Mineralogical Chemistry Characteristics and Geological Significance of the Clinopyroxene from Chaokeshan Gabbro, Inner Mongolia

Paleozoic mafic magmatic rocks are widely developed in Hegenshan belt of Inner Mongolia. In order to explore the magmatic source and petrological genesis of these rocks and to further understand the Paleozoic tectonic setting of the eastern part of the Central Asian orogenic belt, the Chaokeshan ophiolites are studied by mineralogy. Mineral electron probe results show that the monocline in gabbro belongs to diopside, which has both alkaline and tholeitic characteristic, with SiO₂ (50.75% to 52.99%) and high Al₂O₃ (2.03% to 3.77%), and are relatively enriched large ion lithophile elements, but depleted in light rare earth elements ((La/Sm)_N=0.12～0.22) and in high field strength elements (e.g. Nb, Ta, Zr, Hf, Ti), consistent with the characteristics of the whole gabbro rock, indicating that the parent magma of the pluton may be subalkaline tholeitic magma to alkaline basalt magma evolution trend. The temperature and pressure of clinopyroxene are 1099～1242 ℃, 1.5～6.4 kbar and 5～21 km respectively, suggesting obvious deep-derived characteristics. Combined with the previous research results, it’s suggest that the Chaokeshan ophiolites was likely produced in the back-arc tectonic setting.