Guandishan Granitoids of the Paleoproterozoic Lüliang Metamorphic Complex in the Trans-North China Orogen:SHRIMP Zircon Ages,Petrogenesis and Tectonic Implications

The Paleoproterozoic L(u|¨)liang Metamorphic Complex(PLMC) is situated in the middle segment of the western margin of the Trans-North China Orogen(TNCO),North China Craton(NCC). As the most important lithological assemblages in the southern part of the PLMC,Guandishan granitoids consist of early gneissic tonalities,granodiorites and gneissic monzogranites,and younger gneissic to massive monzogranites.Petrochemical features reveal that the early gneissic tonalities and granodiorites belong to the medium-K calc-alkaline series;the early gneissic monzogranites are transitional from high-K calc-alkaline to the shoshonite series;the younger gneissic to massive monzogranites belong to the high-k calc-alkaline series,and all rocks are characterized by rightdeclined REE patterns and negative Nb,Ta,Sr,P,and Ti anomalies in the primitive mantle normalized spidergrams.SHRIMP zircon U-Pb isotopic dating reveals that the early gneissic tonalities and granodiorites formed at～2.17 Ga,the early gneissic monzogranites at～2.06 Ga,and the younger gneissic to massive monzogranites at～1.84 Ga.Sm-Nd isotopic data show that the early gneissic tonalities and granodiorites haveε(t) values of +0.48 to -3.19 with Nd-depleted mantle model ages (T) of 2.76-2.47 Ga,and early gneissic monzogranites haveε(t) values of-0.53 to -2.51 with Fof 2.61-2.43 Ga,and the younger gneissic monzogranites haveε(t) values of -6.41 to -2.78 with a Tof 2.69-2.52 Ga.These geochemical and isotopic data indicate that the early gneissic tonalities, granodiorites,and monzogranites were derived from the partial melting of metamorphosed basaltic and pelitic rocks,respectively,in a continental arc setting.The younger gneissic to massive monzogranites were derived by partial melting of metamorphosed greywackes within the continental crust.Combined with previously regional data,we suggest that the Paleoproterozoic granitoid magmatism in the Guandishan granitoids of the PLMC may provide the best geological signature for the complete spectrum of Paleoproterozoic geodynamic processes in the Trans-North China Orogen from oceanic subduction,through collisional orogenesis,to post-orogenic extension and uplift.