The stability and composition of phengitic muscovite and associated phases from 5.5 to 11 GPa: Implications for deeply subducted sediments
The stability and composition of phengitic muscovite and associated phases from 5.5 to 11 GPa: Implications for deeply subducted sediments
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DOI：
10.1016/s0016-7037(96)00241-4
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发表时间：
1996-11
影响因子：
5
通讯作者：
K. Domanik;J. Holloway
中科院分区：
文献类型：
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作者：
K. Domanik;J. Holloway
在多砧合成实验中，研究了白云母在5.5 ~ 11 GPa， 700 ~ 1150℃范围内的稳定性和组成。起始材料由天然矿物组成，其体积组成类似于缺钾的中间二八面体-三八面体云母。腐殖白云母在900℃下，在5.5 ~ 11 GPa范围内是稳定的。在7 - 8gpa和1000-1050℃和10gpa温度下，辉长石熔化发生在1075-1150℃之间。在10-11 GPa温度下，观察到800°C的八面体阳离子缺陷（OCD）白云母和K-hollandite，而不是苯云母。白云母中白云石的平均含量与压力呈显著正相关，压力范围为3.65 ~ 3.81 Si pfu （5.5 GPa）。稳定白云母中最大白云石含量为3.80 ~ 3.85 Si pfu。大多数云母矿表现出至少少量的云母矿固溶体，平均为2.04±0.06 （2σ）八面体阳离子pfu。水相白云石、lawsonite、黄玉- oh和Mg-pumpellyite分布在6 - 8gpa， 700-900°C之间。随着压力的增加，lawsonite和Mg-pumpellyite在8 - 9gpa之间脱水形成石榴石。随着温度的升高，mg -泵辉石、lawsonite和黄石- oh在900-1000℃和7 - 8gpa之间析出形成石榴石和蓝晶石。腐殖白云母和黄玉- oh在冷却成熟俯冲带的含水沉积物中稳定到深度超过360 km，而褐煤和镁-泵长石则稳定到240-300 km，允许这些相中所含的水进入上地幔深处。在较温暖的俯冲带，镁-泵长石、钙长石和黄玉- oh脱水；此外，在180-240千米深处，云母岩的融化也会导致流体的释放。在远比弧下熔体生成带更深的深度（100-150公里）存在的白云石需要一种机制，如将K、Be、B、Ba和Rb划分为迁移流体，而不是简单地在弧下将白云石脱水，以便为这些板状特征元素从白云石转移到弧岩浆中提供条件。
The stability and composition of phengitic muscovite was investigated from 5.5–11 GPa, 700–1150°C in synthesis experiments performed in a multianvil apparatus. Starting materials consisted of natural minerals with a bulk composition similar to that of a K-deficient, intermediate dioctahedral-trioctahedral mica. Phengitic muscovite was found to be stable from 5.5–11 GPa at 900°C. Phengite melting occurs between 1075–1150°C at 7–8 GPa and 1000–1050°C at 10 GPa. At 10–11 GPa, 800°C octahedral cation deficient (OCD) muscovite and K-hollandite are observed rather than phengite. The average phengite content of muscovite is positively correlated with pressure ranging from 3.65 Si pfu at 5.5 GPa to 3.81 Si pfu at 11 GPa. The maximum phengite content of stable muscovite appears to be 3.80–3.85 Si pfu. Most phengite examined exhibits at least minor solid solution towards phlogopite, averaging 2.04 ± 0.06 (2σ) octahedral cations pfu. The hydrous phases phengite, lawsonite, topaz-OH, and Mg-pumpellyite occur between 6–8 GPa, 700–900°C. With increasing pressure lawsonite and Mg-pumpellyite dehydrate to form garnet between 8–9 GPa. With increasing temperature Mg-pumpellyite, lawsonite, and topaz-OH devolatilize to form garnet and kyanite between 900–1000°C at 7–8 GPa. Phengitic muscovite and topaz-OH would be stable in hydrous sediments in cool mature subduction zones to depths exceeding 360 km while lawsonite and Mg-pumpellyite would be stable to 240–300 km allowing the transport of H2O contained in these phases deep into the upper mantle. In warmer subduction zones the dehydration of Mg-pumpellyite, lawsonite, and topaz-OH; as well as the melting of phengite would result in fluid release at depths of 180–240 km. The presence of phengite at far greater depths than the zone of melt generation beneath arcs (100–150 km) requires a mechanism such as the partitioning of K, Be, B, Ba, and Rb into migrating fluids rather than the simple dehydration of phengite beneath arcs in order to provide for the transfer of these slab signature elements from phengite into arc magmas.