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| Keywords | |
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meimechitic rocks |
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petrology |
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mineralogy |
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geochemistry |
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tectonic significance |
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Karakoram |
| Authors | |
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YANG Wan-zhi |
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TIAN Jiang-tao |
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GUO Xiu-wei |
| PubMed | |
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Article by Yang W |
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Article by Tian J |
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Article by Guo X |
Identification of meimechitic rocks from Chalukou area in Karakoram and its tectonic significance: petrological，mineralogical and geochemical evidence
YANG Wan-zhi，TIAN Jiang-tao，GUO Xiu-wei
1. Xinjiang Institute of Geological Survey，Urumqi 830000，China;
2. School of Mechanics and Engineering Science，Shanghai University，Shanghai 200444，China
The ultramafic lavas in the Chalukou area is mainly composed of vitric dunites and vitric pyroxene peridotites，which are interlayered in basalts，basaltic volcanic rocks and siliceous rocks，and generally constitute a deep marine volcanic-sediment formation． The olivine phenocrysts in the vitric dunites and vitric pyroxene peridotites are mostly euhedral to subhedral． The 25 analysis spots of 11 samples have SiO2 contents of 38. 68% ～40. 58%，MgO contents of 44. 43% ～ 46. 72%，Ni concentrations of 1 100 × 10 － 6 ～ 2 381 × 10 － 6，and the calculated Fo values of 85. 60 ～ 87. 71，respectively． In terms of whole rock geochemical compositions，SiO2 content is
38. 51% ～ 42. 86%，MgO content is 26. 81% ～ 31. 28%，TFeO content is 12. 17% ～ 14. 52%，TiO2 content is 1. 00% ～ 1. 45%，and Na2O + K2O content is 0. 17% ～ 0. 67%． They belong to meimechite by petrochemical classification． In consideration of the presence of pyroxene phenocrysts in the vitric pyroxene peridotites，it is obviously different from the traditional definition of meimechite． Therefore，the authors refer to the newly discovered ultramafic lavas in the study area as“meimechitic rocks”． Using the highest Fo value of olivine and the TFeO content
of its host rock，the MgO content in the parent magma of the meimechitic rocks is estimated to be ≥18. 18%．Based on this evidence，the mantle melting temperature and pressure are limited to be higher than 1 580℃ and 3. 9
GPa，respectively． The meimechitic rocks in the Chalukou area show OIB-like trace element characteristics． This，along with the results of previous studies，suggests that the meimechitic rocks in the area were formed in the Late
Permian to Late Triassic extensional setting related to the mantle plume．
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