Late Triassic Jurassic Research Articles

Sauropodomorph evolution across the Triassic\u2013Jurassic boundary: body size, locomotion, and their influence on morphological disparity

Sauropodomorph dinosaurs were the dominant medium to large-sized herbivores of most Mesozoic continental ecosystems, being characterized by their long necks and reaching a size unparalleled by other terrestrial animals (> 60 tonnes). Our study of morphological disparity across the entire skeleton shows that during the Late Triassic the oldest known sauropodomorphs occupied a small region of morphospace, subsequently diversifying both taxonomically and ecologically, and shifting to a different and broader region of the morphospace. After the Triassic–Jurassic boundary event, there are no substancial changes in sauropodomorph morphospace occupation. Almost all Jurassic sauropodomorph clades stem from ghost lineages that cross the Triassic–Jurassic boundary, indicating that variations after the extinction were more related to changes of pre-existing lineages (massospondylids, non-gravisaurian sauropodiforms) rather than the emergence of distinct clades or body plans. Modifications in the locomotion (bipedal to quadrupedal) and the successive increase in body mass seem to be the main attributes driving sauropodomorph morphospace distribution during the Late Triassic and earliest Jurassic. The extinction of all non-sauropod sauropodomorphs by the Toarcian and the subsequent diversification of gravisaurian sauropods represent a second expansion of the sauropodomorph morphospace, representing the onset of the flourishing of these megaherbivores that subsequently dominated in Middle and Late Jurassic terrestrial assemblages.

Early mesozoic arc–back-arc system in the leading edge of the Tibetan Plateau

The southern Lhasa subterrane is the leading edge of the Tibetan Plateau and preserves important records of the Neo-Tethyan oceanic subduction and India–Asia collision. However, the early tectonic evolutionary history of the Neo-Tethyan oceanic subduction remains unclear. Here we present results from a systematic study on the early Mesozoic (Middle Triassic–Late Jurassic) magmatic and sedimentary rocks in the southern Lhasa subterrane. These rocks are distributed zonally along the southern and northern parts of the subterrane, and have been classified into the north and south belts. The magmatic rocks in the north belt show a back-arc basin affinity, with accreted bimodal volcanic sequence and sediments from central and southern Lhasa subterranes, whereas the magmatic rocks in the south belt reveal typical magmatic arc characteristics. The sediments were derived from southern Lhasa subterrane, without the input of clastic components from the central Lhasa subterrane. Based on geochronological, geochemical, and sedimentary records from both belts, we conclude that the early Mesozoic magmatism was triggered by the northward subduction of the Neo-Tethyan oceanic slab, and its initial subduction likely occurred before the Middle Triassic (ca. 240 Ma). During the Early–Middle Jurassic (ca. 193–165 Ma), a short-lived episode of back-arc extension, we attribute to roll-back of the subducting Neo-Tethyan slab, resulted in the single magmatic arc that existed during the early stages (ca. 240–194 Ma) and evolved gradually into an arc–back-arc system. The north belt represents a back-arc basin setting associated with a continental arc, whereas an intra-oceanic and continental (island) arc simultaneously developed in the south belt, and both these belts were possibly generated under the same subduction system.

Rapid Initial Morphospace Expansion and Delayed Morphological Disparity Peak in the First 100 Million Years of the Archosauromorph Evolutionary Radiation

Adaptive radiations have played a major role in generating modern and deep-time biodiversity. The Triassic radiation of the Archosauromorpha was one of the most spectacular vertebrate radiations, giving rise to many highly ecomorphologically varied lineages—including the dinosaurs, pterosaurs, and stem-crocodylians—that dominated the larger-bodied land fauna for the following 150 Ma, and ultimately gave rise to today’s > 10,000 species of birds and crocodylians. This radiation provides an outstanding testbed for hypotheses relating to adaptive radiations more broadly. Recent studies have started to characterize the tempo and mode of the archosauromorph early adaptive radiation, indicating very high initial rates of evolution, non-competitive niche-filling processes, and previously unrecognized morphological disparity even among non-crown taxa. However, these analyses rested primarily either on discrete characters or on geometric morphometrics of the cranium only, or even failed to fully include phylogenetic information. Here we expand previous 2D geometric morphometric cranial datasets to include new taxa and reconstructions, and create an analogous dataset of the pelvis, thereby allowing comparison of anatomical regions and the transition from “sprawling” to “upright” posture to be examined. We estimated morphological disparity and evolutionary rates through time. All sampled clades showed a delayed disparity peak for sum of variances and average nearest neighbor distances in both the cranium and pelvis, with disparity likely not saturated by the end of the studied time span (Late Jurassic); this contrasts with smaller radiations, but lends weight to similar results for large, ecomorphologically-varied groups. We find lower variations in pelvic than cranial disparity among Triassic-Jurassic archosaurs, which may be related to greater morphofunctional constraints on the pelvis. Contrasting with some previous work, but also confirming some previous findings during adaptive radiations, we find relatively widespread evidence of correlation between sampled diversity and disparity, especially at the largest phylogenetic scales and using average displacement rather than sum of variances as disparity metric; this also demonstrates the importance of comparing disparity metrics, and the importance of phylogenetic scale. Stem and crown archosauromorphs show a morphological diversification of both the cranium and pelvis with higher initial rates (Permian–Middle Triassic and at the base of major clades) followed by lower rates once diversification into niches has occurred (Late Triassic–Jurassic), indicating an “early burst” patternsensu lato. Our results provide a more detailed and comprehensive picture of the early archosauromorph radiation and have significant bearing on the understanding of deep-time adaptive radiations more broadly, indicating widespread patterns of delayed disparity peaks, initial correlation of diversity and disparity, and evolutionary early bursts.

Generation potential, distribution area and maturity of the Barents-Kara Sea source rocks

Identification of the source rock potential and distribution area is the most important stage of the basin analysis and oil, and gas reserves assessment. Based on analysis of the large geochemical and geological data base of the Petroleum geology department of the Lomonosov Moscow State University and integration of different-scale information (pyrolysis results and regional palaeogeographic maps), generation potential, distribution area and maturity of the main source rock intervals of the Barents-Kara Sea shelf are reconstructed. These source rocks wide distribute on the Barents-Kara Sea shelf and are characterized by lateral variability of generation potential and type of organic matter depending on paleogeography. During regional transgressions in Late Devonian, Early Permian, Middle Triassic and Late Jurassic, deposited source rocks with marine organic matter and excellent generation potential. However in the regression periods, during the short-term transgressions, formed Lower Carboniferous, Upper Permian, Induan, Olenekian and Late Triassic source rocks with mixed and terrestrial organic matter and good potential. Upper Devonian shales contain up to 20.6% (average – 3%) of marine organic matter, have an excellent potential and is predicted on the Eastern-Barents megabasin. Upper Devonian source rocks are in the oil window on the steps, platforms and monoclines, while are overmature in the basins. Lower Permian shale-carbonate source rock is enriched with marine organic matter (up to 4%, average – 1.4%) and has a good end excellent potential. Lower Permian source rocks distribute over the entire Barents shelf and also in the North-Kara basin (Akhmatov Fm). These rocks enter the gas window in the Barents Sea shelf, the oil window on the highs and platforms and are immature in the North-Kara basin. Middle Triassic shales contain up to 11.2% of organic matter, there is a significant lateral variability of the features: an excellent generation potential and marine organic matter on the western Barents Sea and poor potential and terrestrial organic matter in the eastern Barents Sea. Middle Triassic source rocks are in the oil window; in the depocenters it generates gas. Upper Jurassic black shales are enriched with marine and mixed organic matter (up to 27,9%, average – 7.3%) and have an excellent potential. On the most Barents-Kara Sea shelf, Upper Jurassic source rock are immature, but are in the oil window in the South-Kara basin and in the deepest parts of the Barents Sea shelf.

The prospectivity of the Late Triassic intervals in the outboard Exmouth Plateau, Western Australia

The Exmouth Plateau is a deep-water plateau on the Australian continental margin underlain by 10–15 km of flat-lying, tilted and block-faulted Paleozoic–Mesozoic sedimentary rocks, which were deposited predominantly during periods of extension before continental break-up commenced in the middle Jurassic. The recent acquisition of the Mawson MC3D broadband seismic survey provides a modern, high-quality dataset located ~230 km to the north-west of Dampier, in the outboard Exmouth Plateau, in a relatively under-explored portion of the Northern Carnarvon Basin. The Late Triassic Mungaroo Formation is the primary reservoir target for the majority of the exploration in the Exmouth Plateau to date. A detailed investigation into the reservoir potential and prospectivity of the Mungaroo Formation is possible by utilising this modern dataset. The high-quality data presents a high-resolution view of the Rhaetian carbonate reef platforms and pinnacle reef complexes that are present within the Mawson survey footprint, revealing an under-explored play type within the region. The development of a detailed stratigraphic framework through the Late Triassic–Jurassic, combined with the use of attribute analyses and amplitude versus offset products can help de-risk identified prospects and highlight further prospectivity during the exploration process.

Multi-phase dolomitization and recrystallization of Middle Triassic shallow marine–peritidal carbonates from the Mecsek Mts. (SW Hungary), as inferred from petrography, carbon, oxygen, strontium and clumped isotope data

Abstract Shallow marine to peritidal carbonates of the Triassic Csukma Formation in the Mecsek Mts. of SW Hungary are made up of dolomites, limestones and dolomitic limestones that show evidence of a complex diagenetic history. Integration of petrographic, conventional stable oxygen and carbon isotope, clumped isotope, and strontium isotope data with the paleogeography, paleoclimate, and burial history of the region revealed four major diagenetic stages. Stage 1: The peritidal carbonates were dolomitized penecontemporaneously during the Middle Triassic by refluxing evaporatively concentrated brines. Stage 2: Increasing burial during the Late Triassic–Jurassic resulted in recrystallization of the Kan Dolomite Member in an intermediate burial setting. Stage 3: During the Early Cretaceous seawater was drawn down and circulated through rift-related faults, causing renewed recrystallization of the Kan Dolomite Member as well as dolomitization of the Kozar Limestone Member and the underlying limestones in a deep burial setting, but only in the vicinity of the faults. Stage 4: During the Late Cretaceous and Cenozoic thrusting resulted in tectonic expulsion of basinal fluids and precipitation of multiple saddle dolomite cement phases near the faults. The results of this study imply that the clumped isotope method integrated with other geochemical data can successfully be applied to identify the nature and potential sources of extra-formational diagenetic fluids responsible for dolomitization and recrystallization. This study provides conclusive evidence for multi-phase dolomitization and dolomite recrystallization over several millions of years (Middle Triassic through Early Cretaceous) and several thousands of meters of burial in the Csukma Formation in SW Hungary. Furthermore, this study is the first to identify fault-controlled dolomitization by circulating Cretaceous seawater within Triassic carbonates of central Europe, further supporting the viability of the interpretation of dolomitization by seawater initially drawn down and then geothermally circulated through faults in extensional basins.

Rare Earth Elements Geochemistry and C–O Isotope Characteristics of Hydrothermal Calcites: Implications for Fluid-Rock Reaction and Ore-Forming Processes in the Phapon Gold Deposit, NW Laos

The Phapon gold deposit is located in the northern Laos and the northern segments of the Luang Prabang–Loei metallogenic belt. The lode-gold orebodies consist of auriferous calcite veins in the middle, and the surrounding siderite alteration and hematite alteration zones in red color. This deposit is hosted in Lower Permian limestone and controlled by a NE-trending ductile–brittle fault system, and it is characterized by the wallrock alteration of carbonatization and lack of quartz and metal sulfides. The hydrothermal calcite from auriferous calcite veins and red alteration zone, as well as the wall rocks of limestone and sandstone were selected for rare earth elements (REE) and C–O isotope analyses. The two types of calcite and limestone have generally consistent REE patterns and δEu and δCe values, which are completely different from those of sandstone. Calcites from the auriferous vein show slight light rare earth elements (LREE)-depleted patterns and higher Tb/La and Sm/Nd ratios than the ones from the red alteration zone with slight LREE-enriched patterns. These values indicate that the calcites from the auriferous veins and the red alteration zones are products of homologous fluids, but the former ones are generally likely to form later than the latter ones. The hydrothermal calcites have C–O isotope compositions within the range of marine carbonate, and markedly different from the magmatic or mantle reservoir values. Taking the Y/Ho–La/Ho and Tb/Ca–Tb/La variations into consideration, we believe the hydrothermal calcites could be formed from remobilization and recrystallization of the ore-hosted limestone, and the fluid-wallrock interaction played a major role in the gold mineralization in Phapon. In combination with the regional and local geology, the ore-forming process is suspected to be primarily associated with dehydration and decarbonisation of the Lower Permian limestone and Middle–Upper Triassic sandstones. The Phapon gold deposit could have been formed during the Late Triassic–Jurassic regional dynamic metamorphism driven by Indochina–Sibumasu post-collisional magmatism. A number of features in Phapon are similar to epizonal orogenic deposit, but it is still a unique calcite vein type gold deposit in the Luang Prabang-Loei metallogenic belt.

Post-remagnetisation vertical axis rotation and tilting of the Murihiku Terrane (North Island, New Zealand)

ABSTRACTWe collected palaeomagnetic sample sets from Murihiku Terrane, North Island to constrain its palaeolatitude during the Late Triassic–Jurassic. The majority of the sample host rocks were remagnetised. However, a few samples show a magnetic signal that possibly recorded a primary remanent magnetisation. These samples preliminarily indicate that Murihiku Terrane was located at c. 63°S during the Early Jurassic. The remagnetised samples reveal significant post-remagnetisation tectonic rotation and tilting of the host rocks. We estimated an 83 ± 5 Ma timing of remagnetisation by plotting the palaeolatitude data on the apparent polar wander path of northern Zealandia. Samples from southernmost sites have lower inclination, which we interpret as reflecting eastward post-remagnetisation tilt of this region by 20°. In addition, declination data indicate large-scale post-remagnetisation rotation of Port Waikato and Awakino Gorge areas. This study contributes to the ongoing debate on the age and tectonic origin of oroclines in New Zealand basement.

Origin of the mafic microgranular enclaves (MMEs) and their host granitoids from the Tagong pluton in Songpan–Ganze terrane: An igneous response to the closure of the Paleo-Tethys ocean

The Songpan–Ganze terrane is mainly composed of a Triassic sedimentary sequence and late Triassic–Jurassic igneous rocks. A large number of plutons were emplaced as a result of tectono-magmatic activity related to the late stages of Paleo-Tethys ocean closure and ensuing collision. Granitoids and their hosted mafic enclaves can provide important constraints on the crust–mantle interaction and continental crustal growth. Mesozoic magmatism of Songpan–Ganze remains enigmatic with regard to their magma generation and geodynamic evolution. The Tagong pluton (209Ma), in the eastern part of the Songpan–Ganze terrane, consists mainly of monzogranite and granodiorite with abundant coeval mafic microgranular enclaves (MMEs) (ca. 208–209Ma). The pluton comprises I-type granitoid that possesses intermediate to acidic compositions (SiO2=61.6–65.8wt.%), high potassium (K2O=3.2–4.1wt.%), and high Mg# (51–54). They are also characterized by arc-type enrichment of LREEs and LILEs, depletion of HFSEs (e.g. Nb, Ta, Ti) and moderate Eu depletions (Eu/Eu*=0.46–0.63). Their evolved zircon Hf and whole-rock Nd isotopic compositions indicate that their precursor magmas were likely generated by melting of old lower continental crust. Comparatively, the MMEs have lower SiO2 (53.4–58.2wt.%), higher Mg# (54–67) and show covariation of major and trace elements, coupled with field and petrographic observations, such as the disequilibrium textures of plagioclase and amphibole, indicating that the MMEs and host granitoids were originated from different magma sources but underwent mafic–felsic magma mixing process. Geochemical and isotopic data further suggest that the precursor magma of the MMEs was formed in the continental arc setting, mainly derived from an ancient metasomatized lithospheric mantle wedge.The Triassic granitoids from the Songpan–Ganze terrane show remarkable temporal–spatial-petrogenetic affinities to the counterparts of subduction zones in the Yidun and Kunlun arc terranes, plausibly support a double-sided subduction of the Paleo-Tethys ocean. The mixing mechanism for the formation of the Tagong pluton was likely associated with the break-off of a subducted slab of the Paleo-Tethys ocean, which triggered subsequent upwelling of hot asthenosphere beneath accreted arc fragments and induced lithospheric mantle-derived magmas suffice to underplate and mix with the lower crust-derived felsic magma. Collectively, the late Triassic igneous rocks record significant crustal growth and continental development as response to the final demise of the Paleo-Tethys ocean (ca. 210Ma), and marks the last episode of orogenic magmatism in the Songpan–Ganze terrane after which the region entered into post-orogenic phase of evolution.

Tracking the multi-stage exhumation history of the western Chinese Tianshan by apatite fission track (AFT) dating: Implication for the preservation of epithermal deposits in the ancient orogenic belt

The western Chinese Tianshan, located in the southern domain of the Central Asian Orogenic Belt (CAOB), was originally established by multiple accretion-collision processes in the Paleozoic, and was modified by complicated intracontinental tectonic evolution in the Mesozoic to Cenozoic. Understanding the timing and mechanism of the latter geological processes is critical to unravel the preservation conditions of the epithermal deposits in the western Chinese Tianshan. This work presents new apatite fission track (AFT) data for three mountain ranges (Keguqinshan, Wusunshan and Nalatishan) of the western Chinese Tianshan to track their exhumation history. Our AFT data gave a wide range of ages from 76.8±5.5Ma to 182.3±9.9Ma, and the mean confined fission track lengths are between 9.8±0.5μm and 12.3±0.2μm. The new data, in combination with the thermal history modeling results, allow us to summary three main episodes of exhumation in the western Chinese Tianshan, including the Early Permian (300–280Ma), Late Triassic–Late Jurassic (230–140Ma), and Late Oligocene–Early Miocene (30–20Ma). The first episode may have been caused by terrane accretion-collision in the late Paleozoic, leading to uplift of the Keguqinshan that supplied abundant sediments to form a critical cover of ca. 4km thick on these epithermal deposits. The second episode was likely related to closure of the Mongol-Okhotsk Ocean in the Mesozoic, and an extremely slow exhumation rate (ca. 0.0083mm/y) as well as a moderate erosion of ca. 0.8km thick are estimated. The last episode is regarded to be the result of collision between the Indian Plate and the Eurasia Plate in the Cenozoic, and this significant tectonic event triggered rapid exhumation (up to ca. 0.1mm/y) of the whole region in the western Chinese Tianshan, which removed more than ca. 3.2km pre-Cenozoic sedimentary cover and sent the epithermal deposits to the subsurface level.

New geological and geochronological data of the Placer de Guadalupe uplift, Mexico: a new piece of the Late Triassic–Jurassic Nazas Arc?

Basement exposed in the Placer de Guadalupe–Plomosas uplift in northern Mexico provides important clues for the geologic evolution of the region. The stratigraphic units form stacked thrust sheets of psammitic and calcareous formations, interlayered with magmatic rock. The eastern calcareous and quartzite formations exhibit structures associated with ductile deformation, whereas the upper stratigraphic units only contain structures formed via younger brittle deformation. Porphyry interlayered in the upper Plomosas Formation has a U-Pb zircon age of 171 ± 1 Ma. This age is consistent with its stratigraphic position, interbedded quartzarenites with a maximum depositional age of ~168 Ma. Granite flakes within the Horquilla Formation are dated at 209 ± 3 Ma, and the La Viñata quartzite exhibits a maximum age of ~193 Ma. The Upper Plomosas Formation correlates well with the arc-related Middle Jurassic Nazas Formation of northeastern Mexico, constituting the first report of a Jurassic continental margin arc outcrop in the ‘Central Mexican Gap zone’. We document Late Norian to Bajocian ages for the stratigraphic units cropping out in the Placer de Guadalupe area. The Jurassic age cluster indicates that the Nazas Arc magmatism in the region occurred during the Late Triassic and ended in the Middle Jurassic times. Permian ages previously assigned to these rocks and the occurrence of a Permo–Triassic deformation event have to be dismissed.

Detrital zircon U–Pb ages of Late Triassic–Late Jurassic deposits in the western and northern Sichuan Basin margin: constraints on the foreland basin provenance and tectonic implications

Upper Triassic to Upper Jurassic strata in the western and northern Sichuan Basin were deposited in a synorogenic foreland basin. Ion–microprobe U–Pb analysis of 364 detrital zircon grains from five Late Triassic to Late Jurassic sandstone samples in the northern Sichuan Basin and several published Middle Triassic to Middle Jurassic samples in the eastern Songpan–Ganzi Complex and western and inner Sichuan Basin provide an initial framework for understanding the Late Triassic to Late Jurassic provenance of western and northern Sichuan Basin. For further understanding, the paleogeographic setting of these areas and neighboring hinterlands was constructed. Combined with analysis of depocenter migration, thermochronology and detrital zircon provenance, the western and northern Sichuan Basin is displayed as a transferred foreland basin from Late Triassic to Late Jurassic. The Upper Triassic Xujiahe depocenter was located at the front of the Longmen Shan belt, and sediments in the western Sichuan Basin shared the same provenances with the Middle–Upper Triassic in the Songpan–Ganzi Complex, whereas the South Qinling fed the northern Sichuan Basin. The synorogenic depocenter transferred to the front of Micang Shan during the early Middle Jurassic and at the front of the Daba Shan during the middle–late Middle Jurassic. Zircons of the Middle Jurassic were sourced from the North Qinling, South Qinling and northern Yangtze Craton. The depocenter returned to the front of the Micang Shan again during the Late Jurassic, and the South Qinling and northern Yangtze Craton was the main provenance. The detrital zircon U–Pb ages imply that the South and North China collision was probably not finished at the Late Jurassic.

Constraints on the paleogeographic evolution of the North China Craton during the Late Triassic–Jurassic

This paper reports U–Pb–Hf isotopes of detrital zircons from Late Triassic–Jurassic sediments in the Ordos, Ningwu, and Jiyuan basins in the western-central North China Craton (NCC), with the aim of constraining the paleogeographic evolution of the NCC during the Late Triassic–Jurassic. The early Late Triassic samples have three groups of detrital zircons (238–363Ma, 1.5–2.1Ga, and 2.2–2.6Ga), while the latest Late Triassic and Jurassic samples contain four groups of detrital zircons (154–397Ma, 414–511Ma, 1.6–2.0Ga, and 2.2–2.6Ga). The Precambrian zircons in the Late Triassic–Jurassic samples were sourced from the basement rocks and pre-Late Triassic sediments in the NCC. But the initial source for the 238–363Ma zircons in the early Late Triassic samples is the Yinshan–Yanshan Orogenic Belt (YYOB), consistent with their negative zircon εHf(t) values (−24 to −2). For the latest Late Triassic and Jurassic samples, the initial source for the 414–511Ma zircons with εHf(t) values of −18 to +9 is the Northern Qinling Orogen (NQO), and that for the 154–397Ma zircons with εHf(t) values of −25 to +12 is the YYOB and the southeastern Central Asian Orogenic Belt (CAOB). In combination with previous data of late Paleozoic–Early Triassic sediments in the western-central NCC and Permian–Jurassic sediments in the eastern NCC, this study reveals two shifts in detrital source from the late Paleozoic to Jurassic. In the Late Permian–Early Triassic, the western-central NCC received detritus from the YYOB, southeastern CAOB and NQO. However, in the early Late Triassic, detritus from the CAOB and NQO were sparse in basins located in the western-central NCC, especially in the Yan’an area of the Ordos Basin. We interpret such a shift of detrital source as result of the uplift of the eastern NCC in the Late Triassic. In the latest Late Triassic–Jurassic, the southeastern CAOB and the NQO restarted to be source regions for basins in the western-central NCC, as well as for basins in the eastern NCC. The second shift in detrital source suggests elevation of the orogens surrounding the NCC and subsidence of the eastern NCC in the Jurassic, arguing against the presence of a paleo-plateau in the eastern NCC at that time. It would be subsidence rather than elevation of the eastern NCC in the Jurassic, due to roll-back of the subducted paleo-Pacific plate and consequent upwelling of asthenospheric mantle.

The Mesozoic Tectonic Dynamics and Chronology in the Eastern North China Block

Mesozoic tectonic events in different areas of the eastern North China Block (NCB) show consistency in tectonic time and genesis. The Triassic collision between NCB and Yangtze results in the nearly S-N strong compression in the Dabie, Jiaodong, and west Shandong areas in Middle Triassic-Middle Jurassic. Compression in the Yanshan area in the north part of NCB was mainly affected by the collision between Mongolia Block and NCB, as well as Siberia Block and North China-Mongolia Block in Late Triassic-Late Jurassic. However, in the eastern NCB, compressive tectonic system in Early Mesozoic was inversed into extensional tectonic system in Late Mesozoic. The extension in Late Mesozoic at upper crust mainly exhibits as extensional detachment faults and metamorphic core complex (MCC). The deformation age of extensional detachment faults is peaking at 120–110 Ma in Yanshan area and at 130–110 Ma in the Dabie area. In the Jiaodong area eastern to the Tan-Lu faults, the compression thrust had been continuing to Late Mesozoic at least in upper crust related to the sinistral strike slipping of the Tan-Lu fault zone.The extensional detachments in the eastern NCB would be caused by strong crust-mantle action with upwelling mantle in Late Mesozoic.

Lower Cretaceous strata of the Sonora Bisbee Basin: A record of the tectonomagmatic evolution of northwestern Mexico

Lower Cretaceous strata of the Sonora Bisbee Basin record four discrete Paleozoic and Mesozoic magmatic episodes and indicate a previously unrecognized Early Cretaceous regional tectonic event along the southwestern margin of North America. Strata of the Bisbee Group in the Sonora Bisbee Basin overlie Upper Jurassic strata on an angular unconformity. Cretaceous strata are predominantly continental fluvial deposits. Bisbee Group sandstones are sublitharenites and litharenites rich in paleovolcanic lithic fragments. Detrital-zircon age populations form five main groups—Proterozoic, Early Permian–Early Triassic, Late Triassic–Jurassic, earliest Cretaceous, and late Early Cretaceous (Aptian). U-Pb zircon ages from three types of conglomerate clasts in the Morita Formation match these age groups: (1) Quartzite clasts are dominated by Proterozoic ages; (2) rhyolite clasts are Middle Jurassic (ca. 172 Ma); (3) andesite clasts are earliest Cretaceous (ca. 140 Ma). Proterozoic zircons and quartzite clasts were recycled from strata of the Caborca block, whereas Permian and Mesozoic grains and andesite and rhyolite clasts were derived from volcanic arc rocks to the west and northwest. We identify two separate episodes of Early Cretaceous volcanism recorded in the basin, the first between 145 and 133 Ma and the second beginning ca. 125 Ma and continuing into the Albian. The presence in the Sonora Bisbee Basin of near-source fluvial detritus from the first of these episodes requires either the presence of a continental arc along the North American margin during the earliest Cretaceous or the accretion of similar-aged material to the margin prior to ca. 130 Ma. Neovolcanic zircon grains in the upper part of the Morita Formation record the initiation of volcanism in the Alisitos arc, an Early Cretaceous volcanic arc presently exposed in the Peninsular Ranges of Baja and southern California. Structural, stratigraphic, and detrital-zircon data suggest that a heretofore unrecognized episode of regional shortening, uplift, and incision occurred to the southwest of the study area in the interval 148–130 Ma.

Tectonics changes in NW South American Plate and their effect on the movement pattern of the Boconó Fault System during the Mérida Andes evolution

Abstract The NE–SW trending Merida–Andes fold-and-thrust belt, in the southern boundary of the Maracaibo Block, formed by a collisional event in Late Miocene at the boundary of the Maracaibo Block and Guyana Shield in the northwestern South American plate. The 500 km long, NE–SW striking right-lateral strike-slip Bocono Fault System lies in the Merida–Andes area. Mylonitic fault rocks along the Bocono Fault System developed during pre-Late Miocene-Early Pliocene. Microscopic and mesoscopic structures such as mica fish, asymmetrical porphyroclasts, S–C shear bands, and asymmetrical ductile folds in Bocono Fault mylonite indicate a sinistral movement along the fault. The movement is probably related to pre-collision extensional tectonics that began in the Late Triassic–Jurassic interval, and continued until the Late Cretaceous or Middle Eocene. Following the collision of the Panama Arc and the South American plate in the Late Miocene, and the change from extensional to contractional tectonic regime, the Bocono was reactivated as a dextral fault system.

Review on the monograph Historical Minerageny volumes 1–3, 2005–2008 by N. N. Zinchuk, A. D. Savko, and L. T. Shevyrev; Voronezh State University

A major review of the deposits of mineral resources of all ages and all types on the Earth’s surface has recently been published. Data on the main types of metallic and nonmetallic deposits of the world from the Archean to the Cenozoic are systematized. The huge body of data is of considerable importance both for the comprehensive analysis of mineragenic pro� cesses and for revealing geodynamic trends in the crust and mantle, as well. The material is presented in three volumes. Volume 1 is concerned with a global review of the data on the spatiotemporal distribution of mineral resources; Vol� ume 2 is devoted to the mineral resources of ancient platforms; and Volume 3 comprises a description of deposits in mobile belts (fold regions). The descrip� tions of objects (deposits and their groups) are system� atic, complex, and comprehensive. A convenient hier� archic system is elaborated for easy orientation among the multitude of different objects. The succession of “mineragenic process” (forma� tion of metallic and nonmetallic mineral resources) is considered in two dimensions. The first coordinate— type of geodynamic settings—is expressed in the data arrangement by volumes: the first volume is devoted to global trends in the distribution of deposits; the second volume deals with deposits on platforms; and the third volume concerns deposits in orogenic belts. The sec� ond coordinate is distribution in time according to the basic orogenic epochs: Early Precambrian, Riphean (Late Precambrian), Caledonian (Early Paleozoic), Early Hercynian (Middle Devonian–Early Carbonifer� ous), Late Hercynian (Middle Carboniferous–Middle Triassic), Kimmerian (Late Triassic–Jurassic), Early Alpine (Cretaceous), and Late Alpine (Cenozoic). Voluminous factual material is generalized in the

Variability in fluid sources in the fluorite deposits from Asturias (N Spain): Further evidences from REE, radiogenic (Sr, Sm, Nd) and stable (S, C, O) isotope data

Fluorite deposits in Asturias (Iberian Peninsula, N Spain) are hosted in Permo -Triassic and Paleozoic rocks. The three main districts of Berbes, La Collada and Villabona preferentially occur along the margins of a Mesozoic basin and comprise veins and stratabound mineralization composed of fluorite, barite, calcite, dolomite, quartz and sulphides. Although the geological framework is similar and fluorite dominates in all deposits, variability in sources and processes has led to each area having its own distinctive characteristics. Sr isotope data of fluorite, calcite and barite ( 87Sr/ 86Sr = 0.7080 to 0.7105) are compatible with a mixing between seawater and an evolved groundwater that interacted with basement rocks. Sm/Nd ratios in fluorites from Villabona district provide an isochron age of 185 ± 28 Ma (Late Triassic–Late Jurassic), consistent with other hydrothermal events in the Iberian Peninsula and Europe. The total REE content of fluorite increases from Berbes to Villabona by an order of magnitude (0.4 to 9.3). The La/Lu ratio in fluorites decreases from a mean value of 0.36 in Berbes, 0.17 in La Collada to 0.09 in Villabona indicating a strong fractionation between LREE and HREE. Calculated δ 18O of fluids ranges from 0.3 to + 7.4‰ during barite precipitation, from + 0.8 to + 4‰ during quartz formation and around + 3‰ during carbonate deposition. The δ 34S of barite (+ 17 to + 56‰), is explained by sulphate reduction processes (either thermochemically or bacterially mediated) in a system closed with respect to sulphate. The δ 34S of sulphide (+ 0.6 to − 32‰) is compatible with these processes although bacterial processes must have dominated at Villabona. Organic matter was an important source of C in the fluids especially in Villabona ( δ 13C = − 14.8 to − 2.5‰ in calcites and from − 7.9 to − 2.2‰ in dolomites). Differences in host rock and position within the basin, and the lithology of the basement, seem to have exerted a strong control on the chemistry of mineralizing fluids providing each district with distinctive characteristics.

The Eo-Cimmerian (Late? Triassic) orogeny in North Iran

Abstract The Eo-Cimmerian orogen results from the Late Triassic collision of Iran, a microplate of Gondwanan affinity, with the southern margin of Eurasia. The orogen is discontinuously exposed along the northern side of the Alborz Mountains of North Iran below the siliciclastic deposits of the Shemshak Group (Late Triassic–Jurassic). A preserved section of the external part of the belt crops out in the Neka Valley (eastern Alborz) south of Gorgan. Here the Mesozoic successions (Shemshak Group–Upper Cretaceous limestones) overlay a pre-Jurassic Eo-Cimmerian thrust stack with a sharp unconformity. The stack includes the Gorgan Schists, an Upper Ordovician–Lower Silurian low-grade metamorphic complex, overthrusted southward above a strongly deformed Late Palaeozoic–Middle Triassic succession belonging to north Iran. In the Talesh Mountains (western Alborz), the Shanderman Complex, previously interpreted as an ophiolitic remnant isolated along the Eo-Cimmerian suture, is considered an allochthonous nappe of deeply subducted continental crust. The new evidence for this is the occurrence of previously unknown eclogites dating to the Carboniferous, and probably related to the Variscan history of Transcaucasia. South of the Shanderman Complex, Upper Palaeozoic slates and carbonates occurring below the Lower Jurassic Shemshak Group also record the occurrence of an Eo-Cimmerian metamorphic event. Based on our new data, the Eo-Cimmerian structures exposed in the Alborz appear to be remnants of a collisional orogen consisting mainly of deformed continental crust where no ophiolites are preserved.

Post-Early Cretaceous Mississippi Valley-type Zn-Pb Mineralization in the Bongara Area, Northern Peru: Fluid Evolution and Paleo Flow from Fluid Inclusion Evidence

The Bongara area, northern Peru, contains Zn-Pb mineralization with characteristics typical of Mississippi Valley-type (MVT) systems. The northwest–southeast-trending late Triassic–Jurassic carbonate host rocks of the Pucara Group were locally replaced by early (D1) and late (D2) dolomite. Fluid inclusion microthermometric data from dolomite and sphalerite are typical of MVT ore fluids (78° to 187°C; ~15–23 wt.% CaCl 2 equivalent), and do not show apparent covariation between temperature and salinity. Homogenization temperature data from D1 and D2 dolomite show a decrease from northern (mean Th = 138°C) to central (mean Th = 126°C) to southern areas (mean Th = 102°C), suggesting fluid flow from north to south. Assuming a geothermal gradient of ~30°C/km and an average surface temperature of ~20°C, the lower temperature limits might approximate the ambient host-rock temperatures, whereas the upper temperature limits may represent minimum temperatures of a deeper aquifer, probably at a maximum depth of ~6000 m. The lower temperature limits are also similar to the estimated temperatures if dolomitization and mineralization took place in the Late Cretaceous at ~2000–3000 m depth, probably during the formation of the Peruvian fold and thrust belt near the present day Peru–Ecuador border. Fluid inclusion data show that the fluids in each studied location had relatively uniform temperatures and salinities during dolomitization and mineralization. A significant salinity drop and a slight temperature decrease are observed during late calcite precipitation, suggesting mixing of brines with dilute, cooler fluids.