Abstract: The Ordovician sedimentary rocks of the South Mayo Trough in western Ireland represent three different sedimentary basins. A northern basin records the erosion of an uplifted ophiolite that had been emplaced onto the Laurentian margin. A southern basin records the erosion of a volcanic complex rooted on continental crust and has clear sedimentary linkage with Connemara. These two separate basins were juxtaposed along a tectonic structure running through the Erriff Valley before being overlain by a third succession (represented by the Glenummera and Mweelrea formations) that formed due to local extension. The southern succession overlies the Cambro-Ordovician Lough Nafooey Arc rocks that, along with the Laurentian margin, have a strong magnetic signature that can be traced through exposed inliers and beneath the Carboniferous cover to Tyrone. To the northeast of South Mayo, the arc and the Laurentian margin are juxtaposed and the original forearc and hyperextended Laurentian margin is interpreted to have underthrust the main body of Laurentia. Connemara is interpreted to have formed as a detached microcontinental block in similar manner to Slishwood. Preservation of the South Mayo successions is partly due to an original bend in the Laurentian margin and partly to strike-slip and rotation of Connemara during the later stages of the Grampian orogeny.

Most of the Connemara granites, including the Galway Granite batholith, have a clearly defined circular or ellipsoidal outcrop shape and are I-Type granites often with K-feldspar phenocrysts, whereas the Oughterard Granite (OG) forms numerous small intrusions scattered east-west over 40km with two larger linked bodies near Oughterard and is S-Type and aphyric. The only comprehensive mapping, mineralogical and chemical study of the OG was published over 50 years ago before the important 1974 recognition of the distinction of I- and S-Type granites was first made. New mapping of the southern Oughterard area with small OG intrusions is presented and many scattered published chemical and Rb, Sr, S and Pb isotopic studies integrated to confirm overall their individual conclusions that the peraluminous OG is of S-Type, being formed from melted Dalradian rocks as are the fluid-carried associated uneconomic mineral deposits. The OG is confined to the high sillimanite zone, mostly south of, and mainly later than, the 465-464Ma D4 Connemara Antiform, where a wide (>15km N-S) >70km E-W band of 469Ma gabbros and 467Ma quartz diorite gneisses intruded into already hot Dalradian rocks undergoing regional metamorphism. This generated the OG magmas by partial melting of pelites and semi-pelites. The upward intrusion of the OG magma was significantly delayed, as has been shown by precise dating in other granites elsewhere, to ~464-461Ma during the late stages and mostly after D4 but before the country rocks had completely cooled. The OG intrusions as a whole probably form the second largest area of S-Type granite in Ireland, after the Leinster Granite.

In Joyces Country in western Ireland, the ~ E-W striking axial plane of the D7 Ben Levy anticline folded Dalradian and unconformable Silurian rocks. The north side of the fold is mostly coincident with the contemporaneous ESE-WNW striking steeply dipping Coolin Fault close to the Dalradian-basal Silurian contact. This fault was first initiated by sinistral strike-slip motion, probably of Ordovician age, and then secondly used by post-Wenlock down throw on the north side to form the D7 anticline. Later a newly recognised third motion of reverse reactivation on the fault uplifted the north limb of the fold and locally overturned the Silurian succession against irregularities in the SSW dip of the fault. Still later, but pre-374Ma (Devonian), NE-SW faulting exposed different previous levels of the Coolin Fault zone. The superb Dalradian rock exposure provides details not generally apparent on other reactivated faults in Connemara.

The Killary Harbour–Joyce Country succession of Silurian rocks forms the remnant of one of three successor basins that developed after the Grampian Orogeny and which are preserved in western Ireland. Its outcrop everywhere obscures the contact between the Dalradian rocks of Connemara and the Ordovician rocks of the South Mayo Trough. The outcrop is bisected by the prominent north-west trending Maam Valley Fault Zone that is shown to have a component of synsedimentary movement down-throwing to the southwest. The original basin margins lay well outside the current outcrop area. North-south shortening and inversion of the basin was accomplished by reactivation and inversion of earlier fault structures and was exclusively in the brittle zone. Folding of the Silurian rocks with weak to moderate cleavage and deformation of the basement rocks of Connemara was accomplished by largely vertical movements along numerous strike parallel and oblique fractures. Break-back inversion structures were developed along the southern margin of the South Mayo Trough, which include thrusting associated with footwall shortcut faults and clockwise rotation. Although the timing of deformation overlaps that of diorite sill emplacement, it remains poorly constrained in absolute terms.

The Clifden district, illustrated with an accompanying new detailed 1:12,500 geological map and fold trace map, includes most of the stratigraphy of the Connemara Dalradian and is used to summarise present understanding of the older geological history of Connemara in the light of new structural work and recent age determinations. The Grampian metamorphism peaked with sillimanite formation during and after the late D2 syntectonic intrusions of metagabbros at 475–470Ma and the formation of the major D2 Derryclare fold which was then repeatedly folded by numerous major D3 folds synchronous with the injection in the south of the 467Ma Quartz diorite gneiss suite, maintaining the high-grade metamorphism. Late D3 saw the general initiation of cooling and uplift, the latter pronounced in eastern Connemara above and around the subterranean gathering of the Oughterard Granite magma, plus movement on the late D3 Renvyle-Bofin slide, generating an area of lower pressure metamorphism with cordierite and andalusite not found in the Clifden area.

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The discovery of a sapphire (blue corundum) bearing erratic on the granite island of Lettermore, south Connemara, has led to further discoveries of generally non-gem-grade sapphire in hornfelsed desilicated pelitic xenoliths within the 470Ma metagabbros of Connemara's Grampian Metagabbro-Gneiss Suite. The petrology and mineralogy of the erratic and the desilicated pelitic xenoliths are described. Well-established constraints on the timing of magmatism and on metamorphic conditions show that colourless corundum and a hercynite-magnetite spinel formed 470Ma ago at >900°C and the spinel later (~468Ma) unmixed to corundum, which was sometimes sapphire, and magnetite at temperatures of ~750°C and 3.5–6kb. Consideration of global sapphire occurrences indicates that sapphire can form over a wide range of P and T, i.e. greenschist to granulite facies. The Connemara sapphire formed during contact granulite facies metamorphism.

The petrochemistry of the major elements (33 new rock analyses) of the Dalradian Glencolumbkille metadolerite sills, now amphibolite, shows them to have been quartz tholeiites like those of most of Donegal. Their compositions overlap with those of Connemara (Co. Galway) and Knapdale (Scotland), except the latter two also extend into the olivine tholeiite field. The syn-D2 (~470Ma) sheared schistose margins of the Glencolumbkille bodies are garnet amphibolites, unlike the generally garnet-free centres, and have suffered fluid-derived metasomatism and garnet growth. Garnets are postulated to have been nucleated by the activation energy from the shearing, but the main garnet growth and metamorphism was under static post-D2 pre-D3 conditions in certain favourable rock compositions. Garnet growth in the Glencolumbkille and Connemara amphibolites was generally restricted to rocks with low Mg/Fe, low Fe2O3/FeO and high MnO compositions, whether original or metasomatic. The long-standing puzzle as to why amphibolites that were originally dolerite sills in the Dalradian succession are clustered at certain horizons (at Glencolumbkille in and near the 654–635Ma Marinoan glaciation Portaskaig Tillite Formation) is examined. The clustering is suggested to be partly explained by recent structural research showing that the intrusion of widespread lateral sheets of basaltic magma is restricted to closely interbedded competent beds with thin incompetent pelites. The former act as lids, while the latter allow lateral expansion of the original sills. The whole magmatic suite studied intruded sediments deposited before 600Ma. It is thought to be part of the major ~600Ma magmatism and crustal extension that affected the Scottish Highlands and eastern North America as the supercontinent Rodinia split apart and the Iapetus Ocean opened. Of the metabasites, only the Knapdale ones have been U-Pb dated, yielding a magmatic 600Ma age and thus definitely shown to be pre-D1.

A new detailed (1:25,000) geological map, cross-sections and descriptions are presented of a large part of Joyces Country, consisting of Connemara Dalradian Schists unconformably overlain by both Silurian (Upper Llandovery to Wenlock) and Carboniferous (Tournaisian to Lower Visean) rocks; only the edge of the last has been mapped. The Dalradian rocks contain D2, D3 and D4 folds and are of staurolite to sillimanite grade with late andalusite and cordierite, constrained to between 470 and 463 Ma. Major D3 folds are folded by the D4 Connemara Synform and the complementary D4 Joyces Antiform, which predate the intrusion of the 462 Ma Oughterard Granite. The folding of the Silurian rocks, termed Scandian as it was intra-Silurian, is identified precisely as a short late Wenlock to early Ludlow episode, (430 to 424 Ma; Gradstein et al. 2012), probably Gorstian Stage (427 ± 3 Ma), and hence not end-Silurian (419 Ma). The mechanism whereby the Scandian open folding of the Silurian rocks took place above the relatively high-level rigid Dalradian basement in the northern part of the area is shown to be by closely-spaced nearly vertical E–W faulting and shearing along the strike of the sub-vertical foliation in the Dalradian Schists. This controlled the trend of the folds in the Silurian rocks. At deeper levels in the basement in the southern part of the area, far fewer, and more widely spaced faults involving larger movements are probably related to syn-Scandian folding. At least five major folds in the exposed Silurian are identified. There would have been more folds (now eroded away) in the south of the area above the Dalradian rocks. The area is crucial in exposing part of the brittle-ductile transition in the Dalradian during the Scandian folding and the solution of the reciprocal problems of how the basement controlled the folding of the Silurian rocks and how their folding affected the Connemara basement.

Manganocummingtonite occurs with spessartine, quartz and pyrolusite in the Chikmara area, Sausar fold belt, central India. Its composition is [Ca0.3–0.35(Mg3.3–3.5Mn1.6–1.8Fe2+ 1.4–1.5)(Si7.931–7.997Aliv 0.003–0.069)O22(OH1.5–2.0F0.0–0.5)] being fairly rich in Ca, which is indicative of metamorphic temperature in the amphibolite facies. The garnet contains 77.5% spessartine, 13% almandine and minor andradite, grossular and pyrope components. Unusually, there is no carbonate, pyroxene, pyroxmangite, rhodonite, magnetite or hematite. The available Al in the rock stabilized garnet and this mineral incorporated minor Fe3+ present in the rock as andradite component. The manganocummingtonite-garnet pairs developed at ∼600°C during amphibolite facies metamorphism in low \(X_{CO_2 } \) system, stabilized with \(X_{Mn/(Mn + Fe^{2 + } + Mg)} \) = 0.25 to 0.28 in the amphibole and 0.85 in the garnet and formed under unusually low fO 2 conditions for the Sausar region, near channelized fluids which deposited quartz may have controlled the fO 2 .

New geological mapping in the centre of the Galway Granite at Camus, Co. Galway, reveals a major north—south thrust zone, the Furnace Thrust, typically dipping east at 35°, which thrust up westward deeper-crystallised granite, including two minor late intrusions, on top of a higher-level granite footwall. Al-in-hornblende geobarometry of the footwall and the hanging wall confirms the thrusting. At 2km east of the thrust, both the footwall and the hanging wall of the thrust sheet were later substantially further uplifted by the steeper Shannawona Fault. At 6km east of this fault, the granite contains post-400—395Ma, pre-370—378Ma thrusts that moved south-eastward, so a major block of the deep ∼400—395Ma Megacrystic Granite has been squeezed upward. This granite still farther east was later uplifted more by the steep Shannapheasteen Fault, which is connected with the late (?380Ma) central intrusion of the Shannapheasteen Granite, which pushed its roof upward. The uplift of the Central Block with its deeply crystallised Megacrystic Granite was therefore the result of thrusts and faults connected in a complex way with the coeval intrusive pressures of the late emplacement of the Shannapheasteen Granite and six other late granites. All seven late granites are confined to the Central Block and, having low densities, exerted protracted buoyancy uplift forces. This modifies the previous partly correct, but mechanically difficult, explanation for the origin of the Central Block of the Galway Batholith.

Gregory arrived in Melbourne, without his family, and was welcomed by the Professorial Board on 23 February 1900. He probably stayed initially with the Professor of Biology, Walter Baldwin Spencer (1860–1929), an enthusiast for fieldwork, who had written to him offering the use of his house as his wife and children were away (letter with A. Mendell). He must have made a favourable impression amongst the academic community because he was awarded a Melbourne University DSc almost immediately by ‘ ad eundem gradum ’ (Univ. Melb. Archives). This was not an honorary degree but recognition that he had achieved the same degree in another university of repute, in this instance, London. Of course, since his 1893 London DSc, he had published more than enough to gain another DSc if he had chosen to apply. According to Lim (1975), his duties were to devote the whole of his time to the work of his department; to conduct and mark examinations and to deliver two courses of lectures of three hours a week each and associated fieldwork instruction. According to the newspaper The Age of 26 February 1900, Gregory's predecessor at Melbourne (who had come from a Chair at Queen's University, Belfast to the Chair in 1854, initially taught almost all the science in the university), ‘the late Sir Frederick McCoy never took his students into the field at all so they had no such practical work or contact with mining in the colony whereas Dr Gregory intends to promote field work, mineralogy, links with mining and palaeontology teaching in geology, especially as regards the sequence of beds’ (Fig. 13.1). Fig. 13.1. Professor Frederick McCoy, later knighted (Selleck 2003). With permission of the University of Melbourne Archives. Although he had been led to believe that the university had a ‘very fair collection …