Snowdon basalts and the cessation of Caledonian subduction by the Longvillian

Leat, P. T.; Thorpe, R. S.

doi:10.1144/gsjgs.146.6.0965

Cited by 13 publications

(7 citation statements)

References 31 publications

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“…Subduction around the northern margins of the Midlands Microcraton resulted in consumption of oceanic lithosphere until late Ordovician-early Silurian times, followed by phases of transtension and transpression during the late Silurian and Devonian (Pickering, Bassett & Siveter, 1988;Woodcock et al 1988). This is consistent with the proposed cessation of subduction during Caradoc times (Leat & Thorpe, 1989).…”

Section: Introductionsupporting

confidence: 82%

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Composite Ordovician lamprophyre (spessartite) intrusions around the Midlands Microcraton in central Britain

1993

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Lamprophyre sills and dykes of Ordovician age were emplaced within Cambrian–Lower Ordovician sedimentary rocks around the northern margins of the Midlands Microcraton. The intrusions show internal mineralogical and chemical variations indicating emplacement as multiple intrusions of co-magmatic pulses. The chemical characteristics of the lamprophyre magmas indicate formation by small-degree volatile-rich partial melting of lithospheric mantle enriched and modified by Lower Palaeozoic subduction (Th/Ta 5.3–11.6, La/Ta 29–82.3), together with a contribution from within-plate mantle source (Zr/Yc. 6) and/or mineralogically heterogeneous lithosphere, followed by varying degrees of fractional crystallization during uprise.

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Section: Introductionsupporting

confidence: 82%

“…The samples have high and ) and thus plot in subduction-related (or volcanic arc) fields in the Th-Hf/3-Ta diagram of Wood, Joron & Treuil (1979) and Wood (1980) (cf. figs 1 and 2 in Leat & Thorpe, 1989). The geochemical characteristics of the intrusions are illustrated in a mid-ocean ridge basalt (MORB)-normalized diagram in Figure 6.…”

Section: Geochemistrymentioning

confidence: 99%

Composite Ordovician lamprophyre (spessartite) intrusions around the Midlands Microcraton in central Britain

1993

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“…In the British Isles, south of the Iapetus Suture, subduction-related igneous activity is recorded in the Tremadoc (earliest Ordovician) to earliest Caradoc (mid-Ordovician) with a rapid change to a more alkaline and peralkaline signature (Leat & Thorpe 1989) and abrupt cessation in the Longvillian (mid-Caradoc).…”

Section: Middle Ordovician Ridge-trench Collision Below Eastern Avaloniamentioning

confidence: 99%

Arcs and backarc basins in the Early Paleozoic lapetus Ocean

Pickering

Smith

1995

Island Arc

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Understanding the evolution and destruction of past oceans not only leads to a better understanding of earth history, but permits comparison with extant ocean basins and tectonic processes. This paper reviews the history of the Early Paleozoic circum‐Atlantic oceans by analogy with the Pacific Ocean and Mesozoic Tethys. Rifting and continental separation from 620 to 570 Ma led to the development of passive margins along parts of the northern margin of Gondwana (the western coast of South America); eastern Laurentia (eastern North America, NW Scotland and East Greenland), and western Baltica (western Scandinavia). Meagre paleomagnetic data suggest that western South America and eastern North America could have been joined together to form facing margins after breakup. Although western Baltica is an apparently obvious candidate for the margin facing NW Scotland and East Greenland, the paleomagnetic uncertainties are so large that other fragments could have been positioned there instead. The Iapetus Ocean off northeastern Gondwana was probably a relatively wide Pacific‐type ocean with, during the late Precambrian to early Ordovician, the northern margin of Gondwana as a site of continentward‐dipping subduction zone(s). The 650‐500 Ma arc‐related igneous activity here and the associated deformation gave rise to the Cadomian, ‘Grampian’, Penobscotian, and Famantinian igneous and orogenic events. By 490‐470 Ma, marginal basins had formed along the eastern Laurentian margin as far as NE Scotland, along parts of the northern margin of Gondwana, and off western Baltica, but none are known from the East Greenland margin. These basins closed and parts were emplaced as ophiolites shortly after their formation by processes that, at least in some cases, closely resemble the emplacement of the late Cretaceous Semail ophiolite of Oman. This orogenic phase seems to have involved collision and attempted subduction of the continental margin of Laurentia, Gondwana and Baltica. In Baltica it gave rise to some eclogite facies metamorphism. Marginal basin development may have been preceded by arc formation as early as ca 510 Ma. A double arc system evolved outboard from the eastern Laurentian and western Baltica margins, analogous to some of the arc systems in the present‐day western Pacific. At 480‐470 Ma, there was a second phase of breakup of Gondwana, affecting the active Gondwanan margin. Eastern and Western Avalonia, the Carolina Slate Belt, Piedmont, and other North American exotic continental blocks rifted away from Gondwana. Farther east, Armorica, Aquitainia, Iberia and several European exotic continental blocks also rifted away, though it is unlikely that they all rifted at the same time. Between 460‐430 Ma, peaking at ca 450 Ma, orogenic events involved continuing arc‐continent collision(s). From 435‐400 Ma the remaining parts of the Eastern Iapetus Ocean were destroyed and the collision of Baltica with Laurentia caused the 430‐400 Ma Scandian orogeny, followed by suturing of these continents during the Siluro‐Devo...

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“…Several lines of evidence support the intrusive rocks being of Caradoc age. They have geochemical signatures indicative of formation in an extensional, within-plate environment considered typical of the tectonic regime present during the Caradoc (Croudace 1982;Campbell et al 1985Campbell et al , 1988Ball & Merriman 1989, Leat & Thorpe 1989 …”

Section: Constraints On the Age Of The Intrusive Rocksmentioning

confidence: 99%

Resetting of Rb–Sr whole-rock ages during Acadian low-grade metamorphism in North Wales

Evans¹

1991

JGS

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Ordovician volcanic rocks and associated sub-volcanic intrusions in North Wales give Devonian, metamorphic Rb-Sr whole-rock ages. Isotopic resetting is not confined to acid volcanic rocks. Three intrusions preserve Ordovician ages. The closed system resetting is not directly related to metamorphic grade, but appears to correlate with the extent to which the secondary metamorphic mineral assemblage is developed. Rocks giving Devonian ages have a well developed secondary mineralogy whereas those retaining Ordovician ages are less extensively altered. The metamorphic ages combine to give a Lower Devonian mean age and weighted 2a error of 399 f 9 Ma. Metamorphism is therefore synchronous with Acadian deformation in the North Wales area.

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Snowdon basalts and the cessation of Caledonian subduction by the Longvillian

Cited by 13 publications

References 31 publications

Composite Ordovician lamprophyre (spessartite) intrusions around the Midlands Microcraton in central Britain

Composite Ordovician lamprophyre (spessartite) intrusions around the Midlands Microcraton in central Britain

Arcs and backarc basins in the Early Paleozoic lapetus Ocean

Resetting of Rb–Sr whole-rock ages during Acadian low-grade metamorphism in North Wales

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