Late Neoproterozoic to Carboniferous genesis of A-type magmas in Avalonia of northern Nova Scotia: repeated partial melting of anhydrous lower crust in contrasting tectonic environments

Murphy, J. Brendan; Shellnutt, J. Gregory; Collins, William J.

doi:10.1007/s00531-017-1512-7

Cited by 20 publications

(13 citation statements)

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“…Basement rock exposures near the study area are characterized by Neoproterozoic arc-related volcanic and sedimentary rocks (Georgeville Group) truncated by Ediacaran plutonic rocks [15,16], which are unconformably overlain by a Cambrian to Lower Ordovician succession of sedimentary rocks that contain fauna diagnostic of Avalonia (e.g., [17,18]). Following an Early Ordovician episode of compressive deformation [11,16] and subsequent rifting from Gondwana [3], Middle to Upper Ordovician volcanic rocks of the Dunn Point and McGillivray Brook Formations [19,20] were emplaced on the drifting microcontinent of Avalonia [6,14] ( Figure 2).…”

Section: Geological Settingmentioning

confidence: 99%

“…As such, its evolution constrains events leading to the amalgamation of Pangea (e.g., [8]). The area of Arisaig, Nova Scotia, Canada (Figure 1), includes the only known succession of Middle to Upper Ordovician volcanic rocks in West Avalonia (i.e., the North American portion of Avalo-nia) and has been extensively studied to shed light on the tectonic and paleogeographic history of the terrane during this pivotal time interval (e.g., [9][10][11][12][13][14][15]). Until recently, only mafic and felsic volcanic rocks were known from that locality and were interpreted as the bimodal products of back-arc extension [13][14][15] [23,68]), as well as the location of the study area within Avalonia.…”

Section: Introductionmentioning

confidence: 99%

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Evolution of Subduction Dynamics beneath West Avalonia in Middle to Late Ordovician Times

et al. 2020

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Middle to Upper Ordovician volcanic rocks in the Arisaig area of Nova Scotia, Canada, constitute the only known record of volcanism in West Avalonia during that interval. Hence, they have been extensively studied to test paleocontinental reconstructions that consistently show Avalonia as a drifting microcontinent during that period. Identification of volcanic rocks with an intermediate composition (the new Seaspray Cove Formation) between upper Darriwilian bimodal volcanic rocks of the Dunn Point Formation and Sandbian felsic pyroclastic rocks of the McGillivray Brook Formation has led to a reevaluation of magmatic relationships in the Ordovician volcanic suite at Arisaig. Although part of the same volcanic construction, the three formations are separated by significant time-gaps and are shown to belong to three distinct magmatic subsystems. The tectonostratigraphic context and trace element contents of the Dunn Point Formation basalts suggest that they were produced by the high-degree partial melting of an E-MORB type source in a back-arc extensional setting, whereas trace element contents in intermediate rocks of the Seaspray Cove Formation suggest that they were produced by the low-degree partial melting of a subduction-enriched source in an arc setting. The two formations are separated by a long interval of volcanic quiescence and deep weathering, during which time the back-arc region evolved from extension to shortening and was eventually onlapped by arc volcanic rocks. Based on limited field constraints, paleomagnetic and paleontological data, this progradation of arc onto back-arc volcanic rocks occurred from the north, where an increasingly young Iapetan oceanic plate was being subducted at an increasingly shallow angle. Partial subduction of the Iapetan oceanic ridge is thought to have subsequently generated slab window magmatism, thus marking the last pulse of subduction-related volcanism in both East and West Avalonia.

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Section: Geological Settingmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Evolution of Subduction Dynamics beneath West Avalonia in Middle to Late Ordovician Times

et al. 2020

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“…Group iii) xenolits are the most abundant, and are derived from sources formed during the subvolcanic process; The two xenoliths of granitic rocks selected for U-Pb geochronology had elongated shapes and were sub-angular to rounded, with a diameter of more than 20 centimetres. They were remarkably fresh, contrary Leveridge and Shail, 2011;Murphy et al, 2018;Oliveira and Quesada, 1986;Oliveira, 1990;Pereira et al, 2020;Sánchez García et al, 2019;Shail and Leveridge, 2009;White et al, 2018).…”

Section: Rationale and Samplingmentioning

confidence: 83%

“…In the Meguma terrane, the Early Paleozoic sequence is intruded by c. 382-357Ma plutons (including the South Mountain and Musquodoboit batholiths, Clarke et al, 1997;Tate and Clarke, 1995). In Nova Scotia, the Late Devonian sequence comprises sedimentary rocks interbedded with volcanic rocks (Doig et al, 1996;Murphy et al, 2018;Pe-Piper et al, 2004). Zircon and monazite U-Pb ages obtained from from granulite facies metasedimentary xenoliths from a Late Devonian mafic dyke that intrudes the Meguma terrane, yielded three age groups at c. 399, 377 and 354Ma, interpreted as representing metamorphic events (Greenough et al, 1999;Shellnutt et al, 2018).…”

Section: Discussionmentioning

confidence: 99%

Age of the basement beneath the Mesozoic Lusitanian Basin revealed by granitic xenoliths from the Papôa volcanic breccia (West Iberia)

Pereira

Gama

Silva

et al. 2020

GeA

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The dyke of the Papôa volcanic breccia cross-cutting the Lower Jurassic sequence of the Lusitanian Basin (West Iberia) contains granitic xenoliths. In this study, for the first time, U-Th-Pb zircon analysis of two xenoliths yielded 298±4Ma for biotite granite and of 292±2Ma for two-mica granite, indicating that the pre-Mesozoic basement of the Lusitanian Basin includes Permian intrusions. These ages are close within the margin of error of the age of the Late Carboniferous granites of the Berlengas isle that with the Late Devonian high-grade metamorphic rocks of the Farilhões isles, located northwest of the study area, which form the pre-Mesozoic basement of the Lusitanian Basin. These new geochronological findings enable it to be established that Permo-Carboniferous magmatism lasted at least 13Ma, in this region of the Appalachian-Variscan belt. Furthermore, a comparison with available data from Paleozoic tectonic units of the Appalachian-Variscan belt located both in the Iberian Massif and outside it enables the suggestion to be made that the Lusitanian Basin (Peniche) most probably rests on the South Portuguese Zone, which may also be correlated with the Rhenohercynian Zone present in southwest England, and the Meguma terrane of Nova Scotia.

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“…Therefore, we infer that the highly variable Nd compositions of the Chaya pluton resulted from modification of the upper mantle by subducted sediments (and/or melts derived thereof), rather than metasomatism by fluids/ melts released from a subducting slab. This hypothesis is supported by the high Al 2 O 3 concentrations (16.28-18.16 wt%) and low Ce/Pb ratios (0.4-1.7) in Chaya pluton samples, which also suggest the involvement of subducted sedimentary materials in the source region (Murphy et al, 2018). The positive ε Nd and ε Hf values of the Chaya samples mean that these samples generally plot in the mid-ocean-ridge basalt (MORB) field of a ε Nd (t) versus ε Hf (t) diagram (Fig.…”

Section: Origin Of the Chaya Plutonmentioning

confidence: 86%

Geochronological, geochemical, and Sr-Nd-Hf isotopic characteristics of granitoids in eastern Tibet and implications for tectonic correlation with southeastern Asia

Wang

Yao

2019

Lithosphere

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Understanding the configuration of continental blocks within the Tibetan orogen prior to Indo-Asian collision is vital to determining their accretionary history. However, complex tectonic overprinting, including the development of the eastern and western Himalayan syntaxes, has hampered the investigation of correlations between tectonic blocks in the Tibetan Plateau with those in southeastern Asia. The North Lancangjiang tectonic belt is known to connect with the Longmu Co-Shuanghu suture to the west and the Changning-Menglian suture to the south, but limited work has been undertaken in eastern Tibet, and no ophiolite suites or high-pressure (HP) to ultrahigh-pressure (UHP) metamorphic belts have been identified within this belt. This paper presents new in situ zircon U-Pb, whole-rock major-and traceelement, and whole-rock Sr-Nd-Hf isotopic data for three granitic plutons (Chaya, Jinba, and Batang) within the North Qiangtang block. These plutons yield ages from ca. 265 Ma (Chaya) to ca. 230 Ma (Batang). The Chaya and Batang granites are chemically similar to I-type granites, whereas the Jinba granite is an S-type granite. Sr-Nd-Hf isotopic data suggest that the Chaya granite formed from magmas generated by the partial melting of subduction-modified mantle wedge material and that the Jinba granite formed from magmas generated by the partial melting of Precambrian metasedimentary rocks mixed with a small amount of juvenile mantle-derived crustal material. The Batang granite formed from magmas generated by the partial melting of mafic lower-crustal material. The convergence of the North Qiangtang block with neighboring blocks was a consequence of the closure of the Paleo-Tethys Ocean, and the plutons in this area record subduction-related or syncollisional magmatism. New data from granites within the North Lancangjiang magmatic belt and the Jinshajiang suture indicate that the North Lancangjiang Paleo-Tethyan slab subducted eastward, whereas the Jinshajiang Paleo-Tethyan slab subducted westward under the North Qiangtang block at ca. 267 Ma. The timing and style of block convergence between North Qiangtang-Simao-Indochina and neighboring blocks are similar to those recorded within central Tibet and southeastern Asia. This, combined with the presence of similar Middle Mesoproterozoic-Lower Paleozoic basement materials and Paleozoic sediments hosting Cathaysian warm-climate fossils, indicates that North Qiangtang, Simao, and Indochina represent a single block.

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Late Neoproterozoic to Carboniferous genesis of A-type magmas in Avalonia of northern Nova Scotia: repeated partial melting of anhydrous lower crust in contrasting tectonic environments

Cited by 20 publications

References 78 publications

Evolution of Subduction Dynamics beneath West Avalonia in Middle to Late Ordovician Times

Evolution of Subduction Dynamics beneath West Avalonia in Middle to Late Ordovician Times

Age of the basement beneath the Mesozoic Lusitanian Basin revealed by granitic xenoliths from the Papôa volcanic breccia (West Iberia)

Geochronological, geochemical, and Sr-Nd-Hf isotopic characteristics of granitoids in eastern Tibet and implications for tectonic correlation with southeastern Asia

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