U–Pb geochronology of the Raglan gabbro belt, Central Metasedimentary Belt, Ontario: implications for an ensialic marginal basin in the Grenville Orogen

1996 ◽  
Vol 33 (5) ◽  
pp. 691-702 ◽  
Author(s):  
Sally Pehrsson ◽  
Simon Hanmer ◽  
Otto van Breemen
Keyword(s):  
Shear Zone ◽  
Hanging Wall ◽  
Island Arc ◽  
Northwestern Part ◽  
Marginal Basin ◽  
Arc Model ◽  
Minimum Age ◽  
Thrust Zone ◽  
Stiff Material ◽  
Central Gneiss Belt

The Raglan gabbro belt of the Ontario Grenville Orogen is coincident with the top of the Central Metasedimentary Belt boundary thrust zone, a major mid-crustal shear zone separating the Central Gneiss Belt in the footwall from the Central Metasedimentary Belt in the hanging wall. It has been suggested that the gabbros making up the belt are coeval, that they formed in a marginal basin within the Central Metasedimentary Belt, and that they formed a horizon of Theologically stiff material that controlled the localization of the top of the boundary thrust zone during its initiation as the marginal basin closed at ca. 1190 Ma. U–Pb zircon dating of plutons within the Raglan gabbro belt was undertaken to test the coeval nature of intrusions in the belt. Magmatic crystallization ages for three of the gabbros fall in the range 1246–1227 Ma, and a fourth yields a minimum age of ca. 1175 Ma. The results are permissive of a common origin for the gabbros and allow that the Raglan gabbro belt may have been related to the marginal basin, at least with respect to the later stages of its evolution. Inherited 1440–1301 Ma zircons in the gabbros suggest interaction with underlying Central Gneiss Belt crust during magmatism and support an ensialic marginal-basin model, as opposed to an island-arc model, for the evolution of the northwestern part of the Central Metasedimentary Belt.

Age of deformation within the Central Metasedimentary Belt boundary thrust zone, southwest Grenville Orogen: constraints on the collision of the Mid-Proterozoic Elzevir terrane

1993 ◽  
Vol 30 (6) ◽  
pp. 1155-1165 ◽  
Author(s):  
Sally J. McEachern ◽  
Otto van Breemen
Keyword(s):  
Shear Zone ◽  
Hanging Wall ◽  
Amphibolite Facies ◽  
Marginal Basin ◽  
Structural Nature ◽  
Thrust Zone ◽  
Laurentian Margin ◽  
Weak Structure ◽  
Scale Shear

U–Pb zircon and titanite geochronology on syntectonic intrusions from the Ontario Central Metasedimentary Belt boundary thrust zone has constrained the timing of two major periods of northwest-directed ductile thrusting on this crustal-scale shear zone. Initiation of deep-seated uppermost amphibolite facies deformation is constrained to a period before 1190 Ma, over 100 Ma earlier than previous estimates. Major reimbrication of the shear zone took place ca. 1080 – 1060 Ma and was more pronounced in the southwestern segment. The initiation of deformation within the boundary thrust zone coincides with the emplacement of the hanging wall Elzevir terrane of the Central Metasedimentary Belt onto the Mid-Proterozoic Laurentian margin. The structural nature and temporal and kinematic consistency of the reimbrication phase along the 200 km exposed length of the shear zone is thought to be due to within-plate reactivation of the existing, rheologically weak structure, a result of continent–continent collision ca. 1080–1060 Ma during the later stage of the Grenville orogenic cycle.Collision of the Elzevir terrane, interpreted to be an ensialic marginal basin, with the Laurentian margin along the Central Metasedimentary Belt boundary thrust zone is thought to potentially record closure of the marginal basin ca. 1190 Ma. A distinctive tonalitic suite of rocks preserved in the boundary thrust zone may be composed of fragments of the remnant arc to the marginal basin.

Timing of events in an Early Cretaceous island arc–marginal basin system on South Georgia

1979 ◽  
Vol 116 (3) ◽  
pp. 167-179 ◽  
Author(s):  
P. W. G. Tanner ◽  
D. C. Rex
Keyword(s):  
Continental Crust ◽  
Island Arc ◽  
Magmatic Arc ◽  
South Georgia ◽  
Marginal Basin ◽  
Early Mesozoic ◽  
Mafic Complex ◽  
Minimum Age ◽  
Radiometric Ages ◽  
Basin System

Summary19 new K–Ar mineral ages of 78-201 Ma and 3 Rb–Sr whole rock isochron ages of 81 ± 10, 127±4 and 181±30 Ma are presented from units of continental crust, mafic complex and island arc assemblage on South Georgia. The Drygalski Fjord Complex, part of the possible floor of the marginal basin in the southern part of the island, includes granodiorite and gabbro plutons of minimum age 180–200 Ma. Together with older metasediments they have been affected by a major thermal event at about 140 Ma, thought to have resulted from the emplacement of a mafic complex (Larsen Harbour Formation) during the initial opening of the marginal basin. Rocks of the Larsen Harbour Formation are cut by the Smaaland Cove intrusion dated by Rb–Sr whole rock isochron at 127±4 Ma. An island arc assemblage exposed to the SW of South Georgia consists of pyroclastic rocks cut by monzodiorite and andesite intrusions, which give radiometric ages of 81–103 Ma. These data suggest that the marginal basin opened during the late Jurassic (pre-140 Ma); that part of an earlier (early Mesozoic) magmatic arc is preserved in continental crust making up part of the floor of the basin; and that subduction continued beneath the island arc until at least the Senonian time. The younger plutons in the arc were emplaced at roughly the same time as turbidite facies rocks at deep levels in the marginal basin were being affected by penetrative deformation and metamorphism. The timing of events on South Georgia agrees closely with that deduced for the continuation of the same island arc–marginal basin system in South America. The 180–200 Ma plutons correlate with an older suite of plutonic rocks reported from the Antarctic Peninsula and southern Andes; they are part of a once-continuous magmatic arc related to subduction of the Pacific plate beneath Gondwanaland during the early Mesozoic.

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

Paleoproterozoic reworking of an Archean thrust fault in the Hearne domain, Western Churchill Province: U–Pb geochronological constraints

2005 ◽  
Vol 42 (7) ◽  
pp. 1313-1330 ◽  
Author(s):  
K MacLachlan ◽  
W J Davis ◽  
C Relf
Keyword(s):  
Shear Zone ◽  
Hanging Wall ◽  
Thrust Fault ◽  
Lake Area ◽  
High Grade ◽  
Facies Metamorphism ◽  
Minimum Age ◽  
Geochronological Constraints ◽  
Basement Deformation ◽  
And Control

The nature, timing and control of Archean crustal architecture on the distribution of Proterozoic reworking in Western Churchill Province are investigated in the Yathkyed Lake area, central Nunavut. The Tyrrell shear zone (TSZ) marks the boundary between the northwestern and central Hearne subdomains, respectively, in the hanging wall and footwall. Metamorphism and deformation in the hanging wall are ca. 2.66–2.50 Ga. Two episodes of metamorphism are recorded in a foliated granodiorite in the footwall, at 1818+5–2 and 1827 ± 5.6 Ma. The latter age is interpreted as the time of amphibolite-facies metamorphism and deformation in the footwall. A crosscutting dyke provides a minimum age of 1818 ± 2 Ma for this metamorphism and deformation. The TSZ is dominated by dextral oblique-slip shear fabrics. A suite of leucogranite dykes provide a maximum age of 1816 ± 2 Ma for dextral shearing. Dextral deformation is bracketed between 1815 ± 2 and 1811 ± 1 Ma, the ages of two other granitoid dykes. In an area of low dextral strain, there are proto-sheath folds related to Neoarchean thrusting. Paleoproterozoic transtensional shearing in the TSZ was localized along a preexisting late Archean thrust fault. The prior existence of this structure resulted in localization of penetrative Paleoproterozoic deformation in its footwall. This domain of high-grade Proterozoic deformation was uplifted in a regional, antiformal, metamorphic culmination, in part, by dextral-normal shearing along the TSZ. Penetrative basement deformation at depth played a role in transmitting farfield stresses related to the Trans-Hudson Orogen into its hinterland.

Terranes

1992 ◽  
Vol 13 (1) ◽  
pp. 1-4 ◽  
Author(s):  
B. J. Bluck ◽  
W. Gibbons ◽  
J. K. Ingham
Keyword(s):  
Hanging Wall ◽  
Fault System ◽  
Upper Proterozoic ◽  
Lower Proterozoic ◽  
Central Highland ◽  
Thrust Zone ◽  
Lower Palaeozoic ◽  
Moine Thrust Zone ◽  
Shallow Marine Sediments ◽  
Northern Highlands

AbstractThe Precambrian and Lower Palaeozoic foundations of the British Isles may be viewed as a series of suspect terranes whose exposed boundaries are prominent fault systems of various kinds, each with an unproven amount of displacement. There are indications that they accreted to their present configuration between late Precambrian and Carboniferous times. From north to south they are as follows.In northwest Scotland the Hebridean terrane (Laurentian craton in the foreland of the Caledonian Orogen) comprises an Archaean and Lower Proterozoic gneissose basement (Lewisian) overlain by an undeformed cover of Upper Proterozoic red beds and Cambrian to early mid Ordovician shallow marine sediments. The terrane is cut by the Outer Isles Thrust, a rejuvenated Proterozoic structure, and is bounded to the southeast by the Moine Thrust zone, within the hanging wall of which lies a Proterozoic metamorphic complex (Moine Supergroup) which constitutes the Northern Highlands terrane. The Moine Thrust zone represents an essentially orthogonal closure of perhaps 100 km which took place during Ordovician-Silurian times (Elliott & Johnson 1980). The Northern Highlands terrane records both Precambrian and late Ordovician to Silurian tectonometamorphic events (Dewey & Pankhurst 1970) and linkage with the Hebridean terrane is provided by slices of reworked Lewisian basement within the Moine Supergroup (Watson 1983).To the southwest of the Great Glen-Walls Boundary Fault system lies the Central Highlands (Grampian) terrane, an area dominated by the late Proterozoic Dalradian Supergroup which is underlain by a gneissic complex (Central Highland Granulites) that has been variously interpreted as either older

scholarly journals Monazite U–Th–Pb geochronology of the Central Metasedimentary Belt Boundary Zone (CMBbz), Grenville Province, Ontario Canada

2018 ◽  
Vol 55 (9) ◽  
pp. 1063-1078 ◽  
Author(s):  
Michelle J. Markley ◽  
Steven R. Dunn ◽  
Michael J. Jercinovic ◽  
William H. Peck ◽  
Michael L. Williams
Keyword(s):  
Shear Zone ◽  
Crustal Thickening ◽  
Boundary Zone ◽  
Grenville Province ◽  
Metamorphic History ◽  
Crustal Thinning ◽  
Tectonic Significance ◽  
History Of ◽  
Central Gneiss Belt ◽  
Scale Shear

The Central Metasedimentary Belt boundary zone (CMBbz) is a crustal-scale shear zone that juxtaposes the Central Gneiss Belt and the Central Metasedimentary Belt of the Grenville Province. Geochronological work on the timing of deformation and metamorphism in the CMBbz is ambiguous, and the questions that motivate our study are: how many episodes of shear zone activity did the CMBbz experience, and what is the tectonic significance of each episode? We present electron microprobe data from monazite (the U–Th–Pb chemical method) to directly date deformation and metamorphism recorded in five garnet–biotite gneiss samples collected from three localities of the CMBbz of Ontario (West Guilford, Fishtail Lake, and Killaloe). All three localities yield youngest monazite dates ca. 1045 Ma; most of the monazite domains that yield these dates are high-Y rims. In comparison with this common late Ottawan history, the earlier history of the three CMBbz localities is less clearly shared. The West Guilford samples have monazite grain cores that show older high-Y domains and younger low-Y domains; these cores yield a prograde early Ottawan (1100–1075 Ma) history. The Killaloe samples yield a well-defined prograde, pre- to early Shawinigan history (i.e., 1220–1160 Ma) in addition to some evidence for a second early Ottawan event. In other words, the answers to our research questions are: three events; a Shawinigan event possibly associated with crustal thickening, an Ottawan event possibly associated with another round of crustal thickening, and a late Ottawan event that resists simple interpretation in terms of metamorphic history but that coincides chronologically with crustal thinning at the base of an orogenic lid.

scholarly journals Tectono-stratigraphic correlations between Northern Evvoia, Skopelos and Alonnisos, and the postulated collision of the Pelagonian carbonate platform with the Paikon forearc basin (Pelagonian–Vardar zones, Internal Hellenides, Greece)

2020 ◽  
Vol 2 (1) ◽  
Author(s):  
Rudolph Scherreiks ◽  
Marcelle Boudagher-Fadel
Keyword(s):  
Shear Zone ◽  
Early Cretaceous ◽  
Carbonate Platform ◽  
Leading Edge ◽  
Island Arc ◽  
Ductile Shear Zone ◽  
Forearc Basin ◽  
Platform Carbonates ◽  
Geochemical Analyses ◽  
Uplift And Erosion

The Pelagonian stratigraphy of the Internal Hellenides consists of a Permo-Triassic basement and an Upper Triassic and Jurassic carbonate platform formation that has been overthrust by the Eohellenic ophiolite sheet during the Early Cretaceous. Intensive erosion, during the Cretaceous, removed most of the ophiolite and parts of the Jurassic formation. It is hypothesised that uplift and erosion of eastern Pelagonia was triggered by the break-off of the subducted oceanic leading edge of the Pelagonian plate. An investigation of the rocks that succeed the erosional unconformity shows that they constitute a shear-zone that is tectonically overlain by Cretaceous platform carbonates. Geochemical analyses of the shear-zone rocks substantiate that they are of mid-oceanic ridge and island arc provenience. Eastern Pelagonia collided with a Cretaceous carbonate platform, probably the Paikon forearc basin, as the Almopias ocean crust subducted beneath that island–arc complex. The Cretaceous platform, together with a substrate of sheared-off ocean floor mélange, overthrust eastern Pelagonia as subduction continued, and the substrate was dynamically metamorphosed into cataclastic rocks, mylonite, phyllonite and interpreted pseudotachylite. This complex of Cretaceous platform rocks and a brittle-ductile shear-zone-substrate constitute the here named Paikon–Palouki nappe, which was emplaced during Early Palaeocene. The Paikon–Palouki nappe did not reach Evvoia. Seismic tomographic models of the Aegean region apparently depict images of two broken-off ocean-plate-slabs, interpreted as Almopias-lithosphere-slabs. It is concluded that the western Almopias slab began to sink during the Early Cretaceous, while the eastern Almopias slab broke off and sank after the Paikon–Palouki nappe was emplaced in the Early Palaeocene.

The Parry Sound domain: a far-travelled allochthon? New evidence from U–Pb zicon geochronology

1996 ◽  
Vol 33 (7) ◽  
pp. 1087-1104 ◽  
Author(s):  
N. Wodicka ◽  
R. A. Jamieson ◽  
R. R. Parrish
Keyword(s):  
Source Region ◽  
Detrital Zircons ◽  
Absolute Maximum ◽  
Present Position ◽  
Mafic Dyke ◽  
Metasedimentary Rocks ◽  
Thrust Zone ◽  
Tonalitic Gneiss ◽  
Central Gneiss Belt ◽  
New Evidence

We report U–Pb zircon ages for metaplutonic and metasedimentary rocks from three lithotectonic assemblages within the Parry Sound allochthon of the Central Gneiss Belt, southwestern Grenville Orogen: the basal Parry Sound, interior Parry Sound, and Twelve Mile Bay assemblages. Magmatic crystallization ages for granitic to tonalitic gneisses from the basal Parry Sound assemblage fall in the range 1400–1330 Ma. Younger intrusions include the Parry Island anorthosite dated at 1163 ± 3 Ma and a crosscutting mafic dyke bracketed between 1151 and 1163 Ma. Dated at [Formula: see text] a tonalitic gneiss from the overlying interior Parry Sound assemblage is slightly younger than the older group of rocks from the basal Parry Sound assemblage. 207Pb/206Pb ages for zircons from a quartzite of the basal Parry Sound assemblage range from 1385 Ma to the Neoarchaean. An absolute maximum age for this quartzite is 1436 ± 17 Ma. In contrast, detrital zircons from a quartzite of the Twelve Mile Bay assemblage constrain the age of deposition at post-ca. 1140–1120 Ma. We speculate that Grenvillian-age zircons within this quartzite were derived from rocks in the Adirondack Highlands and Frontenac terrane, implying that part of the Parry Sound domain and these terranes were contiguous during deposition of the quartzite. Our data support previous interpretations that the Parry Sound domain is allochthonous with respect to its surroundings, and suggest that the most likely source region of the basal Parry Sound domain lies southeast of the Central Gneiss Belt, within the Central Metasedimentary Belt boundary thrust zone or the Adirondack Highlands. This implies the possibility of 100–300 km of displacement of the domain. Emplacement of the Parry Sound domain into its present position must have occurred relatively late in the orogen's history, by about 1080 Ma.

U–Pb constraints on the thermotectonic evolution of the Vernon antiform and the age of the Aberdeen gneiss complex, southeastern Canadian Cordillera

2006 ◽  
Vol 43 (2) ◽  
pp. 213-244 ◽  
Author(s):  
P Glombick ◽  
R I Thompson ◽  
P Erdmer ◽  
L Heaman ◽  
R M Friedman ◽  
...  
Keyword(s):  
Shear Zone ◽  
Hanging Wall ◽  
Ductile Deformation ◽  
Granitic Rocks ◽  
Tectonic Activity ◽  
Canadian Cordillera ◽  
Metamorphic Complex ◽  
Seismic Reflection Data ◽  
Gneiss Complex ◽  
Shuswap Metamorphic Complex

The Aberdeen gneiss complex is composed of complexly deformed migmatitic orthogneiss and paragneiss situated within the core of the Vernon antiform, a structure defined by a series of subparallel reflectors visible at upper to middle crustal depths (6–18 km) in seismic reflection data from the Vernon area of the Shuswap metamorphic complex. The Vernon antiform and the Aberdeen gneiss complex lie within the footwall of the gently west dipping (top to the west) Kalamalka Lake shear zone. Migmatitic gneiss exposed within the antiform records evidence (recorded as age domains in complexly zoned zircon grains) of three metamorphic events, occurring at 155–150, 90, and 66–51 Ma. The timing of magmatic events within the antiform includes emplacement of diorite at ~232 Ma, tonalite at ~151 Ma, granodiorite at 102 Ma, and monzonite at 52 Ma. Middle to Late Jurassic metamorphism resulted in widespread migmatization. Early Tertiary metamorphism (66–51 Ma) was coeval with the emplacement of granitic rocks and exhumation typical of other areas of the Shuswap metamorphic complex. Highly deformed orthogneiss situated within the hanging wall of the Kalamalka Lake shear zone, comprising the superstructure, was emplaced at ~171 Ma. Ductile deformation had ceased by 162 Ma. The complex metamorphic and magmatic evolution of the Vernon antiform, which is similar to other areas of the southern Canadian Cordillera including the Nicola horst, Mount Lytton – Eagle plutonic complex, Cariboo Mountains, and Mica Creek area, may reflect episodic tectonic activity at the plate margin.

Sign in / Sign up

Export Citation Format

Share Document