Structure, Petrography and Emplacement of Plutonic Rocks

Troll, Georg; Weiss, S.

doi:10.1007/978-3-642-76145-4_3

Cited by 10 publications

(6 citation statements)

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“…This is consistent with geological evidence of gradational contacts between appinitic and dioritic magmas, and dioritic and granitic magmas, suggesting that each successive magmatic phase was intruded while the previous phase was still at least partly molten (Troll & Weiss 1991). A short-lived duration of magmatism, as suggested by indistinguishable ages from different phases of the complex, is also consistent with results of thermal modelling, which match the temperature conditions reconstructed from the thermal aureole by assuming essentially instantaneous emplacement of the Ballachulish Igneous Complex at temperatures of c. 1100 8C (Buntebarth 1991).…”

Section: Discussion Of Ages From the Ballachulish Igneous Complexsupporting

confidence: 86%

“…1), where appinitic rocks crop out over an area of several hundred square metres. This appinitic body has been mapped as a mafic stock but has complex, gradational relationships with the adjacent diorites of the Ballachulish Igneous Complex, which suggest that it closely predates the diorites (Troll & Weiss 1991). The sample contains an igneous assemblage of plagioclase, clinopyroxene, biotite and minor K-feldspar.…”

Section: -B-20 Appinitementioning

confidence: 98%

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Age of the Ballachulish and Glencoe Igneous Complexes (Scottish Highlands), and paragenesis of zircon, monazite and baddeleyite in the Ballachulish Aureole

Fraser

Pattison

Heaman

2004

JGS

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U-Pb zircon ages are presented for the Ballachulish Igneous Complex ( 207 Pb-206 Pb age 427 AE 1 Ma; 206 Pb-238 U age 423 AE 0.3 Ma) and Glencoe Volcanic Complex ( 207 Pb-206 Pb age 406 AE 6 Ma) of the Scottish Highlands. These ages are significantly more precise than pre-existing age constraints, and discriminate a previously unresolved age difference of c. 20 Ma between the two complexes. This difference in age provides an explanation for the c. 10 km difference in crustal level between the two magmatic events, and constrains exhumation rates for the Argyll region to be on average c. 0.4 km Ma À1 over the period c. 425-405 Ma. With improved age constraints on the Ballachulish Igneous Complex in place, the associated metamorphic aureole is used as a type locality to investigate the metamorphic behaviour of the U-bearing accessory minerals baddeleyite, zircon and monazite. Baddeleyite formed in impure dolomites by the reaction of detrital zircon with dolomite and gives the same U-Pb age as the intrusive complex, consistent with its contact metamorphic origin. Detrital zircon appears to be inert throughout much of the metamorphic aureole, with contact metamorphic zircon growth being restricted to migmatite-grade rocks. A possible exception is the development of enigmatic, very narrow overgrowths at temperatures between c. 500 and 600 8C. Monazite exhibits a variety of textures in lower-grade parts of the aureole (,550 8C), but occurs as distinctive clusters and trails of tiny ovoid grains at temperatures above about 560-600 8C. Monazite thus appears sensitive to metamorphism at lower temperatures than zircon and may therefore be a better target for metamorphic age measurements in rocks that reach mid-amphibolite facies but do not experience partial melting.

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Section: Discussion Of Ages From the Ballachulish Igneous Complexsupporting

confidence: 86%

Section: -B-20 Appinitementioning

confidence: 98%

Age of the Ballachulish and Glencoe Igneous Complexes (Scottish Highlands), and paragenesis of zircon, monazite and baddeleyite in the Ballachulish Aureole

Fraser

Pattison

Heaman

2004

JGS

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“…Eggins & Hensen 1987), rather than migmatitically layered rocks, 2) the high-temperature assemblage orthopyroxene -clinopyroxenebiotite (cf. Naney 1983, Weiss & Troll 1989, Troll & Weiss 1991, Kilpatrick & Ellis 1992 followed in the order of crystallization by hornblende of igneous appearance, 3) geochemical trends indicating increasing fractionation with more hydrous compositions (cf. Petersen 1980), and 4) simple morphology and U-Pb systematics of zircon (Percival et al 1992).…”

Section: Low-p High-t Metamorphism and Magmatismmentioning

confidence: 99%

Tectonothermal Evolution of the Northern Minto Block, Superior Province, Quebec, Canada

Percival

Skulski

2000

The Canadian Mineralogist

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Previously considered one of Earth's largest granulite terranes, the Minto block, in northern Quebec, consists dominantly of granitic rocks with sparse supracrustal remnants that record low-pressure, high-temperature metamorphism to the amphibolite and granulite facies at ca. 2.7 Ga. Much of the region is underlain by plutonic rocks, including igneous charnockitic bodies, that provide little evidence of metamorphism. In contrast, pelitic assemblages in low-grade greenstone belts and their higher-grade shoulders define four metamorphic zones: 1) sub-staurolite-grade slates, found only in the Duquet belt, 2) staurolite -andalusite -sillimanite -garnet-zone schists, present in all belts, 3) marginal garnet -sillimanite ± kyanite migmatites, and 4) garnetsillimanite ± cordierite and garnet -orthopyroxene granulites, as enclaves within plutonic units. A prograde low-pressure, hightemperature regional facies-series is defined by andalusite -sillimanite assemblages, thermobarometric analyses that indicate peak conditions ranging from 3 kbar, 560°C to 8.4 kbar, 840°C, and short segments of anticlockwise P-T trajectories preserved in two of the lowest-grade areas. Kyanite occurs in migmatites in the vicinity of a ca. 2.81 Ga shear zone bounding two distinct supracrustal assemblages and marks an earlier Barrovian event. All belts are polydeformed, with a common, broadly synmetamorphic, NNW-striking, steep foliation and down-dip lineation related to regional-scale F 2 folds. Distributed late-metamorphic dip-slip shear appears responsible in some areas for cross-strike juxtaposition of low-and high-grade metamorphic zones. Older, generally poorly preserved D 1 deformation, recognized in several belts, may represent accretionary structures. Variably developed younger deformation includes NNW dextral transcurrent brittle-ductile shear zones (S 3 ), variably developed east-trending F 4 folds, and WNW-striking pseudotachylite zones. U-Pb monazite ages of 2702 Ma date high-grade metamorphism of a pelitic granulite, crystallization of two diatexites, and staurolite-zone metamorphism in one schist. Together with similar zircon ages of crust-derived granites, these data point to a major collisional orogeny at this time. Older titanite (2748-2765 Ma) indicates areas that escaped >650°C metamorphism during the 2.7 Ga event. Younger monazite occurs in a migmatite-grade rock (2688, 2672 Ma) and staurolite-zone schists (2679( -2642( , 2648( , 2637( , and 2642( -2628, similar to titanite ages in greenstones (2643-2550 Ma) and 40 Ar/ 39 Ar hornblende ages (2.64-2.56 Ga). These post-peak metamorphic ages in the greenstone belts based on monazite and titanite are attributed to hydrothermal growth from fluids channeled along permeable zones; they may reflect late reheating events observed throughout the Superior Province as leucogranitic magmatism, metamorphism in the deep crust, and mineral growth in shear zones. SOMMAIRELe socle de Minto, dans le nord du Québec, considéré antérieurement comme un des plus vastes terrains de roches transformé...

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“…Field observations suggest that, at the time of the granitic intrusion, the diorite consisted of a partially consolidated centre (Troll and Weiss 1991). Calculation 1 and 4 do not satisfy this prerequisite.…”

Section: T-t Modelling and Ti Contentmentioning

confidence: 88%

“…Field evidence suggests that the complex was produced by two distinct magmatic events which affected the regionally deformed and metamorphosed Dalradian metasediments at c. 425 ± 4 Ma (Fraser et al 2004). Troll and Weiss (1991) concluded that during crystallization of the first dioritic magma (emplacement temperature c. 1,100°C) a monzodioritic envelope developed, enclosing a quartz diorite centre. The second granitic magma (emplacement temperature c. 850°C) mixed with the partially consolidated quartz diorite which was then at 950-850°C and deformed the monzodiorite envelope.…”

Section: Geological Settingmentioning

confidence: 98%

The recognition of multiple magmatic events and pre-existing deformation zones in metamorphic rocks as illustrated by CL signatures and numerical modelling: examples from the Ballachulish contact aureole, Scotland

Bergman

Piazolo

2011

Int J Earth Sci (Geol Rundsch)

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The combination of cathodoluminescence (CL) analysis, temperature and temperature-time calculations, and microstructural numerical modelling offers the possibility to derive the time-resolved evolution of a metamorphic rock. This combination of techniques is applied to a natural laboratory, namely the Ballachulish contact aureole, Scotland. Analysis of the Appin Quartzite reveals that the aureole was produced by two distinct magmatic events and infiltrated by associated fluids. Developing microstructures allow us to divide the aureole into three distinct regions. Region A (0-400 m, 663°C \ T max \ 714°C) exhibits a three-stage grain boundary migration (GBM) evolution associated with heating, fluid I and fluid II. GBM in region B (400-700 m, 630°C \ T max \ 663°C) is associated with fluid II only. Region C ([700 m of contact, T max \ 630°C) is characterised by healed intragranular cracks. The combination of CL signature analysis and numerical modelling enables us to recognise whether grain size increase occurred mainly by surface energy-driven grain growth (GG) or strain-induced grain boundary migration (SIGBM). GG and SIGBM result in either straight bands strongly associated with present-day boundaries or highly curved irregular bands that often fill entire grains, respectively. At a temperature of *620°C, evidence for GBM is observed in the initially dry, largely undeformed quartzite samples. At this temperature, evidence for GG is sparse, whereas at *663°C, CL signatures typical for GG are commonplace. The grain boundary network approached energy equilibrium in samples that were at least 5 ka above 620°C.

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Structure, Petrography and Emplacement of Plutonic Rocks

Cited by 10 publications

References 0 publications

Age of the Ballachulish and Glencoe Igneous Complexes (Scottish Highlands), and paragenesis of zircon, monazite and baddeleyite in the Ballachulish Aureole

Age of the Ballachulish and Glencoe Igneous Complexes (Scottish Highlands), and paragenesis of zircon, monazite and baddeleyite in the Ballachulish Aureole

Tectonothermal Evolution of the Northern Minto Block, Superior Province, Quebec, Canada

The recognition of multiple magmatic events and pre-existing deformation zones in metamorphic rocks as illustrated by CL signatures and numerical modelling: examples from the Ballachulish contact aureole, Scotland

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