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首页> 外文期刊>Palaeogeography, Palaeoclimatology, Palaeoecology: An International Journal for the Geo-Sciences >Provenance of sediments during subduction of Palaeotethys: Detrital zircon ages and olistolith analysis in Palaeozoic sediments from Chios Island, Greece
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Provenance of sediments during subduction of Palaeotethys: Detrital zircon ages and olistolith analysis in Palaeozoic sediments from Chios Island, Greece

机译：古生代俯冲过程中的沉积物来源：希腊希俄斯岛古生代沉积物中的碎屑锆石年龄和橄榄石分析

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摘要

Detrital zircon geochronology and analysis of fossiliferous olistoliths from Chios Island, Greece, are used here to constrain terrane accretion processes and the provenance of crustal sources for sediments during the subduction of (a branch of) the Palaeotethys Ocean. U/Pb ages obtained by ion microprobe (SHRIMP-II) analyses of detrital zircons from a Carboniferous greywacke belonging to the tectonostratigraphic Lower Unit of Chios gave major age groups of 2150–1890 Ma, 640–540 Ma, 505–475 Ma and 365–322 Ma. Detrital zircons from a Permian–Triassic sandstone yielded prominent age clusters of 2200–1840 Ma, 1100–910 Ma, 625–560 Ma and 385–370 Ma. The lack of zircon ages between 1.8 and 1.1 Ga in both samples, coupled with the occurrence of ca. 2 Ga-old zircons, imply a northern Gondwana (NW Africa) source. The conodont fauna recovered from an ‘Orthoceras’-bearing limestone lens from the Carboniferous succession of the Lower Unit indicates a Late Silurian age. The fauna is typical of the Ludfordian Polygnathoides siluricus conodont zone. The material has a conodont colour alteration index (CAI) of about 1–2, indicating very low-grade thermal alteration of less than 100 °C. The closest localities with similar conodont-bearing limestones are to be found in the Balkan region and in the Istanbul Zone of northern Turkey. The occurrence of ‘Orthoceras Limestone’ can be used as an indicator of palaeosource reconstruction. Our new zircon ages in conjunction with provenance analysis of Silurian to Lower Carboniferous olistoliths strongly suggest that the clastic succession of Chios received its detritus from basement rocks of the Sakarya microcontinent in western Turkey and time and facies equivalents of Palaeozoic units from the Istanbul Zone in northern Turkey and the Balkan region due to subduction of a branch of Palaeotethys close to the southern active margin of Eurasia in Late Palaeozoic times. The multidisciplinary approach of this study underlines the importance of terrane accretion during stepwise closure of Palaeotethys.
机译：来自希腊希俄斯岛的碎屑锆石地球年代学和化石橄榄石的分析，在这里被用来限制地层的积聚过程以及在古海洋（一个分支）俯冲过程中沉积物的地壳来源。通过离子微探针（SHRIMP-II）分析来自希俄斯构造地层下部的石炭纪灰w的碎屑锆石获得的U / Pb年龄，其主要年龄段为2150-1890 Ma，640-540 Ma，505-475 Ma和365 –322马。二叠纪-三叠纪砂岩的碎屑锆石产生了明显的年龄群，分别为2200-1840 Ma，1100-910 Ma，625-560 Ma和385-370 Ma。两种样品中锆石年龄均在1.8至1.1 Ga之间，并伴有ca的出现。 2个Ga老锆石，暗示着冈瓦纳北部（非洲西北部）来源。从下部单元的石炭纪演替过程中，从带有“ Orthoceras”的石灰岩晶状体中发现的牙形动物区系，是志留纪晚期。该动物区系是Ludfordian Polygnathoides siluricus牙形石带的典型特征。该材料的牙形变色指数（CAI）约为1-2，表明低于100°C的极低级热变。在巴尔干地区和土耳其北部的伊斯坦布尔地区，发现了带有类似牙形石的石灰石的最近地区。 “ Orthoceras石灰石”的出现可以用作古资源重建的指示。我们的新锆石年龄与志留纪至低石炭纪的橄榄石的物源分析相结合，有力地表明，希俄斯的碎屑演替是从土耳其西部萨卡里亚微大陆的基底岩石中获取碎屑，以及北部伊斯坦布尔地区的古生代单位的时间和相等价的。土耳其和巴尔干地区由于古生代晚期俯冲了靠近欧亚大陆南部活跃边缘的古生物的分支。这项研究的多学科方法强调了在逐步封闭古生物的过程中增加地体的重要性。

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