scholarly journals Geological and geochemical implications of the genesis of the Qolqoleh orogenic gold mineralisation, Kurdistan Province (Iran)

Geologos ◽  
2015 ◽  
Vol 21 (1) ◽  
pp. 31-57 ◽  
Author(s):  
Batoul Taghipour ◽  
Farhad Ahmadnejad
Keyword(s):  
Shear Zone ◽  
Early Stage ◽  
Hanging Wall ◽  
Regional Metamorphism ◽  
Shear Zones ◽  
Northwestern Part ◽  
Type I ◽  
Two Phase ◽  
Mean Values ◽  
Calcite Veins

Abstract The Qolqoleh gold deposit is located in the northwestern part of the Sanandaj-Sirjan Zone (SSZ), within the NE-SW trending Qolqoleh shear zone. Oligocene granitoids, Cretaceous meta-limestones, schists and metavolcanics are the main lithological units. Chondrite-normalised REE patterns of the ore-hosting metavolcanics indicate REE enrichment relative to hanging wall (chlorite-sericite schist) and footwall (meta-limestone) rocks. The pattern also reflects an enrichment in LREE relative to HREE. It seems that the LREE enrichment is related to the circulation of SO42- and CO2-bearing fluids and regional metamorphism in the Qolqoleh shear zone. Both positive and negative Eu anomalies are observed in shear-zone metavolcanics. These anomalies are related to the degree of plagioclase alteration during gold mineralisation and hydrothermal alteration. In progressing from a metavolcanic protomylonite to an ultramylonite, significant changes occurred in the major/trace element and REE concentration. Utilising an Al-Fe-Ti isocon for the ore-hosting metavolcanics shows that Sc, Y, K, U, P, and M-HREE (except Eu) are relatively unchanged; S, As, Ag, Au, Ca, LOI, Rb and LREE are enriched, and Sr, Ba, Eu, Cr, Co and Ni decrease with an increasing degree of deformation. Based on geochemical features and comparison with other well-known shear zones in the world, the study area is best classified as an Isovolume-Gain (IVG) type shear zone and orogenic type gold mineralisation. Based on the number of phases observed at room temperature and their microthermometric behaviour, three fluid inclusion types have been recognised in quartz-sulphide and quartz-calcite veins: Type I monophase aqueous inclusions, Type II two-phase liquid-vapour (L-V) inclusions which are subdivided into two groups based on the homogenisation temperature (Th): a) L-V inclusions with Th from 205 to 255°C and melting temperature of last ice (Tm) from -3 to -9°C. b) L-V inclusions with higher Th from 335 to 385°C and Tm from -11 to -16°C. Type III three-phase carbonic-liquid inclusions (liquid water-liquid CO2-vapour CO2) with Th of 345-385°C. The mean values of the density of ore-forming fluids, pressure and depth of mineralisation have been calculated to be 0.79-0.96 gr/cm3, 2 kbar and 7 km, respectively. The δ18Owater and δD values of the gold-bearing quartz-sulphide veins vary from 7.2‰ to 8‰ and -40.24‰ to -35.28‰, respectively, which are indicative of an isotopically heavy crustal fluid and likely little involvement of meteoric fluid. The δ18Owater values of the quartz-calcite veins have a range of -5.31‰ to -3.35‰, and the δD values of -95.65‰ to -75.31‰, which are clearly lower than those of early-stage quartz-sulphide-gold veins, and are close to the meteoric water line. Based on comparisons of the D-O isotopic systematics, the Qolqoleh ore-mineralising fluids originated from metamorphic devolatilisation of Cretaceous volcano-sedimentary piles. Devolatilisation of these units occurred either synchronously with, or postdates, the development of penetrative (ductile) structures such as shear zones and during overprinting brittle deformation

Gold Deposits of the ~15-Moz Ahafo South Camp, Sefwi Granite-Greenstone Belt, Ghana: Insights into the Anatomy of an Orogenic Gold Plumbing System

2021 ◽  
Author(s):  
Quentin Masurel ◽  
Paul Morley ◽  
Nicolas Thébaud ◽  
Helen McFarlane
Keyword(s):  
Rock Mass ◽  
Shear Zone ◽  
Gold Mineralization ◽  
Hanging Wall ◽  
Spatial Association ◽  
Sedimentary Rocks ◽  
Shear Zones ◽  
Gold Deposits ◽  
Orogenic Gold ◽  
Plutonic Rocks

Abstract The ~15-Moz Ahafo South gold camp is located in southwest Ghana, the world’s premier Paleoproterozoic gold subprovince. Major orogenic gold deposits in the camp include Subika, Apensu, Awonsu, and Amoma. These deposits occur along an ~15-km strike length of the Kenyase-Yamfo shear zone, a major tectonostratigraphic boundary juxtaposing metamorphosed volcano-plutonic rocks of the Sefwi belt against metamorphosed volcano-sedimentary rocks of the Sunyani-Comoé basin. In this study, we document the geologic setting, structural geometry, and rheological architecture of the Ahafo South gold deposits based on the integration of field mapping, diamond drill core logging, 3-D geologic modeling, and the geologic interpretation of aeromagnetic data. At the camp scale, the Awonsu, Apensu, and Amoma deposits lie along strike from one another and share similar hanging-wall plutonic rocks and footwall volcano-sedimentary rocks. In contrast, the Subika gold deposit is hosted entirely in hanging-wall plutonic rocks. Steeper-dipping segments (e.g., Apensu, Awonsu, Subika) and right-hand flexures (e.g., Amoma, Apensu) in the Kenyase-Yamfo shear zone and subsidiary structures appear to have represented sites of enhanced damage and fluid flux (i.e., restraining bends). All gold deposits occur within structural domains bounded by discontinuous, low-displacement, sinistral N-striking tear faults oblique to the orogen-parallel Kenyase-Yamfo shear zone. At the deposit scale, ore-related hydrothermal alteration is zoned, with distal chlorite-sericite grading into proximal silica-albite-Fe-carbonate mineral assemblages. Alteration halos are restricted to narrow selvages around quartz-carbonate vein arrays in multiple stacked ore shoots at Subika, whereas these halos extend 30 to 100 m away from the ore zones at Apensu and Awonsu. There is a clear spatial association between shallow-dipping mafic dikes, mafic chonoliths, shear zones, and economic gold mineralization. The abundance of mafic dikes and chonoliths within intermediate to felsic hanging-wall plutonic host rocks provided rheological heterogeneity that favored the formation of enhanced fracture permeability, promoting the tapping of ore fluid(s). Our interpretation is that these stacked shallow-dipping mafic dike arrays also acted as aquitards, impeding upward fluid flow within the wider intrusive rock mass until a failure threshold was episodically reached due to fluid overpressure, resulting in transient fracture-controlled upward propagation of the ore-fluid(s). Our results indicate that high-grade ore shoots at Ahafo South form part of vertically extensive fluid conduit systems that are primarily controlled by the rheological architecture of the rock mass.

Complex kinematics in a major ductile shear zone, NW Shetland: Evidence of ductile extrusion during Caledonian transpression

2021 ◽  
Author(s):  
Timothy Armitage ◽  
Robert Holdsworth ◽  
Robin Strachan ◽  
Thomas Zach ◽  
Diana Alvarez-Ruiz ◽  
...  
Keyword(s):  
Shear Zone ◽  
Hanging Wall ◽  
Regional Scale ◽  
Shear Zones ◽  
White Mica ◽  
Strike Slip ◽  
Amphibolite Facies ◽  
Lateral Extrusion ◽  
Shear Sense ◽  
Ductile Shear

<p>Ductile shear zones are heterogeneous areas of strain localisation which often display variation in strain geometry and combinations of coaxial and non-coaxial deformation. One such heterogeneous shear zone is the c. 2 km thick Uyea Shear Zone (USZ) in northwest Mainland Shetland (UK), which separates variably deformed Neoarchaean orthogneisses in its footwall from Neoproterozoic metasediments in its hanging wall (Fig. a). The USZ is characterised by decimetre-scale layers of dip-slip thrusting and extension, strike-slip sinistral and dextral shear senses and interleaved ultramylonitic coaxially deformed horizons. Within the zones of transition between shear sense layers, mineral lineations swing from foliation down-dip to foliation-parallel in kinematically compatible, anticlockwise/clockwise-rotations on a local and regional scale (Fig. b). Rb-Sr dating of white mica grains via laser ablation indicates a c. 440-425 Ma Caledonian age for dip-slip and strike-slip layers and an 800 Ma Neoproterozoic age for coaxial layers. Quartz opening angles and microstructures suggest an upper-greenschist to lower-amphibolite facies temperature for deformation. We propose that a Neoproterozoic, coaxial event is overprinted by Caledonian sinistral transpression under upper greenschist/lower amphibolite facies conditions. Interleaved kinematics and mineral lineation swings are attributed to result from differential flow rates resulting in vertical and lateral extrusion and indicate regional-scale sinistral transpression during the Caledonian orogeny in NW Shetland. This study highlights the importance of linking geochronology to microstructures in a poly-deformed terrane and is a rare example of a highly heterogeneous shear zone in which both vertical and lateral extrusion occurred during transpression.</p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.0cf6ef44e5ff57820599061/sdaolpUECMynit/12UGE&app=m&a=0&c=d96bb6db75eed0739f2a6ee90c9ad8fd&ct=x&pn=gepj.elif&d=1" alt=""></p>

Metagabbronorite from DSDP hole 334: an example of high-temperature deformation and recrystallization near the Mid-Atlantic Ridge

1977 ◽  
Vol 14 (4) ◽  
pp. 886-898 ◽  
Author(s):  
Herwart Helmstaedt ◽  
John M. Allen
Keyword(s):  
Shear Zone ◽  
Regional Metamorphism ◽  
Shear Zones ◽  
Granulite Facies ◽  
High Temperature Deformation ◽  
Temperature Deformation ◽  
Mid Atlantic Ridge ◽  
Magmatic History ◽  
Highly Strained ◽  
Zoned Plagioclase

Five gabbros and three peridotites from hole 334 were examined for postmagmatic deformational changes and metamorphic recrystallization. The condition of the gabbros ranges from unaltered, to slightly altered and deformed, to highly deformed and metamorphosed, the latter type being confined to narrow shear zones. Petrofabric studies and electron microprobe analyses of mineral phases of a foliated metagabbronorite from such a shear zone suggest the following post-magmatic history: (1) strong plastic deformation and anhydrous synkinematic recrystallization of igneous plagioclase (An90−85), clinopyroxene, and orthopyroxene to the granulite facies mineral assemblage of strongly zoned plagioclase (An80−65), diopside, and orthopyroxene; relics of the igneous minerals survived as highly strained porphyroclasts; (2) synkinematic growth of amphibole consisting of a patchy intergrowth of tremolite and actinolitic hornblende; the amphibole fabric is compatible with strain estimates by the centre-point method; (3) mainly static hydrous alteration — growth of (?) vermiculite and sericitization.Penetrative deformation probably initiated shortly after intrusion and took place during cooling of the rocks from approximately 800 °C to 300 °C. The bulk of the strain in the metagabbronorite of the shear zone predates the serpentinization of the peridotites. Many textural and fabric features in alpine-type gabbro–peridotite complexes that are ascribed to regional metamorphism and deformation during orogenic emplacement may originate shortly after intrusion near or at an accreting plate margin.

Geology of the shear-hosted Brookbank gold prospect in the Beardmore–Geraldton belt, Wabigoon subprovince, Ontario

2007 ◽  
Vol 44 (7) ◽  
pp. 925-946 ◽  
Author(s):  
Jerry C DeWolfe ◽  
Bruno Lafrance ◽  
Greg M Stott
Keyword(s):  
Shear Zone ◽  
Hanging Wall ◽  
Shear Zones ◽  
Gold Deposits ◽  
Iron Formation ◽  
Alteration Zone ◽  
Gold Deposition ◽  
Low Grade ◽  
Metasedimentary Rocks ◽  
Polymictic Conglomerate

The Beardmore–Geraldton belt consists of steeply dipping, intercalated panels of metavolcanic and metasedimentary rocks along the southern margin of the granite–greenstone Wabigoon subprovince in the Archean Superior Province, Ontario. It is an important past-producing gold belt that includes classic epigenetic iron-formation-hosted deposits near Geraldton and turbidite-hosted deposits, north of Beardmore. The Brookbank gold prospect belongs to a third group of related gold deposits that formed along dextral shear zones localized at contacts between panels of metasedimentary and metavolcanic rocks. The Brookbank prospect occurs along a steeply dipping shear zone at the contact between footwall polymictic conglomerate and hanging-wall calc-alkaline arc basalt. Early during shearing the basalt acted as a structural and chemical trap that localized brittle deformation, veining, and gold deposition, ankerite–sericite–chlorite–epidote–pyrite alteration, and the replacement of metamorphic magnetite and ilmenite by gold-bearing pyrite. This produced a low grade (≤5 g/t Au) ankerite-rich alteration zone that extends up to 20 m into the hanging-wall basalt. Later during shearing, gold was deposited within higher grade (≤20 g/t Au) quartz–orthoclase–pyrite alteration zones superimposed on the wider ankerite-rich alteration zone. Auriferous quartz–carbonate veins oriented clockwise and counter-clockwise to the shear zone walls are folded and boudinaged, respectively, consistent with dextral slip along the shear zone. A key finding of the study is that different groups of gold deposits in the belt, including epigenetic iron formation gold deposits near Geraldton, formed during post-2690 Ma regional dextral transpression across the belt.

Gas Flow Through Water-Saturated Shear Zones: Field and Laboratory Experiments and Their Interpretation

1997 ◽  
Vol 506 ◽  
Author(s):  
P. Marschall ◽  
J. Croisé ◽  
U. Fischer ◽  
R. Senger ◽  
E. Wyss
Keyword(s):  
Shear Zone ◽  
Gas Flow ◽  
Two Phase Flow ◽  
Gas Permeability ◽  
Numerical Models ◽  
Shear Zones ◽  
Parameter Estimates ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Processes

ABSTRACTGas threshold pressure tests and gas tracer tests have been performed at the Grimsel Test Site to study two-phase flow processes in a shear zone. In addition, capillary pressure and gas permeability measurements were carried out in the laboratory on drillcore samples. The laboratory investigations were complemented by assessing the pore structure of the shear zone material. The interpretation of the field tests with numerical models indicated that the structural and two-phase flow parameters to be determined are highly correlated with one another and, consequently, the parameter estimates can be rather uncertain. The joint interpretation of field and laboratory results, however, led to a more stringent description of the two-phase flow processes, expressed by a better overall fit of the test data and smaller uncertainty ranges of the estimated parameters. The results showed that the gas mobility in the shear zone was very high even at high water saturation and gas flow was limited to the narrow zones of brittle deformation along the shear zone.

scholarly journals Fluid inclusion study of shear zone hosted lode gold type deposits: El Bagre mining district, Antioquia-Colombia

2020 ◽  
Vol 24 (3) ◽  
pp. 245-257
Author(s):  
Edwin Naranjo Sierra ◽  
Mauricio Alvaran Echeverri
Keyword(s):  
Fluid Inclusion ◽  
Shear Zone ◽  
Gold Deposits ◽  
Fluid Inclusion Study ◽  
Mining District ◽  
Type I ◽  
Lode Gold ◽  
Calcite Veins ◽  
Inclusion Study ◽  
Homogenization Temperatures

The shear zone hosted lode gold type deposits are located at the northeast part of Antioquia department of Colombia. The characteristics of ore-forming fluids were discussed using fluid inclusion petrography and microthermometry analysis. Two stages, namely quartz-pyrite pre-mineralization stage (1) and reactivation-sulfides-tellurides mineralization stage (2) were included in this study. Two types of fluid inclusions were observed: primary aqueous-carbonic inclusions (type I) are characterized by the presence of clathrate, with salinities between 1.5 and 8.3 %wt NaCl equiv. and homogenization temperatures (to liquid) occurs between 238.1° and 297.1°C. Secondary aqueous inclusions (type II) were trapped in reactivated quartz (type IIa) and cross-cutting calcite veins (type IIb), salinity estimates display a mixing trend from a relatively saline with 9.21 %wt NaCl member (type IIa) to a low salinity one with 3.82 %wt NaCl (type IIb), homogenizations to a liquid phase occur between 150.8° and 184.6°C for type IIa inclusions and 130.3° to 190.4°C for type IIb. Based on these results, the shear zone hosted lode gold type deposits from El Bagre mining district, share similar characteristics with orogenic gold deposits.

Role of Fluid State Mobilization during Metamorphism of the Henderson Ore Bodies, Chibougamau, Quebec, Canada

1975 ◽  
Vol 12 (9) ◽  
pp. 1516-1523 ◽  
Author(s):  
Jayanta Guha ◽  
Jahak Koo
Keyword(s):  
Shear Zone ◽  
Regional Metamorphism ◽  
Volcanic Rocks ◽  
Low Grade ◽  
Fluid State ◽  
Ore Bodies ◽  
Calcite Veins ◽  
Intense Deformation ◽  
State Mobilization

The Henderson Cu-Au deposit occurs in discordant structures within the anorthosite zone of the Doré Lake Complex. The Doré Lake Complex is intruded into volcanic rocks of the Chibougamau greenstone belt on the southeastern side of the Superior Province. Massive to disseminated sulfide ores are associated with sericite, carbonate, chlorite and/or chloritoid schists within a large 'shear zone'. These ores show structural and textural evidence of intense deformation, recrystallization, and metamorphic mobilization.The deposit comprises not only sulfide schist ore with alternating sulfide and schist layers, but also 'hydrothermal' vein-type segregation ore. The latter is characterized by sulfide-bearing quartz-calcite veins that occur in the 'shear zone' and in the subsidiary fractures adjacent to it.The sulfide schist and vein types of ores can be attributed to partly solid state mobilization combined with fluid state mobilization from a pre-existing ore, and is an excellent example of extensive fluid state mobilization of sulfides under relatively low-grade regional metamorphism. It is suggested that fluid state mobilization can play an important role during the metamorphism of a pre-existing sulfide body, especially in the presence of differential stress accompanied with rupture. The deformational features of the ore are the important indication for syn- and/or pre-metamorphic origin of the ore.

scholarly journals Structural and thermal evolution of the eastern Aar Massif: insights from structural field work and Raman thermometry

2021 ◽  
Vol 114 (1) ◽  
Author(s):  
Lukas Nibourel ◽  
Alfons Berger ◽  
Daniel Egli ◽  
Stefan Heuberger ◽  
Marco Herwegh
Keyword(s):  
Shear Zone ◽  
Hanging Wall ◽  
Shear Zones ◽  
Swiss Alps ◽  
Normal Faults ◽  
En Bloc ◽  
Temperature Conditions ◽  
Kinematic Evolution ◽  
Structural Style ◽  
Aar Massif

AbstractThe thermo-kinematic evolution of the eastern Aar Massif, Swiss Alps, was investigated using peak temperature data estimated from Raman spectroscopy of carbonaceous material and detailed field analyses. New and compiled temperature-time constraints along the deformed and exhumed basement-cover contact allow us to (i) establish the timing of metamorphism and deformation, (ii) track long-term horizontal and vertical orogenic movements and (iii) assess the influence of temperature and structural inheritance on the kinematic evolution. We present a new shear zone map, structural cross sections and a step-wise retrodeformation. From $$\text{ca.\;26\,Ma}$$ ca.\;26\,Ma onwards, basement-involved deformation started with the formation of relatively discrete NNW-directed thrusts. Peak metamorphic isograds are weakly deformed by these thrusts, suggesting that they initiated before or during the metamorphic peak under ongoing burial in the footwall to the basal Helvetic roof thrust. Subsequent peak- to post-metamorphic deformation was dominated by steep, mostly NNW-vergent reverse faults ($$\text{ca.}$$ ca.  22–14 Ma). Field investigations demonstrate that these shear zones were steeper than $$50^{\circ}$$ 50 ∘ already at inception. This produced the massif-internal structural relief and was associated with large vertical displacements (7 km shortening vs. up to 11 km exhumation). From 14 Ma onwards, the eastern Aar massif exhumed “en bloc” (i.e., without significant differential massif-internal exhumation) in the hanging wall of frontal thrusts, which is consistent with the transition to strike-slip dominated deformation observed within the massif. Our results indicate 13 km shortening and 9 km exhumation between 14 Ma and present. Inherited normal faults were not significantly reactivated. Instead, new thrusts/reverse faults developed in the basement below syn-rift basins, and can be traced into overturned fold limbs in the overlying sediment, producing tight synclines and broad anticlines along the basement-cover contact. The sediments were not detached from their crystalline substratum and formed disharmonic folds. Our results highlight decreasing rheological contrasts between (i) relatively strong basement and (ii) relatively weak cover units and inherited faults at higher temperature conditions. Both the timing of basement-involved deformation and the structural style (shear zone dip) appear to be controlled by evolving temperature conditions.

scholarly journals Multiple fluid migration events and REE+Th mineralisation during Alpine metamorphism in the Sopron micaschist from the Eastern-Alps (Sopron area, Western Hungary)

2020 ◽  
Vol 150 (1) ◽  
pp. 45
Author(s):  
Kálmán Török
Keyword(s):  
Shear Zone ◽  
Host Rock ◽  
Shear Zones ◽  
Mineral Chemistry ◽  
Eastern Alps ◽  
Aqueous Fluid ◽  
Fluid Migration ◽  
Two Phase ◽  
Quartz Veins ◽  
Alpine Metamorphism

Four fluid migration events were recorded during the Alpine metamorphism in the Sopron micaschist from the Grob gneiss series of the Lower Austroalpine Unit of the Eastern Alps near Sopron, using mineral chemistry data, geothermo-barometry and fluid inclusion studies.1. Tourmaline mineralisation in quartz veins and to some extent in the host rock. Similar mineral compositions in the quartz-tourmaline veins and in the host rock show equilibrium between fluid and the host rock. Geothermo-barometry gives 560-610oC temperature and 950-1230 MPa pressure for the formation of quartz-tourmaline veins which is the same as the determined P-T peak (T=560 and 600°C p= 840-1230 MPa).2. Fluids causing Mg-metasomatism in the shear zones. The result of this fluid invasion was the formation of leucophyllite in the shear zones and Mg-enrichment of some minerals (chlorite, muscovite, garnet) in the close vicinity of the shear zone. The effect of this fluid was confined to the shear zones and the neighbouring host rock.3. The rock was infiltrated along the shear zones and quartz veins with CO2-bearing hypersaline fluids during retrograde metamorphism. The presence of this fluid is evidenced by secondary CO2 inclusions and hypersaline aqueous fluid inclusions ± CO2. The aqueous fluid had high concentrations of Na, Ca, Fe, Al, Cl and contained moderate amounts of Mg, Zn, Ti, K, Mn, S and P. This fluid was the carrier of the REE and Th and locally precipitated florencite, monazite, allanite, apatite, thorite and thorianite in the shear zone. Traces of this mineralisation are found in quartz-tourmaline veins, postdating the tourmaline mineralisation.4. Late retrograde metamorphic fluid represented by two phase (liquid+vapor) aqueous inclusions of the NaCl-CaCl2-H2O system with total salinity between 25 and 28.5% and homogenisation temperatures between 229.6 and 322oC

U/Pb geochronological constraints on Neoarchean tectonism: multiple compressional events in the northwestern Hearne Domain, Western Churchill Province, Canada

2005 ◽  
Vol 42 (1) ◽  
pp. 85-109 ◽  
Author(s):  
Kate MacLachlan ◽  
William J Davis ◽  
Carolyn Relf
Keyword(s):  
Shear Zone ◽  
Hanging Wall ◽  
Shear Zones ◽  
Crustal Thickening ◽  
Lake Area ◽  
Thermal Event ◽  
Grade Metamorphism ◽  
Geochronological Constraints

In the Yathkyed Lake area the Tyrrell shear zone (TSZ) marks the boundary between the northwestern and central Hearne subdomains of the Western Churchill Province. The TSZ is dominated by Proterozoic dextral strain, but in areas of low dextral strain, older shear fabrics are consistent with an earlier thrusting event. Four syntectonic granite sheets from within low-dextral-strain zones in the TSZ and contiguous shear zones at the base of the Yathkyed belt have ages of 2636–2629, 2652 ± 8, 2665–2639, and 2644 ± 3 Ma. The Yathkyed belt occurs in the hanging wall of these shear zones and comprises a greenschist- to amphibolite-grade, overturned panel that is overlain by an upper amphibolite-grade polydeformed panel. The geometry is consistent with a thrust-imbricated stack. Two episodes of deformation in the hanging wall are bracket between ca. 2660 and 2616 +6–4 Ma and between 2616 +6–4 Ma and ca. 2.60 Ga. The Yathkyed belt is interpreted to have initially been emplaced as a thick-skinned, thrust nappe along the TSZ, during 2.66–2.62 Ga tectonism, and reactivated at ca. 2.62–2.60 Ga, causing further crustal thickening. In the Upper Panel, protracted upper amphibolite-grade metamorphism and associated anatectic melting are recorded by zircon, titanite, and monazite ages ranging from ca. 2561 to 2492 Ma. This thermal event is in part attributed to burial in response to ca. 2.62–2.60 Ga thrust reactivation. The timing and means of emplacement of the Upper Panel on top of the Lower Panel is uncertain; however, ca. 2.50 Ga thrusting elsewhere in the northwestern Hearne subdomain provides one possible mechanism.

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