Viscous relaxation of mineral Inclusions and its implications for reaction overstepping calculations in metamorphic rocks

2020 ◽  
Author(s):  
Evangelos Moulas ◽  
Xin Zhong ◽  
Lucie Tajcmanova
Keyword(s):  
Independent Method ◽  
Metamorphic Rocks ◽  
Additional Method ◽  
Natural Systems ◽  
Long Period ◽  
Mineral Inclusions ◽  
Large Peak ◽  
Viscous Relaxation ◽  
T Path ◽  
Temperature Time

<p>Over the recent years, Raman elastic barometry has been developed as an additional method <span>to calculate</span> metamorphic conditions in natural systems. A major advantage of Raman elastic barometry is that it does not depend on thermodynamic databases and classic geobarometry methods <span>but</span> relies on mechanical calculations. As a consequence, Raman elastic barometry offers an independent method for estimating the pressure conditions <span>that prevailed at the</span> <span>time of entrapment</span> of mineral<span>s</span> du<span>ring</span> growth of their host<span>s</span>.</p><p>The di<span>fference between</span> the pressure calculated <span>using</span> elastic geobarometry and <span>that calculated by phase</span> equilibria methods has recently <span>been employed to</span> <span>estimate</span> the extent of metamorphic reaction overstepping in natural systems. <span>Quantification of</span> the <span>latter however implicitly assumes that the rheology</span> of the inclusion-host system <span>is perfectly</span> elastic. This assumption may no<span>t</span> hold at high temperatures, where viscous creep of minerals takes place.</p><p>The amount of viscous relaxation of <span>a host-inclusion</span> system is a path<span>-</span>dependent quantity which mostly depends on the temperature-time (T-t) path <span>followed</span>. <span>Here</span>, we present examples of visco-elastic relaxation of mineral inclusions and calculate the apparent reaction overstepping which results by assuming that the mechanical system is purely elastic. <span>Our modelling shows</span> that host-inclusion systems <span>that</span> experienced large peak temperatures for long period<span>s</span> of time will retain inclusion residual pressures that <span>cann</span>ot be simply related to the growth of the<span>ir hosts</span> and should <span>therefore not</span> be used for reaction overstepping calculations.</p>

scholarly journals Post-entrapment modification of residual inclusion pressure and its implications for Raman elastic thermobarometry

Solid Earth ◽  
2020 ◽  
Vol 11 (1) ◽  
pp. 223-240 ◽  
Author(s):  
Xin Zhong ◽  
Evangelos Moulas ◽  
Lucie Tajčmanová
Keyword(s):  
Thin Section ◽  
Pressure Field ◽  
Residual Pressure ◽  
Mineral Inclusions ◽  
Plastic Yield ◽  
Section Surface ◽  
Temperature And Pressure ◽  
Viscous Relaxation ◽  
T Path ◽  
Differential Expansion

Abstract. Residual pressure can be preserved in mineral inclusions, e.g. quartz-in-garnet, after exhumation due to differential expansion between inclusion and host crystals. Raman spectroscopy has been applied to infer the residual pressure and provides information on the entrapment temperature and pressure conditions. However, the amount of residual pressure relaxation cannot be directly measured. An underestimation or overestimation of residual pressure may lead to significant errors between calculated and actual entrapment pressure. This study focuses on three mechanisms responsible for the residual pressure modification: (1) viscous creep; (2) plastic yield; (3) proximity of inclusion to the thin-section surface. Criteria are provided to quantify how much of the expected residual pressure is modified due to these three mechanisms. An analytical solution is introduced to demonstrate the effect of inclusion depth on the residual pressure field when the inclusion is close to the thin-section surface. It is shown that for a quartz-in-garnet system, the distance between the thin-section surface and inclusion centre needs to be at least 3 times the inclusion radius to avoid pressure release. In terms of viscous creep, representative case studies on a quartz-in-garnet system show that viscous relaxation may occur from temperatures as low as 600–700 ∘C depending on the particular pressure–temperature (P–T) path and various garnet compositions. For quartz entrapped along the prograde P–T path and subject to viscous relaxation at peak T above 600–700 ∘C, its residual pressure after exhumation may be higher than predicted from its true entrapment conditions. Moreover, such a viscous resetting effect may introduce apparent overstepping of garnet nucleation that is not related to reaction affinity.

scholarly journals Intrusion of UHP metamorphic rocks into the upper crust of Kyrgyzian Tien-Shan: P-T path and metamorphic age of the Makbal Complex

2010 ◽  
Vol 105 (5) ◽  
pp. 233-250 ◽  
Author(s):  
Michio TAGIRI ◽  
Shingo TAKIGUCHI ◽  
Chika ISHIDA ◽  
Takaaki NOGUCHI ◽  
Makoto KIMURA ◽  
...  
Keyword(s):  
Tien Shan ◽  
Metamorphic Rocks ◽  
Upper Crust ◽  
T Path

scholarly journals Natural Graphite Cuboids

Minerals ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 110 ◽  
Author(s):  
Andrey Korsakov ◽  
Olga Rezvukhina ◽  
John Jaszczak ◽  
Dmitriy Rezvukhin ◽  
Denis Mikhailenko
Keyword(s):  
Ultrahigh Pressure ◽  
Metamorphic Rocks ◽  
Formation Mechanisms ◽  
Natural Graphite ◽  
Natural Systems ◽  
Magmatic Rocks ◽  
Internal Morphology ◽  
Polycrystalline Aggregates ◽  
Common Center ◽  
Transformation Processes

Graphite cuboids are abundant in ultrahigh-pressure metamorphic rocks and are generally interpreted as products of partial or complete graphitization of pre-existing diamonds. The understanding of the graphite cuboid structure and its formation mechanisms is still very limited compared to nanotubes, cones, and other carbon morphologies. This paper is devoted to the natural occurrences of graphite cuboids in several metamorphic and magmatic rocks, including diamondiferous metamorphic assemblages. The studied cuboids are polycrystalline aggregates composed either of numerous smaller graphite cuboids with smooth surfaces or graphite flakes radiating from a common center. Silicates, oxides, and sulphides are abundant in all the samples studied, testifying that the presence of oxygen, sulfur, or sulphides in natural systems does not prevent the spherulitic growth of graphite. The surface topography and internal morphology of graphite cuboids combined with petrological data suggest that graphite cuboids originated from a magmatic or metamorphic fluid/melt and do not represent products of diamond-graphite transformation processes, even in diamond-bearing rocks.

scholarly journals Sulfides in Metamorphic Rocks of the Fore Range Zone (Greater Caucasus). A New Type of Mineral Container for Peak Metamorphism Mineral Assemblages

Minerals ◽  
2019 ◽  
Vol 9 (11) ◽  
pp. 701 ◽  
Author(s):  
Kamzolkin ◽  
Konilov ◽  
Kulakova ◽  
Latyshev ◽  
Smulskaya ◽  
...  
Keyword(s):  
Metamorphic Rocks ◽  
Low Grade ◽  
Greater Caucasus ◽  
Mineral Inclusions ◽  
Mineral Assemblages ◽  
Peak Metamorphism ◽  
New Type ◽  
Formation Conditions ◽  
Si Content ◽  
Initial Rock

The rocks of the Armovka Formation (the Fore Range zone, Greater Caucasus) have undergone low-grade metamorphism that partially erased information about initial rock formation conditions. We discovered high-pressure mineral inclusions such as omphacite, phengite, garnet, and paragonite enclosed by pyrite and chalcopyrite. Mineral inclusions in sulfides may provide important information about metamorphic pressure−temperature conditions because they are shielded by the host minerals and isolated from significant low-grade overprinting. Calculations performed on phengite inclusions using the phengite Si-content barometry indicate a pressure ranging from 1.7 ± 0.2 to 1.9 ± 0.2 GPa for temperature of 600 ± 40 °C. These data are consistent with estimations obtained for eclogite bodies embedded in rocks of the Armovka Formation. Geothermobarometry of the latest yielded conditions of 680 ± 40 °C and a minimum pressure of 1.6 ± 0.2 GPa to upper pressure boundary at 2.1 GPa. This fact allows us to assume that the metamorphic rocks of the Armovka Formation were immersed in the subduction zone to the conditions of the eclogite facies of metamorphism, forming a coherent subduction complex together with eclogites.

scholarly journals Conditions and timing of low-pressure – high-temperature metamorphism in the Montresor Belt, Rae Province, Nunavut

2019 ◽  
Vol 56 (6) ◽  
pp. 654-671
Author(s):  
Carolyn Dziawa ◽  
Fred Gaidies ◽  
John Percival
Keyword(s):  
White Mica ◽  
Age Dating ◽  
Bulk Rock ◽  
Prograde Metamorphism ◽  
Bulk Rock Chemistry ◽  
T Path ◽  
Temperature Time ◽  
High Bulk ◽  
High Temperature Metamorphism

Pressure–temperature–time (P–T–t) estimates for the Montresor Belt, obtained using phase equilibria and geospeedometry modelling integrated with in situ U–Th–Pb monazite geochronology, shed new light on the tectonometamorphic effects of the Snowbird phase of the Trans-Hudson orogeny. Typical metapelitic assemblages of the lower Montresor group consist of white mica, biotite, plagioclase, quartz, and andalusite, which in some rocks is partly or completely pseudomorphed by white mica. The observed assemblages reflect peak P–T conditions centring at approximately 575 °C and 3 kbar. Rocks with high bulk Fe/Mg contents contain compositionally zoned garnet, permitting the addition of further constraints on the conditions of metamorphism in the Montresor Belt: Core compositions of earliest-grown garnets indicate initial garnet crystallization at approximately 535 °C and 2.3 kbar, suggesting a nearly isobaric P–T path of prograde metamorphism with a gradient of approximately 50 °C·kbar–1. Chemical age-dating of monazite inclusions in garnet yields ages of ca. 1870 ± 9 to 1837 ± 9 Ma. Retrograde, pseudomorphic andalusite replacement by white mica at approximately 540 °C is inferred to have been controlled by variations in bulk rock chemistry. Morphologically corroded and chemically heterogeneous monazite adjacent to white mica pseudomorphs suggests that andalusite replacement took place at ca. 1792 ± 10 Ma, possibly associated with extension and movement along the detachment fault separating the upper and lower Montresor groups. Simulations of diffusion across chlorite- and biotite-filled cracks in garnet assumed to be coeval with andalusite replacement suggest that the rocks have experienced the retrograde event for at least 20 My.

scholarly journals METAMORPHIC EVOLUTION OF GARNET–BIOTITE–MUSCOVITE SCHIST FROM BARRU COMPLEX IN SOUTH SULAWESI, INDONESIA

2015 ◽  
Vol 6 (2) ◽  
Author(s):  
Nugroho Imam Setiawan ◽  
Yasuhito Osanai ◽  
Nobuhiko Nakano ◽  
Tatsuro Adachi
Keyword(s):  
Geothermal Gradient ◽  
Metamorphic Rocks ◽  
Metamorphic Evolution ◽  
First Report ◽  
Geothermal Gradients ◽  
South Sulawesi ◽  
Pelitic Schist ◽  
T Path ◽  
Tectonic Environments

This paper explains the first report in metamorphic evolution of pelitic schist from Barru Complex in South Sulawesi, Indonesia. Garnet-biotitemuscovite schist was examined petrologically to assess the metamorphic evolution history, which has implications on tectonic condition of this region. The rock mainly composed of garnet, biotite, muscovite, epidote, quartz, rutile, hematite, and plagioclase. Inclusions in the garnet preserve records of prograde stage of this rock, which are epidote, titanite, quartz, and apatite. Garnet, biotite, muscovite, quartz, rutile, and plagioclase are concluded as equilibrium assemblages at peak P-T condition of this rock, which estimated at 501–562 ºC and 0.89–0.97 GPa. The result is still on the ranges of the estimated geothermal gradient P-T path of eclogite from Bantimala Complex. Similar geothermal gradients of metamorphisms might be indicated that these metamorphic rocks were metamorphosed on the similar tectonic environments. Keywords: Pelitic schist, Barru Complex, South Sulawesi, metamorphic evolution.

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