Rift Research Articles

Evolution of Cenozoic sedimentary architecture in Central and Southern South China Sea basins

The Central and Southern South China Sea (CSSCS) has a complex tectonic dynamic background and abundant oil and gas resources, which has always been a hot topic of academic and industrial attention. However, systematic analyses are still lacking regarding its sediment filling structure and evolution, mostly due to limited borehole penetration and poor quality of seismic reflection data for deeply buried sequences. No consensus has been reached yet on the sedimentary infilling processes, which impeded the reconstruction of the palaeogeography of Southeast Asia and the oil-and-gas exploration undertakings. Here, we illustrate the Cenozoic sedimentary evolution of the CSSCS region by synthesizing relevant data from previous literature and our own observations and displaying the evolution of depositional systems in sequential reconstructions. Besides, the controlling factors of preferred sedimentary scenarios in the CSSCS incorporate the latest interpretations of the spreading of South China Sea (SCS) as well as the demise of the hypothetical Proto-South China Sea (PSCS). The results show that there are three types of sedimentary basins in the CSSCS (foreland, strike-slip, and rift basins) with different sedimentary filling structures. The foreland basins formed a depositional pattern of ‘transition from deep water to shallow water environments’, dominated by deep-water depositional systems which were formed before the Early Oligocene with submarine fans developed. Later, the foreland basins were gradually dominated by shallow-water depositional systems with deltas and shallow marine facies. The strike-slip basins showed the depositional architecture of ‘transition from lake to marine environments’, i.e. the basins were dominated by lacustrine deposits during the Eocene and evolved into the marine depositional environment since Oligocene with delta developed in the western part of the basin. The depositional evolution of rift basins illustrated the characteristics of ‘transition from clastic to carbonate deposits’, i.e., the rift basins were dominated by Eocene–Oligocene shallow marine clastic depositional systems, while carbonate platforms started to develop since the Early Oligocene from east to west. The above-mentioned differences of depositional architecture in the CSSCS were controlled by the scissor-style closure of the PSCS and the progressive-style expansion of the SCS. Specifically, the early-period deep-water sedimentary environment of CSSCS basins was controlled by the distribution of PSCS in the Eocene. As the scissor-style closure of PSCS progressed from west to east during the Oligocene to Early Miocene, the northwest of Borneo continued to rise, providing a great number of clastic materials to the basins and gradually developing large-scale deltas from west to east. The distribution of early-period lacustrine sedimentation of strike-slip basins was affected by paleo uplift, and the basins transgressed from the northeast and gradually evolved into marine sedimentary environment due to the expansion of SCS. The expansion of SCS also controlled the sedimentary filling evolution of the rift basins, which broke away from the South China continent and drifted southward. Thus, the rift basins lacked the supply of terrigenous clastic sediments which hindered the development of large-scale deltas and formed a clear water environment conducive to the development of carbonate platforms from east to west.

Fault structure, seismicity, and magmatism of the Littoral Fault zone, northern South China sea: Insights from high-resolution seismic reflection data

Four destructive M7+ earthquakes and 18 M6+ earthquakes demonstrate that the Littoral Fault Zone (LFZ) is one of the most seismically active regions in the offshore area of South China. However, the location, geometry, and structural characteristics of the LFZ, which spans over 1000 km, have not been properly examined. In this study, we investigate the precise position of the LFZ offshore East Guangdong (EGD) and map the fault structure using recently acquired high-resolution multi-channel seismic (MCS) reflection data. The LFZ consists of an array of normal faults that collectively form a terraced sidewall fault zone linked to the continental rifting of the South China Sea (SCS). This fault zone is approximately 35–75 km wide and runs parallel to the shoreline. The primary faults of the LFZ EGD segment correlate to a high-gravity gradient zone and serve as the northern boundary of the Zhu-I Depression. During the syn-rift phase, the LFZ experienced significant intra-plate deformation, resulting in fault throws of up to 1000 m. This deformation was locally influenced by pre-existing structures, giving rise to a listric geometry at depth. In the post-rift period, the LFZ exhibited inherited activity along its rift-related faults. The presence of growth fault structures suggests that the LFZ remained active throughout the Cenozoic, with numerous active faults extending practically to the seafloor. The negative flower structure confirms the strike-slip character of the LFZ, which is influenced by the modern tectonic stress field. Intense multi-phase Cenozoic magmatism, including igneous intrusion, volcanism, and lava flows, has been detected in the offshore area of Nan'ao Island. The frequent earthquakes in the study area are primarily attributed to far-field stress release resulting from the subduction of the Philippine Sea Plate beneath the Eurasian Plate. Additionally, the intense magmatism weakens crustal structures, further facilitating stress release and the frequent occurrence of earthquakes.

The 21 March 2022 Mw 5.1 Tampen Spur Earthquake, North Sea: Location, Moment Tensor, and Context

ABSTRACT The 21 March 2022 Mw 5.1 Tampen Spur earthquake is the largest event in the North Sea over the last 33 yr. The earthquake was recorded by a 10,708 sensors permanent reservoir monitoring system (PRM) deployed at the Snorre field only a few kilometers away from the epicenter. The event was also recorded on regional networks, as well as at teleseismic distances. Here, we take advantage of this large number of observations to relocate this seismic event, estimate a moment tensor, and refine the depth of the earthquake. The different data sets and location methods yield similar locations, suggesting a well-constrained earthquake location with a depth of 22 ± 5 km. Furthermore, a moment tensor is estimated, which indicates a thrust fault mechanism. Deep crustal earthquakes (>20 km) have been documented within several continental rifts, for example, in Basin and Range in the United States and in northern Germany. Studying deep intraplate earthquakes such as the event observed here can offer insights into the rheology and structures in the deeper portions of the crust. This thrust earthquake implies the reactivation of an older fault in the lower crust consistent with the ridge-push forces from the mid-Atlantic ridge. Such brittle failure at depth indicates a lower crust with little to no fluids present at this depth within the Tampen Spur region.

Shallow sources of upper mantle seismic anisotropy in East Africa

The East African rift overlies one or more mantle upwellings and it traverses heterogeneous Archaean-Paleozoic lithosphere rifted in Mesozoic and Cenozoic time. We re-analyze XKS shear wave splitting at publicly available stations to evaluate models for rifting above mantle plumes. We use consistent criteria to compare and contrast both splitting direction and strength, infilling critical gaps with new data from the Turkana Depression and North Tanzania Divergence sectors of the East African rift system. Our results show large spatial variations in the amount of splitting (0.1–2.5 s), with fast axes predominantly sub-parallel to the orientation of Cenozoic rifts underlain by thinned lithosphere with and without surface magmatism. The amount of splitting increases with lithospheric thinning and magmatic modification. Nowhere are fast axes perpendicular to the rift, arguing against the development of extensional strain fabrics. Thick cratons are characterized by small amounts of splitting (≤0.5 s) with a variety of orientations that may characterize mantle plume flow. Splitting rotates to rift parallel and increases in strength over short distances into rift zones, implying a shallow depth range for the anisotropy in some places. The shallow source and correlation between splitting direction and the shape of upper mantle thin zones suggests that the combination of channel flow and oriented melt pockets contribute > 1 s to the observed splitting delays. Enhanced flow, metasomatism, and melt intrusion at the lithosphere-asthenosphere boundary suggest that fluid infiltration to the base of the lithosphere may facilitate rifting of cratonic lithosphere.

Tonian basins record rifting of Kalahari from Rodinia and no evidence of a pre-Sturtian Kaigas glaciation

Neoproterozoic strata record evidence for two Snowball Earth glaciations during which ice extended to the equator. Geochronological data have confirmed the multi-million year duration, synchroneity, and global extent of the Cryogenian Sturtian and Marinoan glaciations between 717 and 635 Ma. It has been proposed that an earlier ca. 750 Ma glaciation, referred to as the Kaigas glaciation, included glaciomarine deposits that formed at low-latitude. Here we evaluate this hypothesis at the eponymous location with detailed stratigraphy and geochronology through the Kaigas, Rosh Pinah, and Numees formations on the western margin of the Kalahari craton in southern Namibia. We find that glacial deposits previously assigned to the Kaigas Formation are instead ca. 717–661 Ma diamictites of the Sturtian Numees Formation. Pre-Numees strata, including the Kaigas Formation, host facies associations diagnostic of fan delta deposition along an active normal fault. Interbedded volcanic rocks in the Rosh Pinah Formation overlying the Kaigas Formation were dated with U-Pb CA-ID-TIMS on zircon at ca. 752 Ma. These Tonian deposits are interpreted to have been deposited in an active rift basin without evidence for glaciation. Rosh Pinah magmatism could be broadly correlative with the Mount Rogers Complex in Virginia, USA, consistent with a scenario of the Kalahari craton actively rifting from Laurentia and associated terranes within 20° of the equator at the time. We conclude that, at least in marine settings, evidence for low-latitude glaciation is limited to the 717–635 Ma Cryogenian Period.

The Boipeba member in the Jatobá Rift (northeastern Brazil): Occurrence, facies characterization and palaeoenvironmental implications

Fluvio-aeolian and lacustrine depositional systems are commonly associated with the initial sedimentary processes in rift-type basins, typically indicative of relatively calm tectonic settings. Fluvio-aeolian sandstones from the Boipeba Member of the Aliança Formation have been documented in well-drilled samples from the Recôncavo and Tucano basins, with thicknesses decreasing progressively from south to north. These units constitute the Brotas Group, encompassing deposits from the Jurassic period (Dom João local Brazilian stage). However, due to the absence of any records within the Jatobá Basin up until now, its occurrence in this basin remains uncertain. Based on facies analysis and depositional architectural elements, the fluvio-aeolian system of the Boipeba Member can be categorized into four associations (1) medium to low energy fluvial channels, (2) floodplains, (3) dunes and (4) sand sheets. Palaeocurrent data have indicated a variable paleoflow direction ranging from SW and NW, which is expected for the rift-onset phase fluvial system. Within the broader context of the Recôncavo-Tucano-Jatobá Rift System (RTJ), five distinct fluvial and/or aeolian units can be identified: the Tacaratu Formation (Syneclisis), the Boipeba Member (the basal unit of the Aliança Formation), the Sergi Formation (Early Rift), the São Sebastião Formation (Rift), and the Marizal Formation (Post-Rift). The Boipeba Member is the first unit of the Early Rift Sequence in the RTJ, deposited in a fluvio-aeolian environment until it evolves to the exclusively lacustrine deposition of the Capianga Member (the upper unit of the Aliança Formation). The subsequent recurrence of the fluvio-aeolian cycle is evident in the Sergi Formation. Faciological and petrographic analyses of outcrops in drainage channels in the Tacaratu municipality, located in the southeastern part of the Jatobá Basin, were performed. The rock formations appear as whitish-gray sandstones, typically thin to medium, subrounded, and consistently sorted. Some samples exhibit clay matrix and contain feldspars. Notably, the presence of planar cross-stratifications and a distinct upper contact with sediments of lacustrine origin provide diagnostic features indicating the Boipeba Member. Based on the facies, depositional system and palaeocurrent analyses, the deposits of the Boipeba Member in the Jatobá Basin were interpreted as resulting from fluvial channel sedimentation, followed by subsequent aeolian reworking. This process transitioned gradually to a lacustrine infilling, exemplified by the Capianga Member. Therefore, the Aliança Formation within the Jatobá Basin signifies the complete deposition of a fluvio-aeolian and lacustrine system, exhibiting both of its members, as observed in the other basins of the RTJ.

The hydrocarbon source potential of Permo-Triassic rocks of the Indochina Block adjacent to the Paleo-Tethys suture in Thailand

The main Thailand petroleum systems are found in the syn-rift and post rift sections of Cenozoic rift basins. The Khorat Plateau area is a separate gas province with Permian limestone reservoirs possibly sourced from Triassic lacustrine, and Permo-Carboniferous marine shales. However, these source rocks and those of equivalent age west of the Khorat Plateau are not well described in the literature. This study investigated the source potential of outcropping Permo-Triassic shales from the western margin of the Khorat Plateau and the Khao Khwang Fold and Thrust Belt (KKFTB). The key formations sampled are: Permian: Alum Shale, Nong Pong, Sap Bon, Khao Khad, and Nam Duk formations; Triassic: Pang Asok and Hua Hin Lat Formation. Most potential Permo-Triassic source rocks sampled exhibited little potential due to the dominance of Type IV, non fluorescent amorphous, vitrinite and intertinite mascerals and low <1 % TOC content. Probably the Type IV kerogens are not original, but the product of subsurface alteration of other kerogen types (most likely Type III). The complex burial histories of the formations indicates such alteration could have occurred post-maturation. Probably maximum burial in the KKFTB was attained during the Triassic Indosinian Orogeny when upper diagenetic to anchizone conditions were attained. Significant burial also occurred when the Jurassic-Cretaceous Khorat Group (>2 km thick) was deposited. This later burial could be responsible for later maturation in areas north of the KKFTB. Simply in terms of TOC content >1, the Hua Hin Lat and Khao Khad formations have the most promising source potential.

Colliding cratons: linking the Variscan Orogeny in West Africa and North America

Abstract The Variscan Orogen was formed during the closure of the Rheic Ocean and the final collision between the North American and West African cratons in the Late Paleozoic. This collision led to the multistage building of the Mauritanide Belt to the east of the Variscan suture and to the building of the well-known Appalachian Belt to the west. Both led to opposite vergences in this part of the Variscan belt. The earliest records of the main collision episode begin at ∼360 Ma and end about 250 myr ago, while a late extensional phase lasted until ∼190 Ma. Three distinct stages are recognized in West Africa. The first stage ( c. 350–300 Ma) records the indentation of the Reguibat Shield into the central Appalachian margin of Laurentia. This indentation led to thrusting of the Souttoufide and Akjoujt ‘nappes’ onto the Reguibat Shield, to southward motion of the Senegalese block (SB), and to strike-slip motion in the Appalachians. The motion of the SB to the south is coeval with: (1) folding of the northern part of the Bové Basin, (2) north–south sinistral strike-slip motions in the central Mauritanides, and (3) the end of sedimentation in the Bové and Taoudeni Basins by the Late Devonian. The second stage ( c. 300–250 Ma) involves the eastward motion of the Western Thrust Block (WTB) against the SB and, likely, some of the westward thrusts in the Appalachians. This second ‘Variscan’ event includes: (1) closure of parts of the lower Diourbel Carboniferous basin, which is now concealed beneath the Senegalo-Mauritanian Basin, (2) thrusting to the east of the Simenti Group over the Koulountou Group in the Bassaride Belt, (3) thrusting to the east of the Wa-Wa Group, (4) thrusting of the Mauritanide Belt onto the Taoudeni Basin in the central Mauritanide Belt, and finally (5) thrusting of the Agualilet Group over the Akjoujt nappes and eastward motion of the western units over the Dhloat Ensour (Late Ordovician to early Devonian) autochthonous unit in the Souttoufides. West of the supposed ‘Variscan’ suture, Appalachian thrusting affected parts of Appalachian Belt. The third stage ( c. 250 to 190 Ma) began with the opening of Triassic rift basins in the Senegalo-Mauritanian basin and also in the north of Florida. As numerous previous correlations across the Variscan system do not include the West African part, our sythesis is intended to enhance these correlations.

Architecture of lacustrine deposits in response to early Carboniferous rifting and Gondwanan glaciation, Nova Scotia, south‐east Canada

AbstractUpper Palaeozoic lacustrine basin deposits not only record local tectonism but are also an archive to evaluate global palaeoclimate changes linked to the Late Palaeozoic Gondwanan ice age. The Tournaisian Horton Group of Nova Scotia, south‐east Canada, accumulated in rift basins following the final accretion of peri‐Gondwanan terranes to the Appalachians. Sedimentology, mineralogy and geochemistry of the well‐exposed sandstones and shales at the classic Blue Beach section (ca 353.5 to 352 Ma) reveal the interplay of local tectonism and global climatic controls on lacustrine sedimentation. The lacustrine depositional environment gradually transitioned from deep water offshore at the base of the section to wave‐dominated and fluvial‐dominated nearshore at the top. Multiple small transgressive–regressive sedimentation cycles have an average 21 ka duration, likely related to Milankovitch cyclicity. Unusually abundant soft‐sediment deformation structures and landslides are the sedimentary responses to frequent earthquakes during the most active phase of rift subsidence. The overall succession shows changes from a shallowing‐up balanced‐filled to an overfilled lacustrine basin. The chemical weathering intensity index and the Th/K ratio show a longer‐term trend from dry and cool conditions low in the section to humid and warm conditions near the top, with rapid change in the transition period. The section records the peak of the global mid‐Tournaisian carbon isotope excursion and the corresponding cooling event (354 Ma to approximately 351 Ma). The sedimentary succession is a response to long‐term and short‐term climatic cycles influencing lake level and sediment supply during the time of maximum rift basin subsidence recorded by the soft‐sediment deformation structures.

Hydrocarbon generation and migration in the Fuxin Basin during the Cretaceous evolution of the North China Craton, NE China

The extensive thinning and destruction of North China Craton (NCC) during the Early Cretaceous led to the development of numerous rift basins and petroleum systems. However, the specific relationship between NCC evolution and hydrocarbon generation and accumulation in these sedimentary basins is still unclear. In this study organic geochemistry and oil-source correlation analyses were conducted to investigate the hydrocarbons generation potential and migration pathway in the representative Fuxin Basin. Results demonstrate that the semi-deep lacustrine source rocks were developed in the Jiufotang Formation (K1jf) in the west and the upper Shahai Formation (K1sh) in the east, both of which are enriched with organic matter content and hydrocarbon generation potential of kerogen Types II to III. Based on the hierarchical cluster analysis of crude oils biomarker fingerprints, two crude oil types (A and B) were deduced. The Type A crude oil is characterized by high gammacerane, low pristane/phytane, relatively high C29 regular sterane and methylphenanthrene index, which is consistent with the K1jf biomarker characteristics in the west. Therefore, the Type A crude oil is likely generated from the K1jf source rock that accumulated in turbidite sand bodies of the K1jf and/or migrated to the K1sh reservoir through strike-slip faults. Type B crude oil is dominated by low gammacerane, moderate pristane/phytane, high C27 regular sterane and 1,2,5-trimethylnaphthalenes, which is in good agreement with the K1sh4 features. The basin simulation revealed that hydrocarbon generation of source rocks in the Jiufotang and Shahai formations was linked to a rapid subsidence of the basin, which was induced by intense extension with the NCC destruction during the Early Cretaceous. Subsequently, the rapid subduction of the Western Pacific plate during the earliest Late Cretaceous led to the development of extensive epigenetic fractures, enabling extensive hydrocarbon migration in the Fuxin Basin. This study sheds light on oil sources in sedimentary basins in an extensional setting and provides insights into the dynamic process of hydrocarbon generation and migration associated with NCC evolution.

Ancient slabs beneath Arctic and surroundings: Izanagi, Farallon, and in-betweens

A detailed 3-D tomographic model of the whole mantle beneath the northern hemisphere (north of ~ 30°N latitude) is obtained by inverting a large amount of P-wave arrival time data (P, pP, and PP) to investigate transition of subducted slabs beneath Eurasia–Arctic–North America. We apply an updated global tomographic method that can investigate the whole mantle 3-D structure beneath a target area with high resolution comparable to that of regional tomography. The final tomographic model is obtained by performing independent calculations for 12 different target areas and stitching together the results. Our model clearly shows the subducted Izanagi and Farallon slabs penetrating into the lower mantle beneath Eurasia and North America, respectively. In the region from Canada to Greenland, a stagnant slab lying below the 660-km discontinuity is revealed. Because this slab has a texture that seems to be due to subducted oceanic ridges, the slab might be composed of the Farallon and Kula slabs that had subducted during ~60–50 Ma. During that period, a complex rift system represented by division between Canada and Greenland was developed. The oceanic ridge subduction and hot upwelling in the big mantle wedge above the stagnant slab caused a tensional stress field, which might have induced these complex tectonic events.

Early Cretaceous sedimentary records of the early-stage continental rifting in the Songliao Basin, NE China

Well SK-2, a continental scientific drilling well in the Xujiaweizi fault depression of the Songliao Basin, has drilled through ca 2359 m of the Early Cretaceous Shahezi Formation. Herein, we focus on the sequence groups SSI and SSII in the lower part of the Shahezi Formation (interval 4357.38–5695.02 m) from well SK-2. There are fourteen different lithofacies and seven lithofacies associations. Syn-eruptive pyroclastic deposits and their proportions in successions indicate that SSI varies from dominantly pyroclastic fill to dominantly weathering-derived clastic fill, reflecting the development of volcanism in the early syn-rift stage. SSII exhibits another, similar evolutionary cycle. Whole-rock geochemistry of rocks from the Shahezi Formation reveals that the source rocks are felsic, andesite, and sedimentary rocks from the upper crust, and that the intermediate-acid rocks are originated from partial melting crustal materials and are hybridized with input from the mantle. In the seismic profile that intersects well SK-2, the thinning direction switches back and forth during the formation of the Shahezi Formation’s four sequence groups; that is, there is turnover superimposition in vertical stratigraphic subsidence, demonstrating strike-slipping during deposition of the Shahezi Formation.The major rift stage, especially during the deposition of the lower part of the Shahezi Formation, involved strike-slipping dominated extension. This conclusion is supported by the presence of abundant dark mudstone and coarse clastic progradation in the transgressive stage, as well as by the periodicity of volcanism combined with stratigraphic turnover superimposition.

Review of sedimentary basin evolution in Cambodia based on tectonic setting and logical information

The paper aims to synthesize the evolution of sedimentary basins in Cambodia based on a comprehensive information on tectonic setting and existing database of their formation and sedimentation. The study includes a review on tectonic setting of Indochina, the formation of sedimentary basins around Cambodia, and the accessible data on sedimentary basins in Cambodia. Indochina, as well as Cambodia, had been influenced by the collision of three different plates or terranes such as the South China, Sibumasu-Sukhothai, and Paleo-Pacific that are associated with the evolution of Paleozoic-Mesozoic Basins namely Khorat and Kampong Som Basins. These two oldest basins, are interpreted as a Paleozoic – Mesozoic foreland basin that initially formed due to rifting during the Late Carboniferous to Late Permian, and later basin inversion and erosion took place due to the Mesozoic to earliest Cenozoic uplift. Then, Cambodia was affected by Tertiary strike-slip fault movements that also influenced the formation of Tonle Sap, Svayrieng and Khmer Tertiary rift basins. Tonle Sap and Svayrieng Basins are interpreted to be formed by extension during the Middle Eocene – Early Oligocene and inversion, uplift and denudation during the Miocene. The Khmer Basin was formed by rifting during the Eocene to the Late Oligocene, followed by rapid thermal subsidence from the Early to Middle Miocene. Finally, Khmer basin was affected by the Middle – Late Miocene to Pleistocene inversion.

Normal fault evolution in the Penghu Basin, a Paleogene Rift Basin in Western Taiwan Strait: A test of fault growth models

The growth of normal fault systems affects the development of rift basins. These systems could grow via either non-coherent or coherent models, where segments either develop independently or merge into one fault, respectively. Also, they could experience decreases in fault system lengths, called lateral tip retreat, during the later fault-activity stage. In this study, we investigate the fault growth model by studying the Penghu Basin, a Paleogene rift basin in the western Taiwan Strait, and test the current fault growth models. Our methods include seismic interpretation and fault growth analyses, such as the spatiotemporal distribution of cumulative throw and throw increment and expansion index. In the Penghu Basin, the boundary and transfer fault systems grew via the non-coherent model followed by lateral tip retreat, while other studied fault systems grew via the coherent model before their tips retreated. Furthermore, segments could separate from their parent fault systems prior to the lateral-tip-retreat stage. During the evolution of the fault system, the shifting of a cumulative throw maximum could be accompanied by a throw increment minimum, i.e., segmentation, moving toward the migrated cumulative throw maximum inside segments or by the retreated fault tip of the fault system. This implies a change in the distributions of stress drop and increase regions. Finally, our results indicate that the specific rift phase of basin evolution is highly correlated with the development of fault systems. We suggest that the lateral tip retreat of fault systems marks a change in the rift phase of a basin and implies the end of basin evolution.

Tectono-stratigraphic evolution of salt-influenced normal fault systems: an example from the Coffee-Soil Fault, Danish North Sea

We explore how the relationships between fault activity, salt movement and sediment loading affect the stratal geometry of the hanging wall throughout the evolution of a salt-influenced normal fault system. We examine a c. 65 km long portion of the Coffee-Soil Fault System in the Danish North Sea, the hanging wall of which has been partially influenced by a pre-rift unit of mobile salt. To constrain the tectono-stratigraphic evolution of this fault system, we combine structural observations with seismic stratigraphic analysis of the hanging wall growth strata. We find that the hanging wall of the Coffee-Soil Fault System shows major depocentre shifts through time, along with marked variability in the along- and across-strike stratal geometries. We explain how the development of these characteristics is influenced by: (1) the segmentation and linkage history of the fault system; (2) the evolution of the salt-cored cover monoclines above blind basement fault segments; and (3) changes in the location and rate of accommodation generated by the load-driven withdrawal of salt up the dip-slope of the hanging wall and by fault-related subsidence. Our findings have implications for structural and stratigraphic studies in salt-influenced rift basins, as well as for understanding the potential distribution of geo-storage and hydrocarbon reservoirs in such settings.

The Charnwood Terrane revisited: an integrated petrogenetic and petrophysical model for crustal structure in southern Britain

We based an integrated petrological and petrophysical model for the Ediacaran crust of southern Britain on a review of the c. 570–550 Ma Charnian volcano-sedimentary complex. The latter was emplaced in a magmatic rift wedge within the juvenile continental crust of the c. 720–600 Ma Marches Terrane, a subduction magmatic domain formed at the margin of the Gondwana palaeocontinent. The Charnian magmatic arc is characterized by primitive island arc tholeiite to more evolved calc-alkaline compositions. The inversion of aeromagnetic potential field data and petrophysical modelling reveals details of the internal structure of the Charnian Domain, including a median rift, superimposed annular structures and partitioning lineaments. The modelling suggests that the arc foundation could incorporate magnetite-rich cumulates, which may explain the anomalous geophysical properties, including crustal thickness, rigidity and buoyancy. There is no evidence for significant tectonic displacement between the Charnian Domain and its Marches Terrane host. Instead, the domain likely occupies a wedge-shaped arc/marginal rift basin complex, propagated from a neighbouring ocean into the Gondwana margin. Contemporaneous volcanic rift successions in the Welsh Borderland and Wales of the 570–550 Ma Charnian magmatic phase developed in coeval ensialic rifts within less strongly extended Marches Terrane lithosphere. A comparable diversity of subduction-related magmatism is found in the Neogene–recent Hikurangi destructive margin of New Zealand, providing a plausible analogue for Charnian magmatism. Supplementary material: Supplementary Publication 1 (borehole geophysical log correlation; petrophysical data table; unannotated geophysical maps and sections) and Supplementary Publication 2 (geochemistry analytical conditions and data table) are available at https://doi.org/10.6084/m9.figshare.c.6805248

Two-step exhumation of Caucasian intraplate rifts: A proxy of sequential plate-margin collisional orogenies

Intraplate structural deformation is diagnostic of tectonic stress regime changes linked to plate interactions and can result from superposed tectonic events whose single contributions are hardly distinguishable. In this paper, we present a set of integrated thermochronologic inverse models along a 140 km-long transect across the central Greater Caucasus and the adjacent Adjara-Trialeti fold-and-thrust belt of Georgia, two intraplate orogens produced by structural inversion of parallel continental rift zones located on the Eurasian plate. Our dataset allows to distinguish discrete and superposed deformation episodes and quantify their respective contributions to orogenic exhumation. The integration of (U-Th)/He analysis on apatite and zircon, fission-track analysis on apatite, and peak-temperature determinations (clay mineralogy, organic matter petrography, Raman spectroscopy) shows that structural inversion was punctuated by two incremental steps starting respectively in the latest Cretaceous and the mid-Miocene. Latest Cretaceous partial inversion of the Greater Caucasus is documented here for the first time and placed in a geographically wider context of coeval deformation. The two episodes of intraplate structural inversion, exhumation, and sediment generation are chronologically and physically correlated with docking of (i) the Anatolide-Tauride-Armenian terrane (Late Cretaceous - Paleocene) and (ii) Arabia (Miocene hard collision) against the southern Eurasian plate margin. Intraplate deformation in the Caucasian domain was triggered by far-field propagation of plate-margin collisional stress which focused preferentially along rheologically weak rift zones.

Mid-Mesoproterozoic (ca. 1.37 Ga) anorogenic magmatism in the Dabie orogen, northern Yangtze Craton: Response to the breakup of Columbia

It is evident that the Yangtze Craton was involved in the formation and breakup of the Columbia supercontinent. However, due to the scarcity of Mesoproterozoic geological records and reliable paleomagnetic data, little is known about the timing, paleogeographic position, and geological processes of the Yangtze Craton. We conducted detailed geological mapping, petrographic, geochemical, and in situ zircon U-Pb and Lu-Hf isotopic investigations on newly recognized Mesoproterozoic quartz syenite and monzogranite in the Dabie orogen, northern Yangtze Craton. The results show that the quartz syenite and the monzogranite were emplaced at 1369 ± 12 Ma and 1372 ± 5 Ma, respectively. Both rocks are high in total alkali (K2O + Na2O) content and FeOt/(FeOt + MgO), with elevated diagnostic 10,000*Ga/Al ratios and Zr + Nb + Ce + Y concentrations, and enrichment in light rare earth elements. They are also depleted in heavy rare earth elements with significant negative Eu anomalies but remarkably low Sr, Cr, and Ni contents. These compositions define affinity to A1-type granite. In addition, the quartz syenite displays variable zircon Hf and homogeneous whole-rock Nd isotopic compositions with positive εHf(t) values of +0.7 to +5.7 (average +2.4) and εNd(t) values of −0.1 to +2.5 (average +1.0). In contrast, the monzogranite has homogeneous zircon Hf and whole-rock Nd isotopic compositions with negative εHf(t) values of −5.7 to −2.6 (average −4.8) and εNd(t) values of −3.5 to −1.5 (average −2.2). We propose that the quartz syenite was likely generated by the partial melting of juvenile, crust-derived melt with involvement of minor mantle-derived material, while the monzogranite was likely derived from the partial melting of ancient crust in an extensional tectonic regime (e.g., continental rift). Based on the newly recognized ca. 1.37 Ga granitic magmatism and previously reported magmatic events, we argue that the mid-Mesoproterozoic (ca. 1.37 Ga) magmatism in the Yangtze Craton occurred in response to the breakup of Columbia, and represents the separation of the Yangtze Craton from Columbia. Furthermore, according to comparable magmatic and sedimentary events, we propose that the Yangtze Craton, along with central Hainan Island, may have been linked to northwestern Laurentia, southwestern Siberia, and northeastern Australia during 1.6−1.4 Ga.

Deep Seismic Reflection Imaging of Mesozoic Kachchh Rift, NW India: Implications for Evolution

AbstractDeep crustal seismic reflection profiling is carried out for first time across various tectonic domains of seismically active Mesozoic Kachchh rift basin, formed during the breakup of Gondwanaland. The seismic data, processed using the common reflection surface stack approach, provided maiden images of the shallow and deep sub‐surface structures in the region. These images reveal a 15 km thick subhorizontal lower crustal reflection fabric and crustal‐scale domal‐type structure extending from the surface to the Moho. We interpret the earlier structure represent magmatic underplating and the latter as the Kachchh Mainland uplift. We find large variations in the thickness of sediments from 150 m to 6.5 km and crustal thickness from 45 to 35 km from north to south, with a Moho up warp of 4 km beneath the Kachchh Mainland fault. The Kachchh rift basin exhibits an unusually thick crust of 45 km, contrary to many rift basins. We interpret the syn‐rifting and the Reunion mantle plume activity, manifested as Deccan volcanics, are responsible for magmatic underplating and crustal thickening. Uplift in the region is multi‐genetic in origin. Present study illuminated new faults and nature of various other faults. Moderate to large earthquakes in the region are attributed to the regional and local stresses resulting from the plate boundary and heterogeneous crustal structure. Based on the mafic lower crust and distribution of aftershocks through the entire crust, we interpret the lower crust is brittle, contrary to most models of continental rheology.

The origin of the ultrahigh-pressure Tso Morari complex, NW Himalaya: implication for early Paleozoic rifting

AbstractThe origins and age distribution of the Himalayan high-pressure (HP) and ultrahigh-pressure (UHP) metamorphic rocks are critical for understanding the pre-Himalayan history. Although the protoliths to the UHP Tso Morari eclogites in Ladakh, NW Himalaya are believed to be the Permian Panjal volcanics, the geochronological evidence is absent. Here, we demonstrate that the protoliths of the UHP Tso Morari Complex formed in a continental rift setting at the Indian margin associated with the northern East Gondwana during the Early Paleozoic. Zircon U–Pb dates from eight gneisses and one garnet amphibolite indicate the Early Paleozoic bimodal magmatism of 493–476 Ma, which could be associated with the separation of South China from North India. Except for arc-related eclogites found in the Nidar ophiolite, the eclogites and amphibolites are rift-related, exhibiting enriched light rare earth elements and high concentrations of incompatible elements, along with evidence for crustal contamination. Our findings support the previously reported diversity in the sources and ages of the protoliths of the Himalayan HP–UHP metamorphic rocks along the orogen.