The Guandishan granitoids consist mainly of various granitoid intrusions with different scales, including the Huijiazhuang intrusion, Shizhuang intrusion and Hengjian intrusion, which were formed between 1906 Ma and 1848 Ma. On the basis of geological and petrological characteristics, these granitoids can be classified into two groups: the earlier gneissic granodiorites and monzogranites, and the later massive leuco-monzogranites. Their geochemical and Nd isotopic features indicate that they could be derived from complicated partial melting of supracrustal rocks with an affinity of continental arc materials, such as sandy shale and pelite, and with garnet, pyroxene, hornblende and plagioclase as residual phases. Biotite, feldspar and other minerals were most likely fractionated during the magma evolution. Their source may have an affinity with continental arcs, and the granitoids could be derived from the main syn-collisional to late-orogenic tectonic environment, which may be related to the final amalgamation between the Eastern and Western continental blocks in the North China Craton.
LIU ChaohuiLIU ShuwenLI QiugenLü YongjunK. H. PARKY. S. SONG
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_(Nd)(t) values of +0.48 to -3.19 with Nd-depleted mantle model ages (T_(DM)) of 2.76-2.47 Ga,and early gneissic monzogranites haveε_(Nd)(t) values of-0.53 to -2.51 with F_(DM)of 2.61-2.43 Ga,and the younger gneissic monzogranites haveε_(Nd)(t) values of -6.41 to -2.78 with a T_(DM)of 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
LIU Shuwen LI Qiugen LIU Chaohui LU Yongjun ZHANG Fan
