[SMP29-P09] Primordial Apatite from Ophiolite in Taiwan
Keywords:Apatite, trace element , Ophiolite, Taiwan, Opening of Japan Sea
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
__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.