Fractal analysis of magnetite grains — implications for interpreting deformation mechanism

Mamtani, Manish A.

doi:10.1007/s12594-012-0149-1

Cited by 9 publications

(6 citation statements)

References 20 publications

(28 reference statements)

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“…The curves go through a critical region at rates below 10 À10 s À1 in which instabilities develop. The critical value is within the estimated rate of emplacement (10 À9 e10 À10 s À1 ) of a pluton (Vigneresse, 2004;Mamtani, 2012). On the presented diagram (Fig.…”

Section: Instability Developments Caused By the Rheologysupporting

confidence: 75%

“…The inset of instabilities (in light grey) occurs at lower strain rates (below 10 À10 s À1 ) when the viscosity curve intersects the critical zone. The critical value of 10 À10 s À1 fits with the high rate estimated for magma emplacement (Mamtani, 2012). on melting, and could be considered as restitic on low degree of reheating.…”

Section: System Stabilitysupporting

confidence: 67%

“…It ranges 10 À7.0 to 10 À9.8 s À1 (Mamtani, 2010). Using the same technique, but using 225 magnetite grains in the Godhra granite, in the Aravalli Mountain Belt, Northern India (Mamtani, 2012), results in strain rates a little slower, being inferred between 10 À10 and 10 À14 s À1 . Such values correspond to the assumed strain rate for natural tectonic deformation (Passchier and Trouw, 2005).…”

Section: Estimating the Strain Ratementioning

confidence: 99%

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Textures and melt-crystal-gas interactions in granites

Vigneresse¹

2015

Geoscience Frontiers

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a b s t r a c tFelsic intrusions present ubiquitous structures. They result from the differential interactions between the magma components (crystal, melt, gas phase) while it flows or when the flow is perturbed by a new magma injection. The most obvious structure consists in fabrics caused by the interactions of rotating grains in a flowing viscous melt. New magma inputs through dikes affect the buk massif flow, considered as global within each mineral facies. A review of the deformation and flow types developing in a magma chamber identifis the patterns that could be expected. It determines their controlling parameters and summarizes the tools for their quantification. Similarly, a brief review of the rheology of a complex multiphase magma identifies and suggests interactions between the different components. The specific responses each component presents lead to instability development. In particular, the change in vorticity orientation, associated with the switch between monoclinic to triclinic flow is a cause of many instabilities. Those are preferentially local. Illustrations include fabric development, shear zones and flow banding. They depend of the underlying rheology of interacting magmas. Dikes, enclaves, schlieren and ladder dikes result from the interactions between the magma components and changing boundary conditions. Orbicules, pegmatites, unidirectional solidification textures and miarolitic cavities result from the interaction of the melt with a gaseous phase. The illustrations examine what is relevant to the bulk flow, local structures or boundary conditions. In each case a field observation illustrates the instability. The discussion reformulates instability observations, suggesting new trails for ther description and interpretation in terms of local departure to a bulk flow. A brief look at larger structures and at their evolution tries to relate these instabilities on a broader scale. The helical structures of the Rí cany pluton, Czech Republic and by the multiple granitic intrusions of Dolbel, Niger illustrate such events.Ó 2014, China University of Geosciences (Beijing) and Peking University. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

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Section: Instability Developments Caused By the Rheologysupporting

confidence: 75%

Section: System Stabilitysupporting

confidence: 67%

Section: Estimating the Strain Ratementioning

confidence: 99%

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Textures and melt-crystal-gas interactions in granites

Vigneresse¹

2015

Geoscience Frontiers

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“…However, whereas fractal patterns of various geological deformation structures have been studied at various scales 10,11 , fractal spatial distributions of mineral deposits have been studied mainly at regional-scales 1–4 . Some studies have reported that micro-scale fractal geometries of metal-bearing quartz veins in secondary structures are similar to regional-scale fractal geometries of major structures 12,13 , whereas some studies have linked micro-scale fractal distributions of ore/gangue minerals to regional-scale structural processes 14,15 . No studies, however, have linked micro-scale patterns of ore/gangue minerals to local-scale structures at/near mineral deposits to support the proposition that mineral deposits are fractals.…”

Section: Introductionmentioning

confidence: 99%

Macro-scale ore-controlling faults revealed by micro-geochemical anomalies

Carranza

Filho

Haddad-Martim

et al. 2019

Sci Rep

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Whereas the mechanism of fluid flow, and thus structural control, linked with mineral deposit formation is quite understood, the specific structures that likely provided controls on mineralization at certain geographic scales are not readily known for a given region unless it is well-explored. This contributes uncertainty in mineral prospectivity analysis in poorly-explored regions (or greenfields). Here, because the spatial distribution of mineral deposits has been postulated to be fractals (i.e., the patterns of these features are self-similar across a range of spatial scales), we show for the first time that micro-geochemical anomalies (as proxies of micro-scale patterns of ore minerals), from few discrete parts of the Sossego iron-oxide copper-gold (IOCG) deposit in the Carajás Mineral Province (CMP) of Brazil, exhibit trends of macro-scale faults that are known to have controlled IOCG mineralization in the CMP. The methodology described here, which led to this novel finding, would help towards detecting mineral exploration targets as well as help towards understanding structural controls on mineralization in greenfields.

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“…prove dislocation glide in naturally deformed polymineralic rocks (e.g., Mamtani et al, 2011;Kontny et al, 2012). In addition, since a deformation mechanism map is theoretically calculated based on experiments done on single crystals of a mineral, it may not necessarily be valid for that mineral in a polymineralic rock (e.g., Mamtani, 2012). Thus, the present investigation involving microscale (SEM-EBSD) and nanoscale (TEM) studies enables us to evaluate the deformation mechanism of magnetite in polymineralic rocks.…”

Section: Discussionmentioning

confidence: 99%

Intracrystalline deformation and nanotectonic processes in magnetite from a naturally deformed rock

Mamtani

Резник

Kontny

2020

Journal of Structural Geology

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Although experimental studies have shown dislocation creep to be an important deformation mechanism in magnetite at medium to high temperature, evidence of intracrystalline deformation in magnetite remains to be established in natural tectonically deformed rocks. In this study we investigate intracrystalline deformation features and nanostructures in elongated magnetite from a naturally deformed rock (mylonitized mica schist deformed in a large-scale shear zone of the Seve nappe, Swedish Caledonides). The magnetite grains have very high aspect ratios (up to 10.40) that result in very high degree of magnetic anisotropy in the rock. We show low and high angle grain boundaries (LAGB and HAGB) in magnetite using a combination of electron backscatter diffraction and high-resolution transmission electron microscopy (HRTEM) analysis. HRTEM studies on lamellae excavated perpendicular to the LAGB and HAGB reveal translational and rotational Moir� e fringes, respectively. Dislocations, slip bands, stacking faults, twins and recrystallized domains are observed in the vicinity of the grain boundaries, thus providing unequivocal evidence of intracrystalline deformation of magnetite. Our study also reveals the presence of biotite inclusions intergrown epitaxially with magnetite that show no evidence of lattice defects, thus suggesting that the intracrystalline deformation of magnetite took place under wet conditions. The movement at the grain boundaries is interpreted as a response to regional tectonics with a top-to-NW transport direction. It is established that at the nanoscale, the LAGB and HAGB were favourably oriented to accommodate strain dominantly by translation and rotation, respectively. Thus, the nanotectonic processes are consistent with the regional tectonic reference frame. The importance of evaluating ductile behaviour of magnetite from deformed polymineralic rocks in petrofabric analysis and modeling the relation between strain and rock magnetic anisotropy is discussed.

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Fractal analysis of magnetite grains — implications for interpreting deformation mechanism

Cited by 9 publications

References 20 publications

Textures and melt-crystal-gas interactions in granites

Textures and melt-crystal-gas interactions in granites

Macro-scale ore-controlling faults revealed by micro-geochemical anomalies

Intracrystalline deformation and nanotectonic processes in magnetite from a naturally deformed rock

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