Geochemical Characteristics of Mesozoic Intermediate-acid Intrusive Rocks in Tongling and Adjacent Area of the Middle and Lower Reaches of the Yangtze River and Its Indication to the Deep-seated Magmatism

Numerous Mesozoic intermediate-acid intrusions are exposed in Tongling and adjacent area of the Middle and Lower Reaches of the Yangtze River.Based on the high precision age dating and geochemical characteristics of the rocks,five zones have been delineated: Dabie zone,Luzong zone,Tongling outer zone,Tongling inner zone,and Jiangnan zone.Major element,trace element and rare earth element geochemistry of the rocks in the zones show that magmatism and magmatic evolvement mechanism of the intrusions are distinct different.The Mesozoic intrusions in the Tongling inner zone formed in an extrusional regime,the intrusions in the Tongling outer zone in an extensional regime,and those in the Luzong zone formed during the transition course from extrusional to extensional regime.The Mesozoic intermediate-acid intrusions in the Tongling and adjacent area resulted from the process of the lithospheric thinning occurring in the eastern North China Block.