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首页> 外文期刊>Journal of Asian earth sciences >Tracking the timing of Neotethyan oceanic slab break-off: Geochronology and geochemistry of the quartz diorite porphyries, NE Turkey
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Tracking the timing of Neotethyan oceanic slab break-off: Geochronology and geochemistry of the quartz diorite porphyries, NE Turkey

机译：跟踪Neotethyan海洋板坯的时序分段：石英塞氏斑岩的地理学和地球化学，NE TIRKEY

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The initiation of the break-off of the northern branch of the Neotethyan oceanic lithosphere is an important but poorly understood event in the geology of the Sakarya Zone (SZ) in northeastern Turkey. Although it is wellknown that Latest Cretaceous intrusives (-70 Ma) and early Eocene adakitic magmatic rocks are present in the eastern SZ, the outcrops of the early Eocene non-adakitic rocks are very limited, and their tectono-magmatic evolution has not been studied. We describe a small outcrop of non-adakitic quartz diorite porphyry in the Kov area of the Gumushane region in northeastern Turkey. The genesis of these porphyries is significant in evaluating the syn-to post-collision-related magmatism. The LA-ICP-MS zircon U-Pb dating revealed that the Kov quartz diorite porphyries (KQDP) formed at ca. 50 Ma, coeval with adakitic rocks, and-20 Myr later than the slab rollback-related intrusive rocks. The KQDPs are calc-alkaline in composition and enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs) and depleted in high field strength elements (HFSEs; e.g., Nb, Ta, Ti), with significant negative anomalies of Nb, Ta, and Ti but positive anomalies of Th, U, and Pb. Isotopic compositions of the samples show limited range of variation and slight enrichment of 87Sr/86Sr(t) (0.70489 to 0.70555), epsilon Nd(t) (-1.4 to -1.2) with TDM of 1.11 to 1.61 Ga. Pb isotopic ratios of the samples point to an enriched mantle source. They were likely crystallized from the melt that originated from an EM2-type spinel-facies subcontinental lithospheric mantle (SCLM), followed by the fractionation with insignificant crustal assimilation. The SCLM was metasomatically enriched, and the metasomatic agent was likely H2O-rich fluids rather than sediments released from subducting oceanic crust during the Late Cretaceous closure of the Neotethyan oceanic lithosphere. In conjunction with the geological background and previous data, we propose that the generation of the KQDPs resulted from a slab break-off event that caused ascending or infiltration of hot asthenosphere, triggering mantle melting. Such sporadic occurrences of the KQDPs, with coeval adakitic rocks in the SZ, are likely associated with the onset of extensional tectonics due to the earlier stage of slab break-off along the region during the early Eocene period.
机译：北部海洋岩石圈北部分支的突破的启动是土耳其东北部地区地质学（SZ）的重要但不善的活动。虽然它是众所周知的是，最新的白垩纪侵入性（-70 mA）和早期的胚胎岩石岩石存在于东部的SZ中，但早期的何种酵母岩石的露头是非常有限的，并且他们的构成 - 岩浆进化尚未研究。我们描述了土耳其东北部甘美州地区Kov地区的非AdaAxitic石英Diority斑岩的一个小露品。这些卟啉的成因在评估了与碰撞后相关的岩浆中具有重要意义。 La-ICP-MS ZIRCON U-PB约会显示，KOV石英Diorite Porphyries（KQDP）在CA上形成。 50 mA，与Adakitic岩石的陪同，比平板回滚相关的侵入式岩石和20 myR。 KQDPS在组合物中钙碱性，并富含大离子型鳞片元件（植物）和轻稀土元素（LEREE）并在高场强元件（HFSES;例如，NB，TA，TI）中耗尽，具有显着的阴性异常Nb，ta和ti，但th，u和pb的正异常。样品的同位素组合物显示有限的变化范围和87sr / 86sr（t）的轻微富集（0.70489-0.70555），εnd（t）（-1.4至-1.2），Tdm为1.11-1.61 ga。Pb同位素比例样品指向富集的地幔源。它们可能从源自源于EM2型尖晶石面部亚平坦岩石罩（SCLM）的熔体中结晶，然后用微小的地壳同化分离。 SCLM在富含富含富含H 2 O的液体的富含H 2 O的液体，而不是在新的海洋地壳中释放的沉积物在新白垩纪闭岩岩。结合地质背景和以前的数据，我们提出了由平板断开事件产生的KQDPS产生的，导致热哮喘的上升或渗透，触发搭式熔化。在SZ中具有Coeval Adakitic岩石的这种散发性的散发出发生，并且由于在早期何时期期间，由于沿着该区域的沿着该区域的早期平板断裂阶段的较早阶段，可能与延伸构造的发作相关联。

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