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Since Australia is the driest inhabited continent, it is a natural laboratory to study on a large scale dust, its composition, its sources, transport and geochemical composition. This is necessary as there has been a lack of appreciation of the diversity of the Australian regolith characterized by a great array of ages and compositions. This is particularly true of studies that examined the geochemistry of Australian dusts and links with potential deposition sites such as in Antarctica and comparison with South America. Hence, the first part of this paper provides an overview of the surficial geology of Australia with emphasis on regions from where dust can become deflated. A review follows on the investigations of significant dust transport and events in Australia. The second part of the paper provides a review of the sites of potential deflation of dust. It includes the study of different geomorphological sites of dust deflation, with a discussion on how dust particles can accumulate in regions linked to large playa lakes that are under the influence of groundwater below them. This is an important mode of dust deflation, a process of which had insufficiently been detailed before. The processes involving evaporative pumping are explained and several illustrations are provided to document those processes and location of dust deposits. Another region of importance to dust deflation consists of extensive alluvial plains and these are also documented, with an area in the upper reaches of the Darling River being now documented more fully. Finally, the inter-dunal corridors in large dune fields are also mentioned as a source of dust as previous studies already show. This second part ends with the description of the two main Potential Source Areas (PSA) of dust in Australia and these are the Kati Thanda-Lake Eyre region of central Australia, and the Darling Riverine Plain in the upper reaches of the Darling River. These two regions are important for their geochemical fingerprints for transcontinental studies, and supported by satellite imagery that identify dust plumes originating from these regions. The third part of the paper examines the geochemical composition of Australian PSAs by paying particular attention to Neodymium, Strontium and Lead isotopic ratios from both continents. We also suggest the possibility of combining Nd and Pb isotopes as a way of fingerprinting geochemically between different Australian regions, and for comparison with other continental PSAs. This part also reviews previous studies that aimed at geochemically fingerprinting the Australian regolith by referring also how these studies were applied to reconstruct past environmental conditions. [ABSTRACT FROM AUTHOR]

Iron formations (IF) represent an iron-rich rock type that typifies many Archaean and Proterozoic supracrustal successions and are chemical archives of Precambrian seawater chemistry and post-depositional iron cycling. Given that IF accumulated on the seafloor for over two billion years of Earth's early history, changes in their chemical, mineralogical, and isotopic compositions offer a unique glimpse into environmental changes that took place on the evolving Earth. Perhaps one of the most significant events was the transition from an anoxic planet to one where oxygen was persistently present within the marine water column and atmosphere. Linked to this progressive global oxygenation was the evolution of aerobic microbial metabolisms that fundamentally influenced continental weathering processes, the supply of nutrients to the oceans, and, ultimately, diversification of the biosphere and complex life forms. Many of the key recent innovations in understanding IF genesis are linked to geobiology, since biologically assisted Fe(II) oxidation, either directly through photoferrotrophy, or indirectly through oxygenic photosynthesis, provides a process for IF deposition from mineral precursors. The abundance and isotope composition of Fe(II)-bearing minerals in IF additionally suggests microbial Fe(III) reduction, a metabolism that is deeply rooted in the Archaea and Bacteria. Linkages among geobiology, hydrothermal systems, and deposition of IF have been traditionally overlooked, but now form a coherent model for this unique rock type. This paper reviews the defining features of IF and their distribution through the Neoarchaean and Palaeoproterozoic. This paper is an update of previous reviews by Bekker et al. (2010, 2014) that will improve the quantitative framework we use to interpret IF deposition. In this work, we also discuss how recent discoveries have provided new insights into the processes underpinning the global rise in atmospheric oxygen and the geochemical evolution of the oceans. [ABSTRACT FROM AUTHOR]

Monazite is a light rare earth element (LREE)-rich phosphate mineral that occurs as a trace phase in a wide variety of rock types, where it forms in response to different geological processes from igneous crystallisation, very low- to high-temperature metamorphism, and hydrothermal mineralisation. Monazite is also an ore mineral in some REE-deposits. Owing to its physical and isotopic robustness, high blocking temperature for U-Th-Pb systematics, and widespread occurrence, monazite has become a reliable and versatile geochronometer routinely employed in dating magmatic and higher-grade metamorphic rocks. More recently, it has been increasingly identified in hydrothermal mineral deposits and very low-grade metasedimentary rocks. The ability of monazite to grow at low temperatures can lead to complex age distributions reflecting xenocrystic or detrital grains and multiple episodes of metamorphic or hydrothermal growth. In situ , microbeam analytical techniques, such as SIMS, EPMA and LA-ICP-MS, can provide ages for these low-temperature events. However, textural characterisation and geochemical analysis are required to decipher the petrogenesis of monazite and interpret the meaning of resultant age data. In this paper, we review the petrographic and geochemical characteristics of monazite with well-constrained geological histories, to provide criteria to differentiate monazite that formed in different geological environments. In cases where multiple generations of monazite are present in a sample, differences in chemical composition can often be used as a valuable indicator of origin complementing textural and morphological discrimination. In general, there is a positive correlation between Th contents in monazite and the temperature of the environment in which it crystallised. Magmatic monazite typically contains >3 wt% ThO 2 , as does monazite in high-grade (T > ∼500 °C) metamorphosed rocks. The Th/U ratios of high- T monazites are typically in the range 10–100. Thorium contents of low- T (<350 °C) hydrothermal and metamorphic monazites rarely exceed 3 wt% (mostly <1 wt%, mean 0.6 wt% from data compiled in this study), and their Th/U ratios largely fall between 0.1 and 10. Monazite from carbonatites is characterised by very low U (<30 ppm) and anomalously high Th/U (>300). Thorium content and Th/U ratio of monazite can be used as indicators for distinguishing between low- T metamorphic and hydrothermal, magmatic and high- T metamorphic, and carbonatite-related grains. In comparison with igneous and high- T metamorphic monazites, low- T metamorphic and hydrothermal monazites tend to have depleted Ca and Y, but elevated total REE contents, features which are potentially useful discriminators. On chondrite-normalised REE plots, igneous monazite typically displays a prominent negative Eu anomaly, which is less pronounced in high- T metamorphic monazite. Europium anomalies in low- T metamorphic and hydrothermal monazite range from variably negative in most cases to slightly positive in rare cases. Furthermore, the REE distribution patterns of metamorphic and hydrothermal monazites are widely variable, apparently controlled by compositions of both the fluid phase and the host rock, as well as the P - T conditions under which they formed. The accurate interpretation of monazite age data requires petrographic characterisation combined with high-quality geochemical data. [ABSTRACT FROM AUTHOR]

Inorganic geochemistry is a powerful tool in paleolimnology. It has become one of the most commonly used techniques to analyze lake sediments, particularly due to the development and increasing availability of XRF core scanners during the last two decades. It allows for the reconstruction of the continuous processes that occur in lakes and their watersheds, and it is ideally suited to identify event deposits. How earth surface processes and limnological conditions are recorded in the inorganic geochemical composition of lake sediments is, however, relatively complex. Here, we review the main techniques used for the inorganic geochemical analysis of lake sediments and we offer guidance on sample preparation and instrument selection. We then summarize the best practices to process and interpret bulk inorganic geochemical data. In particular, we emphasize that log-ratio transformation is critical for the rigorous statistical analysis of geochemical datasets, whether they are obtained by XRF core scanning or more traditional techniques. In addition, we show that accurately interpreting inorganic geochemical data requires a sound understanding of the main components of the sediment (organic matter, biogenic silica, carbonates, lithogenic particles) and mineral assemblages. Finally, we provide a series of examples illustrating the potential and limits of inorganic geochemistry in paleolimnology. Although the examples presented in this paper focus on lake and fjord sediments, the principles presented here also apply to other sedimentary environments. • Inorganic geochemical proxies are not universally applicable. • Simple multivariate statistics allow associating elements with sediment components. • Variations in most elements reflect sediment grain size and provenance. • Log-ratios effectively reduce the limitations inherent to XRF core scanner analysis. [ABSTRACT FROM AUTHOR]

Reconstruction of proportions between juvenile and recycled crust remains challengeable because a big part of juvenile source magmatic rocks formed at intra-oceanic arcs, can be destroyed by surface and tectonic erosion leaving, at best, greywacke sandstones. Such sandstones are typically hosted by accretionary complexes, which study, therefore, is of crucial importance. In this paper we review available geological and micropaleontological data and present first U Pb detrital zircon ages, geochemical data and isotope (Sm Nd, Lu Hf) data from sandstones of the late Cambrian-early Ordovician Zasur'ya accretionary complex (AС) of NW Altai. No island-arc units have ever been reported there. The Zasur'ya AC includes ocean plate stratigraphy (OPS) magmatic and sedimentary rocks of three formations, Listvenny (l. Cambrian), Talitsa (Tremadocian) and Marcheta (Floian), which age was constrained by microfossils. The OPS assemblage includes basalt, pelagic chert and hemipelagic siliceous mudstone and siltstone, and sandstone. We analyzed zircons in five samples. The distributions of U Pb ages of detrital zircons from five samples of sandstones are all unimodal with main peaks at ca. 488 Ma (Listvenny Fm.), 491 Ma (Talitsa Fm.) and 485 Ma (Marcheta Fm.). The Precambrian ages are very few. The maximum deposition ages inferred from the youngest populations of zircon ages are ca. 464 Ma. Compositionally, the sandstones are greywackes or feldspar litharenites. The Listvenny and Talitsa sandstones are higher silicic (SiO 2av. = 68.5 wt%) compared to Marcheta samples (SiO 2av. = 60.5 wt%). The major and trace element features of all sandstones are similar to supra-subduction intermediate-felsic (Listvenny, Talitsa) and mafic-intermediate (Marcheta) magmatic rocks. All samples yielded positive values of zircon ɛHf(t) (+4.3 to +20.1) and bulk-rock ɛNd(t) (+0.6 to +4.8) indicating juvenile magmatic rocks in the provenance. However, the Listvenny and Talitsa samples show lower ɛNd(t) (1.3 and 0.8, respectively) than those of the Marcheta Fm. (4.7). Probably the Zasur'ya sandstones were deposited in a back-arc basin (Listvenny, Talitsa), and fore-arc basin (Marcheta). All Zasur'ya greywacke sandstones were derived by destruction of a single late Cambrian - Early Ordovician intra-oceanic arc. The Zasur'ya intra-oceanic arc was identified in NW Altai for the first time and it represents a new site of juvenile crustal growth in the CAOB. [ABSTRACT FROM AUTHOR]

This paper reviews global records of anoxic events of the Middle Devonian – earliest Mississippian, as well as the possible triggers and controls of these events. These "anoxic events" are complex multistage paleoenvironmental disturbances manifested in multiple proxies, which we showcase with the Horn River Group (HRG) – a succession of basinal organic-rich shales and cherts deposited during the latest Eifelian – earliest Late Frasnian (∼386–373 My ago) on the western continental margin of Laurentia near the paleo-equator. Four major events imprinted in the HRG are the Kačák, Frasnes, basal punctata, and late punctata events, but positive δ13C excursions (measured on organic matter) are more numerous and can potentially be matched to other global events. The Kačák event in the base of the HRG manifests as a regional switch from carbonate-platform to anoxic sedimentation. Three major events of the latest Givetian – Middle Frasnian display repeating sequences characterized by: (1) an early shift to heavier δ13C values coupled with siliciclastic enrichment and mercury enrichment spikes of up to 0.48 ppm; (2) late-stage δ13C reversal to background values coincident with the onset of severe anoxia (buildup of authigenic U, Mo, V) and attenuation of siliciclastic supply. Devonian anoxic sediments, including HRG, display widespread presence of chlorobi biomarkers, which indicates episodes of photic-zone euxinia in the water column. Most of these sediments were deposited under open ocean conditions, precluding a Black Sea water-column stratification scenario. These observations indicate Devonian anoxic events are similar to classical Mesozoic oceanic anoxic events (OAEs), consistently with growing evidence for a volcanic trigger for these events (e.g. spikes in Hg and negative 187Os/188Os anomalies). Oxygen minimum zones in a greenhouse ocean, such as the one recorded in basinal HRG, were prone to expansion under volcanic CO 2 reinforcement. This volcanic press-pulse also intensified the hydrological cycle, which resulted in a boost of weathering and eutrophication of shelfal seas. These factors, amplified by deoxygenation and acidification of the habitable upper ocean, drove extinctions of various magnitude. As a proxy for the input of land-plant detritus, the oxygen index from pyrolysis data shows zero response to anoxic events in the HRG, which aligns with broader evidence that counters expanding vascular vegetation to be the driver of the marine biotic crises. Finally, our review highlights how controversial the evidence of high-frequency (3rd to 5th orders) sea-level fluctuations is in the Devonian. In particular, none of the geochemical proxies usually employed to interpret sea-level changes translates unequivocally into transgressions and regressions in the greenhouse world. This sea-level puzzle clearly calls for new scrutiny and justifies scepticism in the validity of the classical "eustatic sea-level curve of the Devonian", as well as estimates of eustatic amplitudes in excess of ∼25 m for 3rd and 4th order cycles. [ABSTRACT FROM AUTHOR]

The tectono-magmatic evolution of the North China Craton (NCC) plays a crucial role in understanding the Jurassic–Early Cretaceous (Yanshanian) intracontinental orogeny in East Asia. A holistic understanding of multi-phased deformation and magmatism in the NCC is greatly complicated by the sporadically distributed Mesozoic strata with significantly different stratigraphic associations in various zones. In this paper, we review the Jurassic–Early Cretaceous litho-stratigraphy with emphasis on unconformities to define a coherent chronostratigraphic framework of the entire NCC. Integrating available data concerning tectonic deformation, and geochemistry and fabric of igneous rocks into the well-established coherent chronostratigraphic framework, a four-stage tectonic evolutionary model of the NCC is proposed, providing new insights into the dynamics of the Yanshanian intracontinental orogeny in East Asia. The first stage concerns a N–S extension in the NCC during the Early–early Middle Jurassic (∼200–170 Ma), expressed by the E–W striking brittle normal faults developed in the Lower–lower Middle Jurassic strata, and magmatism along the southern and northern margins of the NCC. It could be related to the post-orogenic extension after the deep continental subduction of the South China Block beneath the NCC. The second one is characterized by a N–S compression (i.e., Event A of the Yanshanian orogeny) in the late Middle Jurassic (∼170–160 Ma), evidenced by the unconformity above the Lower–lower Middle Jurassic strata and the upper Middle Jurassic syn-tectonic deposition. The associated N–S directed thrusts and fault-related folds were mainly localized in the northern part of the NCC, possibly responding to the far-field compression related to the closure of the Mongol–Okhotsk Ocean. The third stage corresponds to a NW–SE compression (i.e., Event B of the Yanshanian orogeny) during the Late Jurassic–earliest Cretaceous (∼160–135 Ma), illustrated by the NW–SE directed thrusts and the overprint of pre-existing N–S directed thrusts by the latter NW–SE directed thrusts. It was well recorded by the Upper Jurassic–lowermost Cretaceous syn-tectonic deposition and the unconformity above. This NW–SE compression in response to the flat slab subduction of the Paleo-Pacific Plate had influenced the entire NCC. However, the latest Middle–early Late Jurassic (∼165–150 Ma) local NE–SW extension, recorded by ductile and brittle normal faults, magnetic lineation in granitic plutons, and magmatism that extended to Northeast China and its adjacent areas, also occurred in the northeastern part of the NCC. This could be related to tectonic transition from the N–S closure of the Mongol–Okhotsk Ocean to the NNW-directed subduction of the Paleo-Pacific Plate. In the latest stage during the Early Cretaceous (∼135–115 Ma), the large-scale crustal extension, characterized by metamorphic core complexes, magmatism, graben or half-graben basins, occurred in a vast area extending more than 4000 km, from Transbaikalia, through the NCC, to the South China Block. It could be the consequence of the lithospheric thinning and the formation of the wide rift due to the southeastward stress relaxation of the NW–SE convergent East Asian continent as the slab rollback of the Paleo-Pacific Plate. These results provide a notable example of polyphase intra-plate deformation and magmatism paradigm in response to intracontinental orogeny with variable plate-boundary geodynamics. [ABSTRACT FROM AUTHOR]

Peatland development occurs naturally over long periods of time in response to climate, geology, hydrology and vegetation. Open-pit oil sands mining activities in Northern Alberta result in large-scale removal of the surficial landscape, which comprises many (~ 50%) peatlands, approximately 90% of which are fens with a wide range of peat thicknesses (< 1 m to ~ 5 m). Recently, the concept of peatland creation was adapted into the regulatory framework. Two experimental fen peatlands have now been constructed on post-mining landscapes in order to test the design implications and implementation methods and to develop knowledge to advance the concept. These two systems were guided by different conceptual approaches: one utilized numerical modelling for landscape optimization, while the other attempted to mimic the landscape position of natural fen systems (and supported the design with numerical modelling). Both system designs attempt to accelerate succession by adding peat substrate (0.5 m and 2 m) and revegetating, with the belief that the system will stabilize within decades as opposed to millennia. This paper provides an overview of the feasibility of peatland creation, from a primarily hydrologic perspective, and addresses the complexity of determining whether these projects can be deemed a success. Future landscape design plans could benefit from a change of perception of the role of peatlands in the landscape. This change should involve a shift away from viewing wetlands as landforms constrained to low-lying areas within the reclaimed landscape, and towards recognizing that peatlands can function as both a sink and source of water to the remainder of the catchment. Wetland interconnectivity within the reconstructed landscape could increase water detention and storage during wet periods, which would benefit both the wetlands and the forestlands during dry periods. The assessment of the success of these constructed systems should be a reflection of our ability to correctly and accurately predict the influence of external forcings (e.g., climate) on the processes operating within a newly constructed system. Short timeframes (~ 5 years) are sufficient to characterize a range of processes operating in the constructed ecosystems; however, longer time periods will reduce uncertainty in the assessment of the system's successional pathway. The design of future constructed fen peatlands must employ an adaptive approach that assimilates the knowledge developed in the current research and the information attained over the longer-term to guide the design of future fen systems. [ABSTRACT FROM AUTHOR]

The balance between constructive versus destructive processes in the formation and recycling of continental crust over Earth history – or crustal growth – remains contentious; whereas some advocate continuous continental growth, others suggest episodic growth predominantly during periods of supercontinent assembly. In this paper, we review the geological record and present an analysis of time constrained hafnium and oxygen isotopes in dated zircon crystals, and of incompatible elements (Zr, Th) in dated magmatic rocks, to explore the operation of Earth's supercontinent cycle. This analysis reveals the importance of the supercontinent cycle to continental growth by demonstrating a link between periods of enhanced crustal recycling and elevated geochemical proxies of subduction flux. The temporal fluxes in subduction rate suggest a conditioned duality of the Earth system between alternating periods of hot, volatile-rich, and cold, volatile-depleted, mantle relative to an idealised power decrease curve. Hot, volatile-rich mantle periods accompany supercontinent dispersion events and are characterised by mantle superplumes and increased crustal recycling during rapid global subduction. Cool, volatile-depleted mantle periods that accompany aggregated supercontinents are interpreted to arise from a combination of the widespread subduction of cold oceanic lithosphere, volatile depletion arising from the preceding voluminous subduction-related magmatism, and core insulation by the slab graveyards that accompanied formation of the supercontinent: these periods are characterised by enhanced mantle influence on magmas but low rates of continental crust production. Pulses of rapid continental growth that accompanied supercontinent assembly led to crustal oversteps — which can be considered as periods when too much crust had formed relative to the thermal state of the mantle at that time. When combined with the anomalous mantle cooling that accompanied these pulses of rapid crust formation, we postulate that supercontinent assembly led to a stepwise increase in plate size via changes in tessellation during supercontinent dispersal. [ABSTRACT FROM AUTHOR]

Uranium (U) is of enormous global importance because of its use in energy generation, albeit with potential environmental legacies. While naturally occurring U is widespread in the Earth's crust at concentrations of ~ 1 to 3 ppm, higher concentrations can be found, including within organic matter (OM)-rich sediments, leading to economic extraction opportunities. The primary determinants of U behaviour in ore systems are pH, Eh, U oxidation state (U(IV), U(VI)) and the abundance of CO 3 2– ions. The concentration/availability and interrelationships among such determinants vary, and the solubility and mobility of ions (e.g. OH − , CO 3 2– , PO 4 3 − , SiO 4 4 − , SO 4 2 − ) that compete for U (primarily as U(VI)) will also influence the mobility of U. In addition, the presence of OM can influence U mobility and fate by the degree of OM sorption to mineral surfaces (e.g. Fe- and Si- oxides and hydroxides). Within solid-phase OM, microbes can influence U oxidation state and U stability through direct enzymatic reduction, biosorption, biomineralisation and bioaccumulation. The biogenic UO 2 product is, however, reported to be readily susceptible to reoxidation and therefore more likely remobilised over longer time periods. Thus several areas of uncertainty remain with respect to factors contributing to U accumulation, stability and/or (re)mobilisation. To address these uncertainties, this paper reviews U dynamics at both geological and molecular scales. Here we identify U-OM bond values that are in agreement, relatively strong, independent from ionic strength and which may facilitate either U mobilisation or immobilisation, depending on environmental conditions. We also examine knowledge gaps in the literature, with U-OM solubility data generally lacking in comparison to data for U sorption and dissolution, and little information available on multi-component relationships, such as U-OM-V (V as vanadate). Furthermore, the capability of OM to influence the oxidation state of U at near surface conditions remains unclear, as it can be postulated that electron shuttling by OM may contribute to changes in U redox state otherwise mediated by bacteria. Geochemical modelling of the environmental mobility of U will require incorporation of data from multi-corporation studies, as well as from studies of U-OM microbial interactions, all of which are considered in this review. [ABSTRACT FROM AUTHOR]

This paper briefly reviews the application of geoinformatics in exploration geochemistry from the perspective of spatial analysis and visualization, and demonstrates the advantages of geoinformatics in exploring geochemical patterns and identifying geochemical anomalies. In particular, the application of geoinformatics to geochemical mapping, recognition of geochemical anomalies and simulation of geochemical patterns are discussed. The benefits of geoinformatics include: (1) overlay of geochemical data on a geological map, which helps geochemists to understand spatial geochemical patterns and visualize geochemical anomalies; (2) local neighbourhood spatial analysis, which considers the local spatial structure of geochemical patterns, as a powerful tool to identify weak geochemical anomalies; and (3) geochemical patterns simulation based on geological constrains, which helps to understand geological processes. Future researches should focus on development and application of various functions for processing geochemical data in a GIS to promote the progress of geoinformatics in both geochemical exploration and environmental studies. [ABSTRACT FROM AUTHOR]

Kimberlites represent magmas derived from great mantle depths and are the principal source of diamonds. Kimberlites and their xenolith cargo have been extremely useful for determining the chemical composition, melting regime and evolution of the subcontinental mantle. The late-Devonian Udachnaya (means Fortuitous ) pipe hosts the largest diamond deposit in Russia (> 60% diamond quantity and value) and one of the largest in the world, supplying gem-quality diamonds (~ 12% of world production). Since its discovery in 1956, the Udachnaya kimberlite pipe has become a “type locality” for geochemists and petrologists studying mantle rocks and mantle physical–chemical conditions. Apart from hosting a diverse suite of extremely well-preserved mantle xenoliths, the host kimberlite (East body) is the only known occurrence of fresh kimberlite, with secondary serpentine almost absent and uniquely high Na 2 O and Cl (up to 6.2 wt.%) and low H 2 O (< 1 wt.%) contents. The discovery of such compositional features in the only unaltered kimberlite has profound implications for models of parental kimberlite magma compositions, and the significance of the high Na and Cl abundances in the Udachnaya-East pipe has therefore been subjected to vigorous criticism. The main argument against a primary magmatic origin of high Na-Cl levels involves the possibility of contamination by salt-rich sedimentary rocks known in the subsurface of the Siberian platform, either by assimilation into the parental magma or by post-intrusion reaction with saline groundwaters. In this paper we review evidence against crustal contamination of Udachnaya-East kimberlite magma. This evidence indicates that the kimberlitic magma was not contaminated in the crust, and the serpentine-free varieties of this kimberlite owe their petrochemical and mineralogical characteristics to a lack of interaction with syn- and post-magmatic aqueous fluids. The groundmass assemblage of this kimberlite, as well as earlier-formed melt inclusions, contains alkali carbonate, chloride and other Na- and Cl-bearing minerals. This mineralogy reflects enrichment of the parental melt in carbonate, chlorine and sodium. The combination of low H 2 O, high alkali-Cl abundances, lack of serpentine, and the presence of alteration-free mantle xenoliths all indicate that the Udachnaya-East kimberlite preserves pristine compositions in both kimberlite and mantle xenoliths. Evidence for broadly similar chemical signatures is found in melt inclusions from kimberlites in other cratons (South Africa, Canada and Greenland in our study). We demonstrate that two supposedly “classic” characteristics of kimberlitic magmas – low sodium and high water contents – relate to postmagmatic alteration. A “salty” carbonate composition of the kimberlite parental melt can account for trace element signatures consistent with low degrees of partial melting, low temperatures of crystallisation and exceptional rheological properties that enable kimberlite magmas to rise with high ascent velocities, while carrying a large cargo of entrained xenoliths and crystals. Our empirical studies are now supported by experimental data which suggest that carbonate-chloride fluids and melts derived by liquid immiscibility are a crucial factor of diamond formation. [ABSTRACT FROM AUTHOR]

Understanding the natural variability of the Earth’s climate system and accurately identifying potential anthropogenic influences requires long term, geographically distributed records of key climate indicators, such as temperature and precipitation that extend prior to the last 400 years of the Holocene. Reef corals provide an excellent source of high resolution climate records, and importantly represent the tropical marine environment where palaeoclimate data are urgently required. Recent decades have seen significant improvement in our understanding of coral biomineralisation, the associated uptake of geochemical proxies and methods of identifying and understanding the effects of both early and late, post depositional diagenetic alteration. These processes all have significant implications for interpreting geochemical proxies relevant to palaeoclimatic reconstructions. This paper reviews the current ‘state of the art’ in terms of coral based palaeoclimate reconstructions and highlights a key remaining problem. The majority of coral based palaeoclimate research has been derived from massive colonies of Porites . However, massive Porites are not globally abundant and may not provide material of a particular age of interest in those regions where they are present. Therefore, there is great potential for alternate coral genera to act as complimentary climate archives. While it remains critical to consider five key factors – vital effects, differential growth morphologies, geochemical heterogeneity in the skeletal ultrastructure, transfer equation selection and diagenetic screening of skeletal material – in order to allow the highest level of accuracy in coral palaeoclimate reconstructions, it is also important to develop alternate taxa for palaeoclimate studies in regions where Porites colonies are absent or rare. Currently as many as nine genera other than Porites have proven at least limited utility in palaeothermometry, most of which are found in the Atlantic/Caribbean region where massive Porites do not exist. Even branching taxa such as Acropora have significant potential to preserve environmental archives. Increasing this capability will greatly expand the number of potential geochemical archives available for longer term temporal records of palaeoclimate. [ABSTRACT FROM AUTHOR]

Abstract: Records of the frequency and magnitude of floods are needed on centennial or millennial timescales to place increases in their occurrence and intensity into a longer-term context than is available from gauged river-flow and historical records. Recent research has highlighted the potential for lake sediment sequences to act as a relatively untapped archive of high-magnitude floods over these longer timescales. Abyssal lake sediments can record past floods in the form of coarser-grained laminations that reflect the capacity for river flows with greater hydrodynamic energy to transport larger particles into the lake. This paper presents a framework for investigating flood stratigraphies in lakes by reviewing the conditioning mechanisms in the lake and catchment, outlining the key analytical techniques used to recover flood records and highlighting the importance of appropriate field site and methodology selection. The processes of sediment movement from watershed to lake bed are complex, meaning relationships between measureable sedimentary characteristics and associated river discharge are not always clear. Stratigraphical palaeoflood records are all affected to some degree by catchment conditioning, fluvial connectivity, sequencing of high flows, delta dynamics as well as within-lake processes including river plume dispersal, sediment focussing, re-suspension and trapping efficiency. With regard to analytical techniques, the potential for direct (e.g., laser granulometry) and indirect (e.g., geochemical elemental ratios) measurements of particle size to reflect variations in river discharge is confirmed. We recommend care when interpreting fine-resolution geochemical data acquired via micro-scale X-ray fluorescence (μXRF) core scanning due to variable down-core water and organic matter content altering X-ray attenuation. We also recommend accounting for changes in sediment supply through time as new or differing sources of sediment release may affect the hydrodynamic relationship between particle size and/or geochemistry with stream power. Where these processes are considered and suitable dating control is obtained, discrete historical floods can be identified and characterised using palaeolimnological evidence. We outline a protocol for selecting suitable lakes and coring sites that integrates environmental setting, sediment transfer processes and depositional mechanisms to act as a rapid reference for future research into lacustrine palaeoflood records. We also present an interpretational protocol illustrating the analytical techniques available to palaeoflood researchers. To demonstrate their utility, we review five case studies of palaeoflood reconstructions from lakes in geographically varied regions; these show how lakes of different sizes and geomorphological contexts can produce comprehensive palaeoflood records. These were achieved by consistently applying site-validated direct and proxy grain-size measurements; well-established chronologies; validation of the proxy-process interpretation; and calibration of the palaeoflood record against instrumental or historical records. [Copyright &y& Elsevier]

Abstract: The Cretaceous was one of the most remarkable periods in geological history, with a “greenhouse” climate and several important geological events. Reconstructions of atmospheric CO2 using proxies are crucial for understanding the Cretaceous “greenhouse.” In this paper we summarize the major approaches for reconstructing CO2 based on paleobotanical or geochemical data, and synthesize the CO2 variations throughout the Cretaceous. The results show that atmospheric CO2 levels remained relatively high throughout the Cretaceous, but were lower in the early Cretaceous, highest in the mid-Cretaceous and gradually declined during the late Cretaceous. However, this overall trend was interrupted by several rapid changes associated with ocean anoxic events (OAEs) and the end-Cretaceous catastrophic event. New data on paleo-CO2 levels from paleobotanical and paleosol evidences support not only the overall trends indicated by geochemical models, but provide more precise records of the short-term fluctuations related to brief episodes of climate change. Temporal resolution within the long quiet magnetic period in the middle Cretaceous is one of the obstacles preventing us from a more comprehensive understanding of the CO2 climate linkage. But new paleo-CO2 determinations and climatic data from stratigraphic sections of sediments intercalated with datable volcanic rocks will allow a better understanding of the relationships between fluctuations of atmospheric CO2, climate change, and geological events. [Copyright &y& Elsevier]

Abstract: The Cretaceous plutonic suites in the Fujian coastal area include abundant I-type and A-type granitoids and lesser gabbroids. They are important components of the Late Yanshanian magmatic belt along the southeastern coast of China, and define a linear NNE–SSW-trending belt of magmatism. Geochronological, geochemical and geological data from thirty intrusions are summarised in this paper, and the data provide distinct magmatic, geochemical and tectonic patterns in the area. A compilation of geochronological data for these intrusive rocks indicates emplacement mainly from around 125 to 90Ma, with a major peak from 115 to 90Ma, and a subordinate peak from 125 to 115Ma. Besides their temporal and spatial coexistence, all these intrusive rocks have similar geochemical patterns which point to involvement of components from a depleted asthenospheric mantle source for the parental magmas, most probably by magma mixing. The first appearance of sparse I-type granitoids with post-collisional extensional granite affinities, and the emplacement of the Baijuhuajian and Suzhou A-type granites, mark the beginning of extension during the Early Cretaceous at ca. 125 to 119Ma. The subsequent development of bimodal magmatism at 115 to 90Ma, with numerous arc-related mafic gabbros and I-type granites, together with some A-type granites, suggests that this major igneous event took place as a response to back-arc extension. On the basis of petrology, geochronology, tectonics, and elemental and isotopic geochemistry, we speculate that break-off and rollback of the subducting Palaeo-Pacific Plate during the Cretaceous were responsible for the Late Yanshanian regional tectono-magmatic evolution in the area. We suggest that this process facilitated a strong and rapid linear upwelling of the asthenospheric mantle beneath the coastal area of southeastern China, with consequential extension of the overlying continental lithosphere, and ultimately the large-scale Late Yanshanian magmatism of the study area. [Copyright &y& Elsevier]

East Asia is exceptionally rich in diverse geological phenomena related to processes of major global significance in Earth history. Its tectonic evolution is closely related to the subduction of the Izanagi and Pacific plates and the India-Eurasia collision. Thus, this domain presents a vast natural laboratory within which some of the most topical and fundamental problems in Pacific-Asian Tectonics can be addressed. Recent breakthroughs in understanding the tectonic evolution of East Asia have been achieved, involving intraplate deformation, plate fragmentation, plate boundary processes, orogenic collapse, and craton destruction. These advances have been achieved via multidisciplinary work including structural geology, basin research, land and marine geophysics, thermochronology, numerical modeling, geochemistry and classical field geology. In the current context of research in East Asia the time is ripe for a thematic volume of review papers. This special issue is focused on the theme "Pacific-Asian Tectonics". It describes interdisciplinary methods adopted to study Meso-Cenozoic basin-forming mechanisms and evolutionary processes, unravels the timing and characteristics of major intraplate deformation, depicts the spatial-temporal distribution of Meso-Cenozoic igneous rocks, discusses the deep lithospheric structures overlying the subducting oceanic plates, and probes the natures and fates of subduction or collision processes. [ABSTRACT FROM AUTHOR]

Abstract: Sediment fingerprinting is a technique that is increasingly being used to improve the understanding of sediment dynamics within river basins. At present, one of the main limitations of the technique is the ability to link sediment back to their sources due to the non-conservative nature of many of the sediment properties. The processes that occur between the sediment source locations and the point of collection downstream are not well understood or quantified and currently represent a black-box in the sediment fingerprinting approach. The literature on sediment fingerprinting tends to assume that there is a direct connection between sources and sinks, while much of the broader environmental sedimentology literature identifies that numerous chemical, biological and physical transformations and alterations can occur as sediment moves through the landscape. The focus of this paper is on the processes that drive particle size and organic matter selectivity and biological, geochemical and physical transformations and how understanding these processes can be used to guide sampling protocols, fingerprint selection and data interpretation. The application of statistical approaches without consideration of how unique sediment fingerprints have developed and how robust they are within the environment is a major limitation of many recent studies. This review summarises the current information, identifies areas that need further investigation and provides recommendations for sediment fingerprinting that should be considered for adoption in future studies if the full potential and utility of the approach are to be realised. [Copyright &y& Elsevier]

Abstract: Geoscience methods are increasingly being utilised in criminal, environmental and humanitarian forensic investigations, and the use of such methods is supported by a growing body of experimental and theoretical research. Geoscience search techniques can complement traditional methodologies in the search for buried objects, including clandestine graves, weapons, explosives, drugs, illegal weapons, hazardous waste and vehicles. This paper details recent advances in search and detection methods, with case studies and reviews. Relevant examples are given, together with a generalised workflow for search and suggested detection technique(s) table. Forensic geoscience techniques are continuing to rapidly evolve to assist search investigators to detect hitherto difficult to locate forensic targets. [Copyright &y& Elsevier]

Abstract: Cohesive sediment is an important component of aquatic environments, which must be monitored and managed for environmental, engineering, and human health reasons. While the hydrodynamic aspects of sediment erosion and transport are well understood, the erodibility of cohesive sediment has proved more difficult to address and predict. Erodibility is the propensity for the sediment to be eroded, and is represented typically as an erosion threshold or erosion rate. It is an attribute of the sediment itself, and is dependent on the sediment properties that dictate the resistive forces in the sediment, such as gravity, friction, cohesion, and adhesion. This paper reviews recent findings from a range of disciplines to create a comprehensive picture of the physical, geochemical and biological properties that influence the erodibility of cohesive sediment. By identifying these key sediment properties, we provide the background for a discussion on how changes in and interactions between the properties generate significant spatial and temporal variations in erodibility. We discuss the development of a predictive model of erodibility, and emphasize the need for more comparable field and laboratory data. [Copyright &y& Elsevier]

Abstract: Rutile is the most common naturally occurring titanium dioxide polymorph and is widely distributed as an accessory mineral in metamorphic rocks ranging from greenschist to eclogite and granulite facies but is also present in igneous rocks, mantle xenoliths, lunar rocks and meteorites. It is one of the most stable heavy minerals in the sedimentary cycle, widespread both in ancient and modern clastic sediments. Rutile has a wide range of applications in earth sciences. It is a major host mineral for Nb, Ta and other high field strength elements, which are widely used as a monitor of geochemical processes in the Earth''s crust and mantle. Great interest has focused recently on rutile geochemistry because rutile varies not only by bulk composition reflected, for instance, in its Cr and Nb contents but also by the temperature of crystallisation, expressed in the Zr content incorporated into the rutile lattice during crystallisation. Rutile geochemistry and Zr-in-rutile thermometry yield diagnostic data on the lithology and metamorphic facies of sediment source areas even in highly modified sandstones that may have lost significant amounts of provenance information. Rutile may therefore serve as a key mineral in sediment provenance analysis in the future, similar to zircon, which has been widely applied in recent decades. Importantly, rutile from high-grade metamorphic rocks can contain sufficient uranium to allow U–Pb geochronology and (U–Th)/He thermochronology. Furthermore, in situ Lu–Hf isotope analysis of rutile permits insights into the evolution of the Earth''s crust and mantle. Besides that, rutile is also of great economic importance because it is one of the favoured natural minerals used in the manufacture of white titanium dioxide pigment, which is a major constituent in various products of our daily life. Heavy mineral sands containing a significant percentage of rutile are therefore the focus of exploration worldwide. This paper aims to provide an overview of the applications of rutile in earth sciences, based on a review of data published in recent years. After giving a summary of various rutile-bearing lithologies, the focus lies on rutile geochemistry, Zr-in-rutile thermometry, O isotope analysis, U–Pb geochronology, (U–Th)/He thermochronology and Lu–Hf isotope analysis. A final outline of the economic importance of rutile highlights the demand for further rutile-related research in earth sciences. [Copyright &y& Elsevier]

Abstract: One hundred years ago Georg Popp became the first scientist to present in court a case where the geological makeup of soils was used to secure a criminal conviction. Subsequently there have been significant advances in the theory and practice of forensic geoscience: many of them subsequent to the seminal publication of “Forensic Geology” by Murray and Tedrow [Murray, R., Tedrow, J.C.F. 1975 (republished 1986). Forensic Geology: Earth Sciences and Criminal Investigation. Rutgers University Press, New York, 240 pp.]. Our review places historical development in the modern context of how the allied disciplines of geology (mineralogy, sedimentology, microscopy), geophysics, soil science, microbiology, anthropology and geomorphology have been used as tool to aid forensic (domestic, serious, terrorist and international) crime investigations. The latter half of this paper uses the concept of scales of investigation, from large-scale landforms through to microscopic particles as a method of categorising the large number of geoscience applications to criminal investigation. Forensic geoscience has traditionally used established non-forensic techniques: 100 years after Popp''s seminal work, research into forensic geoscience is beginning to lead, as opposed to follow other scientific disciplines. [Copyright &y& Elsevier]

Radiogenic isotopes have wide application to chemical stratigraphy, geochronology, provenance studies, and studies of temporal changes in Earth surface processes. This paper briefly reviews the principles of radiogenic isotope geochemistry and the distribution of a number of elements of interest in the environment, and then uses this information to explore the range of applications to chemical stratigraphy and other fundamental subjects of sedimentary geology. Many of these applications center on the reconstruction of secular variations in paleoseawater isotope signals. These “seawater isotope curves” can be used for stratigraphic correlation and to assess changes through Earth history in processes such as tectonic uplift, climate change, biogeochemical cycling, ocean circulation, crustal growth, and surface water evolution. Understanding the modern biogeochemical cycle of the element/isotope system of interest is essential for gaining the maximum information regarding the operation of ancient cycles. The main sources of uncertainty for reconstructing seawater isotope curves involve diagenetic alteration, sample impurities, and errors in age assignments. Rigorous sample selection criteria and pretreatment methods are keys to reconstructing the most accurate seawater isotope curves. Applications are discussed for the Rb–Sr, Sm–Nd, La–Ce, Lu–Hf, Re–Os, U–Th–Pb, K–Ar, and cosmogenic isotope systems. [Copyright &y& Elsevier]

The North American Cordilleran Anatectic Belt (CAB) is a ~3,000 km long region in the hinterland of the Cordillera that comprises numerous exposures of Late Cretaceous to Eocene intrusive rocks and anatectic rocks associated with crustal melting. As such, it is comparable in size and volume to major anatectic provinces including the Himalayan leucogranite belt. The CAB rocks are chiefly peraluminous, muscovite-bearing leucogranite produced primarily by anatexis of Proterozoic to Archean metasedimentary rocks. The CAB rocks lack extrusive equivalents and were typically emplaced as thick sheets, laccoliths, and dike/sill complexes. The extent, location, and age of the CAB suggests that it is integral to understanding the tectonic evolution of North America, however, the belt is rarely considered as a whole. This paper reviews localities associated with crustal melting in the CAB and compiles geochemical, geochronologic, and isotopic data to evaluate the melt conditions and processes that generated these rocks. The geochemistry and partial melting temperatures (ca. 675–775 °C) support water-absent muscovite dehydration melting and/or water-deficient melting as the primary melt reactions and are generally inconsistent with water-excess melting and high-temperature (biotite to amphibole) dehydration melting. The CAB rocks are oldest in the central U.S. Cordillera and become younger towards both the north and south. At any single location, partial melting appears to have been a protracted process (≥10 Myr) and evidence for re-melting and remobilization of magmas is common. End-member hypotheses for the origin of the CAB include decompression, crustal thickening, fluid-flux melting, and increased heat flux from the mantle. Different parts of the CAB support different hypotheses and no single model may be able to explain the entirety of the anatectic event. Regardless, the CAB is a distinct component of the Cordilleran orogenic system. [ABSTRACT FROM AUTHOR]

The Hawaiian-Emperor volcanic chain (H-E chain) is located in the middle of the North Pacific Ocean. It extends from northwest to southeast, including two segments, the older Emperor chain and the younger Hawaiian chain between which is a 60o change in strike, here termed the H-E bend. The H-E chain is the clearest and most intensively researched hot spot track in terms of plate motion, mantle plumes, tectonics, geochemical evolution, and lithospheric studies. However, debates on the formation of the H-E chain, in particular the H-E bend, concerning its origin in hot spot drift and/or Pacific plate motion change, have been ongoing for several decades. In this paper, we review current understanding and ideas concerning this debate and suggest ways forward. So far, neither hot spot southerly drift nor Pacific plate motion change can perfectly account for the geometry and progression of the H-E chain. In this review, we put forward a joint model where these two competing processes together can reasonably explain the evolution of the H-E chain and the H-E bend. In addition, we proposed three stages for formation of the H-E chain, including: 1) A ridge-plume interaction stage: Meiji~Detroit seamounts and a possible subducted section; 2) A combination of hot spot-Pacific plate motion: South of Detroit seamount ~ H-E bend; and 3) Pacific plate motion with a fixed hot spot: Hawaiian volcanic chain. In addition, any plate movement at the surface must be balanced by motion deeper in the mantle. Therefore, we consider that the surface Pacific plate motion and the state of deep mantle plume at 47–55 Ma are not totally separated but co-evolved. Furthermore, reconstructions of the Pacific plate and its boundaries should be considered if Hawaiian hot spot motion makes great contributions to the formation of the H-E chain. Nevertheless, establishing the causal links between these events and their underlying dynamic triggers requires further, more comprehensive work. [ABSTRACT FROM AUTHOR]

Arclogites, or clinopyroxene-, garnet-, amphibole-, and Fe Ti oxide-bearing cumulates and restites (collectively representing residues) to andesitic continental arc magmas, are reviewed here and in a companion paper (Ducea et al., 2020). Experimental petrology and petrologic observations suggest that these eclogite facies rocks form magmatically in deep crustal hot zones beneath arcs with crustal thicknesses exceeding 35–40 km. Volcanic and plutonic products of thinner arcs may instead be entirely extracted from amphibolite to granulite facies and garnet-free pyroxenite residues. Arclogites are perhaps best known as xenoliths, with notable examples from young (Sierra Nevada and Central Arizona) and modern (Colombia) sub-arc environments. We suspect that arclogite occurs more commonly than currently recognized in the xenolith record from orogenic and cratonic domains. Arclogite is also found as discrete intervals in the deepest exposures of the Kohistan arc and as small volume inclusions in tectonically exposed peridotite massifs (e.g., Beni Bousera, Morocco). Geochemically, these rocks are low silica (SiO 2 < 50%) assemblages with low Nb/Ta and Sr/Y ratios and enrichments in heavy REEs such that they represent the complement to the andesitic-dacitic liquids that make up the surface volcanics and batholiths of most arcs. Virtually all rock-forming minerals in arclogites are of similar or greater density than the underlying mantle, making them ideal candidates for foundering. Arclogites are formed in the lowermost crust of arcs at 35–70 km depth and record high temperatures (~800–1000 °C) at the time of formation which then cool and metamorphose at ~650–750 °C if they remain attached to the crust for an extended period of time. Ages of these rocks are obtainable by Sm Nd and Lu Hf garnet isochron geochronology as well as titanite or rutile U Pb geochronology, although these ages can be reset through long-term storage in hot lower crustal environments. Recent discovery of zircon accessory minerals in arclogites makes these rocks datable with greater precision and greater chance of preserving crystallization ages by U Pb chronology. [ABSTRACT FROM AUTHOR]

Young stresses that the Archaean-Proterozoic transition is one of the most important in geological history, being directly related to the onset of "modern-style" plate tectonics, massive palaeoclimatic upheavals, and the oxygenation of the palaeo-atmosphere; the early Palaeoproterozoic sedimentary record encompasses evidence for Earth's first widespread glacial episodes, defining the Huronian Glacial Event. Despite a change from poorly preserved pre-3.2 Ga fluvial deposits mainly confined to the flanks of volcanoes and volcanic plateaux of the "plume-lid tectonics" era, to the advent of "modern-style" plate tectonics in the Mesoarchaean which led to relatively large braided river systems, there was little change in fluvial style during the Archaean as a whole. The continued use of the "accepted" 2.5 Ga age for the Archaean-Proterozoic boundary can thus be brought into question, as is done in the final paper by Rajat Mazumder et al. based on a review of the Archaean-Palaeoproterozoic geology of Peninsular India. The concept of a gradual and globally diachronous Archaean-Proterozoic transition over some hundreds of million years (wherein a clear definition of a global ~2.5 Ga "boundary" becomes irrelevant), thus contrasts with the suggestion of redefining a new specific boundary globally, or as a possible compromise having a separate such boundary for each major craton. [Extracted from the article]