Geodynamic Processes Research Articles

Determination of the early Paleozoic accretionary complex in Southwestern Yunnan, China: Implications for the tectonic evolution of the Proto-Tethys Ocean

Accretionary complex study provides important knowledge on the subduction and the geodynamic processes of the oceanic plate, which represents the ancient ocean basin extinction location. Nevertheless, there exist many disputes on the age, material source, and tectonic attribute of the Lancang group, located in Southwest Yunnan, China. In this paper, the LA-ICP-MS detrital zircon U-Pb chronology of nine metamorphic rocks in the Lancang group was carried out. The U-Pb ages of the three detrital zircons mainly range from 590–550 Ma, 980–910 Ma, and 1150–1490 Ma, with the youngest detrital zircons having a peak age of about 560 Ma. The U-Pb ages of the six detrital zircons mainly range from 440–460 Ma and 980–910 Ma, and the youngest detrital zircon has a peak age of about 445 Ma. In the Lancang group, metamorphic acidic volcanic rock, basic volcanic rocks, intermediate-acid intrusive rocks, and high-pressure metamorphic rocks are exposed in the form of tectonic lens in schist, rendering typical melange structural characteristics of “block + matrix”. Considering regional deformation and chronology, material composition characteristics, and the previous data, this study thinks the Lancang group may be an early Paleozoic tectonic accretionary complex formed by the eastward subduction of the Changning-Menglian Proto-Tethys Ocean, which provides an important constraint for the Tethys evolution.

Local Moho distribution in the eastern Mediterranean region from gravity inversion: eastern Mediterranean Sea

This study investigates the variations of surface Moho inverted from Bouguer gravity data beneath the northwestern Arabian plate. The results were obtained by applying the 3DINVER program developed in a MATLAB environment using the Parker–Oldenburg method. The calculation results show that the maximum Moho depth observed in the western Arabian shield approaches more than 40 km, while the minimum values of 16–20 km are mainly concentrated beneath the Mediterranean Sea. A key innovation of this study is its implementation of exponential density contrast decrease in the sediment–basement interface in the Syrian part of the Arabian plate. The gravity anomaly of the sediment is computed using a density contrast which varies exponentially with depth, leading to a more accurate representation of the subsurface structure and offering valuable insights into the geodynamic processes and seismogenic potential of the area. To validate the inverted results from the 3DINVER program, the study compares these findings with seismic results that show good agreement with our results from the same region. This leads to a better understanding of the crustal structure and provides insights into its implications for the geodynamic and seismogenic nature of the northwestern Arabian plate—critical for assessing the potential for earthquakes and other geological hazards. The density contrast between the Earth’s crust and mantle can be related to variations in the composition, temperature, and pressure of the rocks. These factors influence the mechanical properties of the crust, ultimately affecting the tectonic processes and seismic activity in the region.

Inferring the Mean Thickness of the Outer Ice Shell of Enceladus From Diurnal Crustal Deformation

AbstractThe thickness of the outer ice shell plays an important role in several geodynamical processes at ocean worlds. Here, we show that observations of tidally driven diurnal surface displacements can constrain the mean ice shell thickness, . Such estimates are sensitive to any significant structural features that break spherical symmetry such as faults and lateral variation in ice shell thickness and structure. We develop a finite‐element model of Enceladus to calculate diurnal tidal displacements for a range of values in the presence of such structural heterogeneities. Consistent with results from prior studies, we find that the presence of variations in ice shell thickness can significantly amplify deformation in thinned regions. If major faults are also activated by tidal forcing—such as Tiger Stripes on Enceladus—their characteristic surface displacement patterns could easily be measured using modern geodetic methods. Within the family of Enceladus models explored, estimates of that assume spherical symmetry a priori can deviate from the true value by as much as ∼41% when structural heterogeneities are present. Additionally, we show that crustal heterogeneities near the South Pole produce differences of up to 35% between Love numbers evaluated at different spherical harmonic orders. A ∼41% range in estimates of from Love numbers is smaller than that found with approaches relying on static gravity and topography (∼250%) or analyzing diurnal libration amplitudes (∼85%) to infer at Enceladus. As such, we find that analysis of diurnal tidal deformation is a relatively robust approach to inferring mean crustal thickness.

The Sr, Nd, Pb and Hf isotopes and crystallization conditions of the middle Eocene Dağdibi Pluton in the eastern Sakarya Zone, Turkey

AbstractMagmatic activity in the Sakarya Zone, an important segment of the Alpine orogenic belt, continues intermittently from the middle Carboniferous to Miocene. In this study, we provide geochronological and geochemical data from the Dağdibi Pluton in the eastern Sakarya Zone to present some inferences on the source region and petrogenesis of the middle Eocene magmatism. U–Pb zircon geochronology from two granodiorite samples gives middle Eocene ages of 44.75 ± 0.92 and 45.01 ± 0.59 Ma. The pluton is mainly composed of K-feldspar, plagioclase, quartz, Mg-hornblende/actinolite, Fe–Ti oxides and small amounts of biotite, and secondary chlorite and epidote. Parental magma of the intrusive rocks has a high-K calc-alkaline affinity with metaluminous character. The oxygen fugacity values vary between −18 and −17. The rocks show slightly radiogenic 87Sr/86Sr(i) (0.704845–0.705726) ratios and ϵNdi values between −0.96 and +0.52. Pb–Pb isotope ratios are typical for those of the lower continental crust. ϵHf(i) values of the zircons range from 0.14 to 10.26. The geochemical and isotopic features of the pluton point to a parental magma derived from a depleted mantle that was metasomatized by fluids during previous subduction events. The volumetric abundances of the rock types are decreased as the silica content increase, implying that the fractional crystallization is the most important process during the formation of the present compositional range of the pluton. Amphibole, plagioclase and Fe–Ti oxides are the fractionated phases while K-feldspar is largely accumulated. In the light of the data presented above, slab breakoff is regarded as the geodynamic process responsible for the formation of the Dağdibi Pluton in the middle Eocene.

New insights into the Cretaceous evolution of the Western Amazonian paleodrainage system

The geological history of the Amazon River is a complex story driven by geodynamic processes operating in the South American plate. In spite of recent research, the pre-Neogene structure of Amazon paleodrainage is still underconstrained. A recent study has suggested that the western Amazonian paleodrainage system was reversed, cratonic in origin during the Cretaceous. However, the extent and duration of this system are not well-constrained. To add new constraints, we investigated the sources of Cretaceous sedimentary rocks in the Brazilian Acre and Peruvian Madre de Dios basins, based on major and trace element concentrations, Sm–Nd isotopic compositions, and U–Pb detrital zircon dating. The late Cretaceous samples of the Acre Basin have εNd(0) values between −21.2 and −8.4 and zircon grains derived from terranes situated in the easternmost part of the Amazonian Craton: Ventuari–Tapajos (2.0–1.82 Ga) and Rio Negro–Juruena (1.82–1.54 Ga). In contrast, the Madre de Dios Basin samples have εNd(0) values ranging from −15.2 to −7.1 and a wide range of U–Pb zircon age distributions. The samples from the northern part of the basin (MD234 and MD238) are dominated by zircon ages between 0.9 and 1.3 Ga (Grenville/Sunsás, 30 %–43 %) and 0.5 and 0.7 Ga (Brazilian/Pampean, 26 %–16 %) with felsic provenance. The oldest MD234 sample also shows a dominant contribution from Paleozoic zircon (20 %). On the other hand, the samples from the southern part of the Madre de Dios Basin (samples MD-2019-4A; MD-2019-10; MD-2019-13; MD-2019-11D and MD-2019-12A) have U–Pb age distributions dominated by zircon ages between 0.9 and 1.3 Ga (Grenville/Sunsás, 30 %–45 %) and 1.54 and 1.3 Ga (Rondonia–San Ignácio, 16 %–43 %), pointing to a cratonic origin for these sedimentary rocks. To elucidate the distinction in provenance between the samples from the northern and southern parts of the Madre de Dios Basin, we suggest that a structural barrier (the Madidi Arch (?)) was active during the late Cretaceous. In this scenario, the northern part of the Madre de Dios Basin had similar sedimentary sources as the nearby basins like Huallaga, Bagua, Ucayali, and Marañón, whereas, in the southern part of the basin, sedimentation was influenced by local sources. Together with previously published studies, these data indicate that the continent-wide cratonic drainage developed between the Cenomanian and Maastrichtian in response to the Purus Arch uplift was probably driven by a geodynamic process related to the post-rift opening of the Atlantic Equatorial Ocean.

A geospatial platform for the tectonic interpretation of low-temperature thermochronology Big Data

Low-temperature thermochronology is a powerful tool for constraining the thermal evolution of rocks and minerals in relation to a breadth of tectonic, geodynamic, landscape evolution, and natural resource formation processes through deep time. However, complexities inherent to these analytical techniques can make interpreting the significance of results challenging, requiring them to be placed in their geological context in 4-dimensions (3D + time). We present a novel tool for the geospatial archival, analysis and dissemination of fission-track and (U-Th)/He data, built as an extension to the open-access AusGeochem platform (https://ausgeochem.auscope.org.au) and freely accessible to scientists from around the world. To demonstrate the power of the platform, three regional datasets from Kenya, Australia and the Red Sea are placed in their 4D geological, geochemical, and geographic contexts, revealing insights into the tectono-thermal evolutions of these areas. Beyond facilitating data interpretation, the archival of fission track and (U-Th)/He (meta-)data in relational schemas unlocks future potential for greater integration of thermochronology and numerical geoscience techniques. The power of formatting data to interface with external tools is demonstrated through the integration of GPlates Web Service with AusGeochem, enabling thermochronology data to be readily viewed in their paleogeographic context through deep time from within the platform.

Key geodynamic processes and driving forces of Tethyan evolution

Key geodynamic processes and driving forces of Tethyan evolution

On unusual conditions for the exhumation of subducted oceanic crustal rocks: How to make rocks hotter than models

The thermal structure of subduction zones controls many important processes such as metamorphic devolatilization, arc magmatism, and seismicity. However, the thermal state of subducted oceanic slab predicted by subduction zone thermal models down to ∼80 km depth is systematically cooler than inferred from exhumed metamorphic slab rocks, raising questions about the current understanding of subduction dynamics portrayed by these models. Upon synthesizing previous petrological studies and estimating slab ages of ancient subduction zones from metamorphic terranes, we think that exhumation of subducted oceanic metamorphic rocks is extremely rare and likely requires unusual processes that are not an integral component of normal subduction dynamics. We construct simple numerical scenarios to illustrate how the thermal regime under some unusual conditions at the beginning and ending stages of a subduction margin may deviate from the normal subduction process. At the beginning stage of subduction, a shallow maximum decoupling depth (MDD) between the slab and mantle wedge enables viscous mantle wedge flow to reach a shallow depth, bringing heat to make slab rocks warmer than in a mature subduction zone. At the ending stage of subduction, if subduction cessation is in the form of slab stalling and if the stalled slab is not immediately exhumed, the slab rocks can be warmed up by the heat from the warm mantle wedge and underlying asthenosphere. In either situation, the slab rocks can be much warmer than normal before they are exhumed by other dynamic processes. Observed exhumed rocks are not expected to represent the normal subduction process and should not be directly compared with thermal models that are designed for the normal process. To extract important information about general geodynamic processes from these rocks, we must first understand the processes these rocks went through.

Radon on Mt. Etna (Italy): a useful tracer of geodynamic processes and a potential health hazard to populations

Radon gas and its radioactive daughters have been extensively studied on Mt. Etna, both in local volcanic rocks and in all types of fluid emissions from the volcano (crater gases, fumaroles, mofettes, soil gases, groundwaters). The first measurements date back to 1976 and were carried out both in local volcanic rocks and in the crater plume. Since then, fifty-four scientific articles have been published. The largest majority of them (more than 50%) correlated radon emissions with volcanic activity and/or magma dynamics inside Mt. Etna. Many others were focused on possible correlations between time variations of in-soil radon and tectonic activity. The concentration of radionuclides in Etna volcanic rocks was measured on several occasions in order to set background values of radon parents and to study the dynamics of Etna magmas. Some articles analyzed the concentrations of radon in Etna groundwaters and their temporal changes in relation to volcanic activity. Only a few studies focused on methodological aspects of radon measurements in the laboratory. Finally, in recent years, geoscientists began to analyze the possible negative effects on human health from high concentrations of indoor radon in houses near active faults. The overall results show that, in most cases, it is possible to understand the endogenous mechanisms that cause changes in soil radon release from rocks and its migration to the surface. Several physical models were produced to explain how those changes were correlated with Etna’s volcanic activity, making them potential precursors, especially in the cases of eruptive paroxysms. More complex is the analysis of radon changes in relation to tectonic activity. Indeed, if measurements of radon in soil is now considered a robust methodology for identifying buried faults, radon time variations are not always clearly correlated with seismic activity. This difficulty is likely due to the complex interplay between tectonic stress, magma migration/eruption and gas release through faults. In any case, the potential high hazard for human health due to high concentrations of indoor radon in houses close to faults seems to be a well-established fact, which requires particular attention both from the scientific community and the public health authorities.

Compositional Mixing Characteristics of Separate Gas and Oil Charges into Oil Field Reservoirs

Many reservoirs worldwide received separate charges of primary biogenic gas and oil. In high pressure provinces such as the Gulf of Mexico, the added gas should be in solution if thoroughly mixed. In addition, this biogenic gas is easily differentiated from thermogenic gas by measurement of methane carbon isotopes and gas composition. Consequently, the extent of mixing can be determined with accuracy, and the gas and oil mixing processes depend on specifics of reservoir charging and can lead to multiple outcomes. The conventional expectation is that the biogenic gas always precedes oil entry into the reservoir. Here, chemical evaluation of reservoir fluids coupled with reservoir understanding of several reservoirs establishes that the oil can arrive prior to biogenic gas. Seismic imaging of gas chimneys provides a plausible explanation for how this can occur. In addition, thermodynamic and geochemical evaluation of the reservoir fluids across the reservoir tightly constrains possible mixing processes. Simple reservoir simulation shows that excellent gas and oil mixing can occur over a wide range of conditions provided that the gas charges into the oil column at its bottom (at the oil–water contact). This modeling exhibits simple fluid mechanics expectations for this reservoir charging process. In addition, since the increase of solution gas destabilizes asphaltenes, fluid geodynamic processes are indicated that can lead to redistributions of asphaltenes. Evaluation of gas and oil mixing processes in reservoirs fits within the framework of the powerful new technical discipline, reservoir fluid geodynamics, for subsurface characterization.

Southern Tibetan rifting since late Miocene enabled by basal shear of the underthrusting Indian lithosphere

Syncontractional extension is prominent in present-day Tibet, but its origin remains vigorously debated. Several deep-seated geodynamic processes (e.g., Indian underthrusting, horizontal flow, and mantle upwelling) have been linked to Tibetan rifting. Indian underthrusting is a good candidate because it can well explain why surface rifts are more prominent south of the Bangong–Nujiang suture; however, how Indian underthrusting causes extension is not well understood and lacks observational constraints. Seismic anisotropy, measured by exploiting the birefringence effect of shear waves, can be indicative of the deformation styles within the crust. Here, we unveil the dominant convergence-parallel alignment of anisotropic fabrics in the deep crust of the southern Tibetan rifts using seismic recordings collected from our recently deployed and existing seismic stations. This finding suggests that the strong north-directed shearing exerted by the underthrusting Indian plate is key to enabling present-day extension in southern Tibet.

Rapid quench piston cylinder apparatus: An improved design for the recovery of volatile-rich geological glasses from experiments at 0.5-2.5 GPa.

The accurate and precise determination of the compositions of silicate glasses formed from melts containing volatile components H2O and CO2 recovered from high-pressure, high-temperature experiments is essential to our understanding of geodynamic processes taking place within the planet. Silicate melts are often difficult to analyze chemically because the formation of quench crystals and overgrowths on silicate phases is rapid and widespread upon quenching of experiments, preventing the formation of glasses in low-SiO2 and volatile-rich compositions. Here, we present experiments conducted in a novel rapid quench piston cylinder apparatus on a series of partially molten low-silica alkaline rock compositions (lamproite, basanite, and calk-alkaline basalt) with a range of water contents between 3.5 and 10 wt%. Quench modification of the volatile-bearing silicate glasses is significantly reduced compared to those produced in older piston cylinder apparatuses. The recovered glasses are almost completely free of quench modification and facilitate the determination of precise chemical compositions. We illustrate significantly improved quench textures and provide an analytical protocol that recovers accurate chemical compositions from both poorly quenched and well-quenched silicate glasses.

Decratonised lithosphere associated with mantle plume upwelling in the Singhbhum craton, eastern India based on geophysical and geodynamic perspective

The mode of crustal and lithospheric mantle evolution of cratonic blocks and their subsequent deformation and decratonisation due to regional plate tectonics and continued intraplate geodynamic process, are not well understood. This is especially true for the highly complex Eoarchean Singhbhum craton, located in the eastern part of the Indian shield, which underwent prolonged episodes of intraplate volcanism, mafic dyke intrusions, rifting, collision and widespread sedimentation lasting for over two billion years, leaving behind noticeable imprints in the crust and mantle lithosphere. Our detailed analysis of the geophysical characteristics indicates high crustal velocities and presence of a pronounced metasomatised zone between the depth 14 km and 30 km, which is characterised by drop in Vs from 3.93 km/s to 3.76 km/s. This zone is further followed by 14 km thick high velocity magmatic crust above the Moho. A substantial part of the upper crust has been eroded away from this craton due to thermal-induced uplifting and massive crustal exhumation, caused by the multiple hot mantle plume interactions during Precambrian period, in which mantle potential temperature and pressure reached as high as 1700 oC and 4.4 GPa respectively. This craton is conspicuously associated with highly positive gravity anomalies (up to +10mGal), which are well correlated with high elevation and the location of mafic volcanic suites. It is also characterised by an unusually thin lithosphere (∼ 60-128 km), high Moho temperatures (910°C) and high dose of heat flow (47mW/m2) emanating from the mantle, which conforms with the estimated low effective elastic thickness of ∼30 km. Transient effects of the paleo-thermal anomalies possibly still persist due to periodic rejuvenation of surrounding rift valleys and suture zones. Eventually, this craton now shows geophysical characters of more or less a mobile belt, not of a typical craton. Since, almost 150-200 km thick mantle lithosphere from the bottom has been eroded away from this region due to persistent thermo-geodynamic activities and mantle upwelling induced rise of mantle isotherms, our study does not favour the idea of cratonic stability and preservation of deep continental roots.

U-Pb Neoproterozoic age and petrogenesis of a calc-alkaline shoshonitic lamprophyre from Simdega area, Chhotanagpur Gneissic Complex (Eastern India): Implication for the evolution of the Central Indian Tectonic Zone and Rodinia tectonics

The age of emplacement and geochemistry of the lamprophyres are of tectonic significance as they have potential to unravel global scale geodynamic processes. We present petrology, U-Pb SHRIMP apatite and titanite ages and bulk-rock Sr-Nd isotope data for an unmetamorphosed and undeformed lamprophyre dyke from the Simdega area of the Chhotanagpur Gneissic Complex (CGC) which is a component of the E-W trending Central Indian Tectonic Zone (CITZ), India. The CITZ is a major intercontinental suture which separates the northern Indian and the southern Indian blocks whose polarity of their subduction is a contentious issue. The lamprophyre exhibits a strong porphyritic-panidiomorphic texture imparted by the megacrysts/phenocrysts of mica and amphibole with feldspar, apatite, titanite, zircon and opaques confined to the groundmass. Based on combined mineralogy and geochemistry, the lamprophyre is classified to be of calc-alkaline variety (minette) with shoshonitic affinities. Mg# (70.7–78.2) contents highlight the primitive melt character whereas incompatible trace element ratios exclude crustal contamination and are indistinguishable from those of the subduction-related global as well as Eastern Dharwar craton (southern India) calc-alkaline lamprophyres. U-Pb dating of apatite gave an emplacement age of 944 ± 82 Ma which is indistinguishable, within the error limits, from the U-Pb titanite age of 942.1 ± 5 Ma demonstrating a Neoproterozoic magmatic emplacement age of the lamprophyre synchronous with the Rodinia assembly. Bulk-rock 87Sr/86Srinitial (0.707239 and 0.708910) and ɛNdinitial (-8.9 to -8.3) highlights the involvement of an enriched mantle source. Calculated Paleoproterozoic model ages (Nd depleted mantle) of 2.1 Ga of the lamprophyre are indistinguishable from those of the co-spatial amphibolite dykes. Petrogenetic modeling involving rare earth elements reveals that the derivation of the lamprophyre magma from 2 to 3% partial melting of a mixed garnet (70%) and spinel (30%) lherzolitic mantle source with minor phlogopite. Our study highlights that the western part of the CGC was less affected, relative to the eastern part, by the M3 regional amphibolite grade metamorphic event (ca. 920-880 Ma) and also supports the geodynamic models involving northward-directed subduction of the Southern Indian block under the Northern Indian block.-

TRIPLE MULTIPLICATIVE THERMORESONANCES ON THE SPECTRA OF EXCHANGE INERTIAL RADIATION GENERATED IN NON-EQUILIBRIUM MEDIA WITH CONTACT GAPS IN ENGINEERING, COSMIC, PSEUDO-ELEMENTARY AND BIOLOGICAL SYSTEMS IN COMPLEX SPACE WITH TRIPLET VIOLATION OF ANTISYMMETRY

Calculated ratios that quantitatively describe the properties of resonance triplets of inertial radiation generated in non-equilibrium systems of various scales and levels of organization are given. The multiplicative nature of the energy of resonant components is revealed, which is significantly different from the additive principles of the formation of known triplet structures. The mechanism of triplet violation of the antisymmetry of the complex space is established, which ensures the avoidance of annihilation of the energy created according to the principle of Creatio ex nihilo in the topological contact gaps between the real and imaginary half-spaces. There is a marked dilution of the dominant energy cascades – direct in the imaginary and inverted in the real half-space. The analysis of resonant triads on nuclear and collider spectra was carried out, the components of these spectra were explained and quantitatively calculated. The muon structure of hadrons was confirmed and the parameters of this structure were calculated, as well as the parameters of the collider proton-muon plasma, alternative to the known models of the quark-gluon plasma. The calculation of the spectra of cosmic rays of low, medium, high and ultra-high energies was made, which quantitatively corresponds to natural data. Triple resonances in the spectra of the Sun’s radiation and the spectra of solar and geomagnetic activity were detected and quantified. It is shown that the solar spectrum is significantly different from the blackbody spectrum, and the main periods of the Sun’s activity are determined by resonant triads on the scale of the heliosphere. Calculated parameters of the cold outer photosphere at the periphery of the Solar System, the background microwave radiation of which is usually erroneously attributed to the account of a “relic” from the so-called Big bang. The analysis of resonant triplets on the spectra of acoustic disturbances in technical systems was carried out. Synchronization of gravitational and electromagnetic modes is noted, which leads to dangerous buffeting modes. The relationship between geodynamic, climatic and biological processes on the planet and the activity of cavitation topological gaps on the periphery of the Solar System has been established. The mechanism of contact capillary thermostabilization of the human body was revealed and the multiplicative triplet coronavirus destruction of this mechanism was noted.

Detrital zircon signals of the late Eocene provenance change of the Pearl River Mouth Basin, northern South China Sea

A provenance change driven by tectonic and climatic forcing records the surface geodynamic processes, and is of great significance for our understanding of evolving continental margins. The Paleogene succession in the Pearl River Mouth Basin (PRMB), northern South China Sea (SCS), records the variation of sediment-routing systems and thus can reveal provenance changes and their association with the regional paleogeographic evolution on the South China margin. We use U–Pb ages and the Eu/Eu* anomalies of detrital zircons from Paleogene samples in Huizhou Sag, northern PRMB to reconstruct the sediment-routing system and the crustal thickness of the South China margin, respectively. The results show that from the middle Eocene to the upper Eocene there was a rapid increase in proportion of old-age zircon populations (>200 Ma), reflecting a provenance change from the intrabasinal Mesozoic basement to the extrabasinal South China Block. Moreover, the Eu/Eu* anomalies in detrital zircons suggest that during Cretaceous the crustal thickness increased from ca. 40 km to ca. 70 km in the South China margin, corresponding to the uplift of the extensive Coastal Mountains along the South China margin. The substantial rock uplift is believed to be related to the subduction between the Cretaceous Izanagi Plate and the South China Block. A new paleogeographic pattern is reconstructed, where we relate the late Eocene provenance change to the relief generated by the Cretaceous orogenic event. Firstly, due to the rain shadow effect, the uplift of the Coastal Mountains prevented pacific air from reaching into the South China hinterland, causing the northwestern side of the Coastal Mountains to be arid whereas the southeastern side being humid. Then, on the humid southeastern foothills, the paleo-Pearl River originated from the Late Cretaceous to the middle Eocene and transported more and more sediments from the South China Block to PRMB since the late Eocene, causing the provenance change from the intrabasinal basement to extrabasinal South China Block.

Late Oligocene Orogen‐Scale Tilting in Northern Tibet: A Response to Northward Injection of the Tibetan Lower Crust?

AbstractThe East Kunlun Shan (EKLS) in northern Tibet occupies boundaries of the low‐relief topography and lower crustal low‐velocity zone in the interior plateau, making it ideal for exploring the relationship of surface deformation with underlying geodynamic processes. We used previous and new apatite (U‐Th)/He data to analyze the exhumation history and pattern throughout the EKLS and link surface deformation to deep structures. Integrated (U‐Th)/He ages reveal the rapid exhumation at 27–25 Ma, due to the coeval orogen‐scale tilting of the EKLS. Along with the crustal structures beneath the EKLS, it is inferred that orogen‐scale tilting is the isostatic response of the nonuniform crustal thickening related to northward injection of the Tibetan lower crust. This study highlights the role of ductile deformation within the lower crust in mountain building in northern Tibet, which shares a similarity with mountain building pattern in the eastern plateau margin.

Cenozoic Uplift and Volcanism of Hangai Dome, Central Mongolia Triggered by Lower Mantle Upwellings

AbstractThe mechanisms of surface uplift of Hangai Dome (>2 km) and formation of Cenozoic intraplate volcanism in central Mongolia remain vigorously debated. Here we directly investigate the mantle transition zone (MTZ) structure beneath central Mongolia to explore whether the deep mantle geodynamical processes have played a role. Our results reveal significant MTZ thinning of 8–13 km in three subareas mainly caused by the uplifted 660‐km discontinuity (∼10 km). In addition, the 410‐km discontinuity is depressed beneath the Hangai Dome (∼6 km) and the northern portion of the study area (10–15 km). These observations provide direct evidences for intracontinental mantle upwellings from the lower to the upper mantle, causing the Cenozoic uplift and basaltic volcanism of central Mongolia. Furthermore, these mantle upwellings are relatively sluggish compared to canonical mantle plumes based on the small magnitude of MTZ thinning and thus relatively moderate thermal anomaly within the MTZ (62–100 K).

Origin of Banded Iron Formations: Links with Paleoclimate, Paleoenvironment, and Major Geological Processes

Banded iron-formations (BIFs) are marine chemical sedimentary rocks composed of siliceous and ferric materials, usually with typical thin layers or sheet structures. BIFs not only record a wealth of information about the state and evolution of the lithosphere, atmosphere, hydrosphere, and biosphere but also host the majority of the economic iron resources in the world. Here, we summarize the types, mineralogical, and geochemical characteristics of BIFs; analyze their formation conditions, their oxidative mechanism, and the absence causes of BIFs; and elucidate the associations between BIFs and major atmospheric oxidation events (Paleoproterozoic great oxidation event (2.4~2.1 Ga) and Neoproterozoic oxidation event (0.8~0.55 Ga)). BIFs are intimately associated with enhanced submarine magmatic–hydrothermal activities. Finally, it is concluded that the deposition and demise of BIFs are closely related to major geological events, and these major geological events interact with each other, jointly constraining the evolution of the atmospheric and marine environment and of geo-biological and geodynamic processes.

Island formation adjacent to a large-scale slope failure in Central Peru: The Nazca Ridge subducted relief hypothesis

Vertical tectonics and mass wasting activity along convergent margins are geodynamic processes commonly associated with the subduction of oceanic plate structures. At the Central Peruvian margin, the connection of the small Hormigas de Afuera Islands (HAI) (12°S) with a large-scale slope failure suggests the surficial expression of the subducted relief of the Nazca Ridge. This hypothesis is supported by the idea that the Tuamotu Ridge relief on the Pacific Plate is the analog of the subducted roughness of the Nazca Ridge based on their mirror-image location relative to the East Pacific Rise. Here, we use bathymetry, multichannel seismic data, subbottom profiling data and published findings to analyze the massive slope collapse near the HAI. At the shelf break, the HAI reflect uplift of the metamorphic basement and mark a N-S transition between post-Pliocene onlapping sediments and seafloor erosion of an uplifted, tectonically deformed sequence. W of the shelf break, the HAI scar is a trench-parallel, two-horseshoe-shaped escarpment in the upper slope (1300 m high and 1690 km2 area) that has lost mass with a total volume of 810 km3. Within this large escarpment, two cliffs show differences in size, seafloor morphology, and basement uplift. An embayment at the base of the HAI scar aligns with a downslope mass of 285 km3 volume in the middle slope. A bathymetric bulge of 800 m height characterizes the toe of this mass deposit. When the HAI are projected onto the Tuamotu Ridge northeastern flank, a seamount-shaped platform-like feature of 12,000 km3 is found. Our study area coincides with the well-known and highly coupled segment of the Central Peru subduction, which suggests an association with the history of large megathrust earthquakes in this area such as the great 1746 MW 8.8 Callao-Lima earthquake. Based on these findings, we postulate that the formation and spatial association of the small HAI with the HAI mass wasting result from the tectonic control imposed by the subducted roughness of the Nazca Ridge.