Tetrad effect of rare earth elements caused by fractional crystallization in high-silica granites: An example from central Tibet
Tetrad effect of rare earth elements caused by fractional crystallization in high-silica granites: An example from central Tibet
复制标题
高硅花岗岩分异结晶引起的稀土元素四分体效应——以西藏中部为例
DOI：
10.1016/j.lithos.2021.105968
复制
发表时间：
2021-03
期刊：
影响因子：
3.5
通讯作者：
Zhao Zhidan
中科院分区：
文献类型：
--
作者：
Shuai Xue;Li Shi-Min;Zhu Di-Cheng;Wang Qing;Zhang Liang-Liang;Zhao Zhidan
确定高硅花岗岩中REE四元效应的形成机制(分步结晶和熔体-流体相互作用)对于理解岩浆和热液演化过程中的痕量元素行为(如稀有金属的富集性)至关重要。本文报道了西藏拉萨地体中部嘎金基岩中高硅花岗岩的新岩石学、锆石U-Pb年龄、痕量元素和Hf同位素及全岩地球化学资料。所有样品的年代都约为100 Ma，可能形成于拉萨-羌塘碰撞期间。这些样品均为正长花岗岩和碱长花岗岩，属高硅质I型花岗岩(SiO_2=74.2~78.2%)，具有高总碱值、低镁值、显著富铅、铀、钍、Rb，钛、铕、磷、锶、钡明显亏损的特征。岩石学和地球化学数据表明，斜长石+钾长石+黑云母(5：3：2)为中等(0-20%)分馏。稀土元素数据清楚地定义了规则的球粒陨石标准化模式(无四分体组)和明显的四分体模式(四分体组)。根据瑞利分馏模型，独居石和尿晶石的分馏作用可以再现四射石群中的稀土元素的踏面效应。对已报道样品的新模拟结果，以及岩相学观察和REE四元效应与孪生元素分馏之间的解耦，表明高硅花岗岩中的REE四元效应继承于分离结晶，而不是广泛认为的熔体-流体相互作用。
Determining the formation mechanism (fractional crystallization vs. melt-fluid interaction) of the REE tetrad effect in high-silica granites is critical for understanding trace elemental behaviors (e.g., enrichment of rare metals) during magmatic and hydrothermal evolution. This study reports new petrography, zircon U-Pb ages, trace elemental and Hf isotopic, and whole-rock geochemical data of high-silica granites from the Gajin Batholith in the central Lhasa Terrane, Tibet. All samples are dated at ca. 100 Ma and likely formed during Lhasa-Qiangtang collision. These samples are syenogranites and alkali-feldspar granites, belonging to high-silica I-type granites (SiO2= 74.2–78.2 wt%), having high total-alkalis, low magnesian, marked enrichments in Pb, U, Th, and Rb, and marked depletions in Ti, Eu, P, Sr, and Ba. The petrological and geochemical data indicate moderate (0–20%) fractionation of plagioclase + K-feldspar + biotite (5:3:2). The REE data clearly define regular chondrite-normalized patterns (No-tetrad Group) and pronounced tetrad patterns (Tetrad Group). The REE tread effect in Tetrad Group can be reproduced by fractionation of monazite and allanite as indicated by a Rayleigh fractionation modeling. New modeling results for samples reported elsewhere, along with petrographic observations and decoupling between the REE tetrad effect and fractionation of twin-elements, demonstrate that the REE tetrad effect in high-silica granites is inherited from fractional crystallization rather than formed by melt-fluid interaction as suggested widely.
登录
查看更多内容
影响因子：
5
作者：
Stefan Prowatke;S. Klemme
通讯作者：
Stefan Prowatke;S. Klemme
影响因子：
5
作者：
Hoskin, PWO
通讯作者：
Hoskin, PWO
西藏特提斯喜马拉雅地区早白垩世（~140 Ma）铝质A型花岗岩：岩石圈伸展过程中壳幔相互作用的产物
影响因子：
3.5
作者：
Ma Lin;Kerr Andrew C.;Wang Qiang;Jiang Zi-Qi;Hu Wan-Long
通讯作者：
Hu Wan-Long
影响因子：
3.5
作者：
Quach Duc-Tin;H. Keppler
通讯作者：
Quach Duc-Tin;H. Keppler
影响因子：
3.5
作者：
L. Zhang;Di‐Cheng Zhu;Qing Wang;Zhidan Zhao;Dong Liu;Jin‐Cheng Xie
通讯作者：
L. Zhang;Di‐Cheng Zhu;Qing Wang;Zhidan Zhao;Dong Liu;Jin‐Cheng Xie