The Wathaman batholith: largest known Precambrian pluton

1984 ◽  
Vol 21 (10) ◽  
pp. 1082-1097 ◽  
Author(s):  
S. L. Fumerton ◽  
M. R. Stauffer ◽  
J. F. Lewry
Keyword(s):  
Shear Zones ◽  
Island Arc ◽  
Pacific Rim ◽  
Early Proterozoic ◽  
Northern Saskatchewan ◽  
Internal Deformation

The Early Proterozoic Wathaman batholith, in northern Saskatchewan and Manitoba, is a 900 km long, megacrystic granite–granodiorite intrusion that straddles the junction between ensialic miogeoclinal and probably ensimatic eugeoclinal–island-arc terranes of the "Trans-Hudson Orogen," of the western Churchill Province. Although the largest Precambrian batholith known, it is, apart from marginal complexities, remarkably homogeneous throughout and, unlike comparably sized and situated Phanerozoic batholiths, shows no evidence of multiple intrusion, nor does it have comagmatic early mafic phases. However, it may be considered as just one phase of a larger batholithic belt that also includes numerous smaller plutons. Taken as a whole the composite batholithic belt is similar in many aspects to Mesozoic Pacific rim batholithic belts, and like them probably was emplaced during plate collision.The batholith is affected by pervasive internal deformation, is bounded on the northwest by major blastomylonite zones, and is transected internally by splaying shear zones. It is a mid- to late-synkinematic Hudsonian intrusion, emplaced within a markedly compressional, crustal regime. On the basis of petrological, geochemical, and isotopic criteria the batholith is an "I-type" intrusion, but the origin of the magma and the emplacement mechanisms are still unresolved problems.

Composition, structure and tectonic analysis of the Shangrimuce arc-continent collision zone on the northern margin of the Central Qilian, NW China

2021 ◽  
Author(s):  
Hongyuan Zhang ◽  
Zhibin Lei ◽  
Bo Yang ◽  
Qing Liu ◽  
Haijun Zhang ◽  
...  
Keyword(s):  
Shear Zones ◽  
Oceanic Lithosphere ◽  
Late Ordovician ◽  
Island Arc ◽  
Qilian Mountain ◽  
Northern Margin ◽  
Early Ordovician ◽  
Collision Zone ◽  
Two Stages ◽  
Back Arc

<p>A 1:50000 regional survey, covering an area of about 2000 km<sup>2</sup>, was carried out in the Shangrimuce area of Qilian Mountain in Northwest China. The results show that during Caledonian, the northern margin of the Central Qilian block experienced collision with mature island arcs and subsequently northward expansion. In the Shangrimuce study area, five geological units have been identified; they are, form south to north, back-arc basin, early Ordovician island arc, inter arc basin, middle Late Ordovician island arc, and fore-arc and oceanic lithosphere amalgamation zone. </p><p>(1) back-arc basin. In the Yangyuchi- Shule River- Cuorigang- Wawusi area, there may be a back-arc spreading basin, and there should be spreading basins in this area. It is speculated that there was a northward reverse subduction in the late Ordovician, accompanied by a syenite body, a broad spectrum dyke swarms and an accretionary wedge zone in the whole area.</p><p>(2) early Ordovician island arc. In the Shangrimuce-Dander area, the Proterozoic basement granitic gneiss, the early Ordovician island arc block and the high-pressure geological body all occur in the form of thrust horses, forming a double metamorphic belt, which reveals the existence of ocean subduction to south in the early Ordovician. </p><p>(3) inter arc basin. On both banks of Tuolai River to the east of Yanglong Township, there are early Middle Ordovician inter-arc basins with oceanic crust. </p><p>(4) middle Late Ordovician island arc. To the north of Tuolai River, there is a middle Late Ordovician island arc belt. Both sides of the island arc zone experienced strong ductile shear deformation, which recorded a complex arc-continent collision. </p><p>(5) fore-arc and oceanic lithosphere amalgamation zone (Fig.1). The Yushigou area has developed a fore-arc and oceanic lithospheric amalgamation zone, with weakly deformed fore-arc flysch basin, strongly deformed siliceous rocks, pillow Basalt, diabase, gabbro, peridotite and other rock assemblages.</p><p>Combined with the characteristics of arc-continent collision zone in the Western Pacific, there are two stages of shear zone series (Fig.2). One is ductile shear zones formed by the South dipping gneissic belt, revealing the existence of oceanic subduction accretion wedge and emplacement of high-pressure rocks. Another superimposed one is north dipping. This indicates that the arc-continent collision caused by back-arc reverse subduction, which ultimately controls the overall geometric and kinematic characteristics of the shear zones in the region.</p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.8219836ca50067454890161/sdaolpUECMynit/12UGE&app=m&a=0&c=40b3389c641f2d0ca723e1527c32927e&ct=x&pn=gepj.elif&d=1" alt=""></p><p>Figure 1 United sections showing a Caledonian trench-arc system in the Qilian Mountain, NW China.</p><p><img src="https://contentmanager.copernicus.org/fileStorageProxy.php?f=gepj.8def566da50066084890161/sdaolpUECMynit/12UGE&app=m&a=0&c=e82258ecc235c4e618abd6c035b58232&ct=x&pn=gepj.elif&d=1" alt=""></p><p>Figure 2 Structural analysis at Hongyahuo, indicating two stages of deformation.</p><p>The research has been supported by projects from the Ministry of Land and Resources (No.201211024-04; 1212011121188) and the 2020 undergraduate class construction project from China University of Geosciences (Beijing) (No. HHSKE202003).</p><p> </p>

Striding-Athabasca mylonite zone: implications for the Archean and Early Proterozoic tectonics of the western Canadian Shield

1995 ◽  
Vol 32 (2) ◽  
pp. 178-196 ◽  
Author(s):  
Simon Hanmer ◽  
Michael Williams ◽  
Chris Kopf
Keyword(s):  
Continental Margin ◽  
Canadian Shield ◽  
Magmatic Evolution ◽  
Tectonic Zone ◽  
Early Proterozoic ◽  
Plate Margin ◽  
Mylonite Zone ◽  
Northern Saskatchewan ◽  
Archean Crust ◽  
Rifted Margin

Study of the northern Saskatchewan–District of Mackenzie segment of the Snowbird tectonic zone suggests that fragments of relatively stiff mid-Archean crust, possibly arc related, have controlled the localization, shape, and complex kinematics of the multistage Striding–Athabasca mylonite zone during the Archean, as well as the geometry of the Early Proterozoic rifted margin of the western Churchill continent. By the late Archean, the Striding–Athabasca mylonite zone was located in the interior of the western Churchill continent, well removed from the contemporaneous plate margins. Except for the Alberta segment, the Snowbird tectonic zone was not the site of an Early Proterozoic plate margin. We suggest that the geometry of the Archean–Early Proterozoic boundary in the western Canadian Shield represents a jagged continental margin, composed of a pair of reentrants defined by rifted and transform segments. These segments were inherited from Early Proterozoic breakup and controlled by the Archean structure of the interior of the western Churchill continent. The geometry of this margin appears to have strongly influenced the Early Proterozoic tectono-magmatic evolution of the western Canadian Shield.

A geological interpretation of gravity and magnetic data, northwest Saskatchewan

1970 ◽  
Vol 7 (3) ◽  
pp. 858-868 ◽  
Author(s):  
R. H. Wallis
Keyword(s):  
Gravity Data ◽  
Magnetic Data ◽  
Early Proterozoic ◽  
Geological Interpretation ◽  
Metasedimentary Rocks ◽  
Lower Proterozoic ◽  
Gravity And Magnetic ◽  
Northern Saskatchewan ◽  
Gravity And Magnetic Data ◽  
Sedimentary Unit

The striking 'fit' of aeromagnetic and gravity data from the Precambrian of northwest Saskatchewan, combined with known and nearby analogous, geological relationships, suggests the presence of a northeast-trending belt, 250 × 20 miles (400 × 30 km), of early Proterozoic (?) metasedimentary rocks, probably magnetite-bearing meta-arkoses. This structural–sedimentary unit might have economic possibilities analogous to other northeast-striking, Precambrian, lower Proterozoic (?), metasedimentary belts of northern Saskatchewan, the Virgin River Belt, and the Wollaston Trend.

scholarly journals The Proterozoic mobile belt in the Ammassalik region, South-East Greenland (Ammassalik mobile belt): an introduction and re-appraisal

1989 ◽  
Vol 146 ◽  
pp. 5-12
Author(s):  
B Chadwick ◽  
P.R Dawes ◽  
J.C Escher ◽  
C.R.L Friend ◽  
R.P Hall ◽  
...  
Keyword(s):  
Shear Zones ◽  
Granulite Facies ◽  
Mobile Belt ◽  
The South ◽  
Southern Limit ◽  
Late Archaean ◽  
Early Proterozoic ◽  
The North ◽  
Layer Cake ◽  
Dyke Swarms

The Ammassalik mobile belt is characterised by a regional layer cake structure of tectonically interleaved sheets of quartzo-feldspathic orthogneisses and supracrustal rocks. The sheets of supracrustal rocks are most abundant in the north of the belt and they include semi-pelitic kyanite-sillimanite gneisses, graphitic schists, marble, amphibolites and local peridotite. The sheets are regarded as parts of a disrupted supracrustal sequence, here termed the Siportoq supracrustal association. Preliminary isotopic age data suggest that most of the orthogneisses are late Archaean, although some have early Proterozoic ages. The Siportoq supracrustal association has yielded an early Proterozoic age. Amphibolite dyke swarms were emplaced at various stages in the evolution of the mobile belt. The Ammassalik belt has an ill-defined northern limit marked by heterogeneous retrogression of a granulite facies terrain up to 100 km wide. Most of the belt is at amphibolite facies, with its southern limit lying to the south of the area considered here. The structure in the south is dominated by nappes and shear zones dipping NE within a wide tract of late Archaean orthogneisses intruded by amphibolite dyke swarms with relatively well preserved primary characteristics. The structure in the north is characterised by more pervasive deformation which gave rise to complex sequences of thrusting and nappe development propagating from the north. Large domes were superimposed on the nappe pile, perhaps as buoyancy phenomena. The dioritic Ammassalik Intrusive Complex (c. 1885 Ma) with its granulite facies assemblages is regarded as a late kinematic phenomenon. Major post-tectonic complexes of granite, diorite and gabbro (c. 1580 Ma) were intruded at a high level well after the close of the tectonism in the Ammassalik mobile belt.

A Discussion on global tectonics in Proterozoic times - The interrelations of fluid transport, deformation, geochemistry and heat flow in early Proterozoic shear zones in the Lewisian complex

1976 ◽  
Vol 280 (1298) ◽  
pp. 569-604 ◽  
Keyword(s):  
Grain Size ◽  
Heat Flow ◽  
Hydraulic Fracturing ◽  
Fluid Transport ◽  
Shear Zones ◽  
Size Reduction ◽  
Dyke Swarm ◽  
Large Temperature ◽  
Early Proterozoic ◽  
General Chemical

The Lewisian complex of northwest Scotland shows a pattern of evolution typical of a number of early Proterozoic provinces. During the period 2500-1600 Ma, deformation occurred along steeply dipping shear zones, resulting in both vertical and lateral movements. The largest of these shear zones, forming the northern boundary to the Scourian granulites (Archaean), must have penetrated to considerable depth, possibly to the mantle. Modal and chemical analysis of rocks from shear zones are presented and discussed in relation to rocks sampled outside shear zones. The mineralogy and composition of all rocks deformed in the shear zones have been considerably altered by synkinematic metasomatism. In the early stages, immediately prior to and during the intrusion of the regional doleritic dyke swarm, this metasomatic activity involved addition of H 2 O and Na to the rocks. Subsequently, more significant changes in rock chemistry occurred addition of H 2 O, K, Na, loss of Fe, Ca, Mg). These changes resulted from the interaction between large volumes of water and the rocks in the shear zones along which the fluid travelled. A combination of modal and chemical data allow general chemical reactions to be written which describe the evolution of the gneisses during reworking and retrogression from pyroxene bearing granulite facies rocks to hornblende and biotite bearing amphibolite facies rocks in shear zones. The reactions are written as ionic equilibria and suggest that the fluid phase in the shear zones had a low pH. Adiabatic transport of water upwards through the crust will result in moderate warming of the fluid, and can cause large temperature increases above the preexisting geothermal gradient in rocks through which the fluid travels. It is suggested that both deformation and metamorphism in these shear zones are related to transport of fluid by hydraulic fracturing. Grain size reduction by hydraulic fracturing increases the strain rate in the shear zones. Deformation may cease in a shear zone when the fluid pressure drops and hydraulic fracturing no longer occurs. Thus fluid transport, mineral reactions, chemical changes, grain size reduction and convective heat flow will cease. A close relation should exist between the intensity of deformation, the extent of metasomatism and the thermal history in these important shear belts.

Striding-Athabasca mylonite zone: Complex Archean deep-crustal deformation in the East Athabasca mylonite triangle, northern Saskatchewan

1994 ◽  
Vol 31 (8) ◽  
pp. 1287-1300 ◽  
Author(s):  
Simon Hanmer ◽  
Randy Parrish ◽  
Michael Williams ◽  
Chris Kopf
Keyword(s):  
Flow Pattern ◽  
Shear Zone ◽  
Crustal Deformation ◽  
Principal Axis ◽  
Shear Zones ◽  
Granulite Facies ◽  
Strike Slip ◽  
Tectonic Zone ◽  
Early Proterozoic ◽  
Lower Deck

The geophysically defined Snowbird tectonic zone is manifested in northernmost Saskatchewan as a deep-crustal, multistage mylonitic structure, the East Athabasca mylonite triangle. The triangle, located at the northeastern apex of a stiff, crustal-scale "lozenge," is composed of mid-Archean annealed mylonites and late Archean ribbon mylonites, formed during two granulite facies events (850–1000 °C, 1.0 GPa). The flow pattern in the mylonites is geometrically and kinematically complex, and corresponds to that expected adjacent to the apex of a stiff elliptical volume subjected to subhorizontal regional extension parallel to its principal axis. The late Archean mylonites are divided into an upper structural deck, entirely occupied by a dip-slip shear zone, and an underlying lower deck. The latter is divided into two upright conjugate strike-slip shear zones, separated by a low-strain septum, which deformed by progressive coaxial flow. The flow pattern in the mid-Archean mylonites is compatible with that of the late Archean mylonites, and suggests that the crustal-scale lozenge influenced deformation since the mid-Archean. In the interval ca. 2.62–2.60 Ga, deformation in the upper and lower decks evolved from a granulite facies pervasive regime to a more localized amphibolite facies regime. With further cooling, deformation was localized within very narrow greenschist mylonitic faults at the lateral limits of the lower deck. By the late Archean, the East Athabasca mylonite triangle was part of a deep-crustal, intracontinental shear zone. This segment of the Snowbird tectonic zone was not the site of an Early Proterozoic suture or orogen.

U–Pb geochronology in the Trans-Hudson Orogen, northern Saskatchewan, Canada

1987 ◽  
Vol 24 (3) ◽  
pp. 407-424 ◽  
Author(s):  
W. R. Van Schmus ◽  
M. E. Bickford ◽  
J. F. Lewry ◽  
R. Macdonald
Keyword(s):  
Granitic Rocks ◽  
Early Proterozoic ◽  
Tectonic Events ◽  
Northern Saskatchewan ◽  
High Grade Metamorphism ◽  
The One ◽  
Relationship Of ◽  
The Relationship ◽  
Orogenic Events ◽  
Archean Basement

We have obtained U–Pb ages on zircons from volcanic and plutonic units in several lithotectonic domains of the southern Trans-Hudson Orogen in northern Saskatchewan. These data constrain the timing of early Proterozoic orogenic events in the region and enhance our understanding of both the relationships among local domains and the relationship of the Trans-Hudson Orogen to other early Proterozoic orogens in North America.With one exception, all units studied so far yield zircon ages of 1890–1835 Ma, most of which are systematically earlier than previously reported Rb–Sr isochron ages on the same or similar units, suggesting open-system behavior in the Rb–Sr systems. Five metarhyolites, from volcanic sequences in the La Ronge domain, Glennie domain, and Hanson Lake block, give ages ranging from 1888 to 1876 Ma. Most of the plutons we dated, ranging from gneissic syntectonic tonalites and granodiorites to less-deformed late intrusions such as the Wathaman batholith and other smaller bodies, yield ages of 1870–1850 Ma, apparently constraining peak plutonic activity to about 1860 ± 10 Ma ago. The youngest unit found is a small discordant pluton with an age of 1836 ± 7 Ma. The concordance of ages of volcanics on the one hand and of plutons on the other suggests that domainal distinctions are mainly lithotectonic rather than temporal.Zircons from the Sahli charnockitic granite in the Hanson Lake block yield equivocal results. Discordia upper and lower intercepts for the Sahli granite suggest that granitic rocks at least 2500 Ma old were subjected to high-grade metamorphism about 1800–1900 Ma ago, with substantial resetting of zircons. Reworked Archean basement is thus present in this domain, supporting previously reported Rb–Sr isochron data from the Sahli granite. No other indications of Archean basement in the Trans-Hudson Orogen are documented, although one sample from the adjacent Peter Lake domain shows that it consists of Archean continental crust.Zircon ages in the range 1890–1835 Ma from this part of the Trans-Hudson Orogen are similar to those obtained from igneous units of the Penokean and Wopmay orogens, in North America, and from the Svecofennian Orogen, suggesting essential synchroneity of igneous and tectonic events in these four major orogens during major Proterozoic continental assembly.

Basement–cover relationships in the East Greenland Caledonides: evidence from the Eleonore Bay Supergroup at Ardencaple Fjord

1993 ◽  
Vol 84 (2) ◽  
pp. 103-115 ◽  
Author(s):  
N. J. Soper ◽  
A. K. Higgins
Keyword(s):  
Shear Zones ◽  
Low Grade ◽  
East Greenland ◽  
Early Proterozoic ◽  
Basement Rocks ◽  
Erosion Level ◽  
Isotopic Studies ◽  
Extensional Faulting ◽  
Proterozoic Basement ◽  
Shed Light

AbstractThe Eleonore Bay Supergroup (EBG) is a 16 km-thick shallow-water sequence of Neoproterozoic age that is preserved within the East Greenland Caledonides in several tracts, surrounded by crystalline gneisses and schistose supracrustal rocks. The apparent downward transition from non-metamorphic EBG into gneiss gave rise to the classic ‘stockwerke’ hypothesis, in which all the metamorphism was regarded as Caledonian, and differences in grade were ascribed to the ascent of a migmatite front to different levels within the orogen. Field and isotopic studies in the 1970s however revealed that the underlying gneisses and schists had undergone orogenic reworking in mid-Proterozoic time; the EBG–basement contact was then interpreted as an approximately bedding-parallel décollement with apparent lag geometry, that is with EBG cover rocks in its hangingwall.Recent work in the northernmost EBG tract, at Ardencaple Fjord, has shed light on the problems posed by the basal relationships of the EBG, and together with regional structural and stratigraphic data leads to the following interpretation. There are two regionally important basement-cover interfaces within the East Greenland Caledonides. The earlier one is between Archaean/early Proterozoic gneisses and early Proterozoic supracrustal rocks, which were pervasively deformed in mid-Proterozoic time and form the basement to the Neoproterozoic Eleonore Bay cover sequence. This was deposited on a vast, continually subsiding shelf that is now preserved in East and NE Greenland and Svalbard, and contains Grenville detritus. EBG deposition was terminated by major extensional faulting of Vendian age; the succeeding Tillite Group is interpreted as a syn-rift sequence, presumably associated with the opening of Iapetus.The EBG–basement contacts that are not late faults are inferred to be extensional shear zones of Vendian age. These were reactivated in compression during the Caledonian orogeny in the Silurian, with metamorphic and fabric convergence, which accounts for the apparent downward transition from sedimentary rocks through schists into gneisses. Caledonian shortening was not large; inversion of the Vendian grabens was incomplete, so that the marginal shear zones retained their lag geometry and large tracts of low grade Eleonore Bay sediments are preserved at the present erosion level, surrounded by Proterozoic basement rocks, within the Caledonian belt of East Greenland.

Relocation of earthquakes west of Vancouver Island, British Columbia, 1965–1983

1992 ◽  
Vol 29 (5) ◽  
pp. 953-961 ◽  
Author(s):  
Rutger Wahlström ◽  
Garry C. Rogers
Keyword(s):  
Shear Zones ◽  
Vancouver Island ◽  
Fault System ◽  
Transform Fault ◽  
Arrival Times ◽  
Magnitude Range ◽  
Juan De Fuca ◽  
Internal Deformation ◽  
Seismograph Network ◽  
Hypocentre Locations

In the tectonically complex region of young plate interaction west of Vancouver Island, 360 earthquakes have been relocated. The earthquakes occurred in the years 1965 – 1983, when the Canadian seismograph network in the region did not significantly change configuration, and are in the magnitude range 3–5. A traveltime model was derived and applied to arrival times for a selected, limited set of station–phase combinations. Time corrections for these combinations were derived from joint-hypocentre locations of earthquakes in specific regions using independently located reference events. An algorithm for routine location of offshore earthquakes in this region is suggested.The correlation between seismicity and mapped bathymetrical features is strong along the Revere–Dellwood transform fault and the northern segments of the Explorer ridge – transform fault system. Considerable seismicity occurs inside the Explorer Plate, indicating internal deformation. The Sovanco and Nootka shear zones, the southern borders of the Explorer Plate, are characterized by broad belts of seismicity and evidently are not simple transform margins. The Explorer and northern Juan de Fuca ridges are aseismic in the investigated magnitude range.

Precambrian geology of Nuussuaq and the area north-east of Disko Bugt, West Greenland

1999 ◽  
pp. 6-40 ◽  
Author(s):  
Adam A. Garde ◽  
Agnete Steenfelt
Keyword(s):  
Hanging Wall ◽  
Shear Zones ◽  
Early Proterozoic ◽  
West Greenland ◽  
Metasedimentary Rocks ◽  
Precambrian Geology ◽  
North East ◽  
Westward Movement ◽  
Area North ◽  
Precambrian Terrain

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Garde, A. A., & Steenfelt, A. (1999). Precambrian geology of Nuussuaq and the area north-east of Disko Bugt, West Greenland. Geology of Greenland Survey Bulletin, 181, 6-40. https://doi.org/10.34194/ggub.v181.5108 _______________ The Precambrian terrain of eastern Nuussuaq and north-east Disko Bugt largely consists of late Archaean (c. 2800 Ma) orthogneisses, intercalated with units of strongly deformed Archaean supracrustal rocks. The latter are up to several kilometres wide and comprise both metavolcanic and metasedimentary rocks within which local occurrences of gold have been found. In central Nuussuaq a layered complex of anorthosite, leucogabbro, gabbro and ultramafic rocks is tectonically intercalated with Archaean orthogneisses, and an intrusive complex of Archaean tonalites and trondhjemites, largely unaffected by Archaean and Proterozoic deformation, occurs in the area north-east of Disko Bugt. Here an up to c. 3.5 km thick sequence of early Proterozoic shallow marine clastic sediments and minor marble unconformably overlies Archaean rocks. Several suites of basic dykes are present, and dykes and small plugs of ultramafic lamprophyre and lamproite (age c. 1750 Ma) are common in the central part of the region. Most of the region was overprinted by early Proterozoic deformation and metamorphism. Prominent Proterozoic flat-lying ductile shear zones with north- or north-westward movement of the hanging wall are overprinted by open folds.

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