Petrogenesis and Geodynamic Setting of Late Triassic Quartz Diorites in Zhiduo Area,Qinghai Province
Zhao Shaoqing
Fu Lebing
Wei Junhao
Tan Jun
Wang Xuchun
Zhao Zhixin
Li Xiang
Abstract：Zircon U-Pb age,major and trace elements and Sr,Nd isotope compositions of the Riariqu quartz diorites from the south of the Ganzi-Litang suture zone,northeastern Qiangtang terrane are studied to decipher its petrogenesis and geodynamic significance.LA-ICP-MS zircon U-Pb dating yields an emplacement age of 218 ± 1 Ma for the intrusion.Bulk-rock analyses show that these rocks belong to the calc-alkaline series,with SiO 2 contents ranging from 53.02% to 62.06%.They are enriched in Al2 O 3 (1 5.84%-1 7.00%)and CaO (6.71%-8.94%),depleted in TiO 2 (0.49%-1.01%)and P2 O 5 (0.04%-0.12%),de-fining their metaluminous characteristics.All samples have high concentrations of MgO (3.31%-5.66%),Cr (33.45×10 -6 -1 76.64×10 -6 )and Ni (13.34×10 -6 -43.62×10 -6 ),and resultant high Mg# (50-62).These rocks are enriched in LREE and LILE,and depleted in HFSE with low REE contents (38.05×10 -6 -61.58×10 -6 ).The (87 Sr/86 Sr)i ratios range from 0.706 8 to 0.707 9,andεNd (t )values vary from -5.5 to -1.6.The geochemical and Sr-Nd isotopic compositions of the Riariqu quartz diorites are similar to those of high-Mg dioritoids/sanukitoids.We contend that the Riariqu quartz diorites were derived from low-degree partial melting (10% - 1 5%)of a phlogopite-bearing spinel lherzolite mantle,which was metasomatized by sedi-ment-derived melts.Fractional crystallization of pyroxene and amphibole might also occur during the magma evolution.The ge-ochemical characteristics indicate that the Riariqu quartz diorites are arc-related magmatic rocks,and were generated in a subduction-related tectonic setting.Combined with the ophiolites and continental marginal arc lavas in the study area,and the regional adakites in the Yidun terrane,it is suggested that the Riariqu quartz diorites might be generated during the southwest-ward subduction of Ganzi-Litang Paleo-Tethys Ocean in the Late Triassic.
Keywords：high-Mg dioriteSanukitoidGanzi-Litang suture beltPaleo-Tethys oceanQiangtang terraneQinghai-Tibet plateaugeochemistry
Publication Date：2015-01-01
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：16( 61-76 )