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首页> 外文期刊>Contributions to Mineralogy and Petrology >Acigol rhyolite field, central Anatolia (part II): geochemical and isotopic (Sr-Nd-Pb, δ～(18)O) constraints on volcanism involving two high-silica rhyolite suites
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Acigol rhyolite field, central Anatolia (part II): geochemical and isotopic (Sr-Nd-Pb, δ～(18)O) constraints on volcanism involving two high-silica rhyolite suites

机译：安纳托利亚中部Acigol流纹岩场（第二部分）：地球化学和同位素（Sr-Nd-Pb，δ〜（18）O）对火山活动的约束，涉及两个高硅质流纹岩套件

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摘要

The Acigol rhyolite field erupted the most recent high-silica rhyolites within the Cappadocian Volcanic Province of central Anatolia, Turkey. It comprises two sequences of domes and pyroclastic rocks with eruption ages of ～150-200 ka (eastern group) and ～ 20-25 ka (western group). Compositionally, the eastern rhyolite group lavas are less evolved (SiO_2 = 74-76 wt%), whereas the western group has higher silica abundance (SiO_2 = ～77 wt%)with extremely depleted feldspar-compatible trace elements. Within each group, compositional variability is small and ~(143)Nd/~(144)Nd (0.51257-0.51265) and Pb isotope compositions ~(206)Pb/~(204)Pb = 18.87-18.88, ~(207)Pb/~(204)Pb = 15.65-15.67 and ~(208)Pb/~(204)Pb = 38.94-38.98) are homogeneous. The western group rhyolites have δ～(18)O(zircon) overlapping mantle values (5.7 ± 0.2%o), whereas eastern group rhyolites are enriched in 5 0 by ～0.5%o, consistent with a tendency to lower eNd values. By contrast, western group rhyolites have markedly more radiogenic ~(87)Sr/~(86)Sr ratios (0.7065-0.7091) compared to those of the eastern group (0.7059-0.7065). The presence of angular granitic xenoliths and a correlation between hydration (based on loss on ignition data) and ~(87)Sr/~(86)Sr in the western lavas, however, indicates that Sr was added during the eruption or post-eruption alteration. Isotope constraints preclude the possibility that the rhyolite magmas formed by partial melting of any known regional crystalline basement rocks. Basalts and andesites erupted in the periphery of the Acigol field arecharacterised by ~(87)Sr/~(86)Sr ratios between 0.7040 and 0.7053, ~(143)Nd/~(143)Nd =0.51259-0.51300, ~(206)pb/204pb =18.85-18.87,~(207)Pb/~(204)Pb = 15.646-15.655,~(208)Pb/~(204)Pb = 38.90-38.97. The isotopic and trace element data favour an origin of the rhyolites by mixing of basaltic/andesitic magmas with minor amounts of crustal melts and followed by extensive fractional crystallization.
机译：Acigol流纹岩场在土耳其中部安纳托利亚的卡帕多西亚火山省爆发了最新的高硅质流纹岩。它由圆顶和火山碎屑岩的两个序列组成，喷发年龄为〜150-200 ka（东部组）和〜20-25 ka（西部组）。成分上，东部流纹岩组熔岩的演化较少（SiO_2 = 74-76 wt％），而西部组的二氧化硅丰度较高（SiO_2 =〜77 wt％），且长石兼容的微量元素极少。在每个组中，组成变异性很小，〜（143）Nd /〜（144）Nd（0.51257-0.51265）和Pb同位素组成〜（206）Pb /〜（204）Pb = 18.87-18.88，〜（207）Pb （〜（204）Pb = 15.65-15.67和〜（208）Pb /〜（204）Pb = 38.94-38.98）是均匀的。西部流纹岩的δ〜（18）O（锆石）地幔重叠值（5.7±0.2％o），而东部流纹岩的5 0富集度为〜0.5％o，这与降低eNd值的趋势一致。相比之下，与东部组（0.7059-0.7065）相比，西部组流纹岩的放射源〜（87）Sr /〜（86）Sr比（0.7065-0.7091）明显更高。西部熔岩中存在角状花岗石异质岩以及水合（基于着火数据的损失）与〜（87）Sr /〜（86）Sr之间的相关性表明，在喷发或喷发后添加了Sr改造。同位素限制排除了流纹岩岩浆通过任何已知的区域性结晶基底岩石部分熔融而形成的可能性。 Acigol场外围喷出的玄武岩和安山岩的特征是〜（87）Sr /〜（86）Sr比在0.7040至0.7053之间，〜（143）Nd /〜（143）Nd = 0.51259-0.51300，〜（206） pb / 204pb = 18.85-18.87，〜（207）Pb /〜（204）Pb = 15.646-15.655，〜（208）Pb /〜（204）Pb = 38.90-38.97。同位素和微量元素数据通过将玄武岩/安山岩岩浆与少量地壳熔体混合，然后进行广泛的分步结晶，有利于流纹岩的起源。

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