Title: Formation age,geochemical characteristics of the Mingshujing pluton in Beishan area of Gansu Province and its geological significance
Abstract: Mingshujing pluton in Beishan area is a multiple intrusion composed of the gabbro,diorite and granite. LA-ICP-MS zircon U-Pb dating yields the206 Pb /238 U ages of 442. 9 ± 1. 2Ma for gabbro,437. 0 ± 2. 3Ma for diorite and 435. 9 ± 2. 2Ma for granite,respectively,being interpreted as their formation ages. The gabbro is calc-alkaline and enriched in Ca O,Fe O T and Mg O,as well as the LREE and LILE,poor HFSE with a positive Pb and negative Nb,Ta,Ti,Zr and P anomalies. They have moderate(86Sr /87Sr)i( 0. 705892),high radioactive Pb and low eNd( t)( 0. 1). Their eHf( t) values range from- 7. 1 to + 8. 3. Both of the diorite and granite are the metaluminous calc-alkaline,and relatively enriched in Na2 O,low Ca O,Fe O T and Mg O. They also show an enrichment of LREE and LILE as well as poor HFSE with evident negative Nb,Ta,Sr,P and Ti and positive Pb anomalies. They have moderate to high(86Sr /87Sr)i( 0. 705951 ~ 0. 706196),low eNd( t)(- 0. 2 ~- 0. 1),and positive eHf( t)(- 1. 1 ~ + 12. 0),displaying a geochemical affinity of magmatic rocks formed in subduction zone. In addition,their variable Hf and much similar Sr-Nd-Pb isotopic compositions suggest that they were resulted from the mixing between crust- and mantle-derived magmas. In which,the crustal magma was formed by the partial melting of Neoproterozoic crust materials,whereas the mantle-derived magma was derived from a mantle modified by the continental crust and the fluids dehydrated from subducted oceanic crust. Subsequently,Mingshujing pluton was a complex intrusions composed of gabbros and granitoids evolved from crustal magma mixed by mantle-derived magmas by the fractional crystallization,representing an important tectono-magmatism related to oceanic slab subduction from the Upper Ordovician to the Late Middle-Silurian in the southern area of Beishan Mountain.
Publication Year: 2015
Publication Date: 2015-01-01
Language: en
Type: article
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Cited By Count: 8
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