本文选取北山造山带公婆泉岛弧中部的尖山和石板井岩体展开研究.尖山花岗闪长岩具有典型埃达克岩特征,如较高SiO2(＞56％)、Al2O3(＞15％)、Sr(＞400 μg/g)含量以及高Sr/Y (60～88)、(La/Yb)N (7.73～15.5)比值,同时具有较高的Na2O含量(Na2O＞ K2O),低Y(8.15～11.2 μg/g)和Yb (0.57～1.01 μg/g)含量,并表现出弱的铕正异常(δEu=1.04～1.27).石板井花岗岩不具有埃达克质特征.两个岩体均富集大离子亲石元素(LILE),而亏损高场强元素(Nb、Ta).两个岩体近同时形成,其中尖山岩体LA-ICP-MS锆石U-Pb年龄为(363.4±2.9)Ma,石板井岩体LA-ICPMS锆石U-Pb年龄为(362.6±3.0)Ma.尖山岩体的Sr-Nd同位素显示弱富集的特征,其中(87Sr/86Sr)0=0.7057～0.7058和εNd(t)=-0.4 ～-1.1,而石板井岩体具有相对高的(87Sr/86Sr)0(0.7070～0.7071)和低的εNd(t)(-2.9～-2.6),推测两者岩浆源区包含有俯冲沉积物组分或岩浆在上升过程中受到了不同程度地壳物质的参与.结合其他的地质、地球化学证据,我们认为晚泥盆世尖山和石板井岩体是小黄山洋向南俯冲作用的结果,另外,晚泥盆世埃达克岩具有较大的斑岩铜矿成矿潜力.%Jianshan and Shibanjing granitic plutons developed in in the middle of the Gongpoquan arc,Beishan orogenic collage.Jianshan granodiorites show characteristics similar to classical adakites,e.g.,high SiO2 (＞ 56％),Al2O3 (＞ 15％),Sr (＞ 400 μg/g) contents and Na2O (Na2O ＞ K2O) values,high Sr/Y (60～88),(La/Yb)N (7.73～15.5)ratios,but low Y (8.15～11.2 μg/g) and Yb (0.57～1.01 μg/g) values with weak positive Eu anomalies (δEu =1.04～1.27),while Shibanjing granites do not show adakitic characteristics.LA-ICPMS zircon U-Pb ages of Jianshan pluton and Shibanjing pluton are (363.44±2.9) Ma and (362.64±3.0) Ma,respectively.Both the two plutons are enriched in large ion lithophile elements (LILEs),depleted in high field strength elements (HFSEs,e.g.,Nb,Ta),and have evolved Sr-Nd isotopes (Jianshan:(87Sr/86Sr)0 (0.7057-0.7058) and εNd (from-0.4 to-1.1);Shibanjing:(87Sr/86Sr)0 (0.7070-0.7071) and eNd(t) (-2.9--2.6)),indicating some crustal contamination.By synthesizing regional data,we suggest that the formation of Jianshan and Shibanjing plutons are related to the southward subduction of the Xiaohuangshan Ocean.Furthermore,the Late Devonian adakites have high ore potential.
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