Metamorphism and Anatexis in the Mafic Complex Contact Aureole, Ivrea Zone, Northern Italy

Barboza, Scott A.; Bergantz, George W.

doi:10.1093/petrology/41.8.1307

Cited by 94 publications

(86 citation statements)

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“…Ivrea zone: Barboza and Bergantz 2000;Malenco unit: Müntener et al 2000;Sesia zone: Lardeaux and Spalla 1991;Rebay and Spalla 2001;Sondalo complex: Braga et al 2001;Braga et al 2003), the UHT conditions in the Gruf complex were achieved during Permo-Triassic rifting (see data and discussion in Galli et al 2012). Intense partial melting of pelitic rocks at deep crustal levels during a rifting-related thermal climax produced orthopyroxene-bearing charnockitic melts and strongly refractory, orthopyroxenesapphirine-bearing granulitic residuals.…”

Section: Discussionmentioning

confidence: 99%

Tectonometamorphic history of the Gruf complex (Central Alps): exhumation of a granulite–migmatite complex with the Bergell pluton

et al. 2013

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We describe field occurrences of sapphirinebearing granulites, charnockites and migmatites in the Gruf complex, Central Alps and present a new geological map and a structural analysis of the entire Gruf complex for the first time. We have carried out an accurate analysis of the relationships between granulite facies metamorphism, migmatisation and deformation within the complex, in relation to the intrusion of the Bergell pluton. Granulites and charnockites display fabrics different from those defined by the regional foliation and lineation, which are, typically for migmatites, disordered on the mesoscale. On a regional scale, strike variations are also related to the structural complexity of migmatites within which no major antiform could be identified. Irregular interfingering of subparallel leucosome veins and back-veining along the contact between the Gruf migmatites and the Bergell tonalite are evidence for contemporaneous emplacement and crystallisation at about 740°C and 6.5-7.5 kbar in Oligocene times (ca 30 Ma). Metamorphic conditions in the charnockites and granulites ([920°C for 8.5-9.5 kbar) largely exceed these regional metamorphic conditions and are dated at 282-260 Ma. We propose that the ascending Bergell pluton entrained the polymetamorphic, granulitic lower crust enclosed within the peripheral migmatitic Gruf complex.

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Section: Discussionmentioning

confidence: 99%

Tectonometamorphic history of the Gruf complex (Central Alps): exhumation of a granulite–migmatite complex with the Bergell pluton

et al. 2013

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“…Temperatures of 900-950 °C for peak conditions in the granulite facies have been derived from Zr-in-rutile thermometry (Luvizotto and Zack 2009;Ewing et al 2013). Several studies have presented field and petrological evidence that the Mafic Complex was not the heat source for regional granulite facies metamorphism (Barboza et al 1999;Barboza and Bergantz 2000;Redler et al 2012). A local contact aureole of 1-3 km around the mafic intrusion is observed in Val Sesia (Fig.…”

Section: Geological Settingmentioning

confidence: 99%

“…Petrological studies found convincing evidence that the HT metamorphic field gradient was established prior to the intrusion of the Mafic Complex (e.g. Zingg et al 1990;Barboza et al 1999;Barboza and Bergantz 2000;Redler et al 2012). The present study, together with literature data, indicates a duration of ~ 60 Myr for the HT conditions in the Kinzigite Formation (Vavra et al 1999;Ewing et al 2013).…”

Section: Implications For the Interpretation Of The Metamorphic Evolumentioning

confidence: 99%

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Zircon ages in granulite facies rocks: decoupling from geochemistry above 850 °C?

Kunz

Regis

Engi

2018

Contrib Mineral Petrol

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Granulite facies rocks frequently show a large spread in their zircon ages, the interpretation of which raises questions: Has the isotopic system been disturbed? By what process(es) and conditions did the alteration occur? Can the dates be regarded as real ages, reflecting several growth episodes? Furthermore, under some circumstances of (ultra-)high-temperature metamorphism, decoupling of zircon U-Pb dates from their trace element geochemistry has been reported. Understanding these processes is crucial to help interpret such dates in the context of the P-T history. Our study presents evidence for decoupling in zircon from the highest grade metapelites (> 850 °C) taken along a continuous high-temperature metamorphic field gradient in the Ivrea Zone (NW Italy). These rocks represent a well-characterised segment of Permian lower continental crust with a protracted high-temperature history. Cathodoluminescence images reveal that zircons in the mid-amphibolite facies preserve mainly detrital cores with narrow overgrowths. In the upper amphibolite and granulite facies, preserved detrital cores decrease and metamorphic zircon increases in quantity. Across all samples we document a sequence of four rim generations based on textures. U-Pb dates, Th/U ratios and Ti-in-zircon concentrations show an essentially continuous evolution with increasing metamorphic grade, except in the samples from the granulite facies, which display significant scatter in age and chemistry. We associate the observed decoupling of zircon systematics in high-grade non-metamict zircon with disturbance processes related to differences in behaviour of non-formula elements (i.e. Pb, Th, U, Ti) at high-temperature conditions, notably differences in compatibility within the crystal structure.

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“…Typically, the latter scenario arises in contact aureoles characterized by rapid heating and cooling (Johnson et al, 2004 - Fig. 8g; Mcfarlane et al, 2003;Ings and Owen, 2002;Barboza and Bergantz, 2000;Wheeler et al, 2004;Daczko et al, 2002;Dasgupta et al, 1997;Joesten and Fisher, 1988), but it can also occur in shock-heated rocks within large impact structures (Gibson, 2002;Ogilvie, 2010).…”

Section: Reaction Kinetics -Diffusionmentioning

confidence: 99%

Arrested development – a comparative analysis of multilayer corona textures in high-grade metamorphic rocks

Ogilvie

Gibson

2017

Solid Earth

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Abstract. Coronas, including symplectites, provide vital clues to the presence of arrested reaction and preservation of partial equilibrium in metamorphic and igneous rocks. Compositional zonation across such coronas is common, indicating the persistence of chemical potential gradients and incomplete equilibration. Major controls on corona mineralogy include prevailing pressure (P ), temperature (T ) and water activity (aH 2 O) during formation, reaction duration (t) single-stage or sequential corona layer growth; reactant bulk compositions (X) and the extent of metasomatic exchange with the surrounding rock; relative diffusion rates for major components; and/or contemporaneous deformation and strain. High-variance local equilibria in a corona and disequilibrium across the corona as a whole preclude the application of conventional thermobarometry when determining P -T conditions of corona formation, and zonation in phase composition across a corona should not be interpreted as a record of discrete P -T conditions during successive layer growth along the P -T path. Rather, the local equilibria between mineral pairs in corona layers more likely reflect compositional partitioning of the corona domain during steadystate growth at constant P and T .Corona formation in pelitic and mafic rocks requires relatively dry, residual bulk rock compositions. Since most melt is lost along the high-T prograde to peak segment of the P -T path, only a small fraction of melt is generally retained in the residual post-peak assemblage. Reduced melt volumes with cooling limit length scales of diffusion to the extent that diffusion-controlled corona growth occurs. On the prograde path, the low melt (or melt-absent) volumes required for diffusion-controlled corona growth are only commonly realized in mafic igneous rocks, owing to their intrinsic anhydrous bulk composition, and in dry, residual pelitic compositions that have lost melt in an earlier metamorphic event.Experimental work characterizing rate-limiting reaction mechanisms and their petrogenetic signatures in increasingly complex, higher-variance systems has facilitated the refinement of chemical fractionation and partial equilibration diffusion models necessary to more fully understand corona development. Through the application of quantitative physical diffusion models of coronas coupled with phase equilibria modelling utilizing calculated chemical potential gradients, it is possible to model the evolution of a corona through P -T -X-t space by continuous, steady-state and/or sequential, episodic reaction mechanisms. Most coronas in granulites form through a combination of these endmember reaction mechanisms, each characterized by distinct textural and chemical potential signatures with very different petrogenetic implications. An understanding of the inherent petrogenetic limitations of a reaction mechanism model is critical if an appropriate interpretation of P -T evolution is to be inferred from a corona. Since corona modelling employing calculated chemical potential gradie...

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Metamorphism and Anatexis in the Mafic Complex Contact Aureole, Ivrea Zone, Northern Italy

Cited by 94 publications

References 65 publications

Tectonometamorphic history of the Gruf complex (Central Alps): exhumation of a granulite–migmatite complex with the Bergell pluton

Tectonometamorphic history of the Gruf complex (Central Alps): exhumation of a granulite–migmatite complex with the Bergell pluton

Zircon ages in granulite facies rocks: decoupling from geochemistry above 850 °C?

Arrested development – a comparative analysis of multilayer corona textures in high-grade metamorphic rocks

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