Tectonic Evolution Research Articles

Magnetostratigraphy of the Late Cretaceous to Early Eocene sediments from the Tulsipur section, western Nepal: Tectonic implications for the Indian northern passive margin

The sedimentary strata from the Late Cretaceous to Early Eocene in the Himalayan foothills offer detailed insights into land collision processes. Unfortunately, a comprehensive dating study on these strata has been lacking, limiting our understanding of the collision and splicing history of the Indian and Lhasa plates. To address this question, we conducted a paleomagnetic study on the Late Cretaceous to Early Eocene succession in the Tulsipur area, western Nepal. The paleomagnetic data obtained from a 357 m thick succession were used to establish a new magnetostratigraphic framework for this region. The observed magnetic polarity sequence contains six normal and six reversed polarity zones, spanning the age range of 68–54 Ma (Maastrichtian to Early Eocene). In addition, two major and two stable sediment accumulation rates (SARs) were identified which were likely controlled by tectonics. The rifting and subsidence events caused by continuous northward movement of the Indian plate might have modulated the shifting of distal offshore to tidal flat settings in this region. We document fifteen (Unit I) and seven (Unit II) transgressive-regressive cycles, indicative of passive margin instability influenced by near-field effects of the India-Asian convergence. This new magnetostratigraphic result is expected to serve as a basic age framework in reconstructing the Late Mesozoic and Early Cenozoic tectonic evolution. Furthermore, it will also facilitate reliable cross-regional correlation between lithostratigraphic units across passive margins in the southern Himalaya and similar strata in the Tethyan Himalaya and active continental margins of the southern Tibetan Plateau.

Early Devonian Post‐collisional Granitic Magmatism in the North Qilian Orogenic Belt, Western China: Insights into Lithospheric Delamination and Orogenic Collapse

AbstractPost‐collisional magmatism contains important clues for understanding the reworking and growth of continental crust, as well as lithospheric delamination and orogenic collapse. Early Devonian magmatism has been identified in the North Qilian Orogenic Belt (NQOB). This paper reports an integrated study of petrology, whole‐rock geochemistry, Sm‐Nd isotope and zircon U‐Pb dating, as well as Lu‐Hf isotopic data, for two Early Devonian intrusive plutons. The Yongchang and Chijin granites yield zircon U‐Pb ages of 394–407 Ma and 414 Ma, respectively. Both of them are characterized by weakly peraluminous to metaluminous without typical aluminium‐rich minerals, LREE‐enriched patterns with negative Eu anomalies and a negative correlation between P2O5 and SiO2 contents, consistent with geochemical features of I‐type granitoids. Zircons from the studied granites display negative to weak positive εHf(t) values (–5.7 to 2.1), which agree well with those of negative εNd(t) values (−6.4 to −2.9) for the whole‐rock samples, indicating that they were derived from the partial melting of Mesoproterozoic crust. Furthermore, low Sr/Y ratios (1.13–21.28) and high zircon saturation temperatures (745°C to 839°C, with the majority being >800°C) demonstrated a relatively shallow depth level below the garnet stability field and an additional heat source. Taken together, the Early Devonian granitic magmatism could have been produced by the partial melting of ancient crustal materials heated by mantle‐derived magmas at high‐temperature and low‐pressure conditions during post‐collisional extensional collapse. The data obtained in this study, when viewed in conjunction with previous studies, provides more information about the tectonic processes that followed the closure of the North Qilian Ocean. The tectonic transition from continental collision to post‐collisional delamination could be constrained to ∼430 Ma, which is provided by the sudden decrease of Sr/Y and La/Yb ratios and an increase in zircon εHf(t) values for granitoids. A two‐stage tectonic evolution model from continental collision to post‐collisional extensional collapse for the NQOB includes (a) continental collision and crustal thickening during ca. 455–430 Ma, characterized by granulite‐facies metamorphism and widespread low‐Mg adakitic magmatism; (b) post‐collisional delamination of thickened continental crust and extensional collapse of orogen during ca. 430–390 Ma, provided by coeval high‐Mg adakitic magmatism, A‐type granites and I‐type granitoids with low Sr‐Y ratios.

Insights Into the Structure of the Mongol‐Okhotsk Suture Zone, Adaatsag Ophiolite, and Tectonic Boundaries of the Central Asian Orogenic Belt (Mongolia) From Electrical Resistivity Imaging and Seismic Velocity Models

AbstractThe Mongol‐Okhotsk suture and the Adaatsag ophiolite belt are associated with the closure of the Mongol‐Okhotsk paleo‐ocean and are located within the Central Asian Orogenic Belt (CAOB) and Mongolia. The suture zone is flanked by volcanic‐plutonic belts that host significant metallogenic zones, containing deposits of copper and gold. The tectonic evolution of this region is not fully understood and the lithospheric structure has been poorly studied. We analyze magnetotelluric data and generate a model of the electrical resistivity distribution across this region. Whereas the northern segment has a sharp transition from a high‐resistivity upper crust to a low‐resistivity lower crust, as observed beneath the Hangai Dome, the southern segment does not show this transition. A wide, low‐resistivity zone (1–100 Ωm) imaged in the crust and lithospheric mantle is coincident with the Mongol‐Okhotsk suture and ophiolite, revealing a clear and significant lithospheric‐scale feature. Across the profile, numerous narrow, vertically oriented, low‐resistivity features (1–100 Ωm) are spatially associated remarkably well with the proposed boundaries of tectonic domains. These results confirm ideas about the development of the CAOB. Some of these low‐resistivity features are beneath the surface locations of large mineral zones, and likely represent fossil fluid pathways. We show congruent seismic velocity models for comparison and the results show a large‐scale low‐velocity anomaly (decrease of 2%–3%) that correlates with the location of the low‐resistivity anomaly below the Mongol‐Okhotsk suture. The geophysical results, combined with geological and geochemical data, provide insights into the structure of this region and help shed light on unanswered questions.

Detrital mode and geochemical constraints on the provenance, paleoweathering and tectonic setting of the Surma sediments of Chittagong-Tripura fold belt, Tripura, India

The Chittagong Tripura Fold Belt (CTFB), the folded eastern part of the Bengal Basin is critical for understanding sediments origin and tectonic evolution linked to interactions among the Indian, Eurasian, and Burma plates. The upper Bhuban and Bokabil sediments (Surma Group) from Atharamura anticline, Tripura, India were analyzed using whole-rock geochemistry and petrography to assess their provenance, tectonics, weathering, and depositional milieu in this least explored area. Petrographic study indicates sub-lithic arenite to sub-arkosic composition, with moderate-high quartz, feldspar poor containing metamorphic and sedimentary lithic fragments (Bh Q88.3F3.0L8.6; Bk Q83.5F7.6L8.8), indicating significant recycled orogen source. Geochemical characteristics such as Eu/Eu* (0.6, 0.7), La/Sc (3.2, 2.4), Th/Sc (1.7, 1.4), Th/Co (1.9, 1.8), CIA/WIP (∼1–2), high Hf, Zr/Sc, low K2O/Al2O3 and enriched LREEs, depleted HREEs, and negative Eu anomalies, indicate a recycled provenance of felsic origin that underwent moderate to intense chemical weathering in active continental margin settings. Radiolarian chert, volcanic lithic fragments with Barail-like recycled sediments strongly suggests an additional detritus from uplifted Indo-Burman Ranges from the east. Elevated Th/U and Th/Rb ratios, sediment immaturity and poor sorting suggest first-cycled detritus. This study indicate that Tripura Neogene sediments are chiefly Himalayan-derived, with minor inputs from IBR and Meghalaya Plateau. Sedimnets deposited under brackish near shore to shallow marine oxic basins to the west of the uplifted IBR during the Miocene. The study offers insights into regional geological processes, facilitating correlation of foreland Neogene basins and enhances understanding of the geological evolution of the CTFB.

Middle Paleozoic metamorphic and sedimentary events in the central Korean Peninsula and their geological implications

The Middle Paleozoic tectonic evolution of the central Korean Peninsula (Gyeonggi Massif, Hongseong-Imjingang, and Okcheon zone of Okcheon Belts) remains controversial. Particularly, the occurrence of high-grade metamorphism and sedimentation need further examination. In this study, we conducted zircon U-Pb-rare earth element analyses from in the ultramafic-mafic complex in the central Korean Peninsula (Cheonan and Gapyeong areas) and the Paleozoic metasedimentary rocks in the Okcheon Zone of the Okcheon Belt to constrain the timing of maximum depositional and metamorphic ages. We also examined the metamorphic P-T-t path from garnet-bearing amphibolite in the central Korean Peninsula by pseudosection modeling and geothermobarometer. The results show that (i) some of the ultramafic-mafic complex and metasedimentary rocks in the central Korean Peninsula formed during the Middle Paleozoic (ca. 450–374 Ma); (ii) garnet-bearing amphibolite underwent successive metamorphism from amphibolite facies condition (7.5–8.0 kbar and 540–630 °C) at pre-peak stage to granulite facies condition (10.9–11.8 kbar and 740–820 °C) at peak stage, and then retrograded into amphibolite facies condition (5.7–7.7 kbar and 530–670 °C) along the clockwise P–T path during ca. 403–362 Ma. This and previous studies suggest that the central Korean Peninsula underwent subduction-related orogenic events during the Middle Paleozoic era, and it is well correlated to those of the orogenic events in the North Qinling belt.

The Role of the Curved Southern Asian Margin Between the Tarim and Tajik Cratons During the Evolution of the Pamir, Insights From Sandbox Modeling

AbstractEnhanced knowledge of the Pamir salient formation can contribute to comprehending the tectonic evolution of Himalaya‐Tibetan orogen. However, whether the Pamir salient formed along a linear or a curved southern Asian margin between the Tarim and Tajik cratons remains controversial. Likewise, the role of the two craton blocks during the evolution of the Pamir salient is unclear. Here we present three sandbox experiments exploring the effect of the geometry of the southern Asian margin, as well as the presence of Tarim and Tajik cratons. The results show that the highly curved shape of the Pamir salient, transpressional faults in its wings and strike‐slip faults within its interior only form along a curved southern Asian margin. A westward‐deflecting arcuate thrust wedge formed along the asymmetric curved southern Asian margin. Together with the Tarim craton and the Tajik craton, this wedge facilitated the westward transfer of materials in the Pamir, and resulted in the westward deflection of the velocity field in Pamir and the formation of the Tajik fold‐thrust belt. The oblique slip of arcuate thrust wedge along the western edge of the Tarim craton generated the Kongur extensional system. Moreover, the Tarim and Tajik cratons concentrated deformation mainly along the non‐cratonic continental margin and promoted the formation of transpressional faults surrounding the Pamir and the strike‐slip faults within the Pamir.

Distinct mafic magmatism of the northeastern Longgang Block: Evidence for coexisting mantle plume and subduction during the Neoarchean North China Craton

The question of which specific tectonic regimes played an essential role in shaping the Neoarchean evolution of the North China Craton (NCC) has been a contentious and controversial topic. Mafic rocks, containing valuable geochemical information from the mantle and deep crust, serve as an important source of data to provide essential constraints on above issue. This study presents bulk-rock geochemistry, zircon U-Pb geochronology and Hf-Nd isotopes for the Neoarchean mafic rocks in the core area of the Longgang Block of the NCC. Petrographically, these mafic rocks are composed of the amphibolite and metadiabase. Zircon U-Pb dating results revealed that they were synchronously emplaced at ca. 2.5 Ga. Geochemically, the amphibolites belong to subalkaline tholeiite series, exhibiting enrichment in light rare earth elements (LREEs), intensely negative Nb, Ta and Ti anomalies, and slightly enriched Nd and relatively variable zircon Hf isotopic compositions. These geochemical and isotopic features show large affinity to arc-like magmatism, implying that they were derived from subduction-related metasomatized lithospheric mantle. In contrast, the metadiabases exhibit high-Ti alkaline basalt affinities, OIB-like REE, and trace element patterns. They also show clearly positive Nb, Ta and Ti anomalies, indicating that they originated from a mantle plume-related tectonic environment. The new geochemical and isotopic data reveal that these Neoarchean mafic rocks could have resulted from coexisting mantle plume and subduction processes. Combined with available regional structural, geochemical, and metamorphic data, it is likely that during the Neoarchean, both a mantle plume and subduction jointly controlled the crustal growth and tectonic evolution of the Longgang Block in the eastern NCC.

Using detrital zircons to constrain the late Paleozoic tectonic evolution of the adjacent tectonic domains of the Tarim Craton, NW China

Late Paleozoic tectonic evolution of adjacent tectonic domains of the Tarim Craton is vital for understanding the basin-mountain coupling and dynamical mechanisms of the Paleo-Asian and Tethys tectonic systems as well as hydrocarbon exploration and development. U−Pb dating and Lu-Hf isotope analyses of detrital zircons of the Late Paleozoic sedimentary successions from three sections across the Tarim basin enable comprehensive identification of provenance changes and reconstruction of the tectonic evolutionary history of the Tarim Basin in the late Paleozoic. A total of 248, 499, and 470 valid ages were obtained for detrital zircon samples from the Kuqa Section in the northern margin of the Tarim Basin; the Xiaohaizi Section in the platform area; and the Aitegou Section in the southwestern margin of the Tarim Basin, respectively. Each age interval corresponds to the geotectonic thermal events of the opening–subduction–closing of the surrounding oceans and the collage/collision of terranes/island arcs. Based on detailed age spectral analysis and other evidence, we propose a tectonic evolutionary model that encompasses the northern and southwestern margins of the Tarim Basin. The South Tianshan Ocean closed completely in the late Carboniferous, resulting in the collision of the Tarim Basin with the Yili–Middle Tianshan Terranes no later than 315 Ma. In the southwestern part of the Tarim Basin, the Tianshuihai Terrane began to approach in the late Carboniferous, gradually amalgamated with the southwestern margin of the Tarim Basin, and finally wholly collided with the Tarim Basin at the end of the Permian, making the Tarim Basin an entirely terrestrial basin. The southwestern Tarim Basin was not an open passive continental margin in the Carboniferous–Permian but a retro-arc basin.

Crustal architecture and tectonic development of western Queensland, Australia, based on deep seismic reflection profiling: Implications for Proterozoic continental assembly and dispersal

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 T2DM 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.

New insights into tectonostratigraphy and structural style of the Late Cretaceous sediments of Gongola Basin, Northern Benue Trough, NE Nigeria

Tectonostratigraphy of the Gongola Basin is still least understood. This study aims to present a new insight into tectonic evolution and structure of Gongola Basin based on field geology. The study revealed that sedimentation processes commenced in the depression created by tectonic subsidence as a result of Early Cretaceous tectonic events, which affected the basin and subsequently, reactivated the Santonian/Maastrichtian compression. The sediments were affected by Santonian and Maastrichtian compressions resulting in syn-sedimentary deformation and post-depositional faulting and folding. The imprints of dextral strike-slip faults and reverse faults on pre-Maastrichtian and Maastritchtian sediments formed as a result of reactivation of the pre-Santonian and Santonian faults. Active rifting phase followed by uplift and subaerial exposure as in Gombe inlier, and adjacent areas such as Teli Fault, Kaltungo, Burashika inliers followed by subsidence allowing for initial deposit of continental sediments and later, marine ingression which causes a change from continental to marine environments during Cenomanian. Eustatic adjustment in Late-Cenomanian to Early-Turonian led to first major transgression and short-regressive phase in middle Turonian-early Santonian. Mid-Santonian compression folded the sediments and was followed by subaerial erosion of parts of the folded sediments. Another eustatic adjustment in Late-Santonian-Campanian led to a short-lived transgression. A gradual retreat of the sea in the Maastrichtian resulted in progradation of Gombe Sandstone. Late Maastrichtian compression in end-Cretaceous tectonic event folded and tilted Gombe Sandstone, responsible for the angular unconformity that existed between Gombe Formation and overlying Paleocene sediments of Kerri-Kerri Formation, mostly restricted to NW of the basin.

Basin Analysis and Tectonic Evolution of the Upper Campanian- Maastrichtian Succession, Southern Iraq

The tectonic development of the Mesopotamia basin in southern Iraq was studied by calculating subsidence and sedimentation rates for eleven wells distributed over the study area. This was done by calculating backstripping for the Upper Campanian-Maastrichtian sequence. The subsidence rates increased in the south of the region near the Su-4, Su-1, and Lu-2 wells in the Hartha Formation, while the basin of the Shiranish Formation appeared to increase towards the northwest near the Ns-2 well. Then, the subsidence rates in the next formation, Tayarat, increase towards the south, near the wells. Su-1, Su-4, Lu-2. The Hartha Basin was divided into two tectonic parts based on the above. The Shiranish Basin was affected by uplift from the northeast and southeast directions, and due to this, an extremely shallow basin formed with its northern portion exposed during the transgression. At the end of this period, it became the regression stage, where the tectonic uplift began to decrease towards the southwest, and this indicates that the tectonic movement's reactivation due to continental collision, which is evident in the next stage with the deposition of the Alaiji Formation. According to these stratigraphic features, the studied area was divided into two tectonic basins, the northeast basin (Samawa-Nasiriya Subzone) and the southwest basin (Zubair Subzone) separated by tectonic lineament extending from Nasiriya-West Qurna and Zubair oil fields.

Deformation, Strength and Tectonic Evolution of Basal Ice in Taylor Glacier, Antarctica

AbstractObservation and measurements of ice structure and deformation made in tunnels excavated into the margin of Taylor Glacier, a polythermal glacier in the McMurdo Dry Valleys of Antarctica, reveal a complex, rapidly deforming basal ice sequence. Displacement measurements in the basal ice, which is at a temperature of −18°C, together with the occurrence of cavities and slickenslides, suggest that sliding or rapid deformation in thin zones of high shear occurs at structural discontinuities within the basal zone. Strain measurements show that the highest strain rates occur in ice with average debris concentrations of 26% followed by ice with debris concentrations of around 12%. The lowest strain rates occur in clean bubbly ice that has very low debris concentrations (<0.02%). Deformation within the basal ice sequence is dominated by simple shear but disrupted by folding which results in shortening of the debris‐bearing ice followed by attenuation of the folds due to progressive simple shear which generates predominantly laminar basal ice structures. About 60% of glacier surface velocity can be attributed to deformation within the 4.5 m thick sequence of basal ice that was monitored for this study, and 15% of motion can be attributed to sliding or very localized shear. The combination of high debris concentrations and high strain rates in the debris‐bearing ice results in high rates of abrasion and the production of striated and facetted clasts typical of temperate glaciers, even though the basal ice is at a temperature of −18°C.

Revisiting the depositional age and provenance characteristics of metasedimentary rocks from the basement units in the Central Pontides (N Turkey): New constraints for tectonic evolution of the southern Black Sea region

The pre-Jurassic tectonic evolution of the Central Pontides in northern Turkey is still poorly understood due to the lack of detailed geochemical and geochronological data from the basement units. Therefore, this study reports for the first time combined whole rock geochemistry, trace element data and U-Pb ages for detrital zircons, and Ar-Ar geochronological data from the metasedimentary rocks of the Devrekani Massif, Geme Complex, and the Serveçay Unit to better understand their provenance, depositional age characteristics, and tectonic evolutions. The detrital zircon U-Pb data of metasedimentary units from the Devrekani Massif, Geme Complex, and the Serveçay Unit yield ca. 191, 185 and 298 Ma maximum depositional ages (youngest age peaks), respectively. The Devrekani Massif is dominated by Permo-Carboniferous-aged detrital zircons (67 %), whereas Neoproterozoic and Devonian-aged detrital zircons are more common in the Geme Complex (47 %) and the Serveçay Unit (53 %). These distinct age distributions clearly indicate that the Devrekani Massif may has been deposited in a dissimilar location compared to the Geme Complex and the Serveçay Unit. Furthermore, in contrast to the Devrekani Massif, the source area of the metasedimentary rocks from the Geme Complex is comparable with that of the Serveçay Unit. Lastly, the obtained detrital zircon U-Pb and mica Ar-Ar ages suggest that the Devrekani Massif and the Geme Complex were deposited and metamorphosed during the Early and Middle Jurassic, respectively. The Serveçay Unit was deposited and metamorphosed in the Permian.

Origin of mafic microgranular enclaves from the Late Triassic Cuojiaoma granitic pluton: Implications for the tectonic evolution of the Yidun arc belt, eastern Tibetan Plateau

In-situ U-Pb ages and Hf-O isotopes of zircon are frequently used to study the petrogenesis of mafic microgranular enclaves (MMEs) in granitoids. However, whether zircons in MMEs have recorded the primary isotopes of their host MMEs is still questionable. In this study, MMEs and host granites from the Cuojiaoma granitic pluton in the Triassic Yidun arc belt, eastern Tibetan Plateau, are studied. LA-ICP-MS zircon U-Pb dating of studied MMEs yields an age of 213 ± 2 Ma. Model calculations indicate that the whole-rock composition of the MMEs was different from the melt composition from which the zircon grains grew. The MMEs crystallized during magma mixing based on analyses of zircon trace element and Zr-Hf isotopes. None of zircons in this study have recorded the primary isotope signature of the mafic endmember of MMEs because they are different from the host granite in terms of zircon morphology, ɛHf values and ΔQFM. The Zr isotopic data demonstrate open-system magmatic crystallization for the host granite and that magma mixing for MMEs play key role in controlling Zr isotopic variations. Initial 87Sr/86Sr ratios of An-rich plagioclase crystals in groundmass from MMEs range from 0.7027 to 0.7058, which are significantly lower than host granites (0.7080 – 0.7089). The lowest initial 87Sr/86Sr ratios (0.7027 – 0.7028) are also lower than arc volcanic rocks and similar to a depleted mantle. Combined with previous studies, we propose that MMEs were generated during post-collision extension by mixing of mafic magma of Xiaxiaoliu basalt and felsic magma from host granite.

Evolution of A-type granites during the Late Paleoproterozoic orogenic cycle of North China craton: Implications for post-collisional magmatism

“A-type” granites were originally considered anorogenic, however current consensus closely associates them with orogenic settings. The correlation between the prolific emergence of A-type granites and the assembly of the Columbia (Nuna) supercontinent during the Late Paleoproterozoic remains ambiguous possibly being indicative of a geodynamic shift from the amalgamation to the fragmentation of the supercontinent. This study identifies a Late Paleoproterozoic pluton exhibiting A2-type granite characteristics in the Shaerqin area of the Khondalite belt, North China craton. The plutonic rocks exhibit evolved whole-rock Nd isotopic (εNd(t) = −6.6 to −8.0) and zircon Hf isotopic (εHf (t) = −6.3 to −2.9) compositions, along with notably high zircon δ18O values (averaging 8.35 ± 0.29 ‰, 1SD). The Hf–Nd–O isotope systematics imply that the Shaerqin A-type granites originated from the partial melting of preexisting crustal materials under conditions of low pressure and high temperature. Incorporating the outcomes of this research with a compiled dataset of 1.9–1.5 Ga A-type granites across the entire craton, we deduce that: 1) Key geochemical ratios and indices, such as 10,000 Ga/Al, Y/Nb, and Zr/Nb, in A-type granites exhibit temporal variations, signifying a transition from A2-type to A1-type granite; 2) There is an increasingly apparent involvement of mantle-derived magmas in their genesis, coupled with a more pronounced role of fractional crystallization in the development of A1-type granites compared to their A2-type counterparts. We contend that these compositional and isotopic transitions reflect the tectonic evolution from post-orogenic extension to anorogenic rifting occurring around 1.7 Ga. The refined geochemical variations revealed in this study may offer a paradigm for post-orogenic evolutionary processes in general.

The role of intra-oceanic arc in the growth of continental crust: Evidence from the Early Paleozoic Bainaimiao arc

The Early Palaeozoic arc-related formations in the northern margin of the North China Craton (NCC) belonging to the Bainaimiao arc belt is an important part of the eastern Central Asian Orogenic Belt (CAOB). The tectonic evolution of this belt remains controversial. Here we present detailed data on the geochronology and geochemistry on a newly identified Early Palaeozoic igneous suite from the Faku area in northern Liaoning. Zircon U–Pb dating of the Faku volcanic and intrusive rocks yielded weighted mean 206Pb/238U ages of ca. 458 Ma and 433–405 Ma, respectively, which represent their crystallization (eruption) times. Zircon Hf isotopic analyses show a low negative to positive εHf (t) values of − 0.33 to + 12.4, implying depleted characteristics of the source. The geochemical features of Laolingshan basaltic andesites display higher TiO2 and lower P2O5 contents, similar to that of mid-ocean ridge basalts, and relatively high Zr/Y and low Ta/Yb ratios, suggesting oceanic island arc basalt affinity. Therefore, we suggest that the Laolingshan basaltic andesites were formed in an intra-oceanic environment. The Bachagou granodiorites, with adakitic geochemical signatures, belong to the calc-alkaline and high-K calc-alkaline series, implying formation in an active continental margin tectonic setting. The Baerhushan granodiorites, which geochemically belong to S-type granites, were probably formed in a syn-collisional environment influenced by arc–continent collision. The Donggou granitoids, which have higher SiO2 and alkali and lower MgO and P2O5, show A-type granite features. Geochemical characteristics of the Donggou A-type granite suggest formation in an extensional setting caused by orogenic intermittent extension. The Baerhushan gabbro diorites, which display properties of both mid-ocean ridge and continental rift basalts, were produced under post-orogenic extensional tectonic setting after the arc–continent collision. Our study traces the Early Palaeozoic tectonic evolution of the south-eastern segment of the CAOB and the related accretionary tectonics.

Paleoclimate changes across the Cenomanian–Santonian transition at the southern Neo-Tethys margin (SW Iran): An integrated approach

The Cenomanian–Santonian (C–S) carbonate successions include valuable petroleum reservoirs in the Zagros Basin. They also provide important information on the paleogeographic setting, paleoclimatic conditions, and tectonic evolution of the southern Neo-Tethys margin. This study focuses on the paleoclimatic changes across the C–S transition using the petrographical, petrophysical, paleontological, major and trace element and isotope geochemical data from three subsurface sections selected from the southern Dezful Embayment and northwestern part of the Persian Gulf. Remarkable differences in allochemical (skeletal and non-skeletal) elements indicate dissimilar paleoclimatic conditions during the Cenomanian–Turonian and Santonian. Paleoexposure events are related to diagenetic processes such as extensive meteoric dissolution (karstification) and the development of bauxitic–lateritic paleosols with high Fe, Al, and kaolinite concentrations indicating warm and humid (tropical) conditions. Increased values of Fe, Al, Rb, and 87Sr/86Sr isotopic ratios and depletion of Ca, Sr, δ18O, and δ13C considered together indicate meteoric diagenetic effects under this paleoclimatic condition. Spectral gamma measurements are used to investigate paleoclimatic conditions. Low content of Uranium (U) throughout the transgressive systems tract (TST) and high concentration in the regressive systems tract (RST) along with low contents of kaolinite within the Santonian sequence denote the predominance of arid conditions. The major fall in U concentrations at the Cenomanian–Turonian interface (CT-Exposure Surface) could be regarded as an outcome of the fall in the relative sea-level and a proxy of oxidizing conditions (Th/U > 7) that could be the consequence of a change in paleoclimate from humid/semi-humid to humid. Evidence for a 3–4 °C decrease in paleo-temperature and increase in aridity are recorded during the Cenomanian–Santonian transition in the Zagros Basin, which is in close agreement with global trends. This cooling pattern is attributed to a decline in atmospheric CO2 levels and alterations in oceanic circulation, specifically an increase in meridional circulation.

Matrix deformation of marls in a foreland fold-and-thrust belt: The example of the eastern Jaca basin, southern Pyrenees

In this study, we used the Anisotropy of Magnetic Susceptibility (AMS) to investigate the matrix strain record of two calcareous shale formations, the Eocene Larrès and Pamplona Marls, along the eastern Jaca foreland fold-and-thrust belt (Southern Pyrenees). More than 1000 unoriented fragments, collected from 62 sites along 4 sub-parallel sections in the footwall of the regional Oturia thrust and through local Yebra anticline, were measured. The analysis of the degree of anisotropy (P’) and shape parameter (T) allowed to identify four types of magnetic fabrics. Type II fabrics associated with poorly deformed rocks are characterized by a relatively high anisotropy and an oblate shape. In contrast, type III fabrics, associated with strongly fractured rocks are characterized by the lowest anisotropy and a triaxial shape. Type IV and type V fabrics are characterized by increasing anisotropy and shape parameters, and are associated with the development of a weak to a slaty cleavage in rocks. The distribution of the magnetic fabric is roughly similar along the four studied sections. In the footwall of the Oturia thrust, magnetic fabrics evolve from the type V to type II over a 1000 m-long interval. By contrast, the distribution of magnetic fabric is roughly symmetric across the Yebra anticline, evolving from a dominating type II fabric in both limbs to mixed type III-type V fabrics within the 1 km-large hinge zone. The succession of the magnetic fabrics is interpreted as recording various degrees of matrix strain in response to thrusting and folding. The correlation of magnetic fabrics between the four sections highlights some along-strike variations in the extension of fabric domains that are interpreted as reflecting the local influence of 2nd-order factors, such as the syn-tectonic sedimentation. Results are integrated within the tectono-sedimentary framework of the studied area to propose a model of matrix strain related to the tectonic and sedimentary evolution of a foreland fold and thrust belt.

Geochemistry and Zircon LA–ICP–MS U–Pb Geochronology of the Shuangwang Au Deposit, Shaanxi Province: Implications for Tectonic Evolution and Metallogenic Age

The Shuangwang Au deposit (with a gold resource of approximately 70 t Au), is located in the Fenxian-Taibai fore-arc basin in the West Qinling Orogen of central China. Igneous intrusions in the region include the Xiba granitic pluton and granite porphyry and lamprophyre dykes. The Xiba pluton is composed of granodiorite and monzonite granite. The granodiorite is typical I-type granite, and it yields a crystallization age of 221.1 ± 1.2 Ma and a two-stage Hf model age of 1432–1634 Ma. The monzonite granite shows a transitional characteristic between I-type and A-type granite, and it yields a crystallization age of 214.8 ± 1.2 Ma and a two-stage Hf model age of 1443–1549 Ma. The granitoid was derived mainly from a crust–mantle mixed source. The ages indicate that the granodiorite and monzonite granite formed during two different stages. The REE distribution patterns of the Xiba granitoid exhibit significant fractionation between LREE and HREE, showing right-dipping curves, with an enrichment of LREE and a deficit of HREE. The granodiorite displays a light negative Eu anomaly, while the monzonite granite displays an obvious negative Eu anomaly. The granite porphyry dikes are distributed in the No. I breccia and Jiupinggou granite porphyry, and they yield crystallization ages of 219.9 ± 1.5 Ma and 213.1 ± 0.89 Ma, respectively, and two-stage Hf model ages of 1382–1501 Ma and 1373–1522 Ma, respectively. The lamprophyre dikes in the deposit yield a crystallization age of 214.4 ± 2.7 Ma. After the collision event between the Yangtze and the North China Plates along the Qinling orogenic belt, at approximately 220 Ma in the Late Triassic, the detachment of the slab produced the upwelling of the asthenosphere material. Under conditions of mantle heat and tectonic stress, widespread partial melting of the subducted continental crust and the upper lithosphere mantle occurred, forming granitoids with various degrees of adakite characteristics.

Disconformity-controlled hydrothermal dolomitization and cementation during basin evolution: Upper Triassic carbonates, UAE

Petrography, fluid-inclusion microthermometry, stable isotope analyses, and radiometric (206Pb/238U) dating of Upper Triassic dolostones, saddle dolomite, and quartz and calcite cements were used to constrain the timing and conditions of dolomitization and cementation in the context of the tectonic evolution of a basin in the northern United Arab Emirates. Dolomitization (ca. 152.4 Ma) and precipitation of saddle dolomite (ca. 146.8 Ma), calcite (ca. 144.6 Ma), and quartz cements are attributed to focused synrifting flow of hot basinal brines into grain-supported limestones in which permeability was enhanced by incursion of meteoric waters beneath a disconformity surface. Another calcite cement generation (ca. 99.7 Ma) was formed by flow of hot brines during tectonic compression related to the obduction of Oman ophiolites in the Late Cretaceous. Thus, this paper provides new insights into (1) stratigraphic controls on and timing of hydrothermal (hot basinal brines) dolomitization, (2) the origin of closely associated intraformational limestones and dolostones, and (3) linkages between diagenesis and thermochemical modifications of basinal brines during tectonic evolution of sedimentary basins.