| 北拉萨块体唐江穷果岩体中由同源岩浆不同期次之间混合产生的暗色包体:一种新的暗色包体岩石成因 |
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| 引用本文： | 陈伟,宋扬,曲晓明,孙渺,丁吉顺,马旭东.北拉萨块体唐江穷果岩体中由同源岩浆不同期次之间混合产生的暗色包体:一种新的暗色包体岩石成因[J].地球科学,2020,45(1):17-30. |
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| 作者姓名： | 陈伟 宋扬 曲晓明 孙渺 丁吉顺 马旭东 |
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| 作者单位： | 1.中国地质科学院矿产资源研究所, 自然资源部成矿作用和资源评价重点实验室, 北京 100037 |
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| 基金项目： | 中国地质调查局项目DD20160026中国地质调查局项目DD20190167 |
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| 摘 要： | 在西藏北拉萨块体中段唐江穷果岩体中发现了一种新的岩石成因的暗色包体.唐江穷果岩体中暗色包体呈椭球状，与寄主岩之间呈不紧密胶结，在暗色包体和寄主岩的接触面上通常形成一个明显的风化间隙面.暗色包体为角闪闪长斑岩，寄主岩为花岗闪长岩，暗色包体明显较寄主岩更基性，更富Na2O、CaO、MgO和Fe2O3T.暗色包体和寄主岩具有明显不同的稀土元素，暗色包体的稀土元素除La、Ce元素外，整体含量较寄主岩高，且轻重稀土分异弱.两者都具有弧岩浆岩的特征，富集Rb、Cs、K等大离子亲石元素和Th、U，而亏损Nb、Ta、Ti等高场强元素.暗色包体成岩年龄为113.9±1.0 Ma，寄主岩的成岩年龄为110±1.1 Ma，暗色包体成岩年龄较寄主岩早约4 Ma.此外，两者具有一致的锆石原位Lu-Hf同位素特征.以上岩相学、年代学、元素地球化学和同位素地球化学证据表明，唐江穷果暗色包体和寄主岩来源于同源母岩浆，暗色包体在二次岩浆房中经历了较弱的斜长石结晶分离作用，寄主岩在二次岩浆房中经历了较强的角闪石结晶分离作用.经过结晶分离作用的寄主岩岩浆在侵位过程中将较早形成处于半塑性状态下的暗色包体裹挟至近地表.唐江穷果暗色包体最可能的成因模式可以解释为同源岩浆不同期次间的物理混合.
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| 关 键 词： | 北拉萨块体 暗色微粒包体 锆石U-Pb定年 地球化学 Lu-Hf同位素 岩石成因 |
| 收稿时间： | 2018-07-03 |
MMEs in the Tangjiangqiongguo Pluton in the North Lhasa Block Formed by Magma Mixing of Different Episodes of the Same Sourced Magma: A New Petrogenetic Model for the MMEs |
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| Abstract: | This paper proposes a new petrogenetic model for the MMEs (mafic microgranular enclaves) based on a study on the Tangjiangqiongguo pluton in the middle part of the North Lhasa Block,Tibet. The MMEs found in the Tangjiangqiongguo host granitic diorites are hornblende diorites usually presenting axiolite and non-compactly cement with the host rock,with an apparent clearance plane with host rocks. The MMEs have higher Na2O,CaO,MgO and Fe2O3T contents than the host rocks. The MMEs have distinct REE characteristics from host rocks,with higher REE contents (except La and Ce) and weaker fractionation between LREE and HREE. Both the MMEs and host rocks show characteristics of arc rocks with enrichment in LILEs (large ion lithophile elements) Rb,Cs,K,etc.,and Th and U elements,but depletion in HFSEs (high field strength elements) Nb,Ta and Ti elements. Zircon LA-ICP-MS U-Pb dating yields a 113.9±1.0 Ma age and a 110±1.1 Ma age for the MMEs and host rocks,respectively. Although the MMEs are 4 Ma earlier than the host rocks,they have consistent zircon Lu-Hf isotopes. Synthesizing above petrography,geochemistry and isotopic evidence,we suggest the MMEs are derived from the same source rocks with host rocks. The MMEs experienced a weak plagioclase fractional crystallization,but the host rocks experienced a relatively strong hornblende fractional crystallization in respective secondary magma chamber. The differential magma of the host rock wrapped and carried the earlier formed MMEs (in semiplastic) to subsurface. The most probable petrogenetic model for the Tangjiangqiongguo MMEs mingling between magmas of different periods sourced from the same rock. |
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