Abstract

Oxygen crystallising was obtained from olivine, chromite separates from host rock samples, and gabbro from ultramafic cumulates, harzburgite, and dunite samples collected from tectonites of the Guleman ophiolites. The study includes the oxygen isotope compositions from the Guleman ophiolite and the evolutionary scenarios of geochemical and isotopic signatures. The olivine and chromitite δ¹⁸O_{olivine/chromite} and δ¹⁸O_melt values point out these minerals and melt isotopic compositions similar to mantle values and rich, heavy stable isotopes. The highest δ¹⁸O_chromite isotopic composition values indicate that as the heavy isotope in the melt increases, the concentration in the mineral increases. Excluding a dunite sample, the values of the δ¹⁸O_{whole rock} of the dunite and pyroxenite samples are similar to mantle values. The gabbro samples have higher δ¹⁸O_{whole rock} values than the two harzburgites. Hereby, the chromite formations are the later fractional crystallisation products than olivine and dunites due to the lowering of δ¹⁸O. The lower oxygen isotopic composition in studied samples than the normal mantle values, and these values point out subducted hydrothermally alteration. The higher δ¹⁸O isotopic compositions could be explained by serpentinization on the ocean floor at low temperatures.

中文翻译：

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土耳其东南部古勒曼蛇绿岩中硅酸盐矿物和铬矿的氧同位素组成

摘要

从橄榄石、来自主岩样品的铬铁矿分离物、来自超镁铁质堆积物的辉长岩、从古勒曼蛇绿岩的构造岩中收集的方辉橄榄岩和纯橄榄石样品中获得氧结晶。该研究包括古勒曼蛇绿岩的氧同位素组成以及地球化学和同位素特征的演化情景。橄榄石和铬铁矿 δ ¹⁸ O_{橄榄石/铬铁矿}和 δ ¹⁸ O_熔体值指出这些矿物和熔体同位素组成与地幔值相似，并且具有丰富的重稳定同位素。最高的 δ ¹⁸ O_铬铁矿同位素组成值表明，随着熔体中重同位素的增加，矿物中的浓度增加。除纯橄榄岩样品外，纯橄榄岩和辉石岩样品的_全岩δ ¹⁸ O值与地幔值相似。辉长岩样品的 δ ¹⁸ O_全岩值高于两种方辉橄榄岩。^{因此，由于 δ 18} O降低，铬铁矿地层是比橄榄石和纯橄榄岩晚的分步结晶产物。研究样品中的氧同位素组成低于正常地幔值，这些值表明俯冲热液蚀变。较高的 δ ¹⁸ O 同位素组成可以通过低温海底的蛇纹石化来解释。