New isotopic age data constrain the depositional age and accretionary history of the Neoproterozoic-Ordovician Mona Complex (Anglesey-Lleyn, Wales)
New isotopic age data constrain the depositional age and accretionary history of the Neoproterozoic-Ordovician Mona Complex (Anglesey-Lleyn, Wales)
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新的同位素年龄数据限制了新元古代-奥陶纪莫纳杂岩（威尔士安格尔西-莱恩）的沉积年龄和增生历史
DOI：
10.1016/j.tecto.2017.03.017
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发表时间：
2017
期刊：
影响因子：
2.9
通讯作者：
B.F. Windely
中科院分区：
文献类型：
--
作者：
H. Asanuma;W. Fujisaki;T. Sato;S. Sakata;Y. Sawaki;K. Aoki;Y. Okada;S. Maruyama;T. Hirata;T. Itaya;B.F. Windely
威尔士安格尔西-莱因地区的莫纳杂岩是新元古代晚期至早古生代阿瓦隆期俯冲和增生的产物。它包括蛇绿岩、高压变质岩、火山碎屑沉积物和混杂岩。然而，了解构造演化一直阻碍了缺乏的年龄限制，因此，只有一个主要的地质年代学研究将足以破译俯冲，增生和折返的历史，这一重要的阿瓦隆造山带。对莫年超群中的碎屑锆石进行了U-Pb定年，以确定最大沉积年龄;对蓝片岩单元、中央剪切带和新港群中的多硅白云母和碎屑锆石进行了K-Ar定年和U-Pb定年，以确定变质事件的时间和持续时间。年代学资料给出多硅白云母的最小（K-Ar）沉积年龄为578-530 Ma，最大（K-Ar）沉积年龄为578-530 Ma，锆石U-Pb沉积年龄为878-550 Ma，表明构造最上部的圭纳群早于中部的新港群沉积（最大沉积年龄为548-515 Ma，本次研究），早于南叠层群最低层（最大沉积年龄为569-522 Ma，本次研究）。蓝片岩单元和CSZ中的富白云母片岩显示出不明显的K-Ar年龄，范围约为578 - 530 Ma。然而，新港群的K-Ar年龄为474 Ma，我们认为这反映了一个较晚的变质事件。在一个更大的角度来看，我们的新时代是广泛的钙碱性大陆弧岩浆活动在威尔士西北部和英格兰中部，形成连续向东俯冲约。711至474马。
The Mona Complex in Anglesey-Lleyn, Wales formed by Avalonian subduction and accretion from the latest Neoproterozoic to early Paleozoic. It comprises an ophiolite, high-pressure metamorphic rocks, volcaniclastic sediments and mélanges. However, understanding of the tectonic evolution has been held back by the paucity of age constraints, thus only a major geochronological study will be sufficient to decipher the subduction, accretion and exhumation history of this significant Avalonian orogen. We conducted U-Pb dating of detrital zircons in the Monian Supergroup in order to constrain the maximum depositional ages, and undertook K-Ar dating of phengites and U-Pb dating of detrital zircons in the Blueschist unit, the Central Shear Zone (CSZ), and the New Harbour Group to estimate the timing and duration of the metamorphic events, and to constrain the minimum depositional ages of the Gwna Group.Our geochronological data give minimum (K-Ar) depositional ages of 578–530 Ma on phengites and maximum (U-Pb zircon) depositional ages of 878–550 Ma, which indicates that the sediments in the structurally uppermost Gwna Group were deposited earlier than those in the middle New Harbour Group (maximum depositional ages of 548–515 Ma, this study) and earlier than in the lowermost South Stack Group (maximum depositional ages of 569–522 Ma, this study). Phengite-rich schists in the Blueschist unit and the CSZ show indistinct K-Ar ages ranging fromca.578 to 530 Ma. However, the K-Ar age of the New Harbour Group isca.474 Ma, which we interpret to reflect a later metamorphic event. In a larger perspective, our new ages are broadly contemporaneous with the calc-alkaline continental arc magmatism in NW Wales and Central England that formed by successive eastward subduction fromca.711 to 474 Ma.