Long-lived granite-related molybdenite mineralization at Connemara, western Irish Caledonides

2010 ◽  
Vol 147 (6) ◽  
pp. 886-894 ◽  
Author(s):  
MARTIN FEELY ◽  
DAVID SELBY ◽  
JON HUNT ◽  
JAMES CONLIFFE
Keyword(s):  
Zircon Geochronology ◽  
Mixing Zone ◽  
Granite Emplacement ◽  
Tectonic Processes ◽  
Slab Breakoff ◽  
Caledonian Orogeny ◽  
Granite Magmatism ◽  
Western Ireland ◽  
Granite Samples ◽  
Caledonian Granite

AbstractNew Re–Os age determinations from the Galway Granite (samples: KMG = 402.2 ± 1.1 Ma, LLG = 399.5 ± 1.7 Ma and GBM = 383.3 ± 1.1 Ma) show that in south Connemara, late Caledonian granite-related molybdenite mineralization extended from c. 423 Ma to c. 380 Ma. These events overlap and are in excellent agreement with the published granite emplacement history determined by U–Pb zircon geochronology. The spatial distribution of the late-Caledonian Connemara granites indicates that initial emplacement and molybdenite mineralization occurred at c. 420 Ma (that is, the Omey Granite and probably the Inish, Leterfrack and Roundstone granites) to the N and NW of the Skird Rocks Fault, an extension of the orogen-parallel Southern Uplands Fault in western Ireland. A generally southern and eastward progression of granite emplacement (and molybdenite mineralization) sited along the Skird Rocks Fault then followed, at c. 410 Ma (Roundstone Murvey and Carna granites), at c. 400 Ma (Errisbeg Townland Granite, Megacrystic Granite, Mingling Mixing Zone Granodiorite, Lough Lurgan Granite and Kilkieran Murvey Granite) and at c. 380 Ma (Costelloe Murvey Granite, Shannapheasteen and Knock granites). The duration of granite magmatism and mineralization in Connemara is similar to other sectors of the Appalachian–Caledonian orogeny and several tectonic processes (e.g. slab-breakoff, asthenospheric flow, transtension and decompression) may account for the duration and variety of granite magmatism of the western Irish Caledonides.

Magmatic and tectonic emplacement of the Pukaskwa batholith, Superior Province, Ontario, CanadaThis article is one of a series of papers published in this Special Issue on the theme of Geochronology in honour of Tom Krogh.

2011 ◽  
Vol 48 (2) ◽  
pp. 187-204 ◽  
Author(s):  
Gary P. Beakhouse ◽  
Shoufa Lin ◽  
Sandra L. Kamo
Keyword(s):  
Partial Melting ◽  
Abrupt Change ◽  
Superior Province ◽  
Density Inversion ◽  
Tectonic Processes ◽  
Slab Breakoff ◽  
Greenstone Belts ◽  
Lower Crustal ◽  
Basaltic Crust ◽  
Structural Dome

The Neoarchean Pukaskwa batholith consists of pre-, syn-, and post-tectonic phases emplaced over an interval of 50 million years. Pre-tectonic phases are broadly synvolcanic and have a high-Al tonalite–trondhjemite–granodiorite (TTG) affinity interpreted to reflect derivation by partial melting of basaltic crust at lower crustal or upper mantle depths. Minor syn-tectonic phases slightly post-date volcanism and have geochemical characteristics suggesting some involvement or interaction with an ultramafic (mantle) source component. Magmatic emplacement of pre- and syn-tectonic phases occurred in the midcrust at paleopressures of 550–600 MPa and these components of the batholith are thought to be representative of the midcrust underlying greenstone belts during their development. Subsequent to emplacement of the syntectonic phases, and likely at approximately 2680 Ma, the Pukaskwa batholith was uplifted as a structural dome relative to flanking greenstone belts synchronously with ongoing regional sinistral transpressive deformation. The driving force for vertical tectonism is interpreted to be density inversion (Rayleigh–Taylor-type instabilities) involving denser greenstone belts and underlying felsic plutonic crust. The trigger for initiation of this process is interpreted to be an abrupt change in the rheology of the midcrust attributed to introduction of heat from the mantle attendant with slab breakoff or lithospheric delamination following the cessation of subduction. This process also led to partial melting of the intermediate to felsic midcrust generating post-tectonic granitic phases at approximately 2667 Ma. We propose that late density inversion-driven vertical tectonics is an inevitable consequence of horizontal (plate) tectonic processes associated with greenstone belt development within the Superior Province.

Late Caledonian transpression and the structural controls on pluton construction; new insights from the Omey Pluton, western Ireland

2015 ◽  
Vol 106 (1) ◽  
pp. 11-28 ◽  
Author(s):  
William McCarthy ◽  
R. John Reavy ◽  
Carl T. Stevenson ◽  
Michael S. Petronis
Keyword(s):  
Spatial Distribution ◽  
Host Rock ◽  
Shear Zones ◽  
Magma Ascent ◽  
Structural Controls ◽  
Rock Structure ◽  
Granite Complex ◽  
Caledonian Orogeny ◽  
Western Ireland

ABSTRACTThe Galway Granite Complex is unique among the British and Irish Caledonian granitoid terranes, as it records punctuated phases of magmatism from ∼425–380 Ma throughout the latest phase of the Caledonian Orogeny. Remapping of the Omey Pluton, the oldest member of this suite, has constrained the spatial distribution and contact relationships of the pluton's three main facies relative to the nature of the host rock structure. The external contacts of the pluton are mostly concordant to the limbs and hinge of the Connemara Antiform. New AMS data show that a subtle concentric outward dipping foliation is present, and this is interpreted to reflect pluton inflation during continued magma ingress. Combined field, petrographic and AMS data show that two sets of shear zones (NNW–SSE and ENE–WSW) cross-cut the concentric foliation, and that these structures were active during the construction of the pluton. We show that regional sinistral transpression at ∼420 Ma would have caused dilation along the intersection of these two fault sets, and suggest that this facilitated centralised magma ascent. Lateral emplacement was controlled by the symmetry of the Connemara Antiform to ultimately produce a discordant phacolith. We propose that regional sinistral transpression at ∼420 Ma influenced the siting of smaller intrusions over NNW–SSE faults, and that the later onset of regional transtension caused larger volumes of magma to intrude along the E–W Skird Rocks Fault at ∼400 Ma.

CASSERITE U-Pb GEOCHRONOLOGY OF THE SANTA BÁRBARA TIN DISTRICT, RONDÔNIA TIN PROVINCE, BRAZIL

2021 ◽  
Author(s):  
Frederico Sousa Guimarães ◽  
Rongqing Zhang ◽  
Bernd Lehmann ◽  
Alexandre Raphael Cabral ◽  
Francisco Javier Rios
Keyword(s):  
Inductively Coupled Plasma ◽  
Rare Metal ◽  
Santa Barbara ◽  
Rare Metal Granite ◽  
Inductively Coupled ◽  
Granite Emplacement ◽  
Amazonian Craton ◽  
Plasma Mass Spectrometry ◽  
Granite Magmatism ◽  
Intrusive Suite

Abstract The Mesoproterozoic Rondônia Tin Province of the Amazonian craton records a protracted history of about 600 m.y. of successive rare-metal granite intrusions and hosts the youngest known event of tin-granite emplacement of the craton—a rare-metal granite suite known as the Younger Granites of Rondônia intrusive suite. The ~1 Ga suite is currently interpreted as intracratonic magmatism resulting from a Grenvillian-age orogeny during the assembly of Rodinia. The Santa Bárbara massif is a tin-granite system of the Younger Granites of Rondônia intrusive suite that hosts Sn-Nb-Ta-W–bearing endogreisen and stockwork, as well as important placer deposits. The Santa Bárbara mine produces about 800 to 1,000 t Sn/year from placers and weathered greisen and represents about 20% of the tin mine output of the Rondônia Tin Province. Here, we report laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) cassiterite U-Pb ages of 989 ± 3 and 987 ± 6 Ma for the Santa Bárbara greisen and the cassiterite-quartz vein system, respectively. Alluvial cassiterite from placer mining has a U-Pb age of 995 ± 4 Ma, which is, within uncertainty, indistinguishable from those of primary cassiterite. These ages agree well with the previously published zircon and monazite U-Pb ages for the Santa Bárbara granite (978 ± 13 and 989 ± 13 Ma), which indicate a coeval relationship between hydrothermal tin mineralization and granite magmatism. The previously suggested 20- to 30-m.y. time span between granite magmatism and hydrothermal tin mineralization, which was based on mica K-Ar and Ar-Ar age data, is likely due to younger thermal disturbance of the isotopic systems.

scholarly journals Multi-chronometer dating of the Souter Head complex: rapid exhumation terminates the Grampian Event of the Caledonian Orogeny

2020 ◽  
Vol 111 (2) ◽  
pp. 95-108
Author(s):  
Darren F. MARK ◽  
Clive M. RICE ◽  
Malcolm HOLE ◽  
Dan CONDON
Keyword(s):  
Ductile Deformation ◽  
Volcanic Complex ◽  
Basic Magmatism ◽  
Peak Metamorphism ◽  
Caledonian Orogeny ◽  
Western Ireland ◽  
Decompressional Melting ◽  
Metamorphic Core ◽  
Orogenic Events ◽  
Rapid Uplift

ABSTRACTThe Souter Head sub-volcanic complex (Aberdeenshire, Scotland) intruded the high-grade metamorphic core of the Grampian Orogen at 469.1 ± 0.6 Ma (uranium-238–lead-206 (238U–206Pb) zircon). It follows closely peak metamorphism and deformation in the Grampian Terrane and tightly constrains the end of the Grampian Event of the Caledonian Orogeny. Temporally coincident U–Pb and argon/argon (40Ar/39Ar) data show the complex cooled quickly with temperatures decreasing from ca.800 °C to less than 200 °C within 1 Ma. Younger rhenium–osmium (Re–Os) ages are due to post-emplacement alteration of molybdenite to powellite. The U–Pb and Ar/Ar data combined with existing geochronological data show that D2/D3 deformation, peak metamorphism (Barrovian and Buchan style) and basic magmatism in NE Scotland were synchronous at ca.470 Ma and are associated with rapid uplift (5–10 km Ma−1) of the orogen, which, by ca.469 Ma, had removed the cover to the metamorphic pile. Rapid uplift resulted in decompressional melting and the generation of mafic and felsic magmatism. Shallow slab break-off (50–100 km) is invoked to explain the synchroneity of these events. This interpretation implies that peak metamorphism and D2/D3 ductile deformation were associated with extension. Similarities in the nature and timing of orogenic events in Connemara, western Ireland, with NE Scotland suggest that shallow slab break-off occurred in both localities.

scholarly journals A Lower Devonian age for the Corvock Granite and its significance for the structural history of South Mayo and the Laurentian margin of western Ireland

2021 ◽  
Author(s):  
John Graham ◽  
Nancy Riggs
Keyword(s):  
Lower Devonian ◽  
Early Devonian ◽  
North East ◽  
The North ◽  
Granite Emplacement ◽  
History Of ◽  
Western Ireland ◽  
Laurentian Margin ◽  
Devonian Age ◽  
Restraining Bend

The Silurian Croagh Patrick succession, which crops out just south of a fundamental Caledonian structural zone near Clew Bay, western Ireland, is a series of psammites and pelites with a strong penetrative cleavage. These rocks are intruded by the Corvock granite. A suite of minor intrusions associated with the granite contains the regional cleavage whereas the Corvock granite is undeformed. New U-Pb dates are 413 + 7 / -4 Ma for a strongly cleaved sill and 410 ± 4 Ma for the main granite and closely constrain the age of crystallization of the granite and coeval cleavage formation as Lower Devonian (Lochkovian or Pragian), implying syn- to late-kinematic granite emplacement. These data are consistent with evidence for strong sinistral shear shown by the Ox Mountains granodiorite just to the north-east dated at 412.3 ± 0.8 Ma. This Devonian cleavage is superimposed on Ordovician rocks of the South Mayo Trough. The localisation of the strong deformation is interpreted as being due to its position at a restraining bend during regional sinistral motion on a segment of the Fair Head-Clew Bay Line to the north. Contemporaneous deformation in the syn-kinematic Donegal batholith suggests a transfer of sinistral motion to this intra-Grampian structure rather than simple along-strike linkage to the Highland Boundary Fault in Scotland. Our new data indicate diachronous deformation during the late Silurian and early Devonian history of the Irish and Scottish Caledonides and also support previous interpretations of diachronous deformation between these areas and the Appalachian orogens.

Tuffisite with topaz from the Nigerian Younger Granite province — the Balfour Hill ‘sediments’

1974 ◽  
Vol 111 (4) ◽  
pp. 337-342 ◽  
Author(s):  
J. B. Wright
Keyword(s):  
Hydrothermal Fluids ◽  
Fracture System ◽  
Volcanic Origin ◽  
Jos Plateau ◽  
Fine Grained ◽  
Granite Emplacement ◽  
Granite Magmatism

SummaryNear one of the Younger Granite intrusives of the Jos Plateau is a series of steeply dipping dark and predominantly fine grained rocks. Originally interpreted as argillaceous sediments thermally metamorphosed by the adjacent granite, with development of andalusite, later work established their volcanic origin but did not account for the andalusite. Field relationships and petrography of the rocks suggest they are tuffisites, emplaced by volcanic fluidization processes into part of the fracture system associated with the Younger Granite magmatism. The ‘andalusite’ is topaz, widespread in this province, mainly in the Younger Granite tin veins and greisens, sometimes as an accessory in the granites themselves, but not known from the volcanics — yet abundant in some of these tuffisites. It occurs in well formed crystals, displaying a ‘chiastolite-cross’ arrangement of inclusions, characteristic of andalusite but appearing not to have been previously recorded in topaz. The origin of the topaz must lie either in late-volcanic emanations or in hydrothermal fluids from the mineralizing stage of Younger Granite emplacement.

New perspectives on the order and style of granite emplacement in the Galway Batholith, western Ireland

1997 ◽  
Vol 134 (4) ◽  
pp. 539-548 ◽  
Author(s):  
Q. CROWLEY ◽  
M. FEELY
Keyword(s):  
Upward Movement ◽  
The West ◽  
Marked Contrast ◽  
Central Block ◽  
The North ◽  
Granite Emplacement ◽  
Field Evidence ◽  
Western Block ◽  
Western Ireland ◽  
Roof Rocks

The late Caledonian Galway Batholith is cut by two major faults which divide it into three separate areas: the western, central and eastern blocks. The upthrown and more deeply eroded central block is bounded by these faults, in the west by the north–northeast trending Shannawona Fault and in the east by the north–northwest trending Barna Fault. We present new granite field relations from part of the central block (Inveran sector) which are fundamental in establishing the order and style of emplacement for the granites of the central block and the batholith as a whole. Unequivocal field evidence from the Inveran sector indicates upward movement of early central block granites which then became the solid roof rocks to subsequent intrusions. In the case of the Knock Granite these earlier intrusions were block stoped. We use this field evidence to review the geology of the central block in a 200 km2 area that incorporates the previously mapped Costelloe and Spiddal areas. Sharp intrusive contacts are a predominant feature of this sector of the central block and are in marked contrast to the gradational contacts recorded elsewhere in the batholith. Whereas juxtaposition of plutons in the western block occurred as the granites were partly crystallized, the central block reveals earlier, deeper level granites that were consolidated by the time they were intruded by late-stage higher level granites.

Mechanism of emplacement and crystallisation history of the northern margin and centre of the Galway Granite, western Ireland

2006 ◽  
Vol 97 (1) ◽  
pp. 1-23 ◽  
Author(s):  
Bernard Elgey Leake
Keyword(s):  
Country Rock ◽  
Late Phase ◽  
Main Phase ◽  
Mixing Zone ◽  
Northern Margin ◽  
Fractionation Scheme ◽  
History Of ◽  
Magma Pulses ◽  
Dyke Injection ◽  
Western Ireland

ABSTRACTThe main phase (∼400 Ma) emplacement of the central and northern part of the reversely zoned Galway Granite was incremental by progressive northward marginal dyke injection and stoping of the 470–467 Ma Connemara metagabbro-gneiss country rock. The space was provided by the synchronous ESE-opening, along the strike of the country rocks, of extensional fractures generated successively northward by a releasing bend in the sinistrally moving Skird Rocks Fault or an equivalent Galway Bay Fault. This fault is a prolongation of the Antrim–Galway (a splay off the Highland Boundary Fault) and Southern Upland Faults. The ESE-strike of the spalled-off rocks controlled the resultant ESE-elongated shape of the batholith. The magma pulses (∼5–30 m in thickness) were progressively more fractionated towards the northern margin so that the coarse Porphyritic (or Megacrystic) Granite (GP; technically granodiorite) in the centre was followed outwards by finer grained, drier and more siliceous granite, until the movements opening the fractures ceased and the magma became too viscous to intrude. ‘Out-of-sequence’ pulses of more basic diorite-granodiorite (including the Mingling–Mixing Zone) and late main phase, more acid, coarse but Aphyric Granite, into the centre of the batholith, complicated the outward fractionation scheme. The outward expansion, caused by the intrusions into the centre, caused a foliation and flattening of cognate xenoliths within the partly crystallised northern marginal granite and in the Mingling–Mixing Zone to the south.Late phase (∼380 Ma) central intrusions of the newly-discovered aphyric Shannapheasteen Finegrained Granite (technically granodiorite), the Knock, the Lurgan and the Costello Murvey Granites, all more siliceous and less dense than the GP, were emplaced by pushing up the already solid and jointed GP along marginal faults. This concentration of lighter granites plus compression shown in thrusting, caused overall fault uplift of the Central Block of the Galway batholith so that the originally deepest part of the GP is exposed where there is the most late phase granite. Chemical analyses show the main and late phase magmas, including late dykes, were very similar, with repetition of the same fractionation except that the late phase magmas were drier and more quickly cooled, giving finer grained rocks.

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