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首页> 外文期刊>Contributions to Mineralogy and Petrology >Empirical calibration of the clinopyroxene-garnet magnesium isotope geothermometer and implications
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Empirical calibration of the clinopyroxene-garnet magnesium isotope geothermometer and implications

机译：斜辉石-石榴石镁同位素地热仪的经验标定及其意义

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The large equilibrium Mg isotope fractionation between clinopyroxene and garnet observed in eclogites makes it a potential high-precision geothermometer, but calibration of this thermometer by natural samples is still limited. Here, we report Mg isotopic compositions of eclogite whole rocks as well as Mg and O isotopic compositions of clinopyroxene and garnet separates from 16 eclogites that formed at different temperatures from the Dabie orogen, China. The whole-rock delta Mg-26 values vary from -1.20 to +0.10 parts per thousand. Among them, 11 samples display limited delta Mg-26 variations from -0.36 to -0.17 parts per thousand, similar to those of their protoliths. The mineral separates exhibit very different delta Mg-26 values, from -0.39 to +0.39 parts per thousand for clinopyroxenes and from -1.94 to -0.81 % for garnets. The clinopyroxene-garnet Mg isotope fractionation (Delta Mg-26(clinopyroxene-garnet) = delta Mg-26(clinopyroxene)-delta Mg-26(garnet)) varies from 1.05 to 2.15 parts per thousand. The clinopyroxene-garnet O isotope fractionation (Delta O-18(clinopyroxene-garnet) = delta O-18(clinopyroxene)-delta O-18(garnet)) varies from -1.01 to +0.98 %. Equilibrium Mg isotope fractionation between clinopyroxene and garnet in the investigated samples is selected based on both the delta Mg-26(gclinopyroxene) versus delta Mg-26(garnet) plot and the state of O isotope equilibrium between clinopyroxene and garnet. The equilibrium Delta Mg-26(clinopyroxene-garnet) and corresponding temperature data obtained in this study, together with those available so far in literatures for natural eclogites, are used to calibrate the clinopyroxene-garnet Mg isotope thermometer. This yields a function of Delta Mg-26(clinopyroxene-garnet) = (0.99 +/- 0.06) x 10(6)/T-2, where T is temperature in Kelvin. The refined function not only provides the best empirically calibrated clinopyroxene-garnet Mg isotope thermometer for precise constraints of temperatures of clinopyroxene- and garnet-bearing rocks, but also has potential applications in high-temperature Mg isotope geochemistry.
机译：在榴辉岩中观察到的斜辉石和石榴石之间的大型平衡Mg同位素分馏使其成为潜在的高精度地热仪，但通过天然样品对该温度计进行校准仍然受到限制。在这里，我们报道了榴辉岩整块岩石的镁同位素组成，以及斜辉石和石榴石的镁和氧同位素组成与来自中国大别造山带的不同温度下形成的16个榴辉岩分离。整个岩石的Mg-26增量值从-1.20到+0.10千分之几。其中，有11个样品显示出Mg-26的变化范围有限，从-0.36到-0.17千分之几，与它们的原石相似。矿物分离物表现出非常不同的Mg-26δ值，斜吡咯烯为-0.39至+0.39千份，石榴石为-1.94至-0.81％。斜茂铁石榴石的Mg同位素分馏（ΔMg-26（斜茂铁-石榴石）=δMg-26（斜茂铁）-δMg-26（石榴石））在千分之1.05至2.15之间变化。 Clinopyroxene-石榴石O同位素分馏（δO-18（clinopyroxene-石榴石）=δO-18（clinopyroxene）-δO-18（石榴石））在-1.01至+ 0.98％之间变化。根据δMg-26（斜晶石）与δMg-26（石榴石）图以及斜晶石与石榴石之间的O同位素平衡状态，选择了研究样品中斜cl烯和石榴石之间的平衡Mg同位素分馏。这项研究中获得的平衡Delta Mg-26（斜环茂石榴石）和相应的温度数据，以及迄今为止在天然榴辉岩文献中可获得的数据，都用于校准斜环茂石榴石Mg同位素温度计。这产生了ΔMg-26（斜环茂石榴石）＝（0.99 +/- 0.06）×10（6）/ T-2的函数，其中T是开氏温度。完善的功能不仅提供了最佳的经验校准的斜发石-石榴石镁同位素温度计，可精确限制斜发石和石榴石的岩石温度，而且在高温镁同位素地球化学中具有潜在的应用。

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