The occurrence of fluor-wagnerite in UHT granulites and its implications towards understanding fluid regimes in the evolution of deep crust: a case study from the Eastern Ghats Belt, India
The occurrence of fluor-wagnerite in UHT granulites and its implications towards understanding fluid regimes in the evolution of deep crust: a case study from the Eastern Ghats Belt, India
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超高温麻粒岩中氟硅镁石的出现及其对理解深部地壳演化中流体状态的意义：印度东高止山脉的案例研究
DOI：
10.1007/s00710-016-0474-y
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发表时间：
2017
影响因子：
1.8
通讯作者：
I. Ohnishi
中科院分区：
文献类型：
--
作者：
K. Das;N. Tomioka;S. Bose;J. Ando;I. Ohnishi
本文报道了一种罕见的磷矿物氟菱矿（mg1.91 ~ 1.94 fe0.06 ~ 0.07 ca <0.01） （p0.99 ~ 1.00o4）（oh0.02 ~ 0.17 f0.98 ~ 0.83）在中-新元古代印度造山带东高止带的分布。研究区高-超高温麻粒岩（~1000℃，8-9 kbar）在侵位后退行至中地壳水平（800-850℃，6-6.5 kbar）。基于矿物化学数据和微拉曼分析，我们记录了f - wagerite的异常高富镁-富f化学，既出现在峰变质卟啉岩组合中，也出现在逆行基质组合中。因此，在没有磷灰石等其他常见磷酸盐的情况下，氟镁矿可以作为含氟流体存在的指示物，用于高镁镁/或fo2的岩石。富f矿物作为流体组成监测物的出现，对黑云母脱水熔融的开始和深部地壳熔体的产生具有重要意义。我们认为氟镁矿可能作为富F流体伴生的副矿物出现在中下地壳岩石中，在调和黑云母-脱水熔融的成岩网格时，应考虑共存矿物中的F。
We report the occurrence of a rare phosphate mineral, fluor-wagnerite (Mg1.91–1.94Fe0.06–0.07Ca<0.01) (P0.99–1.00O4)(OH0.02–0.17F0.98–0.83) from the Eastern Ghats Belt of India, an orogenic belt evolved during Meso- to Neoproterozoic time. The host rock, i.e. high- to ultrahigh temperature (UHT) granulites (~1000 °C, 8–9 kbar) of the studied area was retrogressed after emplacement to mid-crustal level (800–850 °C, 6–6.5 kbar) as deduced from their pressure-temperature histories. Based on mineral chemical data and micro-Raman analyses, we document an unusual high Mg-F-rich chemistry of the F-wagnerite, which occur both in peak metamorphic porphyroblastic assemblages as well as in the retrograde matrix assemblage. Therefore, in absence of other common phosphates like apatite, fluor-wagnerite can act as an indicator for the presence of F-bearing fluids for rocks with highXMgand/orfO2. The occurrence of F-rich minerals as monitors for fluid compositions has important implications for the onset of biotite dehydration melting and hence melt production in the deep crust. We propose that fluor-wagnerite can occur as an accessory mineral associated with F-rich fluids in lower-mid crustal rocks, and F in coexisting minerals should be taken into consideration when reconciling the petrogenetic grid of biotite-dehydration melting.