Geochemical characteristics and tectonic implication of Beitou A type grantic intrusive in South Jiangxi Province
Geochemical characteristics and tectonic implication of Beitou A type grantic intrusive in South Jiangxi Province
复制标题
DOI：
--
复制
发表时间：
2000
期刊：
影响因子：
--
通讯作者：
Fan Chun
中科院分区：
文献类型：
--
作者：
Fan Chun
北头岩体位于赣南龙南县北头镇南岭花岗岩带北部。主要由钾长花岗岩组成，并有一些碱性花岗岩。在北投岩体的碱性花岗岩中发现了钠长石、霓石等碱性矿物，其主要成分为钾长花岗岩，（ANKC=0.94~1.07，平均0.98），以高硅含量为特征（SiO2：71.06%~76.28%），高碱性（K2 O + Na 2 O：8.1%~9.8%），FeOT/MgO较高（9.60~22.00），CaO、MgO含量低稀土总量为271.36~717.75 μg/g，高场强元素（Nb、Zr、Y等）含量较高，以及Ba、Sr、P、Ti、Rb、Th、U的亏损。这些特征与赣南I型和S型花岗岩有很大的不同，而与典型的A型花岗岩（如蒙布拉花岗岩类）有很大的相似性。矿物学、岩石学和地球化学证据表明，北投花岗岩属A型花岗岩类。在微量元素构造图解中（继皮尔斯等人之后，1984），北投侵入体福尔斯落入板内花岗岩中。根据R2 R1图（在Batcholor等人之后，1985年），北投岩体形成于造山后。北头岩体形成于燕山早期，其Rb-Sr等时线年龄为（178.15±0.84）Ma，与该区双峰式火山岩玄武岩的Rb-Sr等时线年龄为（178±7.2）Ma处于同一时代。因此。北头侵入体与双峰式火山岩在时间和空间上关系密切，表明赣南地壳裂陷作用可能始于燕山早期。这一结论对中国东南大陆在燕山运动晚期开始解体的认识提出了质疑。
Beitou intrusive is located in the north part of Nanling Granite Zone, around Beitou town of Longnan County in southern Jiangxi Province. It is mainly consists of potassium feldspar granites and has some alkaline granites. In alkaline granites of Beitou intrusive the alkaline minerals such as arfvedsnite and aegirine are found. The major component of Beitou intrusive, potassium feldspar granite, is metaluminous (ANKC=0.94～1.07, with an average of 0.98) and is characterized by high silica content (SiO2: 71.06%～76.28%), high alkaline (K2O+Na2O: 8.1%～9.8%), rather high ratio of FeOT/MgO (9.60～22.00), low content of CaO and MgO (0.58%～1.16%and 0.07%～0.25%, respectively), abundant amount of REE (total REE: 271.36～717.75 μg/g), quite high quantity of HFSE (Nb, Zr, Y, etc.), and depletion of Ba, Sr, P, Ti, Rb, Th, U. These characteristics are quite different from those observed from I and S type granites in southern Jiangxi Province, but are quite similar to those of typical A type granites such as Mumbulla granitoid. Evidence from mineralogy, petrology and geochemistry shows that these Beitou granites fall into A type granite granitoids. In trace element tectonic diagrams (after Pearce et al., 1984), Beitou intrusive falls into within plate granite. According to the R2 R1 diagram (after Batcholor et al., 1985), Beitou intrusive was formed in post orogenic. Beitou intrusive, which obtains a Rb Sr isochron age of (178.15±0.84) Ma, was formed during the period of early Yanshan movement and was in the same epoch with the basalt, with a Rb Sr isochron age of (178±7.2) Ma, of bimodal volcanic rocks in this district. Therefore. Beitou intrusive is closely related to bimodal volcanic rocks in time and space, suggesting that crustal rifting might start during the period of early Yanshan movement in southern Jiangxi Province. This conclusion poses a doubt to the acknowledgement that the break up of Southeast Continent of China was beginning during the late period of Yanshan movement.