Mesozoic Evolution Research Articles

Tectonic evolution of the Qiangtang Basin (northern Tibet): Constraints from detrital zircon geochronology

The Mesozoic evolution of the Qiangtang Basin in the Tibetan Plateau, which potentially hosts oil and gas resources, is not fully understood, particularly in the context of the opening and closure of the Tethyan oceans. To better understand the tectonic evolution of the Qiangtang Basin and the history of sedimentation, we obtained 788 new U-Pb detrital zircon ages from 12 sandstone samples. Our results show that the provenance of the Mesozoic strata varies both in space and time. In the central part of the basin (Central Qiangtang), older sedimentary rocks are characterized by unimodal age spectra (300–233 Ma) that indicate a proximal arc source. Trace-element compositions of Permian to Triassic zircons from Lower Triassic strata are characteristic of crystallization in arc and backarc environments, thus supporting previous suggestions that the Qiangtang Basin formed as a backarc basin during subduction of the Paleo-Tethys oceanic lithosphere. Younger (Upper Triassic and Jurassic) strata in the Qiangtang Basin received detrital zircons from diverse sources that included Cambrian to Triassic magmatic rocks and Paleozoic strata in the Central Qiangtang, and Triassic flysch deposits in the Songpan-Garze Terrane. We suggest that this change in provenance — from a unimodal arc source that produced zircons in Lower–Middle Triassic rocks to the diverse provenance recognized in the Upper Triassic strata — marks the closure of the Paleo-Tethys Ocean during the Late Triassic. Jurassic sedimentation in the Qiangtang Basin occurred during the expansion of the Meso-Tethys Ocean (Early–Middle Jurassic) and the subsequent subduction of this ocean (since the Callovian). During the Early Cretaceous, the closure of the Meso-Tethys Ocean led to an uplift and a sedimentary hiatus that marked the end of marine sedimentation in the Qiangtang Basin.

The Cretaceous post-rift series from the Portuguese onshore ranges of the West Iberian Margin and their history of research

The thick post-rift series that covers the Triassic to Lower Cretaceous sedimentary succession of the Lusitanian Basin, in west central Portugal, is crucial to understanding the Mesozoic evolution of the West Iberian Margin, motivating a long history of studies, including those by Daniel Sharpe (1806–56). They record platform carbonates interbedded with marginal marine and alluvial facies. The post-rift infill was deposited above a late Aptian breakup unconformity and is organized into three unconformity bounded sequences: ‘UBS-4A’ (upper Aptian–upper Cenomanian), ‘UBS-4B’ (lower Turonian–lower Campanian) and ‘UBS-5B’ (lower Campanian–Maastrichtian). The first comprises alluvial siliciclastics and shallow-marine, carbonate sequences rich in Tethyan faunas with ammonites and rudists. During the late Cenomanian, the carbonate platform entirely covered the onshore sectors of the Lusitanian Basin. Several diapiric axes controlled the differentiation of inner platform areas with corals and rudists. The infill of ‘UBS-4B’ occurred after the tectonic uplift and emersion of the sectors located to the south of first-order Nazaré Fault Zone. The platform carbonate facies were overlain by regressive micaceous and alluvial coarse siliciclastics. The sequence ‘UBS-5’ overlies a lower Campanian unconformity and has a Campanian–Maastrichtian thick record of alluvial to lagoonal, reddish pelites, rich in vertebrate assemblages.

Unravelling the tectonic evolution of the Dinarides—Alps—Pannonian Basin transition zone: insights from structural analysis and low-temperature thermochronology from Ivanščica Mt., NW Croatia

A comprehensive study, including geological mapping, structural and thermochronological analysis, has been carried out on Ivanščica Mountain (NW Croatia), with the aim to reconstruct the tectonic history of the Dinarides, Southern/Eastern Alps and Pannonian Basin transitional zone. Implementation of structural and thermochronological methods enabled a subdivision of Ivanščica Mt. into two structural domains (from bottom to top): Ivanščica Parautochthon and Ivanščica Imbricate Fan and Cenozoic sedimentary cover. In addition, a sequence of deformational events in tectonic history of this transitional zone is proposed, comprising three extensional and four contractional events starting from Middle Triassic until present times. The two oldest deformational events indicate Middle Triassic (D1) and Early Jurassic (D2) extensional pulses and only occur in volcano-sedimentary successions of the Ivanščica Mt. The oldest contractional event (D3) is related to the obduction of a Neotethyan ophiolitic mélange over an Upper Triassic to Lower Cretaceous succession of the eastern margin of the Adriatic microplate, which resulted in thermal overprint of the Ivanščica Imbricate Fan structural domain in Berriasian—Valanginian times (~ 140 Ma). This event was soon followed by a second contractional event (D4), which resulted in thrusting and imbrication of the Adriatic passive margin successions together with previously emplaced ophiolitic mélange, thermal overprint of the footwall successions, fast exhumation and erosion. Apatite fission track data together with syn-tectonic deposits indicate an Hauterivian to Albian age of this D4 event (~ 133–100 Ma). These Mesozoic structures were dextrally rotated in post-Oligocene times and brought from the initially typically Dinaridic SE striking and SW verging structures to the recent SW striking and NW verging structures. The following extensional event (D5) is associated with the formation of SE striking and mostly NE dipping normal listric faults, and ENE striking dextral faults accommodating top-NE extension in the Pannonian Basin. Deformations were coupled with hanging wall sedimentation of Ottnangian to middle Badenian (middle Burdigalian to upper Langhian; ~ 18–14 Ma) syn-rift deposit as observed from the reflection seismic and well data. A short-lasting contraction (D6) was registered in the late Sarmatian (late Serravallian; ~ 12 Ma). The youngest documented deformational event (D7) resulted in reactivation of ENE striking dextral faults, formation of SE striking dextral faults as well as the formation of E to ENE trending folds and reverse faults. This event corresponds to late Pannonian (late Messinian; ~ 6 Ma) to Present NNW-SSE contraction driven by the indentation and counterclockwise rotation of Adriatic microplate. Recognized tectonic events and their timings indicate that Ivanščica was mainly affected by deformational phases related to the Mesozoic evolution of the Neotethys Ocean as well as Cenozoic opening and inversion of the Pannonian Basin. Therefore, the Mesozoic tectono-sedimentary evolution of Ivanščica Mountain proves the paleogeographic affiliation of its non-ophiolitic Mesozoic structural-stratigraphic entities to the Pre-Karst unit of the Dinarides.

Tectono-Metamorphic Evolution of the Cretaceous Kluane Schist, Southwest Yukon

Abstract A wealth of information regarding the Mesozoic evolution of the Northern Canadian and Alaskan Cordillera is held within a series of variably metamorphosed and deformed rocks that formed in Jura-Cretaceous basins. Located at the interface between the pericratonic Intermontane and exotic Insular terranes, these basinal rocks are key to understanding the timing and tectonic style of Insular terrane accretion, a topic of longstanding debate. This study unravels the structural and metamorphic evolution of one of these basins, the Kluane Basin, within southwest Yukon Territory. The Kluane Schist is the primary assemblage of the Kluane Basin. It consists of metamorphosed and deformed low-Al pelites that were intruded by granodioritic plutons of the Paleocene Ruby Range batholith. Previous workers have suggested the variable metamorphic character of the Kluane Schist represents an extensive and static thermal aureole related to Ruby Range batholith emplacement. Our work, however, indicates that the Kluane Schist experienced Buchan-style metamorphism coeval with protracted deformation and can be divided into seven distinct petrologic zones, which, based on their unique combination of mineral assemblage and structure, are incompatible with static thermal metamorphism. Instead, we propose the Kluane Schist experienced two distinct metamorphic phases: (1) an early greenschist-facies phase that resulted in the development of a bedding-parallel chlorite-muscovite-titanite fabric, preserved by its lowest-grade units, and (2) a later amphibolite-facies phase that manifests as the progressive transposition of the earlier chlorite-muscovite-titanite fabric into a penetrative biotite-rich schistosity that transitions upgrade into a segregated gneissic fabric comprised of biotite-cordierite and plagioclase-quartz (± sillimanite-K-feldspar-melt). By integrating the results of detailed petrography and petrological modeling, we demonstrate that the second main metamorphic phase experienced by the Kluane Schist preserves a record of pressures and temperatures that align with other Buchan-style terranes worldwide. Our data defines a field gradient across the Kluane Schist ranging from 3.0–3.5 kbar at 375–400 °C to 4–4.5 kbar at 700–750 °C. This record of a coupled Buchan-style metamorphic-deformational evolution and tops-to-the SW non-coaxial shear structures is consistent with the override of the thermally mature Yukon-Tanana terrane as the principal driver of Kluane Schist metamorphism, with some limited heat likely contributed by the late-syn- to post-tectonic intrusion of the Ruby Range batholith.

First occurrence of family Clavatoraceae (fossil Charophyta) in the Middle Jurassic (Bathonian) of France

AbstractA rich and diverse charophyte flora is described from the Bathonian marginal marine beds of southern France. It includes nine species that belong to the families Porocharaceae, Characeae and Clavatoraceae: Porochara gr. fusca, P. gr. kimmeridgensis subgr. kimmeridgensis, P. gr. kimmeridgensis subgr. westerbeckensis, P. gr. kimmeridgensis subgr. douzensis, P. gr. kimmeridgensis subgr. obovata, Auerbachichara saidakovskyi, A. tataouinensis, Aclistochara mädleri and Echinochara cf. peckii. This is the most diverse Middle Jurassic flora reported from France and Laurasia to date, elucidating a turnover in the evolution of charophytes during this time interval. The occurrence of the clavatoracean Echinochara cf. peckii in these Bathonian deposits represents the oldest record of the genus and of the whole family, c. 10 myr older than previous records. This species is considered to be the most basal species in the phylogeny of Clavatoraceae and during its evolutionary history reached a wide biogeographical range in Laurasia. The new Bathonian charophyte assemblage from southern France provides supplementary evidence that the Middle Jurassic was a reactivation pulse in the Mesozoic evolution of charophytes, rather than a stasis as previously thought. Moreover, it provides further support to the hypothesis that during the Late Jurassic and Early Cretaceous the islands of the Cretaceous Tethyan Archipelago represented one of the most active spots of charophyte diversity.

Metamorphic P-T-t constraint on the Bantimala garnet-epidote-glaucophane schist and its implication on Mesozoic evolution of Western Sulawesi, Indonesia

Bantimala Complex of Western Sulawesi contains a mixed lithology of blueschist and eclogite, which are the ideal rock assemblage for understanding the geodynamic process of the Tethys subduction system. However, previous studies only reported rough P-T ranges and failed to present a systematic P-T evolutionary history for blueschists of this area. In this study, we carried out detailed petrographic, phase equilibrium modelling, and U-Pb and Ar-Ar geochronological analysis on two garnet-epidote-glaucophane schists samples (18SS24–1, 18SS24–2) to construct their metamorphic histories. Results suggest that both samples underwent eclogite-facies metamorphism with peak conditions of 27–28.5 kbar/615–640 °C (18SS24–1) and 23–28 kbar/565–630 °C (18SS24–2). Their P-T paths show hairpin patterns with geothermal gradients of 7–8 °C/km at peak stages. 40Ar/39Ar dating yielded an age of 125.0 ± 0.4 Ma, which is interpreted to postdate HP metamorphism. Compared with other HP eclogite with similar peak conditions worldwide, Bantimala garnet-epidote-glaucophane schists are significantly low in bulk CaO content. This geochemical feature enables them to preserve garnet-glaucophane-dominated peak mineral assemblages instead of garnet-omphacite-dominated ones, though they were subducted over 80 km depth and metamorphosed up to eclogite-facies. The discovery of garnet-epidote-glaucophane schists of eclogite-facies metamorphism corroborated the existence of Franciscan-type metamorphism that is characterized by the cold deep subduction of an oceanic lithosphere between the Sundaland landmass and east Java–west Sulawesi terrane during the Early Cretaceous.

Mesozoic evolution of cicadas and their origins of vocalization and root feeding

Extant cicada (Hemiptera: Cicadoidea) includes widely distributed Cicadidae and relictual Tettigarctidae, with fossils ascribed to these two groups based on several distinct, minimally varying morphological differences that define their extant counterparts. However, directly assigning Mesozoic fossils to modern taxa may overlook the role of unique and transitional features provided by fossils in tracking their early evolutionary paths. Here, based on adult and nymphal fossils from mid-Cretaceous Kachin amber of Myanmar, we explore the phylogenetic relationships and morphological disparities of fossil and extant cicadoids. Our results suggest that Cicadidae and Tettigarctidae might have diverged at or by the Middle Jurassic, with morphological evolution possibly shaped by host plant changes. The discovery of tymbal structures and anatomical analysis of adult fossils indicate that mid-Cretaceous cicadas were silent as modern Tettigarctidae or could have produced faint tymbal-related sounds. The discovery of final-instar nymphal and exuviae cicadoid fossils with fossorial forelegs and piercing-sucking mouthparts indicates that they had most likely adopted a subterranean lifestyle by the mid-Cretaceous, occupying the ecological niche of underground feeding on root. Our study traces the morphological, behavioral, and ecological evolution of Cicadoidea from the Mesozoic, emphasizing their adaptive traits and interactions with their living environments.

Mesozoic evolution of large-scale drainage systems in the Indochina Block: evidence from palaeomagnetic and U–Pb geochronological constraints

The collage of the Indochina Block to the Eurasian continent during the Mesozoic resulted in major changes in source-to-sink systems of East Asia, whilst the sedimentation in the Khorat–Simao Basin of the Indochina Block transited from marine to continental environments. Previous studies uncovered the existence of transcontinental river systems in the East Asia mainland during the Cretaceous to Early Cenozoic, although there have been few studies on pre-Cretaceous drainage systems. To determine the impact on the evolution of palaeo-drainage systems triggered by tectonic movement of the Indochina Block, we performed palaeomagnetic and U–Pb geochronologic analyses on the Late Triassic to Early Cretaceous sedimentary rocks in the Simao Basin. Palaeomagnetic data indicate stable Jurassic tectonic environments between the Indochina and Songpan–Ganzi–South China blocks, following their Late Triassic collision. Based on detrital zircon U–Pb dating, the Late Triassic age spectra consist mainly of Phanerozoic components, while the Jurassic to Cretaceous age spectra display more Precambrian age peaks. The contribution of potential provenance to the Simao Basin changed during the Early Cretaceous, suggesting several sedimentary provenance transitions. Also, we believe that large continental-scale drainage systems flowing through the North Qiangtang, Sichuan, Simao and Khorat Basins were sourced from the Songpan–Ganzi Block since the end of the Late Jurassic. Supplementary material: The findings of a quantitative statistical study (Fig. S1; Table S5), the location of the Late Triassic to Early Cretaceous samples from the Simao Basin (Table S1), palaeomagnetic poles for Eurasia, South China, Indochina, North Qiangtang and Tarim (Table S2), the result of quantitative analysis for the Late Triassic and Middle Jurassic sedimentary rocks from the Simao and Sichuan basins (Table S3), and results of zircon U–Pb dating (Table S4) are available at https://doi.org/10.6084/m9.figshare.c.6862918 Thematic collection: This article is part of the Mesozoic and Cenozoic tectonics, landscape and climate change collection available at: https://www.lyellcollection.org/topic/collections/mesozoic-and-cenozoic-tectonics-landscape-and-climate-change

The evolution of the Mesozoic lithosphere of northwestern Neotethys: a petrogenetic and geodynamic perspective

A complex and chaotic assemblage of the north Croatian inselbergs, considered a geological conundrum, is marked by omnipresent ophiolite mélange. This is a vestige of the unbroken formation of the lithosphere in the northwestern segment of Neotethys during the Mesozoic, spanning from the late Anisian to the late Tithonian. In this contribution, we present detailed mineralogical, petrological, geochemical and isotopic data on the mélange collected from 1991 to 2023. These data include the entire normal ophiolite sequence, from mantle tectonites and cumulate ultramafic rocks through cumulate and isotropic gabbro and sheeted dyke complex to massive and pillow lavas with interbedded radiolarian cherts. We found that the continuous development of oceanic lithosphere during the Mesozoic is recorded by seven geochemical groups of ophiolitic rocks, each representing a distinct basalt–gabbro suite. Based on their geochemical and isotopic characteristics, a sequence of petrogenetic processes and tectonomagmatic events has been reconstructed. Proposed geodynamic models that shed light on the Mesozoic evolution of the northwestern segment of Neotethys are consistent with the current geodynamic understanding of the broader Mediterranean region. The similarities in the tectonomagmatic and geodynamic history of NW Neotethyan ophiolites and ophiolites from the Dinaridic–Albanide–Hellenide belts suggest that they evolved together, probably within a single branch of the Neotethys Ocean during Triassic to Jurassic time. Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists

Late Triassic initial closure of the Mongol-Okhotsk Ocean in the western segment: Constraints from sedimentological, detrital zircon ages and paleomagnetic evidence

The Mesozoic evolution of the Mongol-Okhotsk Ocean (MOO) has significantly affected the configuration of the modern Asian continent. Although a scissor-like closure of the MOO has long been proposed, when and how the MOO closed are still hotly debated, especially the timing of initial closure of the MOO in its western segment, hindering our understanding of both the evolution of the MOO and tectonics of the northern Asian continent. In order to uncover the timing of initial closure of the MOO, we performed a multidisciplinary study in sedimentology, detrital zircon U-Pb dating and paleomagnetic on the Late Triassic clastic strata from the Tarvagatay Block and the Amuria Block (AMB) on the both sides of the Mongol-Okhotsk Suture. The upper Triassic strata on both sides of the suture were dominated by plant fossil-bearing alluvial-fluvial facies sediments, which unconformably overlain pre-Triassic geological units, indicating a terrestrial setting after the closure of the MOO. Detrital zircon U-Pb dating results revealed consistent age distribution patterns for samples from both sides of the suture with a predominant peak at ∼253–251 Ma and a secondary peak at ∼359–357 Ma, representing two main arc magmatic events during the bidirectional subduction of the MOO in the Late Devonian-Early Carboniferous and Late Permian-Early Triassic. Coeval Late Triassic paleomagnetic poles were obtained from the northern AMB and Tarvagatay Block, revealing a comparable paleolatitude of the AMB (∼31–33°) and Tarvagatay Block (∼32–34°) in the Late Triassic, arguing for that the western segment of the MOO should have closed at the Late Triassic. The compilation of sedimentology, detrital zircon U-Pb dating, magmatic and paleomagnetic evidence provides integrated constraints on the Late Triassic initial closure of the MOO in its western segment.

Early Cretaceous magmatism in Yunnan traces the tectonic transition from the Tengchong-Baoshan continental collision to Neo-Tethyan slab rollback

Early Cretaceous magmatic rocks of the Tengchong and Baoshan blocks provide insight into the late Mesozoic evolution of southeastern Tibet—Yunnan. We present LA-ICP-MS U-Pb zircon age, zircon εHf(t) isotope, and whole-rock geochemical and Sr-Nd isotopic data for dioritic porphyrite and rhyolite, outcropping in the Eastern Tengchong Belt and the Gaoligong Belt, respectively. The dioritic porphyrite has a 123.0 ± 1.3 Ma (2σ) age, negative whole-rock ℇNd(t) of −1.99 to −2.16, initial 87Sr/86Sr of 0.70690–0.70734, zircon ℇHf(t) of −1.42 to 4.11, and adakitic geochemical features, suggesting an origin from mixing of mantle- and crust-derived magmas; the rhyolite has a 122.2 ± 1.0 Ma age, low whole-rock ℇNd(t) of −9.69 to −8.83, initial 87Sr/86Sr of 0.71104–0.71246, and zircon ℇHf(t) of −8.55 to −2.59, suggesting crustal derivation. Our data—along with the published data—suggest that the Early Cretaceous rocks (140–109 Ma) comprise two magmatic phases with a geochemical and isotopic transition at ∼123 Ma. The 140–123 Ma phase—mainly outcropping in the Gaoligong Belt—is mainly peraluminous, highly silicic, and has negative zircon εHf(t) values, suggesting derivation from remelting of ancient crust in a postcollisional setting; the 123–109 Ma phase is mainly metaluminous, restricted to the Eastern Tengchong Belt, and formed in a continental-arc setting with mantle melt involved. We propose that the ∼123 Ma geochemical and isotopic change marks the transition from contraction due to the Tengchong-Baoshan collision to extension resulting from slab rollback of the Neo-Tethyan lithospheric slab.

Mesozoic evolution of the Pakchon Basin in the NW Korean peninsula: New insights about the evolution of the Mesozoic basins along the eastern margin of the Sino–Korean Craton

Mesozoic evolution of the Pakchon Basin in the NW Korean peninsula: New insights about the evolution of the Mesozoic basins along the eastern margin of the Sino–Korean Craton

Detrital zircon geochronology from the Nueva Segovia Schist, Nicaragua: evidence for the tectonic evolution of the Chortis Block?

Abstract The Chortis Block of Central America is a cratonic-type peri-Gondwanan terrane and is commonly included in Neoproterozoic–Paleozoic palaeogeographical reconstructions. At present, most research has focused on the Mesozoic evolution of the Chortis Block, however, its earlier history remains poorly constrained. As a result, there is considerable debate surrounding the internal complexities of the Chortis Block and its tectonothermal evolution has not been well established by geochronological and geochemical data. New field investigations from the Nueva Segovia Schist (Northern Nicaragua), considered one of the oldest exposed parts of the Chortis Block, reveal it is composed primarily of deformed sequences of greenschist facies marine clastic and chemical sediments in conformable contact with felsic volcanics. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) detrital zircon data from two samples taken from the Nueva Segovia Schist reveal a youngest age peak of c. 250 Ma with other significant peaks at c. 500 Ma, c. 1.0 Ga and c. 1.2 Ga. Taken together with field observations, these data suggest the Nueva Segovia Schist was likely deposited between c. 250 and 110 Ma proximal to Amazonia during the Late Paleozoic, and they support a Precambrian age for the basement of the East Chortis Terrane. Taken together the data support a Pangaean position of the Chortis Block, adjacent to Amazonia inboard of Oaxaquia.

Mid‐Cretaceous Exhumation of the Central Qiangtang Mountain Range Metamorphic Rocks as Evidenced by the Abushan Continental Redbeds

AbstractMetamorphic rocks and surrounding Paleozoic strata in central Tibet compose the core of an anticlinorium associated with the Central Qiangtang Mountain Range. The analysis of Mesozoic strata flanking the anticlinorium provides insights into the geological and landscape evolution of the range, which is important in determining the Mesozoic evolution of central Tibet and the paleo‐elevation of the Tibetan Plateau. Here we present a detailed stratigraphic study of the Shuanghu Conglomerate and over 1‐km‐thick mid‐Cretaceous continental redbeds of the Abushan Formation, which non‐conformably overlie the Qiangtang metamorphic belt. Pollen assemblages and detrital zircon ages along with published magnetostratigraphic results indicate a mid‐Cretaceous depositional age for the Abushan Formation. The Shuanghu Conglomerate is undated but may have been coeval with the Abushan Formation as suggested by foraminiferal assemblages contained within limestone clasts. The Abushan Formation shows a fining‐ and deepening‐upward megasequence, changing from braided river delta‐plain conglomerate and sandstone to lacustrine delta‐plain and delta‐front sandstone, siltstone and carbonate rocks. Both the Abushan Formation and Shuanghu Conglomerate received metamorphic detritus, indicating that the exhumation of the Qiangtang metamorphic belt to the surface took place at or before mid‐Cretaceous time. The lower member of the Abushan Formation contains dominant limestone clasts, whereas quartz, metamorphic, and volcanic clasts increase in percentage up‐section reflecting an unroofing sequence. The stratigraphic, sedimentologic, and provenance evolution suggests that exhumation of the Central Qiangtang Mountain Range metamorphic rocks may have occurred primarily by tectonic extension after the end of a long period of late Mesozoic Lhasa‐Qiangtang convergence.

GEOCHEMISTRY AND FORMATION CONDITIONS OF GROUNDWATER COMPOSITION IN THE AREA OF MESOZOIC SEDIMENTARY COVER IN TATARSTAN

Mesozoic sediments cover an area of 2870 km2. Mesozoic sedimentary rocks are located in the southwestern part of the Republic of Tatarstan. A thick sequence (up to 390 m) are composed of clay with thin (up to 1 m) layers of sandstone and marl. Permian polygenic sulfate-carbonate-terrigenous deposits underlie the Mesozoic massif. They are exposed in the north of the Mesozoic sediment area.The studied area (~5000 km2) is used for farming. There are no large settlements or industrial enterprises there. The paper considers the specific features of Mesozoic and Permian groundwater composition. There is a trend to improving the groundwater quality with time. The reason of this positive trend is a decreasing technogenic impact and depopulation of the territory. The lateral and vertical hydrogeochemical stratification is identified and characterized. Clay predominating in the massif appears to be the reason for the decreasing intensity of water exchange. Hydrolysis, cation exchange and leaching of carbonate and sulfate minerals add to this trend.The groundwater composition varies widely due to these processes and control specific mineralogical and geochemical features of Mesozoic massif (the saturation of organic substance, the presence of opoques, the primary marine ionic-salt compositions in local areas). Groundwater is more mineralized, with a large amount of organic substance, silicic acid, iron, boron and other micro-components in the area of Mesozoic sediment. The groundwater mineralization increases non-linearly to 6.1 g/l (mainly due to sulfates, chlorides and sodium), and the hardness increases to 50.6 mmol/l in the geological section of this area (up to a depth of occurrence 300 m) in areas with downward filtration. The water hardness decreasess to 1.5–3.9 mmol/l at depths of 100–150 m (up to 200 m) in large areas. Vertical zonality (up to a depth of 150 m) is determined mainly by the leaching processes of carbonate and sulfate rocks outside the Mesozoic development area. Mineralization increases almost according to the linear law to 3.5 g/l (mainly due to sulfates, calcium and magnesium), and hardness – up to 37.7 mmol/ l here.The balneological properties of water are determined by the increased contents of organic substances, silicic acid, iron, hydrogen sulfide, as well as waters of the group “without specific components and properties”.

Polyphase deformation of the Youjiang fold-and-thrust belt during the Mesozoic: Implications for the tectonic transition of the South China block

The South China block (SCB) experienced the tectonic transition from the Paleo-Tethys to the Paleo-Pacific tectonic domains during the Mesozoic, but the transition process is hotly debated. The Youjiang fold-and-thrust belt (YFTB), in the interior of the Youjiang Basin in the southwestern SCB, is located in a junction of these two tectonic domains and thus witnessed their tectonic evolution. It also separates the northern thin-skinned structures from the southern thick-skinned structures in the basin. Therefore, the YFTB is an intriguing window into the Mesozoic evolution in the southwestern SCB and the Mesozoic tectonic transition of the SCB. In this study, we conduct structural analysis at the middle of the YFTB and discuss the Mesozoic tectonic transition of the SCB. Four phases of deformation are identified in the YFTB during the Mesozoic. The first phase of deformation (D1) is characterized by a series of conjugate joints, NW–SE trending thrust faults and folds resulting from NE–SW shortening that was related to the collision between the SCB and Indochina block. The second phase of deformation (D2) is manifested by the pre-existing NW–SE striking thrust faults transformed to normal faults and the Late Triassic mafic magmatism. Our structural observations, combined with previous geochronological data for mafic dykes, suggest the study area experienced post-orogenic extension in the Late Triassic. The third phase of deformation (D3), accompanied with the westward subduction of the Paleo-Pacific oceanic plate, is represented by a series of conjugate joints and NE–SW-striking faults formed by NW–SE compression. As a result of the continuous subduction of the Paleo-Pacific plate and its subsequent slab rollback, the fourth phase of deformation (D4) is featured with normal faults, magmatic-hydrothermal activities, and regional mineralization, which are associated with the nearly E–W extension setting. Our study results indicate that, in the Early Mesozoic, the Youjiang Basin was dominated by the Paleo-Tethys domain and then transitioned to the Paleo-Pacific domain. Together with the magmatic lull between the Triassic and the Early-Middle Jurassic identified in the SCB, we propose that the tectonic transition process manifested in the YFTB more likely initiated in the Early Jurassic.

A new model for the segmentation, propagation and linkage of the Tan-Lu fault zone, East Asia

• The Tan-Lu Fault formed by coalescence of two kinematically independent segments. • The northern and southern Tan-Lu faults exhibit contrasting displacement profiles. • The northern and southern Tan-Lu faults propagated in opposite directions. • Southward indentation of the Siberian craton initiated the northern Tan-Lu Fault. • The northern and southern Tan-Lu faults linked in the early Late Jurassic. The Tan-Lu fault zone (TLF) is a major strike-slip fault with a long and complex history in East Asia, whose evolution provides a new perspective on the formation of large-scale faults (>1000 km long). Fault displacement analysis, geological mapping and U-Pb LA-ICP-MS dating have been performed to understand the evolution of the TLF. Along-strike displacement variation reveals that the TLF consists of two kinematically independent segments, the northern and southern TLF, with opposite long-term propagation directions. Structural and geochronological studies in the eastern Yanshan belt, located around the linkage area of the southern and northern TLF, indicates that NNE-trending sinistral strike-slip faults initiated at 167-164 Ma and were reactivated at 124-121 Ma. Structural analysis suggests that these early NNE-trending strike-slip faults transferred sinistral motion along the northern TLF into southward thrusting along the Yanshan belt, representing the Middle Jurassic southern termination of the northern TLF. Our studies suggest that the through-going TLF formed when the younger southward-propagating northern TLF merged with the older northward-propagating southern TLF in the Late Jurassic. A new model is thus proposed for the Mesozoic evolution of the TLF. The initiation and southward propagation of the northern TLF is interpreted to have resulted from the southward indentation of the Siberian craton into the amalgamated Central Asian Orogenic Belt and North China block. The divergent mega-splays of the northern TLF likely resulted from westward-younging formation during the clockwise rotation of northeast Asia. Coalescence of two genetically unrelated faults could be an alternative mode for large-scale fault formation.

Structural Analysis and Paleostress Evolution in the Imiter Silver Mining Region, Eastern Anti Atlas, Morocco: Implications for Mineral Exploration

Development and concentration of many ore deposits at the regional and district scales closely depend on structural geology, especially in polydeformed basements. The superposition of many deformation periods highlights the complexity of the structural context and expected potential location of mineralization zones. The formation and concentration of hydrothermal ore deposits is highly dependent on structural controls. On the NE flank of the Saghro massif (Eastern Anti-Atlas, Morocco), the Imiter silver mining region has been affected by multiple tectonic events since the Precambrian and throughout the Phanerozoic. In this investigation, a structural analysis of the different geological units revealed multi-stage deformation, beginning with the late Pan-African-Cadomian event, and ending with the last Cenozoic exhumation of the area. At least eight tectonic regimes have been identified. The Imiter basement, formed by the Cryogenian-early Ediacaran “flysch-like” Saghro Group, has been folded in low-grade metamorphic conditions, followed by an ENE-WSW brittle compressive event. These deformations occurred before to the early Ediacaran during the compressional and/or transpressional late Pan-African-Cadomian events (600–580 Ma). The unconformably overlaying deposition of the late Ediacaran Ouarzazate Group takes place in a WNW-ESE extensional setting and then involved in a NNW-SSE compressional event that occurred concurrently with a regional exhumation and erosion stages. A similar extensional event appears to have controlled the middle Cambrian sedimentation, the oldest Paleozoic deposits in this area. During the late Carboniferous, Variscan shortening was recorded by NW-SE transpressional deformation responsible for combined dextral strike-slip and southward thrusts. The Imiter silver mining region is part of the Moroccan Sub-Meseta Zone along with Paleozoic inliers of the Skoura and Tamlelt on the southern side of the High Atlas. The Mesozoic evolution began with the Late Triassic NNW-SSW transtensional tectonic regime with a northeast trending CAMP (Central Atlantic Magmatic Province) dyke during the Pangea breakup. Ultimately, the Imiter silver mining region experienced NNW-SSE Atlasic shortening during the uplift of the adjacent High Atlas. Over time, the direction of implemented tectonic stress and its effect on various geological units can elucidate the relationship between tectonism and hydrothermal silver mineralization in the Imiter region. In conclusion, structural analysis and investigation of paleostress development can be one of the most important factors for successful exploration plan and resource recovery in the Imiter region. An analysis of geological structures in determining feasible mineralization zones is crucial for future safe mining operation in the study area and can be extrapolated to other ore mining regions.

Architecture of Eastern Mediterranean sea rifted margins: observations and uncertainties on their Mesozoic evolution

Architecture of Eastern Mediterranean sea rifted margins: observations and uncertainties on their Mesozoic evolution

Mesozoic tectonic transition from the Tethyan to Paleo-Pacific domains in South China: New insights from Mesozoic igneous rocks in the western Nanling Range

• The studied Mesozoic igneous in the Nanling Rang include post-orogenic ultramafic–mafic rock, subduction-related mafic rocks and other calc-alkaline intermediate-felsic rocks. • Those igneous rock assemblages in the Nanling Rang reflect the tectonic transition of the SCB. • The Nanling Rang was a Tethyan domain before ca. 170 Ma but a Paleo-Pacific domain after that. • The Mesozoic evolution of the SCB involved four stages: post-orogenic extension, slab foundering, and tectonic transition from subduction to rollback, followed by slab rollback. Mesozoic tectono-magmatic evolution of the Nanling Range in the South China Block (SCB) remains controversial, especially about the role of the Tethyan and Paleo-Pacific dynamics in the generation of Mesozoic igneous rocks. The Mesozoic magmatic events have produced a diverse variety of rocks, dominantly granites and spatially associated mafic–ultramafic rocks, lamprophyres and diorites. We present new zircon U-Pb ages and in-situ Hf isotope data, along with whole-rock elemental and Sr-Nd isotopic data for the Mesozoic igneous rocks from the western Nanling Range. The two ca. 200 Ma ultramafic–mafic rocks have low SiO 2 contents (40.00–44.94 wt%) and typical ocean island basalt (OIB)-like trace elemental affinities with positive Nb and Ta anomalies, positive ε Nd (t) (4.47 to 4.88) and variable ε Hf (t) values (–3.65 to 11.91), suggesting that they were generated by partial melting of an asthenospheric mantle source. The ca. 165 Ma Jiangyong lamprophyre dyke has relatively high SiO 2 content (51.70 wt%) and arc-like trace elemental affinities with significantly negative Nb and Ta anomalies and variable ε Hf (t) values (–9.10 to 2.65). They were derived from a lithospheric mantle source previously modified by subducted component, along with a contribution from the asthenospheric mantle. Granites from the ca. 146–137 Ma Taibao granitic pluton have high SiO 2 contents (63.41–66.66 wt%), variable (La/Yb) N and Sr/Y values, and negative to positive ε Hf (t) values (−4.16 to 0.86). These granites have compositions transitional from adakite to arc-type rocks and were likely generated by partial melting of Mesoproterozoic meta -igneous rocks, with an addition of a mantle-derived component. Compared with those granites, diorites of the ca. 99 Ma Eryue pluton exhibit moderate SiO 2 contents (59.90–60.30 wt%), a wide range of zircon ε Hf (t) values (−12.04 to 0.50) and negative ε Nd (t) values (–8.61 to –8.57), and they were probably formed by magma mixing of crust-mantle materials associated with back-arc extension. Our new data, together with other geological evidence, provide further insights for the evolution of the Tethyan and Paleo-Pacific tectonic domains during the Late Triassic to Late Cretaceous in the SCB. In the early stage, the Tethyan tectonic domain, ultramafic–mafic rocks from the Ludong and Fuchuan plutons in the Nanling Range was related to the post-orogenic extension. This domain was gradually changed to the Paleo-Pacific domain during the period from Late Triassic to Early Jurassic and the tectonic transition was accomplished at ∼ 170 ± 5 Ma. In the later stage, the Paleo-Pacific tectonic domain, the Jiangyong lamprophyre, Taibao granites and Eryue diorites were produced via the crustal thickening, localized extension, and large-scale lithospheric extension due to the advancing, slab-foundering, and rollback of the oceanic slab during the period from Middle Jurassic to Late Cretaceous.