Paul D Ryan

• PhD
• Professor Emeritus at Ollscoil na Gaillimhe – University of Galway

Searle (2022) argues, based on data from Scotland alone, that the deformation and metamorphism of the Scottish Highlands is continuously diachronous from the early Ordovician (Grampian) in the Dalradian of the Grampian Highlands to the mid-Silurian (Scandian) in the Moine of the Northwest Highlands. Necessarily, he disputes substantial offset along...

The North American continent has a rich record of the tectonic environments and processes that occur throughout much of Earth history. This Memoir focuses on seven “turning points” that had specific and lasting impacts on the evolution of Laurentia: (1) The Neoarchean, characterized by cratonization; (2) the Paleoproterozoic and the initial assembl...

This chapter first examines the lithologies of the ophiolitic mélange of the Deer Park Complex and the sheared metasediments of the Clew Bay Complex which, together, are interpreted as a Cambrian to mid-Ordovician subduction accretion complex. Two traverses are then made through the Ordovician sediments of the South Mayo Trough, which lie to the so...

Silurian rocks are present in three successor basins that have no spatial and probably no temporal overlap. The southernmost Killary Harbour-Joyce country succession everywhere masks the contact between the Ordovician rocks of the South Mayo Trough and the Connemara Dalradian. It was deposited in c 5 m.y. from mid-Telychian (Late Llandovery) to She...

This short chapter lists some of the principal repositories of open source digital geological, geophysical and geochemical data that may be used for further study to compliment the field geology presented in this guide.

The Central Ox Mountains is a southwest—northeast trending inlier of Dalradian rocks, mostly attributed to the Argyll Group, that lie along a major fault, the Fair Head—Clew Bay Line (FCL). Deposition was associated with rift related magmatism. These rocks were deformed, metamorphosed (up to kyanite zone) and subsequently exhumed during the mid-Ord...

This chapter reviews the evidence found in the remarkable and varied geology of western Ireland (Fig. 1) for the opening and the closing of the Iapetus Ocean adjacent to the Laurentian margin.The geology visited is briefly reviewed along with a short summary of its likely tectonic significance.

The South Connemara Group is a middle Ordovician (Dapingian(?) to Darriwilian) subduction-accretion complex that is preserved onshore as a roof pendant in the Devonian Galway granite and crops out on the islands of Lettermullen and Gorumna on the north shores of Galway Bay. It is in structural continuity with similar lithologies of the offshore Ski...

We identify 14 mechanisms, marine and non-marine, one man made, that result and could result in the formation of boulder deposits after reviewing issues associated with clast shape, size and classification. Four of these mechanisms: storm deposits; waterspouts; cliff collapse; and catastrophic flooding below sea level, may produce deposits stretchi...

The Grampian Orogeny of western Ireland was formed during the mid‐Ordovician Grampian‐Taconic collision between a 5,600‐km system of oceanic arcs and the Laurentian margin. It is remarkable in that it preserves a complete sedimentary record of the arc‐continent collision process in the South Mayo Trough, which can be linked with deformation and met...

The problem of the observed very rapid advection of heat into metamorphic thrust stacks is reviewed. Conductive models relying on the thermal relaxation of a thickened crust will not produce the observed Barrovian (medium temperature, medium pressure) assemblages within some short-lived orogens (e.g., western Ireland and Timor). Studies of the rate...

Significance The origin of boulderite deposits in the geological record is controversial. Many argue that boulders weighing over 30 tonnes characterize tsunamites. We compare and contrast two such deposits with boulders exceeding this weight: a tsunamite from the Miocene of New Zealand and a present-day boulderite at Annagh Head, western Ireland. C...

In the Irish and British Caledonides, the early Ordovician Grampian Orogeny was the result of collision between the Laurentian rifted margin and an oceanic island arc. The Connemara terrain in western Ireland differs in position and character from all other parts of the exposed Dalradian rocks of the Grampian Orogen in lying south of the collided a...

Coesite-bearing eclogites in several deep crustal metamorphic assemblages now exposed in extensionally-collapsed orogens indicate the tectonic denudation of more than 90 km of crustal rocks and pre-collapsed crustal thicknesses of at least 120 km. For mountain ranges and orogenic plateaux up to 5 km in elevation and average crustal densities of abo...

Higher education is fundamental to both national and global contemporary knowledge economies. It is also a driver for social change (see for example) which crucially includes making higher education available and relevant to a wider section of society and improving the mobility and relevance of its graduates in the workplace. New tools are required...

There is no one model that uniquely defines arc-continent collision. Natural examples and modelling show that there is a large degree of, and variation in, complexity that depend on a number of key first-order parameters and the nature of the main players; the continental margin and the arc-trench complex (the arc-trench complex includes the arc an...

The active Banda arc–continent collision (Banda Orogen) provides many new constraints for resolving long-standing issues about the formative stages of collision. Some of these issues include evidence for trench retreat and subduction erosion, depth of continental subduction, emplacement and demise of forearc basement, relative amounts of uplift due...

Modern intra-oceanic subduction zones comprise around 17,000km (~40%) of the convergent margins of the Earth and are subjects of intense cross-disciplinary studies that are reviewed in this chapter. Most of these subduction zones exhibit trench retreat, do not accrete sediments and are affected by back-arc extension processes. Initiation of intra-o...

Intraoceanic island arcs are considered to be fundamental building blocks of continental crust that are accreted during arc–continent collision. P wave velocity models derived from wide-angle seismic surveys can constrain the thickness and composition of arc crust. The variations of P wave velocity with depth of the Aleutian, Izu-Bonin-Mariana, Les...

We offer a kinematic solution to the “ophiolite enigma, paradox or conundrum”, which is that obducted large-slab full-sequence ophiolite complexes must have originated by organized sea-floor spreading (e.g. sheeted dyke complexes), which indicates an origin at oceanic ridges, yet have geochemical affinities that link them to arcs, especially fore-a...

The Northern Appalachian orogen records complex Late Cambrian to Late Silurian closure of the Iapetus Ocean, which led to significant outboard growth of the Laurentian margin over time. The outboard growth during the Ordovician was primarily achieved by progressive accretion of peri-Laurentian and peri-Gondwanan arc, rifted arc and supra-subduction...

Rifted margins develop by the splitting apart of continents and form the trailing edges of ocean basins, to be incorporated into collision zones when those basins eventually close. Magma-poor margins are dominated by tectonic processes, including crustal extension and thinning, mantle serpentinization and the unroofing of broad expanses of lithosph...

Comparison of exposed arc crustal sections from four ancient magmatic arcs reveals a pattern of depth-specific processes that may be typical of arcs worldwide. These processes include (1) fractionation of mafic and ultramafic cumulates from a mafic parental magma in the uppermost mantle and lowermost crust, (2) subsolidus transformation of mafic pl...

The Wopmay Orogen formed between about 1.88 and 1.84Ga as island arcs (Hottah arc and Nahanni/Fort Simpson arc) converged with the western (today’s coordinates) Coronation margin of the Archean Slave craton. Convergence produced virtually all of the regional geological and geophysical hallmarks that are commonly observed in Phanerozoic plate margin...

The geology of western Ireland preserves a record of the collision of the Lough Nafooey arc with the Laurentian margin which caused the mid-Ordovician Grampian Orogeny. Remarkably, a basin, the South Mayo Trough, accumulated some 9km of sedimentary and volcanic rocks before, during and after this event. Thrusting, believed to be during the post-Gra...

The temporal evolution of internal forces in a collision environment controls first-order characteristics such as convergence rate, slab dip, subduction stall, and slab breakoff, amongst others. Foremost among these forces are the positive buoyancy provided by the subduction of felsic continental material and the negative buoyancy associated with t...

The Karakoram/Kohistan/India collision zone provides a rare opportunity to study the roles of subduction and tectonic accretion in crustal growth processes. Magmatic histories and the timing of major tectonic events in this region become acceptably well understood. Creation of crustal material was accomplished by juvenile supra-subduction magmatism...

We present a new compilation of magnetic, geologic, GPS and seismic data and propose that the geometry and kinematics of the Taiwan arc–continent collision are dominated by the partial subduction of a continental margin promontory and associated fracture zone. A prominent magnetic high in the pre-collision zone southwest of Taiwan serves as proxy f...

The major event in the Cenozoic evolution of the Kamchatka orogen was the Early Eocene collision of the Ozernoy-Valagina (Olutorsky) arc terrane with the continental margin of Asia. The arc–continent collision developed progressively from southwest to northeast from the Early Eocene in South Kamchatka to the early Mid Eocene in the Olutorsky region...

The South Mayo Trough, an early Ordovician sedimentary basin, was developed at the southern margin of the Laurentian plate. It controlled deposition of 12.8 km of sediment. Basic vulcanism accompanied the opening of the trough. This was followed by the deposition of turbidites and finally of fluvio-deltaic sediments. Initial island arc vulcanism wa...

Arc-continent collision has been one of the important tectonic processes in the formation of mountain belts throughout geological time, and it continues to be so today along tectonically active plate boundaries such as those in the SW Pacific or the Caribbean. Arc-continent collision is thought to have been one of the most important process involve...

There is no one model, no paradigm, that uniquely defines arc–continent collision. Natural examples and modelling of arc–continent collision show that there is a large degree of, and variation in, complexity that depend on a number of key first-order parameters and the nature of the main players; the continental margin and the arc–trench complex (t...

This paper looks at general and specific external drivers from a variety of national and supranational organizations (professional associations and accreditation authorities, government agencies, government legislation, European Union) that have produced a range of codes, regulations, and educational requirements that affect the way field training...

The 1999–2007 Irish National Seabed Survey is one of the largest ocean floor mapping projects ever attempted. Its aim is to map the ocean floor of the Irish territorial waters (approximately 525000km2). To date, the Geological Survey of Ireland has gathered in excess of 4TB of multibeam sonar data from the Irish National Seabed, and this data set i...

The origin of the Newer Granites is long-standing problem. In the Caledonian orthotectonic zone the intrusions span the period of late orogenic convergence and uplift, but attempts to relate them as a group to late Iapetan subduction have been unsuccessful. A range of rock types is represented, mainly with I-type affinities, and granodiorite is the...

A new model is proposed for the problematic preservation of an Ordovician forearc basin, which records a complete sedimentary record of arc-continent collision during the Grampian (Taconic) orogeny in the west of Ireland. The South Mayo Trough represents an arc and forearc complex developed above a subduction zone in which the slab dipped away from...

High-resolution heavy mineral data from the Ordovician of the South Mayo Trough, western Ireland is subject to a detailed statistical analysis. The aim of this study is to develop new techniques for treating such data thereby providing an independent and objective way to help elucidate the stratigraphy and tectonic history of the region. A new meth...

Recent technological advances have facilitated even greater resolution of palaeontological and palaeoecological analysis. Such studies on soft-bodied fossils have previously been limited to in situ field measurements, however many remains of this type are not amenable for this kind of investigation. However, many of these specimens may instead be s...

The Caledonian geology of western Ireland records the collision of two arc complexes with the Laurentian Margin during the closure of the Iapetus Ocean. An earlier complex collided with this hitherto passive margin in the mid-Ordovician during the Grampian Orogeny. Subsequently, arc magmatism developed along the Laurentian margin and continued unti...

Collision of the oceanic Lough Nafooey Island Arc with the passive margin of Laurentia after 480 Ma in western Ireland resulted in the deformation, magmatism and metamorphism of the Grampian Orogeny, analogous to the modern Taiwan and Miocene New Guinea Orogens. After ∼470 Ma, the metamorphosed Laurentian margin sediments (Dalradian Supergroup) now...

The Neoproterozoic metasediments of northwestern Scotland were deformed during the 470 Ma Grampian orogeny. Their pre-Ordovician history has proved difficult to elucidate, due to conflicting evidence. While the stratigraphic record indicates deposition in intracontinental rift basins associated with the break-up of Rodinia, isotopic dates in the ra...

A comprehensive, but simple-to-use software package for executing a range of standard numerical analysis and operations used in quantitative paleontology has been developed. The program, called PAST (PAleontological STatistics), runs on standard Windows computers and is available free of charge. PAST integrates spreadsheettype data entry with univa...

Structural, geophysical and metamorphic studies show that collisional orogeny thickens the crust by a factor of two or more. A large volume of continental material at the base of the orogen is, therefore, subject to eclogite facies conditions. Phase equilibration results in a loss of buoyancy and thermodynamic heating of this crustal root. This den...

The previous conflict between stratigraphical and geochronological evidence for the age of the Grampian orogeny in Scotland and Ireland has now been largely resolved. Dalradian deposition continued on the Laurentian margin through late Proterozoic into Ordovician time. The Grampian orogeny was a brief, arc-accretion event that took place around the...

The Caledonides of the west of Ireland mark a segment of the Caledonian–Appalachian orogen where the structural grain swings from the NE–SW trend that typifies the Caledonides of northern Britain to an E–W orientation. The origin of this arcuate structure has previously been proposed to be either primary, reflecting the original geometry of promont...

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

In the Irish Caledonides, volcanism has been significant in terrane identification and in reconstructions of the Appalachian/Caledonian orogen. Crucial to these reconstructions is the recognition of ocean margins using obducted ocean floor relics (ophiolites) and supra-subduction zone volcanic assemblages. The volcanic rocks provide much evidence f...

The westward continuation of the Highland Border fault of Scotland (HBFZ) into Ireland is problematic. It is widely thought to follow a pronounced magnetic and gravity lineament, the Fair Head-Clew Bay Line (FCL). The advantage of this interpretation is that it places all the Ordovician ophiolitic complexes and associated sedimentary basins to the...

New palaeomagnetic data from the Caledonides of western Ireland indicate that the Silurian rocks of South Mayo underwent oroclinal bending, following folding, in Siluro-Devonian time. Bending was accommodated on faults cutting the Silurian sequence, and was driven by strike slip motion across the Antrim-Galway Line, a recently recognized major curv...

Early Ordovician volcanic rocks exposed in the South Mayo region of western Ireland document the history of a volcanic arc complex, produced following the initiation of south-dipping subduction within the Iapetus Ocean in the Late Cambrian or Early Ordovician. Lavas of the Lough Nafooey Group (Tremadoc-Arenig) show an eruption history marked by an...

The BIRPS deep seismic reflection data of WIRE (West of IREland) 1/1B from Galway Bay to the Celtic Sea are integrated with geological and other geophysical data to produce a synthesis of the fundamental tectonic charcter of the crust in and around southern Ireland. The Iapetus Suture forms a zone of north-dipping reflectors which projects up betwe...

Deep seismic profiles in the Irish and North seas have successfully imaged crustal structure across the Iapetus suture zone. A problem with current interpretations is that the reflectors chosen as the suture project to the top of the basement well to the south of the Solway Line, the palaeontologically defined trace of the suture. We present a revi...

Geological and geophysical criteria allow division of the Caledonides of western Ireland into four principal zones. Zone 1, in the north, contains Grenvillian basement with late Proterozoic supra-crystals. Zone 2 contains the Westport Complex, the Deer Park Complex and the South Mayo Trough. Connemara and the Delany Dome Formation occupy Zone 3. Zo...

A two day meeting on 28th and 29rh October 1989 attracted an international audience of over 90 scientists principally from academic institutions and the oil and minerals industries to hear 24 papers on the deep geology and geophysics of Ireland and its continental margin. The aim of the meeting was to present and discuss the results of a number of...

New reflection profiles recorded to 18s ( c .60km) along a 600 km north-south transect West of IREland (WIRE lines) provide a cross-section of the Irish Caledonides from Lewisian basement in the north to the Variscan fold-and-thrust belt in the south, and constrain the offshore extrapolations of major Caledonide structures. We interpret the profile...

Recent paleomagnetic data and existing paleontological evidence show that Baltica occupied temperate southern latitudes during Cambrian and Early Ordovician time, but was inverted with reference to its present orientation. Hence the currently opposed margins of the Baltic and Laurentian shield were not conterminous in the early Paleozoic. Laurentia...

Since the pioneer studies of Trueman and others in the 1920s, some palaeontologists have used a considerable variety of statistical techniques to describe and analyse individuals and associations of fossil taxa. The increasing sophistication of the algorithms used partly reflects advancing technology from long-hand calculations to computer-based an...

Based on new palaeomagnetic results from the North Norwegian Caledonides, we propose new apparent polar wander paths for Baltica during the Early–Mid Palaeozoic and discuss their palaeogeographic implications. In Cambrian and Early Ordovician times, Baltica occupied southerly latitudes of the order of 30° to 50°, but was ‘inverted’ with respect to...

The South Mayo Trough, a broad synclinorium containing a 10-km sequence of Early Ordovician turbidites passing up into shallow water sandstones, is interpreted as a forearc basin with an ophiolitic basement that formed a backstop to an accretionary prism on the northern edge of a north-facing arc. The arc collided with the Laurentian margin in Earl...

Dispersion of Cu and Mo in mainly ombrotrophic-type peat and till on mineralized Galway Granodiorite, Ireland, is controlled by high rainfall (leaching of surface peat), organic content of till, limonite/bog iron, Eh and pH. Sampling surface blanket peat should be avoided in mineral exploration due to downward leaching. Copper accumulates more effe...

Up to 4000 μg g−1 Mo exists in surface material (till/peat) in Ireland over porphyry CuMo mineralized granodiorite at Mace Head, Galway. Dispersion of Mo in surface material is controlled by high rainfall, peat, loss on ignition content of till, Eh and pH. It accumulates in organic-rich till, limonite-strained till in oxidizing conditions, and in...

Two new seismic refraction/wide-angle reflection profiles demonstrate that the crust beneath the southern Porcupine Seabight, out to water depths in excess of 4000 m, is of continental type. They also reveal the rifted margin of the Porcupine basin on its eastern side. Crustal thickness under the Seabight, inclusive of sediments which are up to 6 k...

A suite of 10 programs, written for the BBC Model B, uses computer animation techniques to aid in the teaching of the principles of stereographic projection. The representation of the net remains static in the background whilst plotting and rotation occur on a foreground plane. This mimics the actual operations that are required using a net and tra...

The Tuskar Group is a newly recognized succession of cleaved, steeply dipping, north younging basic volcanics, tuffs, tuffaceous sediments, black shales and medium to fine grained greywackes and turbidites which occur largely in the sea area around the Tuskar Rock, Co. Wexford and in xenoliths in the Carnsore Granite on the mainland. Foliated grano...

Two groups of ophiolites are recognized in the Scandinavian Caledonides, group I representing major ocean or alternatively mature marginal basin, and group II small, younger marginal basins. The main field characteristics of group I include a well-developed ophiolite pseudostratigraphy, and a variable development of oceanic sediments. They were app...

In the Caledonides of central Norway, volcano-sedimentary successions, of the Lower and Upper Hovin and Horg Groups (Ordovician to ?Lower Silurian), unconformably overlie a variable substrate which includes fragmented oceanic crust and ensimatic immature arc assemblages initially deformed and metamorphosed in earliest Ordovician times. In western a...

A new 10 nT compilation of magnetic data for Ireland and the immediately adjacent sea area shows distinct geophysical provinces of characteristic magnetic signature separated by major magnetic linears which can be related to important geological lines. In the far northwest there is a structurally coherent Grampian tectonic-thermal zone bounded to t...

The nature of the contact between the orthotectonic (late Pre-cambrian to Cambrian) and the paratectonic (Ordovician and Silurian) Caledonides has long been a source of discussion. In western Ireland this junction occurs in a complex zone which crops out along the southern shores of Clew Bay, County Mayo, where Dalradian (Middle Cambrian) and Ordov...

16 samples of Ordovician basic volcanic rocks of the South Connemara Group, which abut the southern side of the metamorphic rocks of the Connemara massif in western Ireland, have been analysed for both major and trace elements. Although subject to low grade regional metamorphism and subsequently hornfelsed by the Galway Granite (400 Ma), their immo...

Dalyite (M.M. 29-850) is recorded from a potassic peralkaline syenite dyke from the Sunnfjord area of W Norway. Ten microprobe analyses are tabulated and suggest a formula near (K,Na,Fe)2(Zr,Ti)Si6O15. -R.A.H.

Two peralkaline, ultrapotassic syenite dykes yield Middle Permian K/Ar ages. The hydrothermally altered dykes are composed of microcline, Si-rich and Al-poor phlogopite, an Al-deficient brown mica partly altered to saponite, eckermannite, celadonite, apatite, calcite, baryte, and the rare minerals dalyite and labuntsovite. The dykes are strongly en...

The Lough Nafooey Group is divided into 4 formations. The lowermost Bencorragh Formation consists of spilitic pillowed tholeiites, passing up into the blocky andesite flows, breccias, cherts and basic pillow lavas of the Finny Formation. This is overlain by the Knock Kilbride Formation comprised of spilitized calc-alkali basic to intermediate lavas...

The Maumtrasna Group of coarse sandstones and conglomerates with minor acid volcanics in eastern Murrisk, which has been regarded as being part of the Ordovician succession, is seen in the light of reinterpretation and new evidence as being possibly as young as Devonian in age. Recognition of these lightly deformed rocks may be used to infer an end...

Enzyme supports (2g) [activated by stirring with TiCl4 (12.5%, w/v) for 3 hr], were stirred with enzyme solution (10 ml containing 40 mg of enzyme) for 18 hr at 4°C. Unbound enzyme was removed by washing with 1 M NaCl in the buffer used in the assay of the enzyme, followed by washing with the buffer alone. Lactoperoxidase and β fructofuranosidase w...