Several locations with alkaline magmatism are recognised in Silurian-Devonian basins along the southern variscan autochthon units (e.g. Central Iberian Zone) of the northern Gondwana margin. The origin of the Devonian basins and their magmatism has not been studied in the context of the passive margin of Gondwana. The basement of Menorca, Balearic Islands, consists of a deep Devonian-Carboniferous basin with mafic igneous rocks, the Tramuntana Gabbros. In this study, we trace the geodynamic setting and isotopic sources of the Tramuntana Gabbros through elemental geochemistry, isotopic geochemistry (SrNd) and UPb geochronology in zircons. These gabbros are the product of an intraplate alkaline magmatism with immobile trace element and REE contents similar to those of Ocean Island Basalts. Average 87Sr/86Sr(370) of 0.708456 and εNd(370) of +4.0 indicate a source similar to a Type-2 enriched mantle with average TDM of 665 Ma, suggesting a relatively old metasomatized mantle. Concordant UPb ages of c. 597 Ma (Ediacaran, radiometric age) from a single population of 31 zircons separated from the Tramuntana Gabbros (Devonian, biostratigraphic age) reinforce the presence of older units in the corresponding lithospheric mantle. The Tramuntana Gabbros and the Devonian-Carboniferous sequences of Menorca limit the westward extension of the Paleo-Tethys Ocean, whose development never reached these westernmost regions. Assuming a common sublithospheric mantle source for the peri-Gondwanic Devonian alkaline rocks and considering the previous Cadomian (Neoproterozoic) subduction to be the most favourable origin of the separated zircons, the bulk rock TDM and zircon UPb data obtained from the Tramuntana Gabbros track the mixing, recycling, and mantle accretion in this peri-Gondwanic section from Precambrian to Devonian times.

中文翻译：

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梅诺卡岛的碱性泥盆纪岩浆作用：追踪古特提斯洋西部地区的地幔同位素来源


在沿着冈瓦纳大陆北部边缘的瓦里坎原地单元南部（例如伊比利亚中部地带）的志留纪-泥盆纪盆地中，发现了几个具有碱性岩浆活动的地点。泥盆纪盆地的起源及其岩浆作用尚未在冈瓦纳大陆被动边缘的背景下进行研究。巴利阿里群岛梅诺卡岛的基底由深泥盆纪-石炭纪盆地组成，其中含有镁铁质火成岩，即特拉蒙塔纳辉长岩。在这项研究中，我们通过元素地球化学、同位素地球化学 (SrNd) 和锆石中的 UPb 地质年代学来追踪特拉蒙塔纳辉长岩的地球动力学环境和同位素来源。这些辉长岩是板内碱性岩浆作用的产物，其固定微量元素和稀土元素含量与洋岛玄武岩相似。平均 87Sr/86Sr(370) 为 0.708456，εNd(370) 为+4.0，表明其来源类似于 2 型富集地幔，平均 TDM 为 665 Ma，表明存在相对古老的交代地幔。一致的 UPb 年龄 c。从 Tramuntana Gabbros（泥盆纪，生物地层年龄）中分离出来的 31 个锆石单一群中的 597 Ma（埃迪卡拉纪，辐射年龄）证实了相应岩石圈地幔中较古老单位的存在。特拉蒙塔纳辉长岩和梅诺卡岛的泥盆纪-石炭纪序列限制了古特提斯洋的向西延伸，而古特提斯洋的发展从未到达这些最西端的地区。 假设近冈瓦尼泥盆纪碱性岩石有一个共同的岩石圈下地幔来源，并考虑到先前的卡多姆（新元古代）俯冲是分离锆石的最有利来源，从 Tramuntana Gabbros 获得的块体岩石 TDM 和锆石 UPb 数据跟踪混合从前寒武纪到泥盆纪这个近冈瓦尼地段的地幔循环和地幔增生。