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湘中印支期关帝庙岩体地球化学特征及成因 被引量:9

Geochemistry and petrogenesis of the Indosinian Guandimiao granitic pluton in central Hunan
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摘要 关帝庙岩体位于湘中盆地,据年龄资料可分为中三叠世末和晚三叠世中期两个形成时期。中三叠世花岗岩中发育闪长质暗色微粒包体,自早至晚依次为细中粒角闪石黑云母花岗闪长岩、细中粒斑状角闪石黑云母二长花岗岩、细-细中粒(斑状)黑云母二长花岗岩。晚三叠世花岗岩自早至晚依次为细中粒-粗中粒斑状二云母二长花岗岩、细粒二云母二长花岗岩。岩石高硅、富铝、高钾,(Na2O+K2O)含量为6.80%~8.87%,平均7.74%;K2O/Na2O比值在1.35~2.66之间,平均为1.58;ASI值为0.99~1.40。总体属镁质、高钾钙碱性系列过铝质花岗岩类。中三叠世花岗岩Ba、Nb、Sr、P、Ti表现为明显亏损,Rb、(Th+U+K)、(La+Ce)、Nd、(Zr+Hf+Sm)、(Y+Yb+Lu)等则相对富集。中、晚三叠世花岗岩ΣREE含量为121.60~197.56μg/g,平均为158.70μg/g;δEu值0.28~0.68,平均为0.53;(La/Yb)N值为5.94~17.53,平均13.80。中三叠世花岗岩ISr值为0.71302~0.71758,εSr(t)值为121~186,εNd(t)值为-9.95^-8.74,t2DM为1.72~1.82Ga。C/MF-A/MF图解显示源岩主要为碎屑岩、少量基性岩和泥质岩。地质地球化学特征表明,印支期关帝庙花岗岩属S型花岗岩,形成于碰撞-后碰撞构造环境。 The Indosinian Guandimiao granitic pluton in central Hunan is composed of two generations: the latest Middle Triassic and middle Late Triassic granites. The Middle Triassic granites comprise meladioritic micrinites, and consist, in a progressively younger order, of fine- to medium-grained hornblende-biotite granodiorite, fine- to medium-grained porphyritic hornblende-biotite adamellite, and fine- to finely medium-grained (porphyritic) biotite adamellite. The Late Triassic granites consist, in a progressively younger order, of finely medium-grained to coarsely medium-grained porphyritic two-mica adamellite and fine-grained two-mica adamellite. Geochemically, these granites are characterized by high Si, enriched A1, high K, moderate alkali contents, SiO2 contents ranging from 69.50% to 74.53% with an average of 71.68%. The Late Triassic granites have Al2O3 contents from 13. 39% to 16.31% with an average of 14.62% ; K20 contents from 4.15% to 6.45% with an average of 4.71% total alkali ( Na2O + K2O) contents from 6.80% to 8.87% with an average of 7.74% ; K2O/Na2O ratios from 1. 35 to 2.66 with an average of 1.58 ; ASI values from 0.99 to 1.40, indicating the magnesian high-K eale-alkaline peraluminous granites. The Middle Triassic granites are remarkedly depleted in Ba, Nb, Sr, P and Ti, and relatively enriched in Rb, Th + U + K, La + Ce, Nd, Zr + Hf + Sm and Y + Yb + Lu. The EREE contents for the Middle and Late Triassic granites vary from 121.60 to 197.56p, g/g with an average of 158.70μg/g; δEu values from 0.28 to 0.68 with an average of 0.53, and (La/Yb) N values from 5.94 to 17.53 with an average of 13.80. The above-mentioned geological and geochemical signatures show that the Indosinian Guandimiao granites belong to the S-type granites generated in the collision-postcollision tectonic settings.
出处 《沉积与特提斯地质》 CAS CSCD 2014年第4期92-104,共13页 Sedimentary Geology and Tethyan Geology
基金 中国地质调查局"湖南1:25万武冈市和永州市幅区调修测"项目(1212011120793) "中国地质构造区划综合研究与区域地质志修编"项目(1212010811032)联合资助
关键词 地球化学特征 S型花岗岩 中三叠世 晚三叠世 印支运动 关帝庙岩体 湘中 geochemistry S-type granite Middle Triassic Late Triassic Indosinian orogeny Guandimiao granitic pluton central Hunan
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