Uploaded by User19472

SARI - 5 Agustus 2019

advertisement
SARI
Hasil vulkanostratigrafi dan studi petrogenesa Tangkubanparahu diuraikan berikut
ini. Geomorfologi diklasifikasikan kedalam empat satuan, yaitu: (1) Kawah
gunungapi, (2) Lereng gunungapi atas. (3) Lereng gunungapi tengah. (4) Lereng
gunungapi bawah. Khuluk Tangkubanparahu memiliki tiga gumuk poligenetik
dengan sembilan satuan batuan. Material hasil erupsi dan material hasil resedimentasi
vulkaniklastik membentuk struktur primer, sedangkan proses vulkanotektonik dan
proses geomorfik pada gunungapi ini membentuk struktur sekunder. Batuan beku
memiliki kandungan SiO2 antara 49%-58% berat (XRF). Plagioklas berada dalam seri
labradorit, andesin, oligoklas, dan albit, yang umumnya bertekstur aliran. Pola
diferensiasi segmented (diagram bivariat: K2O + NaO vs SiO2), co-magmatic
(diagram variasi unsur vs SiO2). Afinitas magma Tangkubanparahu adalah shoshinite
dan high-K calc-alkaline (K2O vs SiO2). Pembentukan magma primer berada di
wilayah batas lempeng (diagram trivariat: Ti, Zr, Y). Bukan dari zona pemekaran,
tapi dari zona subduksi (diagram bivariat: Th/Yb vs Ta/Yb; dan berdasarkan
kandungan TiO2). Tatanan tektonik pembentuk magma primer adalah busur
kepulauan (diagram bivariat Zr/Y vs Zr; diagram trivariat: TiO2, MnO, P2O5).
Komposisi magma primer berasal dari komposisi kimia MOR-B [diagram multielemen: Rb, Ba, K2O (%), Sr, Ce, P2O5 (%), TiO2, Ni, Cr].
Kata kunci: Tangkubanparahu, vulkanostratigrafi, petrogenesa.
i
ABSTRACT
The results of volcanostratigraphic and petrogenesis study of Tangkubanparahu are
described as follow. Geomorphology classified into four units, namely: (1) Craters,
(2) Upper volcanic slopes. (3) Middle volcanic slope. (4) Lower volcanic slopes.
Khuluk Tangkubanparahu has three poligenetic gumuks with nine rock units.
Material from eruption and from resedimentation form primary structure, while
volcanotectonic process and geomorphic process form secondary structures. Igneous
rock has SiO2 content between 49% -58% by weight (XRF). Plagioclase series are,
labradorite, andesine, oligoclase, and albite, which shows lava flow structures.
Differentiation patterns is segmented (bivariate diagram: K2O + NaO vs. SiO2), comagmatic (variation diagrams of elements vs. SiO2). Magmatic affinity of
Tangkubanparahu is shoshinite and high-K calc-alkaline (K2O vs. SiO2). Primary
magma is generated in the plate margin (trivariate diagram: Ti, Zr, Y). It is
generated from subduction zone, not from MOR (bivariate diagram: Th / Yb vs Ta /
Yb; and based on the composition of TiO2). Island-arc tectonic setting formed
primary magma (bivariate diagram Zr / Y vs. Zr; trivariate diagram: TiO2, MnO,
P2O5). Chemical composition of primary magma is derived from the chemical
composition of MOR-B [multi-element diagram: Rb, Ba, K22O (%), Sr, Ce, P2O5 (%),
TiO2, Ni, Cr].
.
Keywords: Tangkubanparahu, volcanostratigraphy, petrogenesis.
ii
Download