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Geochronology, Petrology and Geochemistry of Xingdi No. 3 Mafic‐Ultramafic Intrusions in the Northeastern Tarim Craton, NW China
Author(s) -
XIA Zhaode,
XIA Mingzhe,
JIANG Changyi
Publication year - 2017
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 - 10.1111/1755-6724.13114
Subject(s) - geology , geochemistry , craton , mafic , ultramafic rock , olivine , zircon , layered intrusion , petrology , fractional crystallization (geology) , geochronology , basalt , tectonics , paleontology
The Xingdi mafic‐ultramafic intrusions occur in the northeastern margin of the Tarim craton. The Xingdi No. 3 intrusion is the smallest of four intrusions, with an exposed area of 1.7 km 2 , and the zircon U‐Pb age of the intrusion is 752±4 Ma. The intrusion consists of gabbros, pyroxenites and peridotites, and exhibits a crystallization sequence of the main rock‐forming minerals as olivine, orthopyroxene, clinopyroxene and plagioclase. Mineralization occurred at or near the boundaries of the intrusion between pyroxenites and peridotites, and appears as a layered or lenticular shape about 500 m long and 4–15 m wide. The primary sulfides have a relatively simple mineralogy dominated by pyrrhotite‐pentlandite‐chalcopyrite assemblages, which occur as droplet, star‐like and graphic texture and locally sideronitic structures. Geochronological and geochemistry investigations suggest that the Xingdi mafic‐ultramafic intrusions and coeval volcanic rock in the Kuluktag area of the Tarim craton formed in an intracontinental breakup environment. Based on the composition of the dominant rock‐forming minerals and covariant relationships of other oxides versus MgO, the parental magma of the Xingdi No. 3 intrusion belongs to high‐Mg tholeiitic basaltic magmas with MgO of 10.78 wt%. The Xingdi No. 3 intrusive rocks are characterized by light REE enrichment relative to heavy REE, negative Nb‐Ta anomalies, low 143 Nd/ 144 Nd ratios (from 0.511183 to 0.511793) and high initial 87 Sr/ 86 Sr ratios (from 0.7051 to 0.7113). The magma was derived from the enriched‐lithospheric mantle and was contaminated during emplacement. According to rock assemblages, mineralization, olivine characteristics, geochemical characteristics and mass balance, there are better copper‐nickel ore prospects in the Xingdi No. 3 intrusion than in the other three intrusions in the area.