【作者】 张金阳；

【导师】 廖群安；

【作者基本信息】 中国地质大学 ， 矿物学、岩石学、矿床学， 2004， 硕士

【摘要】 摘 要西藏定结地区高喜马拉雅淡色花岗岩体紧靠藏南拆离断层内部呈小型岩株产出,多数岩体侵入于基底副变质岩中,大量呈网脉状、似层状及囊状产出的淡色花岗岩脉体亦分布于基底副变质岩中。岩体明显分两期侵入,早期二云母淡色花岗岩,矿物组合为黑云母+白云母±石榴石(石英+斜长石+碱性长石),晚期电气石淡色花岗岩,矿物组合为白云母+电气石±黑云母±石榴石(石英+斜长石+碱性长石)。薄片及探针研究表明岩石中白云母具原生的和次生的两种,黑云母为富铝的铁叶云母。地球化学特征表明,岩石富硅贫钙,高钾富碱,强过铝质,少铁镁质,稀土元素总量低,与洋中脊花岗岩相比,K、Rb、Ba、Th 及 Ta 明显富集,Hf、Zr、Y、Yb 不同程度的亏损,εNd(-12.04—-19.80)很小。电气石淡色花岗岩相对洋中脊花岗岩 Ba 及 Zr 呈低谷,Ta 呈高峰,Nb 含量高于二云母淡色花岗岩,显示后碰撞花岗岩的性质。总体上定结地区淡色花岗岩为典型 S 型花岗岩。基底副变质岩富硅过铝,其稀土元素与淡色花岗岩稀土元素具相似的特征,两者碱金属元素特征体现淡色花岗岩由云母类矿物分解熔融形成的特征。基底副变质岩与淡色花岗岩地球化学特征对比及岩体与实验熔体组成对比表明,两者之间具亲缘关系,基底副变质岩为淡色花岗岩源岩。综合野外地质特征、岩相学特征、地球化学特征及与实验岩石学的对比,本文认为,基底副变质岩为高喜马拉雅淡色花岗岩源岩,其在基底快速隆升降压的条件下发生缺水熔融生成淡色花岗岩浆,淡色花岗岩浆在基底隆升的基础上被动侵位,其中二云母淡色花岗岩先生成先侵位,电气石淡色花岗岩稍后生成,淡色花岗岩形成过程可能体现了构造环境的转换过程。更多还原

【Abstract】 The Higher Himalayan leucogranites in the region of Dinjie, Tibet, are closely near theinner South Tibet Detachments and occur in a series of small stocks. Most of them was emplacedinto the para-metamorphic rocks in the base, and abundant leucogranitic veins occurr as net,stratum or chamber in the para-metamorphic rocks, too. The leucogranites have apparently twoperiods: earlier two mica leucogranites, the mineral assemblages are biotite+muscovite±garnet(quartz+plagioclase+alkaline-feldspar); the later tourmaline leucogranites, the mineralassemblages are muscovite+tourmaline±biotite±garnet(quartz+plagioclase+alkaline-feldspar).According to petrography, muscovites are primary or secondary, and biotites are peraluminoussiderophyllites. Geochemical constraints show the leucogranites are rich in Si, K, (K+Na), Al, LREE, K, Rb,Ba, Th, Ta, and Nb, and poor in Ca and (Fe+Mg), HREE, Hf, Zr, Y and Yb. Tourmalineleucogranites are rich in Nb, Ta, Be and B and poor in Sr, Ba, Zr, Th and Co relative to two micaleucogranites. ε Nd of the leucogranites(-12.04 — -19.80) is small. In the whole theleucogranites are typical S-type granite. The para-metamorphic rocks in the base are abundant with Si and Al, and The REE of themis similar with that of the leucogranites. The characteristics of Rb, Sr and Ba indicates theleucogranites are formed from the dehydration melting of the micas. The geochemical feature ofthe leucogranites and the para-metamorphic rocks suggests two of them has genetic relations, sothe para-metamorphic rocks are the possible sources of the leucogranites. According to field geology, petrography, geochemistry and experimental petrology, theauthor think that the para-metamorphic rocks are the source rocks of the High Himalayanleucogranites, they are melted and formed leucogranites magma in condition of decompressionof the base, and The leucogranites magma were emplaced passively while the base was uplifting.Two mica leucogranites firstly melted and formed, and then tourmaline leucogranites in turn, andthis is the changing process of the structural environments.更多还原