A REE-in-plagioclase–clinopyroxene thermometer for crustal rocks
A REE-in-plagioclase–clinopyroxene thermometer for crustal rocks
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DOI：
10.1007/s00410-016-1326-9
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发表时间：
2017-04
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
基于稀土元素(REE)在斜长石和单斜辉石共存时随温度和成分的分配关系，研制了斜长石-单斜辉石稀土温度计。这种双矿物交换温压计是利用斜长石和斜方辉石中稀土元素 + Y分配的晶格应变模型中的参数构建的，这些参数是根据实验确定的矿物熔体分配数据独立校准的。这种基于稀土元素的温度计的一个重要优点是，它可以通过对稀土元素 + Y作为一个整体进行线性最小二乘分析来提供准确的温度。REE-In-斜长石-单斜辉石温度计在火山岩和堆积岩中的应用表明，新温度计的温度与独立约束的岩浆结晶温度吻合得很好，这为稀土交换温度计在成分范围广泛的天然岩石(即从玄武岩到流纹岩)的应用增加了信心。然而，火山岩和堆积岩的稀土和镁交换温度计之间存在系统的温度差异。通过斜长石-单斜辉石体系中扩散的数值模拟，我们证明：(1)由于扩散速度较慢，矿物中的稀土元素优先记录了岩石的结晶或近结晶温度；(2)对于来自中、缓慢冷却岩浆体的岩石，镁很容易停留在较低的温度，但记录了来自快速冷却岩浆的岩石的初始结晶温度。由于它们对温度变化有不同的扩散响应，这两个温度计记录的稀土和镁闭合温度可以联合用于研究含斜长石和单斜辉石的岩石的热史和岩浆史。
A REE-in-plagioclase-clinopyroxene thermometer has been developed on the basis of the temperature- and composition-dependent rare-earth element (REE) partitioning between coexisting plagioclase and clinopyroxene. This two-mineral exchange thermobarometer is constructed using parameters from lattice strain models for REE + Y partitioning in plagioclase and in clinopyroxene that were independently calibrated against experimentally determined mineral-melt partitioning data. An important advantage of this REE-based thermometer is that it can provide accurate temperatures through linear least-squares analysis of REE + Y as a group. Applications of the REE-in-plagioclase-clinopyroxene thermometer to volcanic and cumulate rocks show that temperatures derived from the new thermometer agree well with independently constrained magma crystallization temperatures, which adds confidence to applications of the REE-exchange thermometer to natural rocks with a wide spectrum of composition (i.e., from basalt to rhyolite). However, systematic temperature differences appear between the REE- and Mg-exchange thermometers for the volcanic and cumulate rocks. Through numerical simulations of diffusion in plagioclase-clinopyroxene systems, we demonstrate that (1) due to their slower diffusion rates, REE in minerals preferentially records crystallization or near-crystallization temperatures of the rock, and that (2) Mg is readily rest to lower temperatures for rocks from intermediately or slowly cooled magma bodies but records the initial crystallization temperatures of rocks from rapidly cooled magmas. Given their distinct diffusive responses to temperature changes, REE and Mg closure temperatures recorded by the two thermometers can be used in concert to study thermal and magmatic histories of plagioclase- and clinopyroxene-bearing rocks.