Petrogenesis of Mesozoic Granite in Wulanhaote Region, amespace prefix = st1 ns = "urn:schemas-microsoft-com:office:smarttags" />ace w:st="on">aceName w:st="on">CentralaceName> aceName w:st="on">GreataceName> aceName w:st="on">HingganaceName> aceType w:st="on">MountainsaceType>ace>: Constraints from Geochemistry and Sr-Nd-Hf Isotope
摘要
AN id=EnChDivSummary name="EnDivSummary">Petrogenesis and tectonic setting of Mesozoic granites in central Da Hinggan Mountains constitute the key to investigating the tectonic and magmatic evolution of Northeast China.Systematical studies of petrology,geochemistry and Sr-Nd and Lu-Hf isotopes of the granites in Wulanhaote-Suolun region indicate that the Middle-Late Triassic Chagan granite is of A2 type.The Early-Middle Jurassic Jingyang granite is an I-type granite and the Dashizhai granite is a very special kind of granite which shows tetrad REE patterns.On the basis of the Sr values,the Early Cretaceous granites can be divided into two types,i.e.,the high-Sr type and the low-Sr type.The two types of granites possess the same or similar magmatic sources but originated in different depths.The high-Sr type granite is similar to C-type adakitic granite which originated from the higher pressure of the lower crust,while the low-Sr type and Yonghetun granite are highly fractionated I-type granites derived from the middle crust of lower pressure.Considering Sr-Nd-Hf isotopic data of granites in the Wulanhaote-Suolun region and the results of previous studies,the authors suggest that crustal growth of the study area occurred in the Phanerozoic.As indicated by the high positive zircon εHf(t) and εNd(t) values and the new young two-stage model age of each of the five intrusions,their magmatic sources must have mainly consisted of new crustal materials during the accretion in Phanerozoic,with the addition of some old crust components.And along with the variation of the emplacement time of the granites gradually towards newness,the εHf(t) values of the zircon change to lowness.The authors consider that magmatic underplating and exhumation of the old crust caused by the mantle upwelling were responsible for the complicatedness of the compositions of the lower crustal source rock.
