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皖南地区燕山期岩浆作用强烈,可划分为早阶段(152~137Ma)和晚阶段(136~122Ma).野外调查发现,屯溪地区沿青山-长陔发育一条燕山期花岗岩带,与钼多金属矿床具有密切的成因关系.黄山岩体是皖南地区代表性的正长花岗岩体,目前尚未发现与成矿有关.锆石LA-ICP-MS定年结果表明,青山-长陔带4个花岗岩体的形成时代一致,介于(140±4)~(141±2)Ma,属于燕山期早阶段岩浆作用.黄山花岗岩体的形成时代为(129±2)Ma,属于晚阶段岩浆作用,青山-长陔带花岗岩具有较高的SiO_2含量,相对富K_2O、低P_2O_5以及中等程度的Al_2O_3含量,属于高钾钙碱性系列准铝质Ⅰ型花岗岩.这些岩石均表现出富集大离子亲石元素和轻稀土元素,亏损高场强元素,中等程度的Eu负异常,为岛弧或大陆壳源岩浆地球化学特征.样品的~(87)Sr/~(86)Sr(t)介于0.7120~0.7125,ε_(Nd)(t)值为-7.24~-4.38,锆石ε_(Hf)(t)值为-4.4~6.7,类似于同时期皖南成矿花岗闪长岩.综合地球化学研究表明,皖南燕山期成矿花岗闪长岩为中-新元古代增生加厚下地壳部分熔融的产物,而青山-长陔带花岗岩为这种岩浆经过斜长石+角闪石+上溪群的结晶分异同化混染(AFC)过程形成.黄山花岗岩富SiO_2和K_2O,Al_2O_3含量中等,具有海鸥式稀土元素配分型式和显著的Eu负异常.相比青山-长陔带花岗岩,黄山岩体具有更加显著的Ba、Sr、P和Ti的负异常,没有Nb和Ta的亏损,为高钾钙碱性准铝质A型花岗岩,其ε_(Hf)(t)值介于-6.6~-1.2,类似于早阶段成矿花岗闪长岩.黄山花岗岩同样起源于中-新元古代增生地壳的深熔作用,但岩浆源区为经过了燕山期早阶段Ⅰ型中酸性岩浆抽取后的残留麻粒岩质地壳.两期花岗岩的比较研究表明,早阶段花岗岩形成于相对厚的下地壳环境,温度较低,源区为中-新元古代增生地壳,富含成矿物质,岩浆AFC演化过程进一步加强了成矿物质的富集;而晚阶段A型花岗岩起源深度较浅,形成温度更高,源区由于早期的岩浆抽取作用而亏损成矿物质,从而成矿能力较弱,指示从早至晚,岩浆作用阶段从后造山转变为非造山.后者对应着古太平洋板块俯冲角度加大背景下的弧后拉张环境.
The Yanshanian magmatism in southern Anhui is intense and can be divided into the early stage (152 ~ 137Ma) and the late stage (136 ~ 122Ma) .It is found in the field survey that a Yanshan granite zone along the Qingshan-Changliu is developed along with the molybdenum polymetallic The Huangshan pluton is a typical orthogranag granito body in southern Anhui Province, and has not been found to be related to metallogenesis. The zircon dating of LA-ICP-MS shows that the four granites in the Qingshan-Changchuan Belt (140 ± 4) ~ (141 ± 2) Ma, which belongs to the magmatism in the early stage of Yanshan.The age of the Huangshan granite body is (129 ± 2) Ma, which belongs to late stage magmatism. Belt granites have high SiO_2 content, relatively rich K_2O, low P_2O_5 and moderate Al_2O_3 content, belonging to the high-K calc-alkaline series of quasi-aluminum type Ⅰ granites.These rocks are characterized by enrichment of large ion lithophile elements and Light rare earth elements, depleted high field strength elements and moderate Eu negative anomalies are geochemical characteristics of the island arc or continental crust. The ~ (87) Sr / ~ (86) Sr (t) , ε_ (Nd) (t) value is -7.24 ~ -4.38, zircon ε_ (Hf) (t) value is -4.4 ~ 6.7, similar to the same period Wannan metallogenic granodiorite.The comprehensive geochemical study shows that the Yanshanian granitoid granodiorite in southern Anhui is the result of the partial melting of the crust under the thickening of the Meso-Neoproterozoic, while the granite of the Qingshan-Changba granite is the The magma is formed through the process of crystal differentiation (AFC) of plagioclase, hornblende and amphibolite + Shangxi group.The content of SiO_2, K_2O and Al_2O_3 in Huangshan granite is medium, with seagull rare earth element type and Eu Anomaly.Compared with the Qingshan-Changbaogai granite, the Huangshan pluton has more significant negative anomalies of Ba, Sr, P and Ti, with no depletion of Nb and Ta, and is a high-K calc-alkaline quasi-Al A granite ε_ (Hf) (t) values range from -6.6 to -1.2, similar to the early stage metallogenic granodiorite.The Huangshan granite also originated from the Meso-Neoproterozoic accretionary crust, but the magmatic source area is After the late Yanshanian type I acid magma extraction residual granulite rock crust.Comparison of two granites shows that the early stage of granite formed in a relatively thick lower crust environment, the temperature is lower, the source area for the - Neoproterozoic accretionary crust, rich in ore-forming materials, magmatic AFC evolution to further strengthen And the enrichment of ore-forming materials. In the late stage, type A granite has a shallow depth and a higher formation temperature, and the source area is depleted in ore-forming materials due to early magmatic extraction. As a result, the metallogenic ability is weak, indicating that from early to late, The magmatic stage changed from post-orogenic to non-orogenic, which corresponds to the post-arc extension environment under the background of subduction of the Paleo-Pacific plate.