Thermal Models of Cooling

Buntebarth, Günter

doi:10.1007/978-3-642-76145-4_18

Cited by 25 publications

(18 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: 78%

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: 78%

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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“…Because of the relatively rapid cooling rate in the aureole (c. lo' years for rocks at the contact to cool below 50O0C, Buntebarth, 1991), the amount of decoupling of Fe-Mg from A1 is expected to be less than in the slowly cooled regional granulites investigated in this study. Preliminary temperature estimates of 764" C from the Harley (1984a) Fe-Mg exchange calibration and 770" C from the Harley & Green (1982) Al-solubility calibrations (Pattison, 1989, table 6) are not significantly different, suggesting minor decoupling of Fe-Mg from A1 in orthopyroxene.…”

Section: A N D Ai-solubility Temperatures Asmentioning

confidence: 97%

Zoning patterns in orthopyroxene and garnet in granulites: implications for geothermometry

Pattison

Bégin

1994

Journal Metamorphic Geology

154

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Compositional maps of orthopyroxene and garnet of contrasting grain size and in contact with different minerals were made from two paragneiss granulites from the Minto terrane of northern Quebec. The compositional maps provide clear evidence of late exchange of Fe/(Fe + Mg) after Ca in garnet and A1 in orthopyroxene had been quenched-in. The extent of late Fe-Mg exchange was controlled by neighbouring minerals, with negligible Fe-Mg gradients against plagioclase and quartz, and substantial gradients against exchangeable Fe-Mg minerals. Cores of grains in contact with exchangeable Fe-Mg neighbours are progressively more reset in Fe/(Fe + Mg) as grain size decreases, whereas cores of even small grains surrounded by only plagioclase and quartz are not significantly different in Fe/(Fe + Mg) than cores of the largest grains. Gradients of Ca in garnet and of Al in orthopyroxene in grains of uniform Fe/(Fe + Mg) preserve a high-temperature retrograde history during which intergranular exchange effected compositional uniformity of mineral rims and intragranular Fe-Mg diffusion in garnet and orthopyroxene was rapid enough to homogenize Fe/(Fe + Mg). The transition from efficient intergranular exchange at relatively high temperatures to local Fe-Mg exchange at lower temperatures may have been controlled by loss of an intergranular exchange medium in the rock, possibly an internally generated dehydration melt phase. Implications for geothermometry of granulites include the following (numerical values are particular to this study): (1) core compositions of garnet and orthopyroxene grains in contact with exchangeable neighbours may be reset in Fe/(Fe + Mg) relative to the most refractory compositions by an amount equivalent to 120°C; (2) Fe-Mg exchange thermometry using even the most refractory Fe/(Fe + Mg) compositions may not record peak granulite conditions, possibly recording instead the temperature at which an intergranular exchange medium was lost from the rock; and (3) temperaturesensitive net transfer equilibria involving Al solubility in orthopyroxene yield temperatures up to 150" C higher than maximum Fe-Mg exchange temperatures, even in grains with flat Fe/(Fe + Mg) compositional profiles, making them a better means of estimating peak granulite temperatures than Fe-Mg exchange thermometry.

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“…Table 2 Starting values for modelling of T-t paths resulting in similar graphs as has been suggested previously (Buntebarth 1991) x (column) z (row) For model GG , the starting material is even grained, strain-free microstructure with no shape-preferred orientation (Fig. 3b).…”

Section: Microdynamic Modelling Of Grain Boundary Migrationmentioning

confidence: 82%

“…Holness and Clemens (1999) suggested that partial melting occurred in the Appin Quartzite up to 500 m from the eastern contact. Buntebarth (1991) conducted theoretical thermal calculations based on detailed mineralogical studies by Pattison andHarte (1985, 1991), indicating that rocks in the entire contact aureole experienced temperatures above c. 550°C for about 500 ka, while those close to the intrusion were above c. 660°C for about 270 ka with a maximum temperature of 750-800°C at the contact. Stable isotopes suggest that, during magma emplacement, no open crack systems allowing circulation of meteoric water were maintained (Harte et al 1999;Holness and Watt 2001).…”

Section: Geological Settingmentioning

confidence: 99%

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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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Thermal Models of Cooling

Cited by 25 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

Zoning patterns in orthopyroxene and garnet in granulites: implications for geothermometry

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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