Geochemistry of the upper Snooks Arm Group basalts, Burlington Peninsula, Newfoundland: evidence against formation in an island arc

1980 ◽  
Vol 17 (7) ◽  
pp. 888-900 ◽  
Author(s):  
G. A. Jenner ◽  
B. J. Fryer
Keyword(s):  
Subduction Zone ◽  
Oceanic Crust ◽  
Sedimentary Rocks ◽  
Oceanic Islands ◽  
Oceanic Island ◽  
Island Arc ◽  
Geochemical Data ◽  
Basaltic Rocks ◽  
Arc Setting ◽  
Back Arc

The Snooks Arm Group of the Newfoundland Appalachians, which includes the Betts Cove ophiolite at its base, has been interpreted as oceanic crust overlain by island arc volcanic and sedimentary rocks. The limited geochemical data available on the upper Snooks Arm Group basalts have been used as evidence for and against their formation in an island arc environment.Reinvestigation of the chemistry of the basaltic rocks of the upper Snooks Arm Group establishes them as large ion lithophile enriched tholeiites. Similar basalts have been found in oceanic islands, on aseismic ridges, and possibly in back-arc basins. Chemically analogous rocks are notably lacking from island arc settings.The geochemistry and geology of the upper Snooks Arm Group suggest that these rocks may have formed in either an oceanic island setting or, as recently suggested by Upadhyay and Neale, as part of a marginal basin. It is not possible to distinguish between these alternate models, although the most similar basaltic rocks occur in the former environment. It is most unlikely that these rocks formed in an early island arc setting and indeed there may be no need for them to be associated with a major subduction zone.

Trace elements and tectonic relationships of basaltic rocks in the Ballantrae igneous complex, Ayrshire

1974 ◽  
Vol 111 (1) ◽  
pp. 35-41 ◽  
Author(s):  
J. M. Wilkinson ◽  
J. R. Cann
Keyword(s):  
Trace Elements ◽  
Subduction Zone ◽  
Oceanic Crust ◽  
Hot Spot ◽  
Island Arc ◽  
Igneous Complex ◽  
Basaltic Rocks ◽  
Genetic Groups ◽  
Tectonic Environment ◽  
Low Potassium

SummaryIn order to obtain further evidence for the tectonic environment of generation of the basaltic rocks of the Ballantrae igneous complex, specimens of pillow lavas, dolerites, glaucophane schists and amphibolites were analysed for Ti, Zr, Y and Nb. Using Ti–Zr–Y, Ti–Zr and Y/Nb diagrams, three different genetic groups have been distinguished – (i) hot-spot basalts round Downan Point, round Bennane Head as far N as Balcreuchan Port, and also within serpentinite around Lendalfoot, (ii) island arc low-potassium tholeiites between Balcreuchan Port and Gamesloup, and (iii) possible ocean floor basalts at Knockormal and Knocklaugh. The interrelationships of these groups are in doubt. The hot-spot basalts may have been erupted through oceanic crust, but they could have formed prior to, or subsequent to, the island arc activity. More likely, the hot-spot basalts formed (possibly on oceanic crust) at a considerable distance from the island arc, and the two were later brought together tectonically, probably at the subduction zone associated with the arc.

scholarly journals The Kohistan between Gilgit and Chilas, northern Pakistan: regional tectonic implications

1996 ◽  
Vol 14 ◽  
Author(s):  
T. Khan ◽  
M. A. Khan ◽  
M. Q. Jan ◽  
M. Latif
Keyword(s):  
Sedimentary Rocks ◽  
Oceanic Island ◽  
Island Arc ◽  
Northern Pakistan ◽  
The Past ◽  
Volcanic Group ◽  
The North ◽  
Regional Tectonic ◽  
Back Arc ◽  
Field Geology

In this paper, we present geological description of an area located between Gilgit and Chilas within the Kohistan terrane. This terrane has been considered an intra-oceanic island arc, formed due to northward subduction of the Neo-tethyan lithospheric plate. At present, it is squeezed between the Karakoram­ Asian and Indian continental plates. Both the contacts are marked by suture zones, that is, Shyok (MKT) in the north and Indus (MMT) sutures in the south, respectively. The investigated area consists of plutonic, metamorphosed volcanic and sedimentary rocks, the Chilas Complex, and the Kamila Amphibolite. The metamorphosed volcanic and sedimentary rocks are packaged into the Jagfot Group. This group comprises basal turbiditic sediments, intercalated with amphibolites and calc-silicates (the Gilgit Formation), followed upward by the Gashu-Confluence Volcanics = Chait Volcanic Group, and finally the Thelichi Formation = Yasin Group of Aptian-Albian age. The Thelichi Formation comprises a volcanic base (Majne volcanics) and overlying turbidites, local intercalation of marbles, volcaniclastics and lava flows. Greenschist and amphibolite facies are common in the Jaglot Group, and particularly the sillimanite in the Gilgit Formation. A pair of anticline (the Gilgit anticline) and syncline (the Jaglot syncline) make up the structural scenario. On the basis of field geology, we conclude that the entire Jaglot Group and its equivalents, the Yasin Group, Chait Volcanic Group in Kohistan, and Burjila Formation, Bauma Harel Formation and Katzarah Formation in Ladakh show intra-oceanic back-arc basin rather than island arc affinities as suggested in the past.

scholarly journals Crustal Evolution of a Paleozoic Intra-oceanic Island-Arc-Back-Arc Basin System Constrained by the Geochemistry and Geochronology of the Yakuno Ophiolite, Southwest Japan

2014 ◽  
Vol 2014 ◽  
pp. 1-10 ◽  
Author(s):  
Yoshimitsu Suda ◽  
Yasutaka Hayasaka ◽  
Kosuke Kimura
Keyword(s):  
East Asian ◽  
Oceanic Island ◽  
Island Arc ◽  
Geochemical Data ◽  
Southwest Japan ◽  
Asian Continent ◽  
Initial Stage ◽  
Back Arc ◽  
Shrimp Zircon ◽  
Analytical Errors

The Yakuno ophiolite in southwest Japan is considered to have been obducted by the collision between an intra-oceanic island-arc-back-arc basin (intra-OIA-BAB) system and the East Asian continent during the late Paleozoic. New SIMS (SHRIMP) zircon U-Pb determinations for amphibolite and metagabbro of BAB origin within the Yakuno ophiolite yield ages of 293.4 ± 9.5 Ma and 288 ± 13 Ma, respectively. These ages are slightly older (however, overlapping within analytical errors) than the magmatic age of arc granitoids (ca. 285–282 Ma) that intruded into the mafic rocks of BAB origin. Results from geochronological and geochemical data of the Yakuno ophiolite give rise to the following tentative geotectonic model for the Paleozoic intra-OIA-BAB system: the initial stage of BAB rifting (ca. 293–288 Ma) formed the BAB crust with island-arc basalt (IAB) signatures, which was brought to the OIA setting, and generated the arc granitoids (ca. 285–282 Ma) by anatexis of the BAB crust. A later stage of BAB rifting (<ca. 285 Ma) formed the BAB crust with IAB to MORB signatures, on which the Permian sediments were conformably deposited. These components collided with the eastern margin of the East Asian continent during the early Mesozoic.

Specifics of the Caledonian Collision in the Ol’khon Region (Lake Baikal, Russia)

2021 ◽  
Vol 62 (4) ◽  
pp. 389-400
Author(s):  
V.A. Makrygina
Keyword(s):  
Subduction Zone ◽  
Oceanic Crust ◽  
Lake Baikal ◽  
Siberian Craton ◽  
Island Arc ◽  
Geophysical Data ◽  
Igneous Rocks ◽  
Fold Belt ◽  
Adjacent Part

Abstract —Analysis of geochemical, geochronological, and new geophysical data on metasedimentary and igneous rocks of the Ol’khon region has made it possible to substantiate: (1) the absence of products of the Caledonian suprasubduction magmatism from the adjacent part of the Siberian craton and (2) the presence of a product of this magmatism in the Anga–Talanchan island arc, namely, the Krestovsky massif with gabbro-diorite to granite phases. This suggests subduction of the Paleoasian oceanic crust under the island arc before the collision. The geophysical data showed a steep sinking of the Siberian craton margin. This sinking and the supposed contrary movement and rotation of the Siberian craton prevented the appearance of a subduction zone beneath the craton during the collision but caused the wide development of fault plates in the fold belt at the late collision stage. The residue of oceanic crust slab was pressed out along the fault planes near the surface and formed a row of gabbro-pyroxenite massifs of the Birkhin Complex in the fold belt, where syncollisional granitic melts (Sharanur Complex) formed at the same time. The interaction of two contrasting melts gave rise to the Tazheran and Budun alkaline syenite massifs and alkaline metasomatites of the Birkhin and Ulanganta gabbroid massifs.

Subduction-related magmatic imprint of most Philippine ophiolites: implications on the early geodynamic evolution of the Philippine archipelago

2004 ◽  
Vol 175 (5) ◽  
pp. 443-460 ◽  
Author(s):  
Rodolfo A. Tamayo* ◽  
René C. Maury* ◽  
Graciano P. Yumul ◽  
Mireille Polvé ◽  
Joseph Cotten ◽  
...  
Keyword(s):  
Partial Melting ◽  
Subduction Zone ◽  
Volcanic Rocks ◽  
The Philippines ◽  
Island Arc ◽  
Island Arcs ◽  
Geodynamic Evolution ◽  
Wide Range ◽  
Opening And Closing ◽  
Back Arc

Abstract The basement complexes of the Philippine archipelago include at least 20 ophiolites and ophiolitic complexes. These complexes are characterised by volcanic sequences displaying geochemical compositions similar to those observed in MORB, transitional MORB-island arc tholeiites and arc volcanic rocks originating from modern Pacific-type oceans, back-arc basins and island arcs. Ocean island basalt-like rocks are rarely encountered in the volcanic sequences. The gabbros from the ophiolites contain clinopyroxenes and plagioclases showing a wide range of XMg and An values, respectively. Some of these gabbros exhibit mineral chemistries suggesting their derivation from basaltic liquids formed from mantle sources that underwent either high degrees of partial melting or several partial melting episodes. Moreover, some of the gabbros display a crystallization sequence where orthopyroxene and clinopyroxene appeared before plagioclase. The major element compositions of coexisting orthopyroxenes and olivines from the mantle peridotites are consistent with low to high degrees of partial melting. Accessory spinels in these peridotites display a wide range of XCr values as well with some of them above the empirical upper limit of 0.6 often observed in most modern mid-oceanic ridge (MOR) mantle rocks. Co-existing olivines and spinels from the peridotites also exhibit compositions suggesting that they lastly equilibrated under oxidizing mantle conditions. The juxtaposition of volcanic rocks showing affinities with modern MOR and island arc environments suggests that most of the volcanic sequences in Philippine ophiolites formed in subduction-related geodynamic settings. Similarly, their associated gabbros and peridotites display mineralogical characteristics and mineral chemistries consistent with their derivation from modern supra-subduction zone-like environments. Alternatively, these rocks could have, in part, evolved in a supra-subduction zone even though they originated from a MOR-like setting. A simplified scenario regarding the early geodynamic evolution of the Philippines is proposed on the basis of the geochemical signatures of the ophiolites, their ages of formation and the ages and origins of the oceanic basins actually bounding the archipelago, including basins presumed to be now totally consumed. This scenario envisages the early development of the archipelago to be largely dominated by the opening and closing of oceanic basins. Fragments of these basins provided the substratum on top of which the Cretaceous to Recent volcanic arcs of the Philippines were emplaced.

The tectonic significance of Ordovician basic igneous rocks in the Southern Uplands, southwest Scotland

1995 ◽  
Vol 132 (5) ◽  
pp. 549-556 ◽  
Author(s):  
E. R. Phillips ◽  
R. P. Barnes ◽  
R. J. Merriman ◽  
J. D. Floyd
Keyword(s):  
Volcanic Rocks ◽  
Accretionary Prism ◽  
Igneous Rocks ◽  
Geochemical Data ◽  
Published Data ◽  
Volcanic Material ◽  
Tectonic Significance ◽  
Arc Setting ◽  
Back Arc ◽  
Midocean Ridge

AbstractIn the northern part of the Southern Uplands, restricted volumes of basic igneous rocks occur at or near the base of the Ordovician sedimentary strata. These rocks have previously been interpreted as ocean-floor tholeiites representative of the subducted Iapetus oceanic plate, preserved as tectonic slivers in a fore-arc accretionary prism. The alternative, back-arc basin model proposed for the Southern Uplands on sedimentological evidence raises questions over the origin of these rocks. New geochemical data and previously published data clearly indicate that the volcanic material does not have a simple single source. The oldest (Arenig) volcanic rocks from the Moffat Shale Group associated with the Leadhills Fault include alkaline within-plate basalts and tholeiitic lavas which possibly display geochemical characteristics of midocean ridge basalts. In the northernmost occurrence, alkaline and tholeiitic basalts contained within the Caradoc Marchburn Formation are both of within-plate ocean island affinity. To the south, in the Gabsnout Burn area, the Moffat Shale Group contains lenticular bodies of dolerite and basalt which have characteristics of island-arc to transitional basalts. This complex association of basaltic volcanic rocks is, at the present time, difficult to reconcile with either a simple fore-arc or back-arc setting for the Southern Uplands. However, the increasing arc-related chemical influence on basic rock geochemistry towards the southeast may tentatively be used in support of a southern arc-terrane, and as a result, a back-arc situation for the Southern Uplands basin. An alternative is that these volcanic rocks may represent the local basement to the basin and include remnants of an arc precursor to the Southern Uplands basin.

The ophiolites of the Tibetan Geotraverses, Lhasa to Golmud (1985) and Lhasa to Kathmandu (1986)

1988 ◽  
Vol 327 (1594) ◽  
pp. 215-238 ◽  
Keyword(s):  
Subduction Zone ◽  
Oceanic Lithosphere ◽  
Island Arc ◽  
Passive Margin ◽  
Jinsha River ◽  
Geochemical Composition ◽  
The North ◽  
Kunlun Mountains ◽  
Slow Spreading ◽  
Back Arc

Ophiolite belts are found in Tibet along the Zangbo, Banggong and Jinsha River Sutures and in the Anyemaqen mountains, the eastern extension of the Kunlun mountains. Where studied, the Zangbo Suture ophiolites are characterized by: apparently thin crustal sequences (3-3.5 k m ); an abundance of sills and dykes throughout the crustal and uppermost mantle sequences; common intraoceanic melanges and unconformities; and an N-MORB petrological and geochemical composition. The ophiolites probably formed within the main neo-Tethyan ocean and the unusual features may be due to proximity to ridge-transform intersections, rather than to genesis at very slow -spreading ridges as the current consensus suggests. The Banggong Suture ophiolites have a supra-subduction zone petrological and geochemical composition — although at least one locality in the Ado Massif shows MORB characteristics. However, it is also apparent that the dykes and lavas show a regional chemical zonation, from boninites and primitive island arc tholeiites in the south of the ophiolite belt, through normal island arc tholeiites in the central belt to island arc tholeiites transitional to N-MORB in the north. The ophiolites could represent fragments of a fore-arc, island arc, back-arc complex developed above a Jurassic, northward-dipping subduction zone and emplaced in several stages during convergence of the Lhasa and Qiangtang terranes. The ophiolites of the Jinsha River Suture have a N-MORB composition where analysed, but more information is needed for a proper characterization. The Anyemaqen ophiolites, where studied, have a within-plate tholeiite composition and may have originated at a passive margin: it is not, however, certain whether true oceanic lithosphere, as opposed to strongly attenuated continental lithosphere, existed in this region.

The Oman ophiolite as a Cretaceous arc-basin complex: evidence and implications

1981 ◽  
Vol 300 (1454) ◽  
pp. 299-317 ◽  
Keyword(s):  
Subduction Zone ◽  
Oceanic Crust ◽  
Significant Proportion ◽  
Dyke Swarm ◽  
Geochemical Analysis ◽  
Oman Ophiolite ◽  
Geochemical Evidence ◽  
Tectonic Development ◽  
High Level ◽  
Back Arc

Geological and geochemical evidence suggest that the Oman ophiolite is a fragment of a submarine arc-basin complex formed above a short-lived subduction zone in the mid-Cretaceous. Detailed studies of the lava stratigraphy and the intrusive relationships of dykes, sills and high-level plutons provide further evidence for the magmatic and tectonic development of the complex in question. Four consecutive events can be recognized to have taken place before emplacement: (1) eruption of basalts of island arc affinity onto pre-existing (Triassic) oceanic crust; (2) creation of new oceanic crust by backarc spreading; (3) intrusion of magma into this back-arc oceanic crust accompanied by eruption of basalts and andesites from discrete volcanic centres; (4) further intrusion of magma accompanied by uplift and eruption of basalts and rhyolites in submarine graben. A combined structural and geochemical analysis of the dyke swarm indicates that extension took place in approximately a N-S (ridge) and an ESE-WNW (leaky transform) direction relative to an inferred direction of subduction to the NE, and that a small but significant proportion of the sheeted dykes were injected during the ‘arc’ rather than the earlier ‘back-arc spreading’ episode. These various observations can be explained in terms of the progressive response of a non-isotropic lithosphere to the stresses induced during subduction.

Tectonic setting of late Archean bimodal volcanism in the Michipicoten (Wawa) greenstone belt, Ontario

1987 ◽  
Vol 24 (6) ◽  
pp. 1120-1134 ◽  
Author(s):  
Paul J. Sylvester ◽  
Kodjo Attoh ◽  
Klaus J. Schulz
Keyword(s):  
Greenstone Belt ◽  
Tectonic Setting ◽  
Volcanic Rocks ◽  
Depositional Environments ◽  
Oceanic Island ◽  
Island Arc ◽  
Basaltic Rocks ◽  
Bimodal Volcanism ◽  
Continental Arc ◽  
Convergent Plate Margin

The tectono-stratigraphic relationships, depositional environments, rock associations, and major- and trace-element compositions of the late Archean (2744–2696 Ma) bimodal basalt–rhyolite volcanic rocks of the Michipicoten (Wawa) greenstone belt, Ontario, are compatible with an origin along a convergent plate margin that varied laterally from an immature island arc built on oceanic crust to a more mature arc underlain by continental crust. This environment is similar to that of the Cenozoic Taupo–Kermadec–Tonga volcanic zone. Michipicoten basaltic rocks, most of which are proximal deposits compositionally similar ([La/Yb]n = 0.63–1.18) to modern oceanic island-arc tholeiites, are interpreted as having formed along the largely submerged island arc. Voluminous Michipicoten rhyolitic pyroclastic rocks ([La/Yb]n = 4.3–18.7, Ybn = 5.7–15.9) probably erupted subaerially from the continental arc, with distal facies deposited subaqueously on the adjacent oceanic island arc and proximal facies deposited in subaerial and shallow subaqueous environments on, or along the flanks of, the continental arc. The compositional similarity between the lower (2744 Ma) and upper (2696 Ma) volcanic sequences of the belt suggests that this island- and continental-arc configuration existed for at least 45 Ma. The Michipicoten belt may be a remnant of a larger, laterally heterogeneous volcanic terrane that also included the Abitibi greenstone belt.

The Northern Suture, Pakistan: margin of a Cretaceous island arc

1986 ◽  
Vol 123 (4) ◽  
pp. 405-423 ◽  
Author(s):  
Carol J. Pudsey
Keyword(s):  
Sedimentary Rocks ◽  
Island Arc ◽  
Two Phase ◽  
The North ◽  
Tethys Ocean ◽  
Radiometric Ages ◽  
Back Arc ◽  
Northwest Himalayas ◽  
Planar Fabric ◽  
Early Late

AbstractThe Northern Suture is a fault separating the Cretaceous Kohistan island arc terrain (northwest Himalayas) from Palaeozoic sediments of the Asian Plate to the north. The Kohistan arc includes volcanic and sedimentary rocks (andesitic lavas, tuffs, volcaniclastics, slates and limestones), metamorphosed to greenschist facies and intruded by the two-phase Kohistan Batholith. Asian continental margin sediments are mainly of shelf type, are variably metamorphosed and intruded by the Karakoram Batholith. The Northern Suture is a zone of melange from 150 m to 4 km wide, and contains blocks of volcanic greenstone, limestone, red shale, conglomerate, quartzite and serpentinite in a slate matrix. It has a strong planar fabric; but in many places bedding is preserved in blocks and matrix, and depositional rather than tectonic contacts are seen between the two. The melange is inferred to be an olistostrome largely derived from the Kohistan arc, formed in a small back-arc basin between Kohistan and Asia. Limestone blocks in the melange are dated as Aptian–Albian; post-tectonic intrusions yield radiometric ages from 111 to 62 Ma. The Northern Suture therefore probably formed in the early Late Cretaceous during closure of the back-arc basin. The Tethys ocean lay south of Kohistan, where the Main Mantle Thrust represents the westward continuation of the Indus–Tsangpo Suture.

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