Discovery of Cenozoic magnetite volcanic rock in High Himalaya and its tectonic significance

Author:	Liu, X.H., Tong, L.X., Shi, R.D., Li, G.W., Chen, S.S., Zhou, X.J., Liu, Z.
Abstract:	Late Cenozoic ultra-mafic magnetite-rich volcanic rocks in the High Himalaya metamorphic belt, southern Tibet, are firstly reported in this study. The rocks are mainly composed of Fe-olivine, Fe oxides, Fe-garnet and potassic-rich glasses. A few euhedral Fe-spinel inclusions are discovered in the Fe-olivine grains. Vesicular structure, vitro basic porphyritic texture and typical spinifex texture are normally observed in the rocks. The bulk rock composition of the rock has a feature of strong Si-unsaturation (18. 8% similar to 29. 7% SiO2) and extreme Fe-richness (56. 2% 74. 2% Fe2O3T). Geochemical analyses show that it is strong rich in LILE of Th and U, relative depletion in high field strong elements such as Nb, Ta and Ti, and obvious negative anomalies for Sr element, indicating a geochemical process related to subduction. The volcanic lava cuts across the regional gneissic foliation, implying that it was probably formed in a post-collisional intracontinental extensional environment. Further, the Fe-rich and Si-unsaturated feature also indicates that it might be formed as a result of eruption along extentional fault and melting of Fe-rich protolith from a deep source. The volcano probably erupted during Pliocene-Pleistocene (2 similar to 4Ma) , based on its K/Ar ages between 4. 76 similar to 7. 25Ma, and surrounding rocks wrapped by lava with an apatite fission track ( AFT) age of 2. 04 +/- 0. 21Ma. Generally, the volcanic rock provides first volcanic evidence for post-collisional extension in the High Himalaya tectonic belt during Late Cenozoic, which is critical to further understand the tectonic framework of the southern Tibet Plateau and its evolutionary processes.
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Page number:	1876-1884
Issue:	7
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PubYear:	2018
Volume:	34
Publication name:	Acta Petrologica Sinica
Abstract:	Late Cenozoic ultra-mafic magnetite-rich volcanic rocks in the High Himalaya metamorphic belt, southern Tibet, are firstly reported in this study. The rocks are mainly composed of Fe-olivine, Fe oxides, Fe-garnet and potassic-rich glasses. A few euhedral Fe-spinel inclusions are discovered in the Fe-olivine grains. Vesicular structure, vitro basic porphyritic texture and typical spinifex texture are normally observed in the rocks. The bulk rock composition of the rock has a feature of strong Si-unsaturation (18. 8% similar to 29. 7% SiO2) and extreme Fe-richness (56. 2% 74. 2% Fe2O3T). Geochemical analyses show that it is strong rich in LILE of Th and U, relative depletion in high field strong elements such as Nb, Ta and Ti, and obvious negative anomalies for Sr element, indicating a geochemical process related to subduction. The volcanic lava cuts across the regional gneissic foliation, implying that it was probably formed in a post-collisional intracontinental extensional environment. Further, the Fe-rich and Si-unsaturated feature also indicates that it might be formed as a result of eruption along extentional fault and melting of Fe-rich protolith from a deep source. The volcano probably erupted during Pliocene-Pleistocene (2 similar to 4Ma) , based on its K/Ar ages between 4. 76 similar to 7. 25Ma, and surrounding rocks wrapped by lava with an apatite fission track ( AFT) age of 2. 04 +/- 0. 21Ma. Generally, the volcanic rock provides first volcanic evidence for post-collisional extension in the High Himalaya tectonic belt during Late Cenozoic, which is critical to further understand the tectonic framework of the southern Tibet Plateau and its evolutionary processes.
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