Silurian A-type metaquartz-syenite to -granite in the Eastern Anatolia: Implications for Late Ordovician-Silurian rifting at the northern margin of Gondwana
Silurian A-type metaquartz-syenite to -granite in the Eastern Anatolia: Implications for Late Ordovician-Silurian rifting at the northern margin of Gondwana
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DOI：
10.1016/j.gr.2020.12.005
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发表时间：
2021-03
影响因子：
6.1
通讯作者：
G. Topuz;O. Candan;Jia-Min Wang;Qiu-li Li;Fu-Yuan Wu;A. Yılmaz
中科院分区：
文献类型：
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作者：
G. Topuz;O. Candan;Jia-Min Wang;Qiu-li Li;Fu-Yuan Wu;A. Yılmaz
特提斯带的安纳托利-陶里德地块代表了整个古生代冈瓦纳古陆的被动北方大陆边缘。在本文中，我们报告了一个相对较大的角闪岩相变石英-正长岩-花岗岩复杂（~ 60平方公里）在安纳托利亚东部，最东部的安纳托利德-金牛座。变质侵入杂岩中的火成结构保存完好。保存的火成岩矿物有中条纹长石+石英±霓辉石±钠质角闪石±钙质角闪石±黑云母和±褐帘石。中粗晶长石是保存完好的火成岩结构中唯一的长石，表明原始石英正长岩到花岗岩的超溶线性质。在重结晶良好的样品中，中条纹长石部分或全部被斜长石和钾长石的离散颗粒所取代。3个样品的岩浆锆石U-Pb定年获得志留纪岩浆结晶年龄（430-440 Ma）。所有岩石类型均具有典型的A型正长岩-花岗岩地球化学特征，FeO*、Na 2 O、K2 O、Nb、Ga、Zr、Ce、Zn相对高丰度，MgO、CaO、Sr相对低丰度，导致Fe/Mg、Ga/Al比值偏高。Nb和Ce相对于Y的富集，以及与洋岛玄武岩相似的Y/Nb、Yb/Ta和Ce/Nb比值，表明A1型正长岩和花岗岩是洋岛玄武岩岩浆的分异产物。根据锆饱和度估计的岩浆温度范围为850至990 °C，表明原始石英正长岩和花岗岩来自高温年轻岩浆。两个样品中岩浆锆石的初始εHf值分别为2.59 ± 1.14和2.30 ± 1.29，δ 18 O值为5.41 ~ 7.32‰，中值为6.50 ± 0.48‰。这些同位素特征表明，石英正长岩-花岗岩来自高温地幔岩浆，地壳同化作用不明显。安纳托利-陶里德地块北方晚奥陶世-志留纪A型火成岩可能与冈瓦纳北方边缘的裂谷事件有关，后者导致古特提斯的开启。这一解释也得到了以下方面的支持：（i）暗示晚奥陶世-志留纪伸展背景的早古生代沉积序列的区域地质特征，（ii）早古生代从冈瓦纳分离的大陆块中志留纪非造山岩浆作用的存在，以及（iii）古特提斯增生杂岩中志留纪深海沉积块的存在。
The Anatolide-Tauride block in the Tethyan belt represented passive northern continental margin of Gondwana throughout Paleozoic time. In this paper, we report on a relatively large amphibolite-facies metaquartz-syenite to -granite complex (~ 60 km2) in the Eastern Anatolia, the easternmost part of the Anatolide-Tauride block. Igneous textures in the metaintrusive complex are variably preserved. The preserved igneous minerals include mesoperthite + quartz ± aegirine-augite ± sodic amphibole ± calcic amphibole ± biotite and ± allanite. Mesoperthite is the sole feldspar in well-preserved igneous textures, suggesting hypersolvus nature of the original quartz syenite to granite. In the well-recrystallized samples, mesoperthite is partially or totally replaced by discrete grains of plagioclase and K-feldspar. U–Pb dating on igneous zircons from three samples yielded Silurian igneous crystallization ages (430–440 Ma). All rock types have typical geochemical characteristics of A-type syenite to granite with relatively high abundances of FeO*, Na2O, K2O, Nb, Ga, Zr, Ce, and Zn, and low abundances of MgO, CaO and Sr, resulting in high ratios of Fe/Mg and Ga/Al. Geochemical features such as (i) the absence of negative Nb–Ta anomalies on multielement variation diagrams, (ii) the enrichment of Nb and Ce relative to Y, and (iii) Y/Nb, Yb/Ta and Ce/Nb ratios similar to those in ocean island basalts point to A1-type syenite and granite which are thought to be differentiates of ocean island basaltic magmas. Estimated magma temperatures based on zirconium saturation range from 850 to 990 °C, indicating derivation of the original quartz syenite and granite from high-temperature juvenile magmas. Initial εHf values of the igneous zircons from two samples are 2.59 ± 1.14 and 2.30 ± 1.29, while δ18O values of the zircons range from 5.41 to 7.32‰ with a median of 6.50 ± 0.48‰. All these isotopic characteristics suggest that the quartz syenite to granite were derived from high-temperature mantle magmas with insignificant crustal assimilation. The Late Ordovician-Silurian A-type igneous rocks in the northern part of the Anatolide-Tauride block were probably related to a rifting event at the northern margin of Gondwana, leading to the opening of the Paleo-Tethys. This interpretation is also supported from (i) regional geological features of the Early Paleozoic sedimentary successions suggestive of extensional setting during the Late Ordovician-Silurian, (ii) the presence of Silurian anorogenic magmatism in continental blocks detached from Gondwana during Early Paleozoic time, and (iii) the presence of Silurian deep sea sedimentary blocks in Paleo-Tethyan accretionary complexes.