Peri-Gondwanan terranes in the Romanian Carpathians:A review of their spatial distribution,origin,provenance,and evolution

The basement of the Romanian Carpathians is made of Neoproterozoic to early Paleozoic peri- Gondwanan terranes variably involved in the Variscan orogeny, similarly to other basement terrains of Europe. They were hardly dismembered during the Alpine orogeny and traditionally have their own names in the three Carpathian areas. The Danubian domain of the South Carpathians comprises the Dragsan and Lainici-Paiius peri-Amazonian terranes. The Dragsan terrane originated within the ocean surrounding Rodinia and docked with Rodinia at -800 Ma. It does not contain Cadomian magmatism and consequently it is classified as an Avalonian extra-Cadomian terrane, The Lainici-Pfiius terrane is a Ganderian fragment strongly modified by Cadomian subduction-related magmatism, It is attached to the Moesia platform. The TisoviD terrane is an ophiolite that marks the boundary between Drfagsan and Lainici-Paius terranes. The other basement terranes of the Romanian Carpathians originated close to the Ordovician North- African orogen, as a result of the eastern Rheic Ocean opening and closure. Except for the Sebes-Lotru terrane that includes a lower metamorphic unit of Cadomian age, all the other terranes （Bretila, Tulghes, Negrisoara and Rebra in the East Carpathians, Somes, Biharia and Baia de Aries in the Apuseni mountains, Fagaras, Leaota, Carat and Pades in the South Carpathians） represent late Cambrian-Ordovician rock assemblages. Their provenance, is probably within paleo-nortbeast Africa, close to the Arabian-Nubian shield. The late Cambrian-Ordovician terranes are defined here as Carpathian-type terranes. According to their lithostratigraphy and origin, some are of continental margin magmatic arc setting, whereas others formed in rift and back-arc environment and closed to passive continental margin settings. In a paleo- geographic reconstruction, the continental margin magmatic arc terranes were first that drifted out, followed by the passive continental margin terranes with the back-arc terranes in their front. They accreted to Laurussia during the Variscan orogeny. Some of them （Sebes-Lotru in South Carpathians and Baia de Aries in Apuseni mountains） underwent eclogite-grade metamorphism. The Danubian terranes, the Bretila terrane and the Somes terrane were intruded by Variscan granitoids.

沉积物再循环引起的地幔氧化及其对地幔富铁熔体成因的启示

地幔起源熔体FeO^tot含量通常在11 wt%左右,但也有些原始熔体异常富铁(FeO^tot>13 wt%).因此富铁熔体是研究地幔不均一性的理想样品,而且一些大型氧化物及硫化物矿床也和其密切相关.然而到目前为止富铁熔体的成因仍没有定论.在内蒙古达里湖武岩中发现了一类比较特殊的地幔橄榄岩包体,其中包含有极高Mg#橄榄石和高Fe^3+/ΣFe比值矿物(镁铁矿及赤铁矿).这些矿物组合记录了地幔强氧化环境.因为这些橄榄岩包体和碳酸岩质包体一同出现,而且其中的单斜辉石具有明显的Sr同位素环带变化,所以强氧化条件可能是由再循环沉积物诱发的.本文模拟了地幔橄榄岩及辉石岩在不同氧逸度条件下的熔融行为,发现高氧逸度条件下形成的熔体具有富铁苦橄岩的典型特征(高FeO和MgO、低Al2O3).这些观察表明氧化地幔熔融可能是富铁熔体的另一种形成机制.