Role of Late Cretaceous volcanic-sedimentary melanges, specifically the Aladağ melange, E Turkey, in the rift-drift-subduction-accretion-emplacement history of the Tethyan Inner Tauride ocean

The Aladağ melange is located between Mesozoic Tauride carbonate platform units and the Late Cretaceous Pozantı-Karsantı ophiolite and its metamorphic sole. The melange comprises a lower, mainly sedimentary unit, composed of variably disrupted thrust sheets of deep-sea sediments, with a localized matrix of mass-flow and turbidity current deposits. The upper, volcanic-sedimentary melange comprises highly disrupted basalt-pelagic carbonate-radiolarite units, rarely associated with gravity-flow deposits. Tholeiitic to alkaline basalts in the melange range from N-MORB, to E-MORB and to OIB, and are dated as Middle Jurassic to Early Cretaceous using Radiolaria from interbedded pelagic sediments. Comparisons with accretionary melanges throughout southern Turkey and elsewhere indicate a similar geochemical pattern of variable ‘enrichment’, commonly coupled with a subduction influence (e.g. negative Nb, Ta anomalies). Geochemically, the subduction-influenced basalts are consistent with an oceanic island arc origin. However, the geological setting of Triassic basalts within some of the melanges (e.g. Mersin) is indicative of a rifted continental margin setting. The Mesozoic basalts within the Turkish melanges considered here erupted along the distal, outer northern margin of the Tauride continent, followed by Late Cretaceous subduction-accretion and supra-subduction zone ophiolite emplacement. Regional to global chemical comparisons suggest that the subduction influence could represent geochemical subduction inheritance rather than contemporaneous subduction.

阿拉达日混杂岩（Aladağ melange）赋存于中生代陶里德碳酸盐岩台地地层与晚白垩世波赞蒂-卡尔桑蒂蛇绿岩（Pozantı-Karsantı ophiolite）及其变质底席（metamorphic sole）之间。该混杂岩可划分为上下两套单元：下部以沉积单元为主，由遭受不同程度破坏的深海沉积物逆冲岩片构成，局部发育由块体流与浊流沉积组成的基质；上部为火山-沉积混杂岩，由强烈破碎的玄武岩-远洋碳酸盐岩-放射虫岩地层组成，仅少量与重力流沉积伴生。混杂岩中的拉斑玄武岩至碱性玄武岩，其地球化学属性涵盖正常型洋中脊玄武岩（N-MORB）、富集型洋中脊玄武岩（E-MORB）及洋岛玄武岩（OIB）；通过夹层远洋沉积物内的放射虫（Radiolaria）定年，其形成时代为中侏罗世至早白垩世。通过与土耳其南部及全球其他地区的增生混杂岩对比可知，这类玄武岩普遍具有“富集”特征的相似地球化学模式，且通常伴随俯冲作用影响（例如铌（Nb）、钽（Ta）负异常）。从地球化学角度来看，受俯冲作用影响的玄武岩符合洋岛弧成因特征。但部分混杂岩（如梅尔辛（Mersin））中产出的三叠纪玄武岩的地质背景，则指示其形成于裂谷型大陆边缘环境。本文所研究的土耳其混杂岩中的中生代玄武岩，均喷发于陶里德大陆远端北外边缘；随后经历了晚白垩世俯冲增生与俯冲带之上蛇绿岩（supra-subduction zone ophiolite）侵位过程。区域乃至全球尺度的地球化学对比研究表明，这种俯冲作用影响可能代表地球化学俯冲继承，而非同期俯冲作用。