Electronic Theses and Dissertation

Daerah Penelitian ini secara administratif terletak pada daerah Kecamatan Geumpang dan sekitarnya, Kabupaten Pidie, Provinsi Aceh. Koordinat geografis daerah penelitian terletak pada 96°6'12,90" BT - 96°9'27,50" BT dan 4°50'24,70" LU – 4°48'14,60" LU dengan luas blok sekitar ± 24 km². Formasi Geumpang yang terletak di Lembar Takengon merupakan salah satu wilayah dengan potensi geologi yang kompleks akibat pengaruh tektonik aktif, keberagaman litologi, dan dinamika geomorfologi. Penelitian ini bertujuan untuk mengkaji kondisi geologi permukaan, menganalisis klasifikasi batuan beku berdasarkan kajian petrologi dan petrografi, serta memahami proses petrogenesa batuan beku basa-intermediet yang berkembang di daerah penelitian. Permasalahan utama yang dikaji meliputi karakteristik geologi regional, pengenalan jenis batuan beku berdasarkan komposisi mineralnya, serta interpretasi asal-usul dan proses pembentukan batuan tersebut dalam kaitannya dengan tatanan tektonik regional. Metode yang digunakan meliputi pemetaan geologi permukaan, analisis geomorfologi untuk identifikasi satuan bentuk lahan, serta analisis laboratorium petrografi untuk mengamati tekstur dan mineralogi batuan. Hasil analisis menunjukkan bahwa wilayah penelitian terbagi ke dalam lima satuan bentang alam, meliputi unit tubuh sungai (F1), unit bentuk lahan dataran banjir (F3), unit bentuk lahan tanggul fluvial, pematang fluvial dan zona pointbar (F4), unit bentuk lahan dataran denudasional (D5) serta unit topografi bergelombang kuat hingga perbukitan (S3). Litologi berdasarkan stratigrafi yang tua hingga muda tersusun atas satuan metagamping Jaleum, sekis Geumpang, andesit Geumpang, serpentinit, serta endapan aluvium. Sesar berarah barat laut–tenggara berdasarkan analisis kekar dan keterdapatan sesar dari Sumatra Fault System (SFS) menjadi elemen struktural utama yang memengaruhi pola sebaran batuan dan deformasi regional. Hasil petrografi menunjukkan bahwa batuan beku termasuk jenis andesit dengan komposisi plagioklas labradorite dan mineral mafik seperti piroksen (klinopiroksen dan ortopiroksen). Proses petrogenesa mengindikasikan bahwa batuan andesit pada Formasi Geumpang terbentuk dari magma intermediet yang berkembang di zona subduksi pada busur pulau samudra (oceanic island). Proses diferensiasi magma dari basal hingga intermediet mencerminkan dinamika tektonik aktif pada tatanan Intra-oceanic.

Kata kunci: Petrografi, Andesit, Magma intermediet, Intra-oceanic.

The study area is administratively located in the Geumpang sub-district and its surroundings, Pidie district, Aceh province.Geographical coordinates the research area is located at 96°6'12.90" East Longitude - 96°9'27.50" East Longitude and 4°50'24.70" North Latitude - 4°48'14.60" North Latitude with a block area of approximately ± 24 km². Geumpang Formation which located in the Takengon Sheet is one of the areas with complex geological potential due to the influence of tectonic geological potential due to the influence of active tectonics, lithologic diversity, and geomorphologic dynamics. This study aims to assess the surface geological conditions, analyze the classification of igneous rocks based on petrological and petrographic studies, and to understand the petrogenesis process of basalt-intermediate igneous rocks that developed in the study area. The main issues studied include regional geological characteristics, introduction of igneous rock types based on their mineral composition, and interpretation of the origin of the mineral composition, and interpretation of the origin and formation process of these rocks in relation to regional tectonic settings. Methods used include surface geological mapping, geomorphological analysis to identify landform units, and petrographic laboratory analysis to observe the texture and mineralogy of rocks. The analysis results show that the study area is divided into five landscape units, including river body units (F1), floodplain landform units (F3), fluvial embankment landform units, fluvial bunds and pointbar zones (F4), denudational plain landform units (D5) and strongly undulating to hilly topographic units (S3). Lithology based on the old to young stratigraphy is composed of Jaleum metalimestone, Geumpang schist, Geumpang andesite, serpentinite, and alluvium deposits. The northwest-southeast trending fault is based on the analysis of the joint and fault occurrences of the Sumatra Fault System (SFS) is the main structural element that influences the pattern of rock distribution and regional deformation. Petrographic results show that the igneous rocks belong to the andesite type with a composition of plagioclase labradorite and mafic minerals such as pyroxene (clinopyroxene and orthopyroxene). The petrogenesis process indicates that the andesite rocks in the Geumpang Formation were formed from intermediate magmas that developed in the subduction zone of the oceanic island arc. The process of magma differentiation from basalt to intermediate reflects the active tectonic dynamics of the Intra-oceanic setting. Keywords: Petrography, Andesite, Intermediate magma, Intra-oceanic.