Combined U-Pb SHRIMP and Hf isotope Complex, Rio Negro Province, Argentina： of the Patagonia composite terrane study of the Late Paleozoic Yaminué Implications for the origin and evolution

We have carried out zircon U-Pb SHRIMP dating and Hf isotope determinations on a biotite paraschist and on a tonalitic orthogneiss of the Yaminue Complex,and re-evaluate this complex in the broader context of the tectonic evolution of the Patagonia composite terrane.In the metasedimentary unit （msuYC）,the youngest detrital zircon dated at 318±5 Ma（Mississippian/Pennsylvanian boundary） indicates a Pennsylvanian（or younger） depositional age.The three main age populations peak at 474,454 and 374 Ma.Preliminary Hf isotope data for two detrital zircons（447 and 655 Ma） yieldedε（Hf） values of -0.32 and 0.48,indicating that their primary sources contained small amounts of recycled crustal components(of Calymmian age;T_DM 1.56 Ga).Zircons from the orthogneiss（miuYC;intrusive into msuYC） show a crystallization age of 261.3±2.7 Ma（Capitanian;late middle Permian） which is broadly coeval with deformation,and Neoarchean-Paleoproterozoic inheritance.Meaningful core-rim relationship between Neoarchean zircon cores and late Permian rims is well defined,indicating the occurrence of Archean crust in this sector of Patagonia.Hf T_DM of Permian zircons is mainly Meso-Paleoarchean（2.97-3.35 Ga）,with highly negativeε（Hf） values（ca.-33）.Hf T_DM of inherited Neoarchean zircon cores is also Meso-Paleoarchean（3.14-3.45 Ga） but more juvenile（ε（Hf） = -0.3）.Hf isotopes reinforce the presence of unexposed ancient crust in this area. Combining geological and isotope data,as well as geophysical models,we identify the Yaminue Complex within the La Esperanza-Yaminue crustal block flanked by two other,distinct crustal blocks:the Eastern block which forms part of the Patagonia terrane sensu stricto,located in the eastern Patagonian region,and the Western block forming part of the Southern Patagonia terrane.Their origins and timing of amalgamation to form the Patagonia composite terrane are also discussed.     

INHIGEO： The International Commission on the History of Geological Sciences

INHIGEO is a long-standing Commission of the International Union of Geological Sciences (lUGS) and an Affiliate of the International Union for the History and Philosophy of Science (Division of History of Science) (IUHPS (DHS)). Of late, its activities are funded by these two bodies in a ratio of about 4:1.     

Carboniferous–Permian Stratigraphy and Sedimentary Environment of Southeastern Inner Mongolia, China: Constraints on Final Closure of the Paleo-Asian Ocean

In this paper we discuss the timing of final closure of the Paleo-Asian Ocean based on the field investigations of the Carboniferous–Permian stratigraphic sequences and sedimentary environments in southeastern Inner Mongolia combined with the geology of its neighboring areas. Studies show that during the Carboniferous–Permian in the eastern segment of the Tianshan-Hinggan Orogenic System, there was a giant ENE–NE-trending littoral-neritic to continental sedimentary basin, starting in the west from Ejinqi eastwards through southeastern Inner Mongolia into Jilin and Heilongjiang. The distribution of the Lower Carboniferous in the vast area is sparse. The Late Carboniferous or Permian volcanic-sedimentary rocks always unconformably overlie the Devonian or older units. The Upper Carboniferous–Middle Permian is dominated by littoral-neritic deposits and the Upper Permian, by continental deposits. The Late Carboniferous–Permian has no trace of subduction-collision orogeny, implying the basin gradually disappeared by shrinking and shallowing. In addition, it is of interest to note that the Ondor Sum and Hegenshan ophiolitic mélanges were formed in the pre-Late Silurian and pre-Late Devonian respectively, and the Solonker ophiolitic mélange formed in the pre-Late Carboniferous. All the evidence indicates that the eastern segment of the Paleo-Asian Ocean had closed before the Late Carboniferous, and most likely before the latest Devonian (Famennian).