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首页> 外文期刊>Contributions to Mineralogy and Petrology >Post-collisional adakitic volcanism in the eastern part of the Sakarya Zone, Turkey: evidence for slab and crustal melting
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Post-collisional adakitic volcanism in the eastern part of the Sakarya Zone, Turkey: evidence for slab and crustal melting

机译：土耳其萨卡里亚地区东部碰撞后的埃达契克火山火山：平板和地壳融化的证据

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摘要

New geochemical and isotopic data for post-collisional Early Eocene and Late Miocene adakitic rocks from the eastern part of the Sakarya Zone, Turkey, indicate that slab and lower crustal melting, respectively, played key roles in the petrogenesis of these rocks. The Early Eocene Yoncalık dacite (54.4 Ma) exhibits high Sr/Y and La/Yb ratios, low Y and HREE concentrations, moderate Mg# (44–65), and relatively high εNd and low ISr values, similar to adakites formed by slab melting associated with subduction. Geochemical composition of the Yoncalık dacite cannot be explained by simple crystal fractionation and/or crustal contamination of andesitic parent magma, but is consistent with the participation of different proportions of melts derived from subducted basalt and sediments. Sr/Y correlates horizontally with Rb/Y, and Pb/Nd correlates vertically with Nd isotopic composition, indicating that Sr and Pb budgets are strongly controlled by melt addition from the subducting slab, whereas positive correlations between Th/Nd and Pb/Nd, and Rb/Y and Nb/Y point to some contribution of sediment melt. In addition to low concentrations of heavy rare earth elements (~2–3 times chondrite), a systematic decrease in their concentrations and Nb/Ta ratios with increasing SiO2 contents suggests that slab partial melting occurred in the garnet stability field and that these elements were mobilized by fluid flux. These geochemical and isotopic signatures are best explained by slab breakoff and fusion shortly after the initiation of collision. Although the Late Micone Tavdağı rhyolite (8.75 Ma) has some geochemical features identical to adakites, such as high Sr/Y and La/Yb ratios, low Y and HREE concentrations, other requirements, such as sodic andesite and/or dacite with relatively high MgO and Mg# (>50), relatively high Ni and Cr, low K2O/Na2O (<0.4), high Sr (>400 ppm), for slab-derived adakites are not provided. It is sodic in composition and shows no traces of fractionation from dacitic parent magma. Low Nd and high Sr isotope ratios suggest derivation by partial fusion of calc-alkaline, juvenile crust with high Sr/Y and La/Yb ratios.
机译：来自土耳其萨卡里亚地区东部的碰撞后的始新世和中新世后埃达克质岩石的新地球化学和同位素数据表明，平板和下地壳熔融分别在这些岩石的成因中起着关键作用。始新世Yoncalık榴辉岩（54.4Ma）表现出高Sr / Y和La / Yb比，低Y和HREE浓度，中等Mg＃（44-65），相对较高εNd和低ISr值，类似于平板形成的ad石与俯冲相关的熔化。 Yoncalıkdacite的地球化学组成不能用简单的晶体分离和/或安山岩母岩浆的地壳污染来解释，但与俯冲玄武岩和沉积物中不同比例熔体的参与是一致的。 Sr / Y与Rb / Y水平相关，而Pb / Nd与Nd同位素组成垂直相关，这表明Sr和Pb的预算受俯冲板熔体添加的强烈控制，而Th / Nd与Pb / Nd之间的正相关， Rb / Y和Nb / Y指出了沉积物融化的某些作用。除了低浓度的重稀土元素（约2〜3倍的球粒晶），随着SiO2含量的增加，其浓度和Nb / Ta比值有系统地下降，这表明在石榴石稳定性场中发生了板坯部分熔化，并且这些元素是由流体通量动员。这些地球化学和同位素特征最好通过碰撞发生后不久的平板破裂和融合来解释。尽管MiconeTavdağı流纹岩（8.75 Ma）具有与ad石相同的一些地球化学特征，例如高Sr / Y和La / Yb比，低Y和HREE浓度，其他要求，例如苏打安山岩和/或榴辉岩相对较高MgO和Mg＃（> 50），相对较高的Ni和Cr，较低的K2O / Na2O（<0.4），较高的Sr（> 400 ppm）均未提供。它的成分是钠盐，没有显示出来自洋生母岩浆的分馏痕迹。低Nd和高Sr同位素比表明钙与碱性，高Sr / Y和La / Yb比的少年地壳的部分融合得到了衍生物。

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