Once widely accepted, the existence of Pannotia as an Ediacaran supercontinent has come into question. In the context of the supercontinent cycle, this development is of fundamental importance since the existence (or not) of Pannotia is central to the nature, duration and evolution of the cycle, and dictates the cycle's geodynamic pathway from the break-up of Rodinia to the amalgamation of Pangaea. Contributing to the growing scepticism in Pannotia, geochronology suggests the putative landmass had begun to break up before it was fully assembled, palaeomagnetic data for the Ediacaran are notoriously equivocal, and the proxy signals of Ediacaran–Cambrian supercontinent amalgamation and break-up, although collectively compelling, can be individually challenged. Efforts to detect the mantle legacy expected of supercontinent tenure, however, support large-scale mantle upwelling in the wake of Pannotia amalgamation. Hence, whether or not it was a supercontinent, its assembly appears to have influenced global mantle convection patterns in a manner consistent with one. This raises the question of whether a full-scale supercontinent is needed as a geodynamic driver of the supercontinent cycle and, if not, whether other such turnovers in mantle convection are manifest in the geological record, and whether the cycle more accurately reflects cycles in mantle convection.

The Neoproterozoic Arabian-Nubian Shield (ANS) is one of the largest juvenile crustal provinces on Earth, providing a natural laboratory for investigating the processes of continental crust formation and stabilization. Although arc accretion is widely regarded as a key mechanism of crustal growth in the ANS, the subsequent transformation of juvenile terranes into stable continental lithosphere remains poorly constrained. Here, we present integrated geochemical, Sr-Nd isotopic, and in-situ zircon U-Pb-Hf-O data from the Ranga volcanic suite to evaluate the tectono-magmatic evolution of the late Neoproterozoic ANS. The Ranga volcanic rocks are bimodal with a tholeiitic affinity and yield a crystallization age of -585 Ma. The mafic rocks are characterized by low SiO2 (49.8-54.1 wt%), high MgO (5.9-9.4 wt%), a negligible Eu anomaly (1.05-1.22), low initial 87Sr/86Sr ratios (0.702829-0.703946), and positive 8Nd(t) (+6.39 to +7.84), indicate that the mafic rocks formed through fractional crystallization of melts derived from a juvenile depleted source. The felsic rocks display high SiO2 (72.5-78.9 wt%), low MgO (0.3-1.4 wt%), a negative Eu anomaly (0.50-0.79), low initial 87Sr/86Sr ratios (0.702994-0.703364), positive 8Nd(t) (+5.94 to +7.13), zircon 8Hf(t) (+7.38 to +15.14) values, and zircon delta 18O signatures (4.37-6.18 parts per thousand), consistent with partial melting of hydrothermally altered, MORB-like lithosphere. These results highlight juvenile magmatism and reworking of pre-existing juvenile crust as key drivers in the stabilization and maturation of juvenile crust within the ANS. Collectively, these data define an autogenic, twostep pathway in which juvenile arc addition is followed by intracrustal melting to yield felsic additions converting juvenile provinces into stable continents, a process likely widespread across accretionary orogens.

Composite intrusions are incrementally constructed over thousands to tens of millions of years. Emplacement of the Donegal composite batholith in NW Ireland was syn- and post-kinematic with respect to the terminal phases of the Caledonian orogeny ( c. 437–415 Ma) in a slab-failure tectonic setting. Published laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U–Pb data from zircon and titanite indicate emplacement occurred between c. 430 and 400 Ma. Here, we use chemical abrasion isotope dilution thermal ionization mass spectrometry (CA-ID-TIMS) to precisely date zircon from three samples; weighted mean 206 Pb/ 238 U dates are 426.77 ± 0.11 (Ardara pluton), 414.71 ± 0.11 (Main Donegal pluton) and 414.25 ± 0.11 Ma (Thorr pluton). Collectively, U–Pb dates from the Donegal composite batholith support interpretations indicating a prolonged and dynamic magma emplacement spanning at least 12 Ma. The new CA-ID-TIMS dates are equivalent to published LA-ICP-MS dates from the same samples. Taken together, these data indicate pulsed batholith emplacement commenced by c. 437 Ma with the emplacement of the appinite suite and associated lamprophyres. By c. 400 Ma, magmatism terminated with the emplacement of the latest phases of the Main Donegal pluton and the Trawenagh Bay pluton.

Late Paleozoic convergence between Gondwana and Laurussia culminated in terminal collisions that produced the Ouachita-Alleghanian-Mauritanian-Variscan orogen within the interior of Pangea. The evolution and architecture of this orogen was profoundly influenced by a series of ca. 400-300 Ma promontory collisions, which terminated 100 m.y. of subduction and terrane accretion along the Laurussian margin and passive margin sedimentation along the Gondwanan margin. These promontory collisions compartmentalized the orogen into several domains with very different subsequent tectonic evolutions. In Europe, the Variscan belt records coeval collisional (e.g. Iberian massif) and “Mediterranean-style” orogens (e.g. Bohemian massif). The former are characterized by crustal thickening, followed by extensional collapse. The latter occur in re-entrants and are characterized by complex orogenic collages of limited lateral extent produced by the opening and closing of ephemeral oceans. This collage includes the products of subduction of varying polarities within these oceans and accretionary collisions of local significance that preceded terminal collision. Late-stage orogenic processes are characterized by the formation of oroclines, extensional collapse, and the transition to Tethyan tectonics. Because part of the Laurentian-Mauritanide domains were located to the southwest of the promontory collisions, remnants of the Rheic Ocean persisted between them and their respective evolutions, as recorded in the Appalachian belt, are dominated by Andean-style orogenesis that preceded terminal collision. The geodynamic driver of Pangea amalgamation, by the Appalachian-Mauritanide-Variscan orogen, is consistent with the principles of orthoversion. In other collisional orogens, determining when geological continuity along converging continental margins gives way to compartmentalization may likewise document when promontory collisions have occurred.

This paper presents new U-Pb detrital zircon ages that constrain the age of deposition of a Cadomian intra-arc succession (Stechovice Group in the Bohemian Massif) overlying one of the best preserved volcanic arcs (Davle volcanic complex) of the Avalonian-Cadomian belt, which rimmed the northern margin of Gondwana in the Neoproterozoic to Cambrian. The record of this active margin is well preserved, but how subduction terminated along it remains a matter of debate. Our new data from the Stechovice Group suggest abrupt arc termination in this region followed by turbidite deposition in a short-lived basin at around 570 Ma. However, the ages of voluminous arc-derived graywackes in a neighbouring accretionary wedge suggest arc magmatism continued until ca. 527 Ma. Regional gravity highs inboard of the Davle volcanic arc indicate the presence of unexposed dense rocks that may represent the missing, post-570 Ma Cadomian arc. If so, the arc axis migrated landward, consistent with the presence of intrusive boninites within the older Davle arc, which would have then occupied a fore-arc position and must have been eroded and submerged prior to the deposition of Stechovice Group. We suggest that the inferred arc migration beginning at around 570 Ma occurred in response to slab flattening due to the arrival of hotter oceanic lithosphere, perhaps in the form of a spreading ridge that migrated eastwards along the Avalonian-Cadomian active margin leaving a dextral transform margin in its wake. Such a ridge is thought to have first impinged on Avalonia to the west at around 600 Ma and later caused arc extinction in the Armorican Massif and Saxothuringian unit at around 570 Ma, with arc migration in the Bohemian Massif at about the same time. The ridge-trench interaction is then inferred for the Bohemian Massif in the early to middle Cambrian (at ca. 527-515 Ma), consistent with ongoing subduction in the more easterly proto-Alps until the mid-Ordovician. How the inferred migration of the ridge-trench-transform system was linked to the movement of Baltica, and whether it could have brought Baltica close enough to supply Mesoproterozoic detritus to Gondwana's northern periphery remain open questions.

Pressure-temperature arrays from several iconic continental arc granitoid batholiths define cool, hydrous adiabatic ascent paths extending to depths >60 km, constrained between the 5 and 15 wt% H2O granite liquidus curves. These paths differ significantly from those of many volcanic arc magmas, which typically form by mantle decompression melting during normal steep subduction. The Cretaceous Fiordland arc, New Zealand, preserves a deep crustal hot zone (DCHZ) of hydrous hornblende gabbros and diorites that was thickened during ongoing magmatism and burial to depths of 50-60 km. Published tomographic imaging suggests that this mantle-dominated (stage 1) magmatic flareup coincided with a transition from normal to flat-slab subduction, which ultimately terminated Fiordland magmatism. In other continental arcs, the return to normal subduction mode (slab steepening) restores normal-thickness (~30-35 km) arc crust. This process destroys the thickened DCHZ through hydrous fluxed melting, generating superhydrous granitoid arc magmas during a crust-dominated (stage 2) flareup. Dense garnet-pyroxenite initially forms as a residue but is progressively removed by vigorous corner flow in the mantle wedge. Once lower-crustal, hydrous fluxed melting is established, ascending granitoid magmas remain cool and near water saturated because water is incrementally degassed as pressure decreases, which explains the high H2O content in many arc melt inclusions. This hydrous melting mechanism establishes cool, transcrustal continental arc batholiths even when episodically rejuvenated by hot, hydrous mafic infusions during mantle decompression melting, which again dominates crustal heat transfer (but not granitoid magma temperature) as the mantle wedge reopens during the transition back to normal-mode subduction.

The Antigonish Highlands form part of Avalonia in mainland Nova Scotia and are predominantly underlain by ca. 620–600 Ma low grade Neoproterozoic arc-related volcanic and sedimentary rocks and coeval plutons. The highlands also preserve a record of magmatism that spans much of the Ordovician (ca. 495–455 Ma), during which time Avalonia drifted from the northern Gondwanan margin and migrated as a microcontinent ca. 2000 km northward before becoming involved in collisions with Baltica and Laurentia in the Silurian to Devonian. The longevity of Ordovician magmatism (ca. 50 Ma) is consistent with a subduction-related environment, a setting that is compatible with most paleogeographic reconstructions. However, the continental tholeiitic-alkalic within-plate affinity of the mafic rocks and the A-type signature of the felsic rocks is more typical of a back-arc setting, rather than that of a typical arc. Furthermore, the A-type felsic rocks were derived from a hotter, drier lower crust than is typical for felsic arc magmas. Whole-rock Sm-Nd isotopic data for both mafic and felsic compositions lie within previously delineated tightly constrained envelopes that define, respectively, the evolution of the Avalonian and sub-continental lithospheric mantle (SCLM), and crustal sources. These data imply that (i) the crust remained coupled to SCLM from the rifting of Avalonia from Gondwana to its accretion to Baltica in the Silurian and to Laurentia in the Early Devonian, and (ii) the Antigonish Highlands were located far from the subduction zone(s) that closed the Iapetus Ocean as it migrated northward, and so were only mildly affected by the resulting collisions.

Appinite plutonic rocks range from ultramafic to felsic in composition, are characterized by idiomorphic hornblende as the dominant mafic mineral in all lithologies, and by spectacularly diverse textures, including planar and linear magmatic fabrics, multiple comb layers, mafic pegmatites and widespread evidence of mingling between mafic and felsic compositions. These features suggest that they are anomalously water-rich mafic magmas. The ca. 607 Ma Greendale Complex in the Antigonish Highlands of Nova Scotia is typical of appinite complexes which commonly occur as small (~2 km diameter) plutons adjacent to major deep crustal faults along the periphery of voluminous granitoid plutons emplaced in the waning stages of regional arc activity. Isotopic data from hornblendes in the Greendale Complex yield δD values ranging from -61 to -72 and δO18 from 3.7 to 7.0, indicating the water in the appinite magma has a strong mantle component. These data suggest the appinites may represent aliquots of hydrous basaltic magma derived from mafic underplates originally emplaced along the base of the crust during protracted subduction. Transfer of heat and fluids to the base of the crust triggered generation of coeval (615-604 Ma) granitoid magmas by partial melting in the overlying MASH zone. The granitoid magmas were emplaced in the shallow crust when transient stresses activated favourably-oriented structures which became conduits for magma transport. The ascent of late mafic magmas within the Antigonish Highlands was impeded by the rheological barriers created by the structurally overlying granitoid magma bodies. Magmas that form the Greendale Complex evaded those rheological barriers because they preferentially exploited the deep crustal Hollow Fault that bounded the plutonic system.Collectively, these mineralogical, textural and geochemical features suggest a complex magmatic history involving repeated water saturation episodes within the plumbing system as mafic, mantle-derived magmas ascended and differentiated at mid-to-upper crustal levels (ca. 3-5 kbar). More generally, the most mafic components of appinite complexes may provide a window into the composition of the mafic underplate and insights into processes that generate granitoid batholiths and crustal growth in arc systems.

Background High-severity burned areas can have lasting impacts on vegetation regeneration, carbon dynamics, hydrology, and erosion. Landscape models can predict erosion from burned areas using the differenced normalized burn ratio (dNBR), but so far post-fire erosion modelling has been limited to areas that already burned. Here, we developed and validated a predictive burn severity model that produces continuous dNBR predictions for recently unburned forest land in Utah. Results Vegetation productivity, elevation and canopy fuels were the most important predictor variables in the model, highlighting the strong control of fuels and vegetation on burn severity in Utah. Final model out-of-bag R2 was 67.1%, residuals showed a correlation coefficient of 0.89 and classification accuracy into three classes was 85%. We demonstrated that dNBR can be empirically modeled relative to fuels and topography and found burn severity was highest in productive vegetation and at relatively cooler sites. Conclusions We found that prediction accuracy was higher when fuel moisture was lower, suggesting drier weather conditions drive more consistent and predictable burn severity patterns across a range of burn severity, vegetation types and geographic locations. Moreover, burn severity predictions from this model can be used to inform hydro-erosion models and subsequent management actions aimed at reducing burn severity and post-wildfire erosion risks.

Neoproterozoic snowball Earth events reflect globally frigid conditions thought to have stimulated changes in geochemical cycling with planetary biotic response. We investigated the impact of these events on sediment dynamics, focusing on the detrital zircon record within the Dalradian Supergroup of Scotland and Ireland. Utilizing U-Pb detrital zircon ages, we analyzed changes in sediment provenance throughout the stratigraphy via bootstrapped variance metrics. The coefficient of variance for the detrital zircon load exhibits a first-order increase stratigraphically upward, with marked changes at glaciogenic layers. Points of increased variance align with inputs of older detritus compared to lower, preglacial stratigraphic levels, suggesting intensified erosion and downcutting linked to wet-based glacial activity, with postglacial sediment redistribution. Average detrital zircon apparent density also changes through the stratigraphy, with implications for uranium cycling from the continents into the oceans. While early Ediacaran shale geochemistry implies postglacial oceanic oxygenation, loss of proportionally more uranium-rich detrital zircon across glaciogenic layers suggests that modification to continental weathering also fundamentally contributed to Neoproterozoic geochemical shifts.

We propose that the 495-470 Ma Ollo de Sapo magmatism in the Iberian Massif was the result of a mantle plume event in the Furongian-Early Ordovician. This plume was located beneath the northwestern margin of Gondwana and caused rapid and extensive melting of Ediacaran arc-related crustal rocks and their derived sediments. Mafic magmas due to plume partial melting underplated the crust and were emplaced at mid-lower crustal levels (similar to 15km), and provided the heat for crustal melting. Manifestations of the plume include (i) pronounced magnetic anomalies in the region which match the distribution of Ollo de Sapo rocks, (ii) the Toledanian unconformity (and gap), which is attributed to thermal doming, and (iii) the significant thickness variations in Lower to Middle Ordovician sedimentary successions in adjacent areas. In a more regional context, we infer that the plume was one of a cluster of plumes impacting the Gondwana periphery and that it contributed to the birth and development of the Rheic Ocean throughout Gondwana margin breakup.

Using Gondwana as an example, we show how the geological record can be interrogated to detect significant changes in mantle convection patterns at critical junctures in Earth's evolution. Evidence of major changes in mantle circulation in the aftermath of late Neoproterozoic-early Paleozoic Gondwana assembly is provided by widespread (i) plume-related magmatism around Gondwana's periphery, (ii) ironstone deposits related to mantle plume-ocean ridge interaction and enhanced hydrothermal activity, and (iii) super-mature clastic deposits that reflect epeirogenic uplift triggered by mantle upwelling beneath Gondwana combined with deep tropical weathering. In our model, Gondwana assembled above a region of mantle downwelling in which subducted slabs between the converging Gondwanan continents descended to the core-mantle boundary. Renewed subduction along Gondwana's periphery yielded early arc magmas. But as downwelling beneath Gondwana evolved into upwelling as a result of the ponding of subducted slabs at the base of the mantle, mantle plumes rose from the margins of the nascent upwelling to interact with the edges of Gondwana, where they penetrated the peripheral subduction zones via slab windows, tears and transform faults to generate voluminous calc-alkalic crustal melts in hydrated arc regions and A-type magmas in dry back-arc regions. The plumes also underplated oceanic lithosphere and interacted with adjacent ocean ridges, thereby enhancing hydrothermal activity and the flux of bioessential nutrients, leading to the recurrence of marine iron-rich sedimentary rocks in the geological record. At the same time, upwelling beneath a tropical to equatorial Gondwana led to epeirogenic uplift, deep weathering and erosion, resulting in the production of widespread super-mature clastic deposits. We contend that major changes in mantle convection patterns were encoded into the geological record of Gondwana assembly, influenced global-scale mantle convection patterns, and should be incorporated into geodynamic models for the assembly of Pangea. (c) 2023 Published by Elsevier B.V. on behalf of International Association for Gondwana Research.

Geodynamic models for Pangaea assembly require knowledge of Paleozoic mantle convection patterns. Application of basic geodynamic principles to Neoproterozoic-Paleozoic plate reconstructions yields Pangaea in the incorrect configuration (predicting that it should have formed by consumption of the exterior palaeo-Pacific Ocean instead of the Iapetus, Rheic and Proto-Tethys oceans). We contend that the mantle legacy of Late Neoproterozoic-Cambrian amalgamation of Gondwana must be factored into models for Pangaea amalgamation. Proxy data suggest that the mantle downwelling driving Pan-African collisions and Gondwana assembly evolved into a mantle upwelling as evidenced by the interplay between subduction-related and plume-related tectonics around the periphery of Gondwana. Orthoversion theory, whereby a supercontinent assembles c. 90 degrees away from the centre of the previous supercontinent, suggests that Gondwana amalgamated above an intense downwelling along a meridional subduction girdle that bisected two antipodal sub-equatorial upwellings. Several processes beneath and around Gondwana reduced the intensity of the original downwelling, as evidenced by plume-related activity along its margins, initiation of subduction zone rollback, and the export of terranes from Gondwana that collided with the margin of Laurentia-Baltica. As upwelling beneath it intensified, Gondwana migrated along the girdle until it collided with Laurentia-Baltica, resulting in the final assembly of Pangaea.

Abstract. Watershed disturbances can have broad, long-lasting impacts that result in a range of streamflow response. Increasing disturbance regimes, particularly from wildfire, is a growing concern for watershed management. The influence of watershed disturbances on rainfall-runoff patterns has proved challenging to isolate from undisturbed streamflow variability due to the role of hydrologic controls that vary through time, including water year type, seasonality, and antecedent precipitation. To better assess the influence of watershed disturbance on rainfall-runoff event patterns we developed the Rainfall-Runoff Event Detection and Identification (RREDI) toolkit. The RREDI toolkit is a novel time-series event separation method that automates the pairing and attribution of precipitation and streamflow events, leveraging and building on existing event separation methods. A rainfall-runoff event dataset of 5042 events was generated by the RREDI toolkit from a collection of nine western US study watersheds spanning a range of streamflow regimes, watershed properties, and burn characteristics. Through analyzing the rainfall-runoff event dataset, we found that water year type and season were significant controls on rainfall-runoff metrics. The significance of antecedent precipitation was variable between watersheds, indicating a more complex relationship for this control. The watershed-specific permutations of significant controls resulted in unique significant condition group trends in the rainfall storm depth and peak runoff relationship in two contrasting watersheds. In general, for each of the significant condition groups post-fire peak runoff was higher than undisturbed peak runoff except during winter in snow-dominated watersheds. Consideration of the time-varying hydrologic controls, particularly water year type and season, were identified as important when untangling the influence of wildfire on the rainfall-runoff patterns. The RREDI toolkit can be further applied to investigate the influence of other watershed disturbances and controls to increase understanding of rainfall-runoff patterns across the landscape.