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We report the first combined geochronologic and paleomagnetic study of volcanic rocks from the Shiquanhe and Yare Basins at the westernmost Lhasa Terrane, which aims to provide an accurate constraint on the shape and paleoposition of the southern margin of Asia prior to the India-Asia collision. Three new 40 Ar/ 39 Ar ages of 92.5 ± 2.9 Ma, 92.4 ± 0.9 Ma, and 79.6 ± 0.7 Ma determined by fresh matrix or feldspar from lava flows suggest a Late Cretaceous age for the investigated units. Characteristic remanent magnetizations have been successfully isolated from 38 sites which pass positive fold and/or reversal, conglomerate tests and are hence interpreted as primary in origin. The two paleopoles obtained from Yare and Shiquanhe yield consistent paleolatitudes of 13.6°N ± 9.6°N and 14.2°N ± 2.7°N, respectively (for a reference site of 31.5°N, 80°E), indicating that the southern margin of Asia near the western syntaxis was located far south during the Late Cretaceous time. A reconstruction of the Lhasa Terrane in the frame of Eurasia with paleomagnetic data obtained from its western and eastern parts indicates that the southern margin of Eurasia probably had a quasi-linear orientation prior to the collision formerly trending approximately 315°E. This is compatible with the shape of the Neo-Tethys slab observed from seismic tomographic studies. Our findings provide a solid basis for evaluating Cenozoic crustal shortening in the Asian interior and the size of Greater India near the western syntaxis.

We carried out a paleomagnetic investigation on Permian volcanic rocks from central eastern Inner Mongolia, NE China, in order to identify the paleoposition of the North China and Songliao‐Xilinhot blocks during Permo‐Carboniferous times and thereby define the spatial‐temporal history of the eastern Paleo‐Asian Ocean (PAO). Two prefolding magnetization components were isolated from the Sanmianjing and Elitu Formations (~283–266 Ma) along the northern margin of North China block (NMNCB) and the Dashizhai Formation (~280 Ma) in the Songliao‐Xilinhot block (SXB). These two results suggest paleolatitudes of ~4.9°N for the SXB and ~22.3°N for the NMNCB. Previously published results are classified according to recently proposed models and evaluated for the influence of inclination shallowing. Combined with earlier multidisciplinary studies, we propose a tentative paleogeographic reconstruction model for the eastern Central Asian Orogenic Belt (CAOB) during the Late Carboniferous to Early Triassic times. Siberia was situated at middle‐high paleolatitudes (~45°–65°N), and the Central Mongolia‐Erguna and South Mongolia‐Xing'an blocks had a middle latitude (~30°–45°N) from the Late Carboniferous to Early Permian. By the Late Permian to Early Triassic (~250 Ma), there was no significant latitudinal difference between the eastern CAOB blocks. Final closure of the eastern PAO along both the Hegenshan‐Heihe and Solonker sutures took place followed by the formation of Cinamuria.

The tectonic blocks that comprise present-day East Asia were amalgamated with Laurussia following the final closure of the Paleo-Asian and Paleo-Tethys oceans in late Paleozoic and Mesozoic times. These events allowed Pangea to reach its maximum packing at 220 Ma prior to supercontinent breakup . Quantifying the movement history of blocks surrounding the Paleo-Asian Ocean (PAO) can provide better understanding on the spatial-temporal evolution of the PAO and shed light on the paleogeography of East Asian blocks during the formation of Pangea.The timing of the PAO's final closure is contentious. Models based primarily on geological evidence (sedimentology, structural geology, metamorphism, provenance analyses, paleobiogeography, petrogeochemistry of igneous rocks, and ophiolites) can be broadly categorized into two end-member groups: (a) Middle-Late Devonian closure mainly supported by two middle Paleozoic orogenic belts recognized near the Solonker and Hegenshan sutures as well as overlying Late Devonian unconformities (e.g.,

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Abstract. Phosphorus is often invoked as the ultimate limiting nutrient, modulating primary productivity on geological timescales. Consequently, along with nitrogen, phosphorus bioavailability exerts a fundamental control on organic carbon production, linking all the biogeochemical cycles across the Earth system. Unlike nitrogen that can be microbially fixed from an essentially infinite atmospheric reservoir, phosphorus availability is dictated by the interplay between its sources and sinks. While authigenic apatite formation has received considerable attention as the dominant sedimentary phosphorus sink, the quantitative importance of reduced iron-phosphate minerals, such as vivianite, has only recently been acknowledged, and their importance remains underexplored. Combining microscopic and spectroscopic analyses of handpicked mineral aggregates with sediment geochemical profiles, we characterize the distribution and mineralogy of iron-phosphate minerals present in methane-rich sediments recovered from the northern South China Sea. Here, we demonstrate that vivianite authigenesis is pervasive in the iron-oxide-rich sediments below the sulfate–methane transition zone (SMTZ). We hypothesize that the downward migration of the SMTZ concentrated vivianite formation below the current SMTZ. Our observations support recent findings from non-steady-state post-glacial sedimentary successions, suggesting that iron reduction below the SMTZ, probably driven by iron-mediated anaerobic oxidation of methane (Fe-AOM), is coupled to phosphorus cycling on a much greater spatial scale than previously assumed. Calculations reveal that vivianite acts as an important burial phase for both iron and phosphorus below the SMTZ, sequestering approximately half of the total reactive iron pool. By extension, sedimentary vivianite formation could serve as a mineralogical marker of Fe-AOM, signalling low-sulfate availability against methanogenic and ferruginous backdrop. Given that similar conditions were likely present throughout vast swathes of Earth's history, it is possible that Fe-AOM and vivianite authigenesis may have modulated methane and phosphorus availability on the early Earth, as well as during later periods of expanded marine oxygen deficiency. A better understanding of vivianite authigenesis, therefore, is fundamental to test long-standing hypotheses linking climate, atmospheric chemistry and the evolution of the biosphere.

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