长江中下游铜陵及邻区中生代中酸性侵入岩地球化学特征及其深部岩浆作用探讨

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

长江中下游铜陵及其邻区的中生代侵入岩极其发育,岩石类型多样。本文通过对该区已获得的高精度成岩年龄数据的综合整理,结合系统的岩石地球化学测试数据,对长江中下游铜陵地区中生代侵入岩进行了岩带划分并提出了可能的岩浆作用模型。铜陵地区中生代中酸性岩浆侵入活动时间集中分段、空间分带明确,从北到南依次分为庐枞带、铜陵外带和铜陵内带,岩浆活动从早到晚为铜陵内带到庐枞带再到铜陵外带。铜陵地区北侧的大别带与南侧的江南带中生代岩浆活动时间与长江中下游铜陵外带相当,但在其内部岩浆活动的空间分带性与时间周期性还不太明确。系统的岩石化学、微量元素、稀土元素分析对比表明,各带岩石地球化学特征区别明显,岩浆演化机制与岩浆成因也不相同。岩浆活动时间的分段性、空间展布的分带性以及岩石地球化学的差异性与深部岩浆作用和构造环境有关。铜陵内带中酸性侵入岩形成于以挤压为主的构造背景下,庐枞带形成于挤压—拉张转化阶段,铜陵外带则完全形成于拉张环境。长江中下游铜陵地区广泛发育的中生代中酸性侵入岩是我国东部岩石圈减薄事件的产物。

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.