Tectonic Uplift Research Articles

Multi-wing butterfly effects on catastrophic rockslides

The catastrophic rockslide, which frequently triggers numerous severe disasters worldwide, has drawn much attention globally; however, understanding the initiation mechanism of catastrophic rockslides in the absence of typical single triggering factors related to strong seismic activity or torrential precipitation continues to be challenging within the global scientific community. This study aims to determine the mechanism of the three largest catastrophic rockslides in the eastern Tibetan Plateau, Yigong, Xinmo, and Baige, over the past 20 years using field investigation, remote sensing, and runoff analysis. Instead of the conventional driving factors of heavy rainfall and strong earthquakes, the multi-wing butterfly effects (MWBE) of climatic factors and weak earthquakes are for the first time identified as drivers of the catastrophic rockslide disasters. First, strong tectonic uplift, fast fluvial incision, high-density faults, and large regional water confluence formed the slopes in the critical regime, creating the source conditions of rockslide. Second, the MWBE of early dry-heat events and antecedent rainfall, combined with imminent weak earthquakes, initiated rockslide. Third, the delayed amplified runoff moving toward the sliding surface and lowering the strength of the locking-rock segment constituted the fundamental mechanism of the MWBE on rockslide. The catastrophic rockslide was ultimately inferred to be a nonlinear chaotic process; however, prediction and forecasting of rockslide based on the MWBE in the early stages are possible and essential. This finding presents a new perspective concerning forecasting progressive landslides.

Numerical examination of the geomorphic indicators for lateral fold growth

Fold-and-thrust belts (FTBs) develop widely in and around active orogenic belts on Earth. With the accumulation of structural shortening, thrust-related folds can grow by increasing their amplitudes and lengths, providing insights into the structural evolution of FTBs. Investigations of fold growth patterns and landscape responses through time and space have important implications for hydrocarbon exploration and geo-hazard assessment. Evidence for lateral fold propagation (i.e., increase in length) usually comes from geochronological constraints based on differences in onset timings along strike. However, these traditional methods are time consuming and economically costly. Alternatively, previous studies have proposed the use of geomorphic features to investigate the lateral fold propagation, including spatial variations in the patterns and densities of river channels, the configuration of the topographic profile along the fold crest, and the occurrence of wind gaps. However, such analyses are based on morphological features of present-day landscapes, which still need process-based validations. Here, we conduct a series of landscape evolution models to reproduce fold growth and their associated geomorphic adjustments. Our results show that deflected rivers and inflected fold-crest elevation profile with decreasing gradient are reliable evidence of lateral fold propagation. The location of propagation is in accordance with the distribution of crest-profile slope breaks and the position where river deflection began. Then, we apply these findings to two natural examples located at the deformation fronts of the Tian Shan (NW China). Results suggest that 1) the Kashi anticline has experienced lateral propagation both westwards and eastwards; and 2) that the Yaken anticline has experienced accelerated tectonic uplift as well as eastwards propagation. These findings are supported by the constraints from geochronological dating and quantitative structural analysis. Future work that integrates folding mechanisms may provide novel insights into landscape response to complex deformation in active FTBs.

Structural control on drainage pattern development of the western Taiwan orogenic wedge

AbstractStructural control on drainage patterns has long been suggested to play an important role in the development of fluvial systems, including their map pattern. Along the western Taiwan orogenic wedge, a prominent drainage pattern change is present, from predominantly orogen parallel drainages in the south to river systems that flow perpendicular to the long axis of the mountain belt in the north. Such change likely reflects the temporal evolutionary process as the Taiwan orogen propagates southward. We propose that the flow direction change of river systems is produced by the development of the fold‐and‐thrust belt on the pro‐wedge side of the mountain belt and is facilitated by drainage reorganization that includes abrupt drainage captures and more gradual divide movements, permitting drainage basins to attain a geometrically stable configuration with time. Our observations in Taiwan demonstrate not only how tectonic uplift is effective at modifying river patterns in the early stages of orogenic development but also how time and increased stream power encourage river networks to adjust to more effective patterns in mature mountain belts.

Geological and biotic context of the Plio-Pleistocene evolution of the Caucasus-Caspian Region (Akchagylian transgression)

We discuss geological and biotic aspects of the extensive Akchagylian transgression that occurred in the Caspian region of Eurasia near the Plio-Pleistocene transition, in Piacenzian and Gelasian. It is shown that the onset of the Akchagylian marine sedimentation in Western Turkmenistan (ca. 3.2 Ma) preceded that in the Kura Basin (ca. 3.0 Ma). The position of the upper boundary of the Akchagylian remains uncertain (ca. 2.1 or 1.8 Ma). The analyzed biotic content of the Akchagylian includes molluscs, microfossils (pollen, dinocysts, foraminifers), and mammals. It is noted that specific forms of the Akchagylian aquatic biota co-occur with microfossils that clearly indicate a connection with the World Ocean or related seas. The palynology of the Akchagylian time signals a directed cooling in the Pliocene and Early Pleistocene with several warm and humid epochs. The Akchagylian transgression was preceded by a change of a structural-sedimentary pattern of the region. In the latest Miocene and Early Pliocene, a pre-existed longitudinal tectonic zonation of the Caucasian-Caspian segment of the Paratethys gradually changed into clearly transverse tectonic zonation. The latter was manifested in the tectonic uplift of the Greater Caucasus, its northern piedmonts and the Lesser Caucasus, and in the subsidence of the western parts of the South and Middle Caspian basins. The interplay of longitudinal and transverse tectonic features shaped the configuration of the Akchagylian brackish-water basin and controlled thickness of its deposits. It was the transverse zonation that dominated in the thickness pattern. The increasing role of the transverse zonation in the post-Akchagylian time is manifested in the magnitudes and rates of the Quaternary tectonic uplift. These parameters were calculated based on current heights of the top of the Akchagylian marine deposits in different parts of the basin. The highest magnitudes of uplift are found in the Eastern Caucasus (up to 1980 m on the NE slope and about 2500 m in the axial part) and in the west of the Lesser Caucasus in eastern Turkey (up to 1750 m). The maximum level of the Akchagylian transgression is estimated at 40–50 m above the present level of the World Ocean. We show a low probability of connection of the Akchagylian basin with the Mediterranean Sea or the Persian Gulf, and a high probability of its connection with the Arctic Ocean through the northern tributaries of the Kama River and the Pechora Basin in the NE of East European Plain.

Magnetostratigraphy of the Tuotuohe Formation in the Tuotuohe Basin, Central-Northern Tibetan Plateau: Paleolatitude and Paleoenvironmental Implications

Paleolatitude evolution could provide a general paleo-location framework for explaining the paleoclimate change and tectonic deformation in geological time. Strengthening the paleolatitude study of the Tuotuohe Basin is important for understanding the history and mechanism of the tectonic uplift process in the north-central Tibetan Plateau. In this study, we introduced the magnetostratigraphy for the Tuotuohe-D (TTH-D) section in the Tuotuohe Basin, central-northern Tibetan Plateau, in order to constrain the chronology and to reconstruct the paleolatitude of the basin during the deposition of the Tuotuohe Formation. The results indicated that the Tuotuohe Formation in the TTH-D section was deposited between 38.5 and ~36.7 Ma. Combining this age with the results from the Tuotuohe section indicates that the age of the Tuotuohe Formation spans the interval from >38.5 Ma to ~33 Ma. Additionally, other paleomagnetic data of the Tuotuohe Formation from the Tuotuohe section, combined with the data from this study, indicate that the paleolatitude of the Tuotuohe Basin during the late Eocene was 25.9 ± 4.2°. That means that the Tuotuohe Basin was located in a subtropical anticyclonic zone and that the paleoenvironment during the late Eocene might be controlled by subtropical high pressure. Additionally, paleomagnetic results from the Qiangtang terrane and the bordering regions are combined with the results of our study, which suggest that the paleolatitude of the Tuotuohe Basin at ~26 Ma coincides well with the Eurasian apparent polar wander path for that interval, and that the N-S India–Asia convergence was reduced or ceased at ~26 Ma in the Tuotuohe Basin.

Stratigraphic and Paleoenvironmental Studies on the Lower Eocene Succession at El-Guss Abu Said Plateau, Farafra Oasis, Western Desert, Egypt

Abstract The Lower Eocene Succession at El-Guss Abu Said Plateau was examined to determine the paleoenvironments and nature of deposition based upon benthic foraminiferal biofacies. Lithostratigraphically, this succession consists of the Esna Formation (shale) at the base, the Nusf Formation (well-bedded marl with occasional limestone ledges), and the Farafra Formation (limestone) at the top. The Esna Formation is an outer shelf-upper bathyal facies rich in planktonic and deeper-dwelling smaller benthic foraminifera. The Nusf Formation and the Farafra Formation are rich in Nummulites and Alveolinids, indicating a carbonate platform facies. Three benthic foraminiferal biofacies, combined with the lithology of the rock units, indicate progressive shoaling, likely associated with tectonic uplift that occurred during the early Eocene in the El-Guss Abu-Said area.

High altitude Pliocene to Pleistocene vegetation and climate change of the Kunlun Pass Basin, NE Tibetan Plateau

The world largest alpine permafrost region, the Tibetan Plateau, will experience amplified warming under global climate change scenarios. Studying its environmental evolution in the geological past is crucial to further our understanding of mechanism and thresholds of climate change. Here we present a 3.5-million-year-long, high-altitude vegetation and climate record from the Kunlun Pass Basin to reconstruct the transition from the sustained warm, high carbon dioxide environment of the Pliocene to the cool glacial and interglacial periods of the Pleistocene, 4.31 to 0.85 million years (Ma) ago. The Early Pliocene pollen record indicates the occurrence of patches of broadleaved and coniferous forests in a semi-desert shrubland at this high-altitude site. Pollen derived quantitative climate estimates based on modern pollen rain transfer functions suggest a moister climate before 4.0 Ma with mean annual temperatures (MATs) > 14 °C warmer than today. The retreat of broadleaved and coniferous forests from the Kunlun Pass Basin area is linked to stepwise cooling at ∼4.0 Ma and during the Plio-Pleistocene transition between 2.7 and 2.6 Ma. Pollen derived climate estimates and Δ47-palaeothermometry indicate an abrupt cooling of ∼4–8 °C resulting in the onset of permafrost condition on the Tibetan Plateau after 2.7 Ma. An expansion of Chenopodioideae dominated xerophytic shrublands after 3.8 Ma and 2.15 Ma indicates a reduction in precipitation on the NE Tibetan Plateau, which appears to be linked to a weakening of the East Asian Summer Monsoon at the Plio-Pleistocene transition. The reconstructed cooling at the Kunlun Pass Basin site reflects the regional expression of global climate change with high-elevation temperature amplification hence rejecting the notion of a major tectonic uplift of the Tibetan Plateau during the Plio-Pleistocene.

Palaeoenvironmental Evolution Based on Elemental Geochemistry of the Wufeng-Longmaxi Shales in Western Hubei, Middle Yangtze, China

The organic-rich shales found in the Wufeng–Longmaxi Formation are typically deposited in oxygen-deficient reducing environments. One of the primary sources of debate revolves around the question of whether the anoxic bottom water found in these shales is either euxinic or ferruginous, and this matter remains unresolved. Previous studies have mostly focused on the Wufeng–Longmaxi Formation as a whole in order to understand the key factors that control organic matter accumulation (OMA). However, research on OMA for each member, including the Wufeng Formation (WF), the lower Longmaxi Formation (LLM), and the upper Longmaxi Formation (ULM), has been insufficient. This paper aims to investigate the palaeoenvironmental conditions and OMA mechanisms of the Wufeng–Longmaxi shales in western Hubei by integrating data on total organic carbon (TOC) content, mineral compositions, major and trace elements, and iron speciation. The results indicate that the Wufeng–Longmaxi shales were deposited under highly restricted hydrographic conditions, except for relatively open and upwelling conditions in the upper WF. Silica in the upper WF was primarily biogenic origin and not hydrothermal. Ferruginous conditions were the primary redox conditions for organic-rich shales except for minor formations in the lower LLM that were deposited under euxinic conditions. Due to the tectonic uplift caused by the Kwangsian Orogeny in the upper LLM, the palaeoenvironment was characterized by a warmer and wetter climate, high terrigenous influx, oxic conditions, and low productivity as the result of the insufficient nutrients caused by the weak upwelling, leading to the turnover of graptolite biozones from LM5 to LM6. The factors influencing OMA changed vertically. TOC contents have a highly positive correlation with Al content, indicating that terrigenous influx was the main factor affecting OMA in the WF, which significantly differed from patterns found in other regions. This suggests that the sedimentation rate of organic matter was higher than the terrigenous dilution rate during the WF stage. The combination of redox conditions and productivity were the main factors affecting OMA in the LLM, while terrigenous influx was the key factor controlling OMA in the ULM, resulting in the dilution of organic matter. Regions in the eastern Yiling block, which are close to the Qinling Ocean, show better prospects for shale gas exploration. This research will further facilitate the development of shale gas in this area.

Causes of permanent vertical deformation at subduction margins: Evidence from late Pleistocene marine terraces of the southern Hikurangi margin, Aotearoa New Zealand

Theoretical studies of the seismic cycle at convergent plate boundaries anticipate that most coseismic deformation is recovered, yet significant permanent vertical displacement of the overriding plate is observed at many subduction margins. To understand the mechanisms driving permanent vertical displacement, we investigate tectonic uplift across the southern Hikurangi subduction margin, Aotearoa New Zealand, in the last ∼200 ka. Marine terraces preserved along the Wellington south coast have recently been dated as Marine Isotope Stage (MIS) 5a (∼82 ka), 5c (∼96 ka), 5e (∼123 ka) and 7a (∼196 ka) in age. We use these ages, together with new reconstructions of shoreline angle elevations, to calculate uplift rates across the margin and to examine the processes responsible for their elevation. The highest uplift rate—1.7 ± 0.1 mm/yr–and maximum tilting—2.9° to the west–are observed near Cape Palliser, the closest site to (∼50 km from) the Hikurangi Trough. Uplift rates decrease monotonically westward along the Palliser Bay coast, to 0.2 ± 0.1 mm/yr at Wharekauhau (∼70 km from the trough), defining a gently west-tilted subaerial forearc domain. Locally, active oblique-slip upper-plate faults cause obvious vertical offsets of the marine terraces in the axial ranges (>70 km from the trough). Uplift rates at Baring Head, on the upthrown side of the Wairarapa-Wharekauhau fault system, are ∼0.7–1.6 mm/yr. At Tongue Point, uplift on the upthrown side of the Ōhāriu Fault is 0.6 ± 0.1 mm/yr. Dislocation and flexural-isostatic modelling shows that slip on faults within the overriding plate—specifically the Palliser-Kaiwhata Fault and the Wairarapa-Wharekauhau fault system—may dominate uplift in their immediate hanging walls. Depending on their slip rate and geometry, slip on these two upper-plate fault systems could plausibly cause >80% of late Pleistocene uplift everywhere along the south coast of North Island. Our modelling suggests that subduction of the buoyant Hikurangi Plateau contributes uplift of 0.1–0.2 mm/yr and uplift due to sediment underplating at Tongue Point and Wharekauhau is likely ≤0.6 mm/yr but could be significantly lower. Earthquakes on the subduction interface probably contribute ≤0.4 mm/yr of late Pleistocene uplift, with ≤10% of uplift due to each earthquake being stored permanently, similar to other subduction zones. These results indicate a significant contribution of slip on upper-plate faults to permanent uplift and tilting across the subduction margin and suggest that in regions where upper-plate faults are prevalent, strong constraints on fault geometry and slip rate are necessary to disentangle contributions of deeper-seated processes to uplift.

Deep‐water sedimentary systems and tectono–sedimentary interactions on the oblique convergent margin in Antarctica

ABSTRACTActive continental margins are tectonic sites with complex sedimentary processes. Tectono–sedimentary interactions occur over geological time and determine the modern morphology of the margin. However, such interactions have been poorly documented in high‐latitude regions. This study focuses on deep‐water sedimentary systems on the South Shetland convergent margin, which is the only remaining active continental margin in Antarctica. Numerous gullies, 20 canyons and three contourite drifts are identified by interpreting bathymetry, oceanography and reflection seismic data. Heavy mineral contents of a gravity core, located at a downslope elongated mounded drift, show the asynchronous interplay of downslope and alongslope processes. The rest of the margin is dominated by turbidity currents. Variations in the slope gradient control thalweg profiles and sinuosity of canyons. Tectonic‐related morphology restricts the distribution of contourite drifts. Earthquakes triggered by underplating and tectonic compression may induce slope instability at the lower flank of the plastered drift. Tectonic uplift influences the amount of sediments transported by ice sheets and controls the shelf stacking pattern. The mixed turbidite–contourite system transitions to separated canyon and drift systems from passive to active continental margins under the influence of the tectonic‐related morphology. A systematic comparison has been made among several convergent margins with similar tectonic settings. Results suggest that submarine canyons on these shelf‐slope systems have similar morphological features and are comparable in size. Coarse sediment input and steep continental slopes (mean slope 7 to 10°) control the canyon morphology on these margins. Therefore, this research has important implications for furthering the current understanding of sedimentary systems on high‐latitude convergent margins and tectono–sedimentary interactions.

Paleohistology of Caraguatypotherium munozi (Mammalia, Notoungulata, Mesotheriidae) from the early late Miocene of northern Chile: A preliminary ontogenetic approach.

The Miocene Caragua fossil fauna in northern Chile contains a considerable number (7) of articulated partial skeletons tentatively assigned to Caraguatypotherium munozi (Notoungulata, Mesotheriidae), which presents up to 40% body size difference. Since either inter- and intra- specific wide size range has been observed in the Mesotheriidae family in general, we wanted explore the ontogenic stage signature of the sample, by carrying out the first comprehensive paleohistological description of the appendicular system in Notoungulata. Results show that: 1) they can be classified as subadults and adults, based on the presence of bone tissues typical of ceased somatic growth; 2) there is a notorious inter-skeletal variation on bone growth rates (skeletal modularity), particularly, the humerus showed a slower diameter growth and less remodelling than the femur, resulting as a better element for ontogenetic analyses; 3) marked cyclical growth is observed, characterised by fast early ontogenic continuous growth, and subsequent fast/slow stratified bone tissue layering. In general, such growth pattern suggests that C. munozi had a similar ontogenetic growth process as other modern mammals, that it should also be influenced by other sex-related, ecological and environmental factors. Likely related to the presence of rapid climatic variations, due to orogenic uplift and concomitant re-organization of the drainage processes along the western tectonic front of the Central Andes at that time.

An Integration of Geophysics and Petrophysics in Study of Rock at Elete, Lokoja Southwestern Nigeria

Granitic Gneiss and Banded Gneiss make up the bulk of the local rock types, and quartz veins are the most common intrusions seen there. Tectonic upheavals in the earth's crust are responsible for the region's structural features, including as foliations, folds, joints, and fissures. The goal of this research is to integrate several scientific techniques to subsurface structure definition. For this study, 16 Vertical Electrical Sounding (VES), petrophysical study, and background knowledge of geology were used to delineate subsurface rock. The Schlumberger array with a maximum electrode separation of 300m was employed for VES. Elete's true aquifer resistivity map shows that the South-Eastern and North-Eastern axis has relatively low resistivity values, which may indicate the presence of an aquiferous zone, while the North-Central and Southern regions have a wider range of resistivity values, which may not be consistent with a water-bearing zone. Additionally, petrographic analysis of the rock reveals that the mineral composition of Granitic Gneiss is Quartz (41.72%), Plagioclase (10.79%), Biotite (25.17%), Muscovite (19.42%), and Opaque (2.87%). While biotite makes up the granite gneiss. Biotite (45%), Muscovite (9.93%), Quartz (36.87%), Plagioclase (4.26%), and Opaque (3. 55%).Hydrogeologically, it stands to reason that Elete and its surroundings are situated in a region with medium to good groundwater potential based on the information at hand and the results of the geophysical investigation. Weathered/fractured basements are anticipated to contain productive aquifers.

The vertical velocity field of the Tibetan Plateau and its surrounding areas derived from GPS and surface mass loading models

Obtaining a precise velocity field of the Earth's surface is critical for probing Earth's tectonic movements. In this contribution we construct a precise vertical velocity field with high-spatial resolution for the Tibetan Plateau (TP) and its surrounding areas using both 113 continuous and 969 campaign GPS time series over the period 2008 to 2019. Specifically, we compared the statistical distribution of residual continuous GPS time series to find the optimal regional surface mass loading (SML) models. The optimal modeled nontectonic displacements were used to correct these campaign GPS time series to reduce their scatter and accordingly improve the precision of the uplift rate estimates. The results showed that we could reduce the root mean square (RMS) on the vertical coordinate time series by more than 75% of the campaign GPS stations. We computed and removed vertical deformation due to horizontal strain rates obtained from GPS time series, and discussed dynamic sources (mantle dynamic topography, isostatic adjustment, and flexural loading) that drive the residual vertical tectonic motion. The study presents the most recent surface kinematic constraints for comprehending the dynamic sources of tectonic uplift or subsidence between and within tectonic units.Plain Language Summary: Movements of the Tibetan Plateau (TP) have a profound impact on adjacent areas. We collected all available GPS data to determine a precise vertical velocity field with high-spatial resolution. We make use of optimal surface mass loading (SML) models to improve estimation accuracy of campaign GPS stations, including an estimate of the vertical movement caused by the horizontal tectonic motions. We combine geological and geophysical data with our vertical velocity field to understand the dynamic sources of uplift or subsidence between and within tectonic units of the TP.

Shaping the Huara Intrusive Complex in the Hyperarid Atacama Desert—Erosional Near‐Stasis Contrasting High Topographic Gradients

AbstractThe Atacama Desert is one of the driest and oldest deserts on Earth, with extremely low precipitation rates (<2 mm/yr). Mostly abiotic hyperarid environmental conditions prevail, and surface processes act at extremely low rates over the long‐term. To gain knowledge about the rate of surface processes and age of landscapes in desert environments, terrestrial cosmogenic nuclide derived erosion rate estimates can be used. Within the Huara Intrusive Complex, situated in the hyperarid core of the Atacama Desert, basin‐averaged bedrock erosion rates from channel sediments are extremely low, that is, less than 1 m/Myr. Such low rates indicate that fluvial processes operate very slowly or are almost absent. Bedrock erosion rates of channel knickpoints, however, reveal one to two orders of magnitude higher erosion rates (2–12 m/Myr). Erosion rates are remarkably low when compared to the steep surrounding topography. Tectonic uplift creates higher gravitational potentials for surface processes, controlling the overall erosion rate capacity. However, erosion itself is taking place by local precipitation capable of exceeding thresholds for surface activity. In the Atacama Desert, this happens only due to rare severe precipitation events, explaining the extremely low erosion rates. The efficiency of these events is modulated by local intrinsic processes and conditions, such as high infiltration capacities of Atacama soils and/or large channel boulder accumulations. Due to the virtual absence of these precipitation events capable of erosion, the landscape appears to be in hibernation.

Deciphering source-to-sink history from a solute perspective: A Sr isotope approach in the Qaidam Basin, NE Tibet

Sediment source-to-sink history is pivotal to investigating the evolution of ancient sedimentary basin. Previous study focuses mostly on reconstruction of various components of siliciclastic sedimentary systems from initial source areas through the dispersal system to deposition areas, but less on the dissolved load that displays distinct transport and deposition dynamics. Here we take the Qaidam Basin (NE Tibet) as a case to provide a solute perspective for deciphering the source-to-sink history of an intracontinental basin. The modern observations exhibit a remarkable contrast of the solute Sr isotopic regime with the northern sources (the Qilian Shan) with high 87Sr/86Sr ratios and the southern sources with low 87Sr/86Sr ratios. The paleowater solute 87Sr/86Sr ratios in the northern basin fluctuate between 0.711 and 0.715 since ∼ 54 Ma. Most of the interval remains a higher 87Sr/86Sr ratio of ∼ 0.713, indicating that the solute Sr was supplied solely by the Qilian Shan. But two periods of low 87Sr/86Sr ratio (0.711–0.712) at ∼ 44.5 - ∼32 Ma and after ∼ 16 Ma suggest that there may be two paleo-megalakes connecting the northern and southern sources, and the solute with low 87Sr/86Sr ratio from the southern sources can thus approach the northern basin via lake water mixing. The two low 87Sr/86Sr paleo-megalakes developed at the northwest of the basin at ∼ 44.5 - ∼32 Ma and at southeast of the basin after ∼ 16 Ma, suggesting a southeastward migration of the basin depocenter that was mainly caused by tectonic uplift with a subordinate impact of climate-induced lake expansion. Our results show a more complex and dynamic solute transport routing history in a large basin than that indicated by coarse clastic provenance studies, and suggest that such a solute Sr approach can be useful to trace sediment routing linked to denudation of high-grade metamorphic rocks and hydrological connections under drainage reorganization.

Compositions and ages of Early Cretaceous volcanic and plutonic rocks in central Tibet: Insights into the magmatic and uplift response to slab breakoff

AbstractWe present new zircon U-Pb ages and Hf isotope compositions as well as whole-rock major- and trace-element geochemical and Sr-Nd isotopic data for silicic plutonic and volcanic rocks from the Duolong area of central Tibet. Combined with existing data, our new data indicate that these plutonic and volcanic rocks were formed in two stages ca. 120 Ma and ca. 110 Ma, respectively, in a postcollisional extensional setting that was triggered by slab breakoff. The similar geochemical compositions of granitoids and rhyolites, combined with their close spatial and temporal relationships, suggest that they were both derived from juvenile crustal material within a single magmatic system. We propose that the two inferred crustal melting events in the Duolong area were caused by two episodes of deep mantle activity triggered by the transition of the plate subduction angle from steep to shallow in response to the ascent of buoyant continental lithosphere during slab breakoff. Furthermore, rapid surface uplift during the late Early Cretaceous caused by slab breakoff made an important contribution to the formation of the proto–Tibetan Plateau. This study provides new insights into postcollisional tectonomagmatism and plateau uplift in central Tibet triggered by slab breakoff. We propose more generally that tectonic uplift during postcollisional processes (i.e., slab breakoff and lithospheric delamination) is a major contributor to plateau uplift in collision zones.

Nanopore Characteristics of the Cambrian Niutitang Formation Organic-Rich Shales in the Middle Yangtze Region and Its Formation Controlling Factors

The shale of Cambrian Niutitang Formation is one of the most important shale gas reservoirs in the Middle Yangtze region, South China. Nanopores are important reservoir spaces for shale gas. The study of pore characteristics and its formation controlling factors is of great significance for the exploration and development of shale gas in the Niutitang Formation. In this study, two drilling core samples and two profile samples were investigated. The laser Raman, X-ray diffraction analysis, FE-SEM, and low-pressure N2 and CO2 adsorption methods are used to study the geochemical and mineral compositions of the shales, and the nanopore characteristics and its formation controlling factors of the shales are discussed. Results show that the shales have the following features: (1) rich in organic matter (OM) and the total organic carbon (TOC) contents ranging from 2.65 to 11.33%, with an average value of 6.81%. (2) The main mineral components of these shales are quartz, feldspar, clay minerals, calcite, and a small amount of pyrite. (3) The samples from the center of the Middle Yangtze region (EY1 well and BGP profile) have a higher maturity value ( Rmc R 0 % = 4.0 %) relatively to the samples from the south of the Middle Yangtze region (XD1 well and JF profile), where the Rmc R 0 % is 2.8%. (4) The maximum N2 adsorption capacity of the four groups of shale samples ranges from 5.090 to 27.333 cm3/g, with an average value of 15.571 cm3/g, while the maximum CO2 adsorption capacity ranges from 2.686 to 5.567 cm3/g, with an average value of 3.776 cm3/g. The higher maturity leads to the EY1 well having the lowest average maximum N2 adsorption capacity, while most of the OM pores in the EY1 well and BGP profile samples are smaller than 10 nm in diameter. The tectonic uplift leads to the profile samples having more meso-macropores than the core samples. The dissolution pores and granular mineral support are the key factors for the better pore structure of the high-evolution stage Niutitang Formation shale.

Provenance evidence for the early-to-middle Pleistocene drainage reorganization of the Songhua River, NE China

The Songhua River, one of seven major water systems in China, is the most famous river in Northeast China. However, it is still unclear whether the paleo-Songhua River had a reversed flow direction in the geological past and what mechanisms controlled changes in the flow direction. This study presents new results utilizing detrital zircon U-Pb geochronology and heavy mineral composition retrieved from a well-dated 102-m sediment core and from fluvial sediments in the Songhua River drainage basin, to reveal the evolution of the river system. A shift in Precambrian (>600 Ma) and 100–400 Ma age spectra can be observed at 62.2 m (∼0.94 Ma) in the core, and the heavy mineral composition also shows remarkable variations above and below 62.2 m. Provenance analysis shows that the sediments above 62.2 m in the core originated from the west (i.e., from the direction of the Songnen Plain), but below 62.2 m were fed from areas in the east (i.e., from the direction of the Jia-Yi divide), indicating that the paleo-Songhua River flowed westwards into the Songnen Plain before 0.94 Ma. A conceptual model is therefore proposed for the Songhua River drainage evolution over the early-to-middle Pleistocene. The westward-flowing paleo-Songhua River was captured by the eastward-flowing paleo-Sanjiang River at the Jia-Yi divide due to headward erosion of the paleo-Sanjiang River, leading to the initiation of a unified eastward flowing river system at ∼ 0.94 Ma. The second reorganization of the Songnen river system occurred at 0.46 Ma, characterized by the termination of the Songnen paleolake and the disintegration of the centripetal river system. The tectonics and climate were the main drivers controlling the evolution processes of the paleo-Songhua River before 1.2 Ma and after 0.94 Ma, respectively, whereas they acted together during 1.2–0.94 Ma. The tectonic uplifting of the Songliao divide and the long-term aridification in the Songnen Plain collectively controlled the second drainage reorganization in the Songnen Plain at 0.46 Ma.

Active and Relict Contact Karst morphological forms of the corrosional plain (Slavinski ravnik, SW Slovenia)

So far, the longest known unroofed cave in Slovenia has been found on the Slavinski ravnik, southwest of Postojna. From its position on the surface, its shape, and its containing sediments, we can infer its spatial and temporal development, as well as the processes and evolution of the contact karst in its hinterland. The corrosional plain Slavinski ravnik is a small area of the Dinaric Karst in Slovenia, located at the contact between impermeable flysch and karstified carbonate rocks, where many contact karst features formed. Due to erosion, multi-phase regional tectonic uplift, and sedimentation, a paragenetic cave system, active and relict blind valleys have formed. During the geomorphological mapping, elements were examined and drawn using ESRI ArcMap and Golden Software Surfer, and the stages of their formation were observed. During the survey, the active cave system Markov spodmol and Vodna jama v Lozi, the relict unroofed cave Brezstropa jama v Lozi, Biščevci blind valley, Sajevško polje blind valley, Ivačevci blind valley, and Sajevško polje sediment accumulation were studied. The changing hydrological regime, the allogenic sediments, the distribution of active and relict ponors, and the placement of active and relict elements of these contact karst forms, show different stages of formation and subsequent development of the northern border of Slavinski ravnik. The geomorphological map of these contact karst features and their following studies give us an insight into the morphogenesis of the southern karst periphery of the Postojna Basin as an exceptional - relatively small but highly variable Slovenian contact karst site.

Mid-cretaceous rapid denudation of Eastern Tibetan plateau: Insights from detrital records at the Southwestern corner of Sichuan basin

Reconstruction of the Cretaceous tectonic evolution of the eastern margin of the Tibetan Plateau is of great significance to understanding the formation and early evolution of the Tibetan Plateau. The thick late Mesozoic sedimentary sequence in the Western Sichuan Basin may record the evolution of the basin itself and the tectonic uplift history of the eastern margin of the Tibetan Plateau during the Cretaceous period. Here we provide new multi-proxy provenance data from conglomerate clast populations, sandstone petrography, heavy mineral assemblages, U-Pb dating of detrital zircon, paleocurrent data, and detrital garnet geochemistry from the Cretaceous clastic units in the southwest corner of Sichuan Basin. Our analysis reveals two distinct changes in sediment provenance recorded in the Cretaceous strata at the southwest corner of the Sichuan Basin. The first significant change of detrital provenance was identified in the mid-Cretaceous Jiaguan Formation. Metamorphic rocks and volcanic rocks clast, as well as feldspar and mica, increased significantly, a heavy mineral assemblage dominated by hematite–limonite and ilmenite with high ATi and RuZi and low ZTR values, predominantly type Bi garnet and mostly 164 Ma, 207 Ma, 440 Ma, 780 Ma–824 Ma, and 1840 Ma detrital zircon ages, interpreted to be sourced from the Songpan-Ganzi fold belt and Longmenshan orogenic belt. The second shift, in the Guankou Formation, is marked by a low compositional maturity, a distinct increase in fossiliferous carbonate clasts and high GZi index with type Bii garnet, and Triassic zircon ages, indicating the exhumation of Longmenshan orogenic belt during the late Cretaceous. These data collectively indicate that the significant surface uplift and rapid denudation of the eastern margin of the Tibetan Plateau were probably initiated in the mid-Cretaceous (∼120 Ma). In conclusion, a detailed hands-on provenance analysis of the clastic sedimentary sequences in the southwest corner of the Sichuan Basin enabled us to determine catchment areas and shifts hitherto unstudied, thus contributing to the exhumation history of the eastern margin of the Tibetan Plateau.