Thermodynamic analysis of garnet growth zoning in eclogite facies granodiorite from M. Mucrone, Sesia Zone, Western Italian Alps

1999 ◽  
Vol 137 (4) ◽  
pp. 289-303 ◽  
Author(s):  
Rubbo Marco ◽  
Borghi Alessandro ◽  
Compagnoni Roberto
Keyword(s):  
Thermodynamic Analysis ◽  
Garnet Growth ◽  
Italian Alps ◽  
Eclogite Facies ◽  
Garnet Growth Zoning ◽  
Growth Zoning

Well‐preserved garnet growth zoning in granulite from the Dabie Mountains, central China

1998 ◽  
Vol 16 (2) ◽  
pp. 213-222 ◽  
Author(s):  
NENG‐SONG CHEN ◽  
MIN SUN ◽  
ZHEN‐DONG YOU ◽  
J. MALPAS
Keyword(s):  
Central China ◽  
Garnet Growth ◽  
Dabie Mountains ◽  
Garnet Growth Zoning ◽  
Growth Zoning

scholarly journals Prograde and retrograde P–T evolution of a Variscan high-temperature eclogite, French Massif Central, Haut-Allier

2020 ◽  
Vol 191 ◽  
pp. 14
Author(s):  
Luc de Hoÿm de Marien ◽  
Pavel Pitra ◽  
Florence Cagnard ◽  
Benjamin Le Bayon
Keyword(s):  
High Pressure ◽  
High Temperature ◽  
Garnet Growth ◽  
French Massif Central ◽  
Temperature Peak ◽  
Massif Central ◽  
Slab Rollback ◽  
High Pressure Granulite ◽  
Garnet Growth Zoning ◽  
Growth Zoning

The P–T evolution of a mafic eclogite sample from the Haut-Allier was studied in order to constrain the dynamic of the Variscan subduction in the eastern French Massif Central. Three successive metamorphic stages M1, M2 and M3, are characterized by assemblages comprising garnet1-omphacite-kyanite, garnet2-plagioclase, and amphibole-plagioclase, respectively, and define a clockwise P–T path. These events occurred at the conditions of eclogite (M1; ∼ 20 kbar, 650 °C to ∼ 22.5 kbar, 850 °C), high-pressure granulite (M2; 19.5 kbar and 875 °C) and high-temperature amphibolite facies (M3; < 9 kbar, 750–850 °C), respectively. Pseudosection modelling of garnet growth zoning and mineralogy of the inclusions reveal a prograde M1 stage, first dominated by burial and then by near isobaric heating. Subsequent garnet1 resorption, prior to a renewed growth of garnet2 is interpreted in terms of a decompression during M2. High-pressure partial melting is predicted for both the M1 temperature peak and M2. M3 testifies to further strong decompression associated with limited cooling. The preservation of garnet growth zoning indicates the short-lived character of the temperature increase, decompression and cooling cycle. We argue that such P–T evolution is compatible with the juxtaposition of the asthenosphere against the subducted crust prior to exhumation driven by slab rollback.

scholarly journals Preservation of Garnet Growth Zoning and the Duration of Prograde Metamorphism

2010 ◽  
Vol 51 (11) ◽  
pp. 2327-2347 ◽  
Author(s):  
Mark J. Caddick ◽  
Jiří Konopásek ◽  
Alan B. Thompson
Keyword(s):  
Garnet Growth ◽  
Prograde Metamorphism ◽  
Garnet Growth Zoning ◽  
Growth Zoning

scholarly journals Deeply subducted continental fragments – Part 1: Fracturing, dissolution–precipitation, and diffusion processes recorded by garnet textures of the central Sesia Zone (western Italian Alps)

Solid Earth ◽  
2018 ◽  
Vol 9 (1) ◽  
pp. 167-189 ◽  
Author(s):  
Francesco Giuntoli ◽  
Pierre Lanari ◽  
Martin Engi
Keyword(s):  
High Pressure ◽  
Diffusion Processes ◽  
Shear Zones ◽  
Granulite Facies ◽  
Thermodynamic Modelling ◽  
Italian Alps ◽  
Eclogite Facies ◽  
Compositional Patterns ◽  
And Diffusion ◽  
Insight Into

Abstract. Contiguous continental high-pressure terranes in orogens offer insight into deep recycling and transformation processes that occur in subduction zones. These remain poorly understood, and currently debated ideas need testing. The approach we chose is to investigate, in detail, the record in suitable rock samples that preserve textures and robust mineral assemblages that withstood overprinting during exhumation. We document complex garnet zoning in eclogitic mica schists from the Sesia Zone (western Italian Alps). These retain evidence of two orogenic cycles and provide detailed insight into resorption, growth, and diffusion processes induced by fluid pulses in high-pressure conditions. We analysed local textures and garnet compositional patterns, which turned out remarkably complex. By combining these with thermodynamic modelling, we could unravel and quantify repeated fluid–rock interaction processes. Garnet shows low-Ca porphyroclastic cores that were stable under (Permian) granulite facies conditions. The series of rims that surround these cores provide insight into the subsequent evolution: the first garnet rim that surrounds the pre-Alpine granulite facies core in one sample indicates that pre-Alpine amphibolite facies metamorphism followed the granulite facies event. In all samples documented, cores show lobate edges and preserve inner fractures, which are sealed by high-Ca garnet that reflects high-pressure Alpine conditions. These observations suggest that during early stages of subduction, before hydration of the granulites, brittle failure of garnet occurred, indicating high strain rates that may be due to seismic failure. Several Alpine rims show conspicuous textures indicative of interaction with hydrous fluid: (a) resorption-dominated textures produced lobate edges, at the expense of the outer part of the granulite core; (b) peninsulas and atoll garnet are the result of replacement reactions; and (c) spatially limited resorption and enhanced transport of elements due to the fluid phase are evident along brittle fractures and in their immediate proximity. Thermodynamic modelling shows that all of these Alpine rims formed under eclogite facies conditions. Structurally controlled samples allow these fluid–garnet interaction phenomena to be traced across a portion of the Sesia Zone, with a general decrease in fluid–garnet interaction observed towards the external, structurally lower parts of the terrane. Replacement of the Permian HT assemblages by hydrate-rich Alpine assemblages can reach nearly 100 % of the rock volume. Since we found no clear relationship between discrete deformation structures (e.g. shear zones) observed in the field and the fluid pulses that triggered the transformation to eclogite facies assemblages, we conclude that disperse fluid flow was responsible for the hydration.

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