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首页> 外文期刊>Contributions to Mineralogy and Petrology >Relative contributions of crust and mantle to generation of Campanian high-K calc-alkaline I-type granitoids in a subduction setting, with special reference to the Harsit Pluton, Eastern Turkey
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Relative contributions of crust and mantle to generation of Campanian high-K calc-alkaline I-type granitoids in a subduction setting, with special reference to the Harsit Pluton, Eastern Turkey

机译：在俯冲环境中，地壳和地幔对生成坎帕尼亚高K钙碱性I型花岗岩的相对贡献，特别涉及土耳其东部的Harsit Pluton

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摘要

We present elemental and Sr–Nd–Pb isotopic data for the magmatic suite (～79 Ma) of the Harsit pluton, from the Eastern Pontides (NE Turkey), with the aim of determining its magma source and geodynamic evolution. The pluton comprises granite, granodiorite, tonalite and minor diorite (SiO_2 = 59.43–76.95 wt%), with only minor gabbroic diorite mafic microgranular enclaves in composition (SiO_2 = 54.95–56.32 wt%), and exhibits low Mg#(<46). All samples show a high-K calc-alkaline differentiation trend and I-type features. The chondrite-normalized REE patterns are fractionated [(La/Yb)_n = 2.40–12.44] and display weak Eu anomalies (Eu/Eu~* = 0.30–0.76).The rocks are characterized by enrichment of LILE and depletion of HFSE. The Harsit host rocks have weak concave-upward REE patterns, suggesting that amphibole and garnet played a significant role in their generation during magma segregation. The host rocks and their enclaves are isotopically indistinguishable. Sr–Nd isotopic data for all of the samples display ISr = 0.70676–0.70708, eNd(79 Ma) = -4.4 to -3.3, with TDM = 1.09–1.36 Ga. The lead isotopic ratios are (~(206)Pb/~(204)Pb) = 18.79–18.87, (~(207)Pb/~(204)Pb) = 15.59–15.61 and (~(208)Pb/~(204)Pb) = 38.71–38.83. These geochemical data rule out pure crustalderived magma genesis in a post-collision extensional stage and suggest mixed-origin magma generation in a subduction setting. The melting that generated these high- K granitoidic rocks may have resulted from the upper Cretaceous subduction of the Izmir–Ankara–Erzincan oceanic slab beneath the Eurasian block in the region. The back-arc extensional events would have caused melting of the enriched subcontinental lithospheric mantle and formed mafic magma. The underplating of the lower crust by mafic magmas would have played a significant role in the generation of high-K magma. Thus, a thermal anomaly induced by underplated basic magma into a hot crust would have caused partial melting in the lower part of the crust. In this scenario, the lithospheric mantle-derived basaltic melt first mixed with granitic magma of crustal origin at depth. Then, the melts, which subsequently underwent a fractional crystallization and crustal assimilation processes, could ascend to shallower crustal levels to generate a variety of rock types ranging from diorite to granite. Sr–Nd isotope modeling shows that the generation of these magmas involved ～65–75% of the lower crustal-derived melt and ～25–35% of subcontinental lithospheric mantle. Further, geochemical data and the Ar–Ar plateau age on hornblende, combined with regional studies, imply that the Harsit pluton formed in a subduction setting and that the back-arc extensional period started by least ～79 Ma in the Eastern Pontides.
机译：我们提供了来自东部蓬蒂德斯（土耳其北部）的Harsit岩体岩浆组（〜79 Ma）的元素和Sr-Nd-Pb同位素数据，目的是确定其岩浆源和地球动力学演化。岩体由花岗岩，花岗闪长岩，斜长石和次要闪长岩组成（SiO_2 = 59.43–76.95 wt％），仅组成了次要辉长岩闪长岩基性微粒状飞地（SiO_2 = 54.95–56.32 wt％），并且Mg＃低（<46） 。所有样品均显示高K钙碱性分化趋势和I型特征。球粒陨石归一化的REE模式被分割[（La / Yb）_n = 2.40–12.44]，并表现出弱的Eu异常（Eu / Eu〜* = 0.30–0.76）。岩石具有LILE富集和HFSE耗尽的特征。 Harsit母岩具有弱的向上凹入稀土元素模式，表明闪石和石榴石在岩浆分离过程中起着重要作用。主体岩石及其飞地在同位素上是无法区分的。所有样品的Sr–Nd同位素数据显示ISr = 0.70676–0.70708，eNd（79 Ma）= -4.4至-3.3，TDM = 1.09–1.36 Ga。铅同位素比为（〜（206）Pb /〜 （204）Pb）= 18.79–18.87，（〜（207）Pb /〜（204）Pb）= 15.59–15.61和（〜（208）Pb /〜（204）Pb）= 38.71–38.83。这些地球化学数据排除了碰撞后伸展阶段纯壳壳岩浆的成因，并暗示了俯冲环境中混合起源岩浆的产生。产生这些高K花岗岩的融化作用可能是由于该地区欧亚大陆块下方的伊兹密尔-安卡拉-埃尔金坎大洋板块在白垩纪上层俯冲作用引起的。弧后伸展事件将导致富集的亚大陆岩石圈地幔融化并形成镁铁质岩浆。镁铁质岩浆对下地壳的底层作用在高K岩浆的产生中起了重要作用。因此，由地下岩浆底部带入热地壳引起的热异常会导致地壳下部部分熔融。在这种情况下，岩石圈地幔衍生的玄武质熔体首先与地壳起源的花岗岩岩浆在深处混合。然后，随后经过分步结晶和地壳同化过程的熔体可能会上升到较浅的地壳水平，从而生成从闪长岩到花岗岩的各种岩石类型。 Sr-Nd同位素模型表明，这些岩浆的产生约占地壳下部熔岩的约65-75％，以及次大陆岩石圈地幔的约25-35％。此外，地球化学数据和角闪石的Ar-Ar高原年龄，再加上区域研究表明，Harsit岩体是在俯冲环境中形成的，而后弧伸展期在东蓬蒂德斯至少开始于〜79 Ma。

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