摘要
四顶黑山岩基是甘肃北山北带规模较大、岩石类型丰富的复式岩基之一,由四顶黑山岩体(早期)、双沟山岩体(中期)和马鞍山北岩体(晚期)组成。同位素测年表明,四顶黑山岩体侵位时代为早石炭世(327~351Ma),双沟山岩体形成于中—晚二叠世(263.5Ma±4.7Ma),而马鞍山北岩体为中三叠世(237.8±4.3Ma)。四顶黑山岩体为一基性—超基性杂岩体,由辉长岩、角闪辉长岩和少量橄榄岩组成,岩石富Mg、Fe,LREE富集,Eu呈正异常,富集相容元素而亏损不相容元素,可能代表了晚古生代底侵到加厚地壳底部的玄武质岩浆。双沟山岩体主要由花岗闪长岩、石英闪长岩组成;而马鞍山北岩体主要由花岗闪长岩和斑状二长花岗岩组成。双沟山岩体和马鞍山北岩体均具有埃达克岩类似的岩石地球化学特征:SiO_2>56%(平均分别为65.94%和66.88%),Al_2O_3≥16%(平均分别为15.77%和15.10%)和MgO<3%(平均分别为1.79%和1.61%),微量元素Sr>400×10^(-6)(平均分别为418×10^(-6)和499×10^(-6));Yb<1.9×10^(-6)(平均分别为1.26×10^(-6)和1.17×10^(-6));Y<18×10^(-6)(平均分别为10.39×10^(-6)和11.44×10^(-6)),LREE富集和Eu为弱负异常—正异常,相对亏损高场强元素(Nb、Hf和Ti等)。结合岩体产出的构造位置及区域地质演化,认为双沟山岩可能是在中—晚二叠世,研究区处于造山后伸展环境,地幔物质上涌,底侵于地壳底部,导致玄武质下地壳发生部分熔融形成,而马鞍山北岩体可能与古特提斯洋板块于晚二叠世到三叠纪向北俯冲诱发了本区陆内俯冲有关。
Sidingheishan batholiths is one of representative example of the Beishan tectonomagmatic belt in Gansu, which is the largest scale and the most rock types, and composed of Sidingheishan pluton, Shuanggoushan pluton and Ma＇anshanbei pluton. U-Pb age determination of zircon shows that Sidingheishan pluton was intruded at 327-351Ma, Shuanggoushan pluton was intruded at 263.5±4.7Ma, and Maanshanbei pluton was intruded at 237.8±4.3Ma. Sidingheishan pluton is basic-to uhrabasic intrusive rocks （gabbroite, Hornblende gabbro and few peridotite） are high Mg and Fe, LREE enrichment, Eu positive anomaly, enriched in compatible elements and low incompatible elememts, which are the products of partial melting of subcontinental lithospheric enrich mantle, and probably represent the underplating basaltic magma below the thickened continental crust during late Paleozoic era. Shuanggoushan pluton are mainly composed of quartz diorite and granodiorite, and Ma＇anshanbei pluton are composed granodiorite and porphyritic monzonite granite. Shuanggoushan pluton and Maanshan plutons have the similar petrological and geochemical characteristics to those of adakite with SiO2〉56%, respectively average 65.94% and 66.88%; Al2O3≥ 16%, respectively average 15.77% and 15.51%, and MgO〈3%, respectively average 1.79% and 1.61%. high Sr content （Sr〉400×10^-6）, Respectively average 418×10×^-6 and 499×10^-6 65.94%; low Y content （Y〈18×10^-6）, respectively average 10.39×10^-6 and 11.44×10^-6, and low Yb content （Yb〈1.9×10^-6）, respectively average 1.26×10^-6 and 1.17×10^-6, LREE enrichment, no obviously Eu anomaly, and relative depletion in the high field strength elements （such as Nb, Hf, Ti）. On the basis of these features, combined with the tectonic locations of granite occurrence and field observation data, Shuanggoushan pluton were most likely derived from the partial melting of basaltic lower crust in the thickened crust resulted from hot mantle material upwelling as several mushroom cloud and the
作者
金霞
黄增保
JIN Xia HUANG Zeng-bao(Geological Survey of Gansu Province, Lanzhou 730000, Chin)
出处
《甘肃地质》
2016年第2期20-28,共9页
Gansu Geology
关键词
岩石地球化学特征
成因
四顶黑山岩基
埃达克质岩石
甘肃北山
petrological and geochemical characteristics
genesis
Sidingheishan complex
adakite-like rock
Beishan, Gansu
