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Discovery and Geological Significance of Early Carboniferous High‐Mg Diorite in the Balikun Area, Eastern Tianshan
Author(s) -
LUO Jinglan,
WANG Chong
Publication year - 2020
Publication title -
acta geologica sinica ‐ english edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.444
H-Index - 61
eISSN - 1755-6724
pISSN - 1000-9515
DOI - 10.1111/1755-6724.14452
Subject(s) - lile , geochemistry , zircon , geology , mafic , partial melting , carboniferous , diorite , ultramafic rock , continental arc , volcanic rock , adakite , primitive mantle , mantle (geology) , subduction , petrology , oceanic crust , tectonics , volcano , paleontology , structural basin
Abstract The granodiorites, monzogranites and diorites are widely developed in the Balikun area of Eastern Tianshan Orogen. Of which, LA–ICP–MS zircon U‐Pb isotopic dating from the diorites revealed that they were emplaced at 327∼333 Ma, representing an important period of magmatism in the Early Carboniferous. Geochemically, they are characterized by moderate SiO 2 (51.33–62.48 wt%), high but variable MgO (2.04–11.16 wt%, average 5.35), higher Mg # (40–73) and TiO 2 (0.67–1.29 wt%), Na 2 O/K 2 O (1.39–2.95) as well as variable Cr (2.49–675 ppm) and Ni (1.31–174 ppm), showing a geochemistry similar to those of high‐Mg diorites or sanukitoids. In addition, they are enriched in the LILE, poor HFSE with an evident negative Nb anomalies and a REE pattern of moderate fractionator between LREE and HREE without or weak negative Eu anomalies. Their ∊ Hf ( t ) are positive (+3.63–+15.65), suggesting a source from the depleted mantle. In addition, they have high TiO 2 and Pb, and large quantity of amphibolite and biotite, indicating that they were most likely derived from the partial melting of depleted mantle metasomatized by the slab‐derived melt under a hydrous condition. Consequently, combined with the contemporary volcanics and granitoids formed in the island arc settings, we proposed that the subduction was continued till Early Carboniferous in the Bogda‐Harlik tectonic belt. After that, wide occurrence of the post‐collisional A‐type granites and mafic‐ultramafic intrusions indicate this tectonic belt entered the post‐collisional environment from Late Carboniferous to Permian.