Fast radio bursts (FRBs), bright transients with millisecond durations at ∼GHz and typical redshifts probably >0.8, are likely to be gravitationally lensed by intervening galaxies. Since the time ...delay between images of strongly lensed FRB can be measured to extremely high precision because of the large ratio ∼10
between the typical galaxy-lensing delay time Formula: see text (10 days) and the width of bursts Formula: see text (ms), we propose strongly lensed FRBs as precision probes of the universe. We show that, within the flat ΛCDM model, the Hubble constant H
can be constrained with a ~0.91% uncertainty from 10 such systems probably observed with the square kilometer array (SKA) in <30 years. More importantly, the cosmic curvature can be model independently constrained to a precision of ∼0.076. This constraint can directly test the validity of the cosmological principle and break the intractable degeneracy between the cosmic curvature and dark energy.
Seismic tomography studies indicate that the Earth's mantle structure is characterized by African and Pacific seismically slow velocity anomalies (i.e., superplumes) and circum‐Pacific seismically ...fast anomalies (i.e., a globally spherical harmonic degree 2 structure). However, the cause for and time evolution of the African and Pacific superplumes and the degree 2 mantle structure remain poorly understood with two competing proposals. First, the African and Pacific superplumes have remained largely unchanged for at least the last 300 Myr and possibly much longer. Second, the African superplume is formed sometime after the formation of Pangea (i.e., at 330 Ma) and the mantle in the African hemisphere is predominated by cold downwelling structures before and during the assembly of Pangea, while the Pacific superplume has been stable for the Pangea supercontinent cycle (i.e., globally a degree 1 structure before the Pangea formation). Here, we construct a proxy model of plate motions for the African hemisphere for the last 450 Myr since the Early Paleozoic using the paleogeographic reconstruction of continents constrained by paleomagnetic and geological observations. Coupled with assumed oceanic plate motions for the Pacific hemisphere, this proxy model for the plate motion history is used as time‐dependent surface boundary condition in three‐dimensional spherical models of thermochemical mantle convection to study the evolution of mantle structure, particularly the African mantle structure, since the Early Paleozoic. Our model calculations reproduce well the present‐day mantle structure including the African and Pacific superplumes and generally support the second proposal with a dynamic cause for the superplume structure. Our results suggest that while the mantle in the African hemisphere before the assembly of Pangea is predominated by the cold downwelling structure resulting from plate convergence between Gondwana and Laurussia, it is unlikely that the bulk of the African superplume structure can be formed before ∼230 Ma (i.e., ∼100 Myr after the assembly of Pangea). Particularly, the last 120 Myr plate motion plays an important role in generating the African superplume. Our models have implications for understanding the global‐scale magmatism, tectonics, mantle dynamics, and thermal evolution history for the Earth since the Early Paleozoic.
Establishing how tectonic plates have moved since deep time is essential for understanding how Earth's geodynamic system has evolved and operates, thus answering longstanding questions such as what ...“drives” plate tectonics. Such knowledge is a key component of Earth System science, and has implications for wide ranging fields from core-mantle-crust interaction and evolution, geotectonic phenomena such as mountain building and magmatic and basin histories, the episodic formation and preservation of Earth resources, to global sea-level changes, climatic evolution, atmospheric oxygenation, and even the evolution of life. In this paper, we take advantage of the rapidly improving database and knowledge about the Precambrian world, and the conceptual breakthroughs, both regarding the presence of a supercontinent cycle and possible dynamic coupling between the supercontinent cycle and mantle dynamics, in order to establish a full-plate global reconstruction from 540 Ma back to 2000 Ma. We utilise a variety of global geotectonic databases to constrain our reconstruction, and use palaeomagnetically recorded true polar wander events and global plume records to help evaluate competing geodynamic models and also provide new constraints on the absolute longitude of continents and supercontinents. After revising the configuration and life span of both supercontinents Nuna (1600—1300 Ma) and Rodinia (900—720 Ma), we present a 2000—540 Ma animation, starting from the rapid assembly of large cratons and supercratons (or megacontinents) between 2000 Ma and 1800 Ma. This occurred after a billion years of dominance by small cratons, and kick-started the ensuing Nuna and Rodinia supercontinent cycles and the emergence of stable, hemisphere-scale (long-wavelength) degree-1/degree-2 mantle structures. We further use the geodynamicly-defined type-1 and type-2 inertia interchange true polar wander (IITPW) events, which likely occurred during Nuna (type-1) and Rodinia (type-2) times as shown by the palaeomagnetic record, to argue that Nuna assembled at about the same longitude as the latest supercontinent Pangaea (320—170 Ma), whereas Rodinia formed through introversion assembly over the legacy Nuna subduction girdle either ca. 90° to the west (our slightly preferred model) or to the east before the migrated subduction girdle surrounding it generated its own degree-2 mantle structure by ca. 780 Ma. Our interpretation is broadly consistent with the global LIP record. Using TPW and LIP observations and geodynamic model predictions, we further argue that the Phanerozoic supercontinent Pangaea assembled through extroversion on a legacy Rodinia subduction girdle with a geographic centre at around 0°E longitude before the formation of its own degree-2 mantle structure by ca. 250 Ma, the legacy of which is still present in present-day mantle.
•Two alternative 2000—540 Ma full-plate global reconstructions linked to global geodynamics.•Revised reconstruction of supercontinents Nuna and Rodinia.•Two types of inertia interchange true polar wander (IITPW) linked to geodynamics.•Palaeolongitude options determined by true polar wander and LIP records.•Transition of global tectonic regime from pre-1.8 Ga cratonic and supercraton assembly to post-1.8 Ga supercontinent cycle.•Multiple geotectonic databases and palaeomagnetic data all in GIS-compatible formats.
This review paper presents a set of revised global palaeogeographic maps for the 825–540Ma interval using the latest palaeomagnetic data, along with lithological information for Neoproterozoic ...sedimentary basins. These maps form the basis for an examination of the relationships between known glacial deposits, palaeolatitude, positions of continental rifting, relative sea-level changes, and major global tectonic events such as supercontinent assembly, breakup and superplume events. This analysis reveals several fundamental palaeogeographic features that will help inform and constrain models for Earth’s climatic and geodynamic evolution during the Neoproterozoic. First, glacial deposits at or near sea level appear to extend from high latitudes into the deep tropics for all three Neoproterozoic ice ages (Sturtian, Marinoan and Gaskiers), although the Gaskiers interval remains very poorly constrained in both palaeomagnetic data and global lithostratigraphic correlations. Second, continental sedimentary environments were dominant in epicratonic basins within Rodinia (>825Ma to ca. 750Ma), possibly resulting from both plume/superplume dynamic topography and lower sea-level due to dominantly old oceanic crust. This was also the case at ca. 540Ma, but at that time the pattern reflects widespread mountain ranges formed during the assembly of Gondwanaland and increasing mean age of global ocean crust. Third, deep-water environments were dominant during the peak stage of Rodinia break-up between ca. 720Ma and ca. 580Ma, likely indicating higher sea level due to increased rate of production of newer oceanic crust, plus perhaps the effect of continents drifting away from a weakening superplume. Finally, there is no clear association between continental rifting and the distribution of glacial strata, contradicting models that restrict glacial influence to regions of continental uplift.
•Updated Neoproterozoic global palaeogeography•A data table showing facies data for seven selected time-windows•Facies data shown in seven selected global palaeographic maps•Sea-level changes linked to global tectonic regimes•Three Neoproterozoic glacial events all spread from tropical to high latitudes.
The South China Block (SCB) has been regarded by many as an integral part of Gondwana, but proposed timing and processes for its accretion to Gondwana vary and remain contentious, largely owing to ...the lack of reliable Pan‐African age paleomagnetic data and tectono‐magmatic records from the SCB. Integrated in situ U‐Pb ages and Hf‐O isotope analyses of detrital zircons from geochronologically well‐calibrated Ediacaran‐Cambrian sedimentary rocks of western SCB reveal age populations of 2.51, 1.85, 1.20, 0.80, and 0.52 Ga. Detrital zircon age spectra indicate a major tectonic transition for the SCB during 0.56–0.54 Ga, interpreted to reflect the beginning of the collision between SCB‐Indochina and NW India blocks. The collisional event lasted until early Ordovician, leading to the suturing of the SCB‐Indochina to the northern margin of East Gondwana.
Plain Language Summary
The South China Block is thought to be a part of the Gondwana superterrane, which was composed of more than half of all continents 650–400 million years ago (Ma). However, questions of when and how the South China Block collided with Gondwana are yet to be answered. In this study, we conducted provenance analyses of sedimentary rocks whose depositional ages were known via radioisotopic dating and chemo‐biostratigraphy in the western South China Block. The results reveal a change in tectonic setting of the South China Block at 560–540 Ma, interpreted as the onset of the collision between the South China Block and India along the northern margin of East Gondwana.
Key Points
1.2‐Ga detrital zircon population is present in age‐calibrated Ediacaran‐Cambrian strata of western South China Block
A major change in tectonic setting of the South China Block occurred in 0.56–0.54 Ga
The connection between the South China Block and NW India Block started in the late Ediacaran
Mantle melts provide a window on processes related to global plate tectonics. The composition of chromian spinel (Cr-spinel) from mafic-ultramafic rocks has been widely used for tracing the ...geotectonic environments, the degree of mantle melting and the rate of mid-ocean ridge spreading. The assumption is that Cr-spinel's core composition (Cr# = Cr/(Cr + Al)) is homogenous, insensitive to post-formation modification and therefore a robust petrogenetic indicator. However, we demonstrate that the composition of Cr-spinel can be modified by fluid/melt-rock interactions in both sub-arc and sub-mid oceanic mantle. Metasomatism can produce Al-Cr heterogeneity in Cr-spinel that lowers the Cr/Al ratio, and therefore modifies the Cr#, making Cr# ineffective as a geotectonic and mantle melting indicator. Our analysis also demonstrates that Cr-spinel is a potential sink for fluid-mobile elements, especially in subduction zone environments. The heterogeneity of Cr# in Cr-spinel can, therefore, be used as an excellent tracer for metasomatic processes.
The South China Block, consisting of the Yangtze and the Cathaysia blocks, is one of the largest Precambrian blocks in eastern Asia. However, the early history of the Cathaysia Block is poorly ...understood due largely to intensive and extensive reworking by Phanerozoic polyphase orogenesis and magmatism which strongly overprinted and obscured much of the Precambrian geological record. In this paper, we use the detrital zircon U–Pb age and Hf isotope datasets as an alternative approach to delineate the early history of the Cathaysia Block. Compilation of published 4041 Precambrian detrital zircon ages from a number of (meta)sedimentary samples and river sands exhibits a broad age spectrum, with three major peaks at ~2485Ma, ~1853Ma and ~970Ma (counting for ~10%, ~16% and ~24% of all analyses, respectively), and four subordinate peaks at ~1426Ma, ~1074Ma, ~780Ma and ~588Ma. Five of seven detrital zircon age peaks are broadly coincident with the crystallisation ages of ~1.89–1.83Ga, ~1.43Ga, ~1.0–0.98Ga and ~0.82–0.72Ga for known igneous rocks exposed in Cathaysia, whereas, igneous rocks with ages of ~2.49Ga and ~0.59Ga have not yet been found. The Hf isotopic data from 1085 detrital zircons yield Hf model ages (TDMC) between ~4.19Ga and ~0.81Ga, and the calculated εHf(t) values between −40.2 and 14.4. The Archean detrital zircons are exclusively oval in shape with complicated internal textures, indicating that they were sourced by long distance transportations and strong abrasion from an exotic Archean continent. In contrast, the majority of detrital zircons in age between ~1.9 and ~0.8Ga are euhedral to subhedral crystals, indicative of local derivation by short distance transportations from their sources. The oldest crustal basement rocks in Cathaysia were most likely formed by generation of juvenile crust and reworking of recycled Archean components in Late Paleoproterozoic at ~1.9–1.8Ga, rather than in the Archean as previously speculated. Reworking and recycling of the continental crust are likely the dominant processes for the crustal evolution of Cathaysia during the Mesoproterozoic to Neoproterozoic time, with an intervenient period of significant generation of juvenile crust at ~1.0Ga.
Precambrian crustal evolutions of the Cathaysia Block are genetically related to the supercontinent cycles. By comparing detrital zircon data from Cathaysia with those for other continents, and integrating multiple lines of geological evidence, we interpret the Cathaysia Block as an orogenic belt located between East Antarctica, Laurentia and Australia during the assembly of supercontinent Columbia/Nuna at ~1.9–1.8Ga. The Cathaysia Block amalgamated with the Yangtze Block to form the united South China Block during the Sibao Orogeny at ~1.0–0.89Ga. The Laurentia–Cathaysia–Yangtze–Australia–East Antarctica connection gives the best solution to the paleo-position of Cathaysia in supercontinent Rodinia. The significant amount of ~0.6–0.55Ga detrital zircons in Cathaysia and West Yangtze have exclusively high crustal incubation time of >300Ma, indicating crystallisation from magmas generated dominantly by crustal reworking. This detrital zircon population compares well with the similar-aged zircon populations from a number of Gondwana-derived terranes including Tethyan Himalaya, High Himalaya, Qiangtang and Indochina. The united South China–Indochina continent was likely once an integral part of Gondwanaland, connected to northern India by a “Pan-African” collisional orogen.
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•Cathaysia Block formed at ~1.9-1.8Ga, rather than in Archean.•Archean detrital zircons found in Cathaysia were likely sourced from East Antarctica.•Cathaysia locates between E. Antarctica, Laurentia and Australia in Columbia/Nuna.•South China most likely locates in the interior, but not on fringe, of Rodinia.•South China connects with Northern India by a “Pan-African” collisional orogeny.
Whether or not mantle plumes and plate subduction are genetically linked is a fundamental geoscience question that impinges on our understanding of how the Earth works. Late Cenozoic basalts in ...Southeast Asia are globally unique in relation to this question because they occur above a seismically detected thermal plume adjacent to deep subducted slabs. In this study, we present new Pb, Sr, Nd, and Os isotope data for the Hainan flood basalts. Together with a compilation of published results, our work shows that less contaminated basaltic samples from the synchronous basaltic eruptions in Hainan–Leizhou peninsula, the Indochina peninsula and the South China Sea seamounts share the same isotopic and geochemical characteristics. They have FOZO-like Sr, Nd, and Pb isotopic compositions (the dominant lower mantle component). These basalts have primitive Pb isotopic compositions that lie on, or very close to, 4.5- to 4.4-Ga geochrons on 207Pb/204Pb versus 206Pb/204Pb diagram, suggesting a mantle source developed early in Earthʼs history (4.5–4.4 Ga). Furthermore, our detailed geochemical and Sr, Nd, Pb and Os isotopic analyses suggest the presence of 0.5–0.2 Ga recycled components in the late Cenozoic Hainan plume basalts. This implies a mantle circulation rate of >1 cm/yr, which is similar to that of previous estimates for the Hawaiian mantle plume. The identification of the ancient mantle reservoir and young recycled materials in the source region of these synchronous basalts is consistent with the seismically detected lower mantle-rooted Hainan plume that is adjacent to deep subducted slab-like seismic structures just above the core–mantle boundary. We speculate that the continued deep subduction and the presence of a dense segregated basaltic layer may have triggered the plume to rise from the thermal–chemical pile. This work therefore suggests a dynamic linkage between deep subduction and mantle plume generation.
•Late Cenozoic basalts in Southeast Asia display primitive Sr, Nd and Pb isotopes.•Coexistence of a 4.5–4.4 Ga-old reservoir and a minor young recycled component.•Support dynamic linkages between deep subduction and mantle plume generation.
It has been widely accepted that an active continental margin existed along the coast of Southeast China during the Mesozoic time that produced extensive magmatism in the region. However, there is ...little constraint as to when this active margin was first initiated. Here we present new SHRIMP U‐Pb zircon ages and geochemical and Sr‐Nd isotopic data for syntectonic granites on Hainan Island. Our data demonstrate that these rocks, dated at 267–262 Ma, are typical of calc‐alkaline I‐type granites formed in continental arc environments. The age of this magmatic arc coincides with a sudden change in sedimentary environments in South China during the Permian time, suggesting that the South China Indosinian Orogeny was likely contemporaneous with the onset of continental arc magmatism.
Cleavage of transfer (t)RNA and ribosomal (r)RNA are critical and conserved steps of translational control for cells to overcome varied environmental stresses. However, enzymes that are responsible ...for this event have not been fully identified in high eukaryotes. Here, we report a mammalian tRNA/rRNA-targeting endoribonuclease: SLFN13, a member of the Schlafen family. Structural study reveals a unique pseudo-dimeric U-pillow-shaped architecture of the SLFN13 N'-domain that may clamp base-paired RNAs. SLFN13 is able to digest tRNAs and rRNAs in vitro, and the endonucleolytic cleavage dissevers 11 nucleotides from the 3'-terminus of tRNA at the acceptor stem. The cytoplasmically localised SLFN13 inhibits protein synthesis in 293T cells. Moreover, SLFN13 restricts HIV replication in a nucleolytic activity-dependent manner. According to these observations, we term SLFN13 RNase S13. Our study provides insights into the modulation of translational machinery in high eukaryotes, and sheds light on the functional mechanisms of the Schlafen family.
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