Geochemical Thermometry of Ore-Bearing Gabbronorites from an Apophysis of the Yoko-Dovyren Massif: Composition, Amount of Olivine, and Conditions of Sulfide Saturation in the Parental Magma

IF 1 4区 地球科学 Q3 GEOCHEMISTRY & GEOPHYSICS
I. V. Pshenitsyn, A. A. Ariskin, S. N. Sobolev
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Abstract

The temperature and compositional parameters of the parental magma of ore-bearing apophysis DV10 of the Yoko-Dovyren massif are estimated by the method of geochemical thermometry based on results of thermodynamic modeling of the equilibrium crystallization of the melts of 24 rocks. The thermometric calculations were carried out using the COMAGMAT-5.3 program with increments of 0.5 mol % to a maximum degree of crystallization 75–85%, under oxygen fugacity controlled by the QFM buffer. The model crystallization sequence of minerals was as follows: olivine (Ol) + Cr-Al spinel (Spl) → plagioclase (Pl) → high-Ca pyroxene (Cpx) → orthopyroxene (Opx). Silicate−sulfide immiscibility was calculated to occur mostly before the onset of plagioclase crystallization, which is consistent with initial sulfide saturation of the parental magma. The calculation results demonstrate the convergence and intersection of the model liquid lines of descent at temperatures of about 1185oC. When applied to the average composition of apophysis DV10, this temperature indicates the existence of suspension of the original crystals, including 52.1 wt % cumulus olivine (Fo83.6), 2.3 wt % plagioclase (An79.7), 0.24 wt % clinopyroxene (Mg# 88.8), 1 wt % aluminochromite (Cr# 0.62), and about 0.2% sulfide liquid in a moderately magnesian melt (53.6 wt % SiO2, 7.4 wt % MgO). Therewith the sulfur concentration at sulfide saturation (SCSS) was estimated at 0.083 wt %. This heterogeneous system had a viscosity of 4.71 log units (Pa s) and integral density of 2929 kg/m3. Such rheological properties do not contradict the possibility of the migration and emplacement of the protocumulus mush from the main Dovyren chamber. However, a more probable scenario is the localized accumulation of olivine in the trough-shaped part of the DV10 subchamber, which preceded or occurred in parallel to the accumulation of segregated sulfides.

Abstract Image

Abstract Image

横沟-多维连地块透辉岩含矿石的地球化学测温:母岩浆中的成分、橄榄石含量和硫化物饱和状态
摘要 根据 24 块岩石熔体平衡结晶的热力学建模结果,采用地球化学测温法估算了横沟-多维连地块 DV10 含矿岩浆母岩的温度和成分参数。测温计算使用 COMAGMAT-5.3 程序进行,增量为 0.5 摩尔%,最大结晶度为 75-85%,氧富集度由 QFM 缓冲控制。矿物的模型结晶顺序如下:橄榄石(Ol)+铬铝尖晶石(Spl)→斜长石(Pl)→高碳辉石(Cpx)→正辉石(Opx)。根据计算,硅酸盐-硫化物互不相溶主要发生在斜长石开始结晶之前,这与母岩浆的初始硫化物饱和是一致的。计算结果证明,模型液体下降线在约 1185 摄氏度的温度下趋同并相交。当应用于透辉石 DV10 的平均成分时,该温度表明存在原始晶体的悬浮物,包括 52.1 重量%的积橄榄石(Fo83.6)、2.3重量%的斜长石(An79.7)、0.24重量%的褐辉石(Mg# 88.8)、1重量%的铝铬铁矿(Cr# 0.62)和约0.2%的硫化物液体。因此,硫化物饱和时的硫浓度(SCSS)估计为 0.083 wt %。该异质体系的粘度为 4.71 对数单位(帕秒),整体密度为 2929 千克/立方米。这样的流变特性与原球茎蘑菇从多维伦主室迁移和移位的可能性并不矛盾。不过,更有可能的情况是,橄榄石在 DV10 亚室的槽形部分局部堆积,这种堆积发生在离析硫化物堆积之前或同时发生。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Petrology
Petrology 地学-地球科学综合
CiteScore
2.40
自引率
20.00%
发文量
27
审稿时长
>12 weeks
期刊介绍: Petrology is a journal of magmatic, metamorphic, and experimental petrology, mineralogy, and geochemistry. The journal offers comprehensive information on all multidisciplinary aspects of theoretical, experimental, and applied petrology. By giving special consideration to studies on the petrography of different regions of the former Soviet Union, Petrology provides readers with a unique opportunity to refine their understanding of the geology of the vast territory of the Eurasian continent. The journal welcomes manuscripts from all countries in the English or Russian language.
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