Cambrian-Ordovician continental magmatic arc at the northern margin of Gondwana: Insights from the Schladming Complex, Eastern Alps

The average thickness of Paleogene sandstones reaches about 3000–4000 m at the northern margin of the Qaidam Basin. However, the provenance and sedimentary environment of these sandstones are uncertain; thus, more comprehensive research is needed. Integrated research is conducted on the provenance and weathering process based on petrographic characteristics, clay minerals, and geochemical compositions of sandstones in the center of the northern Qaidam Basin. The results of lithofacies analysis show that the Paleogene sandstones were mainly derived from an active continental magmatic arc, subduction accretion, or a fold-thrust belt. The average illite content in the Paleogene clay minerals is more than 50%, followed by chlorite and smectite, which reflect climatic and environmental characteristics that were arid to semi-arid, whereas the characteristics of carbon–oxygen isotopes reveal a mainly freshwater sedimentary environment. The corrected chemical index of alteration (CIAcorr) is between 56.3 and 75.7, with an average value of 66.5. These results indicate that the provenance of the Paleogene sandstones in the center of the northern Qaidam Basin mainly formed under cold and dry climatic conditions and experienced limited chemical weathering with a small amount that underwent intermediate chemical weathering under warm and humid conditions.

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Hf isotopic constraints for Austroalpine basement evolution of Eastern Alps: review and new data

10.5194/egusphere-egu21-10909 ◽

2021 ◽

Author(s):

Ruihong Chang ◽

Franz Neubauer ◽

Johann Genser ◽

Yongjiang Liu ◽

Sihua Yuan ◽

...

Keyword(s):

Eastern Alps ◽

Crustal Material ◽

Island Arcs ◽

Magmatic Arc ◽

Depleted Mantle ◽

Close Relationship ◽

Austroalpine Basement ◽

Mountain Belts ◽

Continental Magmatic Arc ◽

Different Sources

<p>The Alps as part of the Alpine mountain belts are one of the classical examples of orogenesis where the Mesozoic-Cenozoic tectonic evolution is well known, but not of the basement because poor age data. New data from the &#160;pre&#8211;Alpine basement of the Austroalpine megaunit indicate that this basement is composed of a series of continental rocks, island arcs, ophiolites and subduction m&#233;langes&#65292;accretionary wedges, and seamounts with different metamorphic, but often amphibolite facies grade. This study presents new results of LA&#8211;ICP&#8211;MS U&#8211;Pb and MC&#8211;ICP&#8211;MS Lu&#8211;Hf dating of zircons from three key areas of Austroalpine basement units: i) the Wechsel&#8211;Waldbach&#8211;Sieggraben, (ii) the Saualpe&#8211;Koralpe &#8211;Pohorje, and (iii) the Schladming Mts. areas. As a result, the Wechsel unit is a continental magmatic arc during 500-560 Ma, and 2.1 to 2.2 Ga-and 2.5 to 2.8 Ga age show the close relationship to northern Gondwana, with depleted mantle model ages as old as 3.5 Ga. Even the Wechsel Phyllite Unit overlying the Wechselgneiss, but they have partly different sources, include juvenile crust formed at ca. 530 Ma. The Waldbach Complex is constantly added new crustal material during 490-470Ma, and considerably more positive &#949;Hf(t) values from 700 to 500 Ma interpreted being part of a magmatic arc during closure of the Prototethys and got metamorphosed during Variscan orogenic events. We consider that Schladming to Wechsel Complexes represent a Cambrian-Ordovician volcanic-magmatic arc system followed proto-Tethys subduction, and the ophiolitic Speik complex represent a back-arc basin. Many granites were formed during Permian (Grobgneiss and various granites in Pohorje Mts.) likely in an extensional environment, remelting a crust with mainly Middle Proterozoic model Hf isotopic model ages. The Plankogel Complex represents accreted oceanic, ocean island and continental-derived materials, it should belong to the accretion complex formed during Permotriassic closure of Paleotethys. We argue that the various basement complexes of the Austroalpine are different sources of ages of different tectonic evolutionary histories and likely represent, different locations before drifting. Consequently, the Austroalpine meagunit represents a composite pre-Alpine mega-unit likely assembled not earlier as Permian or Triassic times.</p>

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THE PROTOGONOS: A LONG LIVED MAGMATIC ARC ALONG THE NORTHERN MARGIN OF GONDWANA-LAND AND ITS DISRUPTION DURING THE HERCYNIAN OROGENY

10.1130/abs/2017am-298567 ◽

2017 ◽

Cited By ~ 1

Author(s):

Nalan Lom ◽

◽

Gursel Sunal ◽

Nurbike G. Sağdıç ◽

A.M. Celâl Şengör

Keyword(s):

Northern Margin ◽

Magmatic Arc ◽

Hercynian Orogeny ◽

Gondwana Land

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Jurassic Arc: Reconstructing the Lost World of eastern Gondwana

Geology ◽

10.1130/g49328.1 ◽

2021 ◽

Author(s):

Elliot K. Foley ◽

R.A. Henderson ◽

E.M. Roberts ◽

A.I.S. Kemp ◽

C.N. Todd ◽

...

Keyword(s):

Detrital Zircon ◽

Tectonic Setting ◽

Magmatic Arc ◽

Continental Arc ◽

Key Factor ◽

Igneous Activity ◽

Competing Models ◽

Juvenile Crust ◽

Sedimentary Fill ◽

Continental Magmatic Arc

The tectonic setting of the Australian sector of the eastern Gondwanan margin during the Jurassic and Cretaceous is enigmatic. Whether this involved convergent tectonism and a long-lived continental magmatic arc or rift-related extension unrelated to subduction is debated. The paucity of Australian Jurassic–Cretaceous igneous outcrops makes resolving these competing models difficult. We used the detrital zircon record of the Jurassic–Cretaceous Great Australian Superbasin (GAS) as a proxy for igneous activity. We attribute the persistent magmatism recorded in GAS sedimentary fill throughout the Mesozoic to ca. 95 Ma to continuation of the established Paleozoic continental arc system. The detrital zircon record signals short (~10 m.y.) pulses of elevated Jurassic and Cretaceous magmatic activity and strongly positive εHf values, indicating juvenile crust or mantle-derived magmatism. Margin reconstruction indicates sustained continental growth at rates of at least ~55 km3 km–1 m.y.–1, mainly to the tract now represented by submerged northern Zealandia, due to the retreat of this arc system. We posit that arc retreat was a key factor in rapid crust generation and preservation, and that continental sedimentary systems globally may host cryptic records of juvenile crustal addition that must be considered in estimating crustal growth rates along convergent plate margins.

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Petrogenesis and U-Pb and Sm-Nd geochronology of the Taquaral granite: record of an orosirian continental magmatic arc in the region of Corumba - MS

Brazilian Journal of Geology ◽

10.1590/2317-488920150030231 ◽

2015 ◽

Vol 45 (3) ◽

pp. 431-451 ◽

Cited By ~ 5

Author(s):

Letícia Alexandre Redes ◽

Maria Zélia Aguiar de Sousa ◽

Amarildo Salina Ruiz ◽

Jean-Michel Lafon

Keyword(s):

Geochemical Data ◽

Alkaline Magmatism ◽

Alluvial Deposits ◽

Mato Grosso ◽

Microgranular Enclave ◽

Magmatic Arc ◽

Rock Types ◽

High K ◽

Continental Magmatic Arc ◽

Shrimp Zircon

The Taquaral Granite is located on southern Amazon Craton in the region of Corumbá, westernmost part of the Brazilian state of Mato Grosso do Sul (MS), near Brazil-Bolivia frontier. This intrusion of batholitic dimensions is partially covered by sedimentary rocks of the Urucum, Tamengo Bocaina and Pantanal formations and Alluvial Deposits. The rock types are classified as quartz-monzodiorites, granodiorites, quartz-monzonites, monzo and syenogranites. There are two groups of enclaves genetically and compositionally different: one corresponds to mafic xenoliths and the second is identified as felsic microgranular enclave. Two deformation phases are observed: one ductile (F1) and the other brittle (F2). Geochemical data indicate intermediate to acidic composition for these rocks and a medium to high-K, metaluminous to peraluminous calk-alkaline magmatism, suggesting also their emplacement into magmatic arc settings. SHRIMP zircon U-Pb geochronological data of these granites reveals a crystallization age of 1861 ± 5.3 Ma. Whole rock Sm-Nd analyses provided εNd(1,86 Ga) values of -1.48 and -1.28 and TDM model ages of 2.32 and 2.25 Ga, likely indicating a Ryacian crustal source. Here we conclude that Taquaral Granite represents a magmatic episode generated at the end of the Orosirian, as a part of the Amoguija Magmatic Arc.

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Evolution of Late Cretaceous to Palaeogene basalt–andesite–dacite–rhyolite volcanic suites along the northern margin of the Ladakh magmatic arc, NW Himalaya, India

Journal of Earth System Science ◽

10.1007/s12040-020-1372-6 ◽

2020 ◽

Vol 129 (1) ◽

Author(s):

Nongmaithem Lakhan ◽

A Krishnakanta Singh ◽

B P Singh ◽

Kshetrimayum Premi ◽

Govind Oinam

Keyword(s):

Late Cretaceous ◽

Nw Himalaya ◽

Northern Margin ◽

Magmatic Arc

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Interplay of Cretaceous transpressional deformation and continental arc magmatism in a long-lived crustal boundary, central Fiordland, New Zealand

Geosphere ◽

10.1130/ges02251.1 ◽

2020 ◽

Vol 16 (5) ◽

pp. 1225-1248

Author(s):

Hannah J. Blatchford ◽

Keith A. Klepeis ◽

Joshua J. Schwartz ◽

Richard Jongens ◽

Rose E. Turnbull ◽

...

Keyword(s):

New Zealand ◽

Thermal Structure ◽

Shear Zones ◽

Arc Magmatism ◽

Magmatic Arc ◽

Continental Arcs ◽

Metasedimentary Rocks ◽

Spatio Temporal ◽

Continental Magmatic Arc ◽

Lower Crustal

Abstract Recovering the time-evolving relationship between arc magmatism and deformation, and the influence of anisotropies (inherited foliations, crustal-scale features, and thermal gradients), is critical for interpreting the location, timing, and geometry of transpressional structures in continental arcs. We investigated these themes of magma-deformation interactions and preexisting anisotropies within a middle- and lower-crustal section of Cretaceous arc crust coinciding with a Paleozoic boundary in central Fiordland, New Zealand. We present new structural mapping and results of Zr-in-titanite thermometry and U-Pb zircon and titanite geochronology from an Early Cretaceous batholith and its host rock. The data reveal how the expression of transpression in the middle and lower crust of a continental magmatic arc evolved during emplacement and crystallization of the ∼2300 km2 lower-crustal Western Fiordland Orthogneiss (WFO) batholith. Two structures within Fiordland’s architecture of transpressional shear zones are identified. The gently dipping Misty shear zone records syn-magmatic oblique-sinistral thrust motion between ca. 123 and ca. 118 Ma, along the lower-crustal WFO Misty Pluton margin. The subhorizontal South Adams Burn thrust records mid-crustal arc-normal shortening between ca. 114 and ca. 111 Ma. Both structures are localized within and reactivate a recently described >10 km-wide Paleozoic crustal boundary, and show that deformation migrated upwards between ca. 118 and ca. 114 Ma. WFO emplacement and crystallization (mainly 118–115 Ma) coincided with elevated (>750 °C) middle- and lower-crustal Zr-in-titanite temperatures and the onset of mid-crustal cooling at 5.9 ± 2.0 °C Ma−1 between ca. 118 and ca. 95 Ma. We suggest that reduced strength contrasts across lower-crustal pluton margins during crystallization caused deformation to migrate upwards into thermally weakened rocks of the mid-crust. The migration was accompanied by partitioning of deformation into domains of arc-normal shortening in Paleozoic metasedimentary rocks and domains that combined shortening and strike-slip deformation in crustal-scale subvertical, transpressional shear zones previously documented in Fiordland. U-Pb titanite dates indicate Carboniferous–Cretaceous (re)crystallization, consistent with reactivation of the inherited boundary. Our results show that spatio-temporal patterns of transpression are influenced by magma emplacement and crystallization and by the thermal structure of a reactivated boundary.

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