Revealing Archaean crust-formation processes requires understanding of geochemical and chronological differences in granitoids. During the early evolution of Earth's felsic crust, large amounts of tonalite-trondhjemite-granodiorites (TTGs) were formed, making up most of the Archaean crust preserved until today. TTGs have two geochemical endmembers, the low-HREE and high-HREE (heavy rare earth elements) TTGs. The genesis of TTGs has been explained by the dehydration melting of basaltic crust, but the formation of the different types of TTGs is a subject of debate. This study provides new U-Pb zircon ages for deciphering the temporal relationships between the different TTG types in the Lake Inari terrain, Arctic Fennoscandia. The interpretation of the FIRE (Finnish Reflection Experiment) 4A line shows the existence of two tectonic blocks for the terrain. Our results from zircon populations of low- and high-HREE TTGs and adjacent porphyritic granitoids show a large time spread suggesting a prolonged migmatization in the Lake Inari terrain from 2900 to 2600 Ma. This supports a long-term source of heat such as a stationary plume related to stagnant or sluggish lid-tectonics. The high- and low-HREE TTGs show parallel ages and occur intermingled, which points to a common source instead of different tectonic settings. There is no distinct age difference between the two tectonic blocks identified in the FIRE 4A seismic reflection profile. Prolonged melting episodes of thickened felsic crust produced porphyritic granites between 2650-2500 Ma. The similar to 1.9 Ga Lapland-Kola orogeny caused minor zircon recrystallization but did not influence Archaean migmatite morphology. The Lake Inari TTGs peak approximately at 2.8 Ga, i.e., 100 Ma before the formation of the suggested Kenorland supercontinent.

The heat transfer from the low latitudes to high latitudes is responsible for maintaining the earth’s climate dynamics. Thus, deciphering the possible mechanism driving the variability of the Indian summer monsoon (ISM) during the Holocene Epoch has been critical to understand the hydroclimatic changes of the low latitudes. Despite several efforts, the teleconnection of ISM with the global climate dynamics remains under-represented and poorly understood. The present study aims to delineate the ISM variability and its possible forcing mechanism from western India (Gujarat). In this study, a sediment core (~65 cm long) was raised from the Jaffrabad mudflat (MIT) in western Gujarat. The sediment samples were subjected to geochemical analysis to investigate paleomonsoon, paleo-sediment source and paleoweathering changes. The results show that, with the addition of intermediate sources, the sediments were principally derived from the hinterland’s Deccan basalts. Further, the study suggested a warm and wet climate due to strong ISM during 10,650−5500 cal yr BP associated with the solar as well as orbital forcings. The weak monsoon during 5500−2700 cal yr BP has been linked with southward migration of the Intertropical Convergence Zone (ITCZ) along with the increased El Niño-like conditions. Further, the wavelet analysis revealed that a combined influence of solar, orbital and North Atlantic forcings led to monsoon variability along western India, during the Holocene Epoch. By reconciling the geochemical proxies, the present study has implications in the reconstruction of paleomonsoon and establishing the possible teleconnection with the global climate system.

Caldera-forming eruptions of silicic volcanic systems are among the most devastating events on Earth. By contrast, post-collapse volcanic activity initiating new caldera cycles is generally considered less hazardous. Formed after Santorini’s latest caldera-forming eruption of ~1600 bce , the Kameni Volcano in the southern Aegean Sea enables the eruptive evolution of a recharging multi-cyclic caldera to be reconstructed. Kameni’s eruptive record has been documented by onshore products and historical descriptions of mainly effusive eruptions dating back to 197 bce . Here we combine high-resolution seismic reflection data with cored lithologies from International Ocean Discovery Program Expedition 398 at four sites to determine the submarine architecture and volcanic history of intra-caldera deposits from Kameni. Our shore-crossing analysis reveals the deposits of a submarine explosive eruption that produced up to 3.1 km 3 of pumice and ash, which we relate to a historical eruption in 726 ce . The estimated volcanic explosivity index of magnitude 5 exceeds previously considered worst-case eruptive scenarios for Santorini. Our finding that the Santorini caldera is capable of producing large explosive eruptions at an early stage in the caldera cycle implies an elevated hazard potential for the eastern Mediterranean region, and potentially for other recharging silicic calderas.

In this study, we present major and trace element concentrations, U-Pb zircon geochronology as well as neodymium isotopic compositions of the banded iron formations (BIFs) from the Bundelkhand Craton, India. The study aims to constrain the source characteristics, depositional age and evaluate the paleoenvironmental implications of the Meso-Neoarchean seawater from which the BIF precipitated. The presence of a 2898 +/- 26 Ma rounded zircon grain in the Girar BIFs indicates their maximum depositional age, which is consistent with the reported age of the metabasalts (2989 +/- 190 Ma). Bearing in mind the errors, we consider the age of the studied BIFs to be ca. 2850 Ma. The BIFs from Mauranipur are associated with 2810 Ma dacite and formed at the same time. They have zircon with ages of 2718 +/- 22, 2573 +/- 66, 2070 +/- 29 and 1934 +/- 39 Ma. The BIFs from Babina are associated with 2540 Ma felsic volcanics and can be considered of the same age. Our study shows that the sedimentation of BIF in the Girar and Mauranipur greenstone belts took place in the Mesoarchean between ca. 2850 and 2810 Ma, respectively, and in the Babina greenstone belt in the Neoarchean at ca. 2540 Ma. A positive correlation between TiO2 and Zr, Al2O3 and Zr, Zr and Th/U, Y and Zr, Ni and Cr, as well as Hf and Zr, may suggest a detrital component to the BIF derived from terrigenous mafic and felsic sources. The PAASnormalized REE patterns of the Bundelkhand BIFs are characterized by depleted LREEs, positive La, Eu, Y anomalies and Y/Ho ratios mostly ranging between 18 and 47. The studied BIFs are broadly similar to worldwide BIF occurrences at the time with the exception of the Mauranipur BIFs, which show elevated MnO concentrations (0.92 to 4.82 wt%). The studied BIF samples from the Bundelkhand Craton display a wide range of epsilon Nd(t) ranging from -6.57 to + 4.12. The broad range of isotopic values along with the above-noted geochemical signatures suggest that the BIF from the Bundelkhand Craton had significant inputs from submarine hydrothermal sources as well as pre-existing continental crust. The elevated manganese concentrations in BIFs from Mauranipur may imply the availability of free oxygen in seawater on the Bundelkhand Craton during the Mesoarchean.

The conversion of basaltic crust into a thick, buoyant felsic crust of tonalite-trondhjemite-granodiorite (TTG) composition has been a fundamental process in the Earth 's evolution during the Archaean Eon (4.03 -2.50 Ga). The proposition that TTGs have formed as a result of the partial melting of hydrated mafic rocks is now well corroborated by geochemical modelling and experimental methods although these processes have only rarely been tested or documented by field studies. Here, we investigate the migmatite structures and major and trace element geochemistry of the 2.9 -2.6 Ga Lake Inari TTG-metabasalt terrain in northern Finland, in the LaplandKola Province of Arctic Fennoscandia. The Lake Inari metabasalts geochemically resemble the flood basalts of the Phanerozoic oceanic plateaus. The TTGs show overall high Si and Na/K characteristics and have two coeval and intermingled geochemical endmembers, the low-HREE and high-HREE TTGs. Their variable geochemical signatures may reflect internal magmatic processes such as mingling of magmas that have experienced different evolutionary paths in terms of source mineralogy, degree of partial melting, differentiation and migration. The bimodal TTG-metabasalt association shows various migmatite structures such as metatexites, metatexitediatexite transitions and massive diatexites that have formed in response to the weakening of the crust, melt segregation, extraction, migration and redistribution (SEMR) processes, and synanatectic strain. Rafts of the metabasalts probably represent the remnants of a basaltic upper 'lid ' layer. We interpret the Lake Inari terrain to represent a widespread migmatization in deeper layers of an overthickened basaltic plateau persisting above a mantle plume, consistent with a stagnant or sluggish lid tectonic setting. Our results suggest that the formation of buoyant TTGs by partial melting of plateau basalts might have set off the evolution of continents.

Large explosive volcanic eruptions from island arcs pour pyroclastic currents into marine basins, impacting ecosystems and generating tsunamis that threaten coastal communities and infrastructures. Risk assessments require robust records of such highly hazardous events, which is challenging as most of the products lie buried under the sea. Here we report the discovery by IODP Expedition 398 of a giant rhyolitic pumice deposit emplaced 520 ± 10 ky ago at water depths of 200 to 1000 m during a high-intensity, shallow submarine eruption of ancestral Santorini Volcano. Pyroclastic currents discharged into the sea transformed into turbidity currents and slurries, forming a >89 ± 8 km 3 volcaniclastic megaturbidite up to 150 m thick in the surrounding marine basins, while breaching of the sea surface by the eruption column laid down veneers of ignimbrite on three islands. The eruption is one of the largest recorded on the South Aegean Volcanic Arc, and highlights the hazards from submarine explosive eruptions.

Himalayan leucogranites are important for understanding the tectonic evolution of collision zones in general and the causes of crustal melting in the Himalayan orogen in particular. This paper aims to understand the melt source and emplacement age of the leucogranites from Sikkim in order to decipher the deep geodynamic processes of the eastern Himalayas. Zircon U-Pb analysis of the Higher Himalayan Sequence (HHS) metamorphic core reveals a prolonged period of crustal melting between > 33 Ma and ca. 14 Ma. Major and trace element abundances are presented for 27 leucogranites from North Sikkim that are classified into two-mica and tourmaline leucogranite types. They are peraluminous in composition, characterized by high SiO2 (70.91-74.9 wt.%), Al2O3 (13.69-15.82 wt.%), and low MgO (0.13-0.74 wt.%). Elemental abundances suggest that Sikkim Himalayan leucogranites are derived from crustal melts. The two-mica leucogranites are derived from a metagreywacke source, whereas the tourmaline leucogranites are sourced from metapelitic sources, with inherited zircons indicating an HHS origin for both types. U-Pb zircon geochronology of the two mica leucogranites indicates ages of ca. 19-15 Ma, consistent with crustal melting recorded in HHS gneisses from Darjeeling. Monazites from both the two-mica and tourmaline leucogranites yield a crystallization age of ca. 15-14 Ma, coeval with movement on the Main Central Thrust and South Tibetan Detachment System which further provides constraints on the timing and mechanism of petrogenesis of leucogranites in the Sikkim Himalayas.

Investigating the geochemical composition of bulk sediments stands as a crucial method for unraveling the complexities of various sedimentary processes. However, the intricacies arising from extensive datasets and alterations in sediment due to diverse factors often impede the clear identification of underlying patterns in geochemical fluctuations. In addressing these, employing multivariate statistical analyses has proven to be an invaluable tool for elucidating intricate patterns within large dataset. In this study, we focus on the utilization of Principal Component Analysis (PCA), a multivariate statistical technique, to uncover the underlying sedimentary processes influencing distinct geochemical dataset. Specifically, our attention is directed towards the examination of geochemical data from the previously published geochemical data of metasediments from Shimla and Chail group (referred to as SCM) and the mudflat sediments of Diu Island (referred to as DMS). Our PCA outcomes reveal that the initial three principal components (PC1, PC2, and PC3) account for 52.51

The sediments have been a ubiquitous archive for paleoclimate reconstruction while the marine sediments are considered to be serene and mostly undisturbed from anthropogenic encroachments. Unlike continental records, the deep-sea sediments elucidated the evidence of at least 50 glacial and interglacial stages during the Quaternary period and thus proved its applicability in quaternary climate reconstruction. The geochemical variations in the marine sediments are often used as a proxy to decode the past productivity, redox, weathering and provenance changes as a function of past climate and oceanographic perturbations. The geochemical behavior of the elements in the sedimentary environment primarily relies on ionic potential along with redox potential and pH which leads to mobility and enrichment of selected elements and thus acting as potential evidence for ambient temporal changes. The present chapter aims to provide an overview of frequently used geochemical proxies and their applicability. Further, the chapter also tries to provide the significance of statistical and machine learning approaches to the geochemical datasets in understanding the climatic processes that led to changes in the geochemical variability.

Petrology, geothermobarometry, and phase equilibrium modelling of garnetiferous felsic gneiss from Grovnes peninsula in the Larsemann Hills of Prydz Bay, East Antarctica provide pristine evidence for the preservation of high-grade metamorphic imprint in the area. The metamorphic evolution of the sample is demonstrated by the development of the assemblage Grt+Bt+Melt+Pl+Sill+Kfs+Qtz+Ilm at peak metamorphic conditions of-790 degrees C and-7.5 kbar, which subsequently underwent retrogression and cooling to lower P-T conditions along a clockwise path. Texturally constrained chemical dating of monazites constrain the timing of peak metamorphism and garnet formation at-575 Ma, whereas the apatite U-Pb ages constrain cooling ages at-518 Ma. The clockwise P-T-t trajectory of the studied samples, together with the Ediacaran-Cambrian metamorphic/cooling ages demonstrate the long-lived nature of metamorphism in Prydz Bay, which is ascribed to collisional tectonism prevalent during the final stages of the assembly of East Gondwana supercontinent. Similar results from adjacent continental fragments including Sri Lanka, Eastern Ghats Belt, Madagascar, and South India suggest their coeval metamorphic evolution during the East African orogeny.

This study investigates the evolution of alkaline silicate rocks in the Southeast of the Sevattur Carbonatite Complex, intruding granite gneiss country rock. These rocks include monzodiorite, monzonite, syenite, albitite, and granite, alongside ultramafic enclaves known as pyroxene hornblendite. The present work unveils the intricate fractional crystallization processes within an alkali-rich basaltic magma system supported by mineralogical and geochemical studies. Mafic minerals such as diopside, pargasite, interstitial magnetite, and ilmenite indicate early cumulate textures forming at high temperatures. Amphibole and diopside alongside apatite inclusions suggest the presence of alkalis, fluorine, phosphorus and H 2 O in the primary magma. A coherent mineralogical and geochemical continuum from pyroxene hornblendite to monzodiorite, monzonite, and syenite with decreasing temperatures indicates fractional crystallization from a common primary magma. Furthermore, the absence of chilled margins and distinct boundaries dismisses a xenolithic origin for pyroxene hornblendite. The formation of granite, likely occurring during late-magmatic to hydrothermal stages, is characterized by K-feldspar, albite, and quartz, with clinozoisite and chlorite. Albitite occurrences as pegmatitic veins in syenite monzonite with shared geochemical traits with syenite and monzonite, suggesting a late-stage derivation from a common magma. Notably, these rocks lack the characteristic alkali-rich mineral assemblages, dispelling the notion of fenitization.

This paper reports the results of the geochemical study of the Jutogh metasedimentary rocks that occur as a tectonic window between the Lesser and the Higher Himalaya. The Jutogh Group of rocks are mostly mica-schists of different metamorphic grade. The weathering intensity parameters, such as chemical index of alteration (CIA), plagioclase index of alteration (PIA), and index of compositional variability (ICV), range from 81 to 65 (mean = 72), 97 to 68 (mean = 84), and 1.9 to 0.6 (mean = 1.2), respectively indicating low to moderate degrees of weathering. Transition element ratios [Ni/Co (6.98 to 2.88), and V/Ni (2.32 to 1.27)], and major and trace element geochemistry imply recycled, felsic to intermediate, Archean to post-Archean are the sources for Jutogh rocks. The tectonic discrimination diagram implies an active continental margin setting for the deposition of the Jutogh metasediments. The geochemical data from the Jutogh rocks, when combined with the S-type Paleoproterozoic granite magmatism, imply the existence of an active tectonic setting during the deposition of the Jutogh sediments at the northern margin of the Indian continent during Nuna assembly.

Reliable estimation of ages and temporal correlations through the Quaternary Period (<2.58 Myr) have led to a better understanding of paleoclimatic changes. Various dating techniques applicable through the Quaternary have received significant impetus from paleoclimate community for high-resolution climatic reconstructions that are supported by robust chronological controls. Radiometric dating of Quaternary samples/archives have extensively progressed due to significant instrumentation developments. The Quaternary studies involve several radiometric dating techniques which include cosmogenic and anthropogenically produced radioisotopes.Radiocarbon (14C) is a cosmogenically produced radionuclide that has been frequently used to date recent archives. Previously, conventional β counting method for radiocarbon dating required ∼ 1 g of carbon extracted from the samples. However, with the introduction and development of Accelerator Mass spectrometry (AMS), it became possible to date these natural archives with a much smaller sample quantity. In addition to its application in 14C dating, AMS also led to a breakthrough in application of other cosmogenic isotopic systems (10Be, 26Al) to understand various earth surface processes (e.g., glacial retreats, denudation rates). The 210Pb dating technique is mainly used to study anthropogenic forcing on annual to decadal climatic changes. The measurement technique for 210Pb commenced with α detectors and involved tedious chemical separation and longer measurement times in attaining secular equilibrium. However, the gradual adoption of β and γ detectors led to rapid analysis with relatively shorter analysis times. This contribution aims to provide an overview of frequently used radiometric (14C, 10Be, 26Al, 210Pb and 137Cs) dating techniques in Quaternary studies and discusses the significant instrumental developments.

AbstractDetrital zircons are frequently used for crustal evolutionary studies as they sample vast regions of the continental crust. In the present study, we utilise newly compiled U-Pb detrital zircon data from the Indian subcontinent as well as a compilation of previously reported global data along with Hf isotopes of modern and ancient sediments in order to understand crustal evolution in the Indian subcontinent. The detrital zircon U-Pb age data from the Indian subcontinent show peaks (at 2400–2700, 1600–1900, 850–1200, and 450–550 Ma) that correlate with the formation of major known supercontinents. In addition, two other peaks at 3200–3400 Ma and <100 Ma do not correspond to periods of supercontinent formation. The former peak may represent uneven geographic sample density due to enhanced erosion and exhumation of Archean sources. The distinctly younger (<100 Ma) detrital zircon age peak may represent zircon preservation due to the Himalayan orogeny. The zircon Hf model ages from the Indian subcontinent suggest that the Precambrian crust was the major source of continental crust with younger ages. The conspicuous shift to positive εHf (t) at ca. 3600 Ma from detrital zircons of the Indian subcontinent may underscore a change in geodynamic processes, while the highly negative values post ~3200 Ma may be associated with the crustal reworking. A wavelet analysis of detrital zircons from the Indian and global databases reveals a prominent cyclicity of ~800 Myr and ∼350 Myr plausibly representing the supercontinent cycle and its half cycle. An incongruence in power between global and Indian εHf (t) could be due to the local subcontinental geologic processes during the Paleo- to Mesoarchean.

The widespread Early Holocene sea-level rise observed along the global coastal realms reinvigorated the need to decipher sea-level variability on a local and regional scale, yet limited attempts were made on simultaneously addressing sea-level and climate variability. The southwest coast of India is endowed with several geomorphic features providing cues on the paleosea-level and climate variability engrossed with its sedimentary sequence in the lowlands. In view of this, the present study aims to decipher the Holocene sea-level and climate variability based on geochemical and palynological proxies supported by 10 AMS radiocarbon ages on a 32 m long sediment core (L7) raised from Upper Kuttanad Kole wetlands (Kuttoor), Kerala, Southwest India.The study demonstrated high sea-level along with warm and wet climate due to Indian summer monsoon (ISM) intensification during 9.69-7.56 ka corroborating with the Holocene Climate Optimum (HCO). However, a break in the sediment deposition is observed between 7.56 and 3.51 ka, the reason for which is yet to be fully understood. During 3.51-2.55 ka, the gradual weakening of ISM has been invoked with an intermittent monsoon spell during 3.20-3.40 ka. After 2.55 ka the sediment core records occurrence of coarser clastics indicating sediment deposition by the migrating distributary channel of the Pamba-Manimala rivers. The high sea level during HCO attests that the core location plausibly represented the southward extension of the Vembanad lagoon which transformed into part of the terrestrial system due to the gradual sea regression during the mid-late Holocene period followed by deposition of alluvial sediments from the hinterland rivers.