Volcanic clasts in Silurian conglomerates of the Midland Valley (Hagshaw Hills inlier) Scotland, and their meaning for Caledonian plate tectonics

Heinz, W.; Loeschke, Jörg

doi:10.1007/bf01832391

Cited by 10 publications

(6 citation statements)

References 33 publications

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“…It thickens to the SE, has a NW palaeofiow and is dominated by silicic volcanic and plutonic clasts (McGiven 1967). There is clearly no obvious source for this clast assemblage in the Southern Uplands to the immediate S (Bluck 1983;Heinz & Loeschke 1988). The succeeding conglomerates contain a similar assemblage of igneous clasts, although in some areas the clast assemblage is dominated by quartzite.…”

Section: The Silurian Inliersmentioning

confidence: 97%

Caledonian and related events in Scotland

Bluck

2000

Earth and Environmental Science Transactions of the Royal Socie

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The Scottish Caledonides, sited near the triple-junction between Laurentia, Amazonia and Baltica, is divided into at least five discrete blocks, each with a history incompatible with that of the block now lying adjacent to it. With the exception of the Hebridian margin, with its extensional Torridonian basins and Cambrian passive margin sequence, all blocks have undergone terrane-scale movements. The Moine, Central Highland Division and the bulk (if not all) of the Grampian Group have shared a common regional metamorphism, involving thickening and uplift, atc. 800 Ma andc. 450–480 Ma. This is incompatible with their being in the extensional regime that appears to characterise much of Neoproterozoic Laurentia. They, along with the polymetamorphic Dalradian block, now replace a region of passive margin and an unknown width of attendant Iapetus oceanic crust. These metamorphic blocks are grossly out-of-place.The Midland Valley is a severely contracted block of ancient crust, once fringed by extensive oceanic basins to the N and S. An Ordovician–Devonian arc was founded on this older craton, and supplied sediment to basins on either side of it. This arc, during its Lower Palaeozoic life, matured, finally to yield relatively quartz-rich sediment, but was re-activated during the Devonian. An arc, similar to that of the Midland Valley, also supplied sediment to the Southern Uplands. Metamorphic debris in the Southern Uplands had a provenance in either this arc-basement or in a basement somewhere along the orogen. No metamorphic detritus in the Highland Border Complex has yet been demonstrated to have a Dalradian source.Much of Scotland was assembled in a strike-slip regime. Evidence for strike-slip tectonics can be seen from the Late Proterozoic through to the Devonian. In periods of transtension, basins opened to accumulate sediment; in periods of transpression, those sediments were compressed and uplifted to yield sediments to successor basins. In the Neoproterozoic, during the phase of transpression, the basins were buried and metamorphosed, but during the Palaeozoic the basins were at a much higher level and escaped metamorphism.A substantial volume of the Neoproterozoic–Palaeozoic sediment that accumulated in Scotland was derived from two orogens, both of which were sited some distance away. During the Neoproterozoic, the Grenville orogen was the main source, and in later (Devonian) time sediment accumulated in Scotland from the major, Late Palaeozoic continent–continent collision of Greenland–Scandinavia. These two external sources were augmented by a substantial contribution of sediment supplied from the Midland Valley arc or its lateral equivalent and by mild uplifts within the Scottish basements.

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Section: The Silurian Inliersmentioning

confidence: 97%

Caledonian and related events in Scotland

Bluck

2000

Earth and Environmental Science Transactions of the Royal Socie

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“…Geochemical studies (Heinz & Loeschke 1988) indicate that these fine-grained igneous rocks belong to calc-alkaline to high-K suites and thus may have been associated with a convergent plate margin, or Tables Table 1. Major and minor detrital components within the main lithostratigraphical units of the Silurian Carmichael, Eastfield and North Esk inliers, and Siluro-Devonian Lanark Group. …”

Section: Discussionmentioning

confidence: 99%

“…Earlier provenance studies of the Silurian and Siluro-Devonian sequences within the Midland Valley Terrane have largely concentrated upon the conglomeratic units present within the southern (McGiven 1967;Bluck 1983;Heinz & Loeschke 1988;Syba 1989) and northern (Bluck 1983;Haughton et al 1990;Haughton & Halliday 1991) parts of this terrane. Work on the Silurian rocks in the southern Midland Valley (McGiven 1967;Bluck 1983;Heinz & Loeschke 1988;Syba 1989) indicates that there is a difference between a southerly derivation direction and the source area presently exposed to the south, i.e.…”

Section: Introductionmentioning

confidence: 99%

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Composition and provenance of the Silurian to Devonian sandstone sequences of the southern Midland Valley

Phillips

Barron

Smith

et al. 2004

SJG

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Synopsis A provenance study of rocks from the Silurian inliers and Siluro-Devonian Lanark Group sandstones of the southern Midland Valley has shown that they are petrographically and compositionally similar, and were derived from the same source terrane. The clast content of these rocks indicates that before widespread Lower Devonian calc-alkaline volcanism, this source terrane included volcanic and hypabyssal igneous rocks that appear to have been associated with a wacke sandstone-dominated sedimentary sequence and a granitic igneous suite. The possibility that the source rocks for these sequences are within the Midland Valley Terrane, but now not exposed, is discussed. Minor differences in sandstone composition between the Carmichael, Eastfield and North Esk inliers are interpreted as reflecting either slight differences in the source or deposition within individual sub-basins. Comparable regional variations within the Swanshaw Sandstone Formation suggest that sub-basin architecture continued to influence sediment dispersal patterns during the deposition of the basal Lanark Group. The onset of Lower Devonian calc-alkaline volcanism coincided with a major change in sandstone composition within the Lanark Group and accompanied the replacement of the relatively small Silurian sub-basins by a single larger basin.

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“…They are believed to have had a source to the SE and the clasts are, sometimes, not well rounded, all of which suggested to McGiven (1967) a source block to the immediate south, where the Southern Uplands are presently situated. Heinz & Loeschke (1988) studied the chemistry of these fine-grained rocks, and suggested a source in a calc-alkaline to high K arc-type complex. The zircon ages collected from the conglomerate are as old as to 445 Ma (Phillips et al 2009) and may suggest a source in late Ordovician-Silurian igneous activity.…”

Section: Parishholm Conglomeratementioning

confidence: 99%

Geotectonic evolution of Midland Scotland from Cambrian to Silurian: a review

Bluck

2013

SJG

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Synopsis During its Lower Palaeozoic history, the Midland Valley of Scotland was subject to compression from the blocks on either side, confirming the views of Kennedy (1958). Cambrian–Llanvirn-aged rocks of the Hebridean craton formed part of a passive margin, which extended to the ESE and is now replaced by the metamorphic complexes of the Moine and Dalradian. Both blocks had undergone metamorphism, uplift and shedding of their covers elsewhere. The ophiolitic part of the Highland Border Complex, which may be a continuation of the structurally foreshortened and rotated Ballantrae Complex, was obducted at c .490 Ma and may have interacted with rocks of the Hebridean passive margin. Ordovician rocks at Girvan are a small remnant of a one-time far larger forearc basin, which formed to the south of a major arc complex, originally situated in the Midland Valley and probably extending from somewhere in the North Sea to offshore Ireland and beyond. The Highland Border Complex includes rocks coeval with the Midland Valley arc at c .470 Ma that formed a back-arc basin. The Southern Uplands have converged on the Midland Valley, with the forearc sequence apparently missing in Scotland. Part of that convergence history is recorded in the Silurian conglomerates of the southern Midland Valley. Silurian sequences in this area contain conglomerates and breccias, derived from the south that record the presence of an igneous and possibly also a metamorphic complex in the region now occupied by the trench sequence of the Southern Uplands. It is suggested that the trench was later thrust over this source block and that the Southern Upland Fault forms part of that thrust sequence. The metamorphic complexes to the north, replacing the Hebridean passive margin, did not interact with the Midland Valley until Lower Devonian times. It follows that there was no mountain-building orogeny in Scotland, other than an arc, a sliver of trench, and numerous examples of crustal contraction by strike-slip and/or thrusting.

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Volcanic clasts in Silurian conglomerates of the Midland Valley (Hagshaw Hills inlier) Scotland, and their meaning for Caledonian plate tectonics

Cited by 10 publications

References 33 publications

Caledonian and related events in Scotland

Caledonian and related events in Scotland

Composition and provenance of the Silurian to Devonian sandstone sequences of the southern Midland Valley

Geotectonic evolution of Midland Scotland from Cambrian to Silurian: a review

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