Orthogonal switching of AMS axes during type-2 fold interference: Insights from integrated X-ray computed tomography, AMS and 3D petrography

Sayab, Mohammad; Miettinen, Arttu; Aerden, Domingo; Karell, Fredrik

doi:10.1016/j.jsg.2017.09.002

Cited by 12 publications

(9 citation statements)

References 40 publications

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“…X-ray computed micro-tomography 3D data acquisition and processing X-ray computed micro-tomography (XCT) allows 3D visualization, mineral quantification, and metamorphic fabric analysis down to the micrometer scale (Sayab et al 2015(Sayab et al , 2017Aerden and Sayab 2017;Suuronen and Sayab 2018). Because the XCT technique differentiates different minerals based on their contrasting densities, the method is particularly useful for analyzing the distribution of sulfide minerals within their host rock (Kyle and Ketcham 2015;Sayab et al 2016).…”

Section: Study Methodsmentioning

confidence: 99%

“…For multi-scale structural analysis, the aerial and field observations were coupled to X-ray computed tomography scans of selected rock samples and high-fidelity reflection seismic profiles across the KiSZ. In addition, the availability of fine-resolution aeromagnetic images of the CLGB along with published regional geology (Nironen 2017) and the known tectonic setting of the area (Sayab et al 2017;Lahtinen et al 2018) has allowed us to extend our open-pit data and interpretations to the regional scale.…”

Section: Introductionmentioning

confidence: 99%

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A succession of near-orthogonal horizontal tectonic shortenings in the Paleoproterozoic Central Lapland Greenstone Belt of Fennoscandia: constraints from the world-class Suurikuusikko gold deposit

et al. 2019

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The relative and absolute timing of orogenic gold deposits in complex structural settings are active and challenging topics of research, especially in Precambrian greenstone belts. The Suurikuusikko gold deposit in Central Lapland Greenstone Belt is currently the largest primary gold producing deposit in Europe, located on a slight bend of the strike-slip Kiistala shear zone (KiSZ). Gold is refractory and locked inside arsenopyrite and pyrite. In this study, different structural features were investigated along the KiSZ from the recently stripped Etelä pit, which is the southern extension of the Suurikuusikko ore body. Our data source ranges from aeromagnetic to high-resolution aerial images, Xray computed tomography scans of selected rock samples and regional geological and geophysical datasets. The KiSZ has recorded five discrete deformation phases, spanning between ca. 1.92 and 1.76 Ga. The refractory gold at the Suurikuusikko deposit formed during E-W contraction related to the D1 thrusting phase. This was followed by a N-S shortening event (D2), where most of the strain was taken up by the northern and southern thrusts. Tectonic vectors then switched from N-S to NE-SW and, as a result, dextral strike-slip regime (D3) commenced along the KiSZ. This event exsolved invisible gold from the sulfides and remobilized it along with fractures. A near-orthogonal switch of the regional stress regime from NE-SW to NW-SE flipped the kinematics of the KiSZ from dextral to sinistral (D4). The last deformation phase (D5) produced widespread veining under E-W contraction and secured gold mineralization at the Iso-Kuotko gold deposit within the KiSZ.

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Section: Study Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

A succession of near-orthogonal horizontal tectonic shortenings in the Paleoproterozoic Central Lapland Greenstone Belt of Fennoscandia: constraints from the world-class Suurikuusikko gold deposit

et al. 2019

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“…During the procedure it is possible to have areas with multiple adjacent local maxima. This issue can be minimized taking only the largest local maxima (Sayab et al, 2017). The MBW algorithm then expand the seeded markers over the related mineral phases (Figures 3E,F) using a landscape function which is defined by the gradient volume (i.e., active contours algorithm).…”

Section: X-ray Computed Tomographymentioning

confidence: 99%

Integrating X-Ray Computed Tomography With Chemical Imaging to Quantify Mineral Re-crystallization From Granulite to Eclogite Metamorphism in the Western Italian Alps (Sesia-Lanzo Zone)

et al. 2019

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Metamorphic transformations and fabric evolution are the consequence of thermodynamic processes, lasting from thousands to millions of years. Relative mineral percentages, their grain size distribution, grain orientation, and grain boundary geometries are first-order parameters for dynamic modeling of metamorphic processes. To quantify these parameters, we propose a multidisciplinary approach integrating X-ray computed microtomography (µ-CT) with X-ray chemical mapping obtained from an Electron MicroProbe Analyzer (EMPA). We used a metapelitic granulite sample collected from the Alpine HP-LT metamorphic rocks of the Mt. Mucrone (Eclogitic Micaschists Complex, Sesia-Lanzo Zone, Western Alps, Italy). The heterogeneous Alpine deformation and metamorphism allowed the preservation of pre-alpine structural and mineralogical features developed under granulite-facies conditions. The inferred granulitic mineral association is Grt + Bt + Sil + Pl + Qtz ± Ilm ± Kfs ± Wm. The subsequent pervasive static eclogite-facies re-equilibration occurred during the alpine evolution. The inferred alpine mineral association is Wm + Omp ± Ky + Qtz + Grt though local differences may occur, strongly controlled by chemistry of microdomains. X-ray µ-CT data extracted from centimeter-sized samples have been analyzed to quantify the volumetric percentage and shape preferred orientation (SPO) for each mineral phase. By combining tomographic phase separation with chemical variation and microstructures (i.e., different grain-size classes for the same phase and morphology of different pre-alpine microdomains) the pre-alpine mineralogical phases from the alpine overprint have been distinguished and quantified. Moreover, the sample preserves 100% of the pre-alpine granulite fabric, which surprisingly corresponds to less than 22% of the corresponding pre-alpine metamorphic assemblages, while the alpine eclogitic static assemblage corresponds to 78% though no new fabric is developed. This contribution

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“…2 are partly inferred. Given the fact that the area is characterized by very low relief without any major vertical exposures, combined with thin-skin thrusting and common type-2 fold interference pattern (D1/D2; Lahtinen et al, 2015a;Sayab et al, 2017), makes that even outcrops nearby can derive from separate thrust sheets, and thus, belong to different lithodemic units.…”

Section: Lithostratigraphic Lithodemicmentioning

confidence: 99%

“…The Martimo-Mellajoki area ( Fig. 1) manifests complex Paleoproterozoic tectonic evolution and five near-orthogonal deformation successions (D1 to D5) were identified (Lahtinen et al, 2015a;Sayab et al, 2017). The earliest deformation (D1) involved east-directed thin-skin thrusting.…”

Section: Introductionmentioning

confidence: 99%

Geochemical and U-Pb and Sm-Nd isotopic constraints on the evolution of the Paleoproterozoic Ylitornio nappe complex, northern Fennoscandia

Lahtinen¹,

Huhma²,

Lauri³

et al. 2019

Bull Geol Soc Finland

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The Ylitornio area in northern Finland is a typical example of a poorly outcropping, multiply deformed, complex Precambrian terrain. U-Pb, Sm-Nd and geochemical data from metavolcanic, metasedimentary and plutonic rocks combined with structural data define the lithodemic units and tectonostratigraphy of the area. The Mellajoki, Martimo, Hosiojoki, Kierovaara and Uusivirka suites form the Ylitornio nappe complex. Although main thrust stacking had occurred between 1.92-1.89 Ga, later reverse faulting probably continued until 1.78 Ga. The Väystäjä bimodal volcanic rocks (2.09-2.05 Ga) from the Martimo suite are plume-related EMORB-OIB rocks formed during a continent breakup. The Kaskimaa greywacke of the Martimo suite is inferred to represent sedimentation in a deepening rift basin in the continental margin. The coeval Hosiojoki felsic rocks with A-type affinity and the Kierovaara suite granites (2.00-1.98 Ga) represent dry melting of a dominantly 2.1-2.05 Ga contaminated mafic underplate, and hydrous melting of both the mafic underplate and a refractory lower crust of Archean age, respectively. The older rocks of the Uusivirka suite are early-collisional (1.92-1.91 Ga) and derived from poorly mixed local sources, whereas younger psammite-pelite associations (Ristivuoma) are syn-collisional (1.91-1.89 Ga) and derive from multiply recycled and thoroughly mixed sources. These rocks were deformed during continued collision with the development of foreland fold-and thrust belt.

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Orthogonal switching of AMS axes during type-2 fold interference: Insights from integrated X-ray computed tomography, AMS and 3D petrography

Abstract: This is an electronic reprint of the original article. This reprint may differ from the original in pagination and typographic detail.

Cited by 12 publications

References 40 publications

A succession of near-orthogonal horizontal tectonic shortenings in the Paleoproterozoic Central Lapland Greenstone Belt of Fennoscandia: constraints from the world-class Suurikuusikko gold deposit

A succession of near-orthogonal horizontal tectonic shortenings in the Paleoproterozoic Central Lapland Greenstone Belt of Fennoscandia: constraints from the world-class Suurikuusikko gold deposit

Integrating X-Ray Computed Tomography With Chemical Imaging to Quantify Mineral Re-crystallization From Granulite to Eclogite Metamorphism in the Western Italian Alps (Sesia-Lanzo Zone)

Geochemical and U-Pb and Sm-Nd isotopic constraints on the evolution of the Paleoproterozoic Ylitornio nappe complex, northern Fennoscandia

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