论文部分内容阅读
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-ICP-MS锆石U-Pb定年结果显示其主体形成时期为140.46±0.59Ma~136.53±0.44Ma,为早白垩世岩浆活动产物.石瑶沟花岗岩SiO2=70.27%~73.22%,Al2O3=12.71%~14.96%,MgO=0.23%~0.54%,全碱(K2O+Na2O)含量(质量百分比)变化范围为6.43%~11.78%,显示高硅、富碱特征.里特曼指数(δ)变化范围为2.11~3.02,AR介于1.48~5.73之间,为钙碱性;ACNK值=0.95~1.01,属准铝质-过铝质I型花岗岩.岩体稀土总量(∑REE)变化于147×10-6~322×10-6,LREE/HREE比值变化于15.2~25.2,LaN/YbN=19.1~50.5×10-6,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Sr含量变化较大(133×10-6~759×10-6,平均371×10-6),Y、Yb含量(Y=10.02×10-6~18.80×10-6,平均12.57×10-6;Yb=1.16×10-6~2.02×10-6,平均1.40×10-6)和Sr/Y比值(12.77~61.66,平均30.44)低,具中等-弱的负Eu异常(δEu=0.53~0.71,平均0.62),反映岩浆发生过长石分离结晶作用.石瑶沟花岗岩Isr=0.707 44~0.713 84,εSr(t)=44.1~134.9,εNd(t)=-12.96~-13.46,其tDM2=2.00~2.01Ga,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.
Shiyaogou granite is the first concealed granite body buried in the ground and related to molybdenum mineralization discovered in recent years in Xiong’ershan area, eastern Qinling Mountains, on the southern margin of the North China block. The main lithology is medium-fine-grained biotite monzogranite and porphyritic The U-Pb dating of granite and zircon LA-ICP-MS shows that the main body was formed from 140.46 ± 0.59Ma to 136.53 ± 0.44Ma, which is the product of the Early Cretaceous magmatic activity. The SiO 2 = 70.27% -73.22% Al 2 O 3 = 12.71% ~ 14.96%, MgO = 0.23% ~ 0.54%, K 2 O + Na 2 O content by mass ranging from 6.43% to 11.78% δ) ranged from 2.11 to 3.02, AR ranged from 1.48 to 5.73, and was calc-alkaline.The ACNK value was 0.95 ~ 1.01, belonging to the quasi-aluminum-petrolatum type I granite.The total amount of rare earth elements ) Varies from 147 × 10-6 to 322 × 10-6, the LREE / HREE ratio changes from 15.2 to 25.2, LaN / YbN = 19.1 to 50.5 × 10-6, and the degree of fractionation of light and heavy rare earths is relatively high. The overall pattern shows light rare earth enrichment and left-leftward-rightward right-inclined type.The content of Sr in rock mass varies greatly (133 × 10-6 ~ 759 × 10-6, average 371 × 10-6) Yb content (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 Sr / Y ratio (12.77 ~ 61.66, average 30.44) δEu = 0.53 ~ 0.71, with an average of 0.62), which indicates that the feldspar was separated and crystallized in the magma. The Shiyaoogou granite is characterized by Isr = 0.707 44 ~ 0.713 84, εSr (t) = 44.1 ~ 134.9 and εNd (t) = - 12.96 ~ 13.46 with tDM2 = 2.00-2.01Ga, indicating that it has homology with the Mesozoic Holocene granite basement in the vicinity. The magmatic source area includes the Nanqinling block, the Yangtze block and some Taihua and Xiong’er groups. Concealed granite features and regional geological evolution can be concluded: Under the pre-Jurassic intracontinental subduction system, the East Qinling area underwent thrust subduction under the South Qinling block and the Yangtze base to thicken the crust beneath the North China block. The Jurassic-Cretaceous The pressure-reduced and temperature-rising environment formed during the transition from crushing to extension in the Jikschulen process resulted in the partial melting of the middle-lower crustal rocks in the area and eventually the formation of Shiyaogou granite in the Early Cretaceous.