Sr, Y, Zr, Nb, Ti, and REE in Grenville amphibolites at Montauban-les-Mines, Quebec

1982 ◽  
Vol 19 (4) ◽  
pp. 633-644 ◽  
Author(s):  
W. H. MacLean ◽  
K. St. Seymour ◽  
M. K. Prabhu
Keyword(s):  
Tectonic Setting ◽  
Island Arc ◽  
The Other ◽  
Ocean Floor ◽  
Grenville Province ◽  
Ree Distribution ◽  
Back Arc ◽  
Ore Deposition

Distribution of Ti, Sr, Y, Zr, Nb, and REE in Proterozoic amphibolites and a rarely preserved pillowed metabasalt in the vicinity of Pb–Zn mineralization at Montauban-les-Mines in the Grenville Province of Quebec are used to assess the tectonic setting of the volcanism and, hence, the environment of ore deposition. Absolute abundances of Ti, Sr, Y, Zr, and Nb are close to those reported for modem island-arc and back-arc basalts. The flat patterns of the chondrite-normalized REE distribution and the discrimination plots of the other elements indicate a tholeiitic affinity for the volcanism. Specifically, plots of Ti against Zr and Ti–Zr–Y are mostly in the fields reported for ocean-floor (MOR and back-arc) basalts, but overlap with arc tholeiites. Cr and Ni are, however, higher than for most arc tholeiites. Overall, the data are most compatible with tholeiitic volcanism in an island-arc (including back-arc) environment.

New insights into the geologic evolution of the Grenvillian Trenton Prong inlier, Central Appalachian Piedmont, USA

2020 ◽  
Vol 57 (7) ◽  
pp. 840-854
Author(s):  
Richard A. Volkert
Keyword(s):  
Tectonic Setting ◽  
Hanging Wall ◽  
Sediment Source ◽  
Slow Cooling ◽  
Grenville Province ◽  
Magmatic Arc ◽  
Metamorphic History ◽  
Arc Setting ◽  
Appalachian Piedmont ◽  
Back Arc

New geochemical and 40Ar/39Ar hornblende and biotite data from the Grenvillian Trenton Prong inlier provide the first constraints for the identification of lithotectonic units, their tectonic setting, and their metamorphic to post-metamorphic history. Gneissic tonalite, diorite, and gabbro compose the Colonial Lake Suite magmatic arc that developed along eastern Laurentia prior to 1.2 Ga. Spatially associated low- and high-TiO2 amphibolites were formed from island-arc basalt proximal to the arc front and mid-ocean ridge basalt-like basalt in a back-arc setting, respectively. Supracrustal paragneisses include meta-arkose derived from a continental sediment source of Laurentian affinity and metagraywacke and metapelite from an arc-like sediment source deposited in a back-arc basin, inboard of the Colonial Lake arc. The Assunpink Creek Granite was emplaced post-tectonically as small bodies of peraluminous syenogranite produced through partial melting of a subduction-modified felsic crustal source. Prograde mineral assemblages reached granulite- to amphibolite-facies metamorphic conditions during the Ottawan phase of the Grenvillian Orogeny. Hornblende 40Ar/39Ar ages of 935–923 Ma and a biotite age of 868 Ma record slow cooling in the northern part of the inlier following the metamorphic peak. Elsewhere in the inlier, biotite 40Ar/39Ar ages of 440 Ma and 377–341 Ma record partial to complete thermal resetting or new growth during the Taconian and Acadian orogens. The results of this study are consistent with the Trenton Prong being the down-dropped continuation of the Grenvillian New Jersey Highlands on the hanging wall of a major detachment fault. The Trenton Prong therefore correlates to other central and northern Appalachian Grenvillian inliers and to parts of the Grenville Province proper.

Geochemical patterns in Norwegian greenstones

1982 ◽  
Vol 19 (3) ◽  
pp. 385-397 ◽  
Author(s):  
G. H. Gale ◽  
J. A. Pearce
Keyword(s):  
Trace Elements ◽  
Rare Earth ◽  
Trace Element ◽  
Tectonic Setting ◽  
Major Elements ◽  
Island Arc ◽  
Ocean Floor ◽  
Spreading Axis ◽  
Southern Norway ◽  
Representative Samples

Representative samples of Caledonian greenstones from the Grong, Joma, Løkken, Støren, Stavenes, and Bømlo areas in central and southern Norway have been analysed for major elements and over 20 trace elements. Ocean-floor tholeiite-normalized trace-element patterns and chondrite-normalized rare-earth patterns both provide clues to the genesis, original tectonic setting, petrologic character, and effects of alteration of these greenstones. We conclude that the Støren, Stavenes, and Løkken greenstones were generated at spreading axes within the Caledonian ocean, the Grong and possibly the Bømlo submarine greenstones were erupted in an island-arc system, and the Joma and Bømlo subaerial greenstones were erupted in a within-plate setting. The Løkken greenstones may have been generated in a marginal basin, whereas those from Støren and Stavenes were probably generated at a rapidly spreading axis in a major ocean.

Geochemical discrimination between ocean-floor and island-arc tholeiites—application to some ophiolites

1979 ◽  
Vol 16 (9) ◽  
pp. 1874-1882 ◽  
Author(s):  
L. Beccaluva ◽  
D. Ohnenstetter ◽  
M. Ohnenstetter
Keyword(s):  
North America ◽  
Oceanic Crust ◽  
Island Arc ◽  
The Other ◽  
Ocean Floor ◽  
Oceanic Ridge ◽  
Marginal Basin ◽  
Discrimination Diagram ◽  
The Mediterranean ◽  
Arc Setting

Two discriminative diagrams are proposed to separate island-arc tholeiites (1AT) and ocean-floor tholeiites (OFT). The first diagram, Ti/Cr vs. Ni, has been drawn using 84 island-arc (IAT) and 178 ocean-floor (OFT) samples with silica contents between 40 and 56%. About 97% of OFT and 93% of IAT samples fall, respectively, on opposite sides of the empirical boundary. In the second diagram, where the Ba/Y is less than 4.4 for the OFT and more than 3.9 for the IAT, the overlap between the two groups is about 6%.Owing to alteration effects, only the discrimination diagram Ti/Cr vs. Ni has been applied to ophiolitic basalts from the Mediterranean belts, Newfoundland, Central and North America, and Mongolia. The effusive and hypabyssal formations plotting either in one group or in the other lead to the suggestion that they have been formed in several possible geotectonical environments. It appears that ophiolites generated in a mid-oceanic ridge are scarce in opposition to those formed in an island-arc setting. In this latter case, ophiolite associations may correspond to the juxtaposition of either island-arc – marginal basin or island-arc – offshore oceanic crust formations.

Geochemistry, geochronology, and geodynamic setting of Ni–Cu ± PGE mineral prospects hosted by mafic and ultramafic intrusions in the Portneuf–Mauricie Domain, Grenville Province, QuebecGéologie Québec Contribution 8439-2008-2009-5. Geological Survey of Canada Contribution 20080511.

2009 ◽  
Vol 46 (5) ◽  
pp. 331-353 ◽  
Author(s):  
A.-A. Sappin ◽  
M. Constantin ◽  
T. Clark ◽  
O. van Breemen
Keyword(s):  
Trace Element ◽  
Crustal Contamination ◽  
Island Arc ◽  
Geodynamic Setting ◽  
Grenville Province ◽  
Magmatic Arc ◽  
Andean Type ◽  
Trace Element Signature ◽  
Arc Setting ◽  
Back Arc

The Portneuf–Mauricie Domain in the Grenville Province consists of the Montauban group rocks (1.45 Ga), intruded by the La Bostonnais complex plutons (1.40–1.37 Ga). This assemblage was formed in a magmatic arc setting. The sequence was intruded by mafic–ultramafic tholeiitic plutons, some of which host Ni–Cu ± PGE (platinum group element) prospects. U–Pb zircon ages determined from these plutons indicate that the mineralized intrusions were emplaced between 1.40 and 1.39 Ga and that they are coeval with the La Bostonnais complex plutons. The Ni–Cu ± PGE-bearing intrusions have mature island-arc trace element signatures, with strong chemical evidence for differentiation (Mg# and Cr content; MgO and TiO2 contents) and crustal contamination (enrichments in K2O, Rb, Ba, Th, and light rare-earth elements; Th/Yb and Ta/Yb ratios). However, one intrusion displays a back-arc trace element signature associated with evidence for weak crust assimilation. The evolution of the Portneuf–Mauricie Domain is interpreted as follows: (1) 1.45 Ga — Northwesterly directed Andean-type subduction beneath the Laurentian craton margin. Furthermore, northwest-dipping intraoceanic subduction offshore from the continent formed the Montauban island arc. (2) 1.45 to 1.40 Ga — Andean-type subduction led to the formation of a back-arc basin behind the Montauban arc. (3) 1.40 Ga — Emplacement of the La Bostonnais complex plutons, some hosting Ni–Cu ± PGE prospects, into the Montauban arc. (4) 1.39 Ga — Subduction beneath Laurentia led to arc–continent collision and to closure of the back-arc basin. Intrusion of the Ni–Cu ± PGE-bearing plutons ceased. (5) 1.37 Ga — Intrusion of all La Bostonnais complex plutons ceased.

Lithostratigraphy and geochemistry of the Cottrells Cove Group, Buchans – Roberts Arm volcanic belt: new constraints for the paleotectonic setting of the Notre Dame Subzone, Newfoundland Appalachians

1997 ◽  
Vol 34 (1) ◽  
pp. 86-103 ◽  
Author(s):  
Tomasz Dec ◽  
H. Scott Swinden ◽  
R. Greg Dunning
Keyword(s):  
Tectonic Setting ◽  
Volcanic Belt ◽  
Island Arc ◽  
Upper Ordovician ◽  
Sedimentary Sequences ◽  
History Of ◽  
Laurentian Margin ◽  
Uplift And Erosion ◽  
Back Arc ◽  
Volcaniclastic Deposits

New sedimentological, geochemical, and geochronological data from the Cottrells Cove Group in central Newfoundland provide important constraints on the nature of the Notre Dame Subzone, its tectonic setting, and the history of the Laurentian margin during the Early Ordovician. The Cottrells Cove Group forms the eastern extension of the Roberts Arm Group and correlates with the Chanceport Group on New World Island. It is represented by two volcano-sedimentary formations that occur in a complex thrust stack. The Fortune Harbour Formation consists of calc-alkalic, island-arc lavas, followed by a 1250 m thick succession of volcaniclastic deposits, radiolarian cherts, and calc-alkalic, mafic flows, which were deposited in a back-arc, basin-plain setting. The volcaniclastic deposits include felsic tuff, which has a U–Pb zircon age of 484 ± 2 Ma and an inheritance component of 2517 ± 26 Ma. These new U–Pb and Nd-isotope data suggest that the island-arc–back-arc volcanism and sedimentation in the Notre Dame Subzone developed in the vicinity of continental margin and approximately 10 Ma earlier than has previously been established. The Moores Cove Formation is undated but contains boulders of calc-alkalic basalt and is presumed to be at least in part younger than the Fortune Harbour Formation. Tholeiitic lavas, together with associated radiolarian cherts and volcaniclastic deposits, constitute the basal part of the Moores Cove Formation and may have been deposited in a back-arc environment synchronously with some parts of the Fortune Harbour Formation. They are conformably followed by an over 1200 m thick, coarsening-upward succession of lower-slope and submarine-fan deposits. The polymictic flysch, containing clasts of island-arc basalt, accompanied by other volcanic, plutonic, ultramafic, and sedimentary detritus, may record Middle or Upper Ordovician uplift and erosion of obducted arc–back-arc, volcano-sedimentary sequences and their ophiolitic substrate.

Stratigraphy, structure and geochemistry of Archaean supracrustal rocks from Oqaatsut and Naajaat Qaqqaat, north-east Disko Bugt, West Greenland

1999 ◽  
pp. 65-78
Author(s):  
Henrik Rasmussen ◽  
Lars Frimodt Pedersen
Keyword(s):  
Tectonic Setting ◽  
Trace Element Geochemistry ◽  
Element Geochemistry ◽  
West Greenland ◽  
North West ◽  
North East ◽  
Metavolcanic Rocks ◽  
Arc Setting ◽  
Area North ◽  
Back Arc

NOTE: This article was published in a former series of GEUS Bulletin. Please use the original series name when citing this article, for example: Rasmussen, H., & Frimodt Pedersen, L. (1999). Stratigraphy, structure and geochemistry of Archaean supracrustal rocks from Oqaatsut and Naajaat Qaqqaat, north-east Disko Bugt, West Greenland. Geology of Greenland Survey Bulletin, 181, 65-78. https://doi.org/10.34194/ggub.v181.5114 _______________ Two Archaean supracrustal sequences in the area north-east of Disko Bugt, c. 1950 and c. 800 m in thickness, are dominated by pelitic and semipelitic mica schists, interlayered with basic metavolcanic rocks. A polymict conglomerate occurs locally at the base of one of the sequences. One of the supracrustal sequences has undergone four phases of deformation; the other three phases. In both sequences an early phase, now represented by isoclinal folds, was followed by north-west-directed thrusting. A penetrative deformation represented by upright to steeply inclined folds is only recognised in one of the sequences. Steep, brittle N–S and NW–SE striking faults transect all rock units including late stage dolerites and lamprophyres. Investigation of major- and trace-element geochemistry based on discrimination diagrams for tectonic setting suggests that both metasediments and metavolcanic rocks were deposited in an environment similar to a modern back-arc setting.

Part 2. The deeper structure of the Atlantic - Geological hypotheses and the earth's crust under the oceans

1954 ◽  
Vol 222 (1150) ◽  
pp. 341-348 ◽  
Keyword(s):  
Heat Flow ◽  
Recent Work ◽  
Sea Water ◽  
Volcanic Rocks ◽  
The Other ◽  
Ocean Floor ◽  
Peridotite Xenoliths ◽  
The Earth ◽  
Southern Rhodesia ◽  
Mohorovičić Discontinuity

Recent work has determined the depth of the Mohorovičić discontinuity at sea and has made it likely that peridotite xenoliths in basaltic volcanic rocks are samples of material from below the discontinuity. It is now possible to produce a hypothetical section showing the transition from a continent to an ocean. This section is consistent with both the seismic and gravity results. The possible reactions of the crust to changes in the total volume of sea water are dis­cussed. It seems possible that the oceans were shallower and the crust thinner in the Archean than they are now. If this were so, some features of the oldest rocks of Canada and Southern Rhodesia could be explained. Three processes are described that might lead to the formation of oceanic ridges; one of these involves tension, one compression and the other quiet tectonic conditions. It is likely that not all ridges are formed in the same way. It is possible that serpentization of olivine by water rising from the interior of the earth plays an important part in producing changes of level in the ocean floor and anomalies in heat flow. Finally, a method of reducing gravity observations at sea is discussed.

Age, chemistry, and tectonic setting of Miramichi terrane (Early Paleozoic) volcanic rocks, eastern and east-central Maine, USA

2021 ◽  
Vol 57 ◽  
pp. 239-273
Author(s):  
Allan Ludman ◽  
Christopher McFarlane ◽  
Amber T.H. Whittaker
Keyword(s):  
New Brunswick ◽  
Subduction Zone ◽  
Tectonic Setting ◽  
Volcanic Rocks ◽  
Calc Alkaline ◽  
East Central ◽  
Arc Volcanism ◽  
Middle Ordovician ◽  
Volcanic Suite ◽  
Back Arc

Volcanic rocks in the Miramichi inlier in Maine occur in two areas separated by the Bottle Lake plutonic complex: the Danforth segment (Stetson Mountain Formation) north of the complex and Greenfield segment to the south (Olamon Stream Formation). Both suites are dominantly pyroclastic, with abundant andesite, dacite, and rhyolite tuffs and subordinate lavas, breccias, and agglomerates. Rare basaltic tuffs and a small area of basaltic tuffs, agglomerates, and lavas are restricted to the Greenfield segment. U–Pb zircon geochronology dates Greenfield segment volcanism at ca. 469 Ma, the Floian–Dapingian boundary between the Lower and Middle Ordovician. Chemical analyses reveal a calc-alkaline suite erupted in a continental volcanic arc, either the Meductic or earliest Balmoral phase of Popelogan arc activity. The Maine Miramichi volcanic rocks are most likely correlative with the Meductic Group volcanic suite in west-central New Brunswick. Orogen-parallel lithologic and chemical variations from New Brunswick to east-central Maine may result from eruptions at different volcanic centers. The bimodal Poplar Mountain volcanic suite at the Maine–New Brunswick border is 10–20 myr younger than the Miramichi volcanic rocks and more likely an early phase of back-arc basin rifting than a late-stage Meductic phase event. Coeval calc-alkaline arc volcanism in the Miramichi, Weeksboro–Lunksoos Lake, and Munsungun Cambrian–Ordovician inliers in Maine is not consistent with tectonic models involving northwestward migration of arc volcanism. This >150 km span cannot be explained by a single east-facing subduction zone, suggesting more than one subduction zone/arc complex in the region.

scholarly journals GEODYNAMICS AND MAGMATISM OF THE PACIFIC-TYPE TRANSFORM MARGINS. ASPECTS AND DISCRIMINANT DIAGRAMS

2021 ◽  
pp. 3-24
Author(s):  
A.V. Grebennikov ◽  
◽  
A.I. Khanchuk ◽  
Keyword(s):  
Continental Margin ◽  
Tectonic Setting ◽  
Island Arc ◽  
Igneous Rocks ◽  
High Alumina ◽  
Plate Boundaries ◽  
Spreading Ridge ◽  
Convergent Margins ◽  
Oceanic Plate ◽  
Plate Movement

Transform margins represent lithospheric plate boundaries with horizontal sliding of oceanic plate, which in time and space replaced the subduction related convergent margins. This happened due to: spreading ridge–trench intersection (California; Queen Charlotte–Northern Cordilleran, West of the Antarctic Peninsula, and probably the Late Miocene–Pleistocene Southernmost South America) or ridge death along continental margin (Baja California); change in the direction of oceanic plate movement (Western Aleutian–Komandorsk; Southernmost tip of the Andes); and island arc-continent collision (New Guinea Island). Post-subduction magmatism is related to a slab window that resulted either from the spreading ridge collision (subduction) with a continental margin or slab tear formation, or slab break-off after subduction cessation due to other reasons. Igneous magmatic series formed in consequence of these events show diversity of tholeiitic (sub-alkaline), alkaline or calc-alkaline, high-alumina and adakitic rocks. The comprehensive geochemical dataset (more than 2400 analyses) on igneous rocks of the model transform and convergent geodynamic settings allowed to substantiate the most informative triple diagrams for the petrogenic oxides TiO2 × 10 – Fe2O3Tot – MgO and trace elements Nb – La– Yb. Mostly approved for the rock compositions with SiO2 < 63 wt. %, the new plots are capable of distinguishing igneous rocks formed above zones of subduction at an island arc and continental margin (related to convergent margins), from those formed in the tectonic setting of transform margins along continents or island arcs.

Growth of wedge-shaped plutons at the base of active half-grabens

2004 ◽  
Vol 95 (1-2) ◽  
pp. 309-317 ◽  
Author(s):  
S. W. Richards ◽  
W. J. Collins
Keyword(s):  
High Temperature ◽  
Structural Model ◽  
Tectonic Setting ◽  
Shear Bands ◽  
Shaped Body ◽  
The Core ◽  
Lachlan Orogen ◽  
Eastern Australia ◽  
Back Arc ◽  
East West

ABSTRACTCombined field and geophysical data show that plutons from the Bega Batholith are elongate, meridional, wedge-shaped bodies which intruded during a period of regional east–west extension in the Palaeozoic eastern Lachlan orogen, eastern Australia. Plutons within the core of the batholith have intruded coeval, syn-rift sediments and co-magmatic volcanics. The batholith is bound by high-temperature, dip-slip faults, and contains several major NE-trending transtensional faults which were active during batholith construction. In the central part of the batholith, the Kameruka pluton is an asymmetric, eastward-thickening, wedge-shaped body with the base exposed as the western contact, which is characterised by abundant, shallow-dipping schlieren migmatites which contain recumbent folds and extensional shear bands. A shallow (<30°), east-dipping, primary magmatic layering in the Kameruka pluton steepens progressively westward, where it becomes conformable to the east-dipping basal migmatites. The systematic steepening of the layering is comparable to sedimentary units formed during floor depression in syn-rift settings. The present authors suggest that the wedge-shaped plutons of the Bega Batholith are the deeper, plutonic expression of a hot, active rift. The batholith was fed and sustained by injection of magma through sub-vertical dykes. Displacement along syn-magmatic, NE-trending faults suggests up to 25 km of arc-perpendicular extension during batholith construction. The inferred tectonic setting for batholith emplacement is a continental back-arc, where modern half-extension rates of 20–40 mm yr−1 are not unusual, and are sufficient to emplace the entire batholith in ∼1 Ma. This structural model provides a mechanism for the emplacement of some wedge-shaped plutons and is one solution to the ‘room problem’ of batholith emplace

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