Alpine Tethys rift-related OIB-type magmatism preserved on Elba Island (Northern Apennines, Italy)

The protoliths of the metabasite bodies exposed in the Mt. Calamita promontory (SE Elba Island, Italy) are postulated to have been formed during a Middle to Upper Triassic mafic magmatic event that intruded the Permo-Triassic sedimentary succession deposited on the thinned Adria paleo-margin during the break-up of Pangea. Although many of the metabasite outcrops in the Northern Apennines have been known since the 1950s, a comprehensive field documentation and an updated geochemical database are still lacking, thus preventing a full assessment of their petrogenesis and leaving the interpretation of the Lower Mesozoic Western Neotethys geodynamic framework incomplete. In this Communication, we describe for the first time the extent of the metabasite bodies and their relationship to the host rocks in Mt. Calamita promontory, thus defining their geochemical features and possible minimum age. Trace element evidence is used to constrain the mantle source and the associated tectonic scenario and indicate an alkaline basalt OIB-type magmatic character developed in an anorogenic divergent/rifted margin setting. When integrated with selected compositional data for Triassic and Early Cretaceous metabasite/mafic rocks from Adria and European paleomargins, a scenario of continental rift-drift and seafloor spreading involving upwelling parcels of enriched mantle is highlighted, defined for the first time as OIB-influenced (plume?) Alpine Tethys rifting.

意大利厄尔巴岛（Elba Island）东南部卡拉米塔山岬角（Mt. Calamita promontory）出露的变基性岩体（metabasite bodies）原岩被推断形成于中三叠世至晚三叠世基性岩浆事件，该岩浆事件侵入了泛大陆（Pangea）裂解时期于减薄的亚得里亚古陆边缘（Adria paleo-margin）沉积的二叠-三叠纪沉积序列。尽管北亚平宁山脉（Northern Apennines）的诸多变基性岩露头自20世纪50年代起便已为人所知，但目前仍缺乏全面的野外实测记录与更新后的地球化学数据库（geochemical database），这阻碍了对其岩石成因（petrogenesis）的完整评估，同时也未能完整阐释下中生代新特提斯洋西部（Western Neotethys）的地球动力学框架。在本研究通讯中，我们首次阐明了卡拉米塔山岬角变基性岩体的分布范围及其与围岩的赋存关系，明确了其地球化学特征与可能的最小形成时代。通过微量元素证据限定了其幔源物质与相关构造背景，结果显示其具有碱性玄武岩类洋岛玄武岩（OIB）型的岩浆属性，形成于非造山伸展/裂谷边缘构造背景。结合亚得里亚与欧洲古陆边缘筛选后的三叠纪及早白垩世变基性岩/基性岩组分数据，本研究揭示了一套涉及富集地幔上涌块体的大陆裂谷-漂移与海底扩张演化场景，该场景首次被定义为受洋岛玄武岩（OIB）影响（地幔柱？）的阿尔卑斯特提斯洋裂谷作用。