KARAKTERISTIK STRUKTUR GEOLOGI DAN PERANANNYA TERHADAP SISTEM PANAS BUMI NAGE, KABUPATEN NGADA, PROVINSI NUSA TENGGARA TIMUR

Abstract

Nage Region is part of Sunda-Banda Arc volcanism which formed an en-echelon array in Flores Island. The complex regional tectonics setting of the study area has created intensively found geological structures in the study area. The study was made through identification of structural geology by topographic lineament analysis, river lineament, circular features, and fault fracture density in DEMNAS image and followed by field observation to identify primary and secondary geological structures in 87 stations.The measurements of 441 geological structures positions in the study area found that secondary geological structures, mainly shear fractures, in order to identify the occurence of minor faults which are found in Quarternary rocks in the study area. Kinematic analysis of minor faults confirms the occurence of NW-SE and NE-SW oblique strike slip faults and also NE-SW directed strike slip fault. Normal faults in the study area are ffound as circular features which has been formed and associated with caldera collapse and crater forming processes. Dynamic analyses of faults are conducted to determine the principle compressive stress orientation which formed the faults has concluded that the compressional regime of the study area occured in the NNE-SSW direction with maximum stress (σ1) direction is 16°, N 203°E and minimum stress (σ3) direction is 17,5°, N 297,1°E. Faults are interpreted to have roles as fluid pathway in the developing geothermal system based on the occurence of hotspring manifestation and hydrothermal alteration. Based on the configuration of faults, geothermal manifestation, and hydrothermal alteration, it can be concluded that there are at least three fluid flow in the study area which are correlated with hydrothermal fluid ascent through fault F1 and bounded by fault F3, hydrothermal fluid ascent through fault F2, and hydrothermal fluid ascent from boiling through fault F10Daerah Nage merupakan bagian dari jalur vulkanisme Busur Sunda-Banda yang membentuk rangkaian en-echelon di Pulau Flores. Tatanan tektonik regional di Pulau Flores yang cukup kompleks menyebabkan adanya struktur geologi yang intensif di daerah penelitian. Metode penelitian yang digunakan meliputi pengamatan struktur geologi melalui analisis kelurusan topografi, kelurusan sungai, fitur melingkar dan densitas kelurusan (fracture fault density) dengan menggunakan citra DEMNAS serta pengukuran secara langsung di lapangan terhadap unsur-unsur struktur geologi primer dan sekunder pada 87 stasiun pengamatan. Pengukuran terhadap 441 kedudukan struktur geologi di daerah penelitian, menunjukkan bahwa struktur geologi sekunder, utamanya berupa kekar gerus, yang berguna untuk membuktikan kehadiran sesar yang memotong batuan berumur Kuarter pada daerah penelitian. Hasil analisis kinematika menyimpulkan bahwa terdapat sesar geser oblik berarah baratlaut-selatan tenggara dan timurlaut-baratdaya serta sesar geser berarah timur laut-baratdaya. Daerah penelitian terdapat fitur melingkar yang berasosiasi dengan peruntuhan kaldera dan pembentukan kawah. Analisis dinamik sesar untuk menentukan arah tegasan kompresif menunjukkan bahwa daerah penelitian mengalami deformasi kompresional berarah utara timurlaut-selatan baratdaya dengan arah tegasan maksimum (σ1) 16°, N 203°E dan arah tegasan minimum (σ3) 17,5°, N 297,1°E. Keberadaan struktur sesar diinterpretasikan memiliki peran sebagai jalur fluida terhadap sistem panas bumi Nage yang tampak dari kehadiran manifestasi panas bumi dan alterasi hidrotermal. Berdasarkan konfigurasi sesar, manifestasi, dan alterasi hidrotermal disimpulkan bahwa setidaknya terdapat tiga aliran fluida, yakni aliran fluida hidrotermal yang naik melalui sesar F1 dan dibatasi sesar F3, aliran fluida yang naik melalui sesar F2, dan aliran fluida hasil pendidihan yang naik melalui F10.