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Title:: Petrogeochemical Methods for Quantitative Estimation of the Crustal Thickness of Orogenic Belt: Overview and Case Studies

Author(s):: GUAN Wen-hui; WANG Yang; School of Earth Sciences and Resources, China University of Geosciences, Beijing 100083, China

Keywords:: crustal thickness; geochemistry; magmatic arc; orogenic belt; Gangdese arc; Yidun island arc; Fujian; Liaoning

Abstract:: The petrogeochemical data, which include K₂O content, w(Sr)/w(Y) and w(La)N/w(Yb)N of calc-alkaline suite, and Na₂O and CaO contents and w(Ce)/w(Y) of basaltic rocks, can be used to quantitatively or semi-quantitatively estimate the crustal thickness of magmatic arc. The quantitative formulas are reliable to calculate the crustal thickness (20-45 km) of subduction orogenic belt. w(Dy)/w(Yb) of intermediate-acidic rocks can constrain the thick crust with more than 50 km. The proper application for quantitatively or semi-quantitatively estimating the crustal thickness of orogenic belt requires that obeying the conditions and scopes of the method, gathering a dataset for analysis as large as possible, and doing data screen and outlier elimination. For the case of Gangdese in the southern Tibet, it concludes that w(La)_N/w(Yb)_N can be used to estimate the thickness of crustal thickness in the post-collisional environment. The remarkable jump of w(Sr)/w(Y) and w(La)_N/w(Yb)_Nof intermediate magmatic rocks in Gangdese terrane since 40 Ma is due to the crust thickening caused by the collision between India plate and Asia continent. The crustal thickness of Triassic Yidun island arc in Sanjiang area is 60 km; that of Early Cretaceous magmatic arc in Changle-Nan’ao tectonic zone of Fujian is 42 km; that of Middle Jurassic-Early Cretaceous volcanic rocks in the western Liaoning is 50-65 km.