Late Paleozoic oceanic basalts hosted by the Char suture-shear zone, East Kazakhstan: Geological position, geochemistry, petrogenesis and tectonic setting

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• 作者：I.Yu. Safonova^a ; ^b ; ^{inna03-64@mail.ru} ; V.A. Simonov^a ; E.V. Kurganskaya^a ; O.T. Obut^c ; R.L. Romer^d ; R. Seltmann^e
• 关键词：Central Asian Orogenic Belt ; Oceanic Plate Stratigraphy ; Accretion ; Major and trace elements ; Isotopes ; MORB ; OIB ; Oceanic plateau ; Water&ndash ; rock interaction
• 刊名：Journal of Asian Earth Sciences
• 出版年：2012
• 期刊代码：40_13679120
• 类别：ear
• 出版时间：30 April, 2012
• 卷：49
• 期：Complete
• 页码：20-39
• 文件大小：3939 K

摘要

The paper presents the first data on geochemistry (major and trace elements, isotopes) of the Late Devonian-Early Carboniferous basalts of the Char suture-shear zone in East Kazakhstan, and includes detailed analysis of their geological relations and petrogenesis (fractional crystallization/melting modeling). Three groups of oceanic basalts coexist in the Char zone. Group 1 basalts are associated with oceanic siliceous sediments and have medium TiO₂, relatively flat REE patterns (La/Sm_n = 0.7, Gd/Yb_n = 1.3), Zr/Nb_av. = 42 and 蔚Nd_av. = 6.3. They formed at high degrees of melting of a depleted mantle source and were erupted in a mid-oceanic ridge setting. Group 2 basalts are associated with both chert and carbonate and have higher TiO₂, Hf, Y, Zr and P₂O₅ than the rocks of Group 1. They are similarly characterized by low Nb (Nb/La_pm < 1) and flat REE patterns (La/Sm_n = 0.6, Gd/Yb_n = 1.1), 蔚Nd_av. = 8.3, and Zr/Nb = 44. Group 2 basalts originated under lower degrees of melting than Group 1 basalts from a depleted mantle source, and possibly formed in a subducting oceanic plateau setting. Group 3 basalts are enriched in incompatible elements, i.e. have high LREE (La/Sm_n = 1.8), differentiated HREE (Gd/Yb_n = 2.3), Nb positive anomalies in the multi-element diagrams (Nb/Th_pm = 1.5, Nb/La_pm = 1.1), low Zr/Nb ratio (鈭?) and lower 蔚Nd_av. = 4.6. They formed at lower degrees of melting, compared to Groups 1 and 2, from a heterogeneous mantle source in the spinel (Gd/Yb_n < 2) and garnet (Gd/Yb_n > 2) stability fields. They possibly represent fragments of oceanic islands/seamounts formed in relation to mantle plume.