Geochemical Characteristics of Late Ordovician Granodiorite in Gouli Area,Eastern Kunlun Orogenic Belt,Qinghai Province:Implications on the Evolution of Proto-Tethys Ocean
Chen Jiajie
Fu Lebing
Wei Junhao
Tian Ning
Xiong Le
Zhao Yujing
Zhang Yujie
Qi Yueqing
Abstract：The Aowade granodiorited in the east-end of Kunnan terrain,a part of Kunlun Orogenic belt,belongs to Proto-Tethyan tectonic domain.Detailed study of the granodiorite can offer important information to constrain the evolution of the Proto-Tethys Ocean.Detailer study of the granodiorite can offer important information to constrain the evolution of the Proto-Tethys Ocean.In this study,LA-ICP-MS zircon U-Pb dating yields a weighted mean age of 454±2 Ma for the intrusion.It is characterized by low K2O/Na2O (0.92-2.68)and Mg#(39-43),and the A/CNK is between 1.00 and 1.03.The REE exhib-its right-dipping patterns with negative anomalies of Eu/Eu*(0.48-0.96)and high (La/Yb)N ratios.LILE(Rb,Ba,K,La, Sr)is enriched in this intrusion,while HFSE(Nb,Ta,P,Ti)is depleted relative to the primitive mantle,and the concentra-tions of transition elements such as Cr and Ni are low.The ratios of Sr/Y (average of 55)are relatively high.All the samples have high initial 87 Sr/86 Sr values (0.7059-0.7063)andεHf (t)(十5.4 to 十9.2),but with relatively lowεNd (t)(-4.1 to-1.9)and old two stage model age (T2DMNd=1.3-1.5 Ga).In combination with the lithology,geochemical signature and iso-topic compositions of the intrusion,we propose that the Aowade granodiorite was derived from melting of the subducted ocean-ic crust with minor involvement of continent crust.The possible residual of the source region is garnet amphibolite.Fractional crystallization of pyroxene,amphibole and plagioclase may have also occurred during the evolution of magma.Integrating evi-dences from the geodynamic setting of the Aowade granodiorite,the ophiolites in the Kunzhong structure zone,and the meta-morphic rocks,arc-related igneous rocks on either side of the Kunzhong structure zone,it is concluded that the Aowade grano-diorite was formed during the subduction of Proto-Tethys Ocean,which further reveals the nature of bidirectional subduction of the Proto-Tethys in the Late Ordovician.
Keywords：low-Mg adakitic granodioriteLate OrdovicianKunzhong suture beltProto-Tethys Oceanbidirectional subduc-tioneastern Kunlungeochemistry.
Publication Date：2016-01-01
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：20( 1863-1882 )