粤北红山岩体形成时代及成因研究

Research on the age and origin of Hongshan pluton in north Guangdong

红山岩体位于诸广山岩体南部,岩性为细粒-中细粒黑云母-二云母花岗岩,锆石SHRI MP U-Pb年龄为155±2 Ma,属于燕山早期岩浆活动产物。该岩体主量元素显示其富硅(Si O2=76.08%~77.25%)、富碱(K2O+Na2O=8.78%~9.43%)、低的ACNK值(0.94~1.07)和CaO/Na2O值(0.10~0.19)等特征。微量元素特征是富集Rb、Th、U,亏损Ba、Sr、P、Ti以及具有高的Rb/Sr值(30.02~930.9)和Rb/Ba值(18.91~231.8);LREE/HREE值较低(1.99~2.40),Eu亏损明显(δEu=0.01~0.07),具有低的∑Nd(t)值(-10.2^-12.0)和古老的Nd模式年龄(1777~1923 Ma)。上述特征表明,红山岩体属于S型花岗岩范畴。笔者认为,中生代太平洋板块的俯冲作用,导致粤北地区骑田岭-诸广山断裂带重新复活,红山岩体可能是在此构造背景下由古元古代地壳通过部分熔融方式形成的。

Located in the midwest of south Zhuguangshan composite pluton,Hongshan pluton is constituted by biotite granite and two-micro granite.The SHRIMP U-Pb age of zircons from the pluton is 155±2 Ma,which belongs to Yanshanian.Hongshan pluton is rich in silicon（SiO2=76.08%～77.25%）and alkali（K2O＋Na2O=8.78%～9.43%）,low in ACNK value（0.94～1.07）and CaO/Na2O value（0.10～0.19）.In trace elements,the pluton is rich in Rb,Th,U,depleted in Ba,Sr,P,Ti and has high Rb/Sr（30.02～930.9）,Rb/Ba（18.91～231.8）,has low LREE/HREE value（1.99～2.40）and remarkable Eu depletion（δEu=0.01～0.07）,has low ∑Nd（t）value（-10.2～-12.0）and old Nd model age（1777～1923 Ma）.All the evidence indicate that it have the characteristic of S type granite.Hongshan pluton is believed to be formed by partial melting of protozoic rocks,which related to the reactivation of Qitianling-Zhuguangshan（east-west）fracture zones resulted from the subduction of Pacific plate.