Title: Petrology and Zircon Crystal Morphology of the Granitic Rocks from the Basement, Cheju Volcanic Island, Korea: (II) Pre-Cretaceous Granite
Abstract:A granite drilling core (-1350 m) obtained from the basement in northeastern part of Cheju volcanic island was studied on the petrology and the zircon crystal morphology. The rock is pinkish, fine-gra...A granite drilling core (-1350 m) obtained from the basement in northeastern part of Cheju volcanic island was studied on the petrology and the zircon crystal morphology. The rock is pinkish, fine-grained alkali-feldspar granite with miarolitic cavities. It mainly consists of quartz, alkali feldspar, plagioclase, biotite, and minor amounts of opaque minerals, chlorite, epidote, sericite and zirwn, and characteristically shows micrographic texture. The age (66.4±1.7 Ma), rock face and whole rock chemistry of the rock is analogous to micrographic granites in southern wastal area of the Korean peninsula. The SiO₂ content of granitic rock is 75.3∼76.3 wt% and shows extensively fractionated fades. The trace element composition and REE pattern of micrographic granitic rocks, which are characterized by a high LILE/ HFSE ratio and enrichment of LREE, suggest that they are typical of island-arc calc-alkaline igneous rocks produced in the subduction environment. The shapes of the zircon crystals are all short prismatic, and all are dominant in {110}= {100} prism and in {101} pyramid with average PI of 0.41, EI of 0.37 (low), and PY of 0.36 (low). Average zircon index is 4448 (60). The creating temperature for crystallization of zircon crystals in the alkali feldspar granite magma is 800℃ and the crystallization finished at 650℃. It shows relatively extensive, but gap around 720℃. And zircon crystal forms are scissors-shaped in PPEF diagram. It suggest that it might have underwent magma mixing around 720℃ during the fractional crystallization.Read More
Publication Year: 1998
Publication Date: 1998-01-01
Language: en
Type: article
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Cited By Count: 3
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