Featuring 3 000-km-long large and hot orogen, the Mantiqueira Province provides a rare opportunity to study the process of gravitational collapse at mid to deep crustal levels. Distinct but contemporary (similar to 500 Ma) post-collisional intrusions show structures and anisotropy of magnetic susceptibility (AMS) fabrics related to their emplacements, recording different flow patterns. In southern deep-seated intrusions, ellipsoidal-shaped roots with gabbroic-to-hybrid cores surrounded by granitic rocks show concentric patterns of AMS fabrics that cut across the NE-trending regional foliation. In contrast, northern intrusions, exposed as the upper sections of batholith-size bodies of coarse-grained granite emplaced at the shallow to mid-crust, show general NS-trending magnetic fabrics roughly parallel to strike of the orogen and the regional foliation of host rocks. These contrasting magnetic patterns from shallow to deeper crust suggest vertical magma migration from the overthickened orogenic core to be emplaced across its thinner stretched flanks during the gravitational collapse of the orogenic edifice.

Southwest Amazonia is proposed to have collided with southeast Laurentia during the Grenville orogeny. In Laurentia, the collision produced a continental-scale late Mesoproterozoic to early Neoproterozoic clastic wedge dominated by detrital zircon (DZ) sourced from Grenvillian magmatic rocks (major Geon 11 and 10, with minor Geon 13, 12, and 9 ages: the "Great Grenvillian Sedimentation Episode"). New DZ ages in clastic units from southwestern Brazil permit testing the hypothesis that Grenvillian sediment from southeast Laurentia spilled onto western Amazonia during Rodinian assembly. Late Mesoproterozoic arenites are dominated by Geons 18, 17, 15, 14, and 13 ages sourced from Amazonia basement provinces. Two samples exhibit major Geon 12 and 11 ages with minor Geon 18-13 ages. Geon 12 and 11 correspond to a conspicuous age gap in Amazonian magmatic events. Latest Neoproterozoic samples exhibit minor Geon 13 to 9 ages interpreted to be sourced from the Rondonia-San Ignacio or Sunsas provinces of western Amazonia. Late Neoproterozoic and Devonian age spectra exhibit multiple Amazonian age modes 2500 to 500 Ma but with no dominant modes. The age distributions for all samples indicate a lack of Laurentian Grenville sediment influx to southwest Amazonia during Rodinian assembly and breakup. The enigmatic Geon 12 ages are interpreted to corre-spond to a buried Andean source or the southwestern Grenville province in Laurentia. In contrast to exposed basement in southwestern Amazonia, Andean basement clastic sequences and Pleistocene to Recent Amazon River sediments exhibit Grenville dominance of DZ ages, strikingly similar to eastern Laurentia clastic systems. The Andean Grenville dominance may be accounted for by extensive Grenvillian crust beneath the Andean clastic wedge containing a major component of Geons 12, 11 and 10 magmatic rocks, and which was not being fully exhumed until the Neoproterozoic, similar to Laurentian Grenville.(c) 2022 Published by Elsevier B.V. on behalf of International Association for Gondwana Research.

ABSTRACT The Mesoproterozoic southeastern margin of Laurentia, which consisted primarily of the ca. 1.5–1.35 Ga Granite-Rhyolite Province, was extensively reworked during ca. 1.3–0.9 Ga phases of the Grenville orogenic cycle. Questions remain for much of southeastern Laurentia regarding the transition from the Granite-Rhyolite Province to Grenville orogenic cycle, and for potential collisional interaction with Amazonia, due to Paleozoic sedimentary cover or tectonic reworking. Basement rocks sampled by drill core in the east-central United States include 1.5–1.35 Ga magmatic rocks, some overprinted by late Geon 10 (Ottawan) orogenesis, which are the most outboard evidence of Granite-Rhyolite Province crust. Newly recognized 1.35–1.30 Ga (pre-Elzevirian) granitic orthogneisses within the Mars Hill terrane of southeastern Laurentia (1) expand the along-strike distribution of the earliest crustal age components of the Grenville orogenic cycle in Appalachian basement inliers; (2) contain Geon 19–16 inherited zircons; and (3) were metamorphosed during late Ottawan to Rigolet tectonism. Paragneisses enveloping the Geon 13 orthogneisses are dominated by Geon 19–16 and Geon 13–12 detrital zircons overgrown by Geon 10–9 metamorphic zircon. The zircon age systematics require the paragneiss protoliths to be younger than orthogneiss protoliths and be partly sourced from the latter. Orthogneisses and paragneisses have Pb isotope compositions that overlap those of south-central Appalachian and southwest Amazonia basement, both of which are distinct from Laurentian Pb isotope compositions. The boundary between Amazonian (southern Appalachian) and Laurentian (northern Appalachian) Pb isotope compositions is thus a terrane boundary, with Geon 13 magmatic rocks being the youngest common crustal component. In comparison, the Paraguá block of the southwestern margin of Amazonia consists of a Geon 19–16 basement complex intruded by the batholithic-scale Geon 13 San Ignacio granite suite. The latter also contains inherited Geon 19–16 zircon and has Pb isotope compositions that help define the Amazonian trend. The correspondence of magmatic, inherited, and detrital ages and similarity in Pb isotope compositions are consistent with an origin for the exotic/orphaned Mars Hill terrane as an outboard sliver of the Paraguá block that developed before Grenvillian orogenesis (Geons 12–9). Manifestations of the latter are concentrated around the margins of the Paraguá block in the Sunsás (southwest), Nova Brasilândia (north), and Aguapeí belts (east). The Sunsás belt is a mostly low-grade metasedimentary belt with only minor Geon 10–9 magmatism and no Geon 12 or 11 magmatism, thus distinguishing it from the Mars Hill terrane. The Arequipa-Antofalla terrane, exposed in Andes basement inliers, lies outboard of the Sunsás belt and has Pb isotope and geochronologic characteristics that permit a correlation with the Mars Hill terrane and a paleogeographic position between the Mars Hill terrane and the Sunsás belt. The histories of the Mars Hill terrane, Arequipa-Antofalla terrane, and Paraguá block merge during Geons 10–9 and final collisional orogenesis between southeast Laurentia and southwestern Amazonia.

We report evidence for Milankovitch cycles discovered in Middle Permian strata of the fluvial Abrahamskraal formation, lower Beaufort Group, in Karoo Basin of the Northern Cape Province, South Africa. Statistical analyses of ranked lithologies and of major element oxides have been used to obtain clusters of elements that capture lithological variations and reflect changes of the sedimentary environment through time. Spectral analysis of these elemental statistical groups reveal significant meter-scale sedimentary cycles of 67 m, 17.5 m, 5.9 m and 3.5-2.8 m, which can be interpreted as the sedimentary expression of astronomical forcing, based on the available estimate of sedimentation rate. The identified periods of short-eccentricity, precession and obliquity show a good match with those predicted for Middle Permian times, providing a data-based validation of the astronomical theory. Cycle counting integrated with available U-Pb dating, provides a cyclochronological calibration for Wordian normal magnetozones and, combined with radiometric ages, indicates an age of 266.5 +/- 0.26 Ma for the end of Kiaman superchron. Recognition of the orbitally driven sedimentation in Gondwana supercontinent suggest a global extension of astronomical influence of Permian climate and confirms empirical knowledge of Earth's astronomical parameters before 260 million years ago. The new data demonstrate a rare case of astronomically paced cyclicity in fluvial deposits and a unique cyclostratigraphic record of the Middle Permian Gondwana supercontinent whose sedimentation reflects orbitally-paced precipitation changes.

Despite their importance in constraining the dynamics of Gondwana's final phase of assembly, Cambrian paleomagnetic data from Gondwana are sparse. The Cambrian paleomagnetic dataset of Western Gondwana is especially poor, being defined by only a handful of poles. Here we contribute new Furongian paleomagnetic data from the similar to 500 Ma post-collisional, Santa Angelica and Venda Nova plutons from the southern portion of the Aracuai orogen in SE Brazil. The characteristic magnetization isolated from both plutons reveals two groups of directions that are demonstrated to be antipodal. On the basis of a thermal diffusion model, we attribute these antipodal directions to primary thermoremanent magnetizations acquired by cooling of the plutons in the presence of a reversing field. Together, paleomagnetic results from 35 sites distributed between the two plutons allows computation of a new similar to 500 Ma paleopole: 4.7 degrees. N, 332.2 degrees. E, A(95) = 4.06 and K = 68.82. This pole does not resemble any younger paleomagnetic poles either from Gondwana or the independent South American plate after the demise of Pangea, but instead closely corresponds to the Miaolingian and Furongian sector of reference apparent polar wander paths for Gondwana. It also agrees well with the limited existing individual early Paleozoic poles from Western Gondwana. Our new result may thus be regarded as a reference pole for Western Gondwana in Furongian time. Considerations of the Cambrian paleomagnetic data from Eastern and Western Gondwana suggest that while the supercontinent was amalgamated by similar to 500 Ma, there was likely significant motion between Eastern and Western Gondwana in earlier Cambrian time.

The Neoproterozoic-Paleozoic transition (similar to 541 Ma) was a turning point in Earth's history resulting in great biological changes between the microbial Precambrian life and the Ediacaran biotic revolution with the occupation of the sedimentary substrate, the dawn of biomineralization and the appearance of the earliest multicellular organisms. In parallel, this period is marked by a large plate reorganization leading to the assembly of Gondwana and by major climatic changes (extreme glacial events). Due in part to a poor paleomagnetic database for the different cratons in the Ediacarian-Cambrian times, the global paleogeography at that time remains controversial. In this study we present a new high-quality paleomagnetic pole (R = 7) for the Monteiro dyke swarm in the Borborema Province (NE Brazil) located at 18.2 degrees S and 344.9 degrees E (A95 = 11.7 degrees K = 9.3). They are fine-grained hornblende dolerite dated by U-Pb on zircon at similar to 538 Ma. Rock magnetic data indicate that magnetite and pyrrhotite are the main remanence carriers. Positive baked-contact tests support the primary remanence obtained for these dykes (19 sites). A positive reversal test (classified C) was also obtained from the 14 sites with negative inclination and the 5 sites with positive inclination, indicating that the paleosecular variation was eliminated. Our new key pole is not consistent with the classical apparent polar wander path of the Gondwana which consists of a long track from a southern polar position at similar to 590 Ma to an equatorial position at similar to 520 Ma, and suggests instead rapid and small oscillations of the APW, after the end of the large IITPW at ca. 560 Ma. These TPWs are supposedly caused by changes in the inertia tensor of the Earth due to internal mass redistribution, related to rapid changes in subduction velocity. Links of these rapid oscillations and the timing of the Cambrian radiation could be crucial to understand the early history of animal life.

In 40Ar/39Ar geochronology, excess Ar is 40Ar that does not derive from the in situ radioactive decay of K-40, or from the measurable input of atmospheric Ar, and results in increased daughter-parent ratios that correspond to anomalously old apparent dates without geological age significance. Excess 40Ar is commonly identified by a saddle-shaped 40Ar/39Ar degassing spectrum. However, biotite from the east Albany-Fraser Orogen of Western Australia contains excess 40Ar, but yields well-defined 40Ar/39Ar plateau dates, reproducible upon replicate analysis of biotite from the same sample. This "cryptic excess 40Ar" is inferred where plateau dates (1) are older than existing time constraints on cooling, such as U/Pb zircon ages for amphibolite to granulite facies metamorphism, and (2) vary between multiple samples from the same outcrop that have experienced the same thermal history. Rb/Sr geochronology is used to test the geologic significance of 40Ar/39Ar plateau dates, as the closure temperatures of both chronometers are similar, and the two chronometers are expected to yield similar cooling dates in an undisturbed system. Six Rb/Sr biotite-whole rock isochron ages from three outcrops yield a weighted mean age of 1133 +/- 3 Ma (MSWD = 1.13, P = 0.34), and are interpreted to record post-orogenic cooling. 40Ar/39Ar plateau dates from the same samples are 31-394 Ma older, and in six of nine samples cannot be explained by simple monotonic cooling, by low-temperature biotite recrystallisation, or by alteration; instead, biotite contains cryptic excess 40Ar. Diffusion modelling of 40Ar/39Ar step-heating plateaus suggests that Ar, both excess and radiogenic, is homogeneously distributed within the crystal lattice, and was incorporated during biotite crystallisation. Biotite likely crystallised in a rock with a high partial pressure of Ar, possibly due to a high rate of radiogenic 40Ar generation in a K-rich lithology, together with a poorly-connected intergranular fluid network that inhibited Ar loss from the rock volume. This is supported by a homogeneous distribution of Ar at the cm scale, with reproducible biotite 40Ar/39Ar dates from each sample. Patchy fluid circulation during metamorphism led to the pervasive but heterogeneous distribution of excess 40Ar across outcrops. Due to the presence of the 40Ar/39Ar plateau, cryptic excess 40Ar is difficult to identify a priori, without comparison to additional geochronological constraints. Where cryptic excess 40Ar on a regional scale has been identified, such as in the eastern Biranup Zone of the Albany-Fraser Orogen, Rb/Sr geochronology may provide a more robust alternative to constrain the cooling path of rocks from high temperatures. (C) 2021 Elsevier Ltd. All rights reserved. In 40Ar/39Ar geochronology, excess Ar is 40Ar that does not derive from the in situ radioactive decay of K-40, or from the measurable input of atmospheric Ar, and results in increased daughter-parent ratios that correspond to anomalously old apparent dates without geological age significance. Excess 40Ar is commonly identified by a saddle-shaped 40Ar/39Ar degassing spectrum. However, biotite from the east Albany-Fraser Orogen of Western Australia contains excess 40Ar, but yields well-defined 40Ar/39Ar plateau dates, reproducible upon replicate analysis of biotite from the same sample. This "cryptic excess 40Ar" is inferred where plateau dates (1) are older than existing time constraints on cooling, such as U/Pb zircon ages for amphibolite to granulite facies metamorphism, and (2) vary between multiple samples from the same outcrop that have experienced the same thermal history. Rb/Sr geochronology is used to test the geologic significance of 40Ar/39Ar plateau dates, as the closure temperatures of both chronometers are similar, and the two chronometers are expected to yield similar cooling dates in an undisturbed system. Six Rb/Sr biotite-whole rock isochron ages from three outcrops yield a weighted mean age of 1133 +/- 3 Ma (MSWD = 1.13, P = 0.34), and are interpreted to record post-orogenic cooling. 40Ar/39Ar plateau dates from the same samples are 31-394 Ma older, and in six of nine samples cannot be explained by simple monotonic cooling, by low-temperature biotite recrystallisation, or by alteration; instead, biotite contains cryptic excess 40Ar. Diffusion modelling of 40Ar/39Ar step-heating plateaus suggests that Ar, both excess and radiogenic, is homogeneously distributed within the crystal lattice, and was incorporated during biotite crystallisation. Biotite likely crystallised in a rock with a high partial pressure of Ar, possibly due to a high rate of radiogenic 40Ar generation in a K-rich lithology, together with a poorly-connected intergranular fluid network that inhibited Ar loss from the rock volume. This is supported by a homogeneous distribution of Ar at the cm scale, with reproducible biotite 40Ar/39Ar dates from each sample. Patchy fluid circulation during metamorphism led to the pervasive but heterogeneous distribution of excess 40Ar across outcrops. Due to the presence of the 40Ar/39Ar plateau, cryptic excess 40Ar is difficult to identify a priori, without comparison to additional geochronological constraints. Where cryptic excess 40Ar on a regional scale has been identified, such as in the eastern Biranup Zone of the Albany-Fraser Orogen, Rb/Sr geochronology may provide a more robust alternative to constrain the cooling path of rocks from high temperatures. (C) 2021 Elsevier Ltd. All rights reserved. In 40Ar/39Ar geochronology, excess Ar is 40Ar that does not derive from the in situ radioactive decay of K-40, or from the measurable input of atmospheric Ar, and results in increased daughter-parent ratios that correspond to anomalously old apparent dates without geological age significance. Excess 40Ar is commonly identified by a saddle-shaped 40Ar/39Ar degassing spectrum. However, biotite from the east Albany-Fraser Orogen of Western Australia contains excess 40Ar, but yields well-defined 40Ar/39Ar plateau dates, reproducible upon replicate analysis of biotite from the same sample. This "cryptic excess 40Ar" is inferred where plateau dates (1) are older than existing time constraints on cooling, such as U/Pb zircon ages for amphibolite to granulite facies metamorphism, and (2) vary between multiple samples from the same outcrop that have experienced the same thermal history. Rb/Sr geochronology is used to test the geologic significance of 40Ar/39Ar plateau dates, as the closure temperatures of both chronometers are similar, and the two chronometers are expected to yield similar cooling dates in an undisturbed system. Six Rb/Sr biotite-whole rock isochron ages from three outcrops yield a weighted mean age of 1133 +/- 3 Ma (MSWD = 1.13, P = 0.34), and are interpreted to record post-orogenic cooling. 40Ar/39Ar plateau dates from the same samples are 31-394 Ma older, and in six of nine samples cannot be explained by simple monotonic cooling, by low-temperature biotite recrystallisation, or by alteration; instead, biotite contains cryptic excess 40Ar. Diffusion modelling of 40Ar/39Ar step-heating plateaus suggests that Ar, both excess and radiogenic, is homogeneously distributed within the crystal lattice, and was incorporated during biotite crystallisation. Biotite likely crystallised in a rock with a high partial pressure of Ar, possibly due to a high rate of radiogenic 40Ar generation in a K-rich lithology, together with a poorly-connected intergranular fluid network that inhibited Ar loss from the rock volume. This is supported by a homogeneous distribution of Ar at the cm scale, with reproducible biotite 40Ar/39Ar dates from each sample. Patchy fluid circulation during metamorphism led to the pervasive but heterogeneous distribution of excess 40Ar across outcrops. Due to the presence of the 40Ar/39Ar plateau, cryptic excess 40Ar is difficult to identify a priori, without comparison to additional geochronological constraints. Where cryptic excess 40Ar on a regional scale has been identified, such as in the eastern Biranup Zone of the Albany-Fraser Orogen, Rb/Sr geochronology may provide a more robust alternative to constrain the cooling path of rocks from high temperatures. (C) 2021 Elsevier Ltd. All rights reserved.

Late Devonian time was a period of rapid upheaval in the Earth system, including climate change, sea level changes, widespread ocean anoxia, and the Frasnian-Famennian mass extinction; the cause(s) of these changes remain(s) uncertain. The Lennard Shelf of the Canning Basin in Western Australia contains carbonate reef sections spanning much of the Late Devonian Epoch and has been sampled for paleomagnetic analysis with studies by Hansma and colleagues in 2015 and Playton and colleagues in 2016. However, previous paleomagnetic directions were scattered and their use for magnetostratigraphy has been questioned. Here, rock magnetic data and magnetostratigraphy for a late Devonian drill-core from the Lennard Shelf were analyzed. Three magnetostratigraphic interpretations were made using different paleopoles that showed good correlation with each other and the earlier interpretations by Playton and colleagues in 2016. Additionally, the rock magnetic data revealed the samples contain various mixtures of detrital and diagenetic minerals, the former of which should be viable recorders of primary magnetic signatures. Even in samples with these detrital phases, paleomagnetic data were often noisy and produced ambiguous polarity assignments, likely due to the anomalously weak Devonian field. Because of this ambiguity and the absence of a robust paleopole, broader correlations for this critical time-period will be difficult without additional paleomagnetic data from the late Devonian Period. Expanded data for this interval could eventually shed light on the timing, causes, and rates of the Frasnian-Famennian mass extinction and other environmental shifts in the late Devonian Epoch.

Large, hot orogens are characterized by an orogenic plateau supported by a zone of weak ductile flow. During the collision phase, the magnitude of the belt and the temperature increase as radioactive crustal material is accreted, buried and heated. After convergence ends, no material is added to the orogenic system and the orogen undergo gravitational (or extensional) collapse that results from the lateral flow of the hot orogenic infrastructure. In the Araçuaí-West Congo orogen (AWO), the high temperatures, slow cooling, and excessive amount of melt in the hinterland, in the northern part of the belt, imply that a high temperature was maintained for a long time. Geochronologic results suggest that this internal domain was hot for a long time, cooling at < 3°/Myr since 600 Ma until 500 Ma, and cooling through the Ar/Ar retention temperature for biotite occurred around 470 Ma. In the south the collapse of the orogen is marked by the widespread intrusion of bimodal, composite plutons at ~500 Ma. Here we use the magnetic fabric (i.e. low-field anisotropy of magnetic susceptibility) of intrusions in the north and south sectors to track the kinematics and rheological changes across the belt. In the northern part of the AWO we studied the Padre Paraíso Charnockite and the southern part of the AWO we studied the Conceição de Muqui and Santa Angélica plutons. The Padre Paraíso charnockite has a coherent magnetic fabric, with magnetic foliations trending N-S, following the general structure of the belt in that sector. In turn, Conceição de Muqui and Santa Angélica plutons show a concentric distribution of foliations and lineations, in starking contrast with the general NE-SW trend of the belt in the south. This contrasting structural pattern for coeaval plutons along the AWO belt reveal the strain partitioning at the scale of the orogenic belt during the cooling of the AWO. At 500 Ma the hot northern sector remains warm enough to allow a coherent deformation of intrusions and host rocks. At the same time, more material was being added to the margins of the hot orogen, which already cold, with the diapire-like plutons structure being dominantly controlled by the forces of magma ascent and emplacement.

The Aracuai Orogen (AO) has been interpreted as a Neoproterozoic example of a large, "hot" orogen, based on a broad zone (250 km) of midcrustal metamorphic assemblages with a long, 70-Myr history of crustal melting and episodic magmatism throughout the late Neoproterozoic and earliest Paleozoic. Here, we present results of U-Pb sensitive high-resoution ion microprobe (SHRIMP) zircon dating and detailed anisotropy of magnetic susceptibility (AMS) study on a late Cambrian, bimodal pluton related to final period of collapse of the AO. New U-Pb zircon ages constrain the crystallization age of different suites within the Santa Angelica Pluton, 506 +/- 3 Ma for the early felsic phase and 498 +/- 5 Ma for the mafic core. New AMS data indicate that the emplacement of the Santa Angelica Pluton corresponds to two coupled plutons with concentric structures arrayed about a twin, bull's eye pattern. During the final stages of intrusion, upward relative movement of the northeastern lobe exposed the deeper levels of the intrusion, relative to the more shallowly eroded southwestern lobe. These observations suggest that magma emplacement was controlled by magma buoyancy forces, with little influence of regional tectonic stress. This behavior contrasts with the well-defined, tectonic-controlled fabrics of coeval plutons occurring to the north which was still hot, therefore highlighting the contrasting thermal evolution between different sectors of the orogen during its final stages.

The Mesoproterozoic to Paleozoic history of the southeastern Laurentian margin involved repeated collisional and accretionary tectonomagmatic events that reworked and recycled older continental crust of preceding events. The Great Smoky Mountains Basement Complex (GSMBC) within the southern Appalachian Blue Ridge exposes complexly deformed orthogneiss and paragneiss that preserve a record of Laurentian margin evolution from ca. 1.9 Ga to 450 Ma. The GSMBC consists primarily of: (1) 1.34 to 1.31 Ga (pre-Elzevirian) granodioritic orthogneiss and entrained mafic xenoliths that represent some of the oldest crust in Appalachian Grenville massifs (correlated with pre-Elzevirian crustal components in the Adirondack, Green Mountains, New Jersey Highlands, and French Broad massifs), (2) ca. l.15 to 1.05 Ga augen and granitic orthogneiss produced during Shawinigan and Ottawan phases of Grenville-age magmatism and metamorphism, respectively, and (3) paragneiss derived from protoliths with either Grenville-age (1.1–1.0 Ga) or post-Grenville (Neoproterozoic) depositional ages based on presence/absence of ca. 1.0 Ga metamorphic zircon and 1.9 to 1.1 Ga detrital zircon. All lithologies experienced Taconian metamorphism and variable migmatization. Pre-Ottawan paragneiss exhibits major detrital zircon ages modes at 2.0 to 1.6 and 1.4 to 1.3 Ga that require a component of older Proterozoic crust in the sediment source region. Detrital zircon grains in post-Ottawan paragneiss exhibits the full spectrum of Grenville-age modes that correlate with the five phases of Grenville magmatic/metamorphic events in eastern Laurentia. These paragneiss samples also contain scattered 750 to 600 Ma detrital zircon grains that constrain their maximum depositional age to late Neoproterozoic. The sedimentary protoliths of the latter paragneiss consist largely of detritus from exhumation of all Grenville crustal age components during post-orogenic exhumation and crustal extension leading up to Late Neoproterozoic breakup of Rodinia. Most zircon U-Pb age systematics exhibit variable discordance that can be attributed to disturbance of the U-Pb system and/or new zircon growth during either high-grade Ottawan (ca. 1.04 Ga) or Taconian (ca. 0.46 Ga) regional metamorphism and migmatization. Neodymium TDM model ages for granodioritic orthogneiss and paragneiss range from 1.8 to 1.6 Ga, indicating that the rocks were derived from recycling of Proterozoic crust (that is, they are not juvenile), consistent with the 1.9 to 1.6 Ga detrital zircon grains in pre-Ottawan paragneiss and with 1.8 to 1.7 Ga inherited zircon in some 1.33 Ga orthogneisses and a 1.35 Ga xenolith. Whole rock Pb isotope compositions of GSMBC rocks overlap the field of compositions characteristic of Amazonian crust and of other basement rocks from the south-central Appalachians. The Pb isotopes and geochronology in orthogneiss, mafic xenoliths, and pre-Ottawan paragneiss are consistent with a correlation of the GSMBC with the Mars Hill terrane within the French Broad massif and with the greater Grenvillian south-central Appalachian basement (SCAB) that is considered exotic to Laurentia, and transferred during Rodinian collision prior to ca. 1.2 Ga. Similarities in protolith ages and Pb isotopes point to the Paraguá terrane of Amazonia (southwestern Brazil and eastern Bolivia) as a likely match for SCAB. Initial Amazonia-Laurentia collision occurred at ca. 1.35 to 1.32 Ga with final transfer of SCAB to Laurentia occurring after 1.20 Ga within the sinistral oblique collision zone between Laurentia and Amazonia defined by previous workers.

Eastern Australian hotspots produce the longest continental tracks on Earth (>2,000 km). These hotspots are generally assumed to be stationary with respect to one another, an observation reinforced by our analysis. If any motion between them occurred, it is within our 95% uncertainties of 370 km of accumulated motion between hotspots. In contrast, motion between eastern Australian hotspots and the spin axis is indicated by changing paleolatitudes of hotspots through time. Reconstructing Australian hotspot paleolatitudes makes use of the global reference frame established by the geocentric axial dipole hypothesis. The classic paleomagnetic approach to establishing paleolatitude typically uses studies of discrete formations of known age, but the nearly continuous record of volcanism over 34 Ma permit using paleomagnetic data from multiple, different studies that overlap in magnetization age in conjunction. This improves the robustness and precision of our paleolatitude estimates for Eastern Australian hotspot volcanoes. A northward shift of hotspot paleolatitudes between 15-24 Ma of similar to 300-1,010 km (95% confidence limits) is observed for volcanoes along the Comboyne, Canobolas and Tasmantid tracks, and for interpolated positions along the Cosgrove and Lord Howe tracks but is significantly resolved only for volcanoes along Comboyne and Canobolas tracks, as well as for two ages from the Stradbroke and Britannia seamounts on the Tasmantid track. Before 24 Ma most data plot to the North of a fixed present day hotspot location in the paleomagnetic reference but 95 % confidence limits overlap with it. Notable exceptions are an age from Hillsborough Volcano (Cosgrove Hotspot), and an age from Horse Head (Lord Howe Hotspot) that lie a small distance to the North km, and kmNorth, respectively. Importantly, paleolatitude changes observed along eastern Australian tracks are all explainable by the net rotation of the solid Earth, or true polar wander, with hotspots embedded in the global moving hotspot reference frame

We report three high-quality paleomagnetic poles for Oligocene Australia from volcanic provinces along the Cosgrove hot spot track in central Queensland, NE Australia. We present paleomagnetic poles for Springsure (27.3-28.9 Ma: phi = 300.6 degrees E, lambda = 70.5 degrees N, K = 13.7, A(95) = 9.7 degrees, N = 18/22, Q = 6), Peak Range (28.2-31.2 Ma: phi = 291.8 degrees E, lambda = 64.6 degrees N, K = 10.1, A(95) = 8.8 degrees, N = 29/31, Q = 6), and Hillsborough volcanic provinces (33.1-34.1 Ma: phi = 301.4 degrees E, lambda = 67.1 degrees N, K = 32.2, A(95) = 7.1, N = 14/18, Q = 7), as well as data from Buckland and Nebo volcanic provinces. Using our new results, we resolve ambiguities present in published paleomagnetic data for Australia during the Oligocene epoch (23-34 Ma) and calculate a combined Oligocene paleomagnetic pole of phi = 289.2 degrees E, lambda = 71.0 degrees N, (K = 24.6, A(95) = 1.9 degrees, N = 227/274, Q = 6). We update the continental apparent polar wander path for Australia and find evidence for accelerated seafloor spreading in the Southern Ocean after similar to 34 Ma (anomaly C13). Lastly, we take advantage of the large number of paleomagnetic sites (N = 97) along the Cosgrove hot spot track to empirically evaluate the TK03.GAD geomagnetic field model. Paleomagnetic directions from rocks along the Cosgrove track have an elongation (E) of 1.6, remarkably consistent with TK03.GAD expected values for hot spot paleolatitudes (E = 1.4-1.6, lambda = 36.6-43.3 degrees S).

The petrological information preserved in the trace element signature of titanite is a valuable complement to in situ U/Pb geochronology, and can be used to refine interpretations on the growth of this mineral. We present trace element and U/Pb isotopic compositions of titanite grains in five amphibolite- to granulite-facies samples from the east Albany-Fraser Orogen of Western Australia. Chondrite-normalised rare earth element (REE) abundance patterns discriminate between titanite populations and correlate with backscatter electron (BSE) zonation. In two samples, titanite REE composition correlates with proximity to garnet, and in one sample titanite composition correlates with gneissic compositional banding. The Dy/Yb ratio can be used as a geochemical indicator to link titanite growth to garnet growth. Titanite that crystallised in a garnet-bearing assemblage is HREE-depleted with Dy/Yb > 2, whereas titanite that crystallised in a garnet-free assemblage typically has flat HREE patterns with Dy/Yb < 2. The titanite grains investigated in this study have a wide range of Eu and LREE signatures, with no obvious correlation to mineralogy, lithology, or growth environment. Furthermore, the Th/U ratio is not uniquely diagnostic of metamorphic or magmatic titanite. For the five samples reported here, Eu, LREE and Th/U are useful to discriminate between titanite populations, but not necessarily as growth process indicators. By integrating the REE signatures with U/Pb data, the five new titanite U/Pb ages can be linked to a range of processes: magmatic titanite crystallisation, metamorphic titanite growth, garnet growth, and/or cooling through the closure temperature for Pb diffusion in titanite.

Los datos paleontológicos, isotópicos y geocronológicos que se resumen a continuación apoyan la correlación paleogeográfica y cronológica entre los Grupos de Itapucumi (Paraguay) y Corumbá (Brasil), sugiriendo una evolución sedimentaria contemporánea entre estas unidades en los márgenes del Cratón Amazónico y del Bloque del Río Apa.

Gondwana changed its high latitude location during the late Paleozoic (338-265 Ma), relative to the South Pole, and the style of glaciation evolved from localized alpine glaciers and ice fields to similar to 30 small ice sheets across the supercontinent. We report the analysis of heavy mineral populations (n = 2217) and the ages of detrital zircons (n = 2920 U-Pb LA-ICPMS results) from Gondwana diamictite deposits from eight landmasses: Africa (5 samples), Antarctica (5), Australia (8), the Ellsworth Mountains terrane (1, Antarctica), the Falkland Islands (2, diamictite plus U-Pb SHRIMP ages on granite clasts), India (1), Madagascar (1), Oman (3), the equatorial Lhasa terrane (2), the equatorial North Qiantang terrane (2) and South America (10). Heavy mineral separations (SEM-WDS analysis) identified one anomaly, pyrope garnets present only in Dwyka Group and Dwyka-equivalent samples suggesting an ultramafic Antarctic source. Statistical analysis of detrital zircon age distributions support the inference of local transport of sediment from many small ice centers with five examples of far-field ice transport ( > 1000 km; four with ice flow > 2000 km), and three from ice fields located along coastal Antarctica. We propose that ice was distributed from five main ice-caps of different ages in southern Gondwana with ice flow away from central Gondwana. We also confirm that the Permo-Carboniferous detrital zircon populations of Euramerica (eolian and fluvial) and Gondwana (ash, detrital-glacial) are not mixed across the equator or seaway and ponder the possibility of a late Paleozoic snowball Earth.