Gondwana Research最新文献

Geochronological and geochemical investigation of the magmatic and sedimentary rocks from the south-eastern tip of the Bayankhongor Zone (central Mongolia) constrains the Neoproterozoic evolution of the northern margin of the Baidrag Block. There, ultramafic to felsic igneous rocks of the Khan-Uul Massif intruded the volcano-sedimentary sequence of the Ulziit Gol Unit. U–Pb zircon ages show that both the plutonic and volcanic rocks were coeval products of the same Ediacaran (598–564 Ma) magmatism. Most of the samples have low contents of high field strength elements typical of arc-related magmas; however, some mafic rock samples display N-MORB-like chemistry. Magmatic rocks in the Khan-Uul Massif and Ulziit Gol Unit yielded exclusively positive initial ${\epsilon }_{\mathrm{Hf}}$ in zircon values (+4.9 to +13.8), implying derivation from depleted-mantle sources. Furthermore, heterogeneity of the whole-rock initial ${\epsilon }_{\mathrm{Nd}}$ values (–4.0 to +2.1) documents that fractional crystallization was accompanied by variable crustal contamination. The detrital zircon age patterns of the sandstone and tuffites in the Ulziit Gol Unit indicate that the sequence was filled dominantly by Ediacaran magmatic detritus derived from the Khan-Uul Massif and its volcanic equivalents, while the older cratonic material from the Baidrag basement represented only a subordinate component. Combined magmatic and sedimentary records imply that both the Khan-Uul Massif and the Ulziit Gol Unit may have formed in the same back-arc basin environment. This challenges the previous view that the entire Bayankhongor Zone was ophiolitic in nature. Distribution of coeval Ediacaran supra-subduction systems on the scale of the Mongolian Collage indicates the closure of multiple oceanic basins rimming the Siberian Continent. Following Rodinia break-up, this peri-Siberian realm was presumably formed by sub-parallel continental ribbons and oceanic basins. It is proposed that the amalgamation of these blocks and closure of intervening oceans reflected the Ediacaran advancing mode of the Palaeo-Pacific subduction.

The closure of the Mongol-Okhotsk Ocean (MOO) marks the final suturing of the Central Asian Orogenic Belt, one of the largest accretionary orogens on Earth and a region that is considered an archetype for crustal growth during the Phanerozoic. Abundant Permian to Triassic magmatism in Mongolia extended into the Jurassic on the eastern side of the Mongol-Okhotsk Belt (MOB), the orogenic belt produced by the closure of the MOO. Magmatic belts formed north and south of the suture along the MOB provide insight into the dynamics of the subduction system and the magmatic, crustal, and mantle processes pre-, syn- and post- collision within this accretionary margin. One of the main questions regarding the magmatism in the region is: Was the magmatism formed during active subduction or during the collision and closure of the basin? Here we compile geochemical data (major and trace elements, and isotopes) from the Permian to Jurassic magmatic rocks in the MOB and analyze their spatiotemporal characteristics. Our goal is to assess how magmatism changed in time and space during the closure of the Mongol-Okhotsk Ocean and how those changes relate to first-order tectono-magmatic processes right before or during the collisional event that closed the basin. Our results show a general enrichment in fluid mobile elements, LILE, and LREE and depletion in HFSE, and HREE in mafic and felsic rocks, which indicates a mantle metasomatized by subduction-related fluids regardless of crustal contamination. Our analysis supports higher enrichment in sediment melts, especially along its western and older extent, and the assimilation of juvenile crustal components without producing abundant S-type peraluminous magmatism which indicates mantle and crustal contributions. Thus, we conclude that magmatism formed above a sediment-rich retreating margin was able to recycle and stabilize young and compositionally evolved crustal material in the Central Asian Orogenic Belt.

The Investigator Ridge, located along the prominent Investigator Fracture Zone in the Wharton Basin, northeast Indian Ocean, was chosen to investigate the temporal and geochemical evolution of the Indian upper mantle. We present new ⁴⁰Ar/³⁹Ar age, as well as major and trace element and Sr-Nd-Pb-Hf isotope data, from a large part of this so far scarcely sampled ridge. The ⁴⁰Ar/³⁹Ar ages range from 100.0 Ma to 64.1 Ma, and except for the two youngest samples (65.5 and 64.1 Ma) of likely Christmas Island Seamount Province (CHRISP) origin, display decreasing ages along the ridge from south to north. This pattern is consistent with the ages derived from paleomagnetic anomalies on the local oceanic crust that also decrease in age northwards and suggests an origin of the studied rocks at or near the now extinct Wharton spreading center. These ages also provide information about the displacements along the multiple Investigator Fracture Zones indicating large left-lateral as well as right-lateral offsets of the paleo spreading axis. The fracture zone also shows signs of recent tectonic reactivation. The Investigator Ridge samples are derived from a DUPAL-like mantle source similar to present-day Indian MORB. This source contains a depleted mantle type component, an enriched, moderately HIMU-like, component such as common “C” or “FOZO”, and an additional enriched component of recycled subcontinental lithospheric mantle material. In both the Investigator Ridge and CHRISP samples, the trace element and isotope compositions systematically change with age implying a temporal geochemical evolution of the Indian Mantle Domain in this region. It contained higher proportions of subcontinental lithospheric material delaminated during breakup of Gondwana and mixed with depleted upper mantle material in its early phase. With time, the source evolved in the direction of “C” or “FOZO”, which then became the dominant enriched component and is observed in the youngest samples.

Subduction initiation of oceanic lithosphere is the key scientific problem of the plate tectonics on Earth. When, where, and how an oceanic subduction began remained obscure because of little geological records. Here, we report a newly documented ophiolitic sequence, including ultra-slow spreading ridge fragments (V1) and associated fore-arc lavas (V2) units in the Bangong-Nujiang suture zone, north-central Tibetan Plateau. The V1 units are controlled by detachment fault with peridotite, gabbro and pillow basalt. Peridotite exhibits uniform characteristics of abyssal peridotite, representing residues after low-degree melting of asthenospheric mantle. Mafic rocks display geochemical features of normal mid-ocean ridge basalt (N-MORB). These features, combined with zircon U-Pb dating, indicate that formation of the oceanic lithosphere occurred along an ultra-slow spreading ridge around 177–170 Ma in this area. The V2 units occur as a complete sequence from bottom to top of fore-arc basalt (FAB), basaltic andesite, boninite, and high-Mg arc-related rocks with formation ages of 160–150 Ma, which directly extruded and overlay on the V1 units. This sequence is identical to those of the Izu-Bonin-Mariana (IBM) fore-arc, and represent magmatic response to subduction initiation (SI). Thus, we propose that the Beila ophiolite preserved an entire process of oceanic transition from ultra-slow spreading oceanic ridge to the SI. Subduction initiation in the Beila area was induced by southward subduction transition after the closure of the northern branch of the Bangong-Nujiang Meso-Tethys Ocean and subsequent continental collision. This study provides direct geological evidence for delineating the geodynamic mechanism of an oceanic initial subduction.

The Cenozoic depositional history of central Sundaland is well known from subsurface studies of the numerous basins that litter the region, which record an Eocene to Miocene rift–inversion basin evolution. However, as is common with offshore studies, these often lack the 3D spatial observations and sedimentary provenance data required to link depositional environments, sediment pathways, and tectonic events at scale. The benefits of onshore analogue studies for understanding offshore stratigraphy are well recorded and they are of particular importance in the largely submerged area of Sundaland. Here we provide new facies analysis, sedimentary provenance data, and palaeogeographic histories for Eocene to Pleistocene sediments from Natuna Island, off the northwest coast of Borneo. Natuna Island sits atop the Natuna Arch, a structural high that straddles the East and West Natuna basins. This research records a well-preserved source-to-sink package, including an uplifted granitic basement that eroded into conglomerates and quartz-rich sandstones deposited in deltaic and paralic environments with intermittent volcanism throughout the Cenozoic. U-Pb zircon geochronology, heavy minerals, and light minerals record dominantly local sourcing with periodic influx of more diverse sources during the post-rift basin interlinkage phase (e.g., Peninsular Malaysia and West Borneo). Uplift of the Natuna Arch during two basin inversion events since the Eocene has led to the erosion of the granitic basement into a series of sandstones and overlying siltstones that now form the lowlands of the island (the Raharjapura and Pengadah formations, respectively). These onshore sediments correlate directly in both age and sedimentology with Oligocene to Pliocene successions in the West and East Natuna basins that flank the island (e.g., the Gabus, Arang, and Muda formations). These comprehensive onshore studies provide insights into larger drainage patterns and sediment transport pathways along with the linkage of basins and emergence of land at key intervals.

Mountains and mountain ranges, often situated at convergent plate margins, play a pivotal role in many fields of the Earth, climate, and biological sciences. Reconstructing past episodes of mountain building from the geological rock record is one of the main challenges for unravelling the ancient physical geography of Earth’s surface. Established methods for quantifying past elevations traditionally relied on sedimentary rocks, but in recent years, alternative approaches have emerged on the basis that geochemical signatures of magmatic rocks formed in convergent settings correlate with crustal thickness or elevation. Consequently, methods based on igneous samples have the potential to allow quantitative mapping of past topographic change for large spans of space and time where existing maps are largely based on a qualitative approach. Here, we investigate the application of paleoelevation estimates derived from geochemistry using the western margin of South America as a case study. We investigate their consistency with independent indicators of past elevations such as stratigraphy, stable isotopes, fossils etc. for Cenozoic samples along the Andean margin. For older times, we compare the estimated paleoelevations with more general aspects of the geological record, as well as paleoelevations from global paleogeography models widely used in climate modelling studies, to evaluate the extent to which these models are consistent with the igneous geochemical proxies. We find that estimates based on multiple geochemical proxies, and which account for variations in elevation as a function of MgO, are preferable to those based on individual proxies. The multi-mohometer estimates yield estimates of elevation that better match both present-day topography and Cenozoic paleoelevations, and retain more samples during the data filtering stage. In deeper time, we show that igneous geochemistry quantifies changes in elevation related to documented phases of crustal thickening and thinning, and is thus likely to allow improvements to existing maps of paleotopography.

China’s rapid technological advancement and the growth of its tech sector have raised concerns about their impact on environmental sustainability. The current analysis aims to contribute to the existing literature by offering a fresh perspective on China’s environmental sustainability, as the existing literature tends to overlook the role of the size of the technological market, which is closely connected with several Sustainable Development Goals (SDGs)—SDG 7, SDG 9, SDG 11, SDG 12 and SDG 13. China can make significant strides towards achieving these goals by harnessing the potential of the technological market and aligning it with environmental sustainability objectives. This study also investigates the roles of urbanization and economic growth and examines the existence of the inverted N-shaped Environmental Kuznets Curve hypothesis in 31 Chinese provinces from 2004 to 2021. Robust tests are employed to analyse the data, including the Cointegrated Structural Auto Regressive Distributed Lag approach (CS-ARDL) and the Augmented Mean Group(AMG) method. The results indicate that economic growth, urbanization, and the size of the technological market can reduce SO₂ emissions, demonstrating a positive environmental impact through China’s inverted N-shaped Environmental Kuznets Curve. Additionally, the Dumitrescu-Hurlin Granger causality test showed evidence of bidirectional causality between the size of the technological market and SO₂ emissions. Based on the findings, the study proposes sustainable development policies for China, in line with the SDG targets. In this context, the country’s rapid economic growth and strategies for industrial competitiveness need reassessment. The objective should be to redesign these strategies to increase the proportion of high-tech activities in overall manufacturing and promote the adoption of renewable energy in the country’s total energy consumption. Consequently, Chinese policymakers should prioritize the implementation of regulations that uphold fundamental principles to enhance environmental quality while maintaining rapid economic growth and a competitive advantage in the industrial sector.

This paper presents zircon U–Pb dating and Hf isotopic, and whole-rock geochemical and Sr–Nd isotopic data for early Paleozoic igneous rocks as well as zircon U–Pb dating for the sedimentary rocks of the Songnen Massif within the eastern Central Asian Orogenic Belt (CAOB), aiming to reveal arc magma evolution process. The zircon U–Pb dating results of the siltstone of the Xiaojingou Formation yielded 450 Ma, 471 Ma, 502 Ma, 773 Ma, 818 Ma and 949 Ma age peaks, as well as multi-episodic Paleo-proterozoic ages (2486-1612 Ma), implying its deposition time is younger than ∼ 450 Ma. The zircon U–Pb dating results reveal that the Songnen Massif exists three episodes of volcanic rocks of the middle Cambrian (502 Ma), Middle Ordovician (453-449 Ma) and the Silurian (435-420 Ma). The middle Cambrian basalts are low-K tholeiitic to calc-alkaline series, weakly depleted ε_Hf(t) and ε_Nd(t) values. They were derived from the weakly depleted mantle metasomatized by slab fluid in an immature island arc setting. The Middle Ordovician to Silurian volcanic rocks show SiO₂ of 49.4–58.1 wt%, plotting into high-K calc-alkaline series, which are also featured by higher Th/Nd and (Hf/Sm)_PM ratios, together with moderate depleted ε_Nd(t) values, suggesting their derivation of the depleted mantle wedge metasomatized by sediment-derived melt. In contrast, coeval early Paleozoic volcanic rocks in the eastern Xing’an Massif with the MORB-like ε_Nd(t) values are characterized by an origin of the depleted mantle wedge and the distinct interaction of oceanic crust melt and mantle peridotite. Combined with the variation of calculated crust thickness, we suggested that there was a continental arc in the eastern Songnen Massif, which developed from immaturity to maturity during middle Cambrian to Silurian, while the early Paleozoic island arc in the eastern Xing’an Massif is characterized by ocean ridge subduction process.