Geochemical and Isotopic Constraints on Petrogenesis of the Beypazarı Granitoid, NW Ankara, Western Central Anatolia, Turkey
Geochemical and Isotopic Constraints on Petrogenesis of the Beypazarı Granitoid, NW Ankara, Western Central Anatolia, Turkey
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土耳其安纳托利亚中西部安卡拉西北部贝帕扎里花岗岩岩石成因的地球化学和同位素约束
DOI：
10.3906/vet-1105-2
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发表时间：
2012
影响因子：
1
通讯作者：
Cahit Helvaci Muharrem Satir
中科院分区：
文献类型：
--
作者：
Y. Öztürk;Cahit Helvaci Muharrem Satir
土耳其安卡拉西部的上白垩统贝帕扎里花岗岩类，根据岩石学和地球化学成分，由两个不同的单元组成;它们是花岗闪长岩和闪长岩。花岗岩类为亚碱性，属高钾钙碱性I型花岗岩系列，具有较低的87 Sr/86 Sr初始值（0.7053-0.7070）。结合主要元素、微量元素地球化学数据以及矿物学和结构学证据，这些特征表明贝帕扎里花岗岩形成于火山弧环境，是俯冲改造交代的幔源岩浆，其壳幔组分与上地壳相互混染。岩石的eNd（75 Ma）值在-5.5到-2.0之间。这些特征也表明地壳成分在它们的成因中起着非常重要的作用。利用全岩、石英和硅酸盐矿物的氢氧同位素地球化学研究了出露于安卡拉贝帕扎里附近的中等演化花岗岩类岩株。贝帕扎里花岗岩类的d18 O值始终高于正常I型花岗岩。这与野外观察、岩相学和全岩地球化学数据一致，表明贝帕扎里花岗岩类具有重要的地壳成分。然而，矿物之间的d18 O关系表明，在亚固相线条件下的热液过程的影响很小。贝帕扎里花岗岩类样品的氧同位素系统学结果来自高d18 O流体（岩浆水）的活动，没有明显的低d18 O流体（大气降水）的主要参与。所分析的四个石英-长石对的Dqtz-fsp值在0.5-2.0之间，这与封闭系统条件下的平衡一致。没有发现稳定同位素证据表明花岗岩类与热液流体发生了广泛的相互作用，这与缺乏大规模的贱金属矿化是一致的。
The Upper Cretaceous Beypazari granitoid of the western Ankara, Turkey, is composed of two different units, on the basis of petrography and geochemical composition; these are granodiorite and diorite. The granitoid is subalkaline, belonging to the high-K calc-alkaline I-type granite series, which have relatively low initial 87Sr/86Sr ratios (0.7053-0.7070). All these characteristics, combined with major, trace element geochemical data as well as mineralogical and textural evidence, reveal that the Beypazari granitoid formed in a volcanic arc setting and was derived from a subduction-modified and metasomatized mantle-sourced magma, with its crustal and mantle components contaminated by interaction with the upper crust. The rocks have eNd(75Ma) values ranging from -5.5 to -2.0. These characteristics also indicate that a crustal component played a very important role in their petrogenesis. The moderately evolved granitoid stock cropping out near Beypazari, Ankara, was studied using the oxygen and hydrogen isotope geochemistry of whole rock, quartz and silicate minerals. d18O values of the Beypazari granitoid are consistently higher than those of normal I-type granites. This is consistent with field observations, petrographic and whole-rock geochemical data, which indicate that the Beypazari granitoid has significant crustal components. However, the d18O relationships among minerals indicate a very minor influence of hydrothermal processes in sub-solidus conditions. The oxygen isotope systematics of the Beypazari granitoid samples results from the activity of high-d18O fluids (magmatic water), with no major involvement of low-d18O fluids (meteoric water) evident. The analysed four quartz-feldspar pairs have values of Dqtz-fsp between 0.5-2.0, which are consistent with equilibrium under close-system conditions. No stable isotope evidence was found to suggest that extensive interaction of granitoids with hydrothermal fluids occurred and this is consistent with the lack of large-scale base-metal mineralization.