Distribution of REE between clinopyroxene and basaltic melt along a mantle adiabat: effects of major element composition, water, and temperature
Distribution of REE between clinopyroxene and basaltic melt along a mantle adiabat: effects of major element composition, water, and temperature
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DOI：
10.1007/s00410-011-0700-x
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发表时间：
2010-12
影响因子：
3.5
通讯作者：
Chenguang Sun;Yan Liang
中科院分区：
文献类型：
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作者：
Chenguang Sun;Yan Liang
斜辉石（cpx）与玄武岩熔体之间稀土元素（REE）的分布对解析地幔熔融过程具有重要意义。给定cpx-熔体配分实验的REE和Y配分系数可以用晶格应变模型定量描述。本文采用非线性回归方法对已发表的cpx和玄武岩熔体之间的REE和Y分配数据进行了分析，并将晶格应变模型中的关键分配参数（D0,r0andE）作为压力、温度和cpx和熔体成分的函数进行了参数化。d0与cpx的四面体位Al （AlT）和M2位Mg （MgM2）呈正相关，与熔体温度和含水量呈负相关。r0与Al in M1位点（AlM1）和MgM2in cpx呈负相关。andi与thr0呈正相关。尖晶石热沸石在绝热熔融过程中，温度、AlT和MgM2in cpx均随压力或熔融程度的变化而系统降低。温度和cpx组成之间的竞争效应导致稀土元素分配系数沿地幔绝热线变化很小。较高势温（1400℃）下稀土元素分配系数略低于较低势温（1300℃）下，温度效应压倒了成分效应。因此，一组恒定的REE分配系数可以用来精确地模拟尖晶石-辉橄榄岩沿地幔绝热板部分熔融过程中的REE分馏。由于cpx在高温熔融过程中Al和Mg丰度较低，稀土元素在cpx中的不相容性较强。熔体中稀土元素的大量耗尽可能意味着含水石榴石-辉橄榄岩的深度熔融。在模拟低度含水熔融时，需要考虑与水相关的cpx分配系数。
The distribution of rare earth elements (REE) between clinopyroxene (cpx) and basaltic melt is important in deciphering the processes of mantle melting. REE and Y partition coefficients from a given cpx-melt partitioning experiment can be quantitatively described by the lattice strain model. We analyzed published REE and Y partitioning data between cpx and basaltic melts using the nonlinear regression method and parameterized key partitioning parameters in the lattice strain model (D0,r0andE) as functions of pressure, temperature, and compositions of cpx and melt.D0is found to positively correlate with Al in tetrahedral site (AlT) and Mg in the M2 site (MgM2) of cpx and negatively correlate with temperature and water content in the melt.r0is negatively correlated with Al in M1 site (AlM1) and MgM2in cpx. AndEis positively correlated withr0. During adiabatic melting of spinel lherzolite, temperature, AlT, and MgM2in cpx all decrease systematically as a function of pressure or degree of melting. The competing effects between temperature and cpx composition result in very small variations in REE partition coefficients along a mantle adiabat. A higher potential temperature (1,400°C) gives rise to REE partition coefficients slightly lower than those at a lower potential temperature (1,300°C) because the temperature effect overwhelms the compositional effect. A set of constant REE partition coefficients therefore may be used to accurately model REE fractionation during partial melting of spinel lherzolite along a mantle adiabat. As cpx has low Al and Mg abundances at high temperature during melting in the garnet stability field, REE are more incompatible in cpx. Heavy REE depletion in the melt may imply deep melting of a hydrous garnet lherzolite. Water-dependent cpx partition coefficients need to be considered for modeling low-degree hydrous melting.