An Early Paleozoic Ultramafic Complex in the North Wulan Metamorphic Complex,North Qaidam:Contraints on the Nature of the Alaskan-type Continental Arc Root  

作　　者：SHAN Jinming NIU Manlan LI Xiucai LI Chen WANG Lei ZHANG Shuai 

机构地区：[1]School of Resources and Environmental Engineering,Hefei University of Technology,Hefei 230009,China

出　　处：《Acta Geologica Sinica(English Edition)》2023年第5期1388-1405,共18页地质学报（英文版）

基　　金：financially supported by the National Natural Science Foundation of China(Grant Nos.42272246,41272221,41902235)。

摘　　要：Orogenic peridotite is an important component of orogenic belts and retains crucial information on mantle magmatic activity,slab subduction,and melt or fluid metasomatism.To determine the source of the mantle-derived parental magma of the peridotite and to investigate the metasomatism that it experienced,we undertook an integrated study of the petrography,whole-rock major-and trace-element compositions,in situ zircon U-Pb geochronology,and mineral majorand trace-element compositions of an early Paleozoic ultramafic complex in the North Wulan area of North Qaidam.The Halihatu ultramafic-mafic complex is composed of dunite,pyroxene peridotite,and gabbro,which are characteristic of Alaskan-type complexes.The dunite yields a weighted mean^(206)Pb/^(238)U age of 479±5 Ma(MSWD=0.7),which reflects the age of the metasomatism rather than the crystallization age of the ultramafic magma.The peridotites have high Mg^(#)(89.8-91.8)and Cr contents(2419-5190 ppm),low Al_(2)O_(3)(0.20-1.68 wt%)and Ni(289-1012 ppm)contents,and high olivine Fo contents(87-91),suggesting a large degree(~15%-22%)of partial melting of lithospheric ultramafic rocks followed by variable degrees of fractional crystallization of olivine and pyroxene.This is consistent with estimates of 15%-22.3%partial melting calculated using the Cr#of spinel crystals and with the low Yb(0.04-0.33 ppm)and Y(0.72-1.29 ppm)contents of clinopyroxene crystals.Whole-rock trace-element patterns show enrichment in large ion lithophile elements and depletion in high field strength elements,along with high Al_(2)O_(3)(2.10-6.47 wt%)and low TiO_(2)(0.01-0.21 wt%)contents of clinopyroxene crystals,suggesting an arc magma cumulate trend.These features,along with the high olivine Fo contents(87-91 ppm),imply that the Halihatu peridotite is an Alaskan-type crustal cumulates derived from Mgrich hydrous basaltic melts.The high estimated f O_(2)(FMQ+1.97 to FMQ+3.81)further supports the idea that they formed in an arc setting.The Ni/Co and Ni/Mn ratios and cumulate textures of the oli

关 键 词：Alaskan-type complex orogenic peridotite arc magmatism melt-rock interaction north Qaidam 

分 类 号：P542[天文地球—构造地质学] P588.125[天文地球—地质学]