Search

Voluminous Early Cretaceous granitoids and associated large-scale ore deposits are distributed within the southern Great Xing' an Range (SGXR), NE China. Based on previously published geochronology and zircon Hf-isotope data, Hf isotope mapping is undertaken to improve our understanding of crustal architecture and its controls on ore deposits. The ore-related Early Cretaceous granitoids were sourced predominantly from juvenile crust, with the involvement of variable proportions of ancient crustal materials. The crustal architecture, as inferred from Hf isotopic contour maps, indicates two distinct Hf isotopic domains in SGXR, including (1) a higher-εHf (+7 to +11) juvenile crust containing minor ancient crustal material, and (2) a lower-εHf (+2 to +6) juvenile crust containing a greater proportion of ancient crustal materials. The Hf isotopic maps identify links between crustal architecture and regional metallogeny. Copper deposits and other deposits with significant Cu production are restricted mainly to the higher-εHf juvenile crustal regions in the northern and eastern SGXR. Deposits dominated by other metals (e.g., Mo, Sn, W, Pb, Zn, and Ag) occur mainly in the lower- εHf juvenile crustal regions in the southern and western SGXR. Interaction between juvenile crust-derived melts and ancient crustal components played an important role on the distribution of various ore metals. [ABSTRACT FROM AUTHOR]

This study evaluates the efficacy of GECO gravity data for geophysical studies, mapping structural and tectonic features and their impact on gravity signatures in the study area. Computed correlation coefficient (96–98%), root-mean-square error (5.1–5.3 mGal), and standard deviation (3.9–4.2 mGal) between the GECO model-derived and ship-borne free-air gravity reveal the efficacy of the GECO gravity data for the geophysical studies in the region. A total horizontal derivative approach was used in order to enhance the residual and regional responses of the Bouguer gravity anomaly. The shorter-wavelength lineaments originated from subsurface mass heterogeneities were found trending in the northwest direction, subsequently east, north–northeast and east–northeast directions. In contrast, the longer-wavelength lineaments originating from deep-seated mass heterogeneities dominated in the east-northeast direction, followed by north-northeast and northwest directions. Lineaments occurring at shallower depths are associated with sedimentary/basement columns and could be utilised in basin demarcation for hydrocarbon exploration. In contrast, deep-seated lineaments originated due to deformities at the crust-mantle boundary or in the mantle and could be used in the region's seismicity analysis. Spectral analysis and 2D forward modelling results indicate sediment thickness of ~ 2.0–6.0 km, basement thickness of ~ 6–14 km, and Moho depth of ~ 10–18 km. Delineated lineaments and computed basement and Moho depths were further validated with existing data. Anomalously high and low gravity features were interpreted based on Moho depth, basement thickness, and sediment thickness. This study concludes that anomalous gravity anomalies are mainly controlled by Moho topography despite the relatively thicker crust in the northern region. The crustal thickness mainly controls the southern latitude's gravity signatures. [ABSTRACT FROM AUTHOR]

Continental break‐up can be oftentimes associated with intracontinental wrenching that can lead to the generation of transform margins and transform marginal plateaus. The wrenching phase can be accompanied by complicated processes, which result in heterogeneous structural and crustal architectures. This makes understanding the evolution of such tectonic settings challenging. The Falkland Plateau is an example of a transform marginal plateau where regional wrenching accompanied the incipient stages of Gondwanan continental break‐up to result in a mosaic of crustal types underlying its largest basin: the Falkland Plateau Basin (FPB). The uncertainties in crustal boundaries have led to several models for the evolution of the plateau, which hinder the development of a reliable plate reconstruction of Southern Gondwana. We integrate seismic reflection, gravity and magnetic data to propose an updated crustal architecture of the FPB. The results show that extended continental crust underlies the basin in the west and north. The eastern and central parts consist of a juxtaposition of intruded and underplated continental crust which transitions southwards to a thick oceanic domain. The basin is crosscut by three main NE–SW trending shear zones which facilitated the development of the contrasting crustal and structural domains interpreted across the plateau. This integrated reassessment of the FPB provides new insights into the tectonic evolution of the plateau, the deformation associated with wrenching and transform margin formation and our understanding of the tectono‐stratigraphic evolution of such areas. [ABSTRACT FROM AUTHOR]

The Sanjiang orogenic belt, located in southwestern China and the southeastern Tibetan Plateau, includes a variety of economically important metal deposits. Previous studies have focused on Lu-Hf isotopic mapping to suggest its lithospheric architecture and mineralization. In this study, we provide the results of Nd isotopic mapping and compare them with the results of Hf isotopic mapping based on the similarity of Sm-Nd and Lu-Hf isotope systems, which indicate three juvenile domains with high εNd(t) and young Nd model ages within the Eastern Qiangtang-Simao terrane, while presenting negative εNd(t) values over the entire horizon. The very negative εNd(t) and old Nd model ages found in the Tengchong-Baoshan terrane and Changning-Menglian suture suggest that these terranes are old and might be reworked. The Nd isotopic mapping of the Sanjiang orogenic belt also suggests a relationship between different lithospheric architectures and the locations of distinct ore deposits. Porphyry-skarn Cu–Mo–(Au) deposits occur in the juvenile crust, which has relatively high εNd(t) (−3.3–5.1) and young TDM ages, whereas skarn and hydrothermal vein-type W–Sn deposits and Pb‒Zn‒Cu‒Ag deposits are located in the low-εNd(t) area.

The ca 2.0 Ga Volgo-Don fold-and-thrust belt, about 500 km in width and at least 600 km in length, covering an area of about 300000 square kilometers intervenes between the Archean Sarmatian and Volgo-Uralian proto-cratonic blocks of the East European Craton, both of which are coupled with 200–300 km thick sub-continental lithospheric mantle keels. The focus of this paper is the elucidation of its nature in order to answer the basic question how this and other thrust-and-fold belts could be formed in the Paleoproterozoic, and whether they are the same as or different from modern collision orogens. The active Himalayan-Tibet orogen is commonly thought of as the most extensively studied large, bi-verging fold-and thrust belt continental collision zone which may provide insight into key tectonic mechanisms for an understanding of orogenic processes in the Earth’s geological past. Precambrian orogens are tentatively perceived yet as something that was distinct from recent orogenic styles and was due to the initial elevated geotherm and higher radio-genic heat production in the early Earth.In this paper we report for the first time the revealation of the large, slightly eroded divergent Paleoproterozoic Volgo-Don orogen which is mostly composed of juvenile metasediments and comprises well-preserved patterns of the crustal orogenic architecture which are characteristic of the archetypal Himalayan-Tibet collisional orogen rather than of hot/ultra-hot Precambrian orogens based on numerical modeling.

The stretched structure and heterogeneity of the crust of the Nansha Block, the southern continental margin of the South China Sea (SCS), are not well understood. We used published ocean bottom seismic (OBS)/multichannel reflection seismic (MCS) profiles across the Nansha Block to establish five two-dimensional crustal structure models. Using gravity modelling with magnetic anomaly inversion, we obtained the distribution of density and local magnetic susceptibility of the crust. The models show that the distribution of density and thickness of the upper crust in the Nansha Block is uneven, and the thick upper crust is prevalent in the regions close to the continent-ocean transition (COT) showing different characteristics. The interpreted Mesozoic granite blocks and Precambrian rigid basement reflects the heterogeneity in the material composition of the SCS continental margin. Based on the thinning styles of different crustal layers, we suggest that the Nansha Block has a three-layer thinning pattern. The uppermost pre-rift layer was deformed via brittle fractures, the upper crust was sheared by discrete shear zones, and the lower crust experienced ductile deformation. The inherited pre-rift thermal regime, mechanical state, and material composition of the SCS continental margin affected the extensional structure of the crust. [ABSTRACT FROM AUTHOR]

The Gamburtsev Subglacial Mountains (GSMs) in the interior East Antarctic Craton are entirely buried under the massive East Antarctic ice sheet, with a ~50–60 km thick crust and ~200 km thick lithosphere, but little is known of the crustal structure and uplift mechanism. Here, we use airborne gravity and aeromagnetic anomalies for characteristic analysis and inverse calculations. The gravity and magnetic images show three distinct geophysical domains. Based on the gravity anomalies, a dense lower crustal root is modelled to underlie the GSMs, which may have formed by underplating during the continental collision of Antarctica and India. The high frequency linear magnetic characteristics parallel to the suture zone suggest that the upper crustal architecture is dominated by thrusts, consisting of a large transpressional fault system with a trailing contractional imbricate fan. A 2D model along the seismic profile is created to investigate the crustal architecture of the GSMs with the aid of depth to magnetic source estimates. Combined with the calculated crustal geometry and physical properties and the geological background of East Antarctica, a new evolutionary model is proposed, suggesting that the GSMs are underlain by part of a Pan-African age advancing accretionary orogen superimposed on Precambrian basement. [ABSTRACT FROM AUTHOR]

The present study attempts to structural and tectonic interpretation around the Laccadive ridge in the Western Indian Ocean using EGM2008 Bouguer gravity data. The different derivatives of EGM2008 Bouguer gravity data indicate that the tectonic boundaries are predominantly confined in the N-S and NNW-SSE directions followed by E-W and NE-SW trends. The Euler deconvolution result suggests that the deformities in the region are of both crustal- and lithospheric-scales. The gravity highs/lows in the study area are analyzed based on sediment/crustal thickness and Moho depth estimated using radially averaged power spectrum technique. The study highlights the Moho undulation followed by crustal thickening/thinning underneath the Laccadive ridge and its surroundings for their anomalous gravity signatures. The affinity of the structural pattern observed in the Laccadive ridge region with continent trends, moderate crustal thickness and shallower Moho observed below the Laccadive ridge axis, suggest thinned rifted continental crust with shallow basement. [ABSTRACT FROM AUTHOR]

Integrated coplanar loop electromagnetic conductivity method, electrical resistivity tomography (ERT), and Schlumberger vertical electrical sounding (VES) methods were deployed to investigate the near-surface crustal architecture and geohydrodynamics of the crystalline basement terrain of Araromi, Akungba-Akoko, Ondo State, southwestern Nigeria. The study aimed at understanding the spatial distributions of groundwater, and soil moistures with exhumed crustal structures, to alleviate groundwater deficit, and the failure of engineering structural foundations in this area. Six geophysical survey traverses of varying lengths were explored, with eight VES stations selected for further investigations on the lithostratigraphic model for constraint and deeper probing. The measured conductivities over the study area varied in the range of 3.0–35.19 mS/m. The results coincided with the ERT responses for the motley topsoil, clayey to sandy weathered strata, partially weathered/fractured bedrock, and fresh gneissic bedrock. A, AK, HA, and KQ types of curves pictured the varying depths of the deep-weathered troughs, and the fractures (i.e., F1 to F21), arising from the prevalent intense metamorphism and progressive weathering in the area. The geohydrodynamic systems of the study area's crustal architecture were attributed to water–rock interactions within the geologic structures. Also, the depths of the fractured zones extending more than 52 m in some sections enhanced the spatial groundwater storage, despite the thin overburden (i.e., < 4 m). The residual soils' water retention is credited to clayey soils from the rich feldspathic bedrock. Hence, the results obtained suggest that intended wells and boreholes should take advantage of the deep-weathered and fractured zones, with average depths of 11 m and > 39 m, respectively, to ameliorate the deficit of groundwater supply in the area. Furthermore, failures of engineering structural foundations are likely to occur at highly conductive sections (i.e., > 20 mS/m), oscillating bedrock surfaces, floating boulders, and stiffer soils under incompetent strata, and conductive thin and large-size apertures. The study demonstrated the advantages of integrating multi-geophysical methods of data collection and analysis. [ABSTRACT FROM AUTHOR]

The Gamburtsev Subglacial Mountains (GSMs) in the interior East Antarctic Craton are entirely buried under the massive East Antarctic ice sheet, with a ~50–60 km thick crust and ~200 km thick lithosphere, but little is known of the crustal structure and uplift mechanism. Here, we use airborne gravity and aeromagnetic anomalies for characteristic analysis and inverse calculations. The gravity and magnetic images show three distinct geophysical domains. Based on the gravity anomalies, a dense lower crustal root is modelled to underlie the GSMs, which may have formed by underplating during the continental collision of Antarctica and India. The high frequency linear magnetic characteristics parallel to the suture zone suggest that the upper crustal architecture is dominated by thrusts, consisting of a large transpressional fault system with a trailing contractional imbricate fan. A 2D model along the seismic profile is created to investigate the crustal architecture of the GSMs with the aid of depth to magnetic source estimates. Combined with the calculated crustal geometry and physical properties and the geological background of East Antarctica, a new evolutionary model is proposed, suggesting that the GSMs are underlain by part of a Pan-African age advancing accretionary orogen superimposed on Precambrian basement.

Abstract The open availability of global scientific databases is key to advancing research of the Earth system and facilitating cross‐disciplinary studies. There are numerous data sets available for investigating tectonics, but none that provide an internally consistent representation of the structural framework, crustal architecture, and geodynamics. We present Reclus, a suite of global, integrated databases that fill this gap, thereby providing the community with the key components for investigating the Earth system. Reclus includes databases of the following: (a) structural elements, which define the three‐dimensional geometry of the rock volume, including folds and faults; (b) “crustal” facies describing the geometry and composition/rheology of the lithosphere; (c) igneous features; and (d) geodynamics, representing the dominant thermo‐mechanical processes acting on the lithosphere. These databases and workflows are applied to East Africa to investigate the geometry and heterogeneity of the margin and its hinterland. This margin is often summarized in the literature as a “transform margin,” represented by a single structural feature, the “Davie Fracture Zone,” but it is much more complicated. We show how the pre‐existing structure, the superimposition of successive tectonic cycles, and crustal heterogeneity dictate the complexity observed.

The passive margin of the Guiana Shield formed at the junction of the Central and Equatorial Atlantic Oceans that developed successively by a complex rifting process that achieved the final dispersal of Western Gondwana. Yet, the resulting spatial distribution of crustal thinning along the margin remains to be mapped and its controlling parameters deciphered. We used subsurface data to map the variability of crustal thinning along the margin. We show that the margin segments width primarily depends on their obliquity to rifting extension direction. The necking domain of the transform/oblique margin segments is much narrower (<100 km) than divergent segments that include hyper‐extended or distal margin domains as well (200–300 km). Moreover, for a similar obliquity, the width of margin segments resulting from the Central Atlantic rifting are wider than those resulting from the Equatorial Atlantic rifting. This is primarily due to the higher obliquity and rate of the latter. Additionally, along the Central Atlantic margin segments, thinning was accommodated by lower‐crustal ductile deformation, the thick syn‐rift in‐fill was associated with magmatism and a thicker than average oceanic crust. In contrast, the Equatorial Atlantic margin segments show little ductile deformation, reduced clastic syn‐rift infill and thinner than average oceanic crust. These observations suggest that the lithosphere affected by the Central Atlantic rifting was warmer than that affected by the Equatorial Atlantic rifting. Finally, the two‐step thinning in the overlapping area of the two rift systems individualized a promontory of thinned continental crust that remained as the Demerara Plateau. Plain Language Summary: The continental margin of the Guiana Shield formed at the intersection of the Central and Equatorial Atlantic Oceans that developed one after the other and, in doing so, achieved the break‐up of the Gondwana supercontinent. To form these Ocean, the continent crust was stretched and broke but the way this thinning is actually varying along the margin and the causes are not known so we used offshore industrial data to map it. This allows us showing that the width of the continental margin depends primarily on the direction along which the crust was thinned such that the continental margin width is much wider (200–300 km) in domains where this direction is perpendicular to the margin than in domain where it is oblique (<100 km). This also allow us showing that the continental margin resulting from the opening of the Central Atlantic Ocean is systematically wider than the one resulting from the opening of the Equatorial Atlantic. Additionally, our observations suggest that Central Atlantic Ocean opened under warmer conditions than the Equatorial Atlantic. Finally, the area at the intersection of the Central and Equatorial Atlantic Oceans, individualized a promontory of continental crust that formed the present‐day Demerara Plateau. Key Points: Higher rifting obliquity and rates produced narrower rift and rifted margin segmentsWarmer Central Atlantic rifting produced crustal flow and preserved thick syn‐rift deposits contrary to cooler Equatorial Atlantic riftingLithosphere of the Demerara Plateau was thinned twice and became a buoyant continental raft since the Mid‐Cretaceous [ABSTRACT FROM AUTHOR]

Interpretation of 2014–2015 deep crustal seismic reflection and magnetotelluric data has revised the architecture and geodynamic framework of western Queensland, with implications for the assembly and dispersal of the supercontinents Nuna, Rodinia and Gondwana. In the Mount Isa Province, crustal-scale boundaries of the Leichhardt River Domain, Kalkadoon-Leichhardt Domain and Eastern Subprovince are mapped in the third dimension. The Leichhardt River and Kalkadoon-Leichhardt domains have similar Nd isotopic T 2DM model ages to provinces to the west, indicating they were part of ancestral North Australian Craton (NAC); the Eastern Subprovince is a separate terrane, with the Pilgrim Fault a collisional suture. The Gidyea Suture Zone separates the Mount Isa Province from the subsurface Numil Seismic Province. To the east, the west-dipping Yappar Fault separates east-dipping structures in the west from west-dipping structures in the east, forming a classic doubly vergent orogen within the upper plate of a convergent margin. The northwestern boundary of the Bernfels Seismic Province, the Kynuna Fault, truncates the Gidyea Suture Zone, implying this seismic province was welded to the NAC prior to initial deposition of the Etheridge Province. The Cork Fault truncates the north-south grain of the Mount Isa Province; the easternmost part of the NAC has been excised, presumably during breakup of Nuna. The subsurface Brighton Downs Seismic Province, formerly part of the northern Thomson Orogen, is a discrete seismic province, located between the NAC and the Thomson Orogen, and welded to the NAC during the accretion of Rodinia. Basement to the Thomson Orogen is a collage of microplates, accreted to the Brighton Downs Seismic Province during the assembly of Gondwana. By 530 Ma, eastern Australia faced an open Pacific Ocean, with the Thomson Orogen in a backarc setting. Thus, northeastern Australia contains a record of repeated continental accretion and breakup over at least three supercontinent cycles. • Interpretation of 2014–2015 deep crustal seismic reflection data in western Queensland. • Two new discrete seismic provinces discovered in the subsurface. • At least four Paleoproterozoic terranes recognised in easternmost North Australian Craton. • Part of North Australian Craton excised at Cork Fault during breakup of Nuna. • Northeast Australia records continental assembly and breakup over three supercontinent cycles. [ABSTRACT FROM AUTHOR]

Identification of continental crustal architecture in orogenic belts is essential for understanding the geodynamic evolution of global continental collision systems. However, ongoing debates surrounding the crustal nature of the Lhasa Terrane in the central Tibetan Plateau impede our comprehension of its tectonic evolution. Mesozoic intermediate-felsic magmatism in the Lhasa Terrane offers key insights into the crustal architecture before the India-Asia collision. Here we report zircon U-Pb-Hf isotope, whole-rock element and Sr Nd isotope data from Early Cretaceous granitoids in the Baingoin batholith, northern Lhasa Terrane. These granitoids (127–115 Ma) exhibit variable SiO 2 (62.99–73.86 wt%), K 2 O (1.15–4.74 wt%), and MgO (0.49–2.48 wt%) contents. They are classified as low- to high-K calc-alkaline and metaluminous to peraluminous series, enriched in large ion lithophile elements (e.g., Rb) and light rare earth elements ((La/Yb) N = 7.08–18.3), and depleted in high field strength elements (e.g., Nb, Ta, and Ti). These granitoids display geochemical affinities with I-type granitoid rocks and can be further subdivided into three groups. Group 1 granitoids exhibit the highest zircon ε Hf (t) (−1.57 to 5.85) and whole-rock ε Nd (t) (−3.37 to −2.45), and lowest (87Sr/86Sr) i (0.706018 to 0.706922) values, whereas Group 2 granitoids have wide ranges of zircon Hf (ε Hf (t) = −7.78 to 2.26) and enriched whole-rock Sr Nd isotope compositions ((87Sr/86Sr) i = 0.707214 to 0.707918; ε Nd (t) = −7.38 to −6.14). These suggest that Group 1 and Group 2 granitoids may be dominantly derived from the juvenile and ancient crustal sources, respectively. Group 3 granitoids are characterized by zircon Hf (ε Hf (t) = −2.85 to 3.52) and whole-rock Sr Nd isotope compositions ((87Sr/86Sr) i = 0.706473 to 0.707692; ε Nd (t) = −4.50 to −3.01) falling between the ranges of the previous two groups, likely represent a mixture of juvenile crustal-derived melt with 10–15% of reworked ancient crustal materials. Integrating previous research, we propose that the persistent ancient crustal basement beneath the northern Lhasa Terrane was concurrently undergoing significant modification through juvenile crustal materials during the Early Cretaceous. These Early Cretaceous Baingoin batholith preserves crucial records of crustal evolution and highlights the influence of upwelling asthenosphere during the transition from Bangong-Nujiang oceanic subduction to Lhasa-Qiangtang collision. • Baingoin granitoids in the northern Lhasa Terrane belong to I-type granitoids. • There is a common ancient crustal basement between the northern and central Lhasa Terranes. • Baingoin batholith witnessed the subduction and demise of the Bangong-Nujiang oceanic slab. [ABSTRACT FROM AUTHOR]

The East Orphan, Porcupine, and Galicia Interior basins are several of the most promising basins for hydrocarbon exploration along the rifted continental margins of the southern North Atlantic Ocean. Despite having formed at similar geological times, the basins exhibit fundamental differences in symmetry, crustal thickness, sedimentary cover thickness, and amount of extension. Interpretation of seismic reflection and well data was integrated with published 3D grids of depth-to-basement and Moho proxy depth to interpret and restore select seismic reflection lines. Publicly available kinematic evolution models were also integrated to evaluate and compare the restored seismic reflection lines in a more global regional context. Interpretation of five seismo-stratigraphic units and three tectonostratigraphic megasequences along the East Orphan, Porcupine, and Galicia Interior basins reveals similar seismic character for each unit and comparable tectonic history. The structural restoration of the selected lines indicates that evolution, sedimentary cover thickness, faulting style, crustal structure, and kinematic evolution of the East Orphan and Porcupine basins differ significantly. A variable and asymmetrical crustal structure is found in the East Orphan Basin contrasting with the elongated and symmetric Porcupine and Galicia Interior basins. Rift domain maps of the three basins reveal that they are each underlain by hyperextended crust, with possible exhumed mantle in the centre of the Porcupine Basin. Based on a holistic analysis of the results obtained, the linkage between the East Orphan and the Porcupine basins seems implausible, but rather a contemporaneous relationship is interpreted. Moreover, a potential connection between the Galicia Interior Basin and the Porcupine Basin during the Early to Late Jurassic is proposed. Such scenarios imply an oblique and synchronous rifting evolution around the Bay of Biscay triple junction of the southern North Atlantic. • The connection between the East Orphan and the Porcupine basins is unlikely. • An ancient connection between the East Orphan and the Rockall basins is proposed. • A continuous basin formed by the Porcupine and Galicia Interior basins during the Early to Late Jurassic is proposed. [ABSTRACT FROM AUTHOR]

Palaeogeography is the representation of the past surface of the Earth. It provides the spatial context for investigating how the Earth evolves through time, how complex processes interact and the juxtaposition of spatial information. In hydrocarbon exploration, palaeogeographies have been used to map and investigate the juxtaposition, distribution and quality of play elements (source, reservoir, seal and trap), as boundary conditions for source-to-sink analysis, climate modelling and lithofacies retrodiction, but most commonly as the backdrop for presentations and montages. This paper demonstrates how palaeogeography has been and can be used within an exploration workflow to help mitigate exploration risk. A comprehensive workflow for building palaeogeographies is described which is designed to provide a standard approach that can be applied to a range of tasks in exploration and academia. This is drawn from an analysis of the history of palaeogeography and how it has been applied to exploration in the past and why. Map applications, resolution and content depend on where in the exploration and production (E&P) cycle the map is used. This is illustrated here through three case studies, from the strategic decisions of global new ventures exploration to the more detailed basin and petroleum analyses of regional asset teams evaluating basins and plays. Through this, the paper also addresses three commonly asked questions: (1) How can I use palaeogeography in my workflow? (2) How reliable are the maps? (3) How do I build a palaeogeography? [ABSTRACT FROM AUTHOR]

[Display omitted] • Paleo-Tethys evolution modeling in the EKOB is established using geochemistry dataset. • Crustal architecture evolution during orogeny revealed by element and isotope mapping. • Metallogeny is spatiotemporally and genetically associated with crustal architecture. The Eastern Kunlun Orogenic Belt (EKOB) in the Northern Tibet Plateau hosts a wide variety of metal deposits related to the Late Paleozoic to Mesozoic magmatism. In this study, we investigate the spatio-temporal distribution of the Late Paleozoic to Mesozoic granitic rocks and associated metal deposits in the EKOB and provide a comprehensive compilation of the geochronological, geochemical and isotopic data on these rocks. We compute regional zircon Hf isotope and crustal thickness maps from the data, based on which a comprehensive model is proposed involving subduction (ca. 270–240 Ma), continental collision (ca. 240–224 Ma), and post-collisional extension (ca. 224–200 Ma) for the Late Paleozoic to Mesozoic Paleo-Tethys evolution in the EKOB. Zircon Hf isotopic and crustal thickness mapping of Late Paleozoic to Mesozoic magmatic rocks was carried out to evaluate their spatio-temporal and genetic links with the regional metallogeny. The polymetallic Fe-skarn and porphyry Cu (Mo) deposits in the EKOB are located above the Moho uplift region, featuring a comparatively thin crust. Granites associated with porphyry Cu (Mo) and polymetallic Fe skarn mineralization are commonly characterized by high ε Hf (t) and younger T DM c values, whereas granite related to Cu-Mo-Sn skarn deposits exhibit more variable ε Hf (t) values, T DM c ages, and the crust thickness, which suggest that more crustal materials contributed to the formation of Cu-Mo-Sn skarn deposits than those for porphyry Cu (Mo) and polymetallic Fe skarn mineralization. In contrast, vein-type Au deposits are located primarily where the Moho surface displays a depression, i.e., where the continental crust is relatively thick. The magmatic rocks associated with Au mineralization are characterized by low ε Hf (t) and high T DM c values, representing reworked ancient crustal components, similar to those associated with porphyry Mo and epithermal Ag-Pb-Zn-(Au) deposits. Our study indicates that the emplacement of magmatic-hydrothermal deposits was controlled by the crustal structure and magma sources. [ABSTRACT FROM AUTHOR]

Reconstructions of the opening of the North Atlantic Ocean generally result in the Orphan Basin, offshore Newfoundland, Canada, lying approximately conjugate to the rift basins on the Irish Atlantic margin at the onset of seafloor spreading toward the end of the Early Cretaceous. Most of these plate reconstructions have involved rigid plates with plate motions based solely on the interpretation of oceanic magnetic anomalies. In particular, these reconstructions often show the Rockall Basin, west of Ireland, forming a continuous Mesozoic basin with the West Orphan Basin, offshore Newfoundland. However, more recent plate reconstructions involving deformable plates have called this conjugate relationship into question. The goal of this study is to investigate the validity of this potentially continuous basin system by reconstructing and restoring present-day seismically-constrained geological models both spatially and temporally back to their original configurations pre-rift. By comparing the reconstructions in terms of sedimentary package thicknesses and crustal thicknesses in 3D, using both rigid and deformable plate reconstructions to orient the reconstructed models, we are able to test different basin connectivity scenarios using a multidisciplinary approach. Our analysis provides subsurface geophysical support for the hypothesis that the Rockall Basin was originally conjugate to and continuous with the East Orphan Basin during Jurassic rifting, later linking to the West Orphan Basin as rifting evolved during the Early Cretaceous. This complex basin evolution example highlights the need for using 3D rifting mechanism models to properly understand the fundamental driving forces during rifting and has significant implications for assessing basin prospectivity across conjugate margin pairs.

The south-eastern part of the North China Craton (NCC), the major historical source of gold supply to the former Emperors of China, continues to be a potential target for gold exploration. With a view to gain insights on the crustal architecture and gold metallogeny of this region, this contribution combines geological and Nd–Hf–isotopic data from magmatic rocks associated with the ore mineralisation. We integrate Nd–Hf isotopic data from published works as a tool to present isotopic maps. These maps highlight the location of major tectonic structures, and their relationship with the distribution of mineral deposits in the south-eastern NCC. The porphyry and porphyry–skarn Cu(–Au–Mo) deposits in the Luxi area in eastern NCC are associated with magmatic rocks and are located in zones with variable εNd–εHf values and T DM c –T DM 2 ages representing dominant Paleoproterozoic to Mesoproterozoic and reworked crustal components with minor mantle material. In contrast, the Jiaodong type Au and porphyry–skarn Mo(–W–Cu) deposits are associated with magmatic rocks emplaced in domains with low–εNd–εHf values and older T DM c –T DM 2 ages characterised by dominantly Archean–Paleoproterozoic reworked crustal components in the Jiaobei Terrane and the Sulu Orogen. Our study thus demarcates distinct crustal provinces and source components in generating some of the world-class gold deposits. [ABSTRACT FROM AUTHOR]

For over 35 years, deep seismic reflection profiles have been acquired routinely across Australia to better understand the crustal architecture and geodynamic evolution of key geological provinces and basins. Major crustal-scale breaks have been interpreted in some of the profiles, and are often inferred to be relict sutures between different crustal blocks, as well as sometimes being important conduits for mineralising fluids to reach the upper crust. The widespread coverage of the seismic profiles now allows the construction of a new map of major crustal boundaries across Australia, which will better define the architecture of the crustal blocks in three dimensions. It also enables a better understanding of how the Australian continent was constructed from the Mesoarchean through to the Phanerozoic, and how this evolution and these boundaries have controlled metallogenesis. Starting with the locations in 3D of the crustal breaks identified in the seismic profiles, geological (e.g. outcrop mapping, drill hole, geochronology, isotope) and geophysical (e.g. gravity, aeromagnetic, magnetotelluric) data are used to map the crustal boundaries, in plan view, away from the seismic profiles. Some of the boundaries mapped are subsurface boundaries, and, in many cases, occur several kilometres below the surface; hence they will not match directly with structures mapped at the surface. For some of these boundaries, a high level of confidence can be placed on the location, whereas the location of other boundaries can only be considered to have medium or low confidence. In other areas, especially in regions covered by thick sedimentary successions, the locations of some crustal boundaries are essentially unconstrained, unless they have been imaged by a seismic profile. From the Mesoarchean to the Phanerozoic, the continent formed by the amalgamation of many smaller crustal blocks over a period of nearly 3 billion years. The identification of crustal boundaries in Australia, and the construction of an Australia-wide GIS dataset and map, will help to constrain tectonic models and plate reconstructions for the geological evolution of Australia, and will provide constraints on the three dimensional architecture of Australia. Deep crustal-penetrating structures, particularly major crustal boundaries, are important conduits to transport mineralising fluids from the mantle and lower crust into the upper crust. There are several greenfields regions across Australia where deep crustal-penetrating structures have been imaged in seismic sections, and have potential as possible areas for future mineral systems exploration. [ABSTRACT FROM AUTHOR]

Although it is generally accepted that many distal, magma-poor rifted margins are asymmetric and can be divided into lower and upper plate margins, little is known about the details of how and when this asymmetry evolves and how upper and lower plate margins can be distinguished. This is due to the fact that most papers focused on the so called lower plate margins, while the upper plate margins remained less well understood, mainly due to the lack of public accessible drill hole data. The aim of this paper is to provide a first order description of the global architecture and stratigraphic evolution of an upper plate, magma-poor rifted margin. In order to provide such a template, we focused on 2 seismic sections, the ION-1000 line (East Indian margin), and the SCREECH 2 line (Newfoundland margin) and describe key, km-scale outcrops from the fossil European margin exposed in the Western/Central Alps, all of which document classical upper plate margins. Based on these data we show that upper plate magma-poor rifted margins can be characterized by a staircase type architecture with terraces (T 1 , T 2 , T 3 ) and ramps (R 1 , R 2 ) that result as a consequence of an evolution through a coupling, exhumation and breakup stage. We also defined key stratigraphic levels that we try to link with the evolution of the margin which enables us to link the tectonic evolution with the creation of accommodation space and formation of the staircase architecture that characterizes the upper plate margin. From these observations we develop a conceptual model for the evolution of upper-plate margins and discuss the applicability of this model for different strain rates, rates of subsidence and sedimentation rates. [ABSTRACT FROM AUTHOR]

Orthogneiss and meta-rhyolite bodies from different crustal levels of the Tseel Terrane in the Mongolian Altai were examined using multidisciplinary approach involving structural geology, whole-rock geochemistry and U-Pb zircon geochronology. The orthogneisses form sheet-like bodies parallel with dominant sub-horizontal metamorphic fabric which was heterogeneously verticalized along localized zones of deformation at boundaries of lower and middle crustal domains. Three samples of orthogneisses yielded Late Devonian LA-ICP-MS U-Pb zircon ages of 373±3, 377±5 and 379 ± 2 Ma (2σ), which are interpreted as crystallization ages of felsic magmas. The meta-rhyolite displays poorly constrained, older U-Pb zircon ages of 380±4 and 403±5 Ma, which are also considered as intrusive. Whole-rock geochemistry, including relatively little fractionated REE patterns, as well as radiogenic whole-rock Nd and zircon Hf isotopic signatures point to a rather primitive source of the granitic protoliths. The high-K calc-alkaline chemistry and LILE over HFSE enrichments in the NMORB-normalized spider plots indicate an arc-related origin. Juvenile character of the studied rocks was confirmed by Nd and Hf crustal residence ages that are mostly 0.8-0.9 Ga. The origin of the metaigneous rocks is interpreted in terms of partial melting of Neoproterozoic to Cambrian magmatic arc-derived material, probably dominated by immature psammitic sediments (graywackes). This study brings important arguments that the orthogneisses do not represent an old crystalline basement previously assumed in the Mongolian Altai. A model is proposed suggesting formation of mature and layered continental crust by syn-orogenic melting of youthful volcanosedimentary wedge and emplacement of sub-horizontal syn-orogenic magmatic sheets at all crustal levels during crustal-scale vertical shortening. The vertical shortening was probably connected to lithospheric-scale extensional event associated with massive heat influx and emplacement of juvenile magmas at the bottom of the crust. It is suggested that this mechanism represents potentially a viable model for cratonization of accretionary systems worldwide. [ABSTRACT FROM AUTHOR]

The Western African Sub-Saharan continental margin includes a large region from Cameroon to South Africa comprising distinct margin types – magma-rich, magma-poor and transform margins. The integrated study of geological, seismic and potential field data allows the mapping of a structural framework subdivided in proximal, necking, distal, outer and oceanic domains, characterized by a set of comparable architectural elements and magmatism. These key domains display a strong and consistent continuity along the continental margin. Longitudinal transitional regions occur in a gradual way, but interactions between structural domains along transversal section may also occur, displaying spatial and temporal overprints. Because of this complexity, the outer domain that is the key feature in the magma-rich margin, tends to disappear northwards where the distal and proximal domains of the magma-poor segments become the most important domains of the margin. In the north of Gabon Basin, it is observed both the reappearance of the outer domain and the reworking of the distal domain by fracture zones. The basement of the distal domain within the magma-poor margin is interpreted as made by a hyperextended continental crust but with magmatic additions. Finally, the new proposed continent-ocean boundary (COB) in the region of the Namibe Basin (transitional zone between magma-rich and magma-poor margins) achieves a best fit in a reconstruction model with the limits recognized at the South America side. The results will imply in a drastic reduction on the gap proposed by other recent reconstruction models and also minimize the intraplate deformation required by some other models. • The Western African Sub-Saharan continental margin comprises distinct type: magma-rich, magma-poor and transform margins. • Integrated geological, seismic, and gravity data allows the mapping of the structural framework throughout margin segments. • Longitudinal transitional regions occur in a gradual way. • The new proposed continent-ocean boundary in the region of Namibe Basin achieves a best fit in a reconstruction model. • Obtained results imply in a drastic reduction on the gap and minimizing the intraplate deformation required. [ABSTRACT FROM AUTHOR]

The European Variscan belt is a unique orogen that is covered by comprehensive sets of seismic and potential field data from the Iberian Peninsula in the west to the Polish Sudetes in the east. The combination of both allows for a new interpretation of the structure and evolution of the European Variscides at the continental scale. The European Variscan belt has been divided into three domains according to distinct geological and geophysical characteristics: 1) the North-eastern Variscan Domain (NVD) outcropping in the Bohemian Massif, Black Forest and Vosges Massifs, and the Rhenish Massif, 2) the Central Variscan Domain (CVD) represented by the French Massif Central, Armorican Massif and British Variscides, and 3) The South-western Variscan Domain (SVD) represented by the Iberian Massif. The gravity data show the presence of high amplitude, short-wavelength gravity anomalies that are mainly correlated with the outcrops of eclogites, ultramafic rocks and ophiolites. These anomalies locate the main body of the Mid-Variscan Allochthon in the SVD and CVD and the Devonian Mid-Variscan suture in the NVD. The gravity data also show medium amplitude elongated long-wavelength gravity highs aligned parallel to the structural grain of the Variscan belt, represented by the deformed Teplá-Barrandian-Kraichgau upper crustal rocks, a Devonian supra-subduction basin in the Mid-Variscan Allochthon, and the autochthonous rocks of the Central Iberian Zone in the SVD, the Armorican Massif in the CVD and the Saxothuringian Zone in the NVD. The short wavelength negative gravity anomalies are mainly developed in the central part of the belt and coincide with Carboniferous (330–310 Ma) per- to meta-aluminous magmatic bodies, pre-Variscan orthogneisses and Carboniferous felsic granulite bodies. Noticeably, Permian (300–290 Ma) granitoids do not reveal any gravity lows indicating that these bodies are not deeply rooted. The magnetic data show two belts correlated to Carboniferous Rhenohercynian and Devonian Mid-Variscan magmatic arc granitoids. The Rhenohercynian and Mid-Variscan subduction systems are well imaged by moderately SE dipping primary A-type reflectors in reflection seismic lines in the NVD and CVD, while in the SVD the reflectors related to the Rhenohercynian subduction are dipping to the NE and the seismic signature of the Mid-Variscan suture is weakly developed. In the NVD, a third belt of SE-dipping reflectors is attributed to the Carboniferous subduction of the Saxothuringian continental lithosphere beneath the Mid-Variscan Allochthon. Younger B-type moderately dipping reflectors in the upper-middle crust coincide with outcrops of Carboniferous detachments, sometimes limiting granite plutons and core complexes along-strike the core of the Variscan orogeny. C-type reflectors occur mainly in the deep crust and are considered as an expression of lower crustal flow resulting from extensional re-equilibration of the previously thickened Variscan crust. A synthesis of P-wave velocity logs at the scale of the whole Variscan belt shows the existence of three different continental crusts: (i) cratonic crust marked by a thick, high velocity lower crust, (ii) transitional crust characterised by a relatively thin high velocity lower crust and intermediate velocity middle crust, and (iii) a thin Variscan orogenic crust defined by low velocity lower and middle crust. The latter crustal type coincides with regional outcrops of 330–310 Ma per- to meta- aluminous granitoids and associated gravity lows along-strike the belt. It is argued that the specific "Variscan" orogenic crust originated by Carboniferous extensional thinning and extensive melting of previously thickened "Tibetan" type crust and not from Permian tectogenesis, which is restricted to marginal parts of the orogen. [ABSTRACT FROM AUTHOR]

The structural and stratigraphic characteristics of the central portion of the Tucano Basin, a Cretaceous continental rift basin in northeast Brazil, was investigated, using post-stack 2-D reflection seismic, gravity and well data. Methodology was steered by the principles of seismic stratigraphy, targeting at an adequate identification of stratal terminations and on the mapping of structural features, where a negative flower structure was interpreted. The identification of erosional truncations led to a stratigraphic framework of seven intra-rift unconformities, forming eight third-order rift sequences, while the literature on the Tucano basin recognizes only two depositional sequences forming the rift sedimentary infill. In order to study the abnormal depth of Central Tucano depocenter, gravity data were processed and a spectral analysis was performed, which located the depocenter at approximately 16.8 km, a rare configuration for a rift basin. Gravity models were created in order to verify the seismic interpretation and the depth found by the spectral analysis; and to provide a view of the basin in a regional scale, analysing its crustal architecture. The modelling confirmed the abnormal depth and also indicated a severe crustal thinning under Central Tucano Basin, where the Moho was interpreted around 24 km and a major crustal necking was observed. The models introduced the geometry of the lower continental crust and indicated the presence of a high-density layer (3000 kg/m3) at its base, which this work suggests to be a result of magmatic underplating. The paper closes discussing the role of tectonics and basement inheritance over the Central Tucano Basin structural framework and commenting on the mode of extension for the Recôncavo-Tucano-Jatobá rift system. • Central Tucano Basin has a transtensional tectonic setting. • Eight third-order rift sequences were interpreted in Central Tucano Basin. • The depocenter of Central Tucano Basin has a maximum depth of 16.8 km. • Central Tucano Basin experienced a major crustal thinning. • High-density layer modelled at the lower crust speculated as magmatic underplating. [ABSTRACT FROM AUTHOR]

[Display omitted] • Mesozoic Mo-associated granitoids on the Jiaodong Peninsula occurred at ca.160 Ma and 117 Ma. • North China Block lower crust served as source for the Mo-associated granitoids. • Different magma sources controlled by crustal architectures led to Mo endowment diversity along the Dabie-Sulu Orogen. Recent studies have demonstrated a linkage between the crustal architecture and the location of magmatic–hydrothermal Cu deposits in collisional orogens. However, if and how the crustal architecture controls the distribution of magmatic–hydrothermal Mo deposits in collisional orogens is unclear. Here, we present zircon U–Pb dating, geochemical and Sr–Nd–Hf–O isotopic data for granitoids associated with Mesozoic Mo mineralization on the Jiaodong Peninsula which exhibits substantial endowment differences to the Dabie Orogen. Geochronology data show that the Mo-associated granitoids occurred at ca. 160 Ma and 117 Ma. The Jurassic Mo-associated monzogranite was derived from melting of the thickened North China Block lower crust in a subduction-related setting. The Early Cretaceous Mo-associated granodiorite and granite were originated from a modified North China Block thorough crust–mantle interactions, induced by rollback of the Paleo-Pacific Plate. Our results complemented by published data indicate a crustal architecture characterized by South China Block gneisses overlying North China Block lower crust in the Sulu Orogen and wedging into the North China Block in the Jiaobei Terrane. By comparing the Mo–associated granitoids in Dabie Orogen and Jiaodong Peninsula, we conclude that magma source differences controlled by crustal architectures lead to Mo endowment diversities along the Dabie–Sulu Orogen. [ABSTRACT FROM AUTHOR]

A 300 km long seismic reflection profile was acquired across the Middle and Lower Reaches of the Yangtze River (MLY) metallogenic belt and its adjacent areas. The objective of the survey was to establish the deep architecture and geodynamic framework of the region. Results based on the interpretation of the deep seismic data include (1) Tan-Lu fault appears as a subvertical thrust fault or transpression fault with its deep portion dipping toward the southeast; (2) the Zhangbaling uplift is squeezed out along this fault; (3) complex upper crustal deformation structures beneath the Chuquan depression include both kink bands, thrusts, imbrication and fold structures reflecting contraction deformation, and detachment fault and normal-fault structures reflecting extensional deformation; (4) the “crocodile” reflection structure emerging beneath the Tan-Lu fault and Ningwu–Lishui volcanic basin, which represents the decoupled deformation process of the upper and lower crust associated with intra-continental subduction; (5) further to the southeast, the upper crust deformation shows a large-scale “wave-form” pattern, making crustal scale syncline and anticline; (6) the entire section of the reflection Moho is clearly discernible at depth of 30.0–34.5 km, and the Moho beneath the Middle and Lower Reaches of Yangtze River metallogenic belt is shallowest, while the Moho beneath the North China block is deeper than that beneath the Yangtze block. The Moho offsets could be seen beneath the Ningwu volcanic basin. The seismic reflection data suggest that lithosphere delamination and asthenosphere upwelling that may result from the Mesozoic intra-continental orogenesis is responsible for the formation of large scale magmatism and mineralization in the MLY metallogenic belt. [ABSTRACT FROM AUTHOR]

We have investigated the crustal architecture of the Borborema Province of NE Brazil by constructing common conversion point (CCP) receiver function stacks from teleseismic P-waveforms recorded at 64 seismic stations in the region. The Borborema Province represents the western portion of a larger Neoproterozoic mobile belt that experienced extension in the Mesozoic, leading to the formation of a number of intra-continental rift basins and, eventually, continental breakup. After continental breakup, episodes of uplift in the Province — perhaps related to coeval episodes of Cenozoic volcanism — helped shape the high topographies of the Borborema Plateau. Our receiver function CCP stacks image clear P-to-S conversions at the crust–mantle boundary and confirm independent evidence for a 36–38 km thick crust under the southern portion of the Plateau and a thinner 30–32 km thick crust in the surrounding regions, including the northern Plateau. The cross-sections also reveal the presence of an intra-crustal discontinuity at 9–18 km depth under the regions of thin crust that fades away under the thick southern Plateau. We argue that the thin crust in the Borborema Province is the result of Mesozoic crustal stretching and that the intra-crustal discontinuity represents a low-angle detachment zone that helped accommodate extension in the crust. The thick crust under the southern Plateau would then represent a rheologically stronger portion of the Borborema Province that resisted deformation by Mesozoic extension, while the thin crust under the northern Plateau would be a portion of formerly depressed thin crust that was uplifted during the Cenozoic. [ABSTRACT FROM AUTHOR]

The present comprehensive multidisciplinary geophysical study provides new insights into the structural architecture and tectonic development of the Brazilian Equatorial Margin during the transform opening of the Equatorial Atlantic Ocean. The study integrates magnetic, gravity, and seismic data and adds to the knowledge of the prebreakup geotectonic setting of West Gondwana, shedding light on the role of the Precambrian heritage in the crustal compartmentalization of the Equatorial Atlantic margins into divergent and transform segments. Additionally, we improved previous evolution models of the Brazilian Equatorial Margin, considering the nature of the crustal domains and processes related to the initial breakup of West Gondwana. Our geophysical datasets reveal that the Brazilian Equatorial Margin encompasses two crustal domains with distinct internal architecture and thermomechanical parameters divided by the Transbrasiliano Lineament. The western crustal block is composed of a thicker and older lithosphere, which acted as an obstacle to continental rupture. The resulting breakup occurred further north, while the crustal block east of the Transbrasiliano Lineament disrupted relatively further south. Two different rift systems thinned both crustal domains during a former rift phase before the subsequent and ultimate rift phase broke up the continental crust and initiated seafloor spreading under a transform regime. After the breakup between the South American and African continents, dextral strike-slip movements along oceanic fracture zones divided the Brazilian Equatorial Margin into divergent and transform segments, whose inner and outer intersections are identified in the present study. The marginal ridges represent basement uplifts separated from the continental hinterland by pull-apart basins deformed by negative structure-like flower structures. The prebreakup Precambrian structures played a key role in margin segmentation, behaving as crustal weakness zones and nucleating transform faults at the boundaries of the divergent margin segments. • Geophysical data reveal the crustal structure of the Brazilian Equatorial Margin. • Margin segments were distinguished mainly by inner and outer corners and marginal ridges. • Precambrian inheritance limited the divergent and transform margin segments. • Rifting and continental breakup was oblique to the oceanic fracture zones. • New evolutionary model considers geological domains deformed before breakup. [ABSTRACT FROM AUTHOR]

We present a joint interpretation of the aeromagnetic and gravity anomaly datasets of the Precambrian Eastern Ghats Mobile Belt, eastern India, to delineate the detailed crustal architecture, identify faults and shear zones, as well as boundaries of different terranes throughout this belt. We use geological constrained analysis of the distinct aeromagnetic anomaly signatures to re-interpret the extent of the Jeypore, Krishna, Eastern Ghats, and Rengali Provinces. Forward modelling of paired gravity anomalies and an increase in magnetic response along the craton-mobile belt boundary reveal that it is dominated by high-density and highly magnetic granulite facies rocks that overthrust the low-density and low magnetic older cratonic gneissic rocks along the deep crustal faults, suggesting the Eastern Ghats Mobile Belt terranes are allochthonous in nature. Two high magnetic anomaly belts in the Krishna and Eastern Ghats Provinces define a terrane-scale fold (orocline). The younger normal faults of Godavari Basin overprint the charnockitic belt in the southern part of the Eastern Ghats Province, suggesting that these high magnetic belts pre-date the Pan-African Orogeny. The boundary between the Eastern Ghats Province and Krishna Province is identified by the change in anomalies in magnetic and gravity maps. The Sileru Shear Zone and Kerajung Shear Zone separates the Eastern Ghats Province-Jeypore Province and Eastern Ghats Province-Rengali Province respectively, are characterized by a sharp change in magnetic anomalies. The intra-province Nagavali-Vamsadhara Shear Zone and Mahanadi Shear Zone are characterized by subdued magnetic anomalies. Inversion of the regional gravity anomalies revealed that the Moho is slightly shallower (~5 km) beneath the Eastern Ghats Mobile Belt compared to the neighbouring Cratons. • The subsurface extent of various terranes of the Eastern Ghats Mobile Belt is delineated by structural geophysical analysis. • Crustal architecture of the Eastern Ghats Mobile Belt is redefined from joint interpretation aeromagnetic and gravity data. • The present study reveals that the Eastern Ghats Mobile Belt is an allochthonous. [ABSTRACT FROM AUTHOR]

[Display omitted] • One high-εHf and two low-εHf domains in the Argun massif indicate the Neoproterozoic and Mesoproterozoic to Neoproterozoic crustal zones, respectively. • Transition of magma source from the juvenile crust to ancient crust from south to north during the Mesozoic. • The composition and structure of the crust control the metal associations, deposit types, and localization of ore deposits. The Argun massif is an important micro-continent in the eastern Central Asian Orogenic Belt and hosts a wide variety of Mesozoic hydrothermal Cu(–Mo), Pb–Zn–Ag, and Au deposits such as Wunugetushan Cu(-Mo) and Jiawula Pb–Zn–Ag deposits. In this paper, we integrate geological and zircon U–Pb–Hf isotopic data from Mesozoic Argun igneous rocks to elucidate the crustal architecture, and any spatial–temporal and genetic links with the regional metallogeny. Our results indicate that the porphyry Cu–Mo deposits in the massif were mainly developed in the zones with high-εHf(t) values and Neoproterozoic T DM c ages, representing juvenile lower crustal components. The epithermal Pb–Zn–Ag deposits were mostly developed in zones with variable εHf(t) and Mesoproterozoic to Neoproterozoic T DM c values, representing magma source with reworked ancient or juvenile lower crustal components. In contrast, the major mesothermal and epithermal Au deposits are associated with magmatic rocks emplaced in low-εHf(t) and high-T DM c domains, representing reworked Mesoproterozoic ancient crustal components. [ABSTRACT FROM AUTHOR]

The crustal structure of collisional orogen is critical for deciphering the crustal evolution and geodynamics of an orogen. Metamorphic rocks and post-collisional magmatic rocks are the key subjects to probe the crustal structure. In this study, we conducted an integrated study of zircon U Pb age, Hf and O isotopes for migmatites and post-collisional granites in the southern segment of the Tongbai orogen. Zircon U−Pb dating yields protolith ages of 755 ± 55 to 713 ± 6 Ma and metamorphic ages of 162 ± 11 Ma to 138 ± 2 Ma for the migmatites and intrusion ages of 137 ± 2 Ma for the post-collisional granites. The inherited magmatic cores in the migmatites exhibit similar Hf isotopic compositions to the metamorphic zircons. Their ε Hf (t) values range from 13.5 to −9.5 with crust Hf model ages of 787 Ma to 2233 Ma, indicating that the protoliths were derived from reworking of Paleoproterozoic crust with the addition of juvenile components during the Neoproterozoic. Zircon δ18O of inherited magmatic cores are of −1.45‰ to 5.90‰, signifying the protoliths were formed by remelting of hydrothermally altered low δ18O rocks. By comparison, the post-collisional granites mostly show normal mantle-like O zircon isotope compositions and have lower ε Hf (t) and ε Nd (t) values than the migmatite rocks. These features suggest that the granites were formed by fusion of the ancient crust that might have suffered insufficient water-rock interaction. The discrepancies in O–Hf–Nd isotopic compositions of the studied migmatites and granites might be inherited from their precursors. It is thus inferred that the precursors of the granites might lie at the shoulder of the Neoproterozoic rift and thus might have experienced slight water-rock hydrothermal alteration and crust-mantle interaction; whereas the protoliths of the metamorphic rocks might be located at or near the rift center and thus had suffered intensive water-rock hydrothermal alteration and crust-mantle interaction. Prior to the late Mesozoic magmatism, the Tongbai orogen would have an uncoupled double-layered crust, where the upper layer consists of the metamorphic rocks and the lower is the sources of the post-collisional granites. They were stacked by the Permian-Triassic orogeny. The final architecture of the Tongbai orogen might be constituted by the emplacement of the voluminous granites from the deeper crust and the formation of the migmatites in the Tongbai complex. This configuration might widespread for other collisional orogens. • The protoliths of the migmatites were from the Neoproterozoic rift center. • Post-collisional granites were derived from ancient crust lying away from the rift. • The Tongbai orogen has a double-layered crustal structure. • The architecture of the orogen formed by the collapse of the orogenic root. [ABSTRACT FROM AUTHOR]

• Upright folds overlying a fault zone in the Chicobi belt formed at 2696–2681 Ma. • Integrated data show this fault zone dips northward shallowly at 3–7 km depths. • Crustal architecture and chronology suggest an allochthonous model at ca. 2.7 Ga. Our understanding of crustal architecture and tectonic evolution has advanced due to integrated geological and geophysical research on Precambrian cratons. However, it is still a heated debate whether Archean crust structure developed by an allochthonous model similar to modern plate tectonics or autochthonous model emphasizing in-situ evolution of supracrustal belts. The < ca. 2696 Ma Chicobi belt is a sedimentary basin in the central Abitibi Subprovince of the Superior Province, and as such provides a unique opportunity to contribute to this debate. It comprises both Porcupine-type turbidite and Timiskaming-type polymictic conglomerate and cross-bedded sandstone, and unconformably overlies ca. 2728–2711 Ma metavolcanic rocks, including the Amos Group to the south. The metasedimentary rocks were deposited after an early (D 1 > ca. 2696 Ma) deformation event, which is expressed by internally foliated clasts in conglomerate. The Chicobi belt was regionally folded and cut by shear zones during a second (D 2) deformation event, and was re-folded by Z-shaped folds during a third (D 3) dextral shearing event. The D 2 event is constrained between ca. 2696 Ma, the pre-existing age of detrital zircon in the Scapa Group along strike of the Chicobi belt, and ca. 2681 Ma, the new age of the cross-cutting syenitic Gémini-Saint-Éloi Pluton. New high-resolution seismic reflection and magnetotelluric surveys were conducted along the same transect across the Chicobi belt. The seismic reflection survey imaged subhorizontal to shallowly north-dipping reflective bands at depths of 3–7 km. Regional-scale inversion of new and pre-existing gravity data indicates that these reflective bands are linked to the Beauchamp Fault south of the Amos Group. Magnetotelluric inversion model shows high resistivity (>1000 Ω·m) zones under metasedimentary rocks, as well as a synform defined by low resistivity (10–100 Ω·m) zones, which aligns with folded metavolcanic rocks south of the Chicobi belt. Integration of the geophysical data with surface mapping suggests that the upper-middle crustal architecture of the Chicobi belt is dominated by D 2 upright folds overlying a fault zone. We suggest that deformation of the Chicobi belt is dominated by thrusting and folding, a deformation style compatible with allochthonous growth of the Abitibi Subprovince. [ABSTRACT FROM AUTHOR]

The Tongbai-Hong'an-Dabie orogens constitute the east segment of the Qinling-Dabie orogenic belt, which host several large molybdenum deposits, with a proven reserve of over 8 million tons metal Mo. In this study, we present an integrated study of in situ zircon U Pb dating and Hf O isotopes, in combination with magma oxidation state estimation for the Early Cretaceous granitoids in the Tongbai-Hong'an-Dabie regions. These granitoids can be divided into three groups on the basis of zircon U Pb ages, including early-stage ore-related granitoids from Mushan, Xiaofan and Wangwan deposits (143–136 Ma), ore-barren granites (136–130 Ma), and late-stage ore-related granitoids from Qian'echong, Bao'anzhai, Tangjiaping and Shapinggou deposits (130–110 Ma). Early-stage ore-barren granitoids have the lowest average ε Hf (t) and δ18O values of −27.1 ± 1.6 and 4.25 ± 0.63‰ as well as the oldest two-stage Hf model ages (T DM2) of ~2.8 Ga, which are roughly comparable with the inferred Dabie lower crust, indicating that they were mainly derived from the partial melting of the lower crust. Ore-forming granitoids in two stages show similar two-stage Hf model ages from 2.2 to 2.3 Ga which differ from any inferred layer of crusts, while they exhibit different zircon Hf O isotope and oxygen fugacity evolutionary trends. Granitoids display decreasing average ε Hf (t) and δ18O values from −17.1 ± 1.9 to −27.1 ± 1.6, and 5.71 ± 0.50‰ to 4.25 ± 0.63‰, and increasing average logƒO 2 values from −17.4 ± 4.5 to −6.7 ± 3.8 with a decrease in age from 143 to 130 Ma. In addition, relict zircon cores with Paleoproterozic and Archean ages were observed with ε Hf (t) and δ18O values analogous to those of the Kongling Complex. These characteristics suggest that the early-stage granitoids were possibly produced by the remelting of the subducted lower crust mixed with the Kongling Complex, with the involvement of reducing Mo-rich black shales in the Yangtze Block that seemingly account for the lower oxygen fugacity of ore-forming granitoids with younger two-stage Hf model ages and lead to the formation of those early-stage Mo deposits. As the increasing contributions of the lower crust in the magma source, the metallogenic gap developed from 136 to 130 Ma in the Tongbai-Hong'an-Dabie orogens. Zircon Hf O isotopic compositions of ore-related granitoids increase simultaneously up to −14.2 ± 4.3 and 5.82 ± 0.33‰ respectively at a lower slope after 130 Ma. Part of zircon δ18O values is slightly higher than 6.5‰, implying the involvement of supercrustal materials. Meanwhile, magma oxygen fugacity exhibits an abrupt drop at ca. 130 Ma in the Qian'echong deposit with the lowest average logƒO 2 value (−19.3 ± 4.5) and Ce4+/Ce3+ ratios (1–138), then rises quickly up to a maximum average logƒO 2 value of −7.3 ± 2.3. As such, these granitoids were likely generated by mixing of a blended crustal magma, derived from the lower crust and supercrustal materials, and the mantle-derived component which also contributes to the late-stage Mo mineralization. We propose that not only the highly oxidized magma but also the continuous change of oxygen fugacity in the deep magma chamber may have positive effects on the formation of porphyry Mo deposits. Given the significant geochemical change at ca. 130 Ma instead of 125 Ma, we agree that the intensive magmatism and mineralization in the Tongbai-Hong'an-Dabie orogens are closely associated with the delamination of the thickened lower crust of the Yangtze Block, which caused the asthenosphere upwelling that provided the heat source and led to partial melting of overlaying lower crust. [Display omitted] • Two Creteceous magmatic and metallogenic events in Tongbai-Hong'an-Dabie orogens. • Early granitoids were derived from blended crustal magmas and Mo-rich black shales • Primitive mantle contributes part of the Mo source to the late granitoids • The increasing magma oxygen fugacity benefits porphyry Mo mineralization [ABSTRACT FROM AUTHOR]

While the offshore Irish Atlantic margin and related rift basins have been intensively studied for several decades, the Porcupine Bank, straddling between the well-studied Porcupine and Rockall basins, is a poorly understood region due to lacking sufficient geophysical data coverage. In this study, ten newly acquired long-offset multichannel seismic profiles extending across the western Porcupine Bank margin, combined with potential field data, are used to investigate the crustal architecture, tectonic history, and rift-related magmatism along the margin. Significant margin-parallel and margin-perpendicular structural variations are observed and these are used to map the crustal architecture in terms of rifted margin domains. In the transitional zone between continental and oceanic crust, both peridotite ridges with shallow reflective basement and exhumed serpentinized mantle with deeper and smoother basement are interpreted, similar to the conjugate Iberian and Newfoundland margins, as well as further south at the Goban Spur margin. In addition to inferred variations in extension rate during poly-phased rifting episodes, the reactivation of pre-existing inherited Caledonian and Variscan structural fabrics are proposed to have influenced the variable geometries and distributions of the crustal domains along the Porcupine Atlantic margin. Northwestward increasing volcanism and related reflectivity patterns support the transition from magma-poor rifting in the southeast to magma-rich rifting in the northwest. Rigid plate reconstructions of the Irish Atlantic and the Newfoundland margins, particularly involving the Flemish Cap, back to the Early Campanian period, show asymmetric rifting and final continental breakup migrating toward the Porcupine Bank region. This asymmetry is possibly due to oblique extension between the two margins, and/or oblique deformation on the Porcupine Bank side due to its rotation during the opening of the Porcupine Basin. • Significant margin-parallel and margin-perpendicular variations in crustal architecture along the Porcupine Atlantic margin. • The margin experienced partitioned and localized deformation due to interplay of structural inheritance with Mesozoic rifting. • Northwestward increasing volcanism supports transition from magma-poor to magma-rich rifting along Porcupine Atlantic margin. • Rigid plate restoration between two margins indicates asymmetry of crustal domains and varying extension obliquity. [ABSTRACT FROM AUTHOR]

The architecture of magma-poor continental margins, from break-up to the establishment of an oceanic spreading centre has received significant recent interest. A general consensus as to their characteristics exists and although it has been applied to margins globally is still dominated by the Iberian-Newfoundland "type" margin. Additionally, many studies rely upon sparsely distributed 2D seismic reflection profiles, or single seismic sections. Questions remain as to the validity of the model across other magma-poor margins, in particular the role of magmatic additions during the rifting phase and their relationship to the creation of true oceanic crust at the onset of sea-floor spreading. Our data comprise a 2D seismic reflection survey from the Obbia Basin, northern Somalia passive margin. The data are extremely well imaged to over 13 s two-way time, providing insights into the crustal structure. Here, we present 4 representative sections from this larger survey, which combined with gravity modelling, describe the character and crustal architecture along the margin from the proximal rifted continental crust to the oceanic domain. We find that the Somali margin is a poorly understood example of a magma-poor margin exhibiting Iberian-type architecture. The margin comprises a stretched proximal domain that passes seaward into a strongly thinned necking zone across which the lower crust is completely thinned. We identify a high amplitude reflection (HAR) that corresponds to the decoupling level, and into which crustal faults sole out. Seaward, the HAR merges with the top of the exhumed mantle directly underlying post-rift sediments. In contrast to other magma-poor margins, the Somali margin has a narrow necking zone and a wide zone of exhumed mantle (in excess of 100 km). On most sections true oceanic crust is never encountered, with only the distal portion of one section exhibiting oceanic crustal character. We place the continent-ocean transition zone in excess of 200 km east of the shoreline. In the north, the basin is affected by transform faults; where this occurs we note a presence of volcanics within the crust and post-rift sediments. Gravity modelling supports the addition of magmatic material in these regions. This addition of volcanic material, in contrast to that proposed at transform faults in other passive margins, is spatially restricted to the transform faults, emplaced post-kinematically, and is not associated with oceanic crust formation. The results of this study not only provide new insights into the architecture on non-typical non-magmatic margins but also reveal the importance of incorporating these findings into plate-reconstructions. • The Somali Margin is a good example of a non-magmatic passive margin. • It has an exceptionally wide region of exhumed mantle in the distal domain. • The continent-ocean boundary occurs in excess of 150 km offshore. • Oceanic or proto-oceanic crust is only encountered in the far north- east where it is coincident with a transform fault. • Volcanics are present in the distal domain but are post rift and were not involved in the rifting process. [ABSTRACT FROM AUTHOR]

Reconstructions of the opening of the North Atlantic Ocean generally result in the Orphan Basin, offshore Newfoundland, Canada, lying approximately conjugate to the rift basins on the Irish Atlantic margin at the onset of seafloor spreading toward the end of the Early Cretaceous. Most of these plate reconstructions have involved rigid plates with plate motions based solely on the interpretation of oceanic magnetic anomalies. In particular, these reconstructions often show the Rockall Basin, west of Ireland, forming a continuous Mesozoic basin with the West Orphan Basin, offshore Newfoundland. However, more recent plate reconstructions involving deformable plates have called this conjugate relationship into question. The goal of this study is to investigate the validity of this potentially continuous basin system by reconstructing and restoring present-day seismically-constrained geological models both spatially and temporally back to their original configurations pre-rift. By comparing the reconstructions in terms of sedimentary package thicknesses and crustal thicknesses in 3D, using both rigid and deformable plate reconstructions to orient the reconstructed models, we are able to test different basin connectivity scenarios using a multidisciplinary approach. Our analysis provides subsurface geophysical support for the hypothesis that the Rockall Basin was originally conjugate to and continuous with the East Orphan Basin during Jurassic rifting, later linking to the West Orphan Basin as rifting evolved during the Early Cretaceous. This complex basin evolution example highlights the need for using 3D rifting mechanism models to properly understand the fundamental driving forces during rifting and has significant implications for assessing basin prospectivity across conjugate margin pairs. [ABSTRACT FROM AUTHOR]

The Goban Spur, offshore Ireland, is a magma-poor rifted continental margin conjugate to the well-studied Newfoundland margin, offshore Canada. Published studies demonstrated that a 70-km-wide zone of exhumed serpentinized mantle lies between oceanic crust and stretched continental crust at the seaward limit of Goban Spur. However, the along-strike extent of this serpentinized zone has, until now, been unknown due to insufficient data coverage. The crustal architecture of the margin is complicated due to its multi-staged tectonic history. Here, six newly acquired multi-channel seismic reflection lines are processed and interpreted, along with vintage seismic profiles, to characterize its structure and evolution. These seismic profiles reveal significant along-strike structural variations along the Goban Spur margin, and allow us to delimit five distinct crustal zones related to different rifting stages and their regional extents. The geometries of each crustal domain are variable along the margin strike, probably suggestive of different extension rates during the evolution of the margin or inherited variations in crustal composition and rheology. The transitional zone between oceanic crust and stretched continental crust consists of both shallow peridotite ridges and deeper exhumed serpentinized mantle, much like the conjugate Iberian and Newfoundland margins. Above the top basement in the exhumed domain, the syn-exhumed sediments show strikingly weak reflectivity, rarely seen at other magma-poor margins. Magmatic events occur coincident with each rifting stage, and the volume of magmatic accretions increases from NW to SE, more than previously interpreted. Plate reconstruction of the Goban Spur and its possible conjugate – the Flemish Cap, shows asymmetry in the crustal architectures, likely due to rift evolution involving more 3-D complexity than can be explained by simple 2-D extensional kinematics. • Significant along-strike structural variations along the Goban Spur is revealed; • Five distinct crustal zones related to rifting stages and their regional extents are delimilited across the margin; • The transitional zone consists of shallow peridotite ridges and deeper exhumed serpentinized mantle; • Asymmetric crustal architectures between the Goban Spur and its possible conjugate, likely due to complex 3-D rift evolution. [ABSTRACT FROM AUTHOR]

• Genetic relationship of major units in the Dharwar craton is analyzed. • Closepet granite was derived from the >2.9 Ga ancient middle crust with mantle input. • Charnockite was transformed from the relatively juvenile (<2.8 Ga) lower crust. • Dharwar craton represents a tilted trinity ('sandwich') Archean crustal architecture. • The 'sandwich' architecture indicates vertical growth of continental crust in the Archean. The architecture of the Archean crust is crucial in understanding the geodynamics of cratonization. The Dharwar Craton in the Indian peninsula is well known for its continuous change of metamorphic grades from granulite facies in the south to amphibolite facies in the middle and greenschist facies in the north. Here the genetic relationship of different units is re-analyzed to decipher the crustal architecture of the craton. The major lithologic unit – the granitoids can be subdivided into TTG, charnockite, Closepet granite and anatectic granites/migmatites. The charnockite near Salem has two types of occurrence: one is massive, garnet-free and plutonic, crystallized at ~2560 Ma, and the other is gneissic, garnet-bearing and incipient, metamorphosed at ~2490 Ma. Both types are compositionally close to tonalite-granodiorite, and generally show positive Eu-anomalies. A large proportion of zircons of both types show positive ɛHf t values (varying from −3 to +9), indicating a relatively juvenile parent (<2800 Ma). The garnet-bearing charnockite was probably transformed in situ from the lower crust at granulite facies; whereas the garnet-free charnockite represents exotic magmas originated from the lower crust. The Closepet granite is potassium-rich and high in Mg#, and shows negative Eu-anomalies. It was emplaced at 2520–2510 Ma (simultaneous with the garnet-bearing charnockite), and the igneous zircons show negative ɛHf t values (−9 to +1). It likely originated from relatively ancient (>2900 Ma) crust at medium-pressure (in the middle crustal level) with significant mantle contribution. The genetic relationship of different units, the spatial age difference of greenstone belts and the spatial variation of metamorphic grade in the Dharwar craton suggest a trinity of Archean crustal architecture ('sandwich' structure), with 2700–2500 Ma-dominated uppercrust, 3400–2900 Ma-dominated middle crust, and ~2560 to 2500 Ma anatectic lower crust. This 'sandwich' structure possibly indicates vertical growth of the crust in the Archean. The whole craton was tilted at ~2500 Ma with the southern end uplifted the most by an intra-cratonic process, and then it was shaped by later orogenic events resulting in the formation of the dominantly N-S trending structures in the basement. [ABSTRACT FROM AUTHOR]

The Capricorn Orogen records the Paleoproterozoic amalgamation of the West Australian Craton. 2‐D deep‐seismic reflection data across the Orogen are difficult to interpret due to the complex geology, and fundamental questions remain about the nature of the basement in the northern part of the Orogen. Passive seismic data have been collected along a 250‐km‐long transect across the central part of the Capricorn Orogen. The passive seismic recordings utilized teleseismic arrivals to construct a velocity section using the receiver function common conversion point method and to estimate crustal thickness and Vp/Vs using the H‐k method. A shear velocity cross section was created using ambient noise‐based methods. An integrated interpretation of all the seismic data sets shows that basement in the central Capricorn Orogen comprises a series of distinct terranes. These are recognized based on changes in crustal reflectivity, velocity and Vp/Vs. We interpret these terranes as originating from an island arc caught in the collision between the Glenburgh Terrane and the Pilbara Craton as part of the 2215–2145 Ma Ophthalmia Orogeny. Although passive seismic data do not have the resolution of reflection data, the information gained from the passive data places important constraints on the reflection interpretation and provides complementary information about changes in crustal composition. We propose that passive seismic data represent a cost‐effective complementary geophysical data set that can greatly assist with the interpretation of deep reflection sections in areas of complex geology. Key Points: Deep reflection data in areas of complex geology can be very hard to interpretTeleseismic and ambient noise data are relatively cheap to acquire and provide information complementary to the reflection dataWe present an example where an existing reflection interpretation was modified and improved by working with both kinds of data together [ABSTRACT FROM AUTHOR]