Continental Masses Research Articles

Recycling of subducted continent slab in an accretionary orogen: Insight from the Liangwan potassic granitoids in the Tongbai orogen, Central China

Granitoids provide a vital window to probe the lithological configuration and chemical evolution of orogenic belts. In this contribution, we present an integrated study of mineral compositions, zircon UPb ages and HfO isotopes, titanite UPb ages and SmNd isotopes, as well as whole-rock element and Sr–Nd–Hf isotope compositions of the Liangwan granitic pluton in the northern Paleozoic accretionary orogenic unit of the Tongbai orogen, central China. The Liangwan pluton is composed mainly of monzogranites and contains abundant mafic microgranular enclaves (MMEs). The monzogranites have relatively high silica contents (SiO2 = 67.40–69.91 wt%) and mainly exhibit shoshonite to high-K calc-alkaline and metaluminous features. The MMEs have similar mineral and geochemical compositions and zircon and titanite UPb ages of ca. 129 Ma to the monzogranites, suggesting that they are likely early-crystalized cumulates of the host monzogranites. The MMEs and monzogranites are both characterized by enrichment of large ion lithophile elements but depletion of high field-strength elements. The monzogranites have whole-rock initial Sr (Isr) of 0.7069–0.7074, εNd(t) of −14.2 to −13.7, and εHf(t) of −17.5 to −17.2, zircon εHf(t) of −17.8 to −17.0 and δ18O values of 5.27–5.98 ‰, and titanite εNd(t) of −14.50 to −13.78. These features are distinct from the rocks in the northern Tongbai accretionary orogenic unit but similar to those of the post-collisional granitoids in the southern Tongbai collisional orogenic unit. The Liangwan pluton was likely stemmed from the subducted South China Block (SCB) underneath the northern segment of the Tongbai orogen. Our results show that the subducted continental mass can act as an alternative source for the magmatic rocks occurred in the accretionary unit.

Centres of Development and Patterns of Distribution of the Family Melastomataceae in Indo-Malesia

1.The Melastomataceae is a homogeneous family of about 220 genera and 5300 species and is generally confined to the tropical and subtropical regions, avoiding arid conditions and attaining prolific developments in the rain forests between the tropic of cancer and the tropic of capricorn. More than one half of the World's melastomataceous genera (about 120) and two-thirds of the total number of species (about 3353) are confined to the New World. The melastomataceous flora of Indo-Malesia consists of 64 genera and about 1300 species. In the Old World the incidence of melastomataceous species for Indo-Malesia and Africa is in the ratio of 2:1.2.The present distribution of Melastomataceae in both the New World and the Old World is discussed on the basis of Wegener's hypothesis of "Continental Drift". Instead of considering the island of Madagascar as the centre of origin of the family in a restricted way, it is considered that "Gondwanaland" was ideally suited for the melastomataceous flora and those blocks that moved away after the breaking up of this huge continental mass in the Late Cretaceous, each carried their own share of melastomataceous species which, after gradual establishment in new situations during a long span of time and space, proliferated into several new taxa by an intensive process of evolution.3.The Deccan Peninsula + Ceylon block in drifting over the Indian Ocean must have carried the original Gondwanaland stock and gene-pool of the Melastomataceae which later-when this block was fused with Laurasia and the Tethys Sea had disappeared-became the centre of development of the family in continental Asia. Then Melastomataceae could further develop on the southern part of Laurasia and from there migrate eastward to the Malesian islands, the Western Pacific and northern Australia.This implies the conclusion that, though Australia also formed part of the ancient Gondwanaland, this cannot have carried part of the ancient Gondwanaland Melastomataceae when Australia drifted apart.4.An attempt has been made to assess the centres of distribution of Indo-Malesian Melastomataceae and from this study the following four centres of development are proposed : (i) The Deccan-Ceylon centre, (ii) The Himalayan-Yunnan centre, (iii) The Sunda centre and (iv) The Philippine-Papuan centre.5.The Island of Borneo is unique in having the largest number of genera-42 out of the Indo-Malesian total of 64 genera-and the largest number of species i.e. 257. Perhaps, it is due to the part played by the mountain of Kinabalu in enriching the floristic composition of Borneo. It is generally considered by phytogeographers that Kinabalu is a great sanctuary of flora, past and present, and a nursery of endemic elements.

Late Cretaceous-Early Palaeocene Lepisosteiform and Siluriform fish remains from Central India: palaeoecological, palaeoenvironmental and palaeobiogeographical implications

Late Cretaceous-Early Palaeocene geo-climatic events played an important role in the diversification of the modern ichthyofauna. Lepisosteiformes and Siluriformes are two diverse clades of freshwater fishes, poorly known from India in this time interval. Their fossil record documents their early diversification and can be used to reconstruct palaeobiogeographic relationships among the continental masses during the Late Mesozoic. Indeed, the Cretaceous-Palaeocene is an exceptional time span for the Indian plate as it underwent a primary spatial reorganisation and remarkable geologic and climatic changes with extensive outpouring of the Deccan basaltic magma. Field investigation in a Deccan sedimentary sequence at Kisalpuri, Central India has yielded new, rich, and taxonomically important fossil material of Lepisosteiformes (Lepisosteus indicus, Lepisosteidae) and Siluriformes (Siluriformes indet.), which significantly improves their Cretaceous-Palaeocene fossil record from the Indian subcontinent. These fish lived in freshwater environments such as large rivers, lakes, and coastal areas. Their presence along with other aquatic biotic elements suggests that the Kisalpuri was an abundant aquatic ecosystem rich in nutrients, which attracted a diverse range of organisms to live together with fish. Biostratigraphically, these fishes first emerged in the Late Cretaceous-Early Palaeocene on the Indian subcontinent, and later, they spread to other parts of subcontinent throughout the Cenozoic. Their earliest intra-continental distribution was controlled by the palaeodrainage network influenced by the volcanic flows of the Deccan traps. Their inter-continental palaeobiogeographic distribution was broadly controlled by the sequential break-up of Pangaea. There appear to be close palaeobiogeographic linkages between South America and India during the Cretaceous-Palaeocene era based on the similarity between the Lepisosteiformes and Siluriformes remnants from India and those reported from the Upper Cretaceous of the Bauru Group, Brazil.

The Fossil Record and Diversity of Pycnodontiform Fishes in Non-Marine Environments

Pycnodont fishes were a successful clade of neopterygian fishes that are predominantly found in shallow marine deposits. However, throughout their long 180 million year reign (Late Triassic–end Eocene), they made multiple incursions into both brackish and freshwater environments. This fossil record mostly consists of fragmentary dental material, but articulated specimens are known from Early Cretaceous lacustrine localities in Spain. This review article aims to document all non-marine occurrences of Pycnodontiformes throughout most of the Mesozoic and early Paleogene. This review highlights two interesting trends in the history of non-marine habitat colonization by pycnodonts: (1) a huge spike in non-marine occurrences during the Cretaceous; and (2) that most occurrences in non-marine localities occurred at the latest Cretaceous period, the Maastrichtian. The high number of colonization events within the Cretaceous lines up with extreme climatic events, such as high temperatures resulting in high sea levels which regularly flooded continental masses, allowing pycnodonts easier access to non-marine habitats. The increased presence of pycnodonts in brackish and freshwater habitats during the Maastrichtian might have played a role in their survival through the K/Pg extinction event. Freshwater habitats are not as vulnerable as marine ecosystems to environmental disturbance as the base of their food chain relies on detritus. Pycnodonts might have used such environments as a refuge and began to occupy marine waters after the K/Pg extinction event.

Sedimentology, geochronology and provenance of the late Permian and Triassic Mitu Group in Peru—The evolution of continental facies along a transform margin

AbstractIn the late Permian and Triassic, the continental Mitu Group formed in extensional basins along the length of the Cordillera Oriental and Altiplano of present‐day Peru. Given the presence of coeval arc systems only in northern Chile and southern Ecuador but not in Peru the tectonic setting of the Mitu basin has been interpreted variably as orthogonal continental rift, sinistral transtensional rift, aulacogen and back‐arc basin. The Mitu Group comprises continental mass flow and alluvial fan, fluvial, aeolian and minor lacustrian facies and hosts thick piles of subalkaline and alkaline intermediate and felsic ignimbrites and mafic lavas. The age of the Mitu Group had originally been established as ranging from the Late Permian to the late Triassic on the basis of structural considerations and scarce biostratigraphic data. Recently, U–Pb zircon ages from ignimbrites and sedimentary rocks have been taken to constrain the Mitu Group to the Middle and Late Triassic. We performed a sedimentological, heavy mineral, and zircon geochronological and Lu‐Hf isotope study of the Mitu Group in 14 sections mainly in southern and central Peru, and one section in northern Peru. Ten new U–Pb concordia ages on ignimbrites intercalated in the Mitu Group successions offer a new robust stratigraphic framework and constrain the stratigraphy of the Mitu Group between 260 and 205 Ma. In combination with maximum likelihood ages of deposition derived from detrital zircon, U–Pb geochronology places the deposition of the Mitu Group between ca. 270 and 194 Ma (lower Guadalupian into the Sinemurian). Detrital zircon U–Pb age distributions and heavy mineral assemblages reflect a strongly recycled Precambrian Amazonian and Palaeozoic proto‐Andean provenance. The Palaeozoic detrital age patterns are highly variable, and temporally and spatially random. A local provenance can generally not be identified. εHf(t) values in zircon obtained from ignimbrites and sedimentary rocks indicate variable degrees of crustal recycling. In the course of the Palaeozoic, εHf(t) values become on average progressively less negative, with a large proportion particularly of Mitu age zircons' εHf(t) values encompassing less evolved and moderately juvenile compositions. Along strike of the basin stratigraphic thicknesses, and rates and times of accumulation vary strongly with larger thicknesses and rates being registered in southern Peru. This suggests that the Mitu basin had been divided into a number of subbasins with individual histories of subsidence, accumulation, and volcanism. Absent a magmatic arc, late Permian–Triassic Peru evolved in a sinistral plate tectonic and regional framework expressed particularly in the sinistral Late Gondwanide orogeny predating the Mitu Group. We interpret that a sinistral transform fault linked the subduction zones in southern Ecuador and northern Chile and that the Mitu Group basin has formed by sinistral transtensional and transpressional movements along a related transcurrent fault inboard of the transform margin. In the broader framework of the accretionary Terra Australis orogen along the western Gondwana margin, this interpretation fits its evolution in the Andean segment in an internally consistent way.

Atmospheric Patterns in Porto Velho, Rondônia, Southwestern Amazon, in a Rhythmic Context between 2017 and 2018

This paper aims to analyze the weather conditions in Porto Velho (Rondonia, Brazil, Western Amazon) and the influence of air masses on the climatic elements between 2017 and 2018, using rhythmic analysis. Climatic data were obtained through the official weather station, tabulated and statistically organized, and processed in R Studio programming language. The monitoring of air masses occurred through the synoptic charts of the Navy Hydrography Center. The results were analyzed by dry–rainy transition season, rainy season, wet–dry transition season, and dry season. Thus, the results point out that the Tropical Continental mass (mTc) acted up to 62.9%, responsible for the low precipitation index in October 2017. Although the mass has characteristics of warm and unstable weather, it is even lower than the action of the mEc. In January 2018, there was an 85.5% prevalence of the Continental Equatorial Mass (mEc), added to the action of the South Atlantic Convergence Zone (ZCAS), which contributed to an accumulated rainfall of 443 mm/month. In April 2018, the mEC acted with 56.7%, reaching 35.5% in August. Another highlight was the performance of the Tropical Atlantic mass (mTa) (27.4%) and mTc (19.4%), both of which had a crucial role in the dry season, followed by the Polar Atlantic mass (mPa) (17.7%), that contributed to the phenomenon of “coldness” in the region. Therefore, the mEc is extremely important in the control of the relative humidity of the air and the precipitations, while the mTc is a dissipator of winds that, at times, inhibits the performance of the mEc.

The climate crisis affects Mediterranean marine molluscs of conservation concern

AbstractAimThe Mediterranean Sea is a hotspot of endemism and it is warming at two to three times the rate of the global ocean. The continental masses that surround it constrain species range shifts. Therefore, as seawater temperature increases, distributions of marine species may contract into few small cooler refugia, with consequent risk of extinction from range contraction and fragmentation, particularly for endemics. We assess this risk for 15 molluscs of conservation concern occurring in the Mediterranean Sea. Invertebrates have been rarely assessed so far, despite their diversity and their importance for ecosystem functioning.LocationThe Mediterranean Sea and Eastern Atlantic Ocean.MethodsWe used ensemble species distribution models to project the future range of our target species and assess their IUCN Red List status.ResultsAs hypothesized, our models predicted major range shifts, contractions and fragmentation in the Mediterranean Sea for all species. Under moderate emission scenarios such as RCP4.5, up to 12 of the 15 target species will be eradicated from the eastern and southern warmer sectors. Under severe emission scenarios such as RCP8.5 and by the end of the century, we predict the global extinction of the endemic Patella ferruginea and Pinna nobilis. Non‐endemic species may buffer range loss in the Mediterranean with range gains in the Atlantic Ocean. Still, we predict that only a single species, Zonaria pyrum, will have marginal total range gains in future climate warming scenarios.Main conclusionsEight species will become threatened and the fate of Patella ferruginea and Pinna nobilis contrasts the belief that marine species are less prone to extinction than continental species under a warming climate.

Global Nitrogen Mass Flux From the Active Freshwater Aquifer Element Pool

AbstractThe estimated current global mean nitrogen concentration (geogenic + anthropogenic) in the active continental freshwater aquifer element pool is 1.1 mg/L as N, or between four and five times greater than the assumed geogenic mean. This concentration, combined with groundwater flux, generates a continental mass flux of 17 Tg N/y (teragrams of nitrogen, as N, per year) as a result of direct ocean discharge (0.67 Tg N/y), endorheic basins (1.2 Tg N/y), and cold‐wet (0.82 Tg N/y); cold‐dry (1.4 Tg N/y); warm‐dry (1.6 Tg N/y); and warm‐wet (11 Tg N/y) exorheic basins. These values are derived from a geospatial machine learning algorithm and combined groundwater‐modeled recharge in an ArcGIS environment. This active continental freshwater aquifer mass flux is between 35% and 40% of the continental integrated riverine system discharge, thus a significant component of the Earth's active continental freshwater nitrogen budget. We estimate the active continental freshwater aquifer volume to be between 1.4 and 2.8 million km3 suggesting a legacy of between 1.5 and 3.1 Pg as N (petagrams nitrogen as N) with mean residences of 90–180 years.

Fracture Characterization Explores Potential of Phra Wihan Formation, Thailand

_ This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper IPTC 22845, “Fracture Characterization and Basement Reservoir Potential of Phra Wihan Formation in Southern Part of Uttaradit Province, Northern Thailand,” by Watcharapong Piewmoh, SPE, PTTEP, and Pitsanupong Kanjanapayont, Chulalongkorn University. The paper has not been peer reviewed. Copyright 2023 International Petroleum Technology Conference. Reproduced by permission. _ The complete paper describes the characterization of fractures in the Mesozoic sandstones of the Phra Wihan Formation in northern Thailand. Fracture characterization of outcrop analogs is important to determine the potential of subsurface reservoirs. The methodology used field study and petrography analysis to determine the relationship of fractures and other structures such as bedding planes and fold geometry. In addition, microstructure analysis can assist in the evaluation of a reservoir’s potential. Introduction Basement reservoir sandstones are one of the main targets in a mature onshore oil field in Thailand. But most basement reservoirs of the onshore Tertiary basin are pre-Tertiary and are associated with low quality. Prediction of reservoir quality in low-porosity and -permeability conditions requires an understanding of fractures in the subsurface. Outcrop analogs are key in characterizing fractured reservoirs. Geological Setting The tectonic evolution of Thailand is detailed in the complete paper. The country’s primary geological provinces are subdivided into the following five components, from west to east: - Sibumasu terrane - Inthanon zone - Sukhothai terrane - Nan and Sra Keao sutures - Indochina terrane The Sibumasu and Indochina terranes are major continental masses that collided during the Devonian-Triassic. Two subparallel suture zones exist along the convergence between the Sibumasu and Indochina terranes; one is an accretionary complex defined by the Inthanon zone. Another is a closed back-arc basin defined by the Nan and Sra Keao sutures. The Sukhothai terrane is an island-arc system formed along the margin of the Indochina terrane.

The statherian anorogenic magmatism in the Paramirim Aulacogen, são Francisco-Congo paleoplate: New data, synthesis and regional correlations

Fragmentation of continental masses is usually associated with anorogenic magmatism, and in this context, major silicic magmatic events may be associated with Large Igneous Provinces (LIPs). The Paramirim Aulacogen evolves between 1.77 and 0.67 Ga, filling anorogenic siliciclastic and acidic volcanic rocks with subordinate carbonates. A rhyolite from the Algodão Formation, the oldest unit of the Aulacogen, was dated in this work using the U–Pb method (LA-ICPMS), finding a crystallization age of 1777±1 Ma, with a model age (TDM) of 3.10 Ga and εNd (t) equals −10.4. The anorogenic plutonic magmatism is represented by the Lagoa Real Intrusive Suite, with over 5000 km2. New geochemical and geochronological data are presented, and the integration with the literature allowed the interpretation of four plutonic magmatism cycles: (i) Cycle 1: represented by Lagoa do Barro granitoids (1762 ± 9 Ma) and the metavolcanic rocks of the Algodão Formation (1775 ± 77–1777±1 Ma); (ii) Cycle 2: with the São Timóteo (1741 ± 4–1746 ± 5 Ma) and Caetité (1743 ± 5 Ma) granitoid and syenitoid, in addition to charnockitic rocks (1742±7 Ma); (iii) Cycle 3: is related to phonotephrite, tephriphonolite and phonolite. Trachyte, trachyandesite and trachydacite of São Simão Formation (1731 ± 5 Ma) and tuff layer of Ouricuri do Ouro Formation (1722 ± 13 Ma), as well as rhyolites and dacites that ocurr in the basement of Paramirim Aulacogen. The Caldeirão granitoid and syenitoid (1724 ± 5 Ma) is associated with this cycle; and (iv) Cycle 4: with the Suçuarana intusive rocks (1686 ± 6 Ma) and pyroclastic rocks of trachyandesitic composition. The Sm–Nd model ages (TDM) obtained in this work and the literature varies between 3.1 and 2.2 Ga, with values of εNd (t) between −15.8 and −8.6. The formation of the Statherian magmas possibly occurred by melting the enriched mafic mantle, followed by underplating in the continental crust and assimilation of Archean crustal rocks, with fractionation of hornblende, biotite, apatite, and Fe–Ti oxides during magma evolution. The Lagoa Real Intrusive Suite, and their volcanic correlates, represent part of a Statherian Silicic Large Igneous Province (SLIP) developed in a crust of the Archean-Rhyacian-Orosirian age of the São Francisco-Congo Paleoplate. This magmatism marks the attempt at the breakup of the Columbia supercontinent, with correlates in other regions of Brazil and the world.

Intraplate records of a transform margin formation: Brittle deformation in the basement of the basins from the northeastern extremity of the Brazilian equatorial margin

The diachronous rifting of the Pangea supercontinent, with the dispersion of the continental masses, resulted in the formation of numerous rift systems, which primarily evolved into passive margins, such as the Brazilian Equatorial Margin (BEM). In the South American counterpart, basement structures serve as the primary markers for direct analysis of the nucleation and development of the BEM since much of the rift record occurs in the subsurface. The geodynamic models that explain the evolution of this margin are largely based on geophysical and numerical modeling data. In this paper, we carried out an onshore, multitool, and multiscale structural analysis of the brittle deformation overprinted on the Precambrian basement of the Potiguar and Ceará basins, which led to the proposition of four superimposed events. The D1 event (Late-Brasiliano) is mainly represented by the NE-SW (dextral) stepped fracture systems and the unfilled and quartz- or chalcedony-filled NE-SW to E-W-trending extensional joints. This event is related to NE-SW intraplate transpression, associated with the progressive exhumation of the Brasiliano-Pan African orogenic belt. The D2 event (Jurassic to early Aptian) represents the intracontinental deformation related to the initial rupture of the Pangea. The brasiliano-age ductile shear zones were reactivated (brittle) along with the development of NE-SW normal faults, NNE-SSW en échelon fractures, NE-SW joints, as well as the emplacement of the basic dykes (NE-SW and E-W) related to the Rio Ceará-Mirim magmatism. This event is associated with the NW-SE extension responsible for the origin of the Cariri-Potiguar trend basins. At the beginning of the installation of the equatorial proto-margin, a significant cataclastic process took place, marking the D3 event (post-early Aptian). This enabled the nucleation of hybrid (WNW-ESE, E-W, and NW-SE), shear fractures (WNW-ESE, NNW-SSE, E-W, NNE-SSW, and ENE-WSW), and NW-SE unfilled or filled (chalcedony, iron oxide and hydroxide, and calcite) dilatational joints, which express an E-W dextral transtensional regime related to this event. E-W and NW-SE pull-apart dilatational jogs are characteristic of this event and may be analog to the E-W Messejana and Jacaúna transtensional grabens (western part of the Potiguar Basin). The younger event (D4) is characterized by N–S normal faults and joints, and dry or filled (calcite and iron oxide/hydroxide) NNW-SSE hybrid shear fractures. A clockwise rotation of the South American plate with respect to the African plate and the paleostress field change to N–S compression and E-W extension, are responsible for the formation of D4 structures. The brittle structures developed in the crystalline basement of the Potiguar and Ceará basins represent the intracontinental record of the deformation related to the formation of the Atlantic equatorial margin under a dextral transtensional regime.

Barklice (Insecta: Psocodea) from Early Cretaceous resiniferous forests of Iberia (Spanish amber): New Troctomorpha and a possible Psocomorpha

Psocids, commonly known as barklice, are insects belonging to the order Psocodea, together with the parasitic lice. They usually inhabit forest litter or the bark of tree trunks and branches, showing grazing herbivorous or detritivorous feeding habits. The Cretaceous psocid record is diverse, containing more than 70 described species. Here, we present new psocids (Troctomorpha and possible Psocomorpha) from two Spanish amber outcrops, both Albian (Lower Cretaceous): El Soplao and Ariño. We describe the two new species Azarpsocus anjana Álvarez-Parra and Nel sp. nov. (Manicapsocidae) and Burmacompsocus ojancano Álvarez-Parra and Nel sp. nov. (Compsocidae), and the morphotype Ariño that might belong to Psocomorpha. We discuss the taxonomic placement of the studied specimens and comment on the palaeobiogeography of the Cretaceous psocids. The Cretaceous barklice fauna from Iberia shows more similarities with that from Lebanese (Barremian) and Burmese (Cenomanian) ambers than with that from the palaeogeographically closer French amber (Cenomanian). This finding has been also reported in other insect groups from Spanish amber, and might be the consequence of several factors, such as the palaeoenvironmental conditions of the ecosystems, the palaeogeographical position of the Iberia Island during the latest Jurassic, closer to Gondwana than to Laurasia, and oceanic currents that facilitated or hindered the displacement of insect fauna between continental masses.

From Palaeolithic Caves to Roman Villas: Brittany's Distant Past

As one of the peripheral regions of Europe, the Armorican peninsula is often believed to have been a cultural backwater, hardly ever reached by the major cultural and technological changes taking place in late prehistoric continental cultures. For people living away from the ocean, the latter is often seen as an obscure threat, an awful obstacle, a liquid wall isolating from one another continental masses and cultures. But, as a matter of fact, the ocean was always used as a passageway, a link between countries bordering the Atlantic, from the south of the Iberian Peninsula to the North Sea. In this vast sea-space, the Armorican landmass, situated at the articulation between two maritime zones, the Bay of Biscay to the south, the Irish Sea and the Channel to the north, was a place where various cultural influences would come into contact and interbreed. Far from being a dead end, it was perfectly integrated, during the various phases of its long history, in the major cultural and technological currents running along the western facade of Europe.

A new compositional estimate for refractory lower continental crust with implications for the first terrestrial Pb-isotope paradox

The lower continental crust, representing up to 50% of the continental mass, is largely inaccessible, making its composition difficult to constrain. Previous composite models based on geophysical evidence and geochemical data of granulite terrains and xenoliths have proposed varying results, from a mafic, relatively refractory lower crust to an intermediate-felsic, more enriched composition. Here, we investigated the mineralogy and geochemistry of predominantly mafic granulite xenoliths from eastern Australia and the Kola Peninsula, Russia, using an in situ analytical approach that minimises host magma contamination. The resulting xenolith compositions are variably and often strongly depleted in most highly incompatible trace elements, including the heat-producing elements. These xenoliths represent an extremely refractory component of the lower continental crust, likely formed after high degrees of partial melting or crystallisation from a depleted source. A lower crust composed solely of this refractory endmember would be too exhausted in heat-producing elements to satisfy heat-flow constraints. However, a volumetrically significant component of the lower crust is this mafic and refractory material, combined with undifferentiated material and a felsic or metapelitic portion. Using geophysical constraints on proportions of refractory (55%), undepleted (38%) and enriched (7%) components, a new estimate for average lower continental crust that satisfies heat flow limits was calculated, including for elements such as Be, B, Cs, W and Tl, where previous estimates relied on very few data. Finally, we show that because much of the lower continental crust is so refractory and depleted in incompatible elements, it is unlikely to be a reservoir that can balance radiogenic isotope (unradiogenic Pb) and trace element ratios (e.g. Rb/Cs, Nb/Ta) for which bulk silicate Earth departs from chondritic ratios.

EURASIA'S RESISTANCE TO THE OCEANIC POWERS THE US-RUSSIA CONFLICT AND ITS IMPLICATIONS FOR THE EU, CHINA OR INDIA

Geopolitical Eurasia is the large continental mass with the Heartland core group: Russia, Iran, Kazakhstan, Turkmenistan, Mongolia and so on, exporters of raw materials by direct land and the Continental Rimland: China, Germany, Turkey, Italy, South Korea, India, Pakistan, Thailand and so on, made up of Continental Powers, while the Oceanic Powers, led by the US dominating maritime trade and oceanic embargo capacity, brings together exporting powers: Australia, Canada, Saudi Arabia, UAE and so on and industrialized maritime powers: Great Britain, Japan, etc., alongside exporting states constrained by them, from Africa, Latin America and island Asia. If the US succeeds in the trade blockade of the Heartland, stopping the export of cheap and abundant raw materials, it indirectly brings the European Union, mainland East Asia (China) and South Asia (India) to its knees, delivering four strikes direct and preventing the emergence of a power that would take its place as world leader. If the Rimland manages to bypass the American embargo by continuing to import from Heartaland, Britain will lose dominance in Europe to Germany, Japan will lose the dominance of Asia before China, Saudi Arabia before Iran and India will dominate the Indian Ocean, hence the 3+1 main regions taking over Africa, America and Australia, which will culminate in the decline of the US power, the dominance of the Eurasian world and of the continental powers before the maritime powers.

Oblique rifting along transfer zones: The structural evolution model revealed by physical modeling

Oblique rifting is a common process that acts during the rupture of continental masses and can evolve to the passive margin stage. The inter-rift (or intra-rift) interaction can occur by transfer zones (TZs). These zones can be formed at the most diverse scales and, on a large scale, can result in the development of oblique rifts. To understand how TZs nucleate and evolve at the plate scale, we simulated, through physical modeling, the development of oblique transfer zones that connect two parallel rifts (with no lateral overlap) developed orthogonally to the extensional direction. Our results showed that obliquity and rheology could play an important role in the structural architecture of rifts that originated in such a structural environment. When the obliquity ranges from low to intermediate (i.e., 20°≤ α ≤ 45°), these rifts can be compartmentalized into two main structural domains - extremity, and central regions - with diachronic evolution and distinct kinematics. Extremity regions are characterized by oblique-slip deformation with intense rotation/tilting of the substrate. The central region is dominated by transcurrent (and oblique-slip) deformation with the presence of marginal plateaus, pull-apart, and oblique basins. Small variations in the obliquity (around 5°) are enough to affect parameters like faults' dip and geometry, and depocenters’ width and depth, thereby promoting changes in the morphology, geometry, architecture, and configuration of TZs. In a more mature stage, and on a continental scale, the TZs evolve into oblique rifts whose margins are composed of oblique and transcurrent fault segments (transfer/transcurrent) that together define a typical zig-zag geometry. The sizes and numbers of these segments depend on the obliquity and the rheology. Transcurrent fault segments are more common when the obliquity is 20° and 25°, in the model with quartz sand only. The modeling data presented here can be compared with the equatorial Atlantic margin of South America, assuming that it may represent an important plate-scale oblique transfer zone (20°) developed between the South and Central Atlantic.

Sediments from Purana basins, India: Where were they derived from?

The present exposures of the (Mesoproterozoic to Neoproterozoic) Purana basins of Peninsular India occupy nearly 1.5 × 105 km2 area in the Indian subcontinent, with an equal area being concealed under younger cover or lost to ensuing erosion. These extensional basins evolved on the margins (& with basement) of the existing cratonic blocks during the ‘boring billion years’ of Earth history. They host nearly 0.8 million km3 of epicratonic compacted and lithified sediments derived by weathering and erosion of the adjoining cratonic blocks and deposited on their fringes. The volumetric contents of these basins and their temporal distribution are compiled. The relative distribution and secular variations of sediment contents from these basins appear to synchronise with global Proterozoic supercontinental assembly and dispersal cycles. A comparison of mass-transfer by the erosion of the provenance area and sedimentation in continent margin basins shows that the volumes preserved in the Purana basins are at least 2 magnitudes larger than what can be derived from adjoining cratonic areas within the Indian Subcontinent. Much wider continental masses as well as exhumation (aided by uplift) of km-scale magnitudes of the provenance areas are required to reconcile their volume. Possible linkages with other cratonic blocks within the contemporary supercontinental assemblies are required to resolve this discrepancy.

Late Cryogenian and late Paleozoic ice ages on the São Francisco craton, east Brazil

The miniature paleocontinent in the region of the São Francisco River valley, in eastern Brazil, holds the record of two different glacial epochs. The late Cryogenian Jequitaí Formation from the Bambuí Group is up to 100 m thick and covers areas mainly in the central São Francisco craton. Evidences for glacial sedimentation are beautifully preserved E-W grooves and striations, dropstones within fine-grained rocks, and a full set of diamictites enclosing a rich and complex depositional history. The Jequitaí Formation is in close link with the tectonic evolution of the São Francisco paleocontinent and the West Gondwana amalgamation. From west, the precocious Paranapanema and São Francisco blocks collision in late Cryogenian flexured the foreland lithosphere and created depozones that were infilled by glacial sediments. Toward east, the rifting and opening of the Adamastor Ocean allowed thick glacial and non-glacial deposits to form through subaqueous gravitational sedimentation. From west to east, proximal and distal glaciomarine, glaciocontinental, and non-glacial resedimentation are identified and linked to the evolving continental masses and climate during the Cryogenian and beginning of Ediacaran. The late Paleozoic Santa Fé Group is the youngest record of glaciation on the São Francisco craton. It is 60–80 m thick and yields consistent and confident glacial evidences such as N-S striations on top of Cambrian sandstones, ice-rafted debris, and rain-out diamictite, all preserved in small and patchy areas in the west-central São Francisco craton. Paleocurrents suggest a northern ice center and sedimentary facies indicate deposition in continental lakes and rivers. Although late Paleozoic, its age is poorly constrained and likely correlated with the uppermost Itararé Group (Taciba Formation) of Paraná Basin in south Brazil. Deglaciation and strong isostatic adjustments make up the termination of the Santa Fé Group sedimentary record and depict a glaciocontinental system evolved on an interior stable continental crust. The late Neoproterozoic Jequitaí Formation and the late Paleozoic Santa Fé Group are parts of the earth’s sedimentary history preserving a rich record of climate, tectonic, and surface processes in part controlled by the evolving continental masses on the São Francisco craton.

Investigating assembly timing of Ediacaran Serra dos Órgãos batholith – Hints on prolonged magmatism at Ribeira belt, SE Brazil

The Pan-African/Brasiliano orogeny, result of the West-Gondwana assembly from the Neoproterozoic to Ordovician, had produced the Ribeira and Araçuaí belts at the edges of the São Francisco and Congo cratonic margins. In the central Ribeira belt, the docking of accretionary systems to the reworked continental margin of the São Francisco paleoplate culminated in a complex Ediacaran granite production event. Syn-to late-collisional I- and S-type granites and hybrid granitoids intruded the reworked margins and accreted continental masses, as well as the Tonian to Ediacaran juvenile magmatic arcs represented by the Serra da Prata and Rio Negro Complexes. The Serra dos Órgãos batholith is the main intrusion emplaced at the juvenile crust, forming an elongated NE-SW trending tabular body that crops out in the highland region of Rio de Janeiro State, Southeast Brazil. Geochemical and geochronological data in addition to field and petrological evidence was gathered to explore the assembly timing of the SOB granitic end-member. Zircon U–Pb SHRIMP and LA-ICP-MS geochronological data yield a prolonged emplacement timelapse for the studied granites and, along with published U–Pb ages of the SOB granodioritic end-member, enable the characterization of the Serra dos Órgãos as a composite batholith. The wide time interval of heat input inside intermediate crust is consistent with a prolonged, slow-cooling hot orogenic belt model for the Araçuaí-Ribeira Orogenic System.

Stratigraphy of the Agnew-Wiluna Greenstone Belt: review, synopsis and implications for the late Mesoarchean to Neoarchean geological evolution of the Yilgarn Craton

Our ability to understand the geological evolution of Archean cratons is fundamentally dependent on stratigraphic reconstructions across greenstone belts. Here, we integrate published stratigraphic, geochemical and geochronological data to produce a revised stratigraphic model for the Agnew-Wiluna Greenstone Belt of the Yilgarn Craton. The Agnew-Wiluna Greenstone Belt records ca 130 m.y. of magmatism that occurred between ca 2820 and 2690 Ma and can be divided into three cycles. Cycle 1 is marked by ca 2820–2740 Ma mafic–ultramafic volcanic rock successions. Cycle 2 is associated with ca 2740–2720 Ma felsic volcanic rocks, associated fragmental deposits and contemporaneous mafic–ultramafic intrusions. Cycle 3 consists of ca 2720–2690 Ma mafic–ultramafic volcanic rock successions and co-magmatic intrusions. Exhumation and reworking of these continental rift basin successions after ca 2690 Ma resulted in two younger, additional, depositional cycles in the Agnew-Wiluna Greenstone Belt. Cycle 4 is associated with intermediate to felsic volcanoclastic rocks and epiclastic rocks erupted/deposited between ca 2690 and 2665 Ma. Cycle 5 is associated with the deposition of polymict conglomerates and sandstones in localised depocentres between ca 2665 and 2655 Ma. The stratigraphic scheme identified at the scale of the Agnew-Wiluna Greenstone Belt is the local expression of craton-wide tectono-thermal events. Our revised stratigraphic model for the Agnew-Wiluna Greenstone Belt and proposed correlations at the craton scale support a para-autochthonous model whereby crust from a proto-Yilgarn continental mass was extended/thinned, favouring the activation of translithospheric pathways associated with the ca 2720–2690 Ma Kalgoorlie Large Igneous Province. Inversion of this intra-cratonic rift basin after ca 2680 Ma led to the protracted activation of shear zones and multiple shifts in sedimentary depocentres. The widespread occurrence of previously unidentified fragments of ca 2820–2720 Ma substrate within the Kalgoorlie-Kurnalpi Rift has significant implications for craton-scale stratigraphic reconstructions and challenges existing terrane and domain boundaries. KEY POINTS We propose a revised, coherent and testable stratigraphic model for the Agnew-Wiluna Greenstone Belt of the Kalgoorlie Terrane. We compare our revised stratigraphic model for the Agnew-Wiluna Greenstone Belt with that of the Murchison and Southern Cross domains of the Youanmi Terrane in order to build a new space–time–integrated stratigraphic cross-section across the western half of the Yilgarn Craton. We demonstrate for the first time the existence of a magmatic continuum (i.e. no significant magmatic hiatus) between ca 2820 and 2690 Ma, providing the missing link between the geological record of the Youanmi Terrane and that of the Eastern Goldfields Superterrane.