Abstract Coesite-bearing eclogites in several deep crustal metamorphic assemblages now exposed extensionally-collapsed orogens indicate the tectonic denudation of more than 90 km rocks and pre-collapsed thicknesses at least 120 km. For mountain ranges orogenic plateaux up to 5 elevation average densities about 2.8, thickness cannot exceed 80 unless pre-shortening crustal/lithosphere ratios were less 0.135 or some way can be found preferentially thicken lithospheric mantle. This problem...

The South Mayo Trough, a broad synclinorium containing 10‐km sequence of Early Ordovician turbidites passing up into shallow water sandstones, is interpreted as forearc basin with an ophiolitic basement that formed backstop to accretionary prism on the northern edge north‐facing arc. arc collided Laurentian margin in Llanvirn times deform Dalradian Supergroup rifted clastic sequence. Prior late Llandovery, sinistral transcurrent faulting transposed Connemara terrane its present position...

The previous conflict between stratigraphical and geochronological evidence for the age of Grampian orogeny in Scotland Ireland has now been largely resolved. Dalradian deposition continued on Laurentian margin through late Proterozoic into Ordovician time. was a brief, arc-accretion event that took place around Arenig-Llanvirn boundary, at about 470 Ma, an extension Taconic Appalachians. Exhumation orogen rapid; Rb-Sr mica ages have taken to indicate pre-Ordovician slow cooling are...

New reflection profiles recorded to 18s ( c .60km) along a 600 km north-south transect West of IREland (WIRE lines) provide cross-section the Irish Caledonides from Lewisian basement in north Variscan fold-and-thrust belt south, and constrain offshore extrapolations major Caledonide structures. We interpret as showing Great Glen fault associated, NE-trending strike-slip faults near-vertical structures which cut whole crust uppermost mantle. Beneath surface trace Fair Head-Clew Bay line we...

Deep seismic profiles in the Irish and North seas have successfully imaged crustal structure across Iapetus suture zone. A problem with current interpretations is that reflectors chosen as project to top of basement well south Solway Line, palaeontologically defined trace suture. We present a revised interpretation which reflectivity boundary common all identified leading edge imbricated Avalonian crust, effect footwall This projects surface close obviating need invoke northward backthrusting

Geological and geophysical criteria allow division of the Caledonides western Ireland into four principal zones. Zone 1, in north, contains Grenvillian basement with late Proterozoic supra-crustals. 2 Westport Complex, Deer Park Complex South Mayo Trough. Connemara Delany Dome Formation occupy 3. 4 Group mid- to late-Ordovician Silurian sediments volcanic rocks. The various tectonic models proposed for these zones are discussed a ‘minimum’ model is presented, which involves early Ordovician...

A new 10 nT compilation of magnetic data for Ireland and the immediately adjacent sea area shows distinct geophysical provinces characteristic signature separated by major linears which can be related to important geological lines. In far northwest there is a structurally coherent Grampian tectonic‐thermal zone bounded southeast Fair Head‐Clew Bay Line. Between Line western extension Southern Uplands Line, forms northern margin Scotland, segmented relatively small anomalies bodies mixed...

The Lough Nafooey Group is divided into 4 formations. lowermost Bencorragh Formation consists of spilitic pillowed tholeiites, passing up the blocky andesite flows, breccias, cherts and basic pillow lavas Finny Formation. This overlain by Knock Kilbride comprised spilitized calc-alkali to intermediate lavas, often pillowed, that are interbedded with breccias graptolitic shales. Proximal turbidites containing rhyolite, granite spilite clasts represent highest Derry Bay New palaeontological...

The origin of the Newer Granites is long-standing problem. In Caledonian orthotectonic zone intrusions span period late orogenic convergence and uplift, but attempts to relate them as a group Iapetan subduction have been unsuccessful. A range rock types represented, mainly with I-type affinities, granodiorite most voluminous. contrast, granitic south Moniaive shear in Scotland also north England significant S-type characteristics, trace Iapetus suture ages 400–390 Ma, significantly younger...

The origins of boulderite deposits are investigated with reference to the present-day foreshore Annagh Head, NW Ireland, and Lower Miocene Matheson Formation, New Zealand, resolve disputes on their origin contrast compare tsunamis storms. Field data indicate that which contains boulders in excess 140 tonnes, was produced by a 12- 13-m-high tsunami period order 1 h. at exceed 50 is disputed. We combine oceanographic, historical, field argue this cliff-top storm deposit (CTSD). A numerical...

Research Article| January 01, 1991 Cambrian-Ordovician paleogeography of Baltica Trond H. Torsvik; Torsvik 1Department Earth Sciences, University Oxford, Oxford OX1 3PR, England Search for other works by this author on: GSW Google Scholar Paul D. Ryan; Ryan 2Department Geology, College, Galway, Ireland Allan Trench; Trench David A.T. Harper Geology (1991) 19 (1): 7–10. https://doi.org/10.1130/0091-7613(1991)019<0007:COPOB>2.3.CO;2 Article history first online: 02 Jun 2017 Cite View This...

Based on new palaeomagnetic results from the North Norwegian Caledonides, we propose apparent polar wander paths for Baltica during Early–Mid Palaeozoic and discuss their palaeogeographic implications. In Cambrian Early Ordovician times, occupied southerly latitudes of order 30° to 50°, but was 'inverted' with respect its present orientation. Consequently, Russian Platform faced Avalonia Gondwana, latter continent occupying high latitudes. Closure Tornquist Sea then accompanied by...

Abstract The westward continuation of the Highland Border fault Scotland (HBFZ) into Ireland is problematic. It widely thought to follow a pronounced magnetic and gravity lineament, Fair Head-Clew Bay Line (FCL). advantage this interpretation that it places all Ordovician ophiolitic complexes associated sedimentary basins south FCL, which would represent contact between Laurentia outboard terranes. Its main shortcomings are both deep structure timing strike-slip different on HBFZ FCL. In FCL...

In the Irish and British Caledonides, early Ordovician Grampian Orogeny was result of collision between Laurentian rifted margin an oceanic island arc. The Connemara terrain in western Ireland differs position character from all other parts exposed Dalradian rocks Orogen lying south collided arc fore-arc, having north-verging fold nappes that developed synchronously with intrusion huge volumes calc-alkaline magmas provided heat for regional Barrovian metamorphism. We have tested this...

The Wilson Cycle, the repeated opening and closing of oceans, commonly along roughly same lines, is here attributed to presence eclogite-facies roots partially collapsed orogens. We present a finite-element thermal model that suggests such will weaken orogenic lithosphere relative adjacent foreland for hundreds millions years make it preferred site later rifting.

Early Ordovician volcanic rocks exposed in the South Mayo region of western Ireland document history a arc complex, produced following initiation south-dipping subduction within Iapetus Ocean Late Cambrian or Ordovician. Lavas Lough Nafooey Group (Tremadoc-Arenig) show an eruption marked by initial period tholeiitic basaltic volcanism, followed shift to increasing silica compositions calc-alkaline affinity. Subsequent volcanism Tourmakeady (Arenig) shows mixture rhyolitic and andesitic...

The South Mayo Trough, an early Ordovician sedimentary basin, was developed at the southern margin of Laurentian plate. It controlled deposition 12.8 km sediment. Basic vulcanism accompanied opening trough. This followed by turbidites and finally fluvio-deltaic sediments. Initial island arc replaced a bimodal basalt–rhyolite suite during sedimentation. trough bounded to north south metamorphic source areas, which southerly, Connemara Cordillera, more important. comprised Dalradian...