小秦岭地区早白垩世酸性侵入岩地球化学特征及构造环境

小秦岭地区地处华北地台南缘、豫陕两省交界地段.区内早白垩世酸性岩浆活动强烈.该区内文峪、华山、娘娘山3个花岗岩体的岩石地球化学特征如下:w(SiO2)为68.13％～73.56％,w(Al2O3)为13.50％～16.27％,w(MgO)为0.11％～0.44％,全碱质量分数为7.62％～8.94％,碱度率(AR)2.63～3.67,铝饱和指数(A/CNK)0.95～1.05,属高钾钙碱性Ⅰ型花岗岩.富集大离子亲石元素(LILE) Ba、Rb、Sr和亏损高场强元素(HFSE) Nb、Ta、P、Ti.w(Sr)高达452×10-6～965×10-6,Y和Yb质量分数分别低至5.8×10-6～15.9×10-6和0.63×10-6～1.68×10-6,Cr和Ni含量甚低.稀土元素总量为60.84×10-6～227.44×10-6,轻重稀土元素分馏强烈,[w(La)/w(Yb)]N为12.47～39.19,δ(Eu)为0.73～0.80.岩石具增厚下地壳熔融成因的埃达克岩特征.早白垩世时期,构造体制由挤压向伸展转变、岩石圈大规模减薄是小秦岭及周边地区岩浆活动及金矿大规模成矿作用的地球动力学背景,古老地壳物质在减压作用和底侵幔源岩浆加热的共同作用下发生部分熔融是区内具有埃达克岩特征的花岗岩的成因机制.

Geochemistry of the Early Cretaceous Acidic Intrusions in Xiaoqinling,Central China: Constraints on Tectonic Setting

Xiaoqinling area is located at southern margin of North China Craton,crossing Henan and Shaanxi provinces.Wenyu,Huashan and Niangniangshan granites are main instrusions in Xiaoqinling area.These granites have SiO2 ranging from 68.13% to 73.56%,Al2O3 ranging from 13.50% to 16.27%,MgO ranging from 0.11% to 0.44% respectively.These granites are high K calc-alkaline I type granite,characterized by K2O+Na2O=7.62%-8.94%,AR=2.63-3.67,A/CNK=0.95-1.05.The granites are enriched in LILE(Ba,Rb,Sr) and depleted in HFSE(Nb,Ta,P,Ti).They contain 452×10-6-965×10-6Sr,5.8×10-6-15.9×10-6 Y and 0.63×10-5-1.68×10-6 Yb,poor Cr and Ni.The granites are relatively enriched in LREE and depleted in HREE((La/Yb)N=12.47-39.19),and slightly negative Eu anomalies δEu=0.73-0.80).The rocks have the same geochemical characteristics as adakite.Tectonic regime transformation and lithospheric thinning were the geodynamic background of magmatism and metallogenesis in Xiaoqinling and neighboring regions in Early Cretaceous.Ancient crust partial melting due to decompression and mantle magma underplating was the formation mechanism of the granites in Xiaoqinling area.