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In the Archean Blake River Group, mafic to intermediate fragmental units have controversially been proposed to have formed during the collapse of a giant submarine caldera. This paper describes and interprets these rocks, summarizing their physical characteristics, inferred origins, age relationships, and geochemical signatures. The widespread Stadacona member, south of Rouyn-Noranda, consists of several hundred metres of bedded volcaniclastic rocks interpreted to have been mostly deposited from aqueous density currents fed directly by explosive eruptions. The magmas involved in these eruptions were plagioclase-phyric, tholeiitic to transitional basalts. The similarly widespread D’Alembert tuff, in the northern part of the Blake River Group, shares many physical characteristics with the Stadacona member and is thought to have a similar origin. However, the D’Alembert tuff is approximately six million years younger than the Stadacona member. It is composed mostly of transitional to calc-alkaline andesites and basaltic andesites with very distinct trace element profiles. Volcaniclastic rocks from other areas, such as Tannahill Township in Ontario and the Monsabrais area in Quebec, are interpreted to represent mostly in situ to remobilized hyaloclastite, with no explosive eruptions involved in their genesis. Our observations and interpretations are not compatible with models in which the volcaniclastic units are emplaced during a catastrophic event in relation with the collapse of a giant caldera. Instead, the fragmental rocks were produced by various mechanisms at many distinct times during the evolution of the Blake River Group.

The Archean Blake River Group (BRG) of Ontario and Quebec is dominated by submarine mafic to intermediate lavas, with more restricted felsic volcanic rocks. Given the good quality of outcrop, and high level of preservation of some BRG rocks, the mafic to intermediate lavas were used in the 1970s and 1980s to better understand the evolution of massive and pillowed submarine flows, and their associated fragmental facies (pillow breccias, hyaloclastite). Potentially, the BRG could also represent a useful volcanic succession for the study of explosive submarine eruption products in the ancient record. Before this is possible, however, a regional inventory of the mafic to intermediate volcaniclastic units is needed in order to clarify their characteristics and origins. In this paper, we compare and contrast volcaniclastic rocks from three areas within the same formation of the northern BRG in Quebec: the Monsabrais area, the lac Duparquet area, and the D’Alembert tuff area. Close examination reveals pronounced differences in terms of lateral continuity, thickness, grading, bedding, clast shapes, textures, etc. in the volcaniclastic rocks. These differences are interpreted to reflect vastly different emplacement processes ranging from hyaloclastite generation as a result of self-fragmentation and lava contact with water (dominant in the Monsabrais and lac Duparquet areas) to aqueous density currents likely fed directly by explosive submarine eruptions (dominant in the D’Alembert tuff).

The Thompson Nickel Belt marks the boundary between the Archean Superior Province and the Trans-Hudson Orogen in Canada. It comprises Archean gneisses, and Paleoproterozoic rocks with metasediments and metavolcanites (Ospwagan Group) and intrusions. The gneisses are frequently migmatitic and host numerous pegmatites. The western belt boundary is a fault contact with the Kisseynew Domain of the Reindeer Zone. In the south, the transition zone between the belt and the Kisseynew Domain comprises granitoids and a detrital sequence (Grass River Group), part of which grades into turbidites in the Kisseynew Domain. The eastern belt boundary is a diffuse zone where the Archean east–west (E–W) structural trend changes into the north-northeast (NNE) trend of the belt. This paper presents U–Pb ages for granitoids and 207Pb/206Pb detrital zircon ages from the Ospwagan and Grass River groups. Ages and a comparison of events in the belt and in the eastern Reindeer Zone have major implications. The change from stable platform deposits to syn-tectonic filling and emplacement of mafic intrusions in the Ospwagan Group are attributed to the convergence between the Reindeer Zone and the Superior Province at 1891–1885 Ma. At ca. 1850 Ma, continuing convergence led to drowning of marginal basins of the Superior craton and to the development of a transpressive regime in the belt, the onset of which could be as old as ca. 1885 Ma. Metamorphic ages of 1818–1785 record closure of the Kisseynew basin and crustal thickening. Collision of the new continental block with the Superior Province was accommodated by transpression until 1750–1720 Ma.

Early Cretaceous volcanism is widespread in the eastern Scotian Basin. The stratigraphic position of volcanic rocks within wells was re-evaluated and the volcanological character of the rocks was refined by study of cuttings and well logs. Hauterivian–Barremian volcanic rocks on the SW Grand Banks and Aptian–Albian volcanic rocks in the Orpheus Graben and SE Scotian Shelf resulted from Strombolian type eruptions. More extensive Hawaiian type flows were mapped from seismic profiles near the Mallard and Brant wells on the SW Grand Banks and they appear to have been derived from local basement highs with a positive magnetic anomaly interpreted as volcanic centres. Igneous rocks in the Hesper well on the SE Scotian Shelf are the erosional remnant of basaltic flows that terminated at the paleoshoreline. They correlate with basalt flows both in extensive outcrop on Scatarie Ridge and in several Orpheus Graben wells. The interpretation of the Hesper basalts as an erosional remnant of more extensive basalt flows is consistent with detrital petrographic evidence for substantial uplift of the inboard part of the Scotian Basin in the Hauterivian–Aptian. Widespread volcanic activity indicates a regional and long-lived magma source, which resulted in elevated regional heat flow. Effects of this heat flow are seen in sedimentary rocks of the Sable Subbasin and it had a discernable impact on hydrocarbon maturation.

Fluids responsible for regional 18O-depletion of Neoproterozoic igneous rocks in Avalonia are investigated here through a petrographic, microthermometric, and stable isotopic examination of fluid inclusions and minerals from the abundant vein networks of the Mira terrane, Cape Breton Island. Six categories of vein assemblages — from oldest to youngest — are present: (i) quartz–albite, (ii) quartz–epidote, (iii) quartz, (iv) quartz–chlorite–calcite, (v) quartz–calcite, and (vi) calcite. Vein system temperatures were initially as high as ∼300 °C and gradually decreased to ∼200 °C. Moderate salinities (18O values (–1.9‰ to +1.4‰) calculated for most of the vein assemblages is suggestive of a seawater-dominated system, as are the δDH2O values (–12‰ to –3‰) obtained for epidote. Decreasing fluid salinities, however, suggest that meteoric water became dominant during later stages of vein formation. The carbon isotopic compositions of trace CO2 and CH4 from the fluid inclusions (δ13CCO2 = –22‰ to –4‰; δ13CCH4 = –52‰ to –37‰) are indicative of externally derived (i.e., non-magmatic) fluids of organic origin.

The Red Indian Line is the fundamental Iapetus suture zone in the Newfoundland Appalchians along which the main tract of the Iapetus Ocean was consumed. Despite being the site of the closure of a wide ocean, few vestiges of the Iapetus plate have been accreted along Red Indian Line. Ordovician rocks in the Notre Dame Bay area preserve the only evidence for accretion of a seamount in Newfoundland. The seamount is characterized by alkali basalt and hypabyssal rocks that are juxtaposed with Darriwilian peri-Laurentian volcanic arc rocks (466 ± 4 and 467 ± 4 Ma) along a major mylonite zone. The mylonite zone lacks sedimentary rocks suggesting that the seamount was accreted to the arc along a sediment-starved interface and that significant subduction erosion took place along the Laurentian margin. Identification of subduction erosion indicates that an accretionary prism did not exist outboard of Laurentia in Newfoundland, in contrast to the well developed accretionary prisms of the Caledonides.

Metamorphosed mafic rocks from west-central Vermont crop out in tectonic slices of the Stowe Formation within the Rowe–Hawley Belt of New England. The rocks include greenstone and amphibolite, which are interpreted to have been basaltic flows and gabbroic intrusions, respectively. Even though the rocks have been metamorphosed to greenschist or amphibolite facies, their igneous origins can be deciphered through careful use of geochemistry. Three geochemical types have been identified. Type 1 and 2 samples have geochemical characteristics similar to those found in mid-ocean ridge basalts (MORB), except that they have slightly elevated light rare-earth element (LREE) concentrations and are higher in Nb/Y ratios. Their Nb/Y ratios are similar to basalts found in Iceland and parts of the Afar region of the East African Rift. Types 1 and 2 are similar to metabasalts of the Caldwell and Maquereau formations in southern Quebec. The less-common type 3 samples have highly enriched LREE and are high in Nb/Y and Zr/Y ratios, similar to some alkali basalts from Afar and Iceland. Detailed analysis of the geochemistry suggests that greenstones and amphibolite from the Stowe Formation formed as basaltic eruptions during very late stages in rifting of the Rodinian continent that eventually led to formation of the Iapetus Ocean. This interpretation is consistent with tectonic models of the Vermont and Quebec Appalachians.

Detailed field work conducted in the Dunnage zone of the Quebec Appalachians, is herein combined with 40Ar/39Ar dating on a series of ophiolitic massifs, crosscutting granites, and associated metamorphic rocks occurring along the Baie Verte–Brompton line, the Taconian suture between Laurentia and Lower Paleozoic peri-Laurentian oceanic terranes. Studied massifs are the Lac-Brompton ophiolite and the Rivière-des-Plante Ultramafic Complex in southern Quebec, and the Nadeau Ophiolitic Mélange in the Gaspé Peninsula. Our work suggests that these massifs form remnants of eroded ophiolitic nappes, which are unconformably overlain by the Saint-Daniel and Rivière-Port-Daniel mélanges, and correlate with the Thetford-Mines and Mont-Albert ophiolitic complexes. Our 40Ar/39Ar data and compiled regional age constraints indicate that ophiolite obduction was diachronous along the strike of the orogen. The timing of obduction and mélange formation varies according to the irregular geometry of the Early Paleozoic Laurentian margin, with earlier collision occurring along, or at the margins of promontories. Obduction was initiated with the formation of infraophiolitic metamorphic soles between ca. 479 and 472 Ma in southern Quebec and the Nadeau Ophiolitic Mélange, and possibly as late as ca. 470–466 Ma for the Mont-Albert Complex. These sole rocks were later exhumed and translated onto the Laurentian margin with the overlying ophiolites between 475 and 460–457 Ma. The uplifting and erosion of the orogenic wedge during the waning stages of obduction, has resulted in the sedimentation of olistostromal mélanges and onlapping flysch units above the ophiolitic nappes, as well as foredeep flysch successions during the latest Arenig(?) to earliest Caradoc.

The Newfoundland Appalachians are a classic area for studying the record of arc development and terrane accretion processes with excellent exposure to different crustal levels that are minimally deformed and metamorphosed. This area also provides a link between the once continuous Appalachian and Caledonian orogens. The Annieopsquotch Accretionary Tract lies along the Red Indian Line, within the peri-Laurentian realm of the central Newfoundland Appalachians. The Darriwilian (468–461 Ma) tectonostratigraphic units of the Annieopsquotch Accretionary Tract are commonly characterized by polymictic volcanogenic conglomerate horizons. A conglomerate horizon at the interface between a suprasubduction zone ophiolite and its calc-alkaline volcanic arc cover sequence is herein investigated for zircon and geochemical provenance. Geochronology revealed a maximum age of deposition of 467 ± 4 Ma with zircon inheritance ranging from ca. 500 to 2800 Ma, consistent with a peri-Laurentian continental basement source. Four types of volcanogenic conglomerate clasts are noted on the basis of lithogeochemistry: arc andesite; calc-alkaline basalt; tholeiitic basalt; and non-arc rhyodacite. Tholeiitic basalt clasts are likely locally derived, perhaps from the underlying Skidder Formation. Other volcanic clasts do not have any known geochemical equivalents in the Annieopsquotch Accretionary Tract and hence appear to be exotic. The dominant zircon population suggests that the exotic clasts were derived from a ca. 467 Ma peri-Laurentian andesitic volcanic arc that once formed part of the Annieopsquotch Accretionary Tract.

Previously unrecognized A-type granitoid and gabbroic rocks cover an area of ∼100 km 2 in the central Antigon- ish Highlands in Avalonian northern mainland Nova Scotia. The granitoid rocks in this suite occur, together with minor gab- bro, in separate mappable bodies named the Brora Lake, Haggarts Lake, West Barneys River, McGraths Mountain, and Leadbetter Road plutons and are the focus of this study. They are mainly alkali feldspar granite and quartz syenite with var- ied texture and modal mineralogy. Close spatial association, gradational contact relations, and magma-mingling relationships suggest that all of these rocks, including the gabbro, are coeval. Hence a U-Pb (zircon) age of 469.4 +/- 0.5 Ma obtained for a quartz syenite sample from the Brora Lake pluton is interpreted to indicate a Middle Ordovician age for all of these granitoid and gabbroic rocks. Most granitic and quartz syenitic samples have hypersolvus texture, characterized by strongly perthitic alkali feldspar, and some also contain interstitial granophyre, both features indicative of shallow emplacement. Mafic minerals include iron-rich calcic and calcic-sodic amphibole, hedenbergite, and in some samples fayalite. Most of the rocks have high concentrations of K, Na, P, Ti, and Fe and are alkalic, with agpaitic indices as high as 0.98. Discrimination diagrams indicate that they are A-type granitoid rocks formed in a within-plate extensional setting. Age correlatives of these A-type granitoid and gabbroic rocks are not yet known elsewhere in Avalonia. The available data suggest that this ca. 470 Ma magmatism occurred while Avalonia was a separate microcontinent in the Rheic Ocean. Resume : Des roches gabbroiques et granitoides de type A, auparavant non reconnues, recouvrent un secteur d'environ 100 km 2 dans les hautes terres centrales d'Antigonish dans la partie continentale septentrionale de l'Avalonie en Nouvelle

The Penobscot arc system of the northeastern Appalachians is an Early Cambrian to early Tremadocian (ca. 514- 485 Ma) ensialic to ensimatic arc-back-arc complex that developed along the margin of the peri-Gondwanan microcontinent Ganderia. Remnants of this Paleozoic arc system are best preserved in the Exploits Subzone of central Newfoundland. Cor- relative rocks in southern New Brunswick are thought to occur in the ca. 514 Ma Mosquito Lake Road Formation of the Ellsworth Group and ca. 497-493 Ma Annidale Group; however in the past, the work that has been conducted on the latter has been of a preliminary nature. New data bearing on the age and tectonic setting of the Annidale Group provides more conclusive evidence for this correlation. The Annidale Group contains subalkaline, tholeiitic to transitional, basalts to basal- tic andesites, picritic tuffs and calc-alkaline to tholeiitic felsic dome complexes that have geochemical signatures consistent with suprasubduction zone magmatism that was likely generated in a back-arc basin. New U-Pb ages establish that the Late Cambrian to Early Tremadocian Annidale Group and adjacent ca. 541 Ma volcanic rocks of the Belleisle Bay Group in the New River belt were affected by a period of younger magmatism ranging in age from ca. 479-467 Ma. This provides im- portant constraints on the timing of tectonism in the area. A ca. 479 Ma age for the Stewarton Gabbro that stitches the faulted contact between the Annidale and Belleisle Bay groups, demonstrates that structural interleaving and juxtaposition occurred during early Tremadocian time, which closely coincides with the timing of obduction of Penobscottian back-arc ophiolites onto the Ganderian margin in Newfoundland. Resume : Le systeme d'arc Penobscot du nord-est des Appalaches est un complexe d'arc-d'arriere-arc ensialique a ensima- tique datant du Cambrien precoce au Tremadocien precoce (~514-485 Ma) qui s'est developpe le long de la bordure peri- gondwannienne du microcontinent Ganderia. Des lambeaux de ce systeme d'arc paleozoique sont le mieux conserves dans la sous-zone Exploits du centre de Terre-Neuve. Des roches correlatives dans le sud du Nouveau-Brunswick seraient presen- tes dans la Formation de Mosquito Lake Road (~514 Ma) du Groupe d'Ellsworth et dans le Groupe d'Annidale (~497-493 Ma); toutefois, par le passe, le travail effectue sur ce dernier groupe n'a ete que preliminaire. De nouvelles donnees sur l'âge et l'environnement tectonique du Groupe d'Annidale fournissent des evidences plus concluantes de cette correlation. Le Groupe d'Annidale contient des basaltes a des andesites basaltiques, subalcalins, tholeiitiques a intermediaires, des tufs picritiques et des complexes de domes felsiques, calco-alcalins a tholeiitiques, possedant des signatures geochimiques qui concordent avec un magmatisme de zone de suprasubduction probablement generee dans un bassin d'arriere-arc. De nou- veaux âges U-Pb ont etabli que le Groupe d'Annidale, Cambrien tardif a Tremadocien precoce, et les roches volcaniques ad- jacentes du Groupe de Belleisle Bay (~541 Ma) dans la ceinture de New River ont ete affectes par une periode de magmatisme plus jeune, datant d'environ 479 a 467 Ma. Ces donnees fournissent des contraintes importantes sur le moment du tectonisme dans la region. Un âge d'environ 479 Ma pour le gabbro de Stewarton, qui reunit le contact de faille entre les groupes d'Annidale et de Belleisle Bay, demontre que l'imbrication et la juxtaposition structurales ont eu lieu au debut du Tremadocien, ce qui coincide de pres avec le moment de l'obduction des ophiolites d'arriere-arc de Penobscot par-dessus la bordure de Ganderia a Terre-Neuve. (Traduit par la Redaction)

The ∼470 Ma Ammonoosuc Volcanics of the Bronson Hill terrane of New Hampshire have back-arc basin basalt compositions. Major and trace element compositions compare favorably to coeval volcanic rocks in the Miramichi Highlands of New Brunswick and the Munsangan and Casco Bay volcanics of Maine, back-arc basin basalts of known peri-Gond- wanan origins. Additionally, the Ammonoosuc Volcanics have Nd and Pb isotopic compositions indicative of peri-Gond- wanan provenance. Thus, the Ammonoosuc Volcanics correlate with Middle Ordovician, peri-Gondwanan, Tetagouche- Exploits back-arc rocks of eastern New England and Maritime Canada. This correlation indicates that the Red Indian Line, the principle Iapetus suture, lies along the western margin of the Bronson Hill terrane. However, the younger (∼450 Ma) Oliverian Plutonic Suite rocks that intruded the Ammonoosuc Volcanics, forming domes along the core of the Bronson Hill anticlinorium, have Laurentian isotopic signatures. This suggests that the Ammonoosuc Volcanics were thrust westwardly over the Laurentian margin, and that Laurentian basement rocks are present under the Bronson Hill terrane. A plausible ex- planation for these relationships is that an easterly dipping subduction zone formed the Ammonoosuc Volcanics in the Tetagoughe-Exploits oceanic tract, just east of the coeval Popelogan arc. With the closure of the Iapetus Ocean, this terrane was thrust over the Laurentian margin. Subsequent to obduction of the Ammonoosuc Volcanics, subduction polarity flipped to the west, with the Oliverian arc resulting from a westerly dipping subduction zone that formed under the Taconic Orog- eny-modified Laurentian margin. Resume : Les roches volcaniques Ammonoosuc, ∼470 Ma, du terrane de Bronson Hill au New Hampshire ont des compo- sitions de bassins basaltiques d'arriere-arc. Les compositions en elements majeurs et traces se comparent favorablement aux roches volcaniques contemporaines des terres hautes de Miramichi au Nouveau-Brunswick et les roches volcaniques de Munsangan et de Casco Bay au Maine, des bassins basaltiques d'arriere-arc d'origine peri-gondwanienne connue. De plus, les roches volcaniques Ammonoosuc ont des compositions d'isotopes de Nd et de Pb qui indiquent leur provenance peri- gondwanienne. Ainsi, les roches volcaniques Ammonoosuc sont correlees avec les roches d'arriere-arc Tetagouche-Exploits, Ordovicien moyen peri-Gondwana, de l'est de la Nouvelle-Angleterre et des provinces maritimes canadiennes. Cette correla- tion signifie que la ligne Red Indian, la principale suture Iapetus, se situe le long de la bordure ouest du terrane de Bronson Hill. Toutefois, les roches de la suite plutonique Olivierian, plus jeune (∼450 Ma), formant des domes le long du cœur de l'anticlinorium Bronson Hill, ont des signatures isotopiques laurentiennes. Cela suggere que les roches volcaniques Ammo- noosuc aient ete chevauchees vers l'ouest par-dessus la bordure laurentienne et que les roches du socle laurentien se retrou- vent sous le terrane de Bronson Hill. Une explication plausible pour ces relations est qu'une zone de subduction a pendage vers l'est a forme les roches volcaniques Ammonoosuc dans l'etendue oceanique Tetagouche-Exploits, tout juste a l'est de l'arc Popelogan contemporain. Avec la fermeture de l'Ocean Iapetus, ce terrane a ete chevauche par-dessus la bordure lau- rentienne. Apres l'obduction des roches volcaniques Ammonoosuc, la polarite de la subduction a bascule vers l'ouest; l'arc Oliverian proviendrait d'une zone de subduction a faible pendage vers l'ouest qui s'est formee sous la bordure laurentienne modifiee par l'orogenese taconienne. (Traduit par la Redaction)

The Pikwitonei Granulite Domain located at the northwestern margin of the Superior Province is one of the largest Neoarchean high-grade terranes in the world, with well-preserved granulite metamorphic assemblages preserved in a variety of lithologies, including enderbite, opdalite, charnockite, and mafic granulite. U–Pb geochronology has been attempted to unravel the protolith ages and metamorphic history of numerous lithologies at three main localities; Natawahunan Lake, Sipiwesk Lake, and Cauchon Lake. The U–Pb age results indicate that some of the layered enderbite gneisses are Mesoarchean (3.4–3.0 Ga) and the more massive enderbites are Neoarchean. The high-grade metamorphic history of the Pikwitonei Granulite Domain is complex and multistage with at least four episodes of metamorphic zircon growth identified: (1) 2716.1 ± 3.8 Ma, (2) 2694.6 ± 0.6 Ma, (3) 2679.6 ± 0.9 Ma, and (4) 2642.5 ± 0.9 Ma. Metamorphic zircon growth during episodes 2 and 3 are interpreted to be regional in extent, corresponding to M1 amphibolite- and M2 granulite-facies events, respectively, consistent with previous field observations. The youngest metamorphic episode at 2642.5 Ma is only recognized at southern Cauchon Lake, where it coincides with granite melt production and possible development of a major northeast-trending deformation zone. The timing and multistage metamorphic history recorded in the Pikwitonei Granulite Domain is similar to most Superior Province high-grade terranes and marks a fundamental break in Archean crustal evolution worldwide at the termination of prolific global Neoarchean greenstone belt formation.

The Middle Mountain Metamorphic Domain of the Montana Metasedimentary Terrane, northwestern Wyoming Craton, within the northwestern Tobacco Root Mountains, mainly comprises migmatized tonalitic gneiss interlayered with amphibolitic (hornblende) gneiss, both of which are cut by metamorphosed mafic rocks. Together, these gneisses are defined as Middle Mountain Gneiss. Archean tonalitic gneiss from west of, and amphibolitic gneiss from east of, the Bismark Fault give, from chemically and air-abraded zircon grains, U–Pb ID–TIMS ages of 3325.5 ± 1.7 and 3340 Ma, respectively. These results reflect primary magmatic ages and show that the Middle Mountain Gneiss extends into the northern area of the Central Fault Block, between the Bismark and Mammoth faults. Older crustal processes in the tonalitic gneiss are evidenced by inherited grains, the oldest of which is >3460 Ma. A metabasite hosted in tonalitic gneiss in the Bismark Fault selvage zone yields a zircon age of 2468 Ma, which is interpreted as the time of metamorphism. This date and other ca. 2470 Ma dates known in the region reflect a series of thermotectonic events designated here as the Beaverhead – Tobacco Root Orogeny. Geochemical evidence in the Central Fault Block metabasites suggests that their >2470 Ma precursors evolved in a back-arc – arc-rift setting, whereas their equivalents west of the Bismark Fault were largely mid-ocean ridge basalt-related tholeiites and east of the Central Fault Block were back-arc tholeiites showing some continental affinity. The metabasite was metamorphosed, deformed, and intruded by pegmatite at 1756 Ma during the Big Sky Orogeny. This orogenic event also produced new zircon growth in Archean tonalitic gneiss. Monazite with an age of 75 Ma, found at one location, reflects nearby intrusion of the Cretaceous Tobacco Root Batholith.

High-precision isotope dilution – thermal ionization mass spectrometry (ID–TIMS) U–Pb zircon and baddeleyite ages from the PX1 vertically layered mafic intrusion Fuerteventura, Canary Islands, indicate initiation of magma crystallization at 22.10 ± 0.07 Ma. The magmatic activity lasted a minimum of 0.52 Ma. 40Ar/39Ar amphibole dating yielded ages from 21.9 ± 0.6 to 21.8 ± 0.3, identical within errors to the U–Pb ages, despite the expected 1% theoretical bias between 40Ar/39Ar and U–Pb dates. This overlap could result from (i) rapid cooling of the intrusion (i.e., less than the 0.3 to 0.6 Ma 40Ar/39Ar age uncertainties) from closure temperatures (Tc) of zircon (699–988 °C) to amphibole (500–600 °C); (ii) lead loss affecting the youngest zircons; or (iii) excess argon shifting the plateau ages towards older values. The combination of the 40Ar/39Ar and U/Pb datasets implies that the maximum amount of time PX1 intrusion took to cool below amphibole Tc is 0.8 Ma, suggesting PX1 lifetime of 520 000 to 800 000 Ma. Age disparities among coexisting baddeleyite and zircon (22.10 ± 0.07/0.08/0.15 Ma and 21.58 ± 0.15/0.16/0.31 Ma) in a gabbro sample from the pluton margin suggest complex genetic relationships between phases. Baddeleyite is found preserved in plagioclase cores and crystallized early from low silica activity magma. Zircon crystallized later in a higher silica activity environment and is found in secondary scapolite and is found close to calcite veins, in secondary scapolite that recrystallised from plagioclase. close to calcite veins. Oxygen isotope δ18O values of altered plagioclase are high (+7.7), indicating interaction with fluids derived from host-rock carbonatites. The coexistence of baddeleyite and zircon is ascribed to interaction of the PX1 gabbro with CO2-rich carbonatite-derived fluids released during contact metamorphism.

High-precision U–Pb isotope dilution – thermal ionization mass spectrometry (ID–TIMS) geochronology on chemically abraded zircon grains from a noritic gabbro of the Ni-bearing Suwar mafic–ultramafic layered complex, northwestern Yemen, gives a mean 206Pb/238U age of 638.46 ± 0.73 Ma (2σ; MSWD = 1.4). At Wadi Qutabah, ∼30 km to the north, a similar mafic sample has an identical age of 638.58 ± 0.51 Ma (2σ; MSWD = 0.32), which supports the possibility of there being a single, large intrusive complex with an estimated areal extent of ∼250 km2. This is supported by geochemical data of samples from each locality, which are postkinematic, gabbroic rocks that contain variable amounts of cumulus olivine, plagioclase, orthopyroxene, and ilmenite with intercumulus augite, hornblende, and Ni-sulphides. Straight rare Earth element (REE) patterns, Ba/La ∼30, Rb/Ba ∼0.04, and negative primitive-mantle-normalized P anomalies resemble EM1 (Enriched Mantle 1) of oceanic island basalts and Archean subcontinental mantle lithosphere. The mineralogy and magmatic/tectonic discrimination diagrams suggest within-plate continental tholeiitic and noritic cumulates typical of a rift setting for both intrusions. The complex intrudes retrograded, amphibolite-facies paragneiss of the Pan-African Afif lithotectonic terrane, and is generally undeformed and unaltered, and, therefore, unaffected by the Pan-African orogeny. Emplacement of the 639 Ma complex occurred during a tensional tectonic regime on the Arabian Peninsula and marks the time of proto-Iapetan rifting. The estimated size of the intrusion, its noritic composition, and Archean subcontinental lithospheric mantle signature and its position in thin Proterozoic lithosphere abutting Archean cratonic rocks, give it the key characteristics of known, mostly Proterozoic, intrusions that host world-class Ni–Cu–Co ore deposits.

Reconstructing tectonic histories involving continental collision, subduction, and exhumation at plate-tectonic rates of ∼1 cm/year, requires precise U–Pb zircon geochronology. The Western Gneiss Region has exceptional exposures of high-pressure (HP) and ultra-high-pressure (UHP) rocks. The strategy adopted here involved sampling eclogite and associated late unstrained pegmatites to acquire the time of eclogite crystallization and subsequent exhumation, respectively. The oldest eclogite sampled is 415 ± 1 Ma from layered, probably UHP eclogite at Tevik, Averøya, also with a garnet–hornblende assemblage at 410 ± 1 Ma. The Flem Gabbro eclogite margin, with implied UHP conditions, is 410 ± 2 Ma. Hornblende eclogite at Seth, Lepsøya, never at UHP, is 412 ± 2 Ma. These compare to Devonian ages of 401 ± 1 Ma for overgrowths on Proterozoic baddeleyite in Selnes Gabbro, 402 ± 2 Ma for coesite eclogite at Hareidlandet, 405–400 Ma for coesite eclogite at Flatraket, and 405 ± 2 Ma for near-UHP eclogite at Hjelmelandsdalen. The 415 Ma eclogite at Tevik compares to granitic pegmatite in the same outcrop at 395.2 ± 1.3 Ma and to pegmatite in eclogite at Aspøya at 395.3 ± 2 Ma. The 410 Ma age at Flem compares to nearby pegmatite in eclogite at 396 ± 4 Ma. Collectively, these results imply 14–20 million years between deep eclogite crystallization at ∼130 km and return to amphibolite-facies conditions at ∼30 km, with crystallization of locally derived granitoid melts. Nearby garnet-pyroxenite records older ages (∼430) and greater depths (∼200 km), but on similar exhumation paths at ∼0.4–0.7 cm/year.

The U–Pb geochronology of three granitoid plutons and three granitic pegmatite dykes, largely from the Thompson Nickel Belt located along the northwestern Superior craton margin, was investigated to place constraints on the timing of felsic magmatism associated with closure of the Manikewan Ocean and final continent–continent collision to form the Trans-Hudson Orogen. These data indicate that 1840–1820 Ma granite magmatism along the Superior margin was more active than previously thought and that some magmatism extended beyond the Thompson Nickel Belt sensu stricto, including the 1836 ± 3 Ma Mystery Lake granodiorite, 1822 ± 5 Ma Wintering Lake granodiorite, and the 1825 ± 8 Ma Fox Lake granite located in the Split Lake Block. Granitic pegmatites within the Thompson Nickel Belt were emplaced late in the collisional history in the period 1.79–1.75 Ga and include a 1770 ± 2 Ma dyke exposed at the Thompson pit, a 1767 ± 6 Ma dyke at the Pipe Pit, and a 1786 ± 2 Ma dyke located at Paint Lake. The final stage of crustal amalgamation in the eastern Trans-Hudson Orogen involved Superior Province crustal thickening and partial melting forming 1.84–1.82 Ga granite magmas and then final collision at ∼1.8 Ga between the Superior Province and a continental block to the west consisting of the previously amalgamated Sask and Hearne cratons. Heating of the Superior craton margin and granitic magmatism continued past peak metamorphism (1790–1750 Ma); this thermal event is represented by the emplacement of numerous late pegmatite dykes and evidenced by cooling dates recorded by metamorphic minerals (e.g., titanite) in reworked Archean gneisses and Proterozoic intrusions.

Integrated electron nanobeam (EBSD, CL, EDS) and isotopic measurements (U–Pb, (U–Th)/He) of zircon from the collar and centre of the 80 km wide central uplift of the 2020 ± 3 Ma Vredefort impact structure reveal new shock features in a microstructural progression related to impact basin formation and degree of U–Pb age resetting: (1) planar fractures in {1K0} and {1K2} orientation during initial shock wave compression; (2) curviplanar fractures in {1K1} orientation, now annealed, which host glassy inclusions of partial melt of the host rock; (3) microtwin lamellae in an orientation of 65° about [110], attributed to shock wave rarefaction; (4) nucleation of impact-age crystallites, possibly on microtwins, during post-shock heating by impact melt; and (5) crystal-plastic deformation linked to crater modification of the core of the central uplift. Planar fracturing and microtwinning ≥20 GPa in “cold shock” zircon in granitoid at a radial distance of 25 km failed to reset zircon age. Single-grain ID–TIMS data extend between pre-impact age of 2077 ± 11 Ma and a secondary Pb-loss event at ca. 1.0 Ga — the latter reflecting Kibaran igneous activity between 1.110 and 1.021 Ga. Age resetting by the impact event operated in an ∼15 km wide “hot shock” zone of impact-elevated temperatures ≥700 °C at the core of the central uplift. Mechanisms include internal recrystallization, defect-accelerated Pb diffusion via shock microstructures and melt films, and late crystal-plastic deformation. Igneous zircons from a 2019 ± 2 Ma foliated norite impact melt yield a mean (U–Th)/He date of 923 ± 61 Ma, indicating exposure of the present surface after this time.

The Neoarchean Pukaskwa batholith consists of pre-, syn-, and post-tectonic phases emplaced over an interval of 50 million years. Pre-tectonic phases are broadly synvolcanic and have a high-Al tonalite–trondhjemite–granodiorite (TTG) affinity interpreted to reflect derivation by partial melting of basaltic crust at lower crustal or upper mantle depths. Minor syn-tectonic phases slightly post-date volcanism and have geochemical characteristics suggesting some involvement or interaction with an ultramafic (mantle) source component. Magmatic emplacement of pre- and syn-tectonic phases occurred in the midcrust at paleopressures of 550–600 MPa and these components of the batholith are thought to be representative of the midcrust underlying greenstone belts during their development. Subsequent to emplacement of the syntectonic phases, and likely at approximately 2680 Ma, the Pukaskwa batholith was uplifted as a structural dome relative to flanking greenstone belts synchronously with ongoing regional sinistral transpressive deformation. The driving force for vertical tectonism is interpreted to be density inversion (Rayleigh–Taylor-type instabilities) involving denser greenstone belts and underlying felsic plutonic crust. The trigger for initiation of this process is interpreted to be an abrupt change in the rheology of the midcrust attributed to introduction of heat from the mantle attendant with slab breakoff or lithospheric delamination following the cessation of subduction. This process also led to partial melting of the intermediate to felsic midcrust generating post-tectonic granitic phases at approximately 2667 Ma. We propose that late density inversion-driven vertical tectonics is an inevitable consequence of horizontal (plate) tectonic processes associated with greenstone belt development within the Superior Province.

The Precambrian shield of Madagascar is reevaluated with recently compiled geological data and new U–Pb sensitive high-resolution ion microprobe (SHRIMP) geochronology. Two Archean domains are recognized: the eastern Antongil–Masora domain and the central Antananarivo domain, the latter with distinctive belts of metamafic gneiss and schist (Tsaratanana Complex). In the eastern domain, the period of early crust formation is extended to the Paleo–Mesoarchean (3.32–3.15 Ga) and a supracrustal sequence (Fenerivo Group), deposited at 3.18 Ga and metamorphosed at 2.55 Ga, is identified. In the central domain, a Neoarchean period of high-grade metamorphism and anatexis that affected both felsic (Betsiboka Suite) and mafic gneisses (Tsaratanana Complex) is documented. We propose, therefore, that the Antananarivo domain was amalgamated within the Greater Dharwar Craton (India + Madagascar) by a Neoarchean accretion event (2.55–2.48 Ga), involving emplacement of juvenile igneous rocks, high-grade metamorphism, and the juxtaposition of disparate belts of mafic gneiss and schist (metagreenstones). The concept of the “Betsimisaraka suture” is dispelled and the zone is redefined as a domain of Neoproterozoic metasedimentary (Manampotsy Group) and metaigneous rocks (Itsindro–Imorona Suite) formed during a period of continental extension and intrusive igneous activity between 840 and 760 Ma. Younger orogenic convergence (560–520 Ma) resulted in east-directed overthrusting throughout south Madagascar and steepening with local inversion of the domain in central Madagascar. Along part of its length, the Manampotsy Group covers the boundary between the eastern and central Archean domains and is overprinted by the Angavo–Ifanadiana high-strain zone that served as a zone of crustal weakness throughout Cretaceous to Recent times.

The stratigraphy of Cretaceous rocks in the Western Canada Foreland Basin is well constrained by dense borehole data that allow three-dimensional mapping of transgressive–regressive events, paleogeography, and subsidence patterns. However, it is difficult to estimate rates of change or to place events in a precise temporal framework because very few of the many bentonite beds have been dated using modern techniques. In this study, two bentonites, of at least regional extent, were dated using isotope dilution – thermal ionization mass spectrometry (ID–TIMS) U–Pb methods on chemically abraded zircon crystals. The older bentonite correlates with the “X” bentonite of the late middle Cenomanian and yields an age of 95.87 ± 0.10 Ma. The Bighorn River Bentonite, which lies just below the Cenomanian–Turonian boundary, yields an age of 94.29 ± 0.13 Ma and is interpreted to equate with the “B” bentonite and bed 80 at Pueblo, Colorado. Both bentonites dated here are older than the previously reported 40Ar/39Ar ages from correlative United States samples, supporting the observation that 40Ar/39Ar ages may systematically underestimate ages of Cretaceous bentonites by ∼1%, as suggested by other recent studies. The X bentonite immediately precedes a major late middle Cenomanian eustatic transgression that inundated the Dunvegan delta complex. The new ages for the X and Bighorn River bentonites indicate an average minimum subsidence rate of ∼0.27 mm/year in the most proximal part of the Cenomanian foredeep in northeast British Columbia during this time. The new age of the Bighorn River Bentonite, coupled with the orbitally tuned time scale of Sageman et al. (2006) , suggests a Cenomanian–Turonian boundary age of 94.12 ± 0.13 Ma.

The concepts concerning the origin of the Caledonides of northern Norway have changed rapidly in the last decade thanks largely to the application of modern geological and isotopic methods. This contribution presents U–Pb data obtained by ID–TIMS (isotope dilution – thermal ionization mass spectrometry) on zircon, titanite, and monazite from plutonic and metamorphic rocks. The Gjesvær Migmatite Complex of the Kalak Nappe Complex is shown to be of Grenvillian age, with granite and leucosome emplaced at about 970 Ma in a succession of psammites and amphibolites. It then underwent metamorphism and partial melting at about 425 Ma during Caledonian thrusting. Dating of granitic and gabbroic rocks that intrude the mainly turbiditic Hellefjord Group of the overlying Magerøy Nappe yields ages of 440–435 Ma, confirming that this unit is a correlative of the rocks on the island of Magerøy. A superimposed set of events at 430–425 Ma caused metamorphism forming pegmatites and local leucosome proving that the Magerøy Nappe, and the underlying Kalak Nappe Complex were juxtaposed on Baltica by that time. The age structure and other geological and paleomagnetic constraints suggest that the nappes originated along the Laurentian and perhaps Gondwanan margins and were brought to intersect Baltica by Cordilleran-type terrane translations along sinistral transform fault systems during the oblique convergence of Baltica and Laurentia.

Zircon grains in rocks collected from the Itsaq Gneiss Complex, southwest Greenland, were analyzed for U–Pb and Lu–Hf in the same grain using isotope dilution – thermal ionization mass spectrometry (TIMS) and multicollector – inductively coupled plasma – mass spectrometry (MC–ICP–MS). Grains were pretreated using chemical abrasion or air abrasion to assure that only zircon material unaffected by the migration of parent and daughter elements was analyzed. The data are consistent with derivation of all studied rocks from a single enriched mantle source or mafic crustal protolith with 176Lu/177Hf of 0.022 ± 0.003 that was repeatedly melted and produced tonalitic magmas. The assessment of the primary mantle source from which this mafic protolith was derived, at or before 3.85 Ga, greatly depends on the assumed composition of the bulk silicate Earth. Using the currently accepted Lu–Hf bulk Earth parameters based on the analysis of chondrites yields εHf(T) of 0 to +1 for the 3.80–3.86 Ga rocks, suggesting that the protolith was derived from mantle that underwent moderate depletion shortly before 3.9 Ga. However, using alternative models of the bulk silicate Earth composition, i.e., that account for the possible irradiation-induced accelerated decay of 176Lu in the early Solar System, and (or) loss of the products of early planetesimal or planetary differentiation, can lead to widely variable interpretations of the enrichment or depletion history of the mantle source of the Itsaq protolith.

The Butedale pluton, a ca. 100 km long compositionally zoned batholith, is part of the Coast Plutonic Complex that extends the length of the Canadian Pacific coast. Its age and thermal history are relevant to the Butedale pluton’s role as a test case of the Baja–BC hypothesis, as paleomagnetic evidence suggests that it may have formed thousands of kilometres to the south and moved northward along what is now the Coast Shear Zone. High-resolution U–Pb (chemical abrasion – thermal ionization mass spectrometry (CA–TIMS), zircon) analysis of rocks across the width of the Butedale pluton indicates that it is actually made up of at least two distinct magmatic events that formed the West Butedale pluton (ca. 95 Ma) and the East Butedale pluton (ca. 85 Ma). The East Butedale pluton was reheated by the emplacement of a younger adjacent pluton, which may have caused partial Pb loss and resulting excess scatter of 206Pb/238U zircon ages within individual samples. The West Butedale pluton may be the same age as, and part of, the nearby Ecstall pluton, thereby doubling the length of the Ecstall pluton to ca. 200 km. Single-grain, high-precision U–Pb analysis of zircon reveals previously unknown complexity and detail of emplacement and thermal history in the Butedale plutons.

Combined mapping, U–Pb isotope dilution – thermal ionization mass spectrometry (ID–TIMS) geochronology and geochemical studies in Harvey-Cardiff domain in the western Composite Arc Belt reveal the presence of a long-lived magmatic–metamorphic history between 1290 and 1030 Ma. Following intrusion of gneissic tonalite of the Anstruther and Burleigh gneiss complexes at ca. 1290 Ma, diorite of the Salmon Burn intrusive complex was emplaced at 1242.1 ± 1.1 Ma. A potassium-feldspar megacrystic monzogranite in the Salerno Creek deformation zone that forms the boundary between Harvey-Cardiff domain and Bancroft terrane was emplaced at 1211.3 ± 1.5 Ma, similar to the 1220 ± 1.6 Ma old Junction pluton and a previously reported age of ca. 1229 Ma from another Methuen suite granite in the domain. All three ages are 20 to 30 million years younger than Methuen suite ages elsewhere in the Composite Arc Belt (1250–1240 Ma). Deformation along the Salerno Creek deformation zone is constrained between 1211 Ma, the age of the megacrystic monzogranite, and 1050 Ma, the age of titanite grains from the Salmon Burn intrusive complex and a late alkalic dike. A monzogranite of the newly recognized Catchacoma granite suite yielded an age of 1067 ± 3.7 Ma, similar to the 1059.2 ± 1.6 Ma age obtained from the Cavendish pegmatite vein. These ages suggest a temporal link between late granite and pegmatite emplacement in Harvey-Cardiff domain. Metamorphic zircon, monazite, and titanite ages fall into three clusters (1082–1070, 1063–1045, and 1037–1030 Ma) and may represent a protracted metamorphic event or reflect distinct pulses during the Ottawan orogeny.

The Boothia mainland region of the north-central Rae domain is underlain by remnants of a Neoarchean volcano sedimentary sequence dismembered by two regionally extensive Neoarchean high-potassium granitoid suites with rare occurrences of a structurally interleaved, Paleoproterozoic sedimentary cover sequence. The granitoids and their gneissic equivalents are dominated by variably deformed and metamorphosed I-type, metaluminous, polyphase, commonly porphyritic to augen, biotite ± hornblende monzogranite, and subordinate granodiorite, with rare tonalite. New geochronological results, the first for this area, demonstrate that the widespread Neoarchean granitoid plutonism is dominantly 2.61–2.59 Ga, with a less prominent 2.66 Ga plutonic event. The age of zircon recrystallization suggests that ca. 2.60 Ga Archean metamorphism and fabric development (S1) affected the 2.66 Ga plutons prior to or contemporaneously with intrusion of the voluminous ca. 2.6 Ga suite. εNd(t) for the ca. 2.61–2.59 Ga suite range from 1.4 to –1.9, overlapping with the ca. 2.66 Ga suite that range from 1.4 to 1.5. The Nd isotopic data, coupled with the presence of inherited ca. 2.65, 2.70, and 2.85–2.90 Ga zircon, suggests recycling of older, Neoarchean to Mesoarchean crust in the formation of these suites. Metaplutonic rocks preserve Paleoproterozoic deformation (F4 and F5) and amphibolite-facies metamorphism, sporadically recorded in zircon rims that formed at 1.81 Ga. This event strongly reoriented the Neoarchean fabrics in metaplutonic rocks, generally without the development of a new coaxial Paleoproterozoic fabric, and we attribute this strain and metamorphism to the Hudsonian orogeny.

Seismic-reflection techniques have been applied in several studies over the last 20 years as a uranium-exploration tool within the Athabasca Basin and have been utilized to provide the larger structural context for known uranium deposits within the basin. At the crustal scale, deposits within the eastern Athabasca Basin are shown to be associated with deep-seated shear zones that originated during Trans-Hudson orogeny and have subsequently been reactivated during and subsequent to deposition of the basin-fill sandstones. Seismic properties of the Athabasca sandstones and underlying basement have been determined through in situ borehole measurements. Reflectivity within the sandstones is generally weak. Seismically recognizable signatures are primarily associated with variations in fracture density, porosity, and degree of silicification. The basement unconformity and regolith, a prime target of exploration, is widely imaged as it is characterized by variable but generally distinct reflectivity. Results from the McArthur River mine site suggest that the spatial coincidence of seismically imaged high-velocity zones and deep-seated faults that offset the unconformity may be a more broadly applicable exploration targeting tool. Three-dimensional (3-D) seismic imaging near existing ore zones can define the local structural controls on the mineralization and point the way to new targets, thus leading to more efficient exploration drilling programs. Furthermore, seismically generated structural maps of the unconformity and rock competence properties may play a significant role at the outset of mine planning.

The Abitibi and Wawa subprovinces of the southern Superior Province differ in terms of the extent of pre-existing 2750 Ma sialic crust and relationships between mantle plume type (tholeiitic basalt – komatiite) and arc type (tholeiite to calc-alkaline basalt – andesite – dacite – rhyolite) volcanic successions but evolved in close proximity to each other. Isotopic data, evidence from the Kapuskasing uplift, continuation of major structures associated with large gold deposits from the Abitibi into the Wawa subprovince and the related occurrence of diamonds in lamprophyric rocks in both subprovinces point to a common evolution prior to and during orogeny. Differences preserved in supracrustal sequences of the two subprovinces suggest that the main petrogenetic controls on orogenic gold deposits and lamprophyre-hosted diamond deposits lay in the lower crust and upper mantle. Similar processes must also have been active where gold and diamonds are associated on other Archean cratons, such as the Slave and possibly the Kaapvaal craton. Based on evidence preserved in the Abitibi–Wawa orogen, rapid crustal growth at ∼2.7 Ga was linked to the interplay between plate tectonics and mantle plumes. Key indicators in the model developed for the Abitibi–Wawa arc are the co-existence of plume-related rock types, modern-style adakites, major gold deposits, and lamprophyre-hosted diamond occurrences, at least in cases where shoshonitic host magmas can ascend rapidly through the crust. All of these indicators are now identified on the Kaapvaal craton by 3.1 Ga and many recur together in Paleoproterzoic and younger terranes, suggesting a common mechanism for rapid crustal growth through much of Earth’s history. The variety of granitoid types found within the Abitibi–Wawa orogen demonstrates that local tectonic factors, rather than a hotter average upper mantle, were important in controlling the type of magmas formed. Based on the geodynamic history of the subprovince, mantle plume interaction with an existing volcanic arc and the subduction of oceanic plateau crust played an important role in the formation of magmas similar to Cenozoic adakites. Flat subduction beneath a mantle wedge was probably responsible for the generation of the adakites and also promoted diamond stability at shallow depths while enhancing the reservoirs for subsequent orogenic gold deposits. The history of magmatism and mineralization in the Abitibi and Wawa subprovinces precludes an early or gradual development of a cratonic keel, which instead must have coupled with crust during the latest stages of orogeny.

A review of the ages determined for mantle material (xenoliths and xenocrysts entrained in kimberlite) derived from the Slave Province continental lithospheric mantle (CLM) indicates that a portion of the central Slave lithosphere may be ancient (3.5–3.3 Ga) harzburgite, but the majority of this lithosphere is much younger (2.9–2.0 Ga). Relying on the most robust chronometers, the majority of Slave lithosphere peridotite formed in the Neoarchean (peak at 2.75 Ga), whereas the majority of eclogite formed in the Paleoproterozoic (2.2–2.0 Ga). The northern Slave lithosphere contains evidence of peridotite xenolith ages that young with depth. The Paleoproterozoic eclogites may have multiple origins including remnants of subducted oceanic crust and mafic–ultramafic magmas that crystallized at great depth (100–200 km). Re–Os studies of sulfide inclusions in diamond indicate that some diamonds currently mined are ancient (∼3.5 Ga), but many Slave diamonds could be considerably younger. Most eclogitic diamonds recovered from the Slave craton are interpreted to be related to the formation of Paleoproterozoic eclogite. There is abundant evidence for Mesoproterozoic modification of the Slave lithosphere (e.g., heating by magma emplacement at great depth and metasomatism) and possible new addition to the lithosphere at that time. The Canadian Slave and African Kaapvaal lithospheres have similar peaks in cratonic peridotite formation ages at about 2.8 Ga, indicating that a large portion of the CLM in these two cratons formed and stabilized in the Neoarchean. One difference is that the Slave peridotites are much less enriched in SiO2, possibly reflecting the more metasomatized nature of the Kaapvaal CLM. The dominance of Paleoproterozoic formation ages for Slave mantle eclogites contrasts with the dominance of Neoarchean formation ages for Kaapvaal mantle eclogites.

A detailed study of the geochemical and isotopic characteristics of the volcanic rocks of the Hidden and Louis formations, which make up the hanging wall to the volcanogenic massive sulphide deposits at Flin Flon, Manitoba, was carried out on a stratigraphically controlled set of samples. The stratigraphy consists of the lowermost, dominantly basaltic, Hidden formation, and the overlying, dominantly basaltic, Louis formation. Of importance petrogenetically, is the 1920 unit a basaltic andesite with Nb/Thmn = 0.54–0.62, εNd(1.9Ga) = +3.6–+5.9, εHf(1.9Ga) = +8.5–+9.6, and 204Pb/206Pb = 23.9. The basaltic flows that dominate the Hidden formation have Nb/Thmn = 0.16–0.29, εNd(1.9Ga) = +1.7–+4.4, εHf(1.9Ga) = +7.0–+11.8 and 204Pb/206Pb = 16.9–18.6). The Carlisle Lake basaltic–andesite (top of Hidden formation) is characterized by Nb/Thmn = 0.16–0.14, and 204Pb/206Pb = 21.4. The rhyodacitic Tower member (bottom of Louis formation) has Nb/Thmn = 0.23, εNd1.9Ga = +4.6, εHf1.9Ga = +9.3, and 204Pb/206Pb = 22.2. The basaltic flows that dominate the Louis formation have Nb/Thmn = 0.18–0.25, εNd(1.9Ga) = +3.6–+4.2, εHf(1.9Ga) = +8.4–+11.3 and 204Pb/206Pb = 17.9. The Hidden and Louis formations show dominantly transitional arc tholeiite signatures, with the 1920 unit having arc tholeiite characteristics. It is interpreted to have formed through extensive fractional crystallization of differentiated magmas at shallow levels in oceanic crust. Given the geological, geochemical, and isotopic characteristics of the Hidden and Louis formations, they are interpreted to represent subducted slab metasomatism with minor contamination from subducted sediments.

The hanging wall to the Flin Flon, Callinan, and Triple 7 volcanogenic massive sulphide deposits of the Flin Flon district is composed of the Hidden and Louis formations. The contact between these formations is marked by mafic tuff that represents a hiatus in effusive volcanism. The formations form a composite volcanic edifice that was erupted and grew within a large, volcanic–tectonic subsidence structure (hosting the deposits) that developed within a rifted-arc environment. The formations are evidence of resurgent effusive volcanism and subsidence following a hiatus in volcanism marked by ore formation since they consist of dominantly basaltic flows, sills, and volcaniclastic rocks with subordinate basaltic andesite and rhyodacitic flows and volcaniclastic rocks. The Hidden formation is interpreted to represent a small shield volcano and the Louis formation a separate shield volcano that developed on its flank. Both the Hidden and Louis volcanic edifices were constructed by continuous, low-volume eruptions of pillow lava. A gradual change from a dominantly extensional environment during the formation of the footwall Flin Flon formation to a progressively more dominant convergent environment during the emplacement of the hanging wall suggests that the Hidden and Louis formations are unlikely to host significant volcanogenic massive sulphide-type mineralization. However, synvolcanic structures in the formations define structural corridors that project downwards into the footwall where they encompass massive sulphide mineralization, indicating their control on ore formation, longevity,and reactivation as magma and fluid pathways during the growth of the Hidden and Louis volcanoes.

We present new Sm–Nd isotope data for sediments from a core located on the continental slope of the St. Pierre Bank of Canada’s east coast. The Nd analyses indicate that the sediments were derived from two principal sources: the North American Shield that yields an average early Proterozoic isotopic signature and a younger Proterozoic signature attributed to Appalachian crustal sources. The Appalachian-sourced sediments predominated during the last glacial maximum (LGM) and were associated with low sedimentation rates (

Kimberlite-sourced bentonite layers have been discovered in Late Cretaceous sedimentary drill cores located within the Buffalo Head Hills kimberlite field, north-central Alberta. Two bentonites are unambiguously differentiated from “common” intermediate to felsic volcanic-derived Alberta bentonite by having similar whole-rock geochemical composition to ultramafic rocks from the Buffalo Head Hills kimberlite field and worldwide crater-facies kimberlite. The results demonstrate that the geochemical analysis of bentonite can provide a quick, cost-effective means of testing for low-volume kimberlite volcanism. The kimberlite-sourced bentonite is associated with a cluster of Buffalo Head Hills kimberlites known as the K14 complex. The K14A kimberlite occurrence has a previously reported206Pb/238U perovskite emplacement age of 86.8 ± 2.1 Ma. This age is compatible with early or mid-Cenomanian (∼99–96 Ma) and mid-Coniacian to Santonian (∼88–84 Ma) palynological results for mudstone underlying and bracketing the K14A and K14B kimberlites, respectively. Conversely, biostratigraphically significant palynomorphs in host rock cores bracketing the K14C kimberlite indicate emplacement during the Cenomanian or Turonian (∼96–92 Ma). U–Pb detrital zircon ages from syndepositional kimberlite-sourced bentonite directly adjacent to the K14C kimberlite contains a high frequency of young (∼99–92 Ma) zircon with a best maximum206Pb/238U depositional age of 91.7 ± 2.9 Ma. Thus, this innovative approach may provide evidence of multiple episodes of kimberlite emplacement within or near the K14 complex.

New Rb–Sr phlogopite and U–Pb perovskite age determinations for 12 of 38 known ultramafic bodies in the Buffalo Head Hills area of north-central Alberta show that kimberlitic magmatism occurred in at least two separate episodes during Late Cretaceous and Paleocene time. Nine kimberlites yield Coniacian to Campanian ages of between 88 ± 5 Ma (U–Pb perovskite, K5A) and 81.2 ± 2.3 Ma (Rb–Sr phlogopite, K252). A Danian U–Pb perovskite isochron age of 63.5 ± 0.7 Ma was obtained for the BM2 kimberlite, and Selandian Rb–Sr ages of 59.6 ± 2.8 and 60.3 ± 0.8 Ma were determined for the K1A and K19 bodies, respectively. These specific periods of magmatism correspond to characteristic intra-field features such as kimberlite spatial distribution, diamond content, rock classification, and mechanisms of emplacement. The ∼88–81 Ma group generally occurs in the northwestern part of the field and defines the diamond window for the Buffalo Head Hills kimberlite field. This volcanism is contemporaneous with sedimentary host rock deposition, which has important implications for the size and morphological complexity of the kimberlite bodies. The ∼64 Ma BM2 body represents the only known occurrence of hypabyssal-facies kimberlite in this field and is similar in terms of source composition to the ∼88–81 Ma kimberlites, but is not diamond bearing. The ∼60 Ma group occurs in the southwestern part of the field, is derived from a weakly diamondiferous – barren hybrid ultramafic source and features bodies that are eroded to present-day stratigraphic levels.