东秦岭中生代石瑶沟隐伏花岗岩年代学、 地球化学特征及地质意义
The Chronology, Geochemical Characteristics and Geological Significance of the Mesozoic Shiyaogou Hidden Granite at the East Qinling

石瑶沟花岗岩是华北陆块南缘东秦岭熊耳山地区近年来发现的首个埋藏在地下,与钼矿化有关的隐伏花岗岩体.主要岩性为中-细粒黑云母二长花岗岩和斑状花岗岩,LA - I CP -MS锆石 U - P b定年结果显示其主体形成时期为1 4 0.4 6±0.5 9Ma~1 3 6.5 3±0.4 4Ma,为早白垩世岩浆活动产物. 石瑶沟花岗岩 S i O 2=7 0.2 7%~7 3.2 2%,A l 2O 3=1 2.7 1%~1 4.9 6%,MgO=0.2 3%~0.5 4%,全碱(K 2O+N a 2O)含量(质量百分比)变化范围为6.4 3%~1 1.7 8%,显示高硅、富碱特征.里特曼指数( δ)变化范围为2.1 1~3.0 2,AR 介于1.4 8~5.7 3之间,为钙碱性;ACNK 值=0.9 5~1.0 1,属准铝质-过铝质I型花岗岩.岩体稀土总量(∑REE)变化于1 4 7×1 0-6~3 2 2×1 0-6,LREE /HREE比值变化于1 5.2~2 5.2,L a N/Yb N=1 9.1~5 0.5×1 0-6,轻重稀土分馏程度较高,在球粒陨石标准化分配模式图上总体表现为轻稀土富集、左陡右平的右倾 斜 型. 岩 体 S r含 量 变 化 较 大(1 3 3×1 0-6~7 5 9×1 0-6,平均 3 7 1×1 0-6),Y、Yb 含量(Y=1 0.0 2×1 0-6~1 8.8 0×1 0-6,平 均 1 2.5 7×1 0-6;Yb=1.1 6×1 0-6~2.0 2×1 0-6,平均1.4 0×1 0-6)和S r /Y 比值(1 2.7 7~6 1.6 6,平均3 0.4 4)低,具中等-弱的负 E u异常( δE u=0.5 3~0.7 1,平均 0.6 2),反映岩浆发生过长石分离结晶作用.石瑶沟花岗岩I s r=0.7 0 74 4~0.7 1 38 4, ε S r( t) = 4 4.1~1 3 4.9, εNd( t) =-1 2.9 6~-1 3.4 6,其t DM2=2.0 0~2.0 1G a,显示其与附近中生代合峪花岗岩基具同源性,岩浆源区包括南秦岭地块、扬子陆块以及部分太华群、熊耳群物质.综合石瑶沟隐伏花岗岩特征和区域地质演化,可得出结论:东秦岭地区在侏罗纪前的陆内俯冲体制下,南秦岭地块及扬子基底向华北陆块下俯冲碰撞使地壳加厚,侏罗纪-白垩纪之交的挤压向伸展转换过程中形成的减压增温环境,使该区中-下地壳岩石发生部分熔融,最终在早白垩世形成石瑶沟花岗岩.
The Shiyaogou granite is a related to the molybdenum mineralization hidden granite, which is found for the first time in the Xionger Mountain at the East Qinling, southern margin of North China landmass. The lithology of the granite is mainly medium-fine biotite monzogranite and porphyritic granite, and the LA-ICP-MS zircon U-Pb dating results indicate that it was formed in the early Cretaceous(140.45±0.75Ma-136.64±0.55Ma). The geochemical data show that the granite is characterized by SiO2(70.27%-73.22%)，Al2O3(12.71%-14.96%)，MgO(0.23%-0.54%), the total alkaline(K2O+Na2O) ranging from 6.43% to 11.78wt%, which suggests that the granite has high silicon and rich alkali characteristics. The Rittmann Index (δ) ranges from 2.11 to 3.02, and AR ranges from 1.48 to 5.73, which shows the granite is calc-alkaline series. The A/CNK value is 0.95-1.01, and shows a Aluminumperaluminous I-type granite characteristic. The ∑REE of the granite ranges form 147×10-6 to 322×10-6, the ratio of LREE/HREE ranges from 15.2 to 25.2, and the value of La-N/Yb-N ranges from 19.10×10-6 to 50.50×10-6. The chonrite standardized distribution pattern is characterized by enrichment of LREE in the right-dipping type with medium-weak negative Eu anomalies(δEu=0.53-0.71，average 0.62). The trace elements are characterized by the value of Sr(133×10-6-759×10-6，average 371×10-6), the low value of Y and Yb(Y=10.02×10-6-18.80×10-6，average 12.57×10-6；Yb=1.16×10-6-2.02×10-6，average 1.40×10-6), and the lower ratio of Sr/Y(12.77-61.66,