Modern fluvial sediments provide important information about source-to-sink process and regional tectono-magmatic events in the source area, but many factors, e.g., chemical weathering, sedimentary cycles and source-rock types, can interfere with the establishment of the source-sink system. The Lalin River (LR) and the Jilin Songhua River (JSR) are two important tributaries of the Songhua River in the Songnen Plain in NE China. They have similar flow direction, topography and identical climate backgrounds, but have notably different parent-rock types in the headwater, which provides an opportunity to explore the influencing factors of river sediment composition. To this end, the point bar sediments in the two rivers were sampled for an analysis of geochemistry (including element and Sr-Nd isotopic ratios), heavy mineral and detrital zircon U-Pb dating. The results are indicative of the fact that the two rivers have the similar geochemical composition (e.g., elements and Sr isotopes) as well as chemical weathering (CIA = 51.41–57.60, CIW = 59.68–66.11, PIA = 51.95–60.23, WIP = 56.00–65.47, Rb/Sr = 0.38–0.42) and recycling (SiO2/Al2O3 = 5.79 and 5.03, ICV = 1.0 and 1.2, CIA/WIP = 0.81–1.03) characteristics, showing a major control of climate on the low-level weathering and recycling of the river sediments. However, there are significant differences in the detrital zircon U-Pb age (a significant Mesozoic age peak for the LR but an additional Precambrian peak for the JSR), Nd isotope ratio (−6.2812–8.5830 and −8.1149–10.2411 for the LR and the JSR, respectively) and to a certain extent heavy mineral composition (e.g., for the < 63 μm fraction, a dominance of hornblende and magnetite in the LR, but haematite-limonite in the JSR) in the two river sediments, indicating that source rocks largely control the composition of the river sediments. Some of the major tectono-magmatic events (e.g., crustal growth and cratonisation of the North China Craton, closure of the Paleo-Asian Ocean, subduction and rollback of the Paleo-Pacific plate) occurring in the eastern Songnen Plain are well documented in the JSR sediments but not in the LR, the difference of which is largely regulated by the source rocks in the source area.

The study area Sonapahar is an integral part of Shillong Meghalaya Gneissic Complex (SMGC), which is located in the Northeastern part of India. This complex mainly comprises metamorphic formations spanning from Upper Amphibolite to Ultra-high temperature granulite, interspersed with various igneous intrusions. In this study, particular attention is directed towards unravelling the metamorphic history of Mg-Al granulite. For the very first time, we establish the pressure–temperature (P-T) trajectory of the Mg-Al granulite from Sonapahar, SMGC. Employing conventional thermobarometry along with winTWQ analysis, the inferred metamorphic conditions for this granulite reveal temperatures exceeding 900°C and pressures of approximately >8 kbar. These conditions firmly indicate the presence of ultra-high-temperature metamorphism. By utilizing the Perple_X software in the MnO-Na2O-CaO-K2O-FeO-MgO-Al2O3-SiO2-H2O-TiO2-Fe2O3 compositional system, we construct a P-T pseudosection. This gives a clockwise P-T path, signifying an episode of cooling (+ minor decompression). Such a pattern also suggests rapid cooling of the tectonically-thickened crust. Concurrently, a geochemical exploration of trace and rare earth elements in the rocks offers further insights. These investigations give an idea about the protolith, having a clay-to-sandstone in nature. Additionally, chemical data from monazite within the studied rock provide a weighted mean age of 682 Ma for the peak metamorphic stage. This age aligns with the global Pan-African orogenic events. The biotite K-Ar isotopic geochronology from the symplectite position provides decompression history or cooling age of 442 Ma. This age corresponds to a period after the last peak metamorphic phase that occurred during the Pan-African thermal event.

The Central Asian Orogenic Belt is the world’s largest accretionary orogenic belt, associated with the closure of the Paleo-Asian Ocean (PAO). However, the final closure timing of the eastern PAO remains contentious. The Permian-Triassic sedimentary sequences in the Wangqing area along the Changchun-Yanji suture zone offer important clues into this final closure. New data on petrology, whole-rock geochemistry, zircon U-Pb geochronology and zircon Hf isotopes of sedimentary rocks from the Miaoling Formation and Kedao Group in Wangqing area provide new insights into the final closure of the eastern end of the PAO. The maximum deposition ages of the Miaoling Formation and Kedao Group have been constrained to the Late Permian (ca. 253 Ma) and early Middle Triassic (ca. 243 Ma), respectively. These sedimentary rocks exhibit similar geochemical characteristics, showing low textural and compositional maturities, implying short sediment transport, with all detrital zircons suggesting their origins from felsic igneous rocks. The εHf(t) values of the Miaoling Formation range from −6.09 to 12.43 and from −2.20 to 7.59 for the Kedao Group, implying these rocks originated from NE China. Considering our new data along with previously published data, we propose that a reduced remnant ocean remained along the Changchun-Yanji suture zone in the early Middle Triassic (ca. 243 Ma), suggesting the final closure of the eastern PAO likely occurred between the latest Middle Triassic and early Late Triassic.

The Durness Group of NW Scotland records deposition on the Laurentian margin from the basal Miaolingian (Cambrian, 509 Ma) to the Dapingian–Darriwilian boundary interval (Middle Ordovician, 470.3–468.9 Ma). The 930 m thick succession of peritidal and subtidal carbonates was deposited on the Scottish promontory, a nearly 120° deflection in the Palaeozoic continental margin between the Appalachian and Greenland sectors. These sediments were deposited as part of the Great American Carbonate Bank, a non-uniformitarian, continent-scale carbonate platform developed on the peneplaned craton. Measurement and description of a bed-by-bed composite section through the Durness Group provide a high-resolution reference framework that integrates conodont biostratigraphy, chemostratigraphy and sequence stratigraphy, including correlation with the Sauk megasequence and its subdivisions. The Sauk II–Sauk III sequence boundary marks the base of the group. The top of the group is faulted against rocks of the Moine thrust zone, generated by the Scandian orogeny, but sedimentation was probably terminated by the earlier Grampian arc–continent collision at 470–469 Ma. The highly mature quartz arenites of the underlying Ardvreck Group (Cambrian Series 2) indicate that there was no source-to-sink depositional continuity from the Hebridean foreland to the Dalradian Supergroup, which has coeval clastic sedimentary rocks of contrasting composition.

Measuring chemical weathering histories in submarine fan deposits is critical if the impact of orogenic erosion on atmospheric CO2 levels is to be understood, yet existing records are often noisy and hard to interpret. In this study, we selected mudstones from two International Ocean Discovery Program (IODP) sites from the Indus submarine fan and carefully removed the biogenic carbonate. The resulting records of chemical weathering show two trends, one of reducing chemical alteration since ∼8 Ma and which is associated with the Indus River, while a second trend is linked to sediment delivery from peninsular India. The second trend shows little temporal variation. Sediment deposited at IODP Site U1456 in the central Laxmi Basin is preferentially, but not exclusively, Indus-derived, while that at Site U1457 on the eastern flank of Laxmi Ridge is more peninsula-derived. Both trends show much less variability than seen in earlier studies in which various grain-size fractions were integrated together. The efficiency with which CO2 is removed from the atmosphere during chemical weathering has decreased over time in the Indus River-derived material. This reflects both lower degrees of alteration in the sediment since the late Miocene and increasing derivation of sediment from Himalayan sources, rather than more mafic Karakoram-Kohistan rocks. Previous estimates of CO2 consumption have overestimated the contribution that the Indus Basin has made to reducing atmospheric CO2 by ∼28–68%. This work emphasizes the importance of analysing appropriate largely silt-sized sediment when considering submarine fan records and in rigorously removing biogenic carbonate.

In the Triassic Mercia Mudstone Group of the Bristol Channel area, SW Britain, yellow micritic-oolitic dolomites deposited in a near-shore location of an extensive shallow saline alkaline lake, pass landwards into conglomerates and sandstones of colluvial-fluvial origin (Dolomitic Conglomerate). Offshore facies are red marl (Branscombe Fm.) and grey-green marl (Blue Anchor Fm.) of shallow lake-playa origin. Conspicuous red silicified bands and nodules (cherts) occur within the shoreline dolomites cropping out at Clevedon, 30 km SW of Bristol. The originally aragonitic ooids and lime mud were dolomitized very early on the lake floor and just below, and the presence of pyrite indicates anoxic conditions therein. The silicification is attributed to the influx of meteoric water with near-neutral pH, provided by flash floods and rainstorms as hyperpycnal and hypopycnal flows, interacting with the silica-rich, saline, alkaline lake water and porewater within the lake sediment. Aragonitic ooids picked up in the flows underwent dissolution, then slight compaction of outer dolomitic lamellae, before silica precipitation. The red colour of the chert from detrital finely disseminated hematite also indicates very early precipitation, before suboxic-anoxic conditions developed in the enclosing lake carbonates. These Triassic sediments show features of soft-sediment deformation, attributed to the formation of chert via a silica gel and/or density contrasts of rapid deposition-dewatering, plus possible seismic activity connected to a nearby basin-margin fault.

The emergence of vascular plants, such as Cooksonia, had a profound impact on Earth’s Early Paleozoic biogeochemical cycles (e.g. atmospheric oxygen, nitrogen and CO2), potentially triggering global environmental and biological changes. However, the timing of Cooksonia’s terrestrial emergence remains elusive as phylogenetic models, microfossils and macrofossils provide different timings for land colonization by vascular plants. Here, hundreds of zircon grains from three siltstones were dated using Laser Ablation-Inductively Couple Plasma-Mass Spectrometry (LA-ICP-MS). The study presents detrital zircon U-Pb dates, which refine the current biostratigraphy ages assigned to Cooksonia macrofossils from the three oldest sites globally. Specifically, siltstones hosting Cooksonia macrofossils from Borrisnoe Mountain (Ireland) and Capel Horeb (Wales) yield Gorstian–Homerian maximum depositional ages (MDAs) of 426 ± 2 Ma and 427 ± 2 Ma, respectively. Additionally, Cwm Graig Ddu (Wales) yields a (Pridoli-Ludlow) maximum age of 423 ± 3 Ma. The findings provide the first detrital zircon U-Pb dates for the oldest Cooksonia macrofossils globally and contribute crucial maximum ages. These maximum ages are instrumental in refining future calibrations of molecular clocks and improving phylogenetic models, thus contributing significantly to a better understanding of Cooksonia’s evolutionary history, including its environmental and ecological impacts.

Based on a new cored succession at Winterswijk, evidence is uncovered of the end-Triassic mass-extinction (ETME) event in a subsurface sedimentary succession of the Netherlands. The ETME was one of the most devastating events for the biosphere during the Phanerozoic era. Massive volcanism from the Central Atlantic Magmatic Province initiated the breakup of the supercontinent Pangea and resulted in terrestrial and marine extinction pulses, which drastically altered the course of life on Earth. The newly cored material reveals a sedimentary succession representing a shallow marine setting dominated by laminated black shale and claystone deposits. A high-resolution palynostratigraphic dataset provides evidence for a late Rhaetian vegetation assemblage that displays a stepwise decline of arborescent tree vegetation that is transiently replaced by a community of ferns and fern allies. Geochemical records link this major disturbance in palynofloral biodiversity to a pulse of volcanic activity as evidenced by a negative excursion in stable organic carbon isotopes. Shifts towards drier climate conditions, as inferred from sedimentary elemental composition, suggest continental aridification strongly influenced the terrestrial realm following volcanic pulses. Presence of reworked material suggests unstable soils that were affected by increased erosion rates, inhibiting the re-establishment of conifer tree vegetation. Comparison of our findings with other contemporaneous European Triassic-Jurassic boundary sections confirms the progression of the end-Triassic extinction, which exhibits a two-phased structure. The presence of the ETME in the subsurface of the Netherlands provides further evidence towards our understanding of terrestrial extinction with emphasis on the decline of vegetation.

The Paleoproterozoic Stollberg Zn-Pb-Ag plus magnetite ore field contains SVALS-type stratabound, limestone-skarn hosted sulphide deposits within volcanic (bimodal felsic and mafic rocks)/volcaniclastic rocks metamorphosed to the amphibolite facies. The sulphide ores consist of semi-massive to disseminated to vein-network sphalerite-galena and pyrrhotite (with subordinate pyrite, chalcopyrite, arsenopyrite and magnetite). Thermochemical considerations and stabilities of minerals in the systems K-Al-Si-O-H and Fe-S-O and sulphur isotope values for sulphides of δ34SVCDT = +1.12 to +5.71 ‰ suggest that sulphur most likely formed by inorganic reduction of seawater sulphate that was carried in hydrothermally modified seawater fluid under the following approximate physicochemical conditions: T = 250o–350 oC, δ34SΣS = +3 ‰, I = ∼1 m NaCl and a total dissolved S content of ∼0.01 to 0.1 moles/kg H2O. However, a magmatic contribution of sulphur cannot be discounted. Carbon and oxygen isotope compositions of calcite in altered rocks spatially associated with mineralisation show values of δ13CVPDB = −2.3 to −0.8 ‰ and δ18OVSMOW = +9.5 to +11.2 ‰, with one anomalous sample exhibiting values of δ13CVPDB = −0.1 ‰ and δ18OVSMOW = +10.9 ‰. Most carbonates in ore show lighter C and O isotope values than those of Proterozoic (Orosirian) limestones and are likely the result of premetamorphic hydrothermal alteration involving modified seawater followed by decarbonation during regional metamorphism. The isotopically light C and O isotope values are consistent with those for carbonates spatially associated with other SVALS-type deposits in the Bergslagen ore district and suggest that such values may be used for exploration purposes.

The origin of eclogite-bearing granitoid gneisses and metapelites of the Chuacús Complex is investigated. This complex represents the internal basement massif of the Guatemala Suture Zone, a part of the western North America–Caribbean plate boundary. LA-ICP-MS U-Pb and trace element zircon data are combined with whole-rock Sm-Nd and Lu-Hf isotopes to re-evaluate granitoid petrogenesis and inquire into the sedimentary record. New granitoid ages of ca. 1030–1010 Ma are reported, adding to those already known of ca. 1100, 990 and 225 Ma. Stenian A-type granitoids within the bimodal Cubulco unit formed by mixing of magmas derived from late Palaeoproterozoic crust and mantle-derived melts produced in an extensional setting during Rodinia assembly. During the Tonian, an extended (or later) period of extensional tectonics produced peraluminous granitoids (Pachajob gneiss) by anatexis of rejuvenated late Mesoproterozoic crust. After a hiatus encompassing most of the Neoproterozoic, marine sedimentation occurred between the Ediacaran and the early Palaeozoic as recorded by the Palibatz schist, a sequence formed by detritus sourced from peri-Gondwanan continental areas. No evidence of middle to late Palaeozoic magmatism or sedimentation was found in the studied area. Late Triassic granitoids (Agua Caliente unit) were produced by mixing melts from late Mesoproterozoic crust with enriched mantle magmas in response to post-collisional thinning during the western Pangea breakup. This extensional stage led to considerable thinning of the Chuacús crust and its evolution into a passive margin that would be prone to subduct during the Cretaceous.

Petrographical and geochemical data from the Togo structural unit (TSU), also referred to as the Atacora structural unit, are presented together with the existing dataset; geochemical and age data from the sedimentary and metasedimentary rocks from the passive margin sequences of the Dahomeyide belt in Ghana to infer their provenance and depositional setting and expand the discussion on the Rodina–Gondwana supercontinent assembly during the Pan-African orogeny. The metasedimentary rocks of the TSU are quartzites and phyllites. The framework grains of the quartzites consisting dominantly of quartz and small amounts of feldspar grains and relict lithic fragments classify them as quartz arenite, subarkose and sublitharenite. Generally, the studied rocks show similar rare-earth element and multi-element patterns, which imply derivation from similar sources. Elemental ratios, including (La/Lu)N, Th/Sc and La/Sc, suggest sediments sourced from intermediate to felsic rocks. Provenance and depositional setting indicators of the TSU suggest deposition in a passive margin setting, with the West African and Amazonian cratons’ granitoids and granitic gneisses as possible provenance, akin to siliciclastic rocks of the Buem structural unit and the Voltaian Supergroup of the Volta Basin. The deformational history of the TSU is similar to those of the Buem structural unit and the eastern margin of the Voltaian Supergroup, indicating the effect of the Pan-African orogeny on the passive margin of the Dahomeyide belt. We, therefore, propose the formation and evolution of a Neoproterozoic passive margin unit, which was tectonically deformed during the Rodinia–Gondwana supercontinent cycle.

The Pliensbachian–Toarcian succession of North Yorkshire provides a global reference for the interval incorporating the Toarcian Oceanic Anoxic Event (T-OAE, ∼183 Ma). Major and trace element, carbon stable-isotope (δ13Corg) and total organic carbon (TOC) data for the Dove’s Nest core, drilled close to the classic outcrop sections of the Yorkshire coast, demonstrate geochemical, mineralogical and grain-size trends linked to sea level and climate change in the Cleveland Basin. High-resolution correlation between the core and outcrop enables the integration of data to generate a comprehensive chemostratigraphic record. Palaeoredox proxies (Mo, U, V, TOC/P, DOP and Fe speciation) show a progressive shift from oxic bottom waters in the late Pliensbachian through dysoxic–anoxic conditions in the earliest Toarcian to euxinia during the T-OAE. Anoxia–dysoxia persisted into the middle Toarcian. Elemental and isotope data (Re, Re/Mo, δ34SCAS, δ98Mo and ε205Tl) from the coastal sections evidence global expansion of anoxic and euxinic seafloor area driving drawdown of redox-sensitive metals and sulfate from seawater leading to severe depletion in early Toarcian ocean water. The record of anoxia–euxinia in the Cleveland Basin largely reflects global-scale changes in ocean oxygenation, although metal depletion was temporarily enhanced by periods of local basin restriction. Osmium and Sr isotopes demonstrate a pulse of accelerated weathering accompanying the early Toarcian hyperthermal, coincident with the T-OAE. The combined core and outcrop records evidence local and global environmental change accompanying one of the largest perturbations in the global carbon cycle during the last 200 Ma and a period of major biotic turnover.

The Khopoli intrusion is a small olivine gabbro intrusion exposed in the Konkan Plain, in the western part of the Deccan Traps continental flood basalt province. It intrudes lavas of the Neral and Thakurvadi formations, which belong to the lower part of the Western Ghats stratigraphic sequence and mainly comprise small-scale compound pāhoehoe flows and sheet lobes, respectively. Many of these lavas contain abundant cumulus olivine and clinopyroxene. The Khopoli intrusion is of considerable interest because its olivine gabbros are among the most magnesian Deccan rocks known, with bulk-rock MgO contents reaching 27 wt.%. Textural, mineralogical and geochemical features indicate that the olivine gabbros are olivine-pyroxene cumulates formed from an evolved tholeiitic basalt melt. Much of the original outcrop of the intrusion (mapped in 1980) is now lost owing to large-scale urban and industrial development. We have remapped the intrusion and obtained a 40Ar/39Ar age of 67.3 ± 1.5 Ma (2σ) on fresh intercumulus plagioclase grains separated from one of the olivine gabbros, which is consistent with the age of the host volcanic sequence. Measured true density values of 2.93 to 3.13 g/cm3 for olivine gabbros of the Khopoli intrusion suggest possible shallow causes for at least some of the high gravity anomalies found in the Deccan Traps.

The cliff and foreshore sections at Blue Anchor Bay, north Somerset, provide a detailed picture of the transitional Triassic–Jurassic succession. The site has been recorded as a location for fossil fishes for over 200 years, and yet the assemblages from the bone beds have not been described. Here, we present new observations on the two bone beds and find major faunal differences: the classic basal bone bed at Blue Anchor Bay contains an assemblage dominated by osteichthyan teeth, unexpected because elsewhere the ichthyofauna is usually dominated by chondrichthyans. The upper bone bed at Blue Anchor Bay is indeed more typical, being dominated by teeth of hybodont chondrichthyans. We report two unusual finds, first five teeth of the rare shark Parasycylloides turnerae, only the fifth such record in the UK. Further, we report here for the first time a tooth of the pycnodontiform Eomesodon, the first report of this taxon from the Triassic of the UK or Europe. The two bone beds are distinguished not only by different assemblages, but also by evidence of different degrees of anoxia and water depth: the upper bone bed contains abundant pyrite and marcasite, indicating highly anoxic conditions, and perhaps deposition in deeper water than the basal bone bed.

To define the amount, thermal maturity and type of organic matter (OM), a comprehensive analysis of major and trace elements, organic carbon isotope and organic geochemistry was conducted on Lutetian black shales found in the Everek (Bayburt) region of northeastern Turkey. Total organic carbon (TOC) levels in the shale samples range from 0.62% to 6.75%, and type II–III to type III kerogen is generated, displaying a combination of high terrigenous and low marine OM. The δ13C values (ranging from –28.22‰ to –28.23‰), aromatic hydrocarbon compounds (methyl phenanthrene, dibenzothiophene, tri-aromatic and monoaromatic steroids), saturated hydrocarbon compounds (sterane and terpane), acyclic isoprenoids, n-alkane distribution (n-C13–n-C36) and inorganic geochemical characterization support that the black shales were deposited in a terrestrial-marine transition environment and had a high proportion of terrestrial OM with small amounts of marine OM preserved in relatively arid to hot climate and oxic to suboxic conditions. The analysis of biomarker thermal maturity markers, Tmax (ranging from 449–458 oC) and estimated vitrinite reflectance (varying from 0.92 to 1.08%) values suggest that the black shales have reached the oil window. As a result, black shales are thought to contain low to high amounts of TOC, have a mixed kerogen type, reach a high thermal maturity level and produce little hydrocarbons.

Sediments within accretionary complexes, preserving key information on crust growth history of Central Asian Orogenic Belt, did not get enough attention previously. Here, we conduct comprehensive geochemical study on the turbidites from the North Tianshan Accretionary Complex (NTAC) in the Chinese West Tianshan orogen, which is a good example of sediments derived from juvenile materials. The turbidites, composed of sandstone, siltstone, and argillaceous siliceous rocks, are mainly Carboniferous. All the investigated samples have relatively low Chemical Index of Alteration values (35–63) and Plagioclase Index of Alteration values (34–68), indicating relatively weak weathering before erosion and deposition. The sandstone and siltstone, and slate samples display high Index of Compositional Variability values of 0.89–1.50 and 0.89–0.93, suggesting a relatively immature source. The sandstones and siltstones were mainly derived from intermediate igneous rocks, and the slates from felsic igneous rocks, formed in oceanic/continental arc settings. The investigated samples roughly display high positive εNd(t) values (mainly at +5.5 to +7.9, except one spot at +0.8), with corresponding Nd model ages at 672 Ma–522 Ma (except one at ∼1.1 Ga). Combined with the previous studies, we suggest that the turbidites in the NTAC were mainly derived from intermediate to felsic igneous rocks with juvenile arc signature, and thus the northern Chinese West Tianshan is a typical site with significant Phanerozoic crust growth.

The Indo-Pacific Warm Pool (IPWP) significantly influences the global hydrological cycle through its impact on atmospheric-oceanic circulation. However, gaining a comprehensive understanding of the hydrologic climate dynamics within the IPWP and its broader effects on the global climate have been hindered by spatial and temporal limitations in paleoclimate records on orbital timescales. In this study, we reconstructed precipitation records (approximated from δ18Osw-ivc) over the past 450 kyr, based on planktonic foraminiferal Mg/Ca and δ18O data obtained from International Ocean Discovery Program Site U1486 in the western tropical Pacific. The δ18Osw-ivc record revealed a generally consistent pattern with precession variations over the past 450 kyr, closely corresponding to changes in boreal summer insolation at the equator. The δ18Osw-ivc record displayed an anti-phased relationship with Chinese speleothem δ18O records on the precession band, with lower precipitation in the western tropical Pacific and higher precipitation in the East Asia summer monsoon region during periods of high Northern Hemisphere summer insolation. This anti-phased correlation primarily resulted from the north-south migration of the Intertropical Convergence Zone (ITCZ), influenced by the interhemispheric insolation contrast. By considering additional δ18Osw-ivc records from various locations within the IPWP region, we identified synchronous precipitation changes within the IPWP on the precession band. The synchronization of precipitation on both margins of the ITCZ’s seasonal range and differences between central and marginal regions of the ITCZ within the IPWP revealed the expansion and contraction of the ITCZ on precession band.

The Mayombe chain of Congo is part of the West Congo Belt, which belonged to the western Gondwana supercontinent. It consists of Paleoproterozoic gneisses and schists that are tectonically stacked and overthrust Neoproterozoic low-grade metamorphic rocks. Although Neoproterozoic context of the chain is relatively well established, the tectono-metamorphic evolution of its Paleoproterozoic basement still under discussion.

Petrography, garnet chemistry and phase equilibria modelling were used to constrain tectono-metamorphic evolution of meta-plutonic and meta-sedimentary rocks from the Western Domain of the Mayombe chain. Microprobe analysis reveals three garnet types: (i) 2-stage garnets with distinct cores (Grt1) and rims (Grt2), (ii) unzoned garnet showing narrow diffusion zones along cracks and rims and (iii) syn-kinematic garnet with normal growth zoning. These complex and simple features of garnet growth are, respectively, related to a polycyclic evolution linked in this area to: (i) the superposition of Eburnean (c. 2000 Ma) and Pan-African (c. 600 Ma) orogenies and (ii) a monocyclic evolution related to a single Pan-African event taking into account ages of the protoliths. The oldest metamorphic assemblage (Eburnean) is preserved in amphibolite facies conditions marked by the first generation of garnet, whereas the younger (Pan-African) event varies from amphibolite facies in the southwest (4–6 kbar, 550°C–600°C) to greenschist facies in the northeast (4–6 kbar at 450°C–550°C) confirming the westward increase in metamorphic grade during the Pan-African event. Mineral equilibria modelling shows also a relatively HP episode culminated at 11.5–12.5 kbar and 525°C–550°C which tectonic environment stills less understood.

Contrary to the southern Appalachians, where Alleghanian magmatism is widespread and well documented, the expressions of magmatism in the Canadian Appalachians are limited. In this study, a suite of leucocratic dykes from the Cape Spencer area in southern New Brunswick, Canada, were investigated to determine the nature, timing and source of these magmas using zircon and monazite U-Pb geochronology, whole-rock geochemistry and Nd-Hf isotopes. An LA-ICP-MS U-Pb monazite Alleghanian age of 273.7 ± 1.3 Ma obtained for these dykes constitutes a new example of magmatism in the northern segment of the orogen, where significant strike-slip movement and reheating have been the primary markers of the Alleghanian Orogeny. These metaluminous leucocratic dykes are enriched in light rare elements, U and Th; depleted in high-field strength elements (HFSE; Nb, P, Ti); and have slight negative Europium anomalies [(Eu/Eu*)N = 0.72–0.95]. All the dykes samples have negative εNd(t) values (−9.76 to −5.7), negative εHf(t) values (−1.8 to −1.0) and Mesoproterozoic Nd depleted-model ages (TDM = 1371–1618 Ma). The geochemical and isotopic characteristics suggest that the dykes were formed by the partial melting of lower crust that assimilated Meguma metasedimentary rocks and/or Avalonian sedimentary rocks, following terminal subduction of the Rheic Ocean and thermal re-equilibration during the Alleghanian orogeny. The effects of the closure of the Rheic Ocean in the oblique collision between composite Laurentia and Gondwana were, to a certain extent, accommodated along the Minas Fault Zone, where magmatism and regional fluid flow were concentrated.

Modern studies suggest that the upper ocean heat content (OHC) in the tropical Indian Ocean (TIO) is a better qualitative predictor of the Indian summer monsoon rainfall (ISMR). But it is still unknown how the OHC is mechanically linked to ISMR and whether it can be applied to long-term climate changes. By analyzing reanalysis datasets across the 20th century, we illustrate that in contrast to those anomalies associated with stronger ISM westerlies, higher ISMR is accompanied with summer surface high pressure and east wind anomalies from the South China Sea to the Bay of Bengal (BOB), and is loosely related to increased western TIO OHC during decayed phases of positive Indian Ocean dipole (IOD) and of El Niño. Except for 1944–1968 AD, this interannually lagged ISMR response to winter OHC is insignificant, probably suppressed by those simultaneous effects of positive IOD and El Niño on ISMR. In our paleoclimatic simulations, this modern observed lagged response is interrupted by seasonally reversed insolation anomalies at the 23,000-year precessional band. Our sensitivity experiments further prove that, the ISMR can be simultaneously reduced by positive IOD-like summer OHC anomalies both for modern and precessional situations. This damping effect is mainly contributed by the warmer western TIO that triggers anomalous surface high pressure, easterly winds, and drastically reduced rainfall from BOB to Arabian Peninsula, but with slightly increased rainfall in the northern ISM region. And the cooler southeastern TIO will only moderately increase rainfall in the southern ISM region.