The Zhalaxiageyong lead-zinc-copper polymetallic deposit is a typical porphyry deposit of the Tuotuohe area. Whole-rock geochemical analyses, Zircon U-Pb dating and Hf isotope analysis are undertaken for the ore host trachydacite with the aim of constraining its petrogenesis, magma source and regional tectonic setting. LA-ICP-MS zircon U-Pb dating indicates that the trachydacite was formed in 32.68±0.50 Ma (MSWD=1.6), i.e., Oligocene. The trachydacite is rich in potassium and poor in Mg#(5.10-9.70), belonging to the peraluminous shoshonite series. The rocks are enriched in LILE (large ion lithophile elements) Rb, Ba, K and LREE, depleted in HFSE (high field strength elements) Nb, Ta, P, Ti, with high Sr and low Y and Yb, having the characteristics of the C type adakite. It is calculated that the initial εHf(t) of the zircons range from -0.92 to 2.07 and their two-stage Hf model ages TDM2 range from 978 Ma to 1 169 Ma. The magma source should be mainly the partially melt mafic rocks of the thickened Middle Neoproterozoic lower crust of the Northern Qiangtang massif with the addition of ancient aluminosilica material in the melting process. The rocks formed in the tectonic setting of delamination of lithosphere and extension of the thickened crust. During the period of 40-32 Ma, large-scale potassium rich alkaline magmatism occurred in this area. The porphyry metallogenesis is related to the magmatic activities in this period.
Key words
Zhalaxiageyong /
trachydacite /
geochemistry /
Zircon U-Pb age /
Hf isotope
{{custom_sec.title}}
{{custom_sec.title}}
{{custom_sec.content}}
References
Amelin Y, Lee D C, Halliday A N,et al. 1999. Nature of the Earth's earliest crust from hafnium isotopes in singledetrital zircons.Nature,399:1497-1503.
Defant M J, Drummond M S. 1990. Derivation of some modern arc magmas by melting of young subducted lithosphere.Nature,347:662-665.
Gao S, Jin Z M. 1998. Lower crustal delamination and evolution of continental crust.Geological Journal of China Universities,4(3):241-249. (in Chinese with English abstract)
Hou K J, Li Y H, Tian Y R,et al. 2009. In situ U-Pb zircon dating using laser ablation-multi ion counting-ICP-MS.Mineral Deposits,28(4):481-492. (in Chinese with English abstract)
Hou K J, Li Y H, Zou T R,et al. 2007. Laser ablation-MC-ICP-MS technique for Hf isotope microanalysis of zircon and its geological applications.Acta Petrologica Sinica,23(10):2595-2604. (in Chinese with English abstract)
Hou Z Q, Pan G T, Wang A J,et al. 2006. Metallogenesis in Tibetan collisional orogenic belt:Ⅱ.mineralization in late -collisional transformation setting.Mineral Deposits,25(5):337-358. (in Chinese with English abstract)
Hou Z Q, Qu X M, Yang Z S, et al. 2006. Metallogenesis in Tibetan collisional orogenic belt:Ⅲ mineralization in post -collisional extension setting.Mineral Deposits,25(6):629-651. (in Chinese with English abstract)
Hou Z Q, Song Y C, Li Z,et al. 2008. Thrust-controlled, sediments-hosted Pb-Zn-Ag-Cu deposits in eastern and northern margins of Tibetan orogenic belt:Geological features and tectonic model.Mineral Deposits,27(2):123-144. (in Chinese with English abstract)
Huang J J. 2001. Structural characteristics of basement of the Qiangtang Basin.Acta geologica sinica,75(3):333-337. (in Chinese with English abstract)
Rollison H R. 2000. Rock geochemistry. Hefei:University of Science & Technology China Press, 1-275.
Li H X, Gou F, Li C W,et al. 2010. Late Paleozoic subduction of the Paleo-Asian Ocean:Geochronological and geochemical records from Qianshan mafic intrusion in Hunchun area, NE China.Acta Petrologica Sinica,26(5):1530-1540. (in Chinese with English abstract)
Liu S K. 1992. Earth structure singificance of the Proterozoic group around Jinsha River in Easter Tibet.Geology of Tibet, (1):16-21. (in Chinese with English abstract)
Li W Y, Zhang Z W, Gao Y B,et al. 2011. Important metallogenic events and tectonic response of Qinling, Qilian and Kunlun orogenic belts.Geology in China,38(5):1135-1149. (in Chinese with English abstract)
Ning C Q, Li B L,Wang B, et al. 2016. Zircon U-Pb chronology and geochemistry of Zhalaxiageyong trache in Tuotuohe area, Qinghai.Global Geology,35(4):920-930. (in Chinese with English abstract)
Saunders A D, Norry M J, Tarney J. 1988. Origin of MORB and chemically-depleted mantle reservoirs:Trace element constraints.Journal of Petrology, Special_Volume(1):415-445.
Taylor S R, Mclennan S M. 1995. The geochemical evolution of the continental crust.Reviews of Geophysics,33(2):293-301.
Wang G Z, Wang C S. 2001. Disintegration and agemetamorphic rocks in Qiangtang basement, Tibet.Science in China:Earth Of Science,31(S1):77-82. (in Chinese)
Weaver B L. 1991. The origin of ocean island basalt end-member compositions:trace element and isotopic constraints.Earth & Planetary Science Letters,104(2/4):381-397.
Xu Z Q, Yang J S, Li H B,et al. 2006. The Qinghai-Tibet plateau and continental dynamics:A review on terrain tectonics,collisional orogenesis,and processes and mechanisms for the rise of the plateau.Geology in China,33(2):221-238. (in Chinese with English abstract)
Yao Z F. 1992. Proterozoic stratigraptic features in Changqinke area, Yushu country, Qinghai. Province. Geology of Tibet, (1):1-6.
Zhang Q. 2008.Adakite research:retrospect and prospect.Geology in China,35(1):32-39. (in Chinese with English abstract)
Zhang Q. 2011. Reappraisal of the origin of C-type adakitic rocks from East China.Acta Petrologica et Mineralogica,30(4):739-747. (in Chinese with English abstract)
Zhang Q, Wang Y, Qian Q,et al. 2001.The characteristics and tectonic-metallogenic significances of the adakites in Yanshan period from eastern China. Acta Petrologica Sinica,17(2):236-244. (in Chinese with English abstract)
Funding
Supported by Project of China Geological Survey (No.12120114080901)
PDF(1271 KB)
