The vast eastern-Tethyan oceanic domain that throughout the Mesozoic extended between Gondwana and Eurasia was a puzzle of larger and smaller microcontinents separated by larger and smaller oceans, ...the paleogeographic reconstruction of which poses major challenging problems. This review article summarizes the available stratigraphic, sedimentological, petrological, geochronological, geochemical, tectonic, and paleomagnetic evidence on the Bangong-Nujiang suture zone and adjacent geological domains now at the heart of the Tibetan Plateau, with the final aim to reconstruct the history of the Bangong-Nujiang Ocean from its birth to its growth and final demise. The vivid debate on these highly controversial geological issues touches on several key problems in plate tectonics, including the birth of an ocean, the nature of microcontinents and seamounts, the initiation of oceanic subduction, the implications of subduction polarity, and the timing of continental collision. Rifting between South Qiangtang and the Lhasa blocks took place in the Early to Middle Permian. The Bangong-Nujiang Ocean was still narrow in the Late Permian. The Triassic saw the rapid northward drift of South Qiangtang and active sea-floor-spreading in the Bangong-Nujiang Ocean, which reached a maximum north–south width of ~4000 km in about 50 million years. In the Early Jurassic (~190–180 Ma), Bangong-Nujiang oceanic lithosphere began to subduct northward. After some 30–40 million years of oceanic subduction, documented by arc magmatism and high-pressure metamorphic rocks, the Bangong-Nujiang Ocean closed its northern branch (the Dongqiao-Amdo ocean) in the latest Middle Jurassic (166–163 Ma), when the Amdo and Dongkacuo microcontinents collided with South Qiangtang. The southern oceanic branch (the Beila-Nagqu ocean) closed in the latest Jurassic (150–145 Ma) at the onset of collision between the Lhasa and Qiangtang blocks. Early Cretaceous (140–120 Ma) syncollisional arc-type magmatism was widely distributed in the Lhasa-Qiangtang collisional zone. At earliest Late Cretaceous time, the complete demise of seaways and the transition to widespread deposition of continental red beds along the Bangong-Nujiang suture zone marked the onset of intracontinental convergence leading to initial uplift of the Tibetan Plateau.
•Critical review of geological data related to the Bangong-Nujiang Ocean from its birth to its growth and demise.•Bangong-Nujiang Ocean opened in the Early Permian and started to subduct northward -~190–180 Ma.•Dongqiao-Amdo and Beila-Nagqu oceans closed at 166–163 Ma and 150–145 Ma, respectively.
The opening of the South Atlantic in the Early Cretaceous was the final stage of the complex rifting history of SW Gondwana. In this contribution we reassess the chronology of Mesozoic basin ...formation in southern South America and Africa and integrate it in the long-term breakup history of SW Gondwana. Triassic rifting is characterized by intracontinental rifting in Africa (Karoo I phase), and retro-arc extension on the SW-margin of Gondwana. In the Early Jurassic, the impingement of the Karoo plume triggered rifting in Eastern Africa, producing the Karoo II basins (and the Colorado and Salado basins on the Argentinean shelf). East Africa rifting ultimately lead the breakup of Eastern from Western Gondwana in the Middle Jurassic. In Patagonia, the Austral, Malvinas and other related basins formed in association with the synextensional emplacement of the Chon Aike magmatic province in the Patagonian retro-arc. In the Late Jurassic the Rocas Verdes back-arc basin opened in southern Patagonia, while oblique rifting in the core of the Late Paleozoic Gondwanides orogen produced the Outeniqua and Rawson/Valdés basins. The South Atlantic Rift initiated in the Early Cretaceous associated with present-day E-W extension. Rifting occurred diachronically from south to north, initiating in the previously thinned Rawson/Valdés-Outeniqua segment. A precursor oblique rift system and a larger degree of extension in this segment could explain the lack of Seaward Dipping Reflectors (SDR) south of the Colorado-Cape fracture zones. Rifting and SDR emplacement occurred progressively to the north along different rift segments, producing strongly asymmetric conjugate margins.
•Gondwana experienced poly-phased rifting, related to Mesozoic subduction dynamics.•The Colorado and Salado basins, offshore Argentina, are part of the Karoo system.•Late Jurassic oblique rifting was precursor of spreading in the South Atlantic.•The South Atlantic Rift was a highly-segmented, 500 km-wide, diachronous rift system.•North of Colorado-Cape Fracture Zone (CFZ), magma-rich margins formed product of interaction with the Paraná LIP.
ABSTRACT
Marine and terrestrial animals show a mosaic of lineage extinctions and diversifications during the Jurassic–Cretaceous transition. However, despite its potential importance in shaping ...animal evolution, few palaeontological studies have focussed on this interval and the possible climate and biotic drivers of its faunal turnover. In consequence evolutionary patterns in most groups are poorly understood. We use a new, large morphological dataset to examine patterns of lineage diversity and disparity (variety of form) in the marine tetrapod clade Plesiosauria, and compare these patterns with those of other organisms. Although seven plesiosaurian lineages have been hypothesised as crossing the Jurassic–Cretaceous boundary, our most parsimonious topology suggests the number was only three. The robust recovery of a novel group including most Cretaceous plesiosauroids (Xenopsaria, new clade) is instrumental in this result. Substantial plesiosaurian turnover occurred during the Jurassic–Cretaceous boundary interval, including the loss of substantial pliosaurid, and cryptoclidid diversity and disparity, followed by the radiation of Xenopsaria during the Early Cretaceous. Possible physical drivers of this turnover include climatic fluctuations that influenced oceanic productivity and diversity: Late Jurassic climates were characterised by widespread global monsoonal conditions and increased nutrient flux into the opening Atlantic‐Tethys, resulting in eutrophication and a highly productive, but taxonomically depauperate, plankton. Latest Jurassic and Early Cretaceous climates were more arid, resulting in oligotrophic ocean conditions and high taxonomic diversity of radiolarians, calcareous nannoplankton and possibly ammonoids. However, the observation of discordant extinction patterns in other marine tetrapod groups such as ichthyosaurs and marine crocodylomorphs suggests that clade‐specific factors may have been more important than overarching extrinsic drivers of faunal turnover during the Jurassic–Cretaceous boundary interval.
Clumped isotope based temperature estimates from exceptionally well-preserved belemnites from Staffin Bay (Isle of Skye, Scotland) reveal that seawater temperatures throughout the Middle-Late ...Jurassic were significantly warmer than previously reconstructed by conventional oxygen isotope thermometry. We demonstrate here that this underestimation by oxygen isotope thermometry was likely due to a) using the incorrect calcite thermometry equation for belemnite temperature reconstructions and b) by incorrectly estimating the seawater δ18O (δ18Osw) for the Hebrides Basin. Our data suggests that the fractionation factor for oxygen isotopes in belemnites from seawater was closer to that of slow-growing abiogenic calcites than that of other marine calcifying organisms. Our clumped isotope temperatures are used to reconstruct δ18Osw trends across the Callovian–Kimmeridgian in the Hebrides Basin. The δ18Osw varied significantly in the Hebrides Basin throughout this interval, possibly as a result of changing currents through the Laurasian seaway. Trends in temperature and δ18Osw are compared to published palaeoceanographic studies to shed light on changing palaeoceanography in the Tethyan and Boreal realms throughout the Middle–Late Jurassic.
•Scottish Jurassic seawater were temperatures much warmer than previously thought.•δ18Osw varied significantly throughout Mid-Late Jurassic in the Hebrides Basin.•Changes in current drove the observed temperature changes in the Hebrides Basin.•Belemnites likely precipitate their calcite in equilibrium with seawater.•Belemnite calcite exhibits a different 18O fractionation factor to other biogenic calcites.
This paper presents new zircon and sphene U–Pb ages, biotite and hornblende 40Ar/39Ar ages, Hf isotopic data, and geochemical data for five Mesozoic plutons in the Erguna Massif of NE China. These ...data are used to constrain the late Mesozoic tectonic evolution of the Mongol–Okhotsk orogenic belt. This new dating, when combined with previously published ages, indicates that the Late Jurassic–Early Cretaceous (J3–K1) intrusive rocks can be subdivided into three stages that represent periods of magmatism during the Late Jurassic (~155Ma), early Early Cretaceous (~137Ma), and late Early Cretaceous (~123Ma). In addition, the rocks have undergone later deformation recorded by peak ages of ~137 and ~123Ma. The Late Jurassic and early Early Cretaceous intrusive rocks in the study area are dominantly syenogranites and are either A-type granites or are classified as alkaline series, suggesting that they formed in an extensional environment. The late Early Cretaceous intrusive rocks in this area are generally monzogranitic and were emplaced as dikes in an extensional environment, along with coeval bimodal volcanics. These data, combined with the presence of regional unconformities in the northern part of Hebei Province and western part of Liaoning Province, and the spatial distribution of coeval volcanic rocks in NE China, suggest the Late Jurassic and early Early Cretaceous magmatisms and the early Early Cretaceous deformation in this area occurred in an extensional environment related to the delamination of a thickened part of the crust after closure of the Mongol–Okhotsk Ocean. In comparison, the late Early Cretaceous deformation and magmatism occurred in an extensional environment related to either delamination of the previously thickened crust related to the Mongol–Okhotsk tectonic regime or the subduction of the Paleo-Pacific Plate, or the combined influence of these two tectonic regimes.
•J3–K1 magmatic events in the Erguna Massif can be subdivided into three stages.•J3–K1 intrusive rocks consist mainly of A-type granites and monzonites.•J3–K1 intrusive rocks underwent two stages of deformations.•J3–K1 magmatisms and deformations formed in an extensional environment.
Eastern China provides a precious opportunity to explore how subduction drives evolution of the overlying continental lithosphere and to understand the fate of subducted plates. In this study, a ...synthesis of geochronological, whole-rock geochemical and zircon Hf isotopic data is used to examine temporal and spatial variations in distribution, composition and generation of Mesozoic magmas in the northern North China Craton. A compilation of age data reveals over 1000 km of inland-ward migration of a magmatic belt during 185– 145 Ma and then back again after 145– 140 Ma, coincident with the transition from contractional to extensional deformation regime in the very early Cretaceous. Distinct trends in lithologies, geochemistry and NdHf isotopes as a function of age and location are also observed in these magmas. The Mesozoic magmatism and deformation, as well as the lithospheric destruction, across the northern North China Craton is interpreted as the consequence of a change in subduction geodynamic regime of the Paleo-Pacific slab and its interaction with overlying continental lithosphere, which involves an active continental arc at Korean and Liaodong Peninsulas in the early-middle Jurassic, progressive shallowing of the subducting Paleo-Pacific plate in the middle-late Jurassic, and subsequent slab rollback in the early Cretaceous. Considering that trench retreat and slab-roll back are demonstrated as the pre-request of slab stagnation in the mantle transition zone, we further propose that the big mantle wedge structure in East Asia was probably initiated at 145– 140 Ma and was likely fully developed by ~120 Ma. Such a peculiar deep mantle structure governed the post-Cretaceous evolution of the Asian continental lithosphere by mediating the chemical and physical properties of upper mantle.
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