This study is an investigation into the nature and causes of petrological zonation in calc-alkaline diorite-granite plutons from the Newer granites of the Caledonian orogeny in Scotland. Six plutons were used for the study, namely Garabal Hill-Glen Fyne in the western Highlands, Glen Tilt and Glen Doll in the eastern Highlands, Comrie in the southern Highlands, and Carsphairn and Loch Doon in the Southern Uplands. The petrological zoning is concentric in the Southern Uplands and Comrie and irregular in the other three. The approach has been to acquire data on the petrography, mineral chemistry, and whole rock major and trace element chemistry for representative rock types of the petrological range within each pluton. Variations in mineral compositions are related to equilibrium crystallisation processes and indicate falling crystallisation temperatures with evolving magma composition. Mineral compositions have also been used in chemical models used to explain the observed wide variations in whole rock major oxide compositions. These models are then independently tested using models of trace element behaviour. The principal conclusions are that the main variations within the gabbro-diorite series (including cumulate peridotites and pyroxenites) are best explained by processes of fractional crystallisation from a parental gabbro or diorite magma, but in some cases the more evolved rocks (granites and granodiorites) have a more complex origin including possibly contamination of the parental magma or a distinctive magma source. The assemblage of fractionating minerals in the Garabal Hill, Comrie and Loch Doon plutons is dominated by the relatively anhydrous assemblage of orthopyroxene, clinopyroxene, plagioclase, and biotite whereas in Glen Doll it is a more hydrous assemblage dominated by amphibole. Processes of magma mixing and multi-source pulses are considered appropriate in a few cases. Regional comparisons of the within-pluton compositional variations reveal significant differences. The dominantly calc-alkaline trend shows marked differences in Fe/Mg between plutons as do trace element abundances, reflecting both differences in source region compositions and the influence of fractionating mineral phases. All plutons are I-type and high-K calc-alkaline. Parental magmas for the gabbro-diorite series have features of mantle-derived magmas though the more evolved rock types including granodiorites and granites indicate a significant contribution by crustal anatexis to the magmas.

"The purpose of this dissertation is ... to review the economic geology of primary tin deposits and the geological factors that control grade and tonnage . The work concludes with a discussian of the implications of these geological controls on evaluation"-- Introd., p. 1

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published_or_final_version / abstract / Earth Sciences / Doctoral / Doctor of Philosophy

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No description available.

Critical metals are of growing economic importance for the low carbon sector but are susceptible to resource restrictions and have no viable substitutes in their applications. In this study, 134 samples of the Cornubian Batholith, SW England, with associated early Permian mafic and ultramafic rocks were sampled and analysed by ICP-MS and XRF for their major, trace and critical metal (Li, Be, Ga, Ge, Nb, Ta, In, Sb, W and Bi) abundance. The mineral chemistry of feldspars, micas, tourmaline, topaz and cordierite was determined for 8 samples by EPMA and LA-ICP-MS. The Cornubian Batholith is a peraluminous, composite pluton intruded into Devonian and Carboniferous metasedimentary and volcanic rocks. Geochemical fractionation trends recorded by whole rock geochemistry and mineral chemistry permit trace element modelling of two distinct fractional crystallisation series, biotite-muscovite (>282 Ma) and biotite-tourmaline (<282 Ma). The biotite-muscovite granites formed through muscovite and minor biotite dehydration melting of a metagreywacke source at moderate temperatures and pressures. Fractionation of an assemblage dominated by feldspars and biotite, enriched muscovite granites in Li (average 340 ppm), Be (13 ppm), Nb (16 ppm), Ta (3.7 ppm), In (77 ppb), Sn (17 ppm), W (12 ppm) and Bi (2.6 ppm) and are spatially associated with greisen style Sn-W mineralisation. Muscovite is the major host of In, Sn and W, and as muscovite is late-stage / subsolidus this implies these metals are highly incompatible in magmatic minerals and likely to partition into fluids exsolving from evolved muscovite granites. The biotite-tourmaline granites formed through higher-T melting than the first suite due to underplating of the region by mantle-derived melts during tectonic extension. Fractionation of feldspars, biotite and cordierite enriched Li (average 525 ppm), Ga (28 ppm), In (122 ppb), Sn (14 ppm), Nb (30 ppm), Ta (5.5 ppm), W (7.1 ppm) and Bi (2.7 ppm) in the tourmaline granites with retention of Be in the biotite granite due to partitioning of Be into cordierite. Distribution of Nb and Ta is controlled by accessory phases such as columbite within the evolved tourmaline granites, promoting disseminated Nb and Ta mineralisation. Lithium, In, Sn and W are hosted in biotite group micas which may prove favourable for breakdown on ingress of hydrothermal fluids and partitioning of the critical metals into mineralising fluids emanating from evolved tourmaline granites. Topaz granites are analogues of Rare Metal Granite described in France and Germany. They contain albite, polylithionite and topaz as major minerals and show differing trends on major and trace element plots relative to the other two granite series. These granites are enriched in Li (average 1363 ppm), Ga (38 ppm), Sn (21 ppm), W (24 ppm), Nb (52 ppm) and Ta (15 ppm) and formed through partial melting of a biotite-rich residue left after melting that formed early biotite granites.

Thesis advisor: J. Christopher Hepburn / The Nashoba terrane is a highly metamorphosed and sheared Paleozoic tectonic block in eastern Massachusetts. The metamorphic rocks that compose the terrane are intruded by a series of diorites, tonalites, and granites. The Andover Granite is a complex multiphase granitic suite found in the northern part of the Nashoba terrane and is composed of both foliated and unfoliated granites as well as a granodiorite phase. The Sgr Group of granites is a series of unfoliated granites exposed along the Nashoba-Avalon terrane boundary. New crystallization ages for the foliated Andover Granite and the Sudbury Granite, southernmost body of the Sgr Group of granites, are presented. CA-TIMS U-Pb geochronology on zircons collected from these granites yielded 419.43 ± 0.52 Ma and 419.65 ± 0.51 Ma crystallization ages for the foliated Andover Granite and a 420.49 ± 0.52 Ma crystallization age for the Sudbury Granite. Geochemical and petrographic analysis of these granites indicate that the foliated Andover Granite is a high-K calc-alkaline, peralmuminous, S-type, biotite + muscovite granite and the Sudbury granite is high-K calc-alkaline, metaluminous to slightly peraluminous, I-type, biotite granite. These two granites are interpreted to have formed from the anatexis of either Nashoba terrane metasedimentary rocks and/or its underlying basement just prior to the Acadian orogeny. It is proposed that when Silurian diorite/tonalite magmas intruded into the Nashoba terrane, the influx of magmatic heat was sufficient to trigger crustal melting and promote granite genesis. This petrogenetic scenario fits well with regional tectonic models showing the Silurio-Devonian convergence of Avalonia towards Ganderia (which formed the eastern side of composite Laurentia at the time) in the northern Appalachians. Prior to the collision of Avalonia to composite Laurentia, mafic and intermediate composition arc magmas intruded the eastern Ganderian margin. The large amount of heat that accompanied these intrusions is believed to have contributed to Acadian metamorphism and influenced the formation of granitic plutons along the margin. It is therefore proposed that the plutonic record of the Nashoba terrane shows that by the Late Silurian - Early Devonian, Avalonia was still outboard of Laurentia in the vicinity of southern New England. / Thesis (MS) — Boston College, 2014. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Earth and Environmental Sciences.

O Grupo São Roque caracteriza-se por rochas de baixo grau metamórfico, depositadas em ambiente marinho com atividade vulcânica submarina. As ocorrências da Formação Morro Doce são dominadas por metarcóseos e metarenitos feldspáticos com expressivas lentes metaconglomeráticas, que formam uma seqüência considerada como unidade basal do Grupo São Roque. Os metaconglomerados, com o amplo predomínio de clastos graníticos, têm excelente potencial para identificação de suas fontes e idades. Rochas metavulcânicas ácidas e básicas intercaladas nesta seqüência constituem importante marcador tectônico e cronológico. O estudo petrográfico dos clastos graníticos dos metaconglomerados da Formação Morro Doce permitiu a identificação de quatro variedades petrográficas: biotita monzogranito porfirítico, biotita monzogranito inequigranular, biotita monzogranito equigranular e leucogranito inequigranular. O caráter comagmático entre os clastos é confirmado pelos dados petrográficos e geoquímicos. Rochas metavulcânicas ácidas que ocorrem intercaladas a metarcóseos e metaconglomerados, na região do Morro do Polvilho, correspondem a meta-traquidacitos e metariolitos porfiríticos. Os metarcóseos mostram afinidades geoquímicas com os clastos de granito dos metaconglomerados, e diferenciam-se das rochas metavulcânicas ácidas associadas pela geoquímica e pela petrotrama sedimentar composta predominantemente por feldspatos detríticos sub-angulosos. De características geoquímicas típicas de magmatismo intraplaca, em especial baixo mg# (~20), altos teores de Zr (560-730 ppm), Y e Nb, além de baixo Sr (70-120 ppm), as rochas metavulcânicas ácidas do Grupo São Roque apresentam similaridades com as metavulcânicas ácidas da base do Supergrupo Espinhaço. Datações U-Pb por LA-MC-ICP-MS em cristais de zircão extraídos das variedades predominantes de seixos graníticos revelaram idades Paleoproterozóicas (2199 ± 8.5 Ma e 2247 ± 13 Ma). Idades comparáveis só são encontradas regionalmente em núcleos do embasamento do Supergrupo Espinhaço (Complexo Mantiqueira) e Açungui (núcleos Tigre, Setuva e Betari). A idade de deposição dos metaconglomerados (1.75-1.79 Ga), indicada pelas datações U-Pb em rochas metavulcânicas intercaladas é consistente com a idade dos clastos (granito fonte), datados em 2.2 Ga, e com a ausência de indicações de contribuições de áreas-fontes mais jovens para os metassedimentos da Fm. Morro Doce. / The São Roque Group is composed of low-grade metamorphic rocks deposited in marine environment with coeval volcanic activity. The Morro Doce Formation is dominated by metaarkose and feldspatic meta-sandstone with expressive metaconglomeratic lenses, which form a sequence regarded as the basal unit of São Roque Group. The metaconglomerates with wide prevalence of granite pebbles have excellent potential to identify their sources and ages. Metavolcanic acidic and basic rocks interspersed in this sequence are an important tectonic and geochronologic marker. The petrographic study of the granite pebbles from the Morro Doce Formation metaconglomerates allowed the identification of four petrographic varieties: porphyritic biotite monzogranite, inequigranular biotite monzogranite, equigranular biotite monzogranite and inequigranular leucogranite. The comagmatic character of these pebbles is confirmed by petrographic and geochemical data. Acid metavolcanic rocks interlayered with meta-arkose and metaconglomerates in the Morro do Polvilho region correspond to trachydacite and porphyritic meta-rhyolite. The metaarkose shows geochemical affinities with metaconglomerate granitic pebbles, and differs from the acid metavolcanic rocks both in their geochemical signature and in its sedimentary fabrics defined by the predominance of detritic subangulous feldspars. Their geochemical characteristics are typical of within-plate magmatism, especially the low mg # (~ 20), high Zr (560-730 ppm), Y, Nb, and low Sr (70-120 ppm), and is similar to the acid metavolcanics from the on Espinhaço Supergroup. U-Pb dating by LA-MC-ICP-MS in zircon crystals from the predominant varieties of granitic pebbles revealed Paleoproterozoic ages (2199 ± 8.5 Ma Ma and 2247 ± 13) for the main granitic source of the metaconglomerates. Comparable ages are found in the nuclei of Espinhaço Supergrup basament (Mantiqueira Complex) and Açungui (Tigre, Setuva and Betari nuclei). The depositional age of the metaconglomerates (1.75-1.79 Ga), indicated by U-Pb dating of interlayered metavolcanic rocks, is consistent with the age of the granitic source, (~2.2 Ga), and with the lack of signals of contribution from younger source areas for the Morro Doce Fm metasediments.

O Grupo São Roque caracteriza-se por rochas de baixo grau metamórfico, depositadas em ambiente marinho com atividade vulcânica submarina. As ocorrências da Formação Morro Doce são dominadas por metarcóseos e metarenitos feldspáticos com expressivas lentes metaconglomeráticas, que formam uma seqüência considerada como unidade basal do Grupo São Roque. Os metaconglomerados, com o amplo predomínio de clastos graníticos, têm excelente potencial para identificação de suas fontes e idades. Rochas metavulcânicas ácidas e básicas intercaladas nesta seqüência constituem importante marcador tectônico e cronológico. O estudo petrográfico dos clastos graníticos dos metaconglomerados da Formação Morro Doce permitiu a identificação de quatro variedades petrográficas: biotita monzogranito porfirítico, biotita monzogranito inequigranular, biotita monzogranito equigranular e leucogranito inequigranular. O caráter comagmático entre os clastos é confirmado pelos dados petrográficos e geoquímicos. Rochas metavulcânicas ácidas que ocorrem intercaladas a metarcóseos e metaconglomerados, na região do Morro do Polvilho, correspondem a meta-traquidacitos e metariolitos porfiríticos. Os metarcóseos mostram afinidades geoquímicas com os clastos de granito dos metaconglomerados, e diferenciam-se das rochas metavulcânicas ácidas associadas pela geoquímica e pela petrotrama sedimentar composta predominantemente por feldspatos detríticos sub-angulosos. De características geoquímicas típicas de magmatismo intraplaca, em especial baixo mg# (~20), altos teores de Zr (560-730 ppm), Y e Nb, além de baixo Sr (70-120 ppm), as rochas metavulcânicas ácidas do Grupo São Roque apresentam similaridades com as metavulcânicas ácidas da base do Supergrupo Espinhaço. Datações U-Pb por LA-MC-ICP-MS em cristais de zircão extraídos das variedades predominantes de seixos graníticos revelaram idades Paleoproterozóicas (2199 ± 8.5 Ma e 2247 ± 13 Ma). Idades comparáveis só são encontradas regionalmente em núcleos do embasamento do Supergrupo Espinhaço (Complexo Mantiqueira) e Açungui (núcleos Tigre, Setuva e Betari). A idade de deposição dos metaconglomerados (1.75-1.79 Ga), indicada pelas datações U-Pb em rochas metavulcânicas intercaladas é consistente com a idade dos clastos (granito fonte), datados em 2.2 Ga, e com a ausência de indicações de contribuições de áreas-fontes mais jovens para os metassedimentos da Fm. Morro Doce. / The São Roque Group is composed of low-grade metamorphic rocks deposited in marine environment with coeval volcanic activity. The Morro Doce Formation is dominated by metaarkose and feldspatic meta-sandstone with expressive metaconglomeratic lenses, which form a sequence regarded as the basal unit of São Roque Group. The metaconglomerates with wide prevalence of granite pebbles have excellent potential to identify their sources and ages. Metavolcanic acidic and basic rocks interspersed in this sequence are an important tectonic and geochronologic marker. The petrographic study of the granite pebbles from the Morro Doce Formation metaconglomerates allowed the identification of four petrographic varieties: porphyritic biotite monzogranite, inequigranular biotite monzogranite, equigranular biotite monzogranite and inequigranular leucogranite. The comagmatic character of these pebbles is confirmed by petrographic and geochemical data. Acid metavolcanic rocks interlayered with meta-arkose and metaconglomerates in the Morro do Polvilho region correspond to trachydacite and porphyritic meta-rhyolite. The metaarkose shows geochemical affinities with metaconglomerate granitic pebbles, and differs from the acid metavolcanic rocks both in their geochemical signature and in its sedimentary fabrics defined by the predominance of detritic subangulous feldspars. Their geochemical characteristics are typical of within-plate magmatism, especially the low mg # (~ 20), high Zr (560-730 ppm), Y, Nb, and low Sr (70-120 ppm), and is similar to the acid metavolcanics from the on Espinhaço Supergroup. U-Pb dating by LA-MC-ICP-MS in zircon crystals from the predominant varieties of granitic pebbles revealed Paleoproterozoic ages (2199 ± 8.5 Ma Ma and 2247 ± 13) for the main granitic source of the metaconglomerates. Comparable ages are found in the nuclei of Espinhaço Supergrup basament (Mantiqueira Complex) and Açungui (Tigre, Setuva and Betari nuclei). The depositional age of the metaconglomerates (1.75-1.79 Ga), indicated by U-Pb dating of interlayered metavolcanic rocks, is consistent with the age of the granitic source, (~2.2 Ga), and with the lack of signals of contribution from younger source areas for the Morro Doce Fm metasediments.