A reinterpretation of the Snow Lake gold camp, Trans-Hudson Orogen, Canada: The use of cleavages as markers to correlate structures across deformed terranes

2020 ◽  
Author(s):  
Kate Elizabeth Rubingh ◽  
Bruno Lafrance ◽  
Harold L. Gibson
Keyword(s):  
Boundary Conditions ◽  
Time Lag ◽  
Volcanic Rocks ◽  
Shear Zones ◽  
Thrust Faults ◽  
Volcanic Stratigraphy ◽  
Shear Sense ◽  
Flin Flon ◽  
Shear Sense Indicators ◽  
Superior Craton

The Snow Lake gold camp is located within amphibolite facies volcanic rocks of the ca. 1.88 – 1.87 Ga Flin Flon-Glennie Complex (FFGC) in the Trans-Hudson Orogen, Manitoba. During thrusting and collision with the Archean Sask craton, volcanic rocks were interleaved with turbidites of the ca. 1.855 - 1.84 Ga Burntwood Group and sandstone and conglomerate of the ca. 1.845 - 1.835 Ga Missi Group. The main cleavage in the turbidites was previously attributed to thrusting and used as a marker for correlating structures across the camp. A re-examination of this cleavage suggests that it overprints the thrust faults and formed during later collision between the FFGC and the Archean Superior craton. This has important implications as it further suggests that (1) previously unrecognized, early brittle thrust faults repeat volcanic stratigraphy and may have created the boundary conditions that enabled the formation of ductile thrust faults, fold nappes, and mega sheath folds; (2) shear sense indicators along ductile thrust faults formed during their reactivation as sinistral shear zones rather than during thrusting; and (3) peak metamorphic conditions were caused by thrusting and stacking during collision with the Sask craton but were attained later during collision with the Superior craton due to the time lag between orogenesis and the re-equilibration of regional isotherms. Results from this study may be applicable to other complexly deformed terranes where the dominant regional cleavage differs in expression in mixed volcanic and sedimentary successions and has been used as a marker for correlating structures.

scholarly journals Geology of the orogenic Cheminis gold deposit along the Larder Lake – Cadillac deformation zone, Ontario

2015 ◽  
Vol 52 (12) ◽  
pp. 1093-1108 ◽  
Author(s):  
Bruno Lafrance
Keyword(s):  
Deformation Zone ◽  
Volcanic Rocks ◽  
Tholeiitic Basalt ◽  
Hydrothermal Fluids ◽  
South Side ◽  
Shear Sense ◽  
Abitibi Subprovince ◽  
Deformation Features ◽  
Shear Sense Indicators ◽  
Host Rocks

The Larder Lake – Cadillac deformation zone (LLCDZ) is one of two major, auriferous, deformation zones in the southern Abitibi subprovince of the Archean Superior Province. It hosts the Cheminis and the giant Kerr Addison – Chesterville deposits within a strongly deformed band of Fe-rich tholeiitic basalt and komatiite of the Larder Lake Group (ca. 2705 Ma). The latter is bounded on both sides by younger, less deformed, Timiskaming turbidites (2674–2670 Ma). The earliest deformation features are F1 folds affecting the Timiskaming rocks, which formed either during D1 extensional faulting or during early D2 north–south shortening related to the opening and closure, respectively, of the Timiskaming basin. Continued shortening during D2 imbricated the older volcanic rocks and turbidites and produced regional F2 folds with an axial planar S2 cleavage. D2 deformation was partitioned into the weaker band of volcanic rocks, producing the strong S2 foliation, L2 stretching lineation, and south-side-up shear sense indicators, which characterize the LLCDZ. Gold is present in quartz–carbonate veins in deformed fuchsitic komatiites (carbonate ore) and turbiditic sandstone (sandstone-hosted ore), and in association with disseminated pyrite in altered Fe-rich tholeiitic basalts (flow ore). All host rocks underwent strong mass gains in CO2, S, K2O, Ba, As, and W, during sericitization, carbonatization, and sulphidation of the host rocks, suggesting that they interacted with the same hydrothermal fluids. Textural relationships between alteration minerals and S2 cleavage indicate that mineralization is syn-cleavage. Thus, gold was deposited as hydrothermal fluids migrated upward along the LLCDZ during contractional, D2 south-side-up shearing. The gold zones were subsequently modified during D3 reactivation of the LLCDZ as a dextral transcurrent fault zone.

Unravelling heterogeneities in magnetic fabric record of the strain: a combined AMS and ApARM data analysis applied to intraplate shear zones.

2021 ◽  
Author(s):  
Claudio Robustelli Test ◽  
Elena Zanella ◽  
Andrea Festa ◽  
Francesca Remitti
Keyword(s):  
Cluster Analysis ◽  
Hanging Wall ◽  
Shear Zones ◽  
Magnetic Fabric ◽  
Plate Boundaries ◽  
Thrust Faults ◽  
Localized Deformation ◽  
Main Thrust ◽  
Shear Sense ◽  
And Cluster Analysis

<p>Deciphering the stress and strain distribution across plate boundary shear zones is critical to understanding the physical processes involved in the nucleation of megathrust faults and its behaviour. Plate boundaries at shallow depth represent complex and highly deformed zones showing structures from both distributed and localized deformation.</p><p>As magnetic minerals are sensitive to stress regime, the investigation of the magnetic fabric has proven to be an effective tool in studying faulting processes at intraplate shear zones.</p><p>Anisotropy of magnetic susceptibility (AMS) provides insights into the preferred orientation of mineral grains and the qualitative relationships between petrofabrics and deformation intensity.</p><p>We present an approach of combined Contoured Diagram and Cluster Analysis to isolate the contribution of coexisting petrofabrics to the total AMS and evaluating the significance of magnetic fabric clusters.</p><p>Our results reveal distinct subfabrics with reasonably straightforward correlations with structural data. Specific AMS pattern may be associated to the intensity of the reworking related to tectonic shearing and the structural position within the shear zone (i.e., the proximity to the main thrust faults).</p><p>Close to the main thrust the magnetic fabric is dominantly oblate with magnetic foliation consistent to the S-C fabric and/or mélange foliation and the magnetic lineation parallel to the shear sense.</p><p>Away from the thrust faults the degree of anisotropy as well as the ellipsoids oblateness gradually diminishes. Thus, the presence of subfabrics related to previous tectonic events or less intense deformation (i.e. intersection lineation fabric) became dominant. The discrimination of subfabrics also allowed to unravel the presence of minor thrust plane and qualitatively evaluate the heterogeneous registration of strain (i.e. distributed versus localized deformation).</p><p>An abrupt change in magnetic ellipsoid shape and parameters is also observed below the basal décollements showing purely sedimentary magnetic fabric or previous deformation history with minor to absent evidences of shearing in the hanging wall.</p><p>Then, the integration with anisotropy of magnetic remanence experiments in different coercivity windows (ApARM) allow to separate the contribution of different ferromagnetic subpopulation of grains, constraining the significance of the different magnetic pattern/clusters detected through the AMS analysis.</p><p>In conclusion, our results show the potential of a combination of density diagrams and cluster analysis validated by ApARM experiments in distinguishing the superposition of deformation events, unravelling strain partitioning/concentration and thus to better understand the geodynamic evolution of subduction-accretion complexes.</p>

Regional setting and kinematic features of the Needle Falls Shear Zone, Trans-Hudson Orogen

1993 ◽  
Vol 30 (7) ◽  
pp. 1338-1354 ◽  
Author(s):  
Mel R. Stauffer ◽  
John F. Lewry
Keyword(s):  
Shear Zone ◽  
Simple Shear ◽  
Country Rock ◽  
Shear Zones ◽  
Small Scale ◽  
Lake Zone ◽  
Shear Sense ◽  
Regional Tectonic ◽  
Ductile Shear ◽  
Shear Sense Indicators

Needle Falls Shear Zone is the southern part of a major northeast-trending ductile shear system within the Paleoproterozoic Trans-Hudson Orogen in Saskatchewan. Throughout its exposed length of ~400 km, the shear zone separates reworked Archean continental crust and infolded Paleoproterozoic supracrustals of the Cree Lake Zone, to the northwest, from mainly juvenile Paleoproterozoic arc terrains and granitoid plutons of the Reindeer Zone, to the southeast. It also defines the northwest margin of the ca. 1855 Ma Wathaman Batholith, which forms the main protolith to shear zone mylonites. Although not precisely dated, available age constraints suggest that the shear zone formed between ca. 1855 and 1800 Ma, toward the end of peak thermotectonism in this part of the orogen.In the Needle Falls study area, shear zone mylonites exhibit varied, sequentially developed, ductile to brittle fabric features, including C–S fabrics, winged porphyroclasts (especially delta type), small-scale compressional and extensional microfaults ranging from thin ductile shear zones to late brittle faults, early isoclinal and sheath folds, later asymmetric folds related to compressional microfaults, and variably rotated and (or) folded quartz veins. All ductile shear-sense indicators suggest dextral displacement, as do most later ductile–brittle transition and brittle features. In conjunction with a gently north–northeast-plunging extension lineation, such data indicate oblique east-side-up dextral movement across the shear zone. However, preexisting structures in country rock protoliths rotate into the shear zone in a sense contrary to that predicted by ideal dextral simple shear, a feature thought to reflect significant flattening across the shear zone. Other ductile to brittle fabric elements in the mylonites are consistent with general noncoaxial strain, rather than ideal simple shear. Amount of displacement cannot be measured but indirect estimates suggest approximately 40 ± 20 km.The Needle Falls Shear Zone is too small and has developed too late in regional tectonic history to be considered a crustal suture. Rather, it is interpreted as either a late-tectonic oblique collisional structure or as the result of counterclockwise oroclinal rotation of the southern part of the orogen.

scholarly journals CONTRASTING GEOMETRY BETWEEN ALPINE AND LATE- TO POSTALPINE TECTONIC STRUCTURES IN ANAFI ISLAND (CYCLADES)

2004 ◽  
Vol 36 (4) ◽  
pp. 1688 ◽  
Author(s):  
Konstantinos I. Soukis ◽  
Demetrios J. Papanikolaou
Keyword(s):  
Normal Faults ◽  
Thrust Faults ◽  
High Angle ◽  
Backarc Basin ◽  
Tectonic Structures ◽  
Extensional Deformation ◽  
Upper Miocene ◽  
Deformation Phase ◽  
Shear Sense ◽  
Shear Sense Indicators

A significant change is observed in the geometry of the major faults in Anafi Island from Ν to NE dip in the alpine structures to S to SW dip in the late to post-alpine. Several thrust faults dipping to the NE preserved at the central-eastern part of the island form a nappe pile of Cretaceous HT/LP metamorphic units emplaced over a parautochthonous nonmetamorphic flysch of partly Eocene age without development of metamorphic structures (deformation phase Di). The development of detachment normal faults dipping to the SW (deformation phase D2) deformed the previous thrusts together with the post alpine continental sedimentary sequence of Miocene age, occurring in the northern and western part of Anafi. Asymmetric to the SW folds are observed at the lower part of the Upper Miocene sediments as well as numerous shear sense indicators along the undulating surface of the detachment above the underlying alpine units. The deformation weakens towards the upper part of the Upper Miocene sediments. An intensely sheared molassic type formation of probable ?Oligocene-Early Miocene age was distinguished between the alpine units and the detached Upper Miocene sediments. High angle normal faults dipping to the SW deform all previous structures (D3). The extensional deformation phases D2 and D3 are related to the opening of the Cretan backarc basin during Tortonian - Early Pliocene.

Structure and shear-sense indicators of the Mesoproterozoic basement of the North Tianshan microcontinent: Example of granitoid gneisses of the Karadjilga pluton, NW Kyrgyzstan

2021 ◽  
Author(s):  
Anastasia Kushnareva ◽  
Andrey Khudoley ◽  
Dmitriy Alexeiev ◽  
Eugeny Petrov
Keyword(s):  
Granite Gneiss ◽  
Shear Zones ◽  
Magmatic Complex ◽  
Thin Sections ◽  
Metasedimentary Rocks ◽  
The North ◽  
Rock Types ◽  
Shear Sense ◽  
Granitoid Gneisses ◽  
Shear Sense Indicators

<p>The Mesoproterozoic Karadjilga pluton is a poorly studied fragment of the North Tianshan microcontinent located in the western Central Asian Orogenic Belt. Metasedimentary rocks surrounding the pluton consist of marbles and mica schists of the Mesoproterozoic Ortotau Group. These rocks constitute a major west-northwest trending syncline with steep to subvertical limbs. The hinge of the fold is well expressed in the west part of the syncline and plunges east with 30-40° angle of plunge. Eastern termination of the syncline is cut by faults. Granitoid gneisses and granites of the Karadjilga pluton crop out in the core of the syncline. The contacts of the pluton are sub-parallel to bedding and schistosity in surrounding rocks. Primary magmatic contacts are locally reworked by reverse faults and thrusts. Our detailed mapping and structural study revealed inhomogeneous deformation of rocks of the Karadjilga pluton. The following rock types are identified: 1) undeformed granite 2) foliated granite 3) granite-gneiss and 4) mylonite. Undeformed granites form <25-30% of total volume of the pluton and are most widespread in the northeast part of the pluton. On some geological maps they are shown as Ordovician or Devonian. However, U-Pb dating of 9 zircon grains by SHRIMP-II (VSEGEI, St. Petersburg, Russia) yielded a 1125±5 Ma concordant age. It agrees with previously reported U-Pb SHRIMP ages for deformed granites and gneisses (Degtyarev et al., 2011; Kröner et al., 2013) and indicates that undeformed granites belongs to the same Mesoproterozoic magmatic complex. Foliated granites and gneisses prevail and constitute up to 60-70% of total volume. They form west-northwest trending zones alternating with mylonites or undeformed granite. Mylonites are subordinate and occur mainly along the contacts of the pluton. Shear zones seem to be approximately parallel to the schistosity of deformed granites, but their geometry needs more study and mapping. Shear-sense indicators were studied in the oriented thin sections and are represented mainly by sigma and delta structures and oblique foliation with rare folds and other indicators. In all but one sample only strike-slip displacement has been identified. In the northern part of the pluton sinistral displacement predominates, whereas dextral displacement prevails in the southern part of the pluton. Shear zones are most widespread on the margins of the Karadjilga pluton, but locally also occur in the central part of the pluton, where they form narrow west-northwest trending zones. According to shear-sense indicators, displacement within the Karadjilga pluton occurred mainly in the approximately west-east direction that strongly differs from the north-south sense of displacement in the Paleozoic thrust and fold belts of Tianshan.</p><p>The study was supported by the RFBR project 20-05-00252.</p>

scholarly journals Transpressive dextral shear in the Italva-Itaperuna section, Northern State of Rio de Janeiro, Brazil

2008 ◽  
Vol 80 (3) ◽  
pp. 565-577 ◽  
Author(s):  
Tiago R. Karniol ◽  
Rômulo Machado ◽  
Nolan M. Dehler
Keyword(s):  
Structural Control ◽  
Shear Zones ◽  
Continental Collision ◽  
Southeastern Brazil ◽  
Ductile Shear Zones ◽  
Shear Sense ◽  
Dextral Shear ◽  
Northern State ◽  
Map Scale ◽  
Shear Sense Indicators

Structural analysis carried out on a segment of the Neoproterozoic Ribeira Belt, southeastern Brazil, show that it represents part of the transpressive dextral orogen related to the Central Mantiqueira Province. NNE-trending and steeply dipping regional mylonitic belts form anastomosed geometry, and describe a map-scale, S-C-like structure that is characterized by their deflection towards NE near the Além Paraíba Lineament. Lithological and structural control related to deformation partition were responsible for the formation of felsic mylonitic granulites with S-type granites lenses developed in ductile shear zones, alternated with less deformed intermediate to basic granulites associated with charnockites. The dextral shear sense indicators are consistent with transpressive deformation in the region and are common especially at the border of the main shear zones. The presence of S-type leucogranite may lead to variations of linear and planar relationships, which result in local extension zones. These elements are consistent with oblique continental collision considering the São Francisco Craton as a stable block.

Structure and stratigraphy of the south flank of the Kisseynew Domain in the Trans-Hudson Orogen, Manitoba: implications for 1.845-1.77 Ga collision tectonics

1999 ◽  
Vol 36 (11) ◽  
pp. 1859-1880 ◽  
Author(s):  
Herman V Zwanzig
Keyword(s):  
Volcanic Rocks ◽  
Sedimentary Rocks ◽  
Continental Collision ◽  
High Grade ◽  
The South ◽  
Collision Tectonics ◽  
High Grade Metamorphism ◽  
Thrust System ◽  
Flin Flon ◽  
Superior Craton

On the south flank of the Kisseynew Domain, orthogneisses derived from 1.92-1.85 Ga volcano-plutonic rocks are overlain by paragneisses (Burntwood and Missi groups) derived from 1.855-1.84 Ga marine turbidite and 1.845-1.83 Ga terrestrial clastic and volcanic rocks. The sediments in these groups are interpreted as having been shed into the Kisseynew paleobasin from an active margin bordering the Flin Flon Belt. The sedimentation apparently followed early microcontinental collision and accompanied the last arc magmatism in the Trans-Hudson Orogen. The sedimentary rocks and their basement were deformed into a complexly refolded stack of large recumbent folds. Premetamorphic F1 structures represent a fold and thrust system initiated during the sedimentation. These structures are interpreted as transported toward the Kisseynew Domain in the northeast and the hinterland in the southwest. F2 structures (~1.82 Ga) comprise westerly transported nappes. During 1.82-1.80 Ga high-grade metamorphism, the early structures were overturned, amplified, and refolded. Basement-cored culminations and sheet-like synforms of paragneiss were horizontally attenuated and transported south and southwest. North- and northeast-trending F4 folds and F5 faults formed after 1.79 Ga. The whole cycle of deformation is related to stages of continental collision between the internal (juvenile) zone of the Trans-Hudson Orogen and the three surrounding Archean cratons (Sask, Superior, and Hearne). The F4 upright folds and steep F5 faults are interpreted as the record of intracontinental transpression, strongly controlled by the Superior Craton boundary.

Mafic igneous rocks and mineralisation in the Palaeoproterozoic Ketilidian orogen, South-East Greenland: project SUPRASYD 1996

1997 ◽  
pp. 66-74
Author(s):  
Henrik Stendal ◽  
Wulf Mueller ◽  
Nicolai Birkedal ◽  
Esben I. Hansen ◽  
Claus Østergaard
Keyword(s):  
Mineral Exploration ◽  
Volcanic Rocks ◽  
Shear Zones ◽  
Field Work ◽  
Igneous Rocks ◽  
Border Zone ◽  
The South ◽  
East Greenland ◽  
North West ◽  
Arc Setting

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Stendal, H., Mueller, W., Birkedal, N., Hansen, E. I., & Østergaard, C. (1997). Mafic igneous rocks and mineralisation in the Palaeoproterozoic Ketilidian orogen, South-East Greenland: project SUPRASYD 1996. Geology of Greenland Survey Bulletin, 176, 66-74. https://doi.org/10.34194/ggub.v176.5064 _______________ The multidisciplinary SUPRASYD project (1992–96) focused on a regional investigation of the Palaeoproterozoic Ketilidian orogenic belt which crosses the southern tip of Greenland. Apart from a broad range of geological and structural studies (Nielsen et al., 1993; Garde & Schønwandt, 1994, 1995; Garde et al., 1997), the project included a mineral resource evaluation of the supracrustal sequences associated with the Ketilidian orogen (e.g. Mosher, 1995). The Ketilidian orogen of southern Greenland can be divided from north-west to south-east into: (1) a border zone in which the crystalline rocks of the Archaean craton are unconformably overlain by Ketilidian supracrustal rocks; (2) a major polyphase pluton, referred to as the Julianehåb batholith; and (3) extensive areas of Ketilidian supracrustal rocks, divided into psammitic and pelitic rocks with subordinate interstratified mafic volcanic rocks (Fig. 1). The Julianehåb batholith is viewed as emplaced in a magmatic arc setting; the supracrustal sequences south of the batholith have been interpreted as either (1) deposited in an intra-arc and fore-arc basin (Chadwick & Garde, 1996), or (2) deposited in a back-arc or intra-arc setting (Stendal & Swager, 1995; Swager, 1995). Both possibilities are plausible and infer subduction-related processes. Regional compilations of geological, geochemical and geophysical data for southern Greenland have been presented by Thorning et al. (1994). Mosher (1995) has recently reviewed the mineral exploration potential of the region. The commercial company Nunaoil A/S has been engaged in gold prospecting in South Greenland since 1990 (e.g. Gowen et al., 1993). A principal goal of the SUPRASYD project was to test the mineral potential of the Ketilidian supracrustal sequences and define the gold potential in the shear zones in the Julianehåb batholith. Previous work has substantiated a gold potential in amphibolitic rocks in the south-west coastal areas (Gowen et al., 1993.), and in the amphibolitic rocks of the Kutseq area (Swager et al., 1995). Field work in 1996 was focused on prospective gold-bearing sites in mafic rocks in South-East Greenland. Three M.Sc. students mapped showings under the supervision of the H. S., while an area on the south side of Kangerluluk fjord was mapped by H. S. and W. M. (Fig. 4).

scholarly journals Mise En Évidence De Nouvelles Structures Géologiques Dans La Région De Brobo (Centre De La Côte d’Ivoire). Aide À La Compréhension De La Tectonique Du Paléoprotérozoïque Du Craton Ouest Africain

2018 ◽  
Vol 14 (18) ◽  
pp. 305
Author(s):  
Daï Bi Seydou Mathurin ◽  
Ouattara Gbele ◽  
Koffi Gnammytchet Barthélémy ◽  
Gnanzou Allou ◽  
Coulibaly Inza
Keyword(s):  
Cote D'ivoire ◽  
Field Data ◽  
Côte D’Ivoire ◽  
Volcanic Rocks ◽  
Shear Zones ◽  
Cote D’Ivoire ◽  
Metasedimentary Rocks ◽  
Large Structures ◽  
Côte D'ivoire ◽  
Ductile Shear Zones

The lithological and structural observations of the region of Brobo (Central Côte d'Ivoire) indicate a succession of metasedimentary rocks (micaschists with cordierite, silstones, graphitic sediments, sandstones with amphibole-garnet, etc.) intermixed with volcanic rocks (rhyolite, dacite, andesite, basalt and the volcanoclastics). The whole is intruded by granites with one or two micas, sometimes porphyries, granodiorites, gabbros, and granite gneisses. Interpretations of Landsat ETM+ , RadarSat-1 and SRTM remote sensing imageries, as well as field data, revealed several lineament directions which, after field control, correspond to major faults and shear zones. These large structures show the N-S, NE-SW, NNE-SSW, E-W, NWSE, and NNW-SSE orientations. The field data also made it possible to describe several structures and to propose a preliminary geodynamic model for the setting and structuring of the formations of this region. This model suggests that the geodynamic took place in three stages: distension with a deformation of basement formations generating a gneissocity (D1), as well as deposits of sediments in the basins; followed by a NW-SE to E-W convergence generating a cleavage in the volcanogenic series (D2). This phase of deformation continues while creating, locally, a strain slip cleavage or a transposed schistosity. The third cleavage affects the volcanogenic series (fractures cleavages, D3) and ends in large corridors of ductile shear zones and associated faults.

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