Pulses Of Uplift Research Articles

Evolution of Arc‐Continent Collision in the Southeastern Margin of the South China Sea: Insight From the Isugod Basin in Central‐Southern Palawan

AbstractThe evolution of arc‐continent collision between the Palawan microcontinental block and the Cagayan Ridge in the southeastern margin of the South China Sea (SCS) is vital to understand how this collision correlated with seafloor spreading of the SCS. To address the evolution of arc‐continent collision, we studied the biostratigraphy and provenance of syn‐collisional sediments in the Isugod Basin in central‐southern Palawan. Microfossil analysis indicates a Late Miocene age (11.5–5.6 Ma) for the Isugod and Alfonso XIII Formations and rapid subsidence during initiation of the basin which may have been triggered by local extensional collapse of the wedge in response to forearc uplift. Multidisciplinary provenance analysis reveals that the Isugod and Alfonso XIII Formations were derived from the Middle Eocene–lower Oligocene Panas‐Pandian Formation on the Palawan wedge and the Late Eocene Central Palawan Ophiolite. These results suggest the emergence of both the orogenic wedge and obducted forearc ophiolite at ∼11.5 Ma, implying collision onset before ∼11.5 Ma. The collision initiation in Palawan could be better constrained to ∼18 Ma, based on the drowning of the Nido carbonate platform in the foreland. Therefore, the gravitational collapse of the Palawan wedge and the subsidence/formation of the Isugod Basin might reflect a significant uplift pulse in the hinterland of the wedge beginning within 13.4–11.5 Ma in the late stage of collision. It indicates that although compression originated from spreading of the SCS had ceased at 16–15 Ma, arc‐continent collision in Palawan did not stop and was sustained by compression from the upper plate afterward.

Paleomagnetic chronology and paleoenvironmental records from a drill core in the Liupan Mountain area, NE Tibetan Plateau

The Liupan Mountain area, a north-trending mountain range, located in the northeastern-most active structural margin of the Tibetan Plateau and the convergence zone of the East Asian monsoon region, provides an ideal geological setting for investigating the tectonic events in the northeastern Tibetan Plateau and the Cenozoic evolution of the Asian aridification. We provide magnetostratigraphic and paleoenvironmental records for a Late Cenozoic sedimentary core drilled in the Guyuan in the Liupan Mountain. The lithology of the core can be roughly divided into two parts. The lower part (depths of 795–40 m) is composed of lacustrine sediments and the upper part (depths of 40–0 m) is composed of fluvial deposits. Magnetostratigraphy of the 795 m deep core dates the magnetic polarity sequence between ∼8.2 and 0.03 Ma. The Brunhes/Matuyama, Matuyama/G, and Gauss/Gilbert boundaries are located at depths of 53.55 m, 161.50 m, and 264.75 m, respectively. Four intervals with relatively higher accumulation rates were identified at ca. 7.64–6.03, 5.24–4.18, 3.60–2.58, and 1.07–0.78 Ma. All of this evidence is probably related to the pulses of tectonic uplift of the northeastern (NE) Tibetan Plateau. The frequency-dependent susceptibility values have exhibited obvious decreasing trends since ∼8.2 Ma, indicating obvious aridification in the Guyuan Basin since the Late Miocene, but relatively high values occurred between 4.6 and 3.5 Ma. The enhancement of the aridity in the Liupan Mountain since ∼8.2 Ma was due to the combined effect of global climate cooling and the uplift of the Northern Tibetan Plateau since the Late Miocene.

Deciphering differential exhumation in the Gangdese orogen in southern Tibet using exposed porphyry alteration systems and geomorphic analysis

Topography and exhumation vary strongly in the Tibetan Plateau, reflecting different geodynamics and surface processes. The Gangdese orogen in southern Tibet is characterized by west-to-east variations in topography and occurrences of the Miocene porphyry copper deposits. We integrated remote sensing based hydrothermal alteration mapping and geomorphological analysis to detect patterns of differential exhumation since the Miocene. High abundances of propylitic and potassic alteration of the eastern Miocene granitoids are identified, indicating >2 km of exhumation since the Miocene. The western Gangdese has intensive phyllic and argillic alteration representing ∼1 km of exhumation. Geomorphic analyses also show E-W changes that most likely resulted from differential rock uplift histories. Channel steepness index values indicate the eastern Gangdese has channel gradients between 211 m1.02 and 457 m1.02, compared to values between 30 m1.02 and 160 m1.02 in the west. Linear inversion of tributaries of the Yarlung river shows a pulse of rock uplift between 25 Ma and 7 Ma with a maximum rate of 110 m/ m.y. in the east. In contrast, the western Gangdese exhibits slower and persistent rock uplift rates between 20 m/m.y. and 40 m/m.y. since 20 Ma. The integrated results record differential exhumation and rock uplift since the Miocene. We invoke the geometric variations of the subducted Indian lithosphere to interpret the E-W differential exhumation since the Miocene. Steeper subduction of the Indian lithosphere beneath the eastern Gangdese induced mantle upwelling, triggering rapid rock uplift and deep exhumation. Conversely, the shallower subduction of the Indian slab in the west generated slow and prolonged rock uplift with less exhumation. Our study refines the exhumation process of the Gangdese since the Miocene.

A new early water frog (Telmatobius) from the Miocene of the Bolivian Altiplano

AbstractWe describe the new frog Telmatobius achachila sp. nov. from the late Middle to earliest Late Miocene of Achiri, based on a partial skeleton found at 3960 m above sealevel in the Bolivian Altiplano. This skeleton, attributed to a male adult, constitutes the first documented fossil record of the speciose living genus Telmatobius, endemic to the Andean Cordillera and the Altiplano. Phylogenetic analysis confirms the new species as being part of the crown group, and diverging both later than the T. verrucosus group and earlier than the T. bolivianus, T. marmoratus and T. macrostomus groups. Coupled with its accurate stratigraphic provenance and age, this phylogenetic position provides a relevant calibration point for timing the evolutionary history of these highland, mostly aquatic frogs. The skeleton of T. achachila indicates that several of the osteological peculiarities of extant Telmatobius were already acquired at c. 12 Ma, including some that might be linked to their aquatic lifestyle. Together with mixed montane–rainforest pollen vegetation uncovered in the same level, this fossil specimen further provides key data enabling a more accurate reconstruction of ancestral habitats and elevation ranges of Telmatobius, agreeing with the previously postulated conditions in which these water frogs might have first evolved. Ultimately, this discovery adds to the sparse evidence of a humid tropical Bolivian Altiplano just prior to: (1) the Late Miocene uplift pulse of the Central Altiplano; and (2) the drastic climate deterioration that occurred from Late Miocene time onward, leading to the harsh highland‐steppe environments reigning there today.

Interplay between tectonics and surface processes in the evolution of mountain ranges: Insights from landscape dynamics, uplift, and active deformation of Talesh Mountains (NW Iranian Plateau margin)

Drainage divides are dynamic features of a landscape that migrate over time during the development of river networks. In this study, we focused on the geomorphic response of a landscape to the interaction among tectonics, climate, and lithology in the Talesh Mts. along the northwest of the Iranian Plateau. The footprints of these competing forces have been analyzed by divide stability analysis and applying χ, χQ, and Gilbert metrics. Additionally, we examined the effects of bedrock erodibility on landscape evolution processes by measuring the mechanical rock strength of the lithological units in different sectors of the mountain range. The distribution of the χ values suggests a disequilibrium of the drainage networks across the whole main divide and its tendency to migrate towards the interior of the plateau. In contrast, Gilbert metrics, which focuses on a narrow topographic zone across the divide, suggest that the uppermost divide in the northern and southern Talesh Mts. is stable. Moreover, asymmetry in Gilbert metrics across the central part of the range suggests that the divide might be migrating towards the plateau interior. The possible scenario for the whole divide's behavior is associated with the contrasting erosion rates across the divide. In the northern and southern sectors of the Talesh Mts. range, the erosional wave related to the most recent uplift pulses has not reached the divide yet. Mechanism of topographic rejuvenation is controlled by heterogeneous uplift of strong bedrock units in the northern and southern sectors, and weak bedrock units outcropping in the central sector, initiated topographic rejuvenation largely in the central Talesh Mts. Parallelly, the precipitation has a limited effect in assisting and magnifying the divide mobility, reorganization, and landscape transience. In general, we can infer that divide is in a transient state due to the spatially varying rock uplift and bedrock erodibility.

Holocene vertical velocity fields in the Calabrian Arc (southern Italy): New insights from uplifted sea-level markers in the Crotone Peninsula

The study of fossil coastlines is one of the most widely used methods to unravel the vertical movements of the Earth's solid surface. All along the coast of the Calabrian Subduction Arc, well preserved Pleistocene marine terrace sequences document a protracted uplift history. Although Pleistocene vertical movements have been extensively explored, the Holocene history is not well understood. Numerous uplifted coastlines of the Holocene period have been studied along the Tyrrhenian side of Calabria, but the Ionian coastal sector is considerably under-studied. Our new data from the coast of the Crotone Peninsula fill this crucial data-gap. AMS 14C dating of seventeen sea level markers, elevated above the current mean sea level, show ages between 2300 and 7000 Cal. Yr BP. The elevation of the markers was corrected for the paleo sea level using the most updated GIA models ICE-6G (VM5a) and ICE-7G (VM7). We found that a coastline dated to 7 ka shows uplift rates of 0.8 mm/yr, consistent with late Pleistocene uplift rates (≈0.8 mm/yr). In contrast, a 2.3 ka coastline was uplifted by only 1 m, resulting in lower uplift rates of ≈0.5 mm/yr. However, there are clues that the abandonment of this younger coastline may have occurred with a rapid uplift pulse. Reconstructing the past vertical movements of the Crotone Peninsula reveals an unsteady uplift history. At some times fast uplift rates are required, while for other periods, lasting as long as 3–4 kyr, the uplift rate is slower or zero. An uplift history consisting of periods of accelerated uplift, or even coseismic pulses, would also explain the difference in uplift rates between short term (<5 ka) and long term (>5 ka) markers through a metric we have defined as uplift rate sensitivity. Understanding the details of this uplift history has social relevance. The co-seismic uplift hypothesis requires further investigation but if confirmed would likely affect the seismic and tsunami hazard of the Crotone Peninsula. Similarly, the unsteady uplift rate would cause a risk given the current rapid rate of global sea level rise. Periods of sustained vertical stability would increase the risk of flooding even in areas characterized by long-term uplift and thus considered safe.

Andean evolution, orogenic deformation and uplift of the Western Cordillera and Altiplano of southern Peru, northern Bolivia and Chile: Eocene-Oligocene lithospheric delamination

Reappraisal of Andean evolution in southern Peru, northern Bolivia and northern Chile provides support for models of orogenic cyclicity in which Andean crustal shortening in the Western Cordillera led to Eocene-Oligocene lithospheric delamination which triggered a renewed pulse of Andean uplift. The sedimentary fill of the Arequipa "rift" back-arc basin (Rhaetian-Neocomian) was controlled by two major graben-bounding fault systems: the Condoroma-Caylloma and Cincha-Lluta-Incapuquio; as well as the Cusco-Lagunillas fault system separating the back-arc region from the Cusco-Puno high. These thinned cortical inherited structures, were the most favourable places to undergo a positive tectonic inversion at the beginning of Andean compression (Albian), and then during Late Cretaceous-Paleocene shortening, they continued to develop as east-vergent crustal decollements which allowed crustal doubling and Western Cordillera thickening. The crustal thickening of >45 km took place along the Condoroma-Caylloma inverted graben where the lower crust, which was probably enriched in basalts, was subjected to high-pressure metamorphism leading to eclogitization, and became denser than the underlying mantle lithosphere and therefore delamination occurred. The subsequent asthenospheric upwelling led to lithospheric thinning, asthenospheric mantle magmatism of the first stage of Andahuaylas-Yauri batholith emplacement (∼48-43 Ma), which crystallized under temperatures of 1200–700 °C and pressures of 1.0–0.5 GPa (>40-30 km deep). This process was followed by the rapid surface uplift of the Western Cordillera that reached 3.1 km and fed the Kayra and Lower Moquegua basins, located on the Altiplano and in the forearc respectively. The delamination process was still active during 43–30 Ma, with second-stage magmatism of the Andahuaylas-Yauri batholith, emplaced continuously from deep mafic intrusions (40-30 km) to superficial porphyries (3 km). This indicates an important uplift of the Western Cordillera to 3.3 km, supported by mantle upwelling and the continuous flat-slab compression that prevented normal faults from developing, and rather produced the shortening of the delaminated crust. The Anta-Soncco foreland basins (43-30 Ma) of the Altiplano and Moquegua basin of the forearc, received the products of Cordilleran denudation at a rate of up to 700 m/My. The alkaline potassic magmatism (29–27 Ma) could represent episodes of post-delamination magmatism and the late stage of flat subduction.

Enhanced weathering input from South Asia to the Indian Ocean since the late Eocene

Enhanced silicate weathering induced by the uplift of the Himalayan-Tibetan Plateau (HTP) has been considered as the major cause of pCO2 decline and Cenozoic cooling. However, this hypothesis remains to be validated, largely due to the lack of a reliable reconstruction of the HTP weathering flux. Here, we present a 37-million-year record of the difference in the seawater radiogenic neodymium isotopic composition (ΔεNd) of Ocean Drilling Program (ODP) sites and Fe-Mn crusts between the northern and central Indian Ocean, which indicates the contribution of regional weathering input from the South Asian continent to the Indian Ocean. The results show a long-term increase in ΔεNd and thus provide the first critical evidence of enhanced South Asian weathering input since the late Eocene. The evolution coincided well with major pulses of surface uplift in the HTP and global climatic transitions. Our foraminiferal εNd record suggests that tectonic uplift and silicate weathering in South Asia, especially in the Himalayas, might have played a significant role in the late Cenozoic cooling.

Paleoenvironmental changes recorded at a late Maastrichtian marine succession of northern South America

One of the major environmental and biotic turnovers of the Phanerozoic occurred at the Cretaceous-Paleogene (K-Pg) boundary, being the focus of countless scientific studies that addressed the timing, causes and consequences of this global event. Paleoenvironmental conditions that preceded the K-Pg boundary, however, have been less studied, especially at low latitudes. In order to help reconstructing late Maastrichtian marine environments along the equatorial South American margin, we apply micropaleontological and geochemical techniques to a stratigraphic core that recovered the Colón Formation in northern Colombia. Low abundance foraminiferal assemblages were overall dominated by benthic taxa (Maastrichtian local biozones Siphogenerinoides bramletti and Ammobaculites colombiana), and the planktonic species Guembelitria cretacea. Ostracod assemblages were mainly composed of the genera Veenia, Cytherella, Paracypris, and Cythereis. Calcareous nannofossils were typical of Upper Cretaceous low-latitude successions, with low abundance and diversity assemblages dominated by Micula staurophora, Kamptnerius magnificus and Cervisiella operculata. Sediment elemental ratios (Zr/Rb, Fe/Ca and Sr/Ba), as well foraminiferal, ostracod and nannofossils assemblages, indicate a shallowing upward trend, characterized by a transition from inner platform settings to sublittoral conditions. Input of terrigenous sediments and weathering intensity also increased upward in the section, probably related to the uplift pulses of the Andean orogeny. Proportions of benthic infauna, as well the V/Cr ratio and the distribution of redox-sensitive trace metals (Ni, Cu) along the core, mostly indicate suboxic bottom water conditions in the Colón Formation.

Disequilibrium river networks dissecting the western slope of the Sierra Nevada, California, USA, record significant late Cenozoic tilting and associated surface uplift

Abstract The timing, rates, and spatial patterns of elevation change in the Sierra Nevada, California, USA, have long been the subject of vigorous debate owing to their importance in constraining the tectonic history of western North America and models of orogenesis. Here we present a systematic analysis of multiple measures of fluvial geomorphology along the entire length of the range and interpret these observations using 1-D and 2-D landscape evolution modeling based on the stream power fluvial erosion rule with the rate parameter calibrated from a large data set of millennial-scale erosion rates. We demonstrate that westward-draining rivers in the Sierra Nevada are in a disequilibrium state and that this state is consistent with the transient fluvial response expected from significant down-to-the-west tilting in the last 11 m.y. Assuming rigid-block tilting and using multiple independent measures of tilt magnitude, we find that the magnitude of surface uplift from late Cenozoic tilting appears to have been similar along strike and likely resulted in ~500–1300 m of surface uplift at the crest (0.3–0.8° tilt) from the Yuba through the Stanislaus rivers (~39.2–38.2°N) and 1000–1400 m of surface uplift at the crest (0.6–0.9° tilt) from the Tuolumne River south through the Kings River (~38.2–36.4°N). We show that the transient fluvial response to tilting in the northern Sierra is heavily modulated by heterogeneous lithology and drainage area exchange in a manner that reconciles the high spatial variability in basement incision observed in numerous prior studies. However, we find that heterogeneous lithology alone cannot explain both the transient state and observed patterns in channel steepness, which seem to require late Cenozoic changes in tectonic forcing. Beyond the regional implications of a short-lived rapid pulse of late Cenozoic surface uplift along the entire length of the range, our results demonstrate that a range-wide approach in which river networks are analyzed both in planform and profile can elucidate tectonic histories despite heterogeneous lithology and ongoing changes in network topology.

Provenance Shifts During Neogene Brahmaputra Delta Progradation Tied to Coupled Climate and Tectonic Change in the Eastern Himalaya

AbstractThe Bengal Basin preserves the erosional signals of coupled tectonic‐climatic change during late Cenozoic development of the Himalayan orogen, yet regional correlation and interpretation of these signals remains incomplete. We present a new geologic map of fluvial‐deltaic deposits of the Indo‐Burman Ranges (IBR), five detrital zircon fission track analyses, and twelve high‐n detrital zircon U‐Pb age distributions (dzUPb) from the Barail (late Eocene–early Miocene), Surma (early–late Miocene), and Tipam (late Miocene–Pliocene) Groups of the ancestral Brahmaputra delta. We use dzUPb statistical tests to correlate the IBR units with equivalent age strata throughout the Bengal Basin. An influx of trans‐Himalayan sediment and the first appearance of ∼50 Ma grains of the Gangdese batholith in the lower Surma Group (∼18–15 Ma) records the early Miocene arrival of the ancestral Brahmaputra delta to the Bengal Basin. Contributions from Himalayan sources systematically decrease up section through the late Miocene as the contribution of Trans‐Himalayan Arc sources increases. The Miocene (∼18–8 Ma) deposition of the Surma Group records upstream expansion of the ancestral Brahmaputra River into southeastern Tibet. Late Miocene (&lt;8 Ma) progradation of the fluvial part of the delta (Tipam Group) routed trans‐Himalayan sediment over the shelf edge to the Nicobar Fan. We propose that Miocene progradation of the ancestral Brahmaputra delta reflects increasing rates of erosion and sea level fall during intensification of the South Asian Monsoon after the Miocene Climate Optimum, contemporaneous with a pulse of tectonic uplift of the Himalayan hinterland and Tibet.

Tectonically and climatically driven mountain-hopping erosion in central Guatemala from detrital &amp;lt;sup&amp;gt;10&amp;lt;/sup&amp;gt;Be and river profile analysis

Abstract. The rise of a mountain range affects moisture circulation in the atmosphere and water runoff across the land surface, modifying the distribution of precipitation and drainage patterns in its vicinity. Water routing in turn affects erosion on hillslopes and incision in river channels on surrounding mountain ranges. In central Guatemala, two parallel, closely spaced mountain ranges formed during two consecutive pulses of uplift, the first between 12 and 7 Ma (Sierra de Chuacús–Sierra de las Minas), and the second after 7 Ma (Altos de Cuchumatanes). We explore the climatic and tectonic processes through which the rise of the most recent range drove the slowing of river incision and hillslope erosion over the previously uplifted range. The 40Ar/39Ar dating of perched volcanic deposits documents the sequential rise and incision of these mountain ranges. Terrestrial cosmogenic 10Be in river sediments indicates that currently hillslopes in the older range erode more slowly than in the younger range (20–150 vs. 300 m Myr−1). These differences mimic the current distribution of precipitation, with the younger range intercepting the atmospheric moisture before it reaches the older range. River channel steepness and deformation of paleovalleys in the new range further indicate that the younger range has been rising faster than the older range up to today. We review how atmospheric moisture interception and river long-profile adjustment to the rise of the new range have contributed to the decline of erosion rates over the old range. We also explore the consequences of this decline and of aridification on the topographic evolution of the older range. The older range undergoes a slow topographic decay, dominated by backwearing, by the stacking of slowly migrating erosion waves along the mountain flanks, and by the formation of pediments around its base. The morphology of the old range is therefore transitioning from that of a front range to that of a dry interior range.

Variable Quaternary Uplift Along the Southern Margin of the Central Anatolian Plateau Inferred From Modeling Marine Terrace Sequences

AbstractThe southern margin of the Central Anatolian Plateau (CAP) records a strong uplift phase after the early Middle Pleistocene, which has been related to the slab break‐off of the subducting Arabian plate beneath the Anatolian microplate. During the last 450 kyr the area underwent an uplift phase at a mean rate of ~3.2 m/kyr, as suggested by Middle Pleistocene marine sediments exposed at ~1,500 m above sea level. These values are significantly higher than the 1.0–1.5 m/kyr estimated since the Late Pleistocene, suggesting temporal variations in uplift rate. To estimate changes in uplift rate during the Pleistocene we studied the marine terraces along the CAP southern margin, mapping the remnants of the platforms and their associated deposits in the field, and used the TerraceM software to identify the position and elevation of associated shoreline angles. We used shoreline angles and the timing of Quaternary marine sedimentation as constrains for a Landscape Evolution Model that simulates wave erosion of an uplifting coast. We applied random optimization algorithms and minimization statistics to find the input parameters that better reproduce the morphology of CAP marine terraces. The best‐fitting uplift rate history suggests a significative increase from 1.9 to 3.5 m/kyr between 500 and 200 kyr, followed by an abrupt decrease to 1.4 m/kyr until the present. Our results agree with slab break‐off models, which suggest a strong uplift pulse during slab rupture followed by a smoother decrease.

The Jáchal river cross-section revisited (Andes of Argentina, 30°S): Constraints from the chronology and geometry of neogene synorogenic deposits

In the southern Central Andes, between 27 and 33°S, a flab-slab subduction has been established since the last 10 Ma. This particular subduction geometry has been proposed to control the eastward migration of the deformation, with the Precordillera fold-and-thrust belt development and the uplift of the foreland Sierras Pampeanas basement blocks. In this study, we present a 190 km-long structural section, across the easternmost Cordillera Frontal, the Precordillera and the westernmost sector of the Sierras Pampeanas, and revise both previous kinematic models, and the relationship between the establishment of the flat-slab and deformation in the foreland. For this purpose, we integrate published sedimentological data with a new structural analysis. Our forward kinematic model is fed back by: (i) the geometries of Neogene deformed beds throughout the Precordillera, such as sedimentary wedges and angular unconformities; (ii) flexural subsidence due to the topographic and sedimentary loads for each deformation step, constrained by measured stratigraphic sections; (iii) a revised chronostratigraphy and correlation chart of the Cenozoic sedimentary units; and, (iv) recent constraints on the ages of activity of the faults. This allows us to build a model that considers the timing of deformation for each main structure and its relationship with sedimentation, producing a model with better geometrical, sedimentological and paleogeographical constraints than previous proposals.The results of this modelling are presented in six different evolutionary stages. During the first stage, between 19 and 15 Ma, the eastern Cordillera Frontal is uplifted, associated with subsidence in the Rodeo-Iglesia proximal foreland basin, and low subsidence in the Bermejo distal foreland basin. In the second stage, between 15 and 12 Ma, uplift of the Western Precordillera took place, associated with the creation of a shallow detachment beneath the Rodeo-Iglesia basin. The third stage, between 12 and 8 Ma, was the beginning of the Central Precordillera uplift and the first pulse of uplift in the Valle Fértil range. During the next stage, between 8 and 5 Ma, the Central Precordillera rapidly deformed. Between 5 and 2 Ma, deformation in the Western and Central Precordillera almost ceased, and the focus of contractional deformation shifted to the Eastern Precordillera. The last 2 Ma phase is characterized by strike-slip deformation in the Rodeo-Iglesia basin and contractional deformation in the Eastern Precordillera and the Valle Fértil range.The key results are that the amount of total shortening, 66 km (35%), calculated for the cross-section, is significantly less than previously proposed, and the detachment of the Precordillera fold-and-thrust belt is shallower (~6.5 km vs 16 km) than previous models. This last point allows us to connect the Cordillera Frontal with the Precordillera, with a ramp-plane geometry of the detachment, as previously suggested, but allowing at the same time the subsidence and the generation of the observed geometries in the Rodeo-Iglesia basin.

Petrography and Tectonic Provenance of the Cretaceous Sandstones of the Bredasdorp Basin, off the South Coast of South Africa: Evidence from Framework Grain Modes

The Cretaceous sandstones of the Bredasdorp Basin were investigated to recognize their composition, provenance, and tectonic setting. Ninety-two samples of sandstones from exploration wells E-AH1, E-AJ1, E-BA1, E-BB1, and E-D3 were investigated using both petrographic and X-ray diffraction (XRD) methods. Petrographic studies based on quantitative investigation of the detrital framework grain shows that the Bredasdorp sandstones chiefly consist of quartz (52.2–68.0%), feldspar (10.0–18.0%), and lithic fragments (5.0–10.2%). These sandstones are mostly fine grained, moderately well-sorted, and subrounded to rounded. The modal composition data shows that the sandstones could be classified as subarkosic arenite and lithic arkose. Such a composition of the sandstones perhaps indicates the interplay of pulses of fast uplift of the source area and rapid subsidence of the Bredasdorp Basin, with subsequent periods of calmness within the transgressive-regressive sequence in a rift tectonic regime. The provenance ternary diagrams revealed that the sandstones are mainly of continental block provenances (stable shields and basement uplifted areas) and complemented by recycled sands from an associated platform. The tectonic provenance studies of Bredasdorp Basin revealed that the sandstones are typically rift sandstones and have undergone long-distance transport from the source area along the rift. In the regional context of the evolution of the Bredasdorp Basin, the results presented in this study inferred that the basin developed on a rift passive setting (trailing edge) of the stable continental margins.

Pre-inversion normal fault geometry controls inversion style and magnitude, Farsund Basin, offshore southern Norway

Abstract. Compressional strains may manifest along pre-existing structures within the lithosphere, far from the plate boundaries along which the causal stress is greatest. The style and magnitude of the related contraction is expressed in different ways, depending on the geometric and mechanical properties of the pre-existing structure. A three-dimensional approach is thus required to understand how compression may be partitioned and expressed along structures in space and time. We here examine how post-rift compressional strains are expressed along the northern margin of the Farsund Basin during Late Cretaceous inversion and Palaeogene–Neogene pulses of uplift. At the largest scale, stress localises along the lithosphere-scale Sorgenfrei-Tornquist Zone, where it is expressed in the upper crust as hangingwall folding, reverse reactivation of the basin-bounding normal fault, and bulk regional uplift. The geometry of the northern margin of the basin varies along strike, with a normal fault system passing eastward into an unfaulted ramp. Late Cretaceous compressive stresses, originating from the convergence between Africa, Iberia, and Europe, selectively reactivated geometrically simple, planar sections of the fault, producing hangingwall anticlines and causing long-wavelength folding of the basin fill. The amplitude of these anticlines decreases upwards due to tightening of pre-existing fault propagation folds at greater depths. In contrast, later Palaeogene–Neogene uplift is accommodated by long-wavelength folding and regional uplift of the entire basin. Subcrop mapping below a major, uplift-related unconformity and borehole-based compaction analysis show that uplift increases to the north and east, with the Sorgenfrei-Tornquist Zone representing a hinge line rather than a focal point to uplift, as was the case during earlier Late Cretaceous compression. We show how compressional stresses may be accommodated by different mechanisms within structurally complex settings. Furthermore, the prior history of a structure may also influence the mechanism and structural style of shortening that it experiences.

Boulders as a lithologic control on river and landscape response to tectonic forcing at the Mendocino triple junction

AbstractConstraining Earth’s sediment mass balance over geologic time requires a quantitative understanding of how landscapes respond to transient tectonic perturbations. However, the mechanisms by which bedrock lithology governs landscape response remain poorly understood. Rock type influences the size of sediment delivered to river channels, which controls how efficiently rivers respond to tectonic forcing. The Mendocino triple junction region of northern California, USA, is one landscape in which large boulders, delivered by hillslope failures to channels, may alter the pace of landscape response to a pulse of rock uplift. Boulders frequently delivered by earthflows in one lithology, the Franciscan mélange, have been hypothesized to steepen channels and slow river response to rock uplift, helping to preserve high-elevation, low-relief topography. Channels in other units (the Coastal Belt and the Franciscan schist) may experience little or no erosion inhibition due to boulder delivery. Here we investigate spatial patterns in channel steepness, an indicator of erosion resistance, and how it varies between mélange and non-mélange channels. We then ask whether lithologically controlled boulder delivery to rivers is a possible cause of steepness variations. We find that mélange channels are steeper than Coastal Belt channels but not steeper than schist channels. Though channels in all units steepen with increasing proximity to mapped hillslope failures, absolute steepness values near failures are much higher (∼2×) in the mélange and schist than in Coastal Belt units. This could reflect reduced rock erodibility or increased erosion rates in the mélange and schist, or disproportionate steepening due to enhanced boulder delivery by hillslope failures in those units. To investigate the possible influence of lithology-dependent boulder delivery, we map boulders at failure toes in the three units. We find that boulder size, frequency, and concentration are greatest in mélange channels and that Coastal Belt channels have the lowest concentrations. Using our field data to parameterize a mathematical model for channel slope response to boulder delivery, we find that the modeled influence of boulders in the mélange could be strong enough to account for some observed differences in channel steepness between lithologies. At the landscape scale, we lack the data to fully disentangle boulder-induced steepening from that due to spatially varying erosion rates and in situ rock erodibility. However, our boulder mapping and modeling results suggest that lithology-dependent boulder delivery to channels could retard landscape adjustment to tectonic forcing in the mélange and potentially also in the schist. Boulder delivery may modulate landscape response to tectonics and help preserve high-elevation, low-relief topography at the Mendocino triple junction and elsewhere.

Geology and geochronology of the Tiegelongnan porphyry-epithermal Cu (Au) deposit, Tibet, China: Formation, exhumation and preservation history

The Tiegelongnan (Rongna) deposit is a giant porphyry-epithermal Cu (Au) deposit within the Duolong porphyry district, in the south Qiangtang terrane, central-western Tibet, China. The deposit is centered on multiphase granodiorite porphyry (GP) intrusions intruded in Jurassic sandstone. Phase 1 and 2 GP are associated with biotite and sericite alteration, whereas GP3 and 4 occur in middle and shallow parts of the deposit affected by sericite and advanced argillic alteration (alunite-kaolinite-dickite-pyrophyllite). Sericite alteration is pervasive in the deep part of the deposit replacing biotite alteration and hosting porphyry stage chalcopyrite-bornite-pyrite ± molybdenite mineralization. Advanced argillic alterationis associated with epithermal stage high sulfidation (tennantite, enargite, bornite, and digenite) mineralization, overprints the sericite and biotite alteration from the shallow part of the deposit. The top of the Tiegelongnan hydrothermal system was weathered with a layer of supergene oxidation and enrichment zone, exhumated, and covered by andesite and gravel.Muscovite sampled from deep sericite alteration yields a 40Ar-39Ar age of 120.9 ± 0.8 Ma, which is consistent with previously reported hydrothermal biotite 40Ar-39Ar age of 121.1 ± 0.6 Ma, molybdenite Re-Os ages of 121.2 ± 0.6 and 119.0 ± 1.4 Ma, and GP 1 and 2 zircon U-Pb ages of 121.5 ± 1.5, 120.2 ± 1.0 Ma (LA-ICP-MS results), and 118.7 ± 0.9 Ma (SIMS result). Phase 3 GP 3 yields a CA-ID-TIMS zircon U-Pb age of 119.9 ± 0.2 Ma, which constrains the age of porphyry magmatic-hydrothermal events. The porphyry system was then unroofed, weathered, and superimposed by discrete stages of advanced argillic alteration and high sulfidation mineralization. Two pulses of alunite events yield 40Ar-39Ar ages of 116.3 ± 0.8 Ma and 111.7 ± 1.0 Ma, which represent the principal epithermal alteration and mineralization ages at Tiegelongnan. The first alunite pulse age is consistent with younger porphyry (GP4) age of 116.2 ± 0.4 Ma (zircon LA-ICP-MS age). Weathering and exhumation of the porphyry-epithermal deposit were continuing until the cover of andesite at ~110 Ma and by post-andesite gravel. The andesite was affected by a younger weak hydrothermal alteration at 108.7 ± 0.7 Ma, constrained by a muscovite 40Ar-39Ar age. Another barren alunite yields a 40Ar-39Ar age of 100.6 ± 2.0 Ma, which may represent the youngest hydrothermal event. The long life-span discrete hydrothermal activities from ~120 to ~100 Ma in the Tiegelongnan deposit is consistent with the long-lasting tectonic-magmatic events of the Bangong-Nujiang suture zone.The discrete epithermal mineralization events at Tiegelongan are younger than the porphyry mineralization events, which is analogous to several other epithermal deposits worldwide. The ~10 m.y exhumation history at Tiegelongan is slower than the typical and rapid erosion history of ~1–2 m.y porphyry deposits in low-altitude tropical climates regions, and during a specific abrupt uplift pulse in the Andean region. The slow exhumation at Tiegelongnan is interpreted to be an integrated result of an arid climate environment, relatively flat topography, and a slow uplift condition during Cretaceous in central-western Tibet.

Early Pleistocene uplift of the northeastern Tibetan Plateau: Evidence from the Dunhuang Basin, NW China

The Cenozoic uplift of the Tibetan Plateau plays an important role in global climate change, basin-mountain geomorphology formation and desertification in western China. As an important component, the Early Pleistocene uplift process and its influence on the northeastern Tibetan Plateau has been controversial for many years. Quaternary synorogenic sediments within the Dunhuang Basin on the northeastern Tibetan Plateau record the details of plateau uplift. Detailed grain size analysis, rock magnetic properties, mudstone 36Cl dating and 40Ar/39Ar detrital mica dating were conducted on the Quaternary alluvial-fluvial-lacustrine-aeolian sediments of the Dunhuang Basin. The Aksay section in the southern Dunhuang Basin is dominated by conglomerate, sandstone, siltstone and mudstone. Detrital mica 40Ar/39Ar ages show major age populations of 200–160 Ma, 400–200 Ma and 510–430 Ma from the northeastern Altyn Mountains. The results of 36Cl ages and rock magnetic properties show that the Altyn Mountains rapidly uplifted at 1.16 Ma. From 1.16 to 0.80 Ma, the sedimentary environment was stable with two small-scale uplift pulses at ca. 1.03 Ma and 0.98 Ma. After 0.80 Ma, the climate became arid, and the Kumtag Desert formed in the Dunhuang Basin. These multistage uplifts are also widely found in the northeastern Tibetan Plateau. The Early Pleistocene uplift of the Altyn Mountains, corresponding to the Kunhuang Movement, resulted in the northeastern margin of the Tibetan Plateau reaching its present height and climate changeing towards drought in this region.

Major lineages of Loasaceae subfam. Loasoideae diversified during the Andean uplift

The Loasoideae is the largest clade in the Loasaceae. This subfamily is widespread throughout the Neotropics and centered in the Andes, presenting an excellent opportunity to study diversification across much of temperate and mid to high-elevation areas of South America. Despite that, no studies have addressed the historical biogeography of the Loasoideae to date, leaving an important knowledge gap in this plant group. Here, we used four plastid markers (i.e., trnL–trnF, matK, trnS–trnG, and rps16) and sequenced 170 accessions (134 ingroup taxa) to infer the phylogeny of Loasoideae. We then used this phylogeny as basis to estimate divergence times using an uncorrelated relaxed molecular clock approach and seven fossils as primary calibration points. We employed the Dispersal-Extinction-Cladogenesis (DEC) approach to reconstruct the ancestral ranges of the subfamily. Our results indicate that stem Loasoideae diverged from its sister group in the Late Cretaceous to Early Paleocene (ca. 83–62 Ma). The crown node of the whole clade goes back to the Middle Paleocene to Middle Eocene (ca. 60–45 Ma), corresponding to the earliest diversification events of the extant groups, prior to most of the Andean orogeny and roughly coinciding with the Paleocene-Eocene Thermal Maximum. On the other hand, the crown nodes of most genera appear to have originated in the Oligocene and Miocene (median ages: 28–10 Ma). The diversification of some extant lineages appears to have happened in parallel to Andean uplift pulses that seem to have had an effect on the orogeny and concomitant establishment of new habitats and latitudinal corridors. The most likely ancestral areas retrieved for crown Loasoideae, are the tropical Andes and Pacific arid coast. Most of the extant clades have remained restricted to their ancestral areas. Transoceanic Long Distance Dispersal appears to have been involved in the arrival of Loasoid ancestors to South America, and in the distribution of the small clades Kissenia in Africa and Plakothira on the Marquesas Archipelago. The results presented here suggest that the historical biogeography of the continental scale radiation of Loasoideae, follows the sequence and timing of the development of temperate and mid to high-elevation habitats across South America during the Tertiary.