- Herb Helmstaedt is a geologist and Earth historian who studied at Martin-Luther-University, Halle, and the University... moreHerb Helmstaedt is a geologist and Earth historian who studied at Martin-Luther-University, Halle, and the University of Munich, in Germany, before coming to Canada in 1964 for doctoral studies at the University of New Brunswick, in Fredericton. After obtaining his PhD in 1968, he spent a year as a research associate at Lamont Geological Observatory of Columbia University in New York. He joined the Geological Survey of Canada, in Ottawa, in 1969, and taught three years at McGill University from 1971-1974 while continuing to work for the Geological Survey of Canada during the summer months, mainly in northern Canada. In the fall of 1974, he came to Queen’s University, where he taught structural geology and geo-tectonics and supervised more than 60 graduate students. His main research interests were Precambrian field studies in the Archean Slave and Superior provinces of the Canadian Shield, structural and tectonic controls of mineral deposits, and all things related to kimberlites and diamonds. He consulted widely, in Canada and abroad, and participated in the Canadian LITHOPROBE Program as leader of the Western Superior Transect from 1994 to 2004. After serving as head of department from 1994 to 2003, he became professor emeritus in 2004 but was re-appointed as acting head for another year in 2008/2009. He is now fully retired, though his wife still does not believe it, as he continues to write about things geological. Besides enjoying time with his family, he pursues various outdoor hobbies and sings in a local men’s choir.edit
Research Interests: Geology and Geochemistry
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Research Interests: Geology and Kimberlite
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... field and constructive suggestions. John Percival, Greg Stott, Mary Sanborn-Barrie, Tom Skulski, Vicki McNicoll, and Andrew Hynes provided valuable insight throughout the summer field season. Andreas Lichtblau of the Thunder ...
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... Combined silicate Sm-Nd and Rb-Sr and sulfide Re-Os isotope compositions indicate variable interaction of original convecting mantle magmas with harzburgitic and eclogitic SCLM components during genesis of both the diamonds and the... more
... Combined silicate Sm-Nd and Rb-Sr and sulfide Re-Os isotope compositions indicate variable interaction of original convecting mantle magmas with harzburgitic and eclogitic SCLM components during genesis of both the diamonds and the Bushveld Complex (Richardson and ...
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The Western Superior Lithoprobe transect provides a rare opportunity to integrate a multitude of petrological, geochemical, geochronological and structural studies within a geometric framework based on deep (32 s) vibroseis seismic... more
The Western Superior Lithoprobe transect provides a rare opportunity to integrate a multitude of petrological, geochemical, geochronological and structural studies within a geometric framework based on deep (32 s) vibroseis seismic reflection and refraction/wide-angle reflection data, acquired along a 600 km N-S corridor across the prominent E-W trending structural belts of the Western Superior Province. Previous models suggested accretion of Neoarchean (<2.8 Ga) oceanic crust, island arcs and sedimentary prisms with almalgamated Mesoarchean continental fragments against the southern margin of the more than 3 Ga composite North Caribou terrain during the ca. 2.7 Ga Kenoran orogeny. At surface, the southern margin of the North Caribou terrain shows Neoarchean convergent-margin magmatism. Outboard (south) from the protocraton margin, beneath the "accreted" terranes, two lower crustal sutures are identified, where the reflection Moho is offset by several kilometers, consistent with north over south displacement. Along the northern suture, a Mesoarchean continental fragment of the eastern Wabigoon Subprovince is thrust beneath the North Caribou terrain. This fragment is underplated from the south by a basal crustal layer with high subhorizontal reflectivity, very high crustal p-wave velocities (7.6-7.7 km/s) and intermediate density (3.0-3.1 gm/cc), that tapers northward, truncating the reflection Moho and extending into the upper mantle to at least 16 s TWT. The velocity and density constraints of this layer can be satisfied by amphibolitic rocks with a sub-horizontal N-S lineation, and the layer may thus represent a tectonically underplated slab of Archean oceanic crust. Below the Moho, a north-dipping, 20 km thick layer at 50 to 60 km depth is characterized by 5% p-wave anisotropy (fast direction approximately parallel to tectonic strike). This anisotropy is interpreted as an Archean fossil fabric associated with LPO of olivine. All these observations are consistent with the previously predicted northward subduction of Late Archean oceanic lithosphere.
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Although geochemical and isotopic data from the kimberlitic upper mantle sample and Archean magmatic rocks are consistent with recycling of crustal material along shallow-dipping Archean subduction zones, supporting evidence for such... more
Although geochemical and isotopic data from the kimberlitic upper mantle sample and Archean magmatic rocks are consistent with recycling of crustal material along shallow-dipping Archean subduction zones, supporting evidence for such hypotheses has not been forthcoming from surface structures of Archean terrains. However, drawing an analogy with the belt-like superterranes of the Canadian Cordillera, viewed as type example of a
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The Quebec-Baffin segment of the Paleoproterozoic Trans-Hudson Orogen comprises a collage of tectonostratigraphic elements that accumulated on, or were accreted to, the northern margin of the Archean Superior craton throughout more than... more
The Quebec-Baffin segment of the Paleoproterozoic Trans-Hudson Orogen comprises a collage of tectonostratigraphic elements that accumulated on, or were accreted to, the northern margin of the Archean Superior craton throughout more than 200 million years of divergent and subsequent convergent tectonic activity. The Cape Smith Belt, on the Ungava peninsula in northern Quebec, preserves a series of thrust imbricates of >2.04-1.87 Ga sedimentary and mafic volcanic rocks that record the subsidence and rifting of the Superior craton and subsequent development of an oceanic basin. The structurally highest component of the Cape Smith Belt, the Watts Group, consists of ultramafic and mafic cumulate rocks, gabbros, sheeted mafic dykes, pillowed and massive basalts that are interpreted as the igneous crustal components of a 2.00 Ga ophiolite. Although the rocks have been deformed and metamorphosed, primary igneous features such as cumulate textures, intrusive contacts, chilled dyke margins and pillow selvedges are locally well preserved. The ophiolite is a composite of two physically, chemically and isotopically distinct suites of tholeiitic rocks; the older consists of gabbroic cumulate rocks, pillowed basalts and sheeted mafic dykes, and is similar to suites formed at modern mid-ocean spreading ridges, whereas the younger suite consists of ultramafic and mafic cumulate rocks and mafic dykes, and is analogous to modern hotspot-related oceanic-island complexes such as Hawaii. Reconstructions of the pre-deformation crustal configuration suggest that the mid-ocean ridge suite was at least 5 km thick, and the younger, oceanic-island suite was greater than 4 km thick, a total thickness of this composite oceanic crust of >9 km.
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ABSTRACT Tectonic Relationships Between E-Type Cratonic and Ultra-High-Pressure (UHP) Diamond: Implications for Craton Formation and Stabilization H. H. Helmstaedt Abstract Many eclogite xenoliths from kimberlites show geochemical and... more
ABSTRACT Tectonic Relationships Between E-Type Cratonic and Ultra-High-Pressure (UHP) Diamond: Implications for Craton Formation and Stabilization H. H. Helmstaedt Abstract Many eclogite xenoliths from kimberlites show geochemical and isotopic signatures compatible with an origin by subduction of oceanic crustal rocks, and it has been proposed earlier that progressively metamorphosed coesite- and diamond-bearing eclogitic assemblages and coesite inclusions in E-type diamonds may be viewed as an expression of Archean and Proterozoic UHP metamorphic events. Yet the observation that kimberlite-born cratonic eclogitic diamonds and diamonds in UHP metamorphic terranes lie on opposite ends of the geological age spectrum, is still commonly used to infer that UHP metamorphism is a Neoproterozoic or younger process that was not possible in a much hotter Archean Earth. The present paper re-evaluates the UHP model for the Archean eclogitic upper mantle sample by discussing (1) examples for igneous exhumation of subducted Phanerozoic and Proterozoic UHP eclogites and diamonds; (2) seismic images showing that tectonic accretion of oceanic lithosphere was a major factor during assembly of Paleoproterozoic and Archean cratons, and (3) recently discovered Archean metabasic eclogites representing the oldest surface record for subduction zone metamorphism. It is concluded that crustal UHP melanges and the diamondiferous eclogite upper mantle sample are complementary end products of subduction zone metamorphism. Lower density crustal melanges are tectonically exhumed soon after continental or microcontinental collision. The mantle eclogites and their E-type cratonic diamonds are parts of the higher density oceanic slab subducted prior to collision and accreted to the roots of microcontinental nuclei. They had long mantle residence times and could be exhumed only when picked up by younger igneous transport media (e.g. kimberlites). As shown by *2.9 Ga ages of the oldest known eclogitic diamonds and xenoliths with subduction signatures, deep subduction along UHP-gradients began latest in the Mesoarchean, producing lithospheric roots sufficiently thick and cool to extend into the diamond stability field. The range of Proterozoic E-type diamond ages on several diamondiferous cratons, even within individual kimberlites, suggests that craton roots were repeatedly modified during the Proterozoic. Keywords Eclogitic (E-type) diamond �Archean ultra-high-pressure (UHP) metamorphism �Onset of subduction �Lithosphere stabilization H. H. Helmstaedt (&amp;amp;) Department of Geological Sciences and Geological Engineering, Queen’s University, Kingston, ON K7L 3N6, Canada e-mail: helmstaedt@geol.queensu.ca D. G. Pearson et al. (eds.), Proceedings of 10th International Kimberlite Conference, Volume 1, Special Issue of the Journal of the Geological Society of India, DOI: 10.1007/978-81-322-1170-9_4, � Geological Society of India 2013
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Rocks of the Proterozoic Coldbrook Group on the north shore of the Bay of Fundy, New Brunswick, are bounded to the north by a major northeast trending fault (Lubec–Belleisle). North of the fault Paleozoic rocks of the Mascarene Group are... more
Rocks of the Proterozoic Coldbrook Group on the north shore of the Bay of Fundy, New Brunswick, are bounded to the north by a major northeast trending fault (Lubec–Belleisle). North of the fault Paleozoic rocks of the Mascarene Group are overlain unconformably by Upper Devonian and Lower Carboniferous strata.Both the Coldbrook and Mascarene Groups have been deformed by three phases of deformation. Deformation of the two Groups was coeval; penetrative fabrics first developed during the Acadian (Middle Devonian) orogeny.Pre-Acadian Paleozoic movements were limited to local or regional uplift with possible attendant warping and/or gentle tilting.Mylonitic fabrics formed in Coldbrook rocks during the first two phases of the Acadian polyphase deformation. These northeast trending s- surfaces lie normal to the direction of maximum finite shortening. Also from the orientation of synmylonization quartz deformation lamellae of the second phase, it is apparent that the local trajectory of the maximum principal stress was normal to the s-surfaces of the mylonites.No evidence for major northeast–southwest strike slip faulting has been found. Fracture analyses in Upper Devonian and Lower Carboniferous rocks in the northeast trending fault zone, point to a northwest trending principal compressive stress.It is contended that the bulk of the ductile strain (first two phases) occurred In response to northwest principal compressive stress during the Middle Devonian, and these stresses were re-established in post-Devonian times, resulting in the development of high angle oblique to dip slip movements on the northeast trending faults.
Research Interests: Earth Sciences, Geology, Devonian, Carboniferous, Permian, and 3 moreOrogeny, Paleozoic, and Mylonite
Zoned veins (glass and crushed rock) of pseudotachylite occur in an Archean mylonite near Charron Lake, Manitoba. Glass occupies the centers of some veins and fusion products penetrate symmetrically distributed, crushed rock zones. The... more
Zoned veins (glass and crushed rock) of pseudotachylite occur in an Archean mylonite near Charron Lake, Manitoba. Glass occupies the centers of some veins and fusion products penetrate symmetrically distributed, crushed rock zones. The emplacement of the pseudotachylite postdates the formation of the mylonite fabric, but a later deformation affected both pseudotachylite and mylonite. The average chemical composition of the pseudotachylite veins reflects the composition of the host rocks, although the opaque, marginal crushed rock zones are enriched in iron and the fused centers are depleted in sodium. Glass is confined to crushed rock veins although not all crushed rock veins contain glass; apparently an increase in water pressure led to fusion.
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Research Interests: Geology, Geochemistry, Volcano, Subduction, Xenolith, and 4 moreNavajo, Slab, Suite, and Slab window
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ABSTRACT
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We present the first finding of the high-pressure mineral coesite in lawsonite-bearing eclogite xenoliths from the Colorado Plateau, United States. The presence of coesite in these xenoliths supports the hypothesis that the eclogite... more
We present the first finding of the high-pressure mineral coesite in lawsonite-bearing eclogite xenoliths from the Colorado Plateau, United States. The presence of coesite in these xenoliths supports the hypothesis that the eclogite formed in a low-temperature high-pressure environment such as envisaged inside subducted oceanic lithosphere. Ion-microprobe U-Pb dating of micrometer-scale zircons in the eclogites yields ages ranging from 81
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... The map shows an arenaceous and a politic domain separated by a zone of deformed, authigenicpyrite. Each domain is charac-Fig. ... A. Extension and calcite fibre growth parallel to Si. B. Shortening parallel to Si, rotation of pyrite... more
... The map shows an arenaceous and a politic domain separated by a zone of deformed, authigenicpyrite. Each domain is charac-Fig. ... A. Extension and calcite fibre growth parallel to Si. B. Shortening parallel to Si, rotation of pyrite pieces and deformation of calcite fibres. ...
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ABSTRACT This paper presents the results of a detailed study of the Kiena mine where precise U-Pb zircon dating of an intermineral granodiorite dike assigns a minimum age of 2686 Ma to an Archean intrusion-related gold vein system. The... more
ABSTRACT This paper presents the results of a detailed study of the Kiena mine where precise U-Pb zircon dating of an intermineral granodiorite dike assigns a minimum age of 2686 Ma to an Archean intrusion-related gold vein system. The age reveals that gold mineralization post-dates volcanism (ca. 2718-2700 Ma) but predates regional synmetamorphic deformation (ca. 2677-2645 Ma) and the intrusion of S-type granitoids across the Abitibi and Pontiac subprovinces (ca. 2645-2611 Ma). -from Authors
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An Archean mafic dike complex in the Chan Formation at the base of the mafic volcanic section of the Yellowknife greenstone belt consists of multiple metagabbro dikes and sills separated by screens of pillowed mafic volcanic rocks, which... more
An Archean mafic dike complex in the Chan Formation at the base of the mafic volcanic section of the Yellowknife greenstone belt consists of multiple metagabbro dikes and sills separated by screens of pillowed mafic volcanic rocks, which are cut by a younger postvolcanic metadiabase dike swarm. Field relationships and geochemical characteristics are compatible with a comagmatic origin for the metagabbro and metavolcanic rocks that were fed through and deposited on an older, rift-related, supracrustal sequence of the Dwyer Group. The synvolcanic metagabbro dikes have extended the strike length of the volcanic section by at least 100%. The mafic rocks of the Chan Formation are geochemically similar to mid-ocean ridge basalt, possibly with a minor subduction-zone component. Preliminary εNd values for metagabbroic rocks are consistent with the derivation of magmas predominantly from a normal, depleted-mantle source. The Chan Formation is interpreted to have formed in a marginal basin-like setting, adjacent to a previously rifted and attenuated protocontinental margin.
Research Interests: Earth Sciences, Geology, Geochemistry, Archean, Dike, and 4 moreSill, Basalt, Volcanic Rock, and Plate tectonic
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A new plate-tectonic model accounts for lithological relations and regional structural patterns in late Archean supracrustal domains of the Slave Province. Multiple dykes and pillowed mafic flows, most common in the western part of the... more
A new plate-tectonic model accounts for lithological relations and regional structural patterns in late Archean supracrustal domains of the Slave Province. Multiple dykes and pillowed mafic flows, most common in the western part of the province, suggest sea-floor spreading. The mafic volcanics, lying in narrow homoclinal belts stratigraphically below more extensive turbidites, are viewed as megaxenolithic remnants of oceanic crust preserved on the periphery of granitoid plutons and blocks of sialic crust. Closure of an oceanic basin was marked by emplacement of the granitoid plutons and coeval felsic volcanics, the latter predominating over mafic volcanics in northeastern domains. The felsic calc-alkaline magmas may have risen from a shallow-dipping subduction zone. Westerly verging folds, westerly convex fold arcs, and inclinations of later foliations, particularly in lower level rocks of higher metamorphic grade, are in accord with underthrusting to the east. The zone of underthrusting shifted progressively westward, and calc-alkaline magmatism swept across the western part of the province. Plutons followed crustal fracture systems, some of which were inherited from initial rifts, producing a rectilinear zigzag pattern of contacts between plutons, and mafic volcanics. The fracture systems and rising plutons redirected stresses, resulting in distinctive sets of regional and local foliations that reflect crustal compression only indirectly related to the sense of subduction.