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首页> 外文期刊>Contributions to Mineralogy and Petrology >Source components and magmatic processes in the genesis of Miocene to Quaternary lavas in western Turkey: constraints from HSE distribution and Hf-Pb-Os isotopes
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Source components and magmatic processes in the genesis of Miocene to Quaternary lavas in western Turkey: constraints from HSE distribution and Hf-Pb-Os isotopes

机译：土耳其西部中新世至第四纪熔岩的成因成分和岩浆作用过程：HSE分布和Hf-Pb-Os同位素的制约

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摘要

Hf-Pb-Os isotope compositions and highly siderophile element (HSE) abundance variations are used to evaluate the mantle source characteristics and possible effects of differentiation processes in lavas from western Turkey, where the eruption of Late Miocene to Quaternary OIB-type intraplate mafic alkaline lavas followed pre-Middle Miocene convergent margin-type volcanism. Concentrations of Os, Ir, and Ru (IPGE) in the OIB-type intraplate lavas decrease with fractionation for primitive melts (MgO > 10 wt%), suggesting that these elements reside predominantly in olivine and associated HSE retaining trace phases and behave compatibly during olivine-dominated fractionation. Fractional crystallization trends indicate distinctly lower bulk partition coefficients for IPGE in more evolved lavas, possibly reflecting a change in the fractionating assemblages. Pd and Re in the primitive melts display negative correlations with MgO, demonstrating moderately incompatible behavior of these elements during fractionation, while the significantly scattered variation in Pt against MgO may indicate the effects of micronuggets of a Pt-rich alloy. Os-rich alkaline primary lavas (> 50 ppt Os) exhibit a limited range of Os-187/Os-188 (0.1361-0.1404), with some xenolith-bearing lavas displaying depletions in Os-187/Os-188 (0.1131-0.1232), suggesting slight compositional modification of primitive melts through contamination with highly depleted, Os-rich mantle lithosphere. More radiogenic Os isotope ratios (Os-187/Os-188 > 0.1954) in the evolved lavas reflect contamination of the magmas by high(187)Os/Os-188 crustal material during shallow differentiation. The OIB-type lavas show limited variations in Hf and Pb isotopes with Hf-176/Hf-177 = 0.282941-0.283051, Pb-206/Pb-204 = 18.683-19.091, Pb-207/Pb-204 = 15.57915.646, Pb-208/Pb-204 = 38.550-38.993; Hf-176/Hf-177 ratios correlate negatively with Pb-208*/Pb-206*, suggesting the effects of similar mantle processes on the evolution of time-integrated Th/U and Lu/Hf. These lavas have distinctly higher Hf-176/Hf-177 and lower Pb-208*/Pb-206* than the Early-Middle Miocene lavas of the region, which are interpreted as melts of enriched mantle with an overprint by sediment-derived subduction component. The source region for the OIB-type alkaline melts is interpreted to be a sub-lithospheric reservoir enriched in Hf and Pb isotopes with respect to depleted MORB mantle. Combined evaluation of Hf, Pb, and Os isotopes suggests that the relative enrichment in this domain is related to mixing of ancient oceanic crust with the ambient mantle through long-term plate recycling processes.
机译：使用Hf-Pb-Os同位素组成和高度嗜铁元素（HSE）丰度变化来评估土耳其西部熔岩的地幔源特征和分化过程的可能影响，那里晚中新世喷发到第四纪OIB型板内镁铁质碱性熔岩遵循中新世中期之前的融合边缘型火山作用。 OIB型板内熔岩中Os，Ir和Ru（IPGE）的浓度随原始熔体（MgO> 10 wt％）的分馏而降低，这表明这些元素主要存在于橄榄石和相关的HSE中，并保留痕量相，并且在运行期间具有相容性橄榄石为主的分离。分数结晶趋势表明，在演化程度更高的熔岩中，IPGE的体积分配系数明显较低，这可能反映了分馏组合的变化。原始熔体中的Pd和Re与MgO呈负相关，表明在分馏过程中这些元素的中等不相容行为，而Pt对MgO的显着分散变化可能表明富Pt合金的微熔核的作用。富含Os的碱性原生熔岩（> 50 ppt Os）表现出有限的Os-187 / Os-188（0.1361-0.1404）范围，一些含异岩体的熔岩在Os-187 / Os-188（0.1131-0.1232）中显示出损耗），表明原始熔体的轻微成分改变是由于高度贫化，富含Os的地幔岩石圈受到污染而引起的。演化的熔岩中更多的放射源Os同位素比（Os-187 / Os-188> 0.1954）反映了浅层分化过程中高（187）Os / Os-188地壳物质对岩浆的污染。 OIB型熔岩的Hf和Pb同位素变化有限，Hf-176 / Hf-177 = 0.282941-0.283051，Pb-206 / Pb-204 = 18.683-19.091，Pb-207 / Pb-204 = 15.57915.646， Pb-208 / Pb-204 = 38.550-38.993; Hf-176 / Hf-177比率与Pb-208 * / Pb-206 *负相关，表明类似的地幔过程对时间积分Th / U和Lu / Hf演化的影响。这些熔岩的Hf-176 / Hf-177和Pb-208 * / Pb-206 *均明显高于该地区的中新世早期熔岩，这被解释为富集地幔的熔体，并因沉积物引起的俯冲作用而被覆盖。零件。 OIB型碱性熔体的源区被解释为是相对于贫化的MORB地幔而言富含Hf和Pb同位素的岩下圈储层。对Hf，Pb和Os同位素的综合评估表明，该区域中的相对富集与通过长期的板块再循环过程将古代大洋地壳与周围地幔混合有关。

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