Oscillatory zoning in metamorphic minerals: an indicator of infiltration metasomatism

AbstractExamples of oscillatory zoning in metamorphic minerals, imaged using a Back-Scattered Electron Detector on the SEM, are described from a series of contrasting environments. These are a prehnite vein sampled by drilling in the Mirvalles geothermal field, Costa Rica, a pyroxene vein developed in a regional metamorphic shear zone in the Yilgarn block, Western Australia, and a bedded metasomatic diopside rock from regionally metamorphosed metasediments in Connemara, Ireland. In each case the formation of oscillatory zoning can be ascribed to mineral growth under supersaturated conditions due to fluid infiltration. Oscillations can be related in the first example to periodic episodes of pressure release and boiling in the geothermal field, but in the regional metamorphic examples actualistic models are harder to define. The development of oscillatory zoning is likely to be a characteristic feature of infiltration metasomatism and can be used as a criterion in the recognition of metasomatic mineral growth in metamorphic rocks outside the vein environment.

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Metamorphic Differentiation via Enhanced Dissolution along High Permeability Zones

Journal of Petrology ◽

10.1093/petrology/egaa096 ◽

2020 ◽

Author(s):

Jo Moore ◽

Andreas Beinlich ◽

Sandra Piazolo ◽

Håkon Austrheim ◽

Andrew Putnis

Keyword(s):

Mass Transfer ◽

Shear Zone ◽

Mineral Chemistry ◽

Amphibolite Facies ◽

Metamorphic Rocks ◽

High Permeability ◽

Enhanced Dissolution ◽

Fluid Infiltration ◽

Mass Redistribution ◽

Compositional Variations

Abstract Metamorphic differentiation, resulting in segregated mineral bands, is commonly recorded in metamorphic rocks. Despite the ubiquitous nature of compositionally layered metamorphic rocks, the processes that are responsible for metamorphic differentiation receive very little attention. Here, detailed petrography, quantitative mineral chemistry and bulk rock analyses are applied to investigate compositional variations and assemblage microstructure. Furthermore, thermodynamic modelling is applied to provide additional constraints on the P–T–XH2O conditions of assemblage formation and mass transfer. The studied outcrop, located within the Bergen arcs of southwestern Norway, preserves the hydration of anorthositic granulite at amphibolite-facies conditions. The amphibolite-facies hydration is expressed as both a statically hydrated amphibolite and a shear zone lithology, defined by the interlayering of amphibolite with leucocratic domains. Within the granulite, quartz-lined fractures surrounded by amphibolite-facies alteration haloes represent relics of initial fluid infiltration associated with brittle failure. The fracture assemblage (quartz + plagioclase + zoisite + kyanite ± muscovite ± biotite) is identical to that occurring within leucocratic domains of the shear zone. Consequently, the compositional layering of the shear zone lithology is linked to fluid infiltration along localized zones of high permeability that result from fracturing. Mass-balance calculations indicate that quartz-lined fractures and compositional differentiation of the shear zone resulted from mass redistribution internal to the shear zone rather than partial melting or precipitation of minerals from externally derived fluid. The process of internal fractionation within the shear zone is driven by enhanced dissolution along highly permeable fracture planes resulting in the loss of MgO, Fetot and K2O from the leucocratic domains. Elements dissolved in the fluid are then transported and ultimately either precipitated in comparatively impermeable amphibolite domains or removed from the system resulting in an overall mass loss. The mass transfer causing metamorphic differentiation of the shear zone is the result of coupled reaction and diffusion under differential stress. The mechanisms of mass redistribution observed within this shear zone provides further insight into the processes that facilitate mass transfer in the Earth’s crust.

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Metamorphic differentiation via enhanced dissolution along high strain pathways

10.5194/egusphere-egu2020-12939 ◽

2020 ◽

Author(s):

Jo Moore ◽

Andreas Beinlich ◽

Sandra Piazolo ◽

Håkon Austrheim ◽

Andrew Putnis

Keyword(s):

Shear Zone ◽

Mineral Chemistry ◽

Amphibolite Facies ◽

Metamorphic Rocks ◽

Compositional Variation ◽

Transfer Processes ◽

Enhanced Dissolution ◽

Fluid Infiltration ◽

Mass Transfer Processes ◽

Local Dissolution

Metamorphic differentiation, resulting in the segregation of minerals into compositional bands, is a common feature of metamorphic rocks. Considering the ubiquitous nature of compositionally layered metamorphic rocks, the processes that are responsible for metamorphic differentiation have received very little attention. The studied outcrop, located within the Bergen arcs of southwestern Norway, preserves the hydration of an anorthositic granulite at amphibolite-facies conditions. The amphibolite-facies hydration is expressed as both a statically hydrated amphibolite and a shear zone rock, defined by the interlayering of amphibolite with leucocratic domains. Detailed petrography, quantitative mineral chemistry and bulk rock analyses are applied to investigate compositional variation with assemblage microstructure. Within the outcrop, quartz-filled fractures and their associated amphibolite alteration haloes, are observed crosscutting the granulite. These fractures are demonstrated to be relict of the initial fluid infiltration event. The fracture assemblage (quartz + plagioclase + zoisite + kyanite &#177; muscovite &#177; biotite) is equivalent to that occurring locally within leucocratic domains of the shear zone. Due to the textural and compositional similarities between quartz-filled fractures and leucocratic domains, the compositional layering of the shear zone rock may be directly linked to fracturing during initial fluid infiltration. &#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160;&#160; Mass-balance and thermodynamic calculations indicate quartz-filled fractures and compositional differentiation of the shear zone form by internal fractionation rather than partial melting or precipitation of minerals from an eternally derived fluid. The process of internal fractionation within the shear zone is attributed to enhanced dissolution along fracture pathways, resulting in the loss of MgO, Fe2O3 and K2O within leucocratic domains. These elements, being more mobile in the fluid, are then transported and ultimately either precipitated in amphibolite lithologies or escape with the fluid, resulting in an overall volume loss in the shear zone. This inferred fluid connectivity combined with the enhanced local dissolution indicates the presence of a continuously replenished fluid along fracture pathways, leading to the overall conclusion that the mass transfer processes that result in metamorphic differentiation of the shear zone lithologies are dependent on both continuous fluid flux and heterogeneous strain distribution.

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EVIDENCE FOR METEORIC FLUID INFILTRATION INTO A YOUNG, ACTIVE MID-CRUSTAL SHEAR ZONE: δ2H OF MICA FISH FROM THE CORDILLERA BLANCA SHEAR ZONE, PERUVIAN ANDES

10.1130/abs/2020am-357516 ◽

2020 ◽

Author(s):

Tyler Grambling ◽

◽

Micah J. Jessup ◽

Dennis L. Newell ◽

Katharina Methner ◽

...

Keyword(s):

Shear Zone ◽

Cordillera Blanca ◽

Peruvian Andes ◽

Fluid Infiltration

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Amphibole and mica 40Ar/39Ar ages from the Kaipokok and Aillik domains, Makkovik Province, Labrador: towards a characterization of back-arc processes in the Paleoproterozoic

Canadian Journal of Earth Sciences ◽

10.1139/e01-097 ◽

2002 ◽

Vol 39 (5) ◽

pp. 749-764 ◽

Cited By ~ 6

Author(s):

Nicholas Culshaw ◽

Peter Reynolds ◽

Gavin Sinclair ◽

Sandra Barr

Keyword(s):

Thermal Effect ◽

Shear Zone ◽

Second Order ◽

Greenschist Facies ◽

Metamorphic Rocks ◽

Arc Magmatism ◽

First Order ◽

Back Arc ◽

Order Pattern

We report amphibole and mica 40Ar/39Ar ages from the Makkovik Province. Amphibole ages from metamorphic rocks decrease towards the interior of the province, indicating a first-order pattern of monotonic cooling with progressive migration of the province into a more distal back-arc location. The amphibole data, in combination with muscovite ages, reveal a second-order pattern consisting of four stages corresponding to changing spatial and temporal configurations of plutonism and deformation. (1) The western Kaipokok domain cooled through muscovite closure by 1810 Ma, long after the cessation of arc magmatism. (2) The Kaipokok Bay shear zone, bounding the Kaipokok and Aillik domains, cooled through amphibole closure during 18051780 Ma, synchronous with emplacement of syn-tectonic granitoid plutons. (3) Between 1740 and 1700 Ma, greenschist-facies shearing occurred along the boundary between the Kaipokok domain and Nain Province synchronous with A-type plutonism and localized shearing in the western Kaipokok domain, cooling to muscovite closure temperatures in the Kaipokok Bay shear zone, and A-type plutonism and amphibole closure or resetting in the Aillik domain. (4) In the period 16501640 Ma, muscovite ages, an amphibole age from a shear zone, and resetting of plutonic amphibole indicate a thermal effect coinciding in part with Labradorian plutonism in the Aillik domain. Amphibole ages from dioritic sheets in the juvenile Aillik domain suggest emplacement between 1715 and 1685 Ma. Amphibole ages constrain crystallization of small mafic plutons in the Kaipokok domain (reworked Archean foreland) to be no younger than 16701660 Ma. These ages are the oldest yet obtained for Labradorian plutonism in the Makkovik Province.

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Exotic garnet–clinopyroxene–K-feldspar granulites from the Chepelare shear zone, Central Rhodope massif, Bulgaria: implications for high-pressure granulite facies metamorphism

Geologica Balcanica ◽

10.52321/geolbalc.48.3.49 ◽

2019 ◽

Vol 48 (3) ◽

pp. 49-63

Author(s):

Milena Georgirva ◽

Tzvetomila Vladinova

Keyword(s):

Shear Zone ◽

Thick Layer ◽

Granulite Facies ◽

Mineral Association ◽

Granulite Facies Metamorphism ◽

Fine Grain ◽

Fluid Infiltration ◽

High Pressure Granulite ◽

The Matrix ◽

Homogeneous Matrix

Garnet–clinopyroxene–K-feldspar granulite occurs as a thick layer or boudin within the variegated rocks of the Chepelare shear zone in the Central Rhodope massif, Bulgaria. It consists of several domains: mesocratic homogeneous matrix (clinopyroxene–plagioclase–K-feldspar–quartz ± amphibole), porphyroblastic garnet, K-feldspar and clinopyroxene, and strongly foliated fine-grain bands (chloritized biotite–chlorite–prehnite–albite ± epidote). The origin and nature of the matrix mineral association is still unclear. The peak porphyroblast association forms at the expense of plagioclase from the matrix at higher pressure. The fine-grain deformation zones channel the lattermost fluid infiltration. The clinopyroxene-garnet and Zr-in-titanite thermometry give temperatures higher than 790–860 ºC at 2 GPa and, with thermodynamic modeling, suggests crystallization at ~1.8–2.1 GPa and temperature of ~850 ºC in HP granulite field for the porphyroblast granulite association.

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Arcyria minuta. [Descriptions of Fungi and Bacteria].

IMI Descriptions of Fungi and Bacteria ◽

10.1079/dfb/20123409277 ◽

2012 ◽

Author(s):

T. I. Krivomaz

Keyword(s):

New Zealand ◽

Costa Rica ◽

Geographical Distribution ◽

Western Australia ◽

Dead Wood ◽

Conservation Status

Abstract A description is provided for Arcyria minuta, found on dead wood and bark. Some information on its morphology, associated organisms and substrata, interactions and habitats, dispersal and transmission and conservation status is given, along with details of its geographical distribution (Malawi, Morocco, Reunion, Rwanda, Sudan, Israel, Japan, Kazakhstan, Russia, Turkey, Costa Rica, Canada [Ontario and Quebec], USA [Tennessee and Texas], Venezuela, Australia [Western Australia], New Zealand, Belgium, Denmark, France, Germany, Italy, Lithuania, Montenegro, Netherlands, Poland, Spain, Ukraine and UK).

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Giant quartz vein formation and high-elevation meteoric fluid infiltration into the South Armorican Shear Zone: geological, fluid inclusion and stable isotope evidence

Journal of the Geological Society ◽

10.1144/0016-76492010-186 ◽

2012 ◽

Vol 169 (1) ◽

pp. 17-27 ◽

Cited By ~ 14

Author(s):

Jérémie Lemarchand ◽

Philippe Boulvais ◽

Martin Gaboriau ◽

Marie-Christine Boiron ◽

Romain Tartèse ◽

...

Keyword(s):

Stable Isotope ◽

Fluid Inclusion ◽

Shear Zone ◽

Quartz Vein ◽

High Elevation ◽

The South ◽

Vein Formation ◽

Fluid Infiltration ◽

Isotope Evidence

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Rutile from Panasqueira (Central Portugal): An Excellent Pathfinder for Wolframite Deposition

Minerals ◽

10.3390/min9010009 ◽

2018 ◽

Vol 9 (1) ◽

pp. 9 ◽

Cited By ~ 9

Author(s):

Eleonora Carocci ◽

Christian Marignac ◽

Michel Cathelineau ◽

Laurent Truche ◽

Andreï Lecomte ◽

...

Keyword(s):

Compositional Data ◽

Relative Weight ◽

Rare Metal ◽

Progressive Increase ◽

Oscillatory Zoning ◽

Scattered Electron ◽

Minor Elements ◽

Sector Zoning ◽

Central Portugal ◽

Circulation Dynamics

Abundant W-rich rutile in the tourmalinized wall-rocks from the Panasqueira W-deposit appears to be a marker of the onset of the main wolframite depositing event. Rutile displays spectacular zoning, both sector (SZ) and oscillatory (OZ). An extensive set of compositional data obtained on crystals, beforehand studied using back-scattered electron images and X-ray maps, was used to address (i) the effects of SZ on differential trapping of minor elements, and (ii) the significance of the OZ in deciphering fluid sources and fluid circulation dynamics. Particular attention was paid to Sn, W (Nb, Ta) concentrations in rutile as pathfinders of the W deposition. Concerning the sector zoning, W is more incorporated than (Nb, Ta) onto more efficient faces, whereas Sn contents are nearly not impacted. The net effect of the sector zoning is thus a progressive increase of the relative weight of Sn from pyramid to prism faces, in combination with a less significant increase in the relative weight of Nb + Ta. The oscillatory zoning concerns most minor elements: W, Nb (Ta), Fe, V, Cr and Sn. In the frequent doublets, the clear bands are in general enriched in W relatively to the dark ones, whereas the inverse is true for Nb and Ta. The doublets may be viewed as the result of the successive influx of (i) a W-rich, Nb + Ta poor fluid, abruptly replaced by (or mixed to) (ii) a Nb + Ta-rich and W-poor fluid. The Nb + Ta-rich fluid could be in turn related to a rare-metal granite layer observed atop of the Panasqueira granite.

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