Unraveling the New England orocline, east Gondwana accretionary margin

The New England orocline lies within the Eastern Australian segment of the Terra Australis accretionary orogen and developed during the late Paleozoic to early Mesozoic Gondwanide Orogeny (310–230 Ma) that extended along the Pacific margin of the Gondwana supercontinent. The orocline deformed a pre-Permian arc assemblage consisting of a western magmatic arc, an adjoining forearc basin and an eastern subduction complex. The orocline is doubly vergent with the southern and northern segments displaying counter-clockwise and clockwise rotation, respectively, and this has led to contrasting models of formation. We resolve these conflicting models with one that involves buckling of the arc system about a vertical axis during progressive northward translation of the southern segment of the arc system against the northern segment, which is pinned relative to cratonic Gondwana. Paleomagnetic data are consistent with this model and show that an alternative model involving southward motion of the northern segment relative to the southern segment and cratonic Gondwana is not permissible. The timing of the final stage of orocline formation (~270–265 Ma) overlaps with a majorgap in magmatic activity along this segment of the Gondwana margin, suggesting that northward motion and orocline formation were driven by a change from orthogonal to oblique convergence and coupling between the Gondwana and Pacific plates

Neoproterozoic to early Paleozoic extensional and compressional history of East Laurentian margin sequences: The Moine Supergroup, Scottish Caledonides

Neoproterozoic siliciclastic-dominated sequences are widespread along the eastern margin of Laurentia and are related to rifting associated with the breakout of Laurentia from the supercontinent Rodinia. Detrital zircons from the Moine Supergroup, NW Scotland, yield Archean to early Neoproterozoic U-Pb ages, consistent with derivation from the Grenville-Sveconorwegian orogen and environs and accumulation post–1000 Ma. U-Pb zircon ages for felsic and associated mafic intrusions confirm a widespread pulse of extension-related magmatism at around 870 Ma. Pegmatites yielding U-Pb zircon ages between 830 Ma and 745 Ma constrain a series of deformation and metamorphic pulses related to Knoydartian orogenesis of the host Moinerocks. Additional U-Pb zircon and monazite data, and 40Ar/39Ar ages for pegmatites and host gneisses indicate high-grade metamorphic events at ca. 458–446 Ma and ca. 426 Maduring the Caledonian orogenic cycle.The presence of early Neoproterozoic silici clastic sedimentation and deformation in the Moine and equivalent successions around the North Atlantic and their absence along strike in eastern North America reflect contrasting Laurentian paleogeography during the breakup of Rodinia. The North Atlantic realm occupied an external location on the margin of Laurentia, and this region acted as a locus for accumulation of detritus (Moine Supergroup and equivalents) derived from the Grenville-Sveconorwegian orogenic welt, which developed as a consequence of collisional assembly of Rodinia. Neoproterozoic orogenic activity corresponds with theinferred development of convergent platemargin activity along the periphery of the supercontinent. In contrast in eastern North America, which lay within the internal parts of Rodinia, sedimentation did not commence until the mid-Neoproterozoic (ca. 760 Ma) during initial stages of supercontinent fragmentation. In the North Atlantic region, this time frame corresponds to a second pulse of extension represented by units such as the Dalradian Supergroup, which unconformably overlies the predeformed Moine succession

Linking collisional and accretionary orogens during Rodinia assembly and breakup: Implications for models of supercontinent cycles

Periodic assembly and dispersal of continental fragments has been a characteristic of the solid Earth for much of its history. Geodynamic drivers of this cyclic activity are inferred to be either top-down processes related to near surface lithospheric stresses at plate boundaries or bottom-up processes related to mantle convection and, in particular, mantle plumes, or some combination of the two. Analysis of the geological history of Rodinian crustal blocks suggests that internal rifting and breakup of the supercontinent were linked to the initiation of subduction and development of accretionary orogens around its periphery. Thus, breakup was a top-down instigated process. The locus of convergence was initially around north-eastern and northern Laurentia in the early Neoproterozoic before extending to outboard of Amazonia and Africa, including Avalonia–Cadomia, and arcs outboard of Siberia and eastern to northern Baltica in the mid-Neoproterozoic (~760 Ma). The duration of subduction around the periphery of Rodinia coincides with the interval of lithospheric extension within the supercontinent, including the opening of the proto-Pacific at ca. 760 Ma and the commencement of rifting in east Laurentia. Final development of passive margin successions around Laurentia, Baltica and Siberia was not completed until the late Neoproterozoic to early Paleozoic (ca. 570–530 Ma), which corresponds with the termination of convergent plate interactions that gave rise to Gondwana and the consequent relocation of subduction zones to the periphery of this supercontinent. The temporal link between external subduction and internal extension suggests that breakup was initiated by a top-down process driven by accretionary tectonics along the periphery of the supercontinent. Plume-related magmatism may be present at specific times and in specific places during breakup but is not the prime driving force. Comparison of the Rodinia record of continental assembly and dispersal with that for Nuna, Gondwana and Pangea suggests grouping into two supercycles in which Nuna and Gondwana underwent only partial or no break-up phase prior to their incorporation into Rodinia and Pangea respectively. It was only after this final phase of assembly that the supercontinents then underwent full dispersal

SHORT EPISODES OF CRUST GENERATION DURING PROTRACTED ACCRETIONARY PROCESSES: EVIDENCE FROM CENTRAL ASIAN OROGENIC BELT, NW CHINA

continental crust but the spatial and temporal distribution of crust generation within individual orogens remains poorly constrained. Paleozoic (~540–270 Ma) granitic rocks from the Alati, Junggar and Chinese Tianshan segments of the Central Asian Orogenic Belt (CAOB) have markedly bimodal age frequency distributions with peaks of ages at ~400 Ma and 280 Ma for the Altai segment, and ~430 Ma and 300 Ma for the Junggar and Chinese Tianshan segments. Most of the magma was generated in short time intervals (~20–40 Ma), and variations in magma volumes and in Nd–Hf isotope ratios are taken to reflect variable rates of new crust generation within a long-lived convergent plate setting.Accretionary orogens are major sites of generation of continental crust but the spatial and temporal distribution of crust generation within individual orogens remains poorly constrained. Paleozoic (~540–270 Ma) granitic rocks from the Alati, Junggar and Chinese Tianshan segments of the Central Asian Orogenic Belt (CAOB) have markedly bimodal age frequency distributions with peaks of ages at ~400 Ma and 280 Ma for the Altai segment, and ~430 Ma and 300 Ma for the Junggar and Chinese Tianshan segments. Most of the magma was generated in short time intervals (~20–40 Ma), and variations in magma volumes and in Nd–Hf isotope ratios are taken to reflect variable rates of new crust generation within a long-lived convergent plate setting

Short episodes of crust generation during protracted accretionary processes

This study was supported by funding from the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (grant nos. XDB03010600 and XDB18020204), the National Natural Science Foundation of China (grant nos. 41202041, 41630208 and 41673033), the Key Program of the Chinese Academy of Sciences (QYZDJ-SSW-DQC026), the DREAM Program of China (No. 2016YFC0600407), talent project of Guangdong Province (2014TX01Z079), and GIG–CAS 135 project 135TP201601. PAC and CJH acknowledge support from the Natural Environment Research Council (grant NE/J021822/1). The senior author thanks the grant from the NSC, Taiwan, which supported his one-year academic visit at the NTU. This is contribution no. IS-2352 from GIG–CAS.Accretionary orogens are major sites of generation of continental crust but the spatial and temporal distribution of crust generation within individual orogens remains poorly constrained. Paleozoic (∼540–270 Ma) granitic rocks from the Alati, Junggar and Chinese Tianshan segments of the Central Asian Orogenic Belt (CAOB) have markedly bimodal age frequency distributions with peaks of ages at ∼400 Ma and 280 Ma for the Altai segment, and ∼430 Ma and 300 Ma for the Junggar and Chinese Tianshan segments. Most of the magma was generated in short time intervals (∼20–40 Ma), and variations in magma volumes and in Nd–Hf isotope ratios are taken to reflect variable rates of new crust generation within a long-lived convergent plate setting. The Junggar segment is characterized by high and uniform Nd–Hf isotope ratios (εNd(t) = +5  to  +8; zircon εHf(t) = +10  to  +16) and it appears to have formed in an intra-oceanic arc system. In the Altai and Chinese Tianshan segments, the Nd–Hf isotope ratios (εNd(t) = −7  to  +8; zircon εHf(t) = −16  to  +16) are lower, although they increase with decreasing age of the rock units. The introduction of a juvenile component into the Chinese Tianshan and Altai granitic rocks appears to have occurred in continental arc settings and it reflects a progressive reduction in the contributions from old continental lower crust and lithospheric mantle. Within the long-lived convergent margin setting (over ∼200 Ma), higher volumes of magma, and greater contributions of juvenile material, were typically emplaced over short time intervals of ∼20–40 Ma. These intervals were associated with higher Nb/La ratios, coupled with lower La/Yb ratios, in both the mafic and granitic rocks, and these episodes of increased magmatism from intraplate-like sources are therefore thought to have been in response to lithospheric extension. The trace element and Nd–Hf isotope data, in combination with estimates of granitic magma volumes, highlight that crust generation rates are strongly non-uniform within long-lived accretionary orogens. The estimated crust generation rates range from ∼0.1 to ∼40 km3/km/Ma for the Paleozoic record of the CAOB, and only comparatively short (20–40 Ma) periods of elevated magmatic activity had rates similar to those for modern intra-oceanic and continental arcs.PostprintPeer reviewe

Enhanced continental weathering and large igneous province induced climate warming at the Permo-Carboniferous transition

Tracking climate change and its relationships with chemical weathering and massive volcanic activity in deep-time greatly improves our understanding of the Earth's climate system. The Permo-Carboniferous period is a critical time interval with million year-scale glacial-deglacial cycles and massive basaltic volcanism, such as the Skagerrak-Centered (also named Skagerrak or Jutland) large igneous province. To explore the volcanism-climate interactions in this period, we obtained high precision CA-TIMS U-Pb zircon ages for three tuffaceous layers from a cored upper Pennsylvanian-lower Permian marginal marine succession in southern North China. These ages calibrate the Permo-Carboniferous biostratigraphy between ∼301–296 Ma in North China. From this dated core succession, mudrock samples and their calculated weathering index values were screened to constrain the weathering trends for the source landscapes and demonstrate a rapid increase with a subsequent decrease in source chemical weathering intensity during the period of ∼299 to 296.5 Ma. These trends coincide with the southern Gondwana glacial records, low latitude temperature changes, relative sea-level variations, and shifts in atmospheric pCO2 that together document an earliest Permian climate warming-cooling perturbation with a temperature maximum at ∼298 Ma. This climate warming in the Permo-Carboniferous icehouse correlates with the emplacement of the Skagerrak-Centered large igneous province, which likely released voluminous CO2 that led to climate warming during the Permo-Carboniferous transition. The immediately following cooling could possibly result from the rapid post-eruptional weathering of the massive basaltic rocks of this province in tropical latitudes, which would have sequestered atmospheric CO2 and promoted return to cooler icehouse conditions. This study supports the assertation that massive basaltic volcanism could first cause rapid climate warming and then may have an overall net cooling effect as previously suggested for the Deccan Traps and the Central Atlantic Magmatic Province

The Tonian Embu Complex in the Ribeira Belt (Brazil) : revision, depositional age and setting in Rodinia and West Gondwana

Funding: Conselho Nacional de Desenvolvimento Científico e Tecnológico – CNPq, grants 443439/2014-1 and 305074/2015-6, the Fundação de Amparo à Pesquisa do Estado de São Paulo – FAPESP, grant 2015/04487-7, and the Australian Research Council, grant FL160100168.The Embu Complex in the Neoproterozoic Ribeira Belt of Brazil provides a record of sedimentation associated with the Rodinia supercontinent and its subsequent deformation and metamorphism during assembly of West Gondwana. It is composed of a succession of variably migmatized pelitic schists and paragneisses, as well as minor calcsilicate rocks with quartzite intercalations, and orthogneiss. Detrital zircon U-Pb (LA-ICP-MS and SHRIMP) determinations for key samples of the Embu Complex in its type-area (West and Southwest of São Paulo City), and samples from neighboring units (Votuverava and São Roque groups) indicate distinct provenance histories and in combination with other data, discrete times of sediment accumulation. Detrital zircons from the Embu Complex are characterized by ages in the range 1500-1000 Ma and 2000-1700 Ma, with a very minor number of older ages. The youngest detrital grain is dated at 974 ± 12 Ma. Metamorphic zircon overgrowths range from 850 to 570 Ma with age peaks at ca. 820-790 and 650-570 Ma. Thus, the depositional age of the Embu Complex is constrained to 970-850 Ma. The detrital zircons of the Votuverava and São Roque groups are dominated by ages in the range 2200-2000 Ma, along with minor Paleoproterozoic and Archean ages. The youngest detrital grains are ∼1400 Ma (Votuverava Group) and ∼1750 Ma (São Roque Group). Metamafic rocks from the Votuverava Group have crystallization ages of ca. 1300 Ma, with a higher metamorphic grade amphibolite showing a range of discordant ages with upper and lower intercepts of 1300 Ma and ∼800 Ma, respectively. These results demonstrate that the Embu Complex was probably accreted to the Apiaí Terrane during a Tonian (820-790 Ma) orogenic event, prior to final development of the Ediacaran Ribeira belt arc-related magmatism and a transcurrent shear zone system. The main source area for detrital zircons of the Embu Complex is likely to be the Grenville-Sveconorwegian-Sunsás orogen or time-equivalent regions rather than the central portions of the neighboring cratons. The Embu Complex geological context is consistent with accumulation on the margin of the Rodinia supercontinent.PostprintPeer reviewe

From microanalysis to supercontinents: insights from the Rio Apa Terrane into the Mesoproterozoic SW Amazonian Craton evolution during Rodinia assembly

First published: 10 November 2021Deciphering the tectono-metamorphic evolution of Precambrian terranes can be difficult due to reworking by later superimposed events. Whole-rock elemental and isotopic geochemistry and zircon U–Pb geochronology are often employed in those studies, but these approaches are often not sensitive to the presence of multiple events and medium-grade metamorphic episodes. The Rio Apa Terrane (RAT), an allochthonous fragment of the Amazonian Craton, is a crustal block with a well-characterized evolution but with no detailed thermal constraints for its tectono-metamorphic evolution. In contrast to previous studies, we show the existence of four tectono-metamorphic events at c. 1780 Ma, c. 1625 Ma, c. 1420- 1340 Ma and c. 1300-1200 Ma on the basis of apatite, titanite and rutile U–Pb–REE, in-situ white-mica Rb-Sr and in-situ garnet Lu-Hf geochronology combined with mineral chemistry and phase-equilibria modelling. The c. 1780 Ma event is recorded in the basement of the Western domain, representing an extensional event coeval with the development of its Eastern domain in response to the retreat stage of the accretionary system. This is followed by juxtaposition of the Western and Eastern domains along a major crustal boundary at ca. 1625 Ma, which is defined by the magnetic profiles and zircon U–Pb-Hf data across the boundary. The third and fourth events correspond to progressive high-pressure/medium temperature (HP/MT) metamorphism, characterized by an anticlockwise P-T path, suggesting a convergent-to-collisional tectonic setting. The RAT was accreted to the adjoining Paraguá Terrane at c. 1420-1340 Ma under an isobaric P-T evolution spanning ~530 to 600 °C and ~10.0 kbar. Subsequently, the combined Rio Apa and Paraguá terranes collided with the SW Amazonian Craton at c. 1300-1200 Ma, reaching P-T conditions of ~560-580 °C and ~10.9- 11.7 kbar during crustal thickening. This study reveals for the first time the existence of a HP/MT metamorphic evolution related to the growth of the SW Amazonian Craton as part of an accretionary orogenic system during Rodinia assembly in the Paleo- to Mesoproterozoic.Bruno V. Ribeiro, Melanie A. Finch, Peter A. Cawood, Frederico M. Faleiros, Timothy D. Murphy, Alexander Simpson, Stijn Glorie, Mahyra Tedeschi, Robin Armit, Vitor R. Barrot

MicroRNA Controlled Adenovirus Mediates Anti-Cancer Efficacy without Affecting Endogenous MicroRNA Activity

MicroRNAs are small non-coding RNA molecules that regulate mRNA translation and stability by binding to complementary sequences usually within the 3′ un-translated region (UTR). We have previously shown that the hepatic toxicity caused by wild-type Adenovirus 5 (Ad5WT) in mice can be prevented by incorporating 4 binding sites for the liver-specific microRNA, mir122, into the 3′ UTR of E1A mRNA. This virus, termed Ad5mir122, is a promising virotherapy candidate and causes no obvious liver pathology. Herein we show that Ad5mir122 maintains wild-type lytic activity in cancer cells not expressing mir122 and assess any effects of possible mir122 depletion in host cells. Repeat administration of 2×1010 viral particles of Admir122 to HepG2 tumour bearing mice showed significant anti-cancer efficacy. RT-QPCR showed that E1A mRNA was down-regulated 29-fold in liver when compared to Ad5WT. Western blot for E1A confirmed that all protein variants were knocked down. RT-QPCR for mature mir122 in infected livers showed that quantity of mir122 remained unaffected. Genome wide mRNA microarray profiling of infected livers showed that although the transcript level of >3900 different mRNAs changed more than 2-fold following Ad5WT infection, less than 600 were changed by Ad5mir122. These were then filtered to select mRNAs that were only altered by Ad5mir122 and the remaining 21 mRNAs were compared to predicted mir122 targets. No mir122 target mRNAs were affected by Ad5 mir122. These results demonstrate that the exploitation of microRNA regulation to control virus replication does not necessarily affect the level of the microRNA or the endogenous mRNA targets