Orogenic Activity Research Articles

Comparing the transport-limited and <i>ξ</i>–<i>q</i> models for sediment transport

Abstract. Here I present a comparison between two of the most widely used reduced-complexity models for the representation of sediment transport and deposition processes, namely the transport-limited (or TL) model and the under-capacity (or ξ–q) model more recently developed by Davy and Lague (2009). Using both models, I investigate the behavior of a sedimentary continental system of length L fed by a fixed sedimentary flux from a catchment of size A0 in a nearby active orogen through which sediments transit to a fixed base level representing a large river, a lake or an ocean. This comparison shows that the two models share the same steady-state solution, for which I derive a simple 1D analytical expression that reproduces the major features of such sedimentary systems: a steep fan that connects to a shallower alluvial plain. The resulting fan geometry obeys basic observational constraints on fan size and slope with respect to the upstream drainage area, A0. The solution is strongly dependent on the size of the system, L, in comparison to a distance L0, which is determined by the size of A0, and gives rise to two fundamentally different types of sedimentary systems: a constrained system where L<L0 and open systems where L>L0. I derive simple expressions that show the dependence of the system response time on the system characteristics, such as its length, the size of the upstream catchment area, the amplitude of the incoming sedimentary flux and the respective rate parameters (diffusivity or erodibility) for each of the two models. I show that the ξ–q model predicts longer response times. I demonstrate that although the manner in which signals propagates through the sedimentary system differs greatly between the two models, they both predict that perturbations that last longer than the response time of the system can be recorded in the stratigraphy of the sedimentary system and in particular of the fan. Interestingly, the ξ–q model predicts that all perturbations in the incoming sedimentary flux will be transmitted through the system, whereas the TL model predicts that rapid perturbations cannot. I finally discuss why and under which conditions these differences are important and propose observational ways to determine which of the two models is most appropriate to represent natural systems.

The expanding network of mineral chemistry throughout earth history reveals global shifts in crustal chemistry during the Proterozoic

Earth surface redox conditions are intimately linked to the co-evolution of the geosphere and biosphere. Minerals provide a record of Earth’s evolving surface and interior chemistry in geologic time due to many different processes (e.g. tectonic, volcanic, sedimentary, oxidative, etc.). Here, we show how the bipartite network of minerals and their shared constituent elements expanded and evolved over geologic time. To further investigate network expansion over time, we derive and apply a novel metric (weighted mineral element electronegativity coefficient of variation; wMEECV) to quantify intra-mineral electronegativity variation with respect to redox. We find that element electronegativity and hard soft acid base (HSAB) properties are central factors in mineral redox chemistry under a wide range of conditions. Global shifts in mineral element electronegativity and HSAB associations represented by wMEECV changes at 1.8 and 0.6 billion years ago align with decreased continental elevation followed by the transition from the intermediate ocean and glaciation eras to post-glaciation, increased atmospheric oxygen in the Phanerozoic, and enhanced continental weathering. Consequently, network analysis of mineral element electronegativity and HSAB properties reveal that orogenic activity, evolving redox state of the mantle, planetary oxygenation, and climatic transitions directly impacted the evolving chemical complexity of Earth’s crust.

The discovery of U mineralization in the late Variscan plagiogranite vein of the Shkhara crystalline massif (Greater Caucasus, Georgia)

The Greater Caucasus belt is the northernmost expression of the Caucasus orogen and is linked to the southern margin of the Precambrian Scythian Platform. In the pre-Jurassic crystalline basement of this belt, a plagiogranite vein, exposed in the headwaters of the Enguri River, with elevated radiation (μSv/h range of ~1–3), has been discovered. The vein is located along the Main Thrust of the Greater Caucasus, in the upper Paleozoic biotite migmatites of the Shkhara crystalline massif. It is ~2–3 m thick and represents hydrothermally altered rock (SiO2 content varies from ~75% to ~85%) predominantly composed of a quartz-plagioclase assemblage. LA-ICP-MS 206Pb/238U dating of zircons from the vein indicates an age of 310.2±7.5 Ma that corresponds to the late Variscan orogenic activity. The vein is slightly fragmented and fractured, and fractures and nests are filled with Th-enriched uraninite veins and impregnations. According to ICP-MS-ES analyses, the Th content varies from ~26 ppm to ~50 ppm, and the U varies between ~55 ppm and ~290 ppm. Based on the conducted research, it was found that there is a full correlation between the studied vein and U-bearing granitic veins of different regions of the world by composition, magma series, geodynamic setting, tectonic location and isotopic age. On this basis, it is supposed that the late Variscan hydrothermally altered plagiogranite veins, which are localized in the shear zones of the Shkhara Massif, and entirely in the Main Range Zone of the Greater Caucasus, are potentially U-bearing.

Pleistocene–Holoceneout‐of‐sequence faulting along theMedlicott‐WadiaThrust in theNWHimalaya

AbstractUnderstanding millennial‐scale fault activity and related structural architecture from seismic gaps in active orogens is important for assessment of future seismic risks. Here, we present new Late Pleistocene–Holocene shortening rates across a segment of the 600‐km‐long Medlicott‐Wadia Thrust (MWT) system in the Sub‐Himalaya (SH) from the far‐western Himalayan sector of Jammu. OSL‐dated offset and folded fluvial strath terraces provide a measure for the intra‐wedge convergence and document strain partitioning within the SH, among which the MWT is the most active. Estimated differential uplift rates across the frontal and rear splay of the MWT is 3.2 ± 0.8 mm/a and 3.1 ± 0.4 which translates into a cumulative Late Pleistocene–Holocene shortening rate of 5.5 ± 0.5–5.8 ± 0.5 mm/a on the MWT. Previously published balanced cross‐sections proposed deformation pattern and in range of ~1 mm/a. Our study reaffirms deformation rates from neighbouring MWT fault segments; moreover, it provides independent constraints to the structural architecture of the frontal fold‐and‐thrust belt and implies changes in fault displacement rates on Quaternary time‐scales.

Structural elements and evolution of the Yangmuchuan dome: Constraints on the tectonics of the Paleoproterozoic Jiao-Liao-Ji belt in the Eastern Block of the North China Craton

The nature of assembly of the Columbia supercontinent is well-characterized by the orogenic belts that were formed during amalgamation of continental blocks. The Jiao-Liao-Ji Belt (JLJB) in the eastern North China Craton possesses complex deformation structures that exemplify the Paleoproterozoic orogeny. A series of granitic gneiss domes in the southern JLJB characterizes the structural deformation in the Paleoproterozoic orogenic belts.Located in the middle segment of the JLJB, the Yangmuchuan dome is composed of three major elements, i.e., the Liaoji granites in the core, and sheared metamorphic rocks in the mantle and outer shell. Bedding-parallel ductile shear zones and weakly deformed metamorphic rocks between them are well-preserved in the latter two elements. Structural analysis reveals that the Yangmuchuan dome mainly experienced two deformation stages (D1 and D2). The D1 deformation is characterized by pure shear-dominated deformation structures with occurrence of penetrative foliations, symmetrical boudinages, mineral lineations and rootless folds in all the rocks from the mantle and outer shell. Dominated by simple shearing, the D2 deformation is the key stage contributing to the formation of the dome structure in the area. The D2 deformation is manifested as occurrence of A-type folds, S-C fabrics, mylonitic foliation S2, mineral stretching lineation L2 in granites, and in layered rocks in the mantle and outer shell. They were superposed on and transformed, along high strain zones, D1 deformation structures. Magnetic fabrics of the Liaoji granites from the core show a generally consistent orientation with the foliations and stretching lineations in the sheared granites. LA-ICP-MS zircon U-Pb dating on syn-tectonic leucogranitic dykes indicates that the peak deformation (D2) of the Yangmuchuan dome occurred from >1887 to 1808 Ma. Geometrical and kinematic analysis from the structural, microstructural and magnetic fabric data reveal that formation of the Yangmuchuang gneiss dome resulted from dominant subhorizontal flow and subsidiary vertical flow in the middle and lower crust as the consequence of orogenic activity along the JLJB during the assembly of the Columbia supercontinent.

Tectonic and Climatic Control on Quaternary Exhumation in the Eastern Pamir Domes, Western China: Insights From Geomorphic Approaches

The Kongur Shan and Muztaghata massifs, bounded by the Kongur Shan extensional system (KES), represent tectonic and topographic anomalies in the eastern Pamir region. They are ideal examples to study how normal faulting and surface erosion influence Quaternary exhumation of the dome system. We apply multiple geomorphic parameters, including hypsometric integral, stream length-gradient index, drainage basin shape, drainage basin asymmetry and ratio of valley floor width to valley height, for the catchments on both sides of the range. We first evaluated the validity of various indices and chose three active tectonic-sensitive indices to establish a newly-integrated parameter (Iat) that is used to measure relative intensities of tectonic activity in active orogens. Results suggest stronger tectonic activity west of the domes along the Kongur Shan normal fault (KSF) and Muji dextral strike-slip fault, compared to the eastern side, along the Ghez and Kalagile faults. This first-order observation reflects tectonic control on the topographic development of the domal structure, consistent with eastward crustal tilting, attested by older thermochronology ages to the east. On the western flank of the range, stronger tectonic activity occurs mostly on the Muji fault, Kingata Tagh - Kongur Shan fault segment, as well as along the western and southern Muztaghata segments of the Kongur Shan fault. This is consistent with field investigations of Quaternary offsets of landforms, which suggest continuous activity of the Muji fault and KSF since the late Miocene. Average basin-wide erosion rates derived from stream power models are highest near the Kongur Shan dome, and gradually decrease southwards and northwards, in agreement with the spatial pattern of long-term exhumation rates in the footwall of the KSF obtained by low-temperature thermochronology data. Positive correlation between exhumation/erosion rates and extensional rates along the active faults located west of the domes indicates that extensional deformation likely plays a dominant role in controlling focused dome exhumation/erosion. However, considering peaked exhumation/erosion rates, stronger rock resistivity and steeper glacial landforms, attest to the important role of glacial buzz-saw in reshaping the recent dome’s landscape.

Delayed 10Be dilution in detrital quartz following extensive coseismic landsliding: A 2016 Kaikōura earthquake case study

Large earthquakes play a major role in the topographic evolution of active orogens. Earthquake induced landslides can alter the mass balance of mountain belts for decades to centuries depending on how landslide material is transported and stored. In this study, we analysed in-situ10Be concentrations in fluvial sediments to capture a time series of post-earthquake denudation rates of the Tūtae Putaputa|Conway River catchment, which experienced ∼13 × 106 m3 of landsliding in the 2016 Kaikōura earthquake. 10Be concentrations were determined for detrital samples from the Conway River at the rangefront of the Seaward Kaikōura Mountains, South Island, New Zealand, and near the catchment outlet over three sampling intervals, including after significant precipitation events, 1-2 yr following the earthquake. Our results indicate somewhat higher apparent erosion rates at the rangefront (0.41-0.58 mm/yr) when compared to erosion rates incorporating lower-relief sub-catchments at the river outlet (∼0.28 mm/yr). No changes were found over the same time period in the Hurunui River, a neighbouring catchment that experienced negligible coseismic landsliding during the Kaikōura event. Apparent catchment-averaged erosion rates in the Conway River have remained similar to long-term exhumation rates from previously published thermochronology studies. To explain our results, we explore the observed controls on catchment-wide 10Be concentrations in our study area, such as the spatiotemporal variability in landslide connectivity to the channel and storage within the catchment. Our results highlight that using in-situ cosmogenic 10Be in fluvial deposits as a proxy for changes in sediment fluxes of earthquake-affected landscapes is complex and highly site-specific.

Transitions in subduction zone properties align with long-term topographic growth (Cascadia, USA)

Simple mechanical models of the earthquake cycle assume that interseismic elastic deformation is recovered during earthquakes, closing the strain budget of steady and episodic slip on the deep and shallow subduction interfaces, respectively. However, elevated topography in the forearc high requires that some deformation is not recovered over each elastic cycle. Here, we compare constraints on deformation over decadal to million-year timescales to disentangle contributions from elastic (recoverable) and inelastic (unrecoverable) deformation within the Olympic Mountains of the Cascadia Subduction Zone. Over timescales of 103 – 106 yrs, elevated topography, permanent deformation, and denudation (from thermochronometry and cosmogenic nuclide data) accumulate in an area adjacent, but not identical, to the maximum in geodetically observed reduced vertical velocity and surface upwarping over tens of years. The domains of geodetic and geomorphic maximum uplift occur over a 20-60 km wide zone overlying the up-dip limits of the zone of conditional frictional stability at the subduction interface. We attribute geologic-scale orogenesis, accumulation of topography and advection of rocks in the active orogen to unrecoverable deformation as stress is relayed up-dip through parts of the subduction interface and dissipated in the overriding plate.

Temporal and spatial comparisons of angiosperm diversity between eastern Asia and North America.

Abstract Eastern Asia (EA) and North America north of Mexico (NA) have comparable latitude, land area, and climate, but the overall plant diversity is much higher in EA than in NA. Despite intensive studies on disjunct taxa of the two regions, the temporal and spatial diversity patterns between the two floras remain unclear. Here we explore the floristic differences between EA and NA using the well-studied floras of China and the United States of America (USA) as exemplars, while also employing a newly generated dated phylogeny covering ∼90% of the angiosperm genera of the two countries and comprehensive spatial distribution data. We find that China possesses both higher richness and phylogenetic diversity (PD) for angiosperm genera than the USA. Notably, most lineages contribute to the PD anomaly between the two floras, with 46 of 58 lineages having higher PD in China. Temporally, China has a higher proportion of genera that originated before the Miocene than found in the USA (29.9% vs 23.2%). The eastern USA has more genera that originated during the Paleogene than does the western USA, but the reverse pattern is observed after the middle Miocene, with more genera originating in the west. Spatially, China shows a more distinct east-west deviation in diversity than the USA with eastern China possessing much higher generic richness and PD and more ancient lineages than western China. However, the eastern USA possesses lower generic richness, but higher PD and more ancient lineages than the western USA. Both the floras in China and the USA share a signature of an older east and a younger west, and this pattern may be largely driven by regional orogenic activities and climatic changes in the west of the two regions. Finally, our study indicates that more efforts are needed to enhance biodiversity conservation in southern China and the eastern USA by identifying and protecting phylodiversity hotspots.

Late Quaternary Tectonics along the Peri-Adriatic Sector of the Apenninic Chain (Central-Southern Italy): Inspecting Active Shortening through Topographic Relief and Fluvial Network Analyses

Abstract Active compressional tectonics along the outer front of the Apenninic-Maghrebian chain (Italy) is well documented along the northern and central segments and in Sicily. On the other hand, the Southern Apenninic Outer Front (SAOF) orogenic activity is well established only until the Lower-Middle Pleistocene. We address the hypothesis of its subsequent late Quaternary activity in central-southern Italy (Abruzzo and Molise regions). We integrated topographic and fluvial network analyses along with morphotectonic investigation of fluvial terraces to identify evidence of differential rock uplift. We compared the results with the main geolithological units, known structural elements, and long-term deformation history from seismic line interpretation. We found variable evidence suggesting localized rock uplift in the Abruzzo region along the SAOF (Abruzzo Citeriore Basal Thrust segment) and inward structures on its hanging wall (Casoli-Bomba high), as well as along part of the Struttura Costiera thrust. Middle-to-Late Pleistocene deformation is constrained by terrace tilting and disruption along the Pescara river. Localized shortening along segments of the Apenninic Outer Front could explain the observed pattern of anomalies which is difficult to explain with long-wavelength regional uplift alone. Our reconstruction is consistent with the long-term deformation of the area and agrees with its seismotectonic setting. Despite the low deformation rate context and the peculiar geological setting which challenges the interpretation of the topographic and geomorphic signals, this study compels reconsideration, in terms of seismic hazard assessment, of the existence of late Quaternary active thrusting in central-southern Italy.

Linking sediment supply variations and tectonic evolution in deep time, source-to-sink systems—The Triassic Greater Barents Sea Basin

Abstract Triassic strata in the Greater Barents Sea Basin are important records of geodynamic activity in the surrounding catchments and sediment transport in the Arctic basins. This study is the first attempt to investigate the evolution of these source areas through time. Our analysis of sediment budgets from subsurface data in the Greater Barents Sea Basin and application of the BQART approach to estimate catchment properties shows that (1) during the Lower Triassic, sediment supply was at its peak in the basin and comparable to that of the biggest modern-day river systems, which are supplied by tectonically active orogens; (2) the Middle Triassic sediment load was significantly lower but still comparable to that of the top 10 largest modern rivers; (3) during the Upper Triassic, sediment load increased again in the Carnian; and (4) there is a large mismatch (70%) between the modeled and estimated sediment load of the Carnian. These results are consistent with the Triassic Greater Barents Sea Basin succession being deposited under the influence of the largest volcanic event ever at the Permian-Triassic boundary (Siberian Traps) and concurrent with the climatic changes of the Carnian Pluvial Event and the final stages of the Northern Ural orogeny. They also provide a better understanding of geodynamic impacts on sedimentary systems and improve our knowledge of continental-scale sediment transport. Finally, the study demonstrates bypass of sediment from the Ural Mountains and West Siberia into the adjacent Arctic Sverdrup, Chukotka, and Alaska Basins in Late Carnian and Late Norian time.

Focusing Fluids in Faults: Evidence From Stable Isotopic Studies of Dated Clay‐Rich Fault Gouge of the Alberta Rockies

AbstractIsotopic studies of Canadian Rocky Mountain thrust faults preserve the timing and identity of orogenic fluids and their fault zone pathways. Using previously dated samples, we measure the O‐ and H‐isotopic compositions of fault gouge. These nearly 100% neomineralized gouges and their associated damage zones act as primary orogenic fluid pathways. As such, they provide a specific and local look into the nature of the Late Jurassic to Early Eocene orogenic plumbing system in the Alberta Rockies. Considering clay polytype stability and regional temperature conditions, we obtain a range of geofluid isotopic compositions during Jurassic‐Eocene thrust faulting: δ18Ofluid ranged from ∼−3.3 to 9.2 ± 3.2‰; δDfluid ranged from −119 to −46 ± 13‰ VSMOW. The range of O‐ and H‐isotopic compositions reflects mixing of fluid sources, including the pervasive presence of surface‐sourced fluids (up to ∼90%). The interpreted prevalence of a surface fluid source in fault rocks is in agreement with regional isotopic trends previously observed in undated veins of fractured host rock. Our results confirm that thrust faults of the Alberta Rocky Mountains acted as major fluid‐focusing conduits during orogenic activity. We further show that these faults incorporated both deeply sourced and surface‐sourced fluids into zones of enhanced and dynamic permeability, heterogeneously distributing fluids along fault planes across the fold‐thrust belt, promoting the growth of fault‐zone weakening clay minerals.

First evidence for the subduction initiation and boninitic magmatism from the Armutlu Peninsula (NW Turkey): geodynamic significance for the Cadomian magmatic arc system of the Gondwanan margin

ABSTRACT The Cadomian Orogeny was active along the northern margin of Gondwanaland during the Late Neoproterozoic–Early Cambrian period. Remains of this orogenic activity are traced from Western Europe to the Himalayas, including some metamorphic basement rocks of Turkey. In this study, we provide new whole-rock and mineral chemistry, and zircon U–Pb age data for the metagabbro and metagranites in the Armutlu Peninsula, north of the Intra Pontide suture zone (IPSZ), which are the equivalent of the Cadomian basement of the İstanbul Zone (İZ). Geochemically, the metagabbros show an extreme depletion in Nb, Zr, Th, and Hf; low TiO2 contents; and high Mg# values exhibiting boninitic affinity, which are commonly associated with fore-arc settings. The metagranites are calc-alkaline and high-K calc-alkaline in character. They are slightly enriched in LREE and have similar features to shear-type plagiogranites. The yielded zircon U-Pb crystallization ages are 564 ± 4.4 Ma for metagabbros and 561 ± 9.5 Ma (Late Ediacaran) for metagranites. In this study, we provide additional information for the Cadomian basement of the İZ and the geodynamic evolution of Cadomian magmatism by discussing the tectonic setting for two geochemically contrast but almost coeval magmatic products.

The Bastar Craton of Central India: Tectonostratigraphic evolution and implications in global correlations

The Bastar Craton occupies a key position in the Peninsular India, being located between three cratonic nuclei of India, the Dharwar Craton in the southwest, the Singhbhum Craton in the northeast, and the Bundelkhand Craton in the northwest. The southeastern and the northern margins of the craton are bordered by the Proterozoic orogenic belts constituting the Eastern Ghats Mobile Belt and the Central Indian Tectonic Zone (the Satpura Mobile Belt), respectively. Analysis of the tectonostratigraphic evolution of the craton indicates the formation of the craton during Paleoarchean Era (~3582 Ma). The Archean evolution of the craton is marked by the development of granite-greenstone belts containing chemogenic sediments (Banded Iron Formations) and gold mineralisation . High-grade gneisses and granulites were developed during three orogenic episodes in the terrane (~2700 Ma Bailadila orogeny , ~2900 Ma Bengpal orogeny and ~3400 Ma Sukma orogeny). The Paleoproterozoic evolution of the craton is gleaned from the record of siliciclastic, volcaniclastics and chemogenic precipitates (carbonates, Banded Manganese Formation, and Banded Iron Formation) on the northern margin of the craton, which were deposited during the Great Oxidation Event (GOE; 2500–2300 Ma) and Paleoproterozoic glaciation (2400–2300 Ma) as well as immediately after the GOE (2050–1850 Ma). Effects of orogenic activities in the adjacent mobile belts are marked by the metamorphic and magmatic activities affecting the rocks at the margin of the craton. The Satpura orogenic event on the northern margin of the craton led to the amalgamation of the Bastar Craton with the Bundelkhand Craton at ~2250 and ~2100 Ma, forming the major part of the Peninsular India. Orogenic collapse (extension) developed basins transverse to the orogenic trend, where clastic, volcaniclastic and chemogenic sediments (Khairagarh and Chilpi Groups) were deposited. The southeastern margin of the craton has records of migmatisation and granite emplacement during the Eastern Ghats orogeny at ~1700 Ma. A number of sedimentary basins , aligned along a line parallel to the Eastern Ghats Mobile Belt, were developed during the orogenic collapse of the Eastern Ghats. Later orogenic activities along the Eastern Ghats were responsible for the development of depositional hiatus/unconformity within these sedimentary basins of the craton. Mafic dykes of different generations (2400 Ma, 2100 Ma and 1890 Ma) cutting across the Archean basement complex provide suitable markers for paleomagnetic reconstructions of the craton. The Archean and early Paleoproterozoic rock assemblages and mineralisation patterns in the craton show a broad similarity with the Western Australian Craton, indicating near-neighbourhood positions of the two ancient cratonic blocks. Paleomagnetic studies have shown the separation of these two blocks at ~2000 Ma, with the development of a paleo-ocean which closed subsequently during the amalgamation of the Bastar Craton with the East Antarctic Shield to form the Eastern Ghats Mobile Belt in three phases at ~1700–1600 Ma, ~1050–950 Ma and ~500 Ma, with extensional phase between 1450 and 1100 Ma. The Bastar Craton preserves important clues regarding the evolution of the ocean and atmospheric conditions in the early Earth. • The Bastar and Yilgarn Cratons were juxtaposed at ~2400 Ma. • Bundelkhand-Pilbara Cratons collided with Bastar-Yilgarn Cratons at ~2000 Ma. • Satpura-Singhbhum-Capricorn Orogen developed at ~2000 Ma. • No collision/accretion took place along the CITZ after ~1800 Ma. • New tectonic model for 1950–1000 Ma is proposed for Bastar-Yilgarn Cratons.

Pulsed Mesozoic exhumation in Northeast Asia: New constraints from zircon U-Pb and apatite U-Pb, fission track and (U-Th)/He analyses in the Zhangguangcai Range, NE China

Northeast Asia located at the margin of the Paleo-Pacific/Pacific plate provides a detailed record of subduction-related orogenic activity. In order to shed light on Mesozoic-Cenozoic tectonic processes arising from the complex interaction and juxtaposition of multiple tectonic domains, we performed zircon U-Pb and apatite U-Pb, fission-track (FT) and (U-Th)/He analyses in the Zhangguangcai Range, a major mountain range in northeastern Asia. Our zircon and apatite U-Pb results indicate that most granites in the Zhangguangcai Range were emplaced at shallow crustal levels in the early Jurassic (~200–173 Ma) along with a minor amount of Triassic granites (~232 Ma). Volcanic rocks of the Maoershan and Ningyuancun formations were erupted at ~190–175 Ma and ~182–177 Ma, respectively. This Early Mesozoic magmatic activity is related to subduction of the Mudanjiang oceanic plate that separated the Jiamusi and Songliao blocks. Apatite FT analysis of granites and volcanic rocks reveals three groups of cooling ages clustering at ~193–171 Ma, ~158–129 Ma and ~118–102 Ma, while AHe analysis of granites yielded three groups of cooling ages at ~149–135 Ma, ~106–85 Ma and ~57–48 Ma. Based on these data and thermal history modelling, we propose that the central Zhangguangcai Range experienced episodic, multi-stage exhumation at shallow crustal levels since the Jurassic. Early-Middle Jurassic exhumation took place during the closure of the Mudanjiang Ocean, which resulted in unroofing of granites in the central Zhangguangcai Range and topographic growth of the Songliao block. Late Jurassic-Early Cretaceous exhumation occurred within an extensional tectonic setting, which has previously been documented across northeast Asia. Such exhumation could have been linked to lithosphere delamination and resulted in basin and range topography style, prior to the change in subduction parameters of the Paleo-Pacific plate and/or collision and strike-slip translation of the Okhotomorsk block in the Late Cretaceous.

Controls on the grain size distribution of landslides in Taiwan: the influence of drop height, scar depth and bedrock strength

Abstract. The size of grains delivered to rivers by hillslope processes is thought to be a key factor controlling sediment transport, long-term erosion and the information recorded in sedimentary archives. Recently, models have been developed to estimate the grain size distribution produced in soil, but these models may not apply to active orogens where high erosion rates on hillslopes are driven by landsliding. To date, relatively few studies have focused on landslide grain size distributions. Here, we present grain size distributions (GSDs) obtained by grid-by-number sampling on 17 recent landslide deposits in Taiwan, and we compare these GSDs to the geometrical and physical properties of the landslides, such as their width, area, rock type, drop height and estimated scar depth. All slides occurred in slightly metamorphosed sedimentary units, except two, which occurred in younger unmetamorphosed shales, with a rock strength that is expected to be 3–10 times weaker than their metamorphosed counterparts. For 11 landslides, we did not observe substantial spatial variations in the GSD over the deposit. However, four landslides displayed a strong grain size segregation on their deposit, with the overall GSD of the downslope toe sectors being 3–10 times coarser than apex sectors. In three cases, we could also measure the GSD inside incised sectors of the landslides deposits, which presented percentiles that were 3–10 times finer than the surface of the deposit. Both observations could be due to either kinetic sieving or deposit reworking after the landslide failure, but we cannot explain why only some deposits had strong segregation. Averaging this spatial variability, we found the median grain size of the deposits to be strongly negatively correlated with drop height, scar width and depth. However, previous work suggests that regolith particles and bedrock blocks should coarsen with increasing depth, which is the inverse of our observations. Accounting for a model of regolith coarsening with depth, we found that the ratio of the estimated original bedrock block size to the deposit median grain size (D50) of the deposit was proportional to the potential energy of the landslide normalized to its bedrock strength. Thus, the studied landslides agree well with a published, simple fragmentation model, even if that model was calibrated on rock avalanches with larger volume and stronger bedrock than those featured in our dataset. Therefore, this scaling may serve for future modeling of grain size transfer from hillslopes to rivers, with the aim to better understanding landslide sediment evacuation and coupling to river erosional dynamics.

P-T-D evolution of the southeast Passo Feio Complex and the meaning of the Caçapava Lineament, Dom Feliciano Belt, southernmost Brazil

Metamorphic–deformation paths and interpretations of regional structures are essential for the understanding of how orogens evolve. While in active orogens, structures can be easily mapped for hundreds of kilometres, regional structures in ancient mountain belts may appear only as subsurface geophysical data. In this paper, we constrain the metamorphic–deformation history of the southeastern part of the Passo Feio Complex located in the Neoproterozoic Dom Feliciano Belt in southernmost Brazil. The complex is crosscut by a block-limiting structure defined by magnetometric data, the Caçapava Lineament. Our petrographic interpretations and thermodynamic modelling of pelitic schists of the Passo Feio Complex indicate the beginning of garnet growth at ca. 530–550 °C and 3–4.3 kbar during D1, and metamorphic peak at ca. 560–570 °C and 5–5.5 kbar (M1), during progression to D2. After M1 (~17–19 km depth), the complex was exhumed to at least 14 km (~4 kbar) depth, as the contact metamorphism by the Caçapava Granite (ca. 562 Ma) produced andalusite. The correlation of D3 structures of the Passo Feio Complex (S3 and L3), magmatic structures in the Caçapava Granite, orientation of geophysical anomalies in the region and kinematics of S3 corroborate the interpretation of the Caçapava Lineament as a dextral shear zone. Due to the location of anomalies and previous three-dimensional modelling of the granitic body, we interpret that a curved ENE to NS branch of the NE-striking Caçapava Shear Zone is responsible for the accommodation of the Caçapava Granite. Lastly, we discuss the regional implications of such interpretation, which brings up the question of block-limiting character of the Caçapava Shear Zone and the geotectonic position of the Passo Feio Complex.

Controls on Physical and Chemical Denudation in a Mixed Carbonate‐Siliciclastic Orogen

AbstractMixed siliciclastic‐carbonate active orogens are common on Earth's surface, yet most studies have focused on erosion and weathering in silicate‐rich landscapes. Relative to purely siliciclastic landscapes, the response of erosion and weathering to uplift may differ in mixed‐lithology regions. However, our knowledge of weathering and erosion in mixed carbonate‐silicate lithologies is limited and, thus, so is our understanding of the mechanistic coupling between uplift, weathering, and the carbon cycle. Here, we partition denudation fluxes into erosion and weathering fluxes of carbonates and silicates in the Northern Apennines—a mixed carbonate‐siliciclastic active orogen—using dissolved solutes, the carbonate sand fraction, and existing 10Be denudation rates. Erosion generally dominates total denudation fluxes relative to weathering by an order of magnitude. Carbonate and silicate contributions to erosion vary between lithologic units, but weathering fluxes are systematically dominated by carbonates. Silicate weathering may be kinetically limited, whereas carbonate weathering may be limited by acid supply. Carbonate re‐precipitation estimated by comparing ion ratios (Sr, Ca, Na) from rivers and bedrock suggests that up to 90% of dissolved Ca2+ is lost from carbonate‐rich catchments. Corresponding [Ca2+] estimates for the weathering zone are high, likely driven by high soil CO2 partial pressures (pCO2); however, re‐equilibration with atmospheric pCO2 in rivers converts solutes back into grains that become part of the physical denudation flux. Weathering limits in this landscape therefore differ between the subsurface weathering zone and riverine exports, and our findings suggest that carbon cycle models may overestimate the sensitivity to erosion of solute exports (Ca2+ and HCO3−) derived from carbonate weathering.

Indian plate structural inheritance in the Himalayan foreland basin, Nepal

AbstractThe Himalaya, the Earth's largest active orogen, produces a deep but relatively unexplored foreland basin by loading the Indian Plate. Newly available two‐dimensional seismic data (ca. 5,180 line km) spanning 900 km of the Nepali lowlands allow mapping and interpretation of several regional subsurface markers in two‐way‐travel time and estimated depth. Isopach maps for the major intervals allow us to interpret the interplay between basement structure, flexure, and faulting within the Ganga Basin. The Indian continental lithosphere beneath the foreland basin contains basement ridges oriented at high angles to the thrust belt. These basement structural highs and intervening depressions, tens to hundreds of kilometres wide, influenced deposition of the Precambrian Vindhyan strata and overlying Paleozoic to Mesozoic successions. The overlying Miocene to Quaternary foreland basin shows along‐strike thickness variations across the basement features. Because the foreland basin sediments were mainly deposited in an alluvial plain close to sea‐level, accommodation, and therefore thickness, was predominantly controlled by subsidence of the Indian Plate, providing evidence that the basement features controlled foreland basin development. Subsidence varied in time and space during Neogene basin development. When combined with flexural modelling, these observations imply that the subsidence history of the basin was controlled by inherited lateral variations in the flexural rigidity of the Indian Plate, as it was translated northward beneath the Himalayan Orogen. Basement features continue to play a role in higher levels of the thrust belt, showing that basement features in a down‐going plate may produce non‐cylindrical structures throughout orogen development.

Sedimentary facies of the Mesoproterozoic Srisailam Formation, Cuddapah basin, India: Implications for depositional environment and basin evolution

Sedimentary facies of the Mesoproterozoic (~1400−1327 Ma) Srisailam Formation, exposed in the Srisailam sub-basin in the northern part of the Cuddapah basin, India, were analyzed. It helped in identifying eighteen different facies that can be grouped into six facies associations (FA-I to VI) – alluvial fan/fan-delta, delta top, delta front, lacustrine, fluvial, and aeolian. Hinterland geology, integrated palaeomagnetic, geochemical and sedimentological observations, and inferred palaeohydrological condition and palaeoclimate indicate more control of tectonic regime on the evolution of the facies architecture. Analysis of vertico-lateral disposition of the identified facies suggests that the deposition of the Srisailam sediments was initiated in a number of fault-controlled isolated depocenters (riftogenic lakes). However, those isolated lakes were deep enough to allow the evolution of lacustrine and deltaic depositional regimes. Basin-wide lacustrine environment was established during subsequent rifting and regional peak subsidence (rift-climax) of the basin floor. Cessation of further basin subsidence facilitated progradation of fluvial sediments. During low-stage fluvial sediments were reworked locally by aeolian processes, and during protracted dry periods, aeolian regimes were established over considerable stretches of the Srisailam sub-basin.It is likely that the Srisailam half-graben, adjacent to the Nallamalai Fold Belt, was developed due to lithospheric doming and limited crustal stretching during a mantle upwelling event responsible for lamproite (alkaline) magmatism in the northern part of the Cuddapah basin. The evolution of the Srisailam rift-basin may be compared with the Cenozoic rift system of Europe, where rift development took place simultaneously with the orogenic activity in the Alps and Pyrenees. The style of sedimentation in the Srisailam sub-basin may be considered as a variant of the Newark-type lacustrine facies complex, and the tripartite basin filling model of half-graben lacustrine complexes may possibly be extended to the Mesoproterozoic era.