| Citation: |
XIONG Fa-hui, YANG Jing-sui, GUO Guo-lin, LIU Zhao, XU Xiang-zhen, TIAN Ya-zhou, LAI Sheng-min, CHEN Yan-hong, ZHANG Lan. Exsolutions in Olivine from the Lower Cr#Dunite in the Purang Ophiolite, the Western Portion of the Yarlung-Zangbo Suture Zone in Tibet[J]. Acta Geoscientica Sinica, 2016, (1): 79-89. doi: 10.3975/cagsb.2016.01.08
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Exsolutions in Olivine from the Lower Cr#Dunite in the Purang Ophiolite, the Western Portion of the Yarlung-Zangbo Suture Zone in Tibet
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Abstract
Diopside and magnetite exsolutions occur as oriented intergrowths within olivine of the lower Cr# dunite in the Purang ophiolite, Tibet. The fresh lower Cr# dunite has a mineral assemblage of olivine, spinel and diopside. The Fo content of its olivine is 90.1~90.7, whereas the Cr# of spinel is very lower (about 19.8~20.7), much less than Cr# of the spinel in common dunite from ophiolite mantle (Cr#>60). It is thus held that the formerly depleted mantle harzburgite reacted with the melt containing Ti, Al and Ca, and produced an olivine solid solution with the addition of Ti4+, Al3+, Ca2+, Fe3+, Cr3+, which entered interstitial chromite. Due to the fast cooling rate of the rock or rapid tectonic emplacement, the exsolution textures in olivine and compositional zones of chromite have been preserved. The mineral chemical composition of picotite-olivine indicates<8% partial melting in exsolutions dunite. However, the higher Cr# dunite without exsolutions has highly partial melting (>50%), suggesting reaction with boninitic melt. The authors consider that the Purang ophiolite experienced multi - stage processes. Firstly, UHP minerals were trapped in these magnesiochromite grains. When oceanic crustal slabs were trapped in Mid Ocean Ridge, they were modified by tholeiitic magmas or partial melting, which caused interaction or metasomatism and subsequent reaction with boninitic magma in suprasubduction zones (SSZ).-
Keywords:
- dunite /
- exsolutions /
- Purang ophiolite /
- Yarlung Zangbo suture
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XIONG Fa-hui, YANG Jing-sui, GUO Guo-lin, LIU Zhao, XU Xiang-zhen, TIAN Ya-zhou, LAI Sheng-min, CHEN Yan-hong, ZHANG Lan. Exsolutions in Olivine from the Lower Cr#Dunite in the Purang Ophiolite, the Western Portion of the Yarlung-Zangbo Suture Zone in Tibet[J]. Acta Geoscientica Sinica, 2016, (1): 79-89. doi: 10.3975/cagsb.2016.01.08
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