Age and geochemistry of the Paleoproterozoic Bhatwari Gneiss of Garhwal Lesser Himalaya, NW India: implications for the pre-Himalayan magmatic history of the Lesser Himalayan basement rocks

2018 ◽  
Vol 481 (1) ◽  
pp. 319-339 ◽  
Author(s):  
Aranya Sen ◽  
Koushik Sen ◽  
Hari B. Srivastava ◽  
Saurabh Singhal ◽  
Purbajyoti Phukon
Keyword(s):  
Crystalline Rock ◽  
Arc Magmatism ◽  
Content Type ◽  
Basement Rocks ◽  
Petrographic Analyses ◽  
History Of ◽  
Supplementary Material ◽  
Arc Setting ◽  
Magmatic History ◽  
Log Ratio

AbstractThe Bhatwari Gneiss of Bhagirathi Valley in the Garhwal Himalaya is a Paleoproterozoic crystalline rock from the Inner Lesser Himalayan Sequence. On the basis of field and petrographic analyses, we have classified the Bhatwari Gneiss into two parts: the Lower Bhatwari Gneiss (LBG) and the Upper Bhatwari Gneiss (UBG). The geochemical signatures of these rocks suggest a monzonitic protolith for the LBG and a granitic protolith for the UBG. The UBG has a calc-alkaline S-type granitoid protolith, whereas the LBG has an alkaline I-type granitoid protolith; the UBG is more fractionated. The trace element concentrations suggest a volcanic arc setting for the LBG and a within-plate setting for the UBG. The U–Pb geochronology of one sample from the LBG gives an upper intercept age of 1988 ± 12 Ma (n = 10, MSWD = 2.5). One sample from the UBG gives an upper intercept age of 1895 ± 22 Ma (n = 15, MSWD = 0.82), whereas another sample does not give any upper intercept age, but indicates magmatism from c. 1940 to 1840 Ma. Based on these ages, we infer that the Bhatwari Gneiss has evolved due to arc magmatism and related back-arc rifting over a time period of c. 100 Ma during the Proterozoic. This arc magmatism is related to the formation of the Columbia supercontinent.Supplementary material: LA–ICP-MS calibration and adjusted major element data used for computing the isometric log-ratio transformations are available at https://doi.org/10.6084/m9.figshare.c.4272158

Jurassic–Cretaceous arc magmatism along the Shyok–Bangong Suture from NW Himalaya: Formation of the peri-Gondwana basement to the Ladakh Arc

2021 ◽  
pp. jgs2021-035
Author(s):  
Wanchese M. Saktura ◽  
Solomon Buckman ◽  
Allen P. Nutman ◽  
Renjie Zhou
Keyword(s):  
Late Cretaceous ◽  
Nw Himalaya ◽  
Content Type ◽  
Magmatic Arc ◽  
Basement Rocks ◽  
Ladakh Himalaya ◽  
Accreted Terranes ◽  
Volcaniclastic Rocks ◽  
Supplementary Material ◽  
Depositional Age

The Jurassic–Cretaceous Tsoltak Formation from the eastern borderlands of Ladakh Himalaya consists of conglomerates, sandstones and shales, and is intruded by norite sills. It is the oldest sequence of continent-derived sedimentary rocks within the Shyok Suture. It also represents a rare outcrop of the basement rocks to the voluminous Late Cretaceous–Eocene Ladakh Batholith. The Shyok Formation is a younger sequence of volcaniclastic rocks that overlie the Tsoltak Formation and record the Late Cretaceous closure of the Mesotethys Ocean. The petrogenesis of these formations, ophiolite-related harzburgites and norite sill is investigated through petrography, whole-rock geochemistry and U–Pb zircon geochronology. The youngest detrital zircon grains from the Tsoltak Formation indicate Early Cretaceous maximum depositional age and distinctly Gondwanan, Lhasa microcontinent-related provenance with no Eurasian input. The Shyok Formation has Late Cretaceous maximum depositional age and displays a distinct change in provenance to igneous detritus characteristic of the Jurassic–Cretaceous magmatic arc along the southern margin of Eurasia. This is interpreted as a sign of collision of the Lhasa microcontinent and the Shyok ophiolite with Eurasia along the once continuous Shyok–Bangong Suture. The accreted terranes became the new southernmost margin of Eurasia and the basement to the Trans-Himalayan Batholith associated with the India-Eurasia convergence.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5633162

The influence of volcanic supply on the composition of modern river sands: the case study of the Ofanto river, Southern Italy

2021 ◽  
pp. SP520-2021-89
Author(s):  
Mariano Tenuta ◽  
Paola Donato ◽  
Rocco Dominici ◽  
Rosanna De Rosa
Keyword(s):  
Volcanic Rocks ◽  
Pyroclastic Deposits ◽  
Content Type ◽  
Sedimentary Deposits ◽  
History Of ◽  
Supplementary Material ◽  
High Production ◽  
Volcaniclastic Deposits ◽  
Pyroclastic Fall

AbstractThe Ofanto river drains volcanic rocks from the Monte Vulture, lacustrine-fluviolacustrine deposits associated with the same volcano and sedimentary deposits of the Southern Apennines and the Bradanic foredeep sequences. Comparing the modal composition of river sands and the outcrop area of different lithologies in the different sub-basins, an over-concentration of the volcaniclastic fraction, mainly represented by loose crystals of clinopyroxene, garnet and amphibole, is shown. This has been related to the preferential erosion of pyroclastic deposits, characterized by high production of sand-sized loose minerals, together with the carbonate lability and the low sand-sized detritus production from claystones and marls. The occurrence of volcaniclastic components upstream of Monte Vulture can be explained with a contribution from the lacustrine-fluviolacustrine deposits outcropping in the upstream sector or from pyroclastic fall deposits of Monte Vulture and/or Campanian volcanoes. This research shows that the volcanic record in the fluvial sands of the Ofanto river comes from weathering and sorting processes of volcaniclastic deposits rather than of the lavas building the main edifice. Therefore, caution must be taken during paleoenvironmental and paleoclimatic reconstructions when relating the type and abundance of the volcanic component in sediments to the weathering stage and evolutionary history of the volcano.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5643959

Fluids sources in basement-hosted unconformity-uranium ore systems: tourmaline chemistry and boron isotopes from the Patterson Lake corridor deposits, Canada

2021 ◽  
pp. geochem2021-037
Author(s):  
E.G. Potter ◽  
C.J. Kelly ◽  
W.J. Davis ◽  
G. Chi ◽  
S-Y. Jiang ◽  
...  
Keyword(s):  
Shear Zones ◽  
Isotopic Signature ◽  
Strong Interactions ◽  
Content Type ◽  
B Values ◽  
Isotopic Signatures ◽  
Link Type ◽  
Basement Rocks ◽  
Supplementary Material ◽  
Over Time

The Patterson Lake corridor is a new uranium district located on the southwestern margin of the Athabasca Basin. Known resources extend almost one kilometer below the unconformity in graphite- and sulfide-bearing shear zones within highly altered metamorphic rocks. Despite different host rocks and greater depths below the unconformity, alteration assemblages (chlorite, illite, kaolinite, tourmaline and hematite), ore grades and textures are typical of unconformity-related deposits. This alteration includes at least three generations of Mg-rich tourmaline (magnesio-foitite). The boron isotopic composition of magnesio-foitite varies with generation: the earliest generation only observed in shallow samples from the Triple R deposit (Tur 1) contain the heaviest isotopic signature (δ11B ≈ +26 to +19 ‰), whereas subsequent generations (Tur 2, Tur 3) yield lighter and more homogeneous isotopic signatures (δ11B ≈ +17.5 to +19.9 ‰). These results are consistent with precipitation from low temperature, NaCl- and CaCl2-rich brine(s) derived from an isotopically heavy boron source (e.g. evaporated seawater) that interacted with tourmaline and silicates in the basement rocks and/or fluids derived from depth (with low δ11B values). The lower δ11B values in paragenetically later magnesio-foitite reflect greater contributions of basement-derived boron over time whereas minor compositional variations reflect local metal sources (e.g. Cr, V, Ti) and evolving fluid chemistry (decreasing Na and Ca, increasing Mg) over time. The δ11B and chemical variation in magnesio-foitite over time reinforce the strong interactions with basement rocks in these systems while supporting incursion of basinal brines well below the unconformity contact.Thematic collection: This article is part of the Uranium Fluid Pathways collection available at: https://www.lyellcollection.org/cc/uranium-fluid-pathwaysSupplementary material:https://doi.org/10.6084/m9.figshare.c.5727555

scholarly journals Basement reservoir plumbing: fracture aperture, length and topology analysis of the Lewisian Complex, NW Scotland

2020 ◽  
Vol 177 (6) ◽  
pp. 1281-1293 ◽  
Author(s):  
K. J. W. McCaffrey ◽  
R. E. Holdsworth ◽  
J. Pless ◽  
B. S. G. Franklin ◽  
K. Hardman
Keyword(s):  
Oil And Gas ◽  
Fractured Reservoirs ◽  
Crystalline Basement ◽  
Fracture Aperture ◽  
Power Law Distribution ◽  
Content Type ◽  
Scaling Properties ◽  
Link Type ◽  
Basement Rocks ◽  
Supplementary Material

Upfaulted ridges of Neoarchean crystalline basement rocks formed in the Faeroe-Shetland basin as a consequence of Mesozoic rift processes and are an active target for oil exploration. We carried out a comprehensive fault and fracture attribute study on the extensive exposures of geologically equivalent crystalline basement rocks onshore in NW Scotland (Lewisian Gneiss Complex) as an analogue for the offshore oil and gas reservoirs of the uplifted Rona Ridge basement high. Our analysis shows a power-law distribution for fracture sizes (aperture and length), with random to clustered spacing and high connectivity indices. Regional variations between the Scottish mainland and the Outer Hebrides are recognized that compare directly with variations observed along the Rona Ridge in the Faeroe-Shetland basin. Here we develop a model for the scaling properties of the fracture systems in which variations in the aperture attributes are a function of the depth of erosion beneath the top basement unconformity. More generally, the combination of size, spatial and connectivity attributes we found in these basement highs demonstrates that they can form highly effective, well-plumbed reservoir systems in their own right.Supplementary material: Additional methods and results are available at: https://doi.org/10.6084/m9.figshare.c.5017139Thematic collection: This article is part of the The Geology of Fractured Reservoirs collection available at: https://www.lyellcollection.org/cc/the-geology-of-fractured-reservoirs

Inherited structure as a control on late Paleozoic and Mesozoic exhumation of the Tarbagatai Mountains, southeastern Kazakhstan

2021 ◽  
pp. jgs2020-121
Author(s):  
Jack Gillespie ◽  
Stijn Glorie ◽  
Gilby Jepson ◽  
Fedor Zhimulev ◽  
Dmitriy Gurevich ◽  
...  
Keyword(s):  
Central Asia ◽  
Tectonic Activity ◽  
Late Paleozoic ◽  
Content Type ◽  
Existing Structures ◽  
Tectonic History ◽  
History Of ◽  
Supplementary Material ◽  
Intracontinental Deformation ◽  
Insight Into

Central Asia hosts the Tianshan, the largest intracontinental mountain belt in the world, which experienced major reactivation and uplift since the Oligocene in response to the collision of India with Asia. This reactivation was focused around pre-existing structures inherited from the Paleozoic tectonic history of the region. The significant Cenozoic tectonic reworking of Central Asia complicates efforts to understand earlier phases of intracontinental tectonics during the late Paleozoic and Mesozoic. The Tarbagatai Mountains of eastern Kazakhstan record a thermotectonic history that provides insight into the timing and distribution of intracontinental tectonic activity in Central Asia prior to the India-Eurasia collision. Apatite fission track and (U-Th-Sm)/He analysis of igneous samples from the Tarbagatai Mountains reveals two episodes of cooling as a result of exhumation following Paleozoic amalgamation. Initial intracontinental deformation during the Late Permian drove exhumation synchronous with activity along newly formed strike-slip faults spanning the Central Asian Orogenic Belt. The major Chingiz-Tarbagatai Fault was reactivated during the Early Cretaceous, driving localised exhumation along the fault. The relative lack of Cenozoic tectonic activity in the Tarbagatai Mountains means they provide unique insight into the broader thermotectonic evolution of Central Asia during the late Paleozoic and Mesozoic.Supplementary material: Detailed thermochronological data, including plots and tables can be found in the supplementary data https://doi.org/10.6084/m9.figshare.c.5414555.

The Evolution of the Popocatépetl Volcanic Complex: Constraints on Periodic Edifice Construction and Destruction by Sector Collapse

2021 ◽  
pp. jgs2021-022
Author(s):  
Guillem Gisbert ◽  
Hugo Delgado-Granados ◽  
Martin Mangler ◽  
Julie Prytulak ◽  
Ramón Espinasa-Pereña ◽  
...  
Keyword(s):  
Aerial Imagery ◽  
Volcanic Complex ◽  
Sector Collapse ◽  
Content Type ◽  
Digital Elevation ◽  
History Of ◽  
Supplementary Material ◽  
Complex Constraints ◽  
Elevation Model ◽  
First Time

Popocatépetl is one of the most active volcanoes in North America. Its current predominantly mild activity is contrasted by a history of large effusive and explosive eruptions and sector collapse events, which was first summarised by Espinasa-Pereña and Martin-Del Pozzo (2006). Since then, a wealth of new radiometric, geophysical and volcanological data has been published, requiring a re-evaluation of the evolution of the Popocatépetl Volcanic Complex (PVC). Herein, we combine existing literature with new field observations, aerial imagery and digital elevation model interpretations to produce an updated and improved reconstruction of the growth and evolution of the PVC through all of its history. This will be fundamental for the assessment and mitigation of risks associated with potential future high-magnitude activity of the PVC. The PVC consists of four successive volcanic edifices separated by three sector collapse events producing avalanche deposits: Tlamacas (>538 - >330 ka, described here for the first time), Nexpayantla (∼330 - >96 ka), Ventorrillo (∼96 ka - 23.5 ka) and Popocatépetl (<23.5ka) edifices. The newly described Tlamacas collapse propagated towards ENE forming part of the Mayorazgo avalanche deposit.Supplementary material:https://doi.org/10.6084/m9.figshare.c.5709190

In-situ laser ablation Lu–Hf geochronology of garnet across the Western Gneiss Region: Campaign-style dating of metamorphism

2021 ◽  
pp. jgs2021-094
Author(s):  
Renée Tamblyn ◽  
Martin Hand ◽  
Alexander Simpson ◽  
Sarah Gilbert ◽  
Ben Wade ◽  
...  
Keyword(s):  
Laser Ablation ◽  
Ultrahigh Pressure ◽  
Western Gneiss Region ◽  
Content Type ◽  
Link Type ◽  
Geological Processes ◽  
History Of ◽  
Supplementary Material ◽  
Wilson Cycle

The development of in-situ laser ablation Lu–Hf geochronology of apatite, xenotime and garnet has opened avenues to quickly and directly date geological processes. We demonstrate the first use of campaign-style in-situ Lu–Hf geochronology of garnet across the high- to ultrahigh-pressure Western Gneiss Region in Norway. Mafic eclogites from this region have been the focus of much work, and were clearly formed during continental subduction during the Caledonian Orogen. However, abundant quartzofeldspathic and pelitic lithologies record a more complex history, with some preserving polymetamorphic age data, and most containing no indication of high-pressure mineral assemblages formed during subduction. Twenty metapelitic and felsic samples spanning 160 lateral kilometers across the Western Gneiss Region have been analysed using garnet Lu–Hf geochronology. The results reveal Caledonian ages for the majority of the garnets, suggesting some quartzofeldspathic and metapelitic lithologies were reactive and grew garnet during high- to ultrahigh-pressure metamorphism. However, two ultrahigh-pressure eclogite locations, Verpeneset and Fjørtoft, preserve both Caledonian and Neoproterozoic-aged garnets. Despite significant uncertainties on some of the Lu–Hf geochronologic ages, laser ablation Lu–Hf efficiently identifies the polymetamorphic history of parts of the Western Gneiss Region, illustrating the effectiveness of this novel analytical method for rapid mapping of metamorphic ages.Thematic collection: This article is part of the Caledonian Wilson cycle collection available at: https://www.lyellcollection.org/cc/caledonian-wilson-cycleSupplementary material:https://doi.org/10.6084/m9.figshare.c.5715453

scholarly journals Nature and significance of rift-related, near-surface fissure-fill networks in fractured carbonates below regional unconformities

2020 ◽  
Vol 177 (6) ◽  
pp. 1168-1185 ◽  
Author(s):  
Kit Hardman ◽  
Robert E. Holdsworth ◽  
Edward Dempsey ◽  
Ken McCaffrey
Keyword(s):  
Wall Rock ◽  
Surface Phenomenon ◽  
Low Permeability ◽  
Early Permian ◽  
Near Surface ◽  
Content Type ◽  
Basement Rocks ◽  
Supplementary Material ◽  
Fissure Fill ◽  
Migration Pathways

Fissure-fill networks are a widely recognized, but relatively little described, near-surface phenomenon (<1–2 km) hosted in carbonate and crystalline basement rocks below regional unconformities. Faults and fractures in otherwise tight Devonian carbonate basement rocks of the Tor Bay region, Devon, SW England are associated with the development of millimetre- to decametre-wide fissures containing red-coloured early Permian sedimentary material, vuggy calcite mineralization and wall rock collapse breccia. These features preserve evidence about the style and history of fault deformation and reactivation in near-surface settings and on fluid-related processes, such as elutriation and/or mineralization. Field observations, palaeostress analysis and fracture topology analyses show that the rift-related faults and fractures created a network of long-lived open cavities during the development of the Portland–Wight Basin in the early Permian. Once formed, they were subjected to episodic, probably seismically induced, fluid fluxing events and local karstification. The large, well-connected networks of naturally propped fractures were (and possibly still are) important fluid migration pathways within otherwise low-permeability host rocks. These structures are probably equivalent to those observed in many other rift-related, near-surface tectonic settings and suggest that the Tor Bay outcrops can be used as a global analogue for sub-unconformity open fissure systems hosted in low-permeability basement rocks.Supplementary material: Appendix A is available at https://doi.org/10.6084/m9.figshare.c.5023103

The deformation history of southern England, and its implications for ground engineering in the London Basin

2021 ◽  
pp. qjegh2020-144
Author(s):  
John Cosgrove ◽  
Tom Morgan ◽  
Richard Ghail
Keyword(s):  
Geotechnical Engineering ◽  
Fracture System ◽  
Deformation History ◽  
Content Type ◽  
Southern England ◽  
Basement Rocks ◽  
Ground Investigation ◽  
History Of ◽  
Seismic Sections ◽  
Fault Network

Structures in the basement beneath the London Basin affect the geology of relevance to geotechnical engineering within London. Unfortunately, the basement beneath London is covered by Cretaceous and Tertiary sediments. It is cut by major faults linked to the compressive phases of the Hercynian and Alpine Orogenies and to the regional extension that occurred during the Mesozoic between these compressive events. Evidence is presented that movement on basement fractures beneath London played a major role in the distribution and deformation of sediments within the Basin, causing local folding and faulting significant to engineering works. Basement rocks are exposed in SW England where the type and orientation of these fractures (faults and joints) can be examined in outcrop. This study, complemented by seismic sections in the southern UK, enable the architecture of this fault network within the basement to be determined. Understanding the fracture system in the basement provides a basis for (i), interpreting the lateral facies variations of sediments in the Basin and hence provides a means for predicting from a ground investigation the likely presence, activity or influence on site of such structures at depth and (ii), understanding the extent of local, steeply inclined and sub-horizontal planar zones of shearing when encountered on site.Thematic collection: This article is part of the Geology of London and its implications for ground engineering collection available at: https://www.lyellcollection.org/cc/london-basin

The Age and Paleomagnetism of Jurassic dykes, western Dronning Maud Land: implications for Gondwana breakup

2021 ◽  
pp. SP518-2021-44
Author(s):  
M. A. Morake ◽  
J. N. F. O'Kennedy ◽  
M. W. Knoper ◽  
M. de Kock ◽  
J. D. Kramers ◽  
...  
Keyword(s):  
Southern Africa ◽  
Ocean Floor ◽  
Falkland Islands ◽  
Content Type ◽  
Link Type ◽  
Palaeomagnetic Data ◽  
History Of ◽  
Dronning Maud Land ◽  
Supplementary Material ◽  
Insight Into

AbstractNew 40Ar/39Ar data from dykes intruded into Sverdrupfjella and Ahlmanryggen, Dronning Maud Land, Antarctica, indicate that dyke emplacement commenced at ca. 207 Ma and lasted until ca. 178 Ma. Whereas the ages ascribed to the Karoo-age magmatism contributing to Gondwana breakup are typically inferred as being ca. 182 Ma, the data indicate that ages older than ca.192 Ma in the broader Karoo Province are restricted to western Dronning Maud Land, Antarctica, indicating the locality where break-up was initiated. Limited palaeomagnetic data from ca. 178-185 Ma dykes combined with published palaeomagnetic data from similar aged dykes in Vestfjella and the Ferrar Province, suggest that Antarctica had already drifted/rifted significantly away from southern Africa from ca. 207 Ma to ca. 180 Ma, earlier than previously thought. The data, if correct, require a re-evaluation of the ages ascribed to ocean-floor anomalies used to constrain reconstructions of Gondwana and may provide insight into the history of microcontinental blocks including the Falkland Islands, Haag nunataks, Ellsworth-Whitmore block and Maurice Ewing Bank.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5612838

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