日本地球惑星科学連合2019年大会

講演情報

[E] ポスター発表

セッション記号 S (固体地球科学) » S-MP 岩石学・鉱物学

[S-MP29] Oceanic and Continental Subduction Processes

2019年5月28日(火) 10:45 〜 12:15 ポスター会場 (幕張メッセ国際展示場 8ホール)

コンビーナ:Hafiz Ur REHMAN(Department of Earth and Environmental Sciences, Graduate School of Science and Engineering, Kagoshima University)、辻森 樹(東北大学)、Chin-Ho Tsai(Department of Natural Resources and Environmental Studies, National Dong Hwa University)、岡本 和明(埼玉大学教育学部地学)

[SMP29-P09] 初源的燐灰石の台湾のオフィオライトからの産出

*新妻 信明1高嶋 礼詩2李 元希3 (1.静岡大学理学部地球科学教室、2.東北大学総合学術博物館、3.國立中正大学地球與環境科學系,臺灣)

キーワード:燐灰石、微量成分、オフィオライト、台湾、日本海拡大

Apatite is a common accessory mineral in igneous rocks. Because apatite has a wide range of trace element compositions as well as strong resistance to diagenetic alteration, the trace element composition of apatite has been used for tracing petrogenetic processes of plutonic bodies as well as the tephrochronology of Paleozoic tephras and Quaternary volcaniclastic deposits.

We studied trace element compositions of apatites from Ophiolite in Taiwan. The Ophiolite with mafic-ulatramafic rocks (150811-14) expose along the anticlinal axes of the metamorphic belts in Backbone Range of Taiwan, and exotic gabbro block (MA-15B) in chaotic deposits of Lichi Melange, in the southern end of Longitudinal Valley, in East Taiwan.

Lee (2015 JpGU; Chen et al., 2017 Tectonics) reported that zircon ages of Ophiolites in Taiwan are concentrated to 15 Ma, which should relate with termination of spreading in South China Sea and Shikoku & Parece Vela Basin just before Japan Sea Opening, and large scale igneous activities in the Outer Zone of Southwest Japan just after Japan Sea Opening (Niitsuma & Lee, 2018 JpGU).

Fifteen and twelve apatite phenocrysts from samples of MA-15B and 150811-14 were analyzed for major and minor elements using a JEOL 8530F wavelength dispersive Electron Probe Micro Analyzer (Takashima et al., 2017 Quaternary Geochronology) in weight % as follow;
__major elements: P=17.956 +/-0.100, 17.926 +/-0.129
_________________Ca=38.362 +/-0.329, 38.128 +/-0.273
_________________F=1.082+/-0.151, 0.445+/-0.046
__trace elements: Cl<0.01, 0.04 Mg<0.01, 0.01 Mn<0.04, 0.05
_________________Fe<0.03, 0.17 Ce<0.09, 0.05 Y<0.13, 0.04

The contents of trace elements are extremely low and we concluded the apatite might be primordial without any contaminations and petrogenetic effect, and crystallized directly in the magma above rifted mantle along the northwestern margin of West Philippine Basin just before Japan Sea Opening.