Petrogenesis of Alkaline Basalt from the Darbut Ophiolitic Mélange in West Junggar: The Product of a Late Devonian Mantle Plume?
详细信息
- 责任者：Yang Gaoxue (Key Laboratory of Western China’s Mineral Resources and Geological Engineering ; Ministry of Education ; Earth Science & Resources College ; Chang’an University ; Xi’an 710054 ; China) ; Li Yongjun
- 刊名：Earth Science Frontiers
- 出版年：2013
- 卷期：20(3)
- 关键词：碱性玄武岩 ; alkali basalts ; 准噶尔地块 ; Junggar Massif
- 页码：p.192-203
- 图表：illus., 2 tables, 60 refs.
- 分类号：0801
- issnNo：ISSN1005-2321
- isbnNo：CN11-3370/P
摘要
As a part of Central Asian Orogenic Belt(CAOB),the West Junggar is located at the southern margin of the CAOB.Several ophiolitic mélanges were formed and preserved in the West Junggar.The Darbut ophiolitic mélange(DOM) in the West Junggar is the largest and one of the best-preserved Paleozoic ophiolitic mélanges in the CAOB.Harzburgite,lherzolite,dunite,chromitite,troctolite,gabbro,diabase,pillow lava,massive basalt,and chert occurred as blocks within the serpentinite mélange.Based on petrology,petrography,isotopic geochronology and geochemical analysis for the alkaline basalt in the DOM,the alkaline basalt yielded a weighted mean 206Pb/238U age of(375±2) Ma by Laser Ablation Inductively Coupled Plasma Mass Spectrometry(LA-ICP-MS),suggesting a Late Devonian emplacement.Furthermore,the alkaline basalt have typical geochemical characteristics to those of OIB,with moderate SiO2(45.24%~49.86%),high MgO(2.45%~6.85%),TiO2(3.17%~3.77%) and Na2O+K2O(2.37%~5.34%),characterized by alkaline basalt.The rare earth element(REE) and trace element distribution patterns are similar to those of oceanic island basalt(OIB),with light REE(LREE) and large ion lithophile element(LILE,Rb,Ba,Th) enrichment,no obvious high field strength element(HFSE,Zr,Hf,Nb,Ta) negative anomaly,indicating the origin from enriched mantle that contains 5%~10% spinel and garnet lherzolite partial melting.These observations,in combination with sedimentary and volcanic rocks,and previous work in this region,indicate that the alkaline basalt from the DOM might be correlated with Late Devonian mantle plume-related magmatism of ocean island setting within the ocean floor.That is to say,the alkaline basalt from the DOM is the product of a Late Devonian mantle plume,showing that the Late Devonian mantle plume-related magmatism must exist in the CAOB.If the plume model as proposed here is correct,it would suggest that mantle plume activity might have significantly contributed to the crustal growth in the CAOB.
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