scholarly journals Convergence of the Pamir and the South Tian Shan in the late Cenozoic: Insights from provenance analysis in the Wuheshalu section at the convergence area

Lithosphere ◽  
2019 ◽  
Vol 11 (4) ◽  
pp. 507-523 ◽  
Author(s):  
Xinwei Chen ◽  
Hanlin Chen ◽  
Edward R. Sobel ◽  
Xiubin Lin ◽  
Xiaogan Cheng ◽  
...  
Keyword(s):  
Source Area ◽  
Limited Area ◽  
Late Cenozoic ◽  
Provenance Analysis ◽  
The South ◽  
Active Deformation ◽  
The North ◽  
Large Populations ◽  
A Minor ◽  
Tian Shan

Abstract In response to collision and convergence between India and Asia during the Cenozoic, convergence took place between the Pamir and South Tian Shan. Here we present new detrital zircon U-Pb ages coupled with conglomerate clast counting and sedimentary data from the late Cenozoic Wuheshalu section in the convergence zone, to shed light on the convergence process of the Pamir and South Tian Shan. Large Triassic zircon U-Pb age populations in all seven samples suggest that Triassic igneous rocks from the North Pamir were the major source area for the late Cenozoic Wuheshalu section. In the Miocene, large populations of the North Pamir component supports rapid exhumation in the North Pamir and suggest that topography already existed there since the early Miocene. Exhumation of the South Tian Shan was relatively less important in the Miocene and its detritus could only reach a limited area in the foreland area. Gradually increasing sediment loading and convergence of the Pamir and South Tian Shan caused rapid subsidence in the convergence area. Since ca. 6–5.3 Ma, the combination of a major North Pamir component and a minor South Tian Shan component at the Wuheshalu section is consistent with active deformation of the South Tian Shan and the North Pamir. During deposition of the upper Atushi Formation, a larger proportion of North Pamir–derived sediments was deposited in the Wuheshalu section, maybe because faulting and northward propagation of the North Pamir caused northward displacement of the depocenter to north of the Wuheshalu section.

Geodynamics of the France Southeast Basin

2010 ◽  
Vol 181 (6) ◽  
pp. 477-501 ◽  
Author(s):  
Xavier Le Pichon ◽  
Claude Rangin ◽  
Youri Hamon ◽  
Nicolas Loget ◽  
Jin Ying Lin ◽  
...  
Keyword(s):  
Seismic Activity ◽  
Sedimentary Cover ◽  
Central Basin ◽  
The South ◽  
Western Basin ◽  
Active Deformation ◽  
The North ◽  
The Alps ◽  
Sediment Cover ◽  
Surrounding Areas

AbstractWe investigate the geodynamics of the Southeast Basin with the help of maps of the basement and of major sedimentary horizons based on available seismic reflection profiles and drill holes. We also present a study of the seismicity along the Middle Durance fault. The present seismic activity of the SE Basin cannot be attributed to the Africa/Eurasia shortening since spatial geodesy demonstrates that there is no significant motion of Corsica-Sardinia with respect to Eurasia and since gravitational collapse of the Alps has characterized the last few millions years. Our study demonstrates that the basement of this 140 by 200 km Triassic basin has been essentially undeformed since its formation, most probably because of the hardening of the cooling lithosphere after its 50% thinning during the Triassic distension. The regional geodynamics are thus dominated by the interaction of this rigid unit with the surrounding zones of active deformation. The 12 km thick Mesozoic sediment cover includes at its base an up to 4 km thick mostly evaporitic Triassic layer that is hot and consequently highly fluid. The sedimentary cover is thus decoupled from the basement. As a result, the sedimentary cover does not have enough strength to produce reliefs exceeding about 500 to 750 m. That the deformation and seismicity affecting the basin are the results of cover tectonics is confirmed by the fact that seismic activity in the basin only affects the sedimentary cover. Based on our mapping of the structure of the basin, we propose a simple mechanism accounting for the Neogene deformation of the sedimentary cover. The formation of the higher Alps has first resulted to the north in the shortening of the Diois-Baronnies sedimentary cover that elevated the top of Jurassic horizons by about 4 km with respect to surrounding areas to the south and west. There was thus passage from a brittle-ductile basement decollement within the higher Alps to an evaporitic decollement within the Diois-Baronnies. This shortening and consequent elevation finally induced the southward motion of the basin cover south of the Lure mountain during and after the Middle Miocene. This southward motion was absorbed by the formation of the Luberon and Trévaresse mountains to the south. To the east of the Durance fault, there is no large sediment cover. The seismicity there, is related to the absorption of the Alps collapse within the basement itself. To the west of the Salon-Cavaillon fault, on the other hand, gravity induces a NNE motion of the sedimentary cover with extension to the south and shortening to the north near Mont Ventoux. When considering the seismicity of this area, it is thus important to distinguish between the western Basin panel, west of the Salon-Cavaillon fault affected by very slow NNE gliding of the sedimentary cover, with extension to the south and shortening to the north; the central Basin panel west of the Durance fault with S gliding of the sedimentary cover and increasing shortening to the south; and finally the basement panel east of the Durance fault with intrabasement absorption of the Alps collapse through strike-slip and thrust faults.

PALEOSEISMOLOGICAL INVESTIGATIONS AT THE FRONT OF THE EASTERN SOUTHERN ALPS (NE Italy)

2020 ◽  
Author(s):  
Giulia Patricelli ◽  
Maria Eliana Poli ◽  
Giovanni Paiero ◽  
Giovanni Monegato ◽  
Francesco Marinoni ◽  
...  
Keyword(s):  
Damage Zone ◽  
Southern Alps ◽  
Alluvial Fan ◽  
The South ◽  
Active Deformation ◽  
The North ◽  
Ne Italy ◽  
Structural Framework ◽  
Accademia Dei Lincei ◽  
The Village

<p>In the framework of the III level Seismic Microzonation of the Pieve del Grappa municipality (Treviso, NE Italy), three paleoseismological trenches were dug, in order to investigate activity and capacity of the Crespano del Grappa backthrust.</p><p>The study area is located in the Veneto foothills, where the Plio-Quaternary external front of the Eastern Southern Alps (Castellarin and Cantelli, 2000) presently propagates with a 2-3 mm/y velocity towards the south (Serpelloni et al., 2016). The external front is composed of a series of arcuated WSW-ENE striking, S verging structures (Galadini et al, 2005). Moreover, the area is characterized by a medium-to-low seismicity with only one M>6 earthquake during the last millennium: the 1695 Asolo event, Mw 6.45 (Rovida et al., 2016).</p><p>Regarding the structural framework, the study area is located between the Bassano-Vittorio Veneto Thrust to the north and the Bassano-Cornuda Thrust to the south. The investigated tectonic structure, i.e. the Bassano-Cornuda backthrust, is a N-verging E-W striking reverse structure. Moving from east to the west, it widely crops out near the Castelcucco village, causing a hundred meters displacement in the Miocene Molasse (Braga, 1970). In particular in Crespano village the thrust is responsible of an about 10 m vertical throw in the Quaternary alluvial conglomerates of Lastego river (Parinetto, 1987). Because of the urbanization, the paleoseismological trenches were realized at the eastern (Col Canil) and western (San Vito) borders of the village. In the former case, the trench cut through thick colluvial deposits that probably buried an abandoned valley. Differently, the second and the third trenches affected wide coalescent LGM alluvial fans, which border the southern slope of Mt. Grappa.</p><p>The results testify an intense Pleistocene-Holocene deformation of the Crespano del Grappa backthrust. Particularly, active deformation evidence deals with:</p><ul><li>back-tilting of the Holocene colluvial units;</li> <li>pronounced polyphasic liquefaction episodes, locally completely altering the sedimentary structures of colluvial units;</li> <li>a wide damage zone in the proximity of the morphological scarp and associated with the peak of the induced polarization. This observation testifies that the Crespano del Grappa backthrust reached the surface and displaced topography in the past, probably at the occurrence of one or more events which generated the paleoliquefaction effects;</li> <li>the 3-4 m displacement of the LGM alluvial fan deposits.</li> </ul><p>Concerning the age of the deformation, the dating of the involved units suggests a post LGM activation, probably recent-to-historical.</p><p> </p><p>REFERENCES</p><p>Braga GP, 1970. Rendiconti Fisici dell’Accademia dei Lincei, serie 8, 48(4): 451-455.</p><p>Castellarin A. and Cantelli L., 2000. Journal of Geodynamics. DOI: 10.1016/S0264-3707(99)00036-8.</p><p>Galadini et al., 2005. Geophysical Journal International. DOI: 10.1111/j.1365-246X.2005.02571.x.</p><p>Parinetto A., 1987. Aspetti morfotettonici del versante meridionale del Grappa e delle colline antistanti. Unpublished degree thesis. University of Padova, Italy.</p><p>Rovida et al., 2016. DOI: http://doi.org/10.6092/INGV.IT-CPTI15.</p><p>Serpelloni et al., 2016. Tectonophysics, https://doi.org/10.1016/j.tecto.2016.09.026.</p>

scholarly journals Detrital Zircon Provenance Analysis in the Central Asian Orogenic Belt of Central and Southeastern Mongolia—A Palaeotectonic Model for the Mongolian Collage

Minerals ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 880
Author(s):  
Wilfried Winkler ◽  
Denise Bussien ◽  
Munktsengel Baatar ◽  
Chimedtseren Anaad ◽  
Albrecht von Quadt
Keyword(s):  
Orogenic Belt ◽  
Detrital Zircons ◽  
Central Asian Orogenic Belt ◽  
Provenance Analysis ◽  
The South ◽  
Central Mongolia ◽  
Basin Inversion ◽  
The North ◽  
Central Asian ◽  
Sandstone Provenance

Our study is aimed at reconstructing the Palaeozoic–early Mesozoic plate tectonic development of the Central Asian Orogenic Belt in central and southeast Mongolia (Gobi). We use sandstone provenance signatures including laser ablation U-Pb ages of detrital zircons, their epsilon hafnium isotope signatures, and detrital framework grain analyses. We adopt a well-established terran subdivision of central and southeastern Mongolia. However, according to their affinity and tectonic assemblage we group them into three larger units consisting of continental basement, rift-passive continental margin and arc elements, respectively. These are in today’s coordinates: (i) in the north the late Cambrian collage from which the later Mongol-Okhotsk and the Central Mongolia-Erguna mountain ranges resulted, (ii) in the south a heterogeneous block from which the South Mongolia-Xin’gan and Inner Mongolia-Xilin belts developed, and (iii) in between we still distinguish the intra-oceanic volcanic arc of the Gurvansayhan terrane. We present a model for paleotectonic development for the period from Cambrian to Jurassic, which also integrates findings from the Central Asian Orogenic Belt in China and Russia. This mobilistic model implies an interplay of rift and drift processes, ocean formation, oceanic subduction, basin inversion, collision and suture formation in space and time. The final assemblage of the Central Asian Orogenic Belt occurred in Early Jurassic.

Constraint of Active Deformation between the African Platform and the Maghrebian Thrust Belt: Current Plate Motion from Permanent GNSS data in Algeria

2021 ◽  
Author(s):  
Mustapha Meghraoui ◽  
Hassen Abdellaoui ◽  
Frédéric Masson
Keyword(s):  
Suture Zone ◽  
Plate Motion ◽  
Thrust Belt ◽  
The South ◽  
Active Deformation ◽  
The North ◽  
Gps Velocities ◽  
Gnss Data ◽  
Tectonic Boundary ◽  
North And South

<p>The kinematic of tectonic motions between the African (Sahara) platform and the Maghrebian thrust belt remained unexplored since the onset of space geodesy. Here, we use data of 6 permanent GNSS stations located north and south of the Atlas thrust belt in Algeria to constrain shortening and transpression at the tectonic boundary. The permanent GPS data and results are obtained from the network in Algeria operative from 2013 to 2019, presented with the results of the REGAT network in Algeria since 2007. The south Atlas suture zone constitutes the limit between African (Sahara) shield domain considered as a stable continental interior and the Sahara Atlas that belong to the Alpine orogeny. The tectonic boundary is marked by a E-W to ENE-WSW, en echelon fold belt system with deformed Plio-Quaternary formations to the North and flat laying Mesozoic and Tertiary sedimentary units south of the suture zone. The GNSS data are processed using Gamit-GlobK and results show tectonic motions with a predominant 5 to 6 mm/yr velocities trending NNW-SSE to NW-SE (westward) in the Sahara Platform. The GPS velocities show uniform trend in the African platform from which we infer 0.5 to 1.0 mm/yr convergence across the south Atlas suture zone. The intraplate convergence is attested by the moderate but permanent seismic activity at the tectonic boundary.</p>

Cenozoic tectonic evolution of the Pamir-Tian Shan convergence zone: evidence from detrital zircon U-Pb provenance analysis

2020 ◽  
Author(s):  
Yingying Jia ◽  
Christoph Glotzbach ◽  
Todd Ehlers ◽  
Lixing Lü
Keyword(s):  
Tarim Basin ◽  
Detrital Zircon ◽  
Tectonic Evolution ◽  
Middle Miocene ◽  
Source Area ◽  
Convergence Zone ◽  
Late Cenozoic ◽  
Crustal Shortening ◽  
Early Cenozoic ◽  
Tian Shan

<p><span>The Pamir is an along-strike continuation of the Tibet-Himalaya orogen and penetrated ~300 km into the Tarim and Tajik basins in Cenozoic times. This northward indentation led to regional paleoenvironmental changes and facilitated northward transport of the far-field stress from the India-Asia plate boundary. Due to the compressional stress from the India-Asia boundary and Cenozoic lithosphere delamination, the Pamir underwent intense exhumations, which well recorded its Late Cenozoic mountain building processes. However, the very rapid Late Cenozoic exhumation also erased earlier cooling records and hinders a clear understanding of the Early Cenozoic tectonic evolution of Pamir. Thus, the onset and magnitude of the northward movement of Pamir are loosely constrained (Eocene-Late Oligocene) and long debated. In particular, the Early Cenozoic tectonic evolution of Pamir is unclear.</span></p><p><span>Provenance study of sediments in the adjacent sediment basins is a widely used method to reconstruct the tectonic-geomorphologic evolution of a mountain range. We carried out paleocurrent measurements and detrital zircon analysis of the Cretaceous-Pliocene sediments in the northern Pamir-Tian Shan convergence zone. Our study area, the Tierekesazi section, is located immediately south to the southern Tian Shan and is evolved in the present foreland basin of the southwestern Tian Shan. The provenance data show that the Tian Shan was the primary source area of the northwestern Tarim basin in the Cretaceous. The appearance of the Triassic-Jurassic detrital zircon grains and northward paleo-flow directions in the Eocene (~41 Ma) to Middle Miocene sediments suggest the Pamir became an important source area of the northwestern Tarim basin. Combining with the regional crustal shortening and paleoclimate data, we speculate that the northward indentation of the Pamir initiated before ~41 Ma. In contrast with the northward movement and Middle-Late Miocene accelerated exhumation of the Pamir, the source area of the studied section shifted back to the Tian Shan after the Middle Miocene. It consists with the Middle-Late Miocene uplift of the southwestern Tian Shan. Simultaneously, the crustal shortening of Pamir propagated to its northern foreland. Newly formed fold-and-thrust zones probably blocked the sediment transport from Pamir to the Tierekesazi section, and the present-day east flowing drainage system in the Pamir-Tian Shan convergence zone was established. We infer, in this period, the Pamir likely reached its present position, which is consistent with the appearance of an extreme arid climate in the Tarim basin.</span></p>

Reproductive dynamics of the grooved tiger prawn, Penaeus semisulcatus, in the north-western Gulf of Carpentaria, Australia

1987 ◽  
Vol 38 (1) ◽  
pp. 79 ◽  
Author(s):  
PJ Crocos
Keyword(s):  
Egg Production ◽  
Fishing Effort ◽  
Minimum Size ◽  
Limited Area ◽  
The North ◽  
Penaeus Semisulcatus ◽  
Spawning Stock ◽  
Tiger Prawn ◽  
A Minor ◽  
North Western

The reproductive cycle of female P. semisulcatus was investigated in the region north of Groote Eylandt in the Gulf of Carpentaria from August 1983 to March 1985. Approximately 1750 trawls were carried out over 21 monthly sampling cruises, and 13 748 females were examined. The minimum size at maturity was 29 mm carapace length (CL), and 50% of the population were mature at 39 mm CL. The proportion of females which had mated increased sharply above 34 mm CL with a maximum of 80% of females inseminated in the size range 38-54 mm CL. An index of population egg production, calculated from female abundance, the proportion of females spawning and fecundity according to size, was used as an indicator of reproductive output. Egg production was markedly seasonal, with a major spawning peak in August-September, and a minor one in February. Spawning occurred in a limited area within rhe study area. The spawning stock of P. semisulcatus is likely to be vulnerable to fishing pressure because the area and time of major spawning coincides with the major fishing effort in the region.

scholarly journals Isoprene emissions modelling for West Africa using MEGAN

2010 ◽  
Vol 10 (3) ◽  
pp. 6923-6953 ◽  
Author(s):  
J. Ferreira ◽  
C. E. Reeves ◽  
J. G. Murphy ◽  
L. Garcia-Carreras ◽  
D. J. Parker ◽  
...  
Keyword(s):  
West Africa ◽  
Emission Factors ◽  
Sensitivity Analyses ◽  
Limited Area ◽  
The South ◽  
Area Index ◽  
Mixing Ratios ◽  
Changing Climate ◽  
The North ◽  
The Impact

Abstract. Isoprene emissions are the largest source of reactive carbon to the atmosphere, with the tropics being a major source region. These natural emissions are expected to change with changing climate and human impact on land use. As part of the African Monsoon Multidisciplinary Analyses (AMMA) project the Model of Emissions of Gases and Aerosols from Nature (MEGAN) has been used to estimate the spatial and temporal distribution of isoprene emissions over the West African region. During the AMMA field campaign, carried out in July and August 2006, isoprene mixing ratios were measured on board the FAAM BAe-146 aircraft. These data have been used to evaluate the model performance. MEGAN was firstly applied to a large area covering much of West Africa from the Gulf of Guinea in the south to the desert in the north and was able to capture the large scale spatial distribution of isoprene emissions as inferred from the observed isoprene mixing ratios. In particular the model captures the transition from the forested area in the south to the bare soils in the north, but some discrepancies have been identified over the bare soil, mainly due to the emission factors used. Sensitivity analyses were performed to assess the model response to changes in driving parameters, namely Leaf Area Index (LAI), Emission Factors (EF), temperature and solar radiation. A high resolution simulation was made of a limited area south of Niamey, Niger, where the higher concentrations of isoprene were observed. This is used to evaluate the model's ability to simulate smaller scale spatial features and to examine the influence of the driving parameters on an hourly basis through a case study of a flight on 17 August 2006. This study highlights the complex interactions between land surface processes and the meteorological dynamics and chemical composition of the PBL. This has implications for quantifying the impact of biogenic emissions on the atmospheric composition over West Africa and any changes that may occur with changing climate.

The geology of the Bristol Channel floor

1973 ◽  
Vol 274 (1244) ◽  
pp. 595-626 ◽  
Keyword(s):  
Source Area ◽  
Upper Jurassic ◽  
Lower Jurassic ◽  
Gravity Corer ◽  
Side Scan Sonar ◽  
The North ◽  
Reconnaissance Survey ◽  
Clastic Sediments ◽  
Jurassic Rocks ◽  
A Minor

A reconnaissance survey has been made with side-scan sonar, Boomer and gravity corer of a sea-floor area extending from the mouth of the River Severn to the longitude of Hartland Point, and from the North Devon coast to the latitude of Porthcawl. The results include the recognition of two major WNW -ESE trending synclines arranged en echelon with a minor intervening pericline. The eastern syncline, traceable to the longitude of Watchet and preserving Upper Pliensbachian (Lower Jurassic) rocks in its core, is the seaward extension of the Glastonbury Syncline. The western syncline, of which little more than the eastern half could be investigated, includes a sequence of Jurassic rocks up to high Kimeridge Clay. This Bristol Channel Syncline is cut by a series of N W -SE trending tear-faults analogous to those in southwest England and has its southern m argin truncated by a strike fault with northerly transport. The Jurassic sequence is unusual in its abnormal thickness (in excess of 1600 m) and its predominantly argillaceous nature. Thick limestones are unknown, although cementstone bands occur, mainly in the Lower Lias. Sands and sandstones were found only in beds of Upper Oxfordian and, dubiously, of Portlandian (Middle Volgian) age. Elsewhere in the succession, and notably for the Aalenian-Lower Callovian interval, the correlatives of thick carbonate sequences of m ainland successions are thin sands and sandy clays or non-sequences. The Bristol Channel region may therefore have supported a lesser depth of water than other basins in southern England. Facies changes within the area are small. They offer no support to the hypothesis of a Welsh island, but suggest the possibility of a Cornubian source area for clastic sediments in early Upper Jurassic times.

scholarly journals Fluvial deposits of the Diamante Formation as a record of the Late Cretaceous tectonic activity in the Southern Central Andes, Mendoza, Argentina

2020 ◽  
Vol 47 (2) ◽  
pp. 256
Author(s):  
Ricardo Gómez ◽  
Maisa Tunik ◽  
Silvio Casadío
Keyword(s):  
Source Area ◽  
Important Change ◽  
Tectonic Activity ◽  
Fluvial System ◽  
The South ◽  
The West ◽  
The North ◽  
Neuquen Basin ◽  
Neuquén Basin ◽  
San Rafael

The Upper Cretaceous nonmarine deposits of the Neuquén Basin have an important regional exposure. These deposits are included in the Neuquén Group, a well-studied unit in both the south and central part of the basin. However, the northernmost exposed between the Laguna del Diamante and the Atuel River-assigned to the Diamante Formation-have not been studied in detail. In the studied area, the Diamante Formation corresponds to a braided fluvial system with moderate sinuosity evolving through time towards an anastomosing fluvial system. Petrographic analyses indicate that sandstones belong to feldspatic litharenites and litharenites, while the source area indicates provenance from both a recycled orogen and a transitional arc. The latter could be linked to the exhumation of the Andean orogen located to the west and to the input from the north-eastern border of the Neuquén Basin, represented by the rocks currently exposed in the San Rafael Block. On a macroscopic scale, the presence of calcareous lithic fragments in the mid and upper part of the surveyed stratigraphic section, strongly suggest an input from the west. This indicates an important change in the polarity of the basin and the presence of a deformation front located to the west of the study area in accordance to previous proposals in equivalent deposits to the south of study area.

The Central Brae Field, Blocks 16/07a, 16/07b, UK North Sea

2003 ◽  
Vol 20 (1) ◽  
pp. 183-190 ◽  
Author(s):  
Keith J. Fletcher
Keyword(s):  
Upper Jurassic ◽  
Western Boundary ◽  
The South ◽  
Submarine Fan ◽  
Water Contact ◽  
The North ◽  
Oil Water ◽  
Clay Formation ◽  
A Minor ◽  
North And South

abstractThe Central Brae Oilfield is the smallest of three Upper Jurassic fields being developed in UK, Block 16/07a. The field was discovered in 1976 and commended production in September 1989 through a sub-sea template tied back to the Brae 'A' platform in the South Brae Oilfield. The field Stooip is 244 MMBBLs, and by May 1999 cumulative exports of oil and NGL reached 44 MMBBLs.The Central Brae reservoir is a proximal submarine fan sequence, comprising dominantly sand-matrix conglomerate and sanstone with a minor mudstone units. The sediments were shed eastwards off the Fladen Ground Spur and were deposited as a relatively small and steep fan at the margin of the South Viking Graben. Mudstone facies border the submarine fan deposits to the north and south, forming stratigraphic seals. The structure is a faulted anticline developed during the latest Jurassic and early Cretaceous, initially formed as a hangingwall anticline during extension but subsequently tightened during compressional phases. The western boundary of the field is formed by a sealing fault, whilst to the east, there is an oil-water contact at 13426 ft TVDss. The overlying seal is the Kimmeridge Clay Formation, which also interdigitates with the coarser facies basinwards and provides the source of the hydrocarbons.

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