全文快速搜索:          
引用本文:马铁球 邝 军 柏道远 王先辉. 南岭中段诸广山南体燕山早期花岗岩地球化学特征及其形成的构造环境分析[J]. 中国地质, 2006, 33(1): 119-131.
MA Tie-qiu, KUANG Jun, BAI Dao-yuan, WANG Xian-hui. Geochemical characteristics and tectonic setting of the early Yanshanian South Zhuguangshan granite in the central segment of the Nanling Mountains[J]. Geology in China, 2006, 33(1): 119-131(in Chinese with English abstract).
【打印本页】   【HTML】   【下载PDF全文】   查看/发表评论  下载PDF阅读器  关闭
←前一篇|后一篇→ 过刊浏览    高级检索
本文已被:浏览 1288次   下载 847 本文二维码信息
码上扫一扫!
分享到: 微信 更多
南岭中段诸广山南体燕山早期花岗岩地球化学特征及其形成的构造环境分析
马铁球 邝 军 柏道远 王先辉
湖南省地质调查院, 湖南 湘潭 411100
摘要:
提要:诸广山南体为一复式岩基,形成于加里东期、印支期和燕山早期3个时代。本文着重讨论燕山早期主体花岗岩,即中侏罗世三江口序列。该序列由5个岩石单元组成,岩石类型为角闪石黑云母二长花岗岩—黑云母二长花岗岩—二云母二长花岗岩。较早次单元中富含镁铁质微粒包体,经包体岩相学研究,花岗岩浆具壳幔混合成因。SiO2平均含量从早次68.95%向末次76.30%逐渐增加;全碱较高,Na2O+ K2O在7.11%~8.24%,平均为7.73%,且K2O>Na2O;ASI值平均为1.05(0.92~1.19),岩石为镁质-铁质,准铝质-过铝质,高钾钙碱性岩系。ΣREE含量中等,平均为213 μg/g,为轻稀土富集型,铕亏损程度较大;具Ba、Nb、Sr、P、Ti、Eu、Ba负异常和Rb、U、Th、Nd、Zr、Sm、Y正异常,反映陆内构造-岩浆环境。ISr值为0.7115~0.72466,εNd (t)值平均为-10.97(-10.0~-12.6), t2DM平均为1.84 Ga (1.75~2.0 Ga),与南岭中生代花岗岩平均值(1.7~1.8 Ga)相近,反映成岩物质主要来源于中元古代地壳。多种氧化物与微量元素构造环境判别图解显示,三江口序列花岗岩形成于挤压造山向非造山转换的后造山拉张环境,同时也表明南岭乃至华南地区燕山早期构造环境为后造山而不是陆内裂谷。
关键词:  高钾钙碱性  壳幔混源型  地球化学  后造山环境  诸广山南体  南岭
DOI:
分类号:
基金项目:中国地质调查局地质大调查项目(200213000035)资助。
Geochemical characteristics and tectonic setting of the early Yanshanian South Zhuguangshan granite in the central segment of the Nanling Mountains
MA Tie-qiu, KUANG Jun, BAI Dao-yuan, WANG Xian-hui
Hunan Institute of Geology Survey, Xiangtan 411100, Hunan, China
Abstract:
Abstract: The South Zhuguangshan pluton is a composite granite batholith formed in the Caledonian, Indosinian and early Yanshanian periods. This paper mainly discusses early Yanshanian granites, namely, the Middle Jurassic Sanjiangkou sequence. The sequence is composed of five rock-units, and the rock type is hornblende-biotite monzogranite-biotite monzogranite-two-mica monzogranite. The earlier units contain abundant mafic micro-enclaves, and the petrographic study of the enclaves indicates the crust-mantle mixing origin of the granitic magma. The average content of SiO2 increases from 68.95% in the early-formed granite units to 76.3% in the late-formed granite units. The rocks are alkali-rich. Their Na2O+K2O ranges from 7.11% to 8.24%, with an average of 7.73% and K2O>Na2O, and their ASI values range from 0.92 to 1.19, with an average of 1.05;so they belong to the magnesian-ferruginous, metaluminous-peraluminous, high-K calc-alkaline series. The rocks are of light REE-enriched type, with a moderate ΣREE content of 213μg/g and strong Eu depletion, and have negative anomalies of Ba, Nb, Sr, P, Ti, Eu and Ba and positive anomalies of Rb, U, Th, Nd, Zr, Sm and Y, which indicate an intracontinental tectonomagmatic environment. The rocks have ISr values of 0.7115 to 0.72466, εNd (t) values of -10.0 to -12.6 with an average of -10.97 and t2DM ages of 1.75 to 2.0 Ga with an average of 1.84 Ga. The average age is close to that (1.7 to 1.8 Ga) of Mesozoic granites in the Nanling Mountains, indicating that the rock-forming materials were mainly derived from the Mesoproterozoic crust. The tectonic setting discrimination diagrams based on multiple oxides and trace elements suggest that granites of the Sanjiangkou sequence formed in a post-orogenic extensional environment during the transition from compressional orogeny to non-orogeny. The authors consider that the early Yanshanian tectonic setting in the Nanling Mountains and even South China is post-orogenic rather than an intracontinental rift.
Key words:  high-K calc-alkaline  crust-mantle mixing type  geochemistry  post-orogenic tectonic setting  South Zhuguangshan pluton  Nanling Mountains