/s to 1,80 x 10-10 K/s cooling rate, and 2,49 to 2,59 relative viscosity. The result indicates the different formational of pillow lava in Karangsambung. Pillow lavas in Kali Muncar were formed on the most-gentle slope, the deepest water column depth, a slower cooling time, and decrease cooling rate. In Kali Susu, the pillows were formed on a steeper slope and shallower water column depth than Kali Muncar, but having the fastest cooling time, and increase cooling rate. In contrast, pillow lavas in Kali Mandala were formed on the steepest slope, the shallowest water column depth, the slowest cooling time, and a very decrease cooling rate. The result is concluded there were three conditions of the slope when oceanic spreading floor occur: the most gentle slope, a steeper slope, and the steepest slope