The crustal growth of the North China Craton （NCC） during the Neoarchean time （2.5--2.8 Ga） is a hotly controversial topic, with some proposing that the main crustal growth occurred in the late Neoarch- ean （2.5--2.6 Ga）, in agreement with the time of the magmatism, whereas others suggest that the main crustal accretion took place during early Neoarchean time （2.7-2.8 Ga）, consistent with the time of crustal- formation of other cratons in the world. Zircon U-Pb ages and Hf isotope compositions can provide rigorous constraints on the time of crustal growth and the evolution and tectonic division of the NCC. In this contri- bution, we make a comprehensive review of zircon Hf isotope data in combination with zircon U-Pb geochro- nology and some geochemistry data from various divisions of the NCC with an aim to constrain the Neoarchean crustal growth of the NCC. The results suggest that both 2.7--2.8 Ga and 2.5-2.6 Ga crustal growth are distributed over the NCC and the former is much wider than previously suggested. The Eastern block is characterized by the main 2.7-2.8 Ga crustal growth with local new crustal-formation at 2.5-2.6 Ga, and the Yinshan block is characterized by ~2.7 Ga crustal accretion as revealed by Hf-isotope data of detrital zircons from the Zhaertai Group. Detrital zircon data of the Khondalite Belt indi- cate that the main crustal growth period of the Western block is Paleoproterozoic involving some ~ 2.6 Ga and minor Early- to Middle-Archean crustal components, and the crustal accretion in the Trans-North China Orogen （TNCO） has a wide age range from 2.5 Ga to 2.9 Ga with a notable regional discrepancy. Zircon Hf isotope compositions, coupled with zircon ages and other geochemical data suggest that the southern margin may not be an extension of the TNCO, and the evolution and tectonic division of the NCC is more complex than previously proposed, probably involving multi-stage crustal growth and subduction processes. However, there is no doubt that 2.7--2.8 Ga magmatism and cr
Based on detailed field investigations and petrographic observations,we discovered Neoproterozoic-emplaced granite from the metavolcanics of the Dingyuan Formation in the western Beihuaiyang zone,the Dabie orogen. This study reports the results of zircon U-Pb dating and preliminary petrographic observations on two metagranite samples. The studied rocks experienced epidote-amphibolite facies metamorphism and strong structural deformation. Their U-Pb ages are 726 ± 6 and 758 ± 12 Ma,respectively,similar to those for the Luzhenguan complex in the eastern segment of the Beihuaiyang zone. In combination with previously determined 635 ± 5 Ma low-grade metagabbro,this study suggests the occurrence of at least two types of Neoproterozoic intrusive rocks in the Beihuaiyang zone,the northern margin of the South China Block (SCB):726-758 Ma metagranite and 635 Ma metagabbro. These rocks occur within the metamorphosed Ordovician volcanic zone (originally named the Dingyuan Formation) and are in tectonic contact to each other,but they formed in different tectonic settings. The protolith ages for the Neoproterozoic low-grade metaigneous rocks are in good agreement not only with ages for two episodes of mid-and late-Neoproterozoic mafic and felsic magmatism in the Suizhou and Zaoyang area,Hubei Province,but also agree with protolith ages of ultrahigh-pressure metaigneous rocks in the Dabie-Sulu orogenic belt. In view of their tectonic relationships to country rocks,it appears that these Neoproterozoic low-grade rocks are exotic and they may have been detached and scraped from subducting SCB crust in the early Triassic during the initial continental subduction,and thrusted over Paleozoic metamorphosed rocks in the southern margin of the North China Block during continental collision.
LIU YiCanLIU LiXiangGU XiaoFengLI ShuGuangSONG Biao
