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首页> 外文会议>Conference on Asian Current Research on Fluid Inclusions >Chemical and stable isotopic compositions of volatiles in mantle peridotites of the Yushigou ophiolite in Qilian orogenic belt, western China
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Chemical and stable isotopic compositions of volatiles in mantle peridotites of the Yushigou ophiolite in Qilian orogenic belt, western China

机译：中国祁连源岩石皮带岩石岩石岩石恒星挥发物的化学稳定同位素组成

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Fluid inclusions in olivine and orthopyroxene of mantle peridotites from the Yushigou ophiolite can be divided into three types based on decrepitation temperature, shape and distribution. Type-1 fluid inclusions are characterized by oval or negative crystal shapes and small size ( ＜ 5μm across). They occur in the cores and mantles of the host crystals, and decrepitated at ＞ 840°C. Type-2 fluid inclusions have irregular or tabular shapes with relatively large size (10 ～ 100μm in length). They occur in irregular or circular healed micro-fractures in the host crystals, and decrepitated at 612 ～ 710°C.. Type-3 fluid inclusions have size and shape similar to type-2 fluid inclusions but occur in micro-fractures restricted to the margins of the host crystals, and decrepitated at much lower temperature from 190°C to 340°C. The three different types of fluid inclusions are interpreted to represent primary, metasomatic (pseudo-secondary) and secondary inclusions, respectively. Stepwise heating reveals three concentration peaks of volatiles at 200 ～ 400°C , 400 ～ 800°C and 800 ～ 1200°C released from olivine and orthopyroxene in harzburgite and dunite from the Yushigou ophiolite, which are considered to correspond to the decrepitation of secondary, metasomatic and primary fluid inclusions at similar temperature ranges. CO_2 is a major constituent in the volatiles released at three different temperature intervals. Trace amounts of H_2 and N_2 are present in the volatiles released at ＜ 800°C and trace amounts of H_2O and SO_2 are mainly present in the volatiles at 400 ～ 800°C. The δD ( -95.2‰, -306.3‰) of H_2O and the δ~(13)C ( -15.5 ～ -12.5‰) and δ~(18)O values (1.4 ～ 1.9‰) of CO_2 released at ＜ 800°C are lower than normal mantle values and suggest the mixing origin of crustal fluids (sedimentary organic) with ocean water, implying that Yushigou AOLM had undergone an intensive metasomatism by a fluid composed of CO_2 H_2O and SO_2 , and followed by degassing. In contrast, the volatiles released at 800 ～ 1200°C are characterized by trace amounts of H_2 and CO in dunite and SO_2 in harzburgite, much lighter S C ( —29.1‰ ～ - 19. 5‰) , heavier δ~(13)O(8. 8‰) of CO_2 and positive relationship between these isotopic ratios and the concentration of CO_2. Such features can be best explained by mixing of significant terrestrial crustal (organic) and minor mantle volatiles. We proposed that the Yishigou peridotites are more likely to have derived from a continental lithosphere instead of an oceanic lithosphere comprising the Yishigou gabbros and pillowed basalts. A supra-subduction tectonic setting is thus inferred for the Yushigou ophiolite.
机译：从玉石Ophiolite的鹿茸橄榄石的橄榄石和骨灰烯中的液体夹杂物可以基于颅骨，形状和分布分为三种类型。 1型流体夹杂物的特征在于椭圆形或负晶体形状和小尺寸（横跨<5μm）。它们发生在核和宿主晶体的核心和壁龛中，并在> 840℃下进行裂缝。 2型流体夹杂物具有相对大的尺寸（长度为10〜100μm）的不规则或表格形状。它们在宿主晶体中的不规则或圆形愈合的微骨折中发生，并且在612〜710℃下解体。3型流体夹杂物的尺寸和形状类似于2型流体夹杂物，但在限制的微骨折中发生宿主晶体的边缘，并在190℃至340℃下低得多的温度下衰减。这三种不同类型的流体夹杂物被解释为分别代表初级，态化（伪级）和次级夹杂物。逐步加热揭示从橄榄石和正交释放的200〜400℃，400〜800℃和800〜1200℃，从玉尔古氏菌钛和玉石古石的鹿螨释放的300〜1200℃，认为对应于中学的崩溃，在类似温度范围内的态态和初级流体夹杂物。 CO_2是挥发物的主要组成部分，以三种不同的温度间隔释放。在<800℃的挥发物中存在痕量的H_2和N_2，并且痕量的H_2O和SO_2主要存在于400〜800℃的挥发物中。 H_2O的ΔD（-95.2‰，-306.3μ）和δ〜（13）c（-15.5〜-12.5‰）和δ〜（18）o值（1.4〜1.9‰）在<800°释放C低于正常的地幔值，并建议出壳流体（沉积有机）与海水的混合起源，这意味着Yushigou Aolm通过由CO_2 H_2O和SO_2组成的流体经历了强烈的偏定性，然后脱气。相比之下，在800〜1200℃下释放的挥发物的特征在于哈尔茨堡钛矿中的痕量H_2和CO，如Harzburgite的SO_2，更轻的SC（-29.1℃〜19.5°），较重δ〜（13）o （8.8‰）CO_2和这些同位素比与CO_2浓度之间的阳性关系。通过混合显着的地壳（有机）和轻微的地幔挥发物可以最好地解释这些特征。我们提出叶刚的橄榄石更有可能来自陆地岩石圈，而不是包括尤希沟Gabbros和枕骨玄武岩的海洋岩石圈。因此，为玉石沟ophiolite推断出副俯冲构造环境。

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