Journal articles: 'Arc basalt'

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Morishita, Tomoaki, Naoto Hirano, Hirochika Sumino, Hiroshi Sato, Tomoyuki Shibata, Masako Yoshikawa, Shoji Arai, Rie Nauchi, and Akihiro Tamura. "Alkali basalt from the Seifu Seamount in the Sea of Japan: post-spreading magmatism in a back-arc setting." Solid Earth 11, no. 1 (January 7, 2020): 23–36. http://dx.doi.org/10.5194/se-11-23-2020.

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Abstract. We present geochemical and 40Ar∕39Ar age data for a peridotite xenolith-bearing basalt dredged from the Seifu Seamount (SSM basalt) in the northeast Tsushima Basin, southwest Sea of Japan. An 40Ar∕39Ar plateau age of 8.33±0.15 Ma (2σ) was obtained for the SSM basalt, indicating that it erupted shortly after the termination of back-arc spreading in the Sea of Japan. The SSM basalt is a high-K to shoshonitic alkali basalt that is characterized by light rare earth element enrichment. The trace element features of the basalt are similar to those of ocean island basalt, although the Yb content is much higher, indicating formation by the low-degree partial melting of spinel peridotite. The Nd, Sr, and Pb isotopic compositions of the SSM basalt differ from those of back-arc basin basalts in the Sea of Japan. The Sr–Nd isotopic composition of the SSM basalt suggests its source was depleted mid-ocean ridge mantle containing an enriched mantle (EM1) component. The SSM basalt was formed in a post-back-arc extension setting by the low-degree partial melting of an upwelling asthenosphere that had previously been associated with the main phase of back-arc magmatism.

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Taylor, Brian, and Fernando Martinez. "Back-arc basin basalt systematics." Earth and Planetary Science Letters 210, no. 3-4 (May 2003): 481–97. http://dx.doi.org/10.1016/s0012-821x(03)00167-5.

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Babaie, Hassan A., Abbed Babaei, A. Mohamad Ghazi, and Mohsen Arvin. "Geochemical, 40Ar/39Ar age, and isotopic data for crustal rocks of the Neyriz ophiolite, Iran." Canadian Journal of Earth Sciences 43, no. 1 (January 1, 2006): 57–70. http://dx.doi.org/10.1139/e05-111.

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Trace-element data (including the rare-earth elements) in the crustal sequence of the Neotethyan Neyriz ophiolite in southwest Iran indicate normal mid-ocean ridge basalt (N-MORB) or island-arc tholeiite chemistry for the Tang-e Hana basalt. The data suggest that the Tang-e Hana rhyodacite, basalt, plagiogranite, and gabbro derived from a low-K tholeiitic parent magma. Trace-element distributions in amphibolite clasts, in the sole detachment of the ophiolite south of Lake Neyriz, correlate well with distributions in basalt clasts in the mélange and in the Tang-e Hana basalt. These trace elements suggest that the amphibolite originated from metamorphism and deformation of a tholeiitic basalt protolith. New 40Ar/39Ar incremental heating plateau ages from two hornblende plagiogranite specimens, in the crustal sequence in Tang-e Hana, are 92.07 ± 1.69 and 93.19 ± 2.48 Ma. Isotopic data for five Tang-e Hana basalts yield εNd values of +7.8 and +7.9, and 87Sr/86Sr values of 0.70368 to 0.70476. The isotopic compositions, ophiolite tectonostratigraphy, and correlation of the 40Ar/39Ar cooling (plagiogranite) and deformation (amphibolite) ages suggest emplacement of the Neyriz ophiolite either into an accretionary prism, through offscraping and subduction erosion, and (or) formation in a supra-subduction zone environment, around 8296 Ma. Progressive accretion probably led to the development of a fore-arc basin and deposition of Upper Cretaceous Eocene fore-arc and arc-derived sediments on the ophiolite.

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Brophy, James G. "Can high-alumina arc basalt be derived from low-alumina arc basalt? Evidence from Kanaga Island, Aleutian Arc, Alaska." Geology 17, no. 4 (1989): 333. http://dx.doi.org/10.1130/0091-7613(1989)017<0333:chaabb>2.3.co;2.

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Kara, Jaakko, Markku Väisänen, and Hugh O'Brien. "Zircon dating of the basalt and felsic dyke in Haveri, SW Finland." Bulletin of the Geological Society of Finland 94, no. 2 (December 27, 2022): 109–18. http://dx.doi.org/10.17741/bgsf/94.2.001.

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The E-MORB type Haveri basalt differs from the volcanic arc type rocks in the Tampere belt showing no subduction signature. It is considered to have formed in a marginal basin prior to the volcanic arc. We present here zircon U-Pb dating on two samples. The basalt and the felsic dyke yielded 207Pb/206Pb ages of 1902 ± 5 Ma and 1891 ± 2 Ma, respectively, interpreted as crystallisation ages. The basalt also contains older 1.98 Ga grains while the felsic dyke contains older 1.92 Ga, 1.94 Ga, 1.98 Ga and 2.0 Ga grains, which are inferred as inherited. The age dating of E-MORB type basalts can be used to identify the extensional episodes of the accretionary Svecofennian orogeny.

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Jati Widiatama, Angga, Happy Christin Natalia, Rinaldi Ikhram, Lauti Dwita Santy, Joko Wahyudiono, Lanang Rangga Setia Wiguna, and Syifa Faranabila. "Various sources of rare earth element enrichment at Manamas volcanic rock, Timor Island." IOP Conference Series: Earth and Environmental Science 882, no. 1 (November 1, 2021): 012044. http://dx.doi.org/10.1088/1755-1315/882/1/012044.

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Abstract Manamas volcanic rock formed due to crustal thinning in fore arc setting. This research aims to provide information and the enrichment process of rare earth elements in Manamas Formation on the Timor Island and their tectonic implication. Manamas volcanic rock exposed in Bihati River, Baun, Timor consists of two different types of basalts, namely alkaline basalt and sub alkaline basalt. Analysis using ICP-MS method shows enrichment in large ion lithophile element and high field strength element. Subalkaline basalt has N-MORB patterns and alkaline basalt have OIB patterns. The Nb element is relatively impoverished that indicates influence of subduction activities. Thorium and uranium elements also show significant enrichment, due to sedimentary rocks contamination or continental crust or directly from the asthenosphere due to magma upwelling. The two distinctive patterns interpreted due to slab tear phenomenon beneath Timor Island during Australia oceanic plate subduction and recycled oceanic crust beneath Banda Arc.

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Taylor, Brian, and Fernando Martinez. "Corrigendum to “Back-arc basin basalt systematics”." Earth and Planetary Science Letters 214, no. 3-4 (September 2003): 679. http://dx.doi.org/10.1016/s0012-821x(03)00421-7.

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Simard, Renée-Luce, Jaroslav Dostal, and Maurice Colpron. "Rifting of a Mississippian continental arc system: Little Salmon formation, Yukon–Tanana terrane, northern Canadian Cordillera." Canadian Journal of Earth Sciences 44, no. 9 (September 1, 2007): 1267–89. http://dx.doi.org/10.1139/e07-022.

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The Yukon–Tanana terrane in the northern Canadian Cordillera records the development of a series of mid- to late Paleozoic arc systems, punctuated by intra-arc deformation, uplift, and episodic rifting coeval with back-arc extension, built upon a metasedimentary basement of northwestern Laurentian affinity. In central Yukon, the Little Kalzas formation records the development of one of these Mississippian continental arcs, whereas the Little Salmon formation records the development of an intra-arc rift basin within a continental arc. The Little Salmon formation lower succession comprises mainly volcaniclastic rocks derived from erosion of Early Mississippian and older units, including rocks of the Little Kalzas continental arc. Above a medial limestone member, the upper succession of the Little Salmon formation includes alkali basalt, breccia, and crystal and ash tuffs in the north and predominantly epiclastic rocks interbedded with crystal and ash tuffs in the south. The alkali basalts have the geochemical characteristics of ocean-island basalts and their positive ε Nd 340 (+7.3) and low 87Sr/86Sr values (0.705) suggest a primitive magma source with little or no involvement of continental crust. The transition between the northern and southern facies of the upper succession of the Little Salmon formation coincides with a northeast-trending synvolcanic fault inferred to have controlled alkali basalt eruptions and deposition of Mn-bearing exhalite in the north and basin plain sedimentation in the south. The environment of deposition of the Little Salmon formation resembles that of the modern Sumisu rift in the Izu–Bonin–Mariana arc system or the early stages of development of the Japan island-arc system.

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Haidar, Tanveer, Sagar Misra, Neeraj Vishwakarma, and K. R. Hari. "Geochemical evolution of basaltic flows from Dongargarh Supergroup, Bastar Craton, Central India." IOP Conference Series: Earth and Environmental Science 1032, no. 1 (June 1, 2022): 012001. http://dx.doi.org/10.1088/1755-1315/1032/1/012001.

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Abstract Composition of basalts in magmatic arcs influenced by the subducting lithosphere, mantle wedge, dehydration of oceanic crust, and/or crustal assimilation beneath the arc. In this paper, we compiled earlier published geochemical data of Dongargarh basalts to decipher the genesis of volcanic rocks. SiO2 vs (FeO + MgO) plot of basalt suggests the volcanic rocks are tholeiitic in composition. Primitive mantle and REE normalized plots indicate either the source was enriched mantle or a possible interaction of depleted magmatic source with the Paleoarchean continental crust in the Bastar Craton. The primitive mantle normalized diagram shows a negative anomaly of Nb, Ti, and Ta indicates subduction-related magmatism. In addition to the basalt composition, variation diagrams for tectonic settings represent the continental arc-related magmatism. From the available geochemical data of basalts and earlier studies on Dongargarh volcanic, there was an oceanic ridge that was subducted beneath the continental plate. The source of Pitepani basalts was significantly enriched in HFSE and REE as compared to mid-oceanic basalts. Thus the study finds the volcanic rocks are part of enriched mantle source that formed in the subduction-related magmatism.

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Lodge, Robert W. D., Harold L. Gibson, Greg M. Stott, James M. Franklin, and George J. Hudak. "Geodynamic setting, crustal architecture, and VMS metallogeny of ca. 2720 Ma greenstone belt assemblages of the northern Wawa subprovince, Superior Province." Canadian Journal of Earth Sciences 52, no. 3 (March 2015): 196–214. http://dx.doi.org/10.1139/cjes-2014-0163.

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The greenstone belts along the northern margin of the Wawa subprovince of the Superior Province (Vermilion, Shebandowan, Winston Lake, Manitouwadge) formed at ca. 2720 Ma and have been interpreted to be representative of a rifted-arc to back-arc tectonic setting. Despite a common inferred tectonic setting and broad similarities, these greenstone belts have a significantly different metallogeny as evidenced by different endowments in volcanogenic massive sulphide (VMS), magmatic sulphide, and orogenic gold deposits. In this paper, we examine differences in geodynamic setting and crustal architecture as they pertain to the metallogeny of each greenstone belt by characterizing the regional-scale trace-element and isotopic (Nd and Pb) geochemistry of each belt. The trace-element geochemistry of the Vermilion greenstone belt (VGB) shows evidence for a transition from arc-like to back-arc mafic rocks in the Soudan belt to plume-driven rifted arcs in the ultramafic-bearing Newton belt. The Shebandowan greenstone belt (SGB) has a significant proportion of calc-alkalic, arc-like basalts, intermediate lithofacies, and high-Mg andesites, which are characteristic of low-angle, “hot” subduction. Extensional settings within the SGB are plume-driven and associated with komatiitic ultramafic and mid-ocean ridge basalt (MORB)-like basalts. The Winston Lake greenstone belt (WGB) is characterized by a transition from calc-alkalic, arc-like basalts to back-arc basalts upward in the strata and is capped by alkalic ocean-island basalt (OIB)-like basalts. This association is consistent with plume-driven rifting of a mature arc setting. Each of the VGB, SGB, and WGB show some isotopic evidence for the interaction with a juvenile or slightly older differentiated crust. The Manitouwadge greenstone belt (MGB) is characterized by isotopically juvenile, bimodal, tholeiitic to transitional volcanic lithofacies in a back-arc setting. The MGB is the most isotopically juvenile belt and is also the most productive in terms of VMS mineralization. The Zn-rich VMS mineralization within the WGB suggests a relatively lower-temperature hydrothermal system, possibly within a relatively shallow-water environment. The Zn-dominated and locally Au-enriched VMS mineralization, as well as mafic lithofacies and alteration assemblages, are characteristic of relatively shallower-water deposition in the VGB and SGB, and indicate that the ideal VMS-forming tectonic condition may have been compromised by a shallower-water depositional setting. However, the thickened arc crust and compressional tectonics of the SGB suprasubduction zone during hot subduction may have provided a crustal setting more favourable for the magmatic Ni–Cu sulphide and relative gold endowment of this belt.

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Hollings, Pete, Greg Stott, and Derek Wyman. "Trace element geochemistry of the Meen-Dempster greenstone belt, Uchi subprovince, Superior Province, Canada: back-arc development on the margins of an Archean protocontinent." Canadian Journal of Earth Sciences 37, no. 7 (July 1, 2000): 1021–38. http://dx.doi.org/10.1139/e00-007.

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Comprehensive trace element analyses of mafic and felsic volcanic rocks from the 2.85-2.74 Ga Meen-Dempster greenstone belt reveal a wide compositional diversity. The ~2.85 Ga Kaminiskag assemblage is dominated by mafic tholeiite characterized by predominantly unfractionated REE (La/Smn = 0.8-1.1). Rare intermediate and felsic pyroclastic flows (SiO2 = 62-74) with moderate to pronounced LREE enrichment are intercalated with the tholeiite. The Kaminiskag assemblage is overlain by the ~2825 Ma Meen assemblage, comprising dominantly dacitic tuffs and pyroclastic breccia, displaying enriched LREE (La/Smn = 3.7-7.2) and moderately fractionated HREE, in conjunction with pronounced negative Nb anomalies. Five distinct suites have been recognized in the ~2740 Ma Confederation assemblage: (1) tholeiitic basalt with flat to smoothly depleted REE, (2) tholeiite with flat to weakly depleted LREE in conjunction with pronounced negative Nb anomalies, (3) Fe-rich basalt with elevated Ti and P contents, LREE enrichment, and fractionated HREE, (4) LREE enriched basalt and andesite with negative Nb anomalies, and (5) dacite and rhyolite with enriched LREE, moderately fractionated HREE, and variable high field strength element anomalies. The geochemistry and geochronology of the Kaminiskag and Meen assemblages are consistent with the formation of an oceanic back arc (Kaminiskag assemblage), which formed the basement for a subduction-related arc complex (Meen assemblage) after a 15 Ma hiatus. The Confederation assemblage is interpreted to represent an Archean back arc, where the complex interplay of mantle sources allows for the eruption of tholeiite, subduction-modified tholeiite, ocean island basalt-like basalt, and subduction-related arc-type volcanic rocks. The recognition of back-arc basins within the Meen-Dempster greenstone belt emphasizes a continuity of crustal growth processes from the Archean to the present day.

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Ohba, T., K. Matsuoka, Y. Kimura, H. Ishikawa, and H. Fujimaki. "Deep Crystallization Differentiation of Arc Tholeiite Basalt Magmas from Northern Honshu Arc, Japan." Journal of Petrology 50, no. 6 (June 1, 2009): 1025–46. http://dx.doi.org/10.1093/petrology/egp030.

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Bailes, Alan H., and Alan G. Galley. "Evolution of the Paleoproterozoic Snow Lake arc assemblage and geodynamic setting for associated volcanic-hosted massive sulphide deposits, Flin Flon Belt, Manitoba, Canada." Canadian Journal of Earth Sciences 36, no. 11 (November 10, 1999): 1789–805. http://dx.doi.org/10.1139/e98-111.

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The majority of volcanogenic massive sulphide (VMS) deposits at the east end of the Paleoproterozoic Flin Flon "greenstone" belt occur in the 1.89 Ga Snow Lake arc assemblage. VMS deposits in this isotopically juvenile oceanic arc sequence are hosted within a 6 km thick monoclinal section that records in its stratigraphy and geochemistry a temporal evolution in arc development from primitive, through mature, to arc rift. VMS deposits occur in both the primitive and mature arc sequences and are interpreted to be products of arc extension and accompanying anomolously high heat flow, fracturing, and fluid circulation. Boninites, low-Ti tholeiites, and isotopically juvenile rhyolite flows, a rock association that has been attributed in both modern and Phanerozoic arcs to high-temperature hydrous melting of refractory mantle sources in an extensional and (or) proto-arc environment, forms the primitive arc. Indication that the mature arc also underwent extension includes voluminous volcaniclastic detritus (from fault scarps?), prominent synvolcanic dykes, isotopically juvenile rhyolite flows, and the fact that the mature arc is stratigraphically overlain by arc-rift basalts with MORB-like geochemistry. Interpretation of VMS deposits at Snow Lake as products of an extensional geodynamic setting suggests that the traditional Flin Flon Belt exploration model, invoking "pluton-generated" convective seawater, be augmented by the search for evidence of rifting. Economically significant rock associations at Snow Lake include geochemically primitive refractory mafic magmas (e.g., boninites), isotopically juvenile felsic magmas, bimodal basalt-rhyolite sequences, and arc-rift basalts.

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Dec, Tomasz, H. Scott Swinden, and R. Greg Dunning. "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." Canadian Journal of Earth Sciences 34, no. 1 (January 1, 1997): 86–103. http://dx.doi.org/10.1139/e17-008.

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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.

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Gust, D. A., and M. R. Perfit. "Phase relations of a high-Mg basalt from the Aleutian Island Arc: Implications for primary island arc basalts and high-Al basalts." Contributions to Mineralogy and Petrology 97, no. 1 (September 1987): 7–18. http://dx.doi.org/10.1007/bf00375210.

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Dorais, Michael J., Matthew Harper, Susan Larson, Hendro Nugroho, Paul Richardson, and Nova Roosmawati. "A comparison of Eastern North America and Coastal New England magma suites: implications for subcontinental mantle evolution and the broad-terrane hypothesis." Canadian Journal of Earth Sciences 42, no. 9 (September 1, 2005): 1571–87. http://dx.doi.org/10.1139/e05-056.

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New England and Maritime Canada host two major suites of Mesozoic diabase dykes. The oldest is the Coastal New England dykes that were emplaced between 225 and 230 Ma. These rocks are dominantly alkaline with trace element and isotopic compositions indicative of a high-238U/204Pb mantle (HIMU) source. The oldest of the ~200 Ma Mesozoic rift magmas is represented by the Talcott basalt of the Hartford basin and its feeder dykes. External to the basin is the compositionally equivalent Higganum dyke. The extension of the Higganum, the Onway dyke in New Hampshire, is identical in major and trace element and isotopic compositions indicating that the dyke system represented a feeder to flows of flood basalt proportions. The Talcott system rocks have some trace element similarities with arc basalts and have been interpreted as representing melts of a subduction zone modified mantle beneath the Laurentian- Gondwanan suture. Incompatible trace element ratios and Ba, Th, and U values are, however, unlike arc basalts and are more indicative of crustal contamination of the primary magma. The coastal New England magmas have oceanic island basalt signatures that are generally thought to represent plume-tail magmatism, which is antithetic to a plume-head origin for the younger eastern North America magmas. However, coastal New England rocks have the same trace element signatures as the alkaline rocks of the Loihi seamount, which represent the pre-shield stage to the voluminous tholeiitic magmatism in Hawaii.

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Phillips, E. R., R. P. Barnes, R. J. Merriman, and J. D. Floyd. "The tectonic significance of Ordovician basic igneous rocks in the Southern Uplands, southwest Scotland." Geological Magazine 132, no. 5 (September 1995): 549–56. http://dx.doi.org/10.1017/s001675680002121x.

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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.

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Coombs, April M., Alex Zagorevski, Vicki McNicoll, and John M. Hanchar. "Preservation of terranes during the assembly of the Annieopsquotch Accretionary Tract: Inferences from the provenance of a Middle Ordovician ophiolite to arc transition, central Newfoundland Appalachians1Geological Survey of Canada Contribution 20100463.2This article is one of a series of papers published in this CJES Special Issue: In honour of Ward Neale on the theme of Appalachian and Grenvillian geology." Canadian Journal of Earth Sciences 49, no. 1 (January 2012): 128–46. http://dx.doi.org/10.1139/e11-042.

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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.

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Volkert, Richard A. "New insights into the geologic evolution of the Grenvillian Trenton Prong inlier, Central Appalachian Piedmont, USA." Canadian Journal of Earth Sciences 57, no. 7 (July 2020): 840–54. http://dx.doi.org/10.1139/cjes-2019-0140.

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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.

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Tomkins, Andrew G., Kyle C. Rebryna, Roberto F. Weinberg, and Bruce F. Schaefer. "Magmatic Sulfide Formation by Reduction of Oxidized Arc Basalt." Journal of Petrology 53, no. 8 (April 20, 2012): 1537–67. http://dx.doi.org/10.1093/petrology/egs025.

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Smith, Alan D. "Back-arc convection model for Columbia river basalt genesis." Tectonophysics 207, no. 3-4 (July 1992): 269–85. http://dx.doi.org/10.1016/0040-1951(92)90390-r.

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Barker, F., A. Sutherland Brown, J. R. Budahn, and G. Plafker. "Back-arc with frontal-arc component origin of Triassic Karmutsen basalt, British Columbia, Canada." Chemical Geology 75, no. 1-2 (February 1989): 81–102. http://dx.doi.org/10.1016/0009-2541(89)90022-3.

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Oluyede, Kehinde, Ibrahim Garba, Umar Danbatta, Paul Ogunleye, and Urs Klötzli. "Petrography and geochemistry of the granitoids and associated volcanic rocks of the northern part of Kushaka and Birnin Gwari schist belts, NW Nigeria: implications for provenance and geological setting." International Journal of Advanced Geosciences 9, no. 2 (July 24, 2021): 42. http://dx.doi.org/10.14419/ijag.v9i2.31269.

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The granitoids and the associated volcanic rocks of the northern part of Kushaka and Birnin Gwari schist belts were emplaced in the ca. 3.5 – 1. 0 Ga remobilized basement complex terrain composed of metasedimentary and metaigneous rocks that later underwent medium- to high-grade metamorphism during the Pan-African thermo-tectonic event. They comprise dominantly of diorite, granodiorite, granite, granite gneiss and basalt, and are product of metasomatism and injections. The diorite and granodiorite occur as paleosome and the granite as leucosome with the development of high temperature minerals, locally attaining granulite facie metamorphism. Plagioclase, biotite, hornblende, pyroxene and olivine fractionation played an important role during their genesis through fractional crystallization of basaltic magma and partial melting of older dioritic-granodioritic source rock in the deep crust which were themselves ultimately derived through fusion of mantle materials contaminated by continental crust and enriched by fluids derived from oceanic crust in an arc setting. Geochemical characteristics have revealed different chemical trends in granitoids and basalts. The granitoids are calc-alkaline, ferroan and magnesian, metaluminous and peraluminous in character. They also exhibit I- and S-type signatures with enrichment in LILE, radioelements (Th and U), depletion in Nb, Sr, P and Ti, high LREE fractionation factors (La/Yb) (1.05 to 77.20), and pronounced negative Eu anomalies (Eu/Eu* = 0.34 to 1.10). Similar patterns of spidergrams show that the rocks are genetically related and were emplaced in a volcanic arc and syn-collisional setting. The basalt is tholeiitic, metaluminous and high in Fe and Mg with relative enrichment in LILE, HFSE, low and near flat LREE and HREE, low fractionation [(La/Yb)N = 1.4] with Eu/Eu* value of 1.10. It is evidently a back arc cum mid-ocean ridge (MORB) basalt. The consistent decrease in the content of MgO, Fe2O3 MnO, CaO, Sc, Cr and V of the basalt, diorites, granodiorites, and granites indicates continuous igneous crystallization process. It seems that extrusion of basaltic magmas from the sub-circular Kushaka Complex derived from subduction of oceanic crust resulted in complete change in the genesis of the magmas at the time, in this region. The granitoids and the basalt may have formed behind subducted Pan-African plate due to effects of compressional and tensional forces caused by oceanic plate roll-back which resulted to a zone of extension, parallel to the island arc. The granitoids present similar chemical characteristics to those in the other areas underlain by the basement complex and schist belts in the north and eastern parts of the Pan-African mobile belt, while basalts are similar to ophiolites and amphibolites in other schist belts of Nigeria forming a lateral continuation of the same mobile belt.

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Brophy, James G. "Basalt Convection and Plagioclase Retention: A Model for the Generation of High-Alumina Arc Basalt." Journal of Geology 97, no. 3 (May 1989): 319–29. http://dx.doi.org/10.1086/629305.

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Anehumbu Aye, Beyanu, Primus Azinwi Tamfuh, and Enerst Tata. "Geochemistry of Amphibolites in Akom II, Nyong Series, North Western Border of the Congo Craton, South Cameroon." International Journal of Advanced Geosciences 9, no. 1 (April 21, 2021): 33. http://dx.doi.org/10.14419/ijag.v9i1.31467.

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The garnet amphibolites, from the Akom II area in the Archaean Congo Craton, were examined to determine the geochemical affinity and tectonic environment. The study uses mineral assemblages and whole-rock geochemistry to identify the geochemical affinity and tectonic setting of the amphibolites associated with monzogabbro and pyroxenites. The studied rocks of Akom II are garnet amphibolites. Mineralogically, the rocks contain hornblende + plagioclase + garnet ± quartz ± epidote ± apatite ± opaque, indicating that they could have been formed from a basic igneous protolith. The geochemical signature indicates that the rocks are tholeiitic in nature. They are similar to the metamorphosed equivalents of ocean island basalts (OIB), with characteristics typical of Volcanic Arc-Basalt (VAB). The geotectonic diagrams confirm the tholeiitic nature of these amphibolites. High field strength elements ratios (Nb/Ta) range from 14-16, which corresponds to Volcanic Arc Basalt (VAB). The primitive mantle normalized patterns of these rocks show negative anomalies in Ta and Ti suggesting a geotectonic signature characteristic of a subduction zone, consequently suggesting the existence of a suture zone in the study area.

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Kerrich, Robert, and Chakravadhanula Manikyamba. "Contemporaneous eruption of Nb-enriched basalts – K-adakites – Na-adakites from the 2.7 Ga Penakacherla terrane: implications for subduction zone processes and crustal growth in the eastern Dharwar craton, India." Canadian Journal of Earth Sciences 49, no. 4 (April 2012): 615–36. http://dx.doi.org/10.1139/e2012-005.

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An association of Nb-enriched basalts (NEB), high-MgO andesites (HMA), and flows with adakitic characteristics are interlayered with tholeiitic pillow basalts in the 2.7 Ga Penakacherla greenstone belt of eastern Dharwar craton. Two populations of basalt are present, a high-Mg# Ni (0.65–0.56, 106–52 ppm) and low-Mg# Ni (0.45–0.34, 32–13 ppm) counterpart; Nb spans 6.3–18 ppm relative to “normal” arc tholeiitic basalts, where Nb ∼3 ppm, and hence qualify as NEB. Basalts plot on the low-Ce/Yb trend of intraoceanic arcs, and have fractionated heavy rare-earth elements (HREE) indicative of melting with residual garnet at >90 km. Ratios of Nb/Ta (7.6 ± 0.7), Zr/Hf (44 ± 0.8), and Zr/Sm (27 ± 2.4) are systematically low, high, and similar to respective primitive mantle ratios of 17, 36, and 25, consistent with a mid-ocean ridge basalt-like mantle source in the sub-arc mantle wedge. Intermediate compositions are divided into high-K but low-Na (K2O 1.8–5.3; Na2O 0.5–2.1 wt.%) and low-K but high-Na (K2O 0.10–1.5; Na2O 4.1–5.6 wt.%) populations defining distinct magma series; accordingly, these are termed K-adakitic and Na-adakitic rocks, respectively. The Na-type has SiO2 ≥56 wt.%, MgO <3 wt.%, Mg# ∼0.5, Na2O ≥3.5 wt.%, K2O ≤3 wt.%, Yb ≤1.9 ppm, Cr ≥30 ppm, with slightly lower limits of Al2O3 ≥15 wt.% and La/Yb 7.5–8.2 versus ≥20, thus conforming to most criteria for Na-adakites. NEB are interpreted as melts of mantle wedge hybridized by adakitic melts having residual garnet; and Na-adakites are slab melts of low-Mg basalt in the garnet–amphibolite facies. K-adakitic flows are melts of mafic lower crust, or melts of lower crust delaminated into mantle wedge asthenosphere.

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Cahoon, Emily B., Martin J. Streck, Anthony A. P. Koppers, and Daniel P. Miggins. "Reshuffling the Columbia River Basalt chronology—Picture Gorge Basalt, the earliest- and longest-erupting formation." Geology 48, no. 4 (January 31, 2020): 348–52. http://dx.doi.org/10.1130/g47122.1.

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Abstract The Columbia River Basalt Group (CRBG) is the world’s youngest continental flood basalt province, presumably sourced from the deep-seated plume that currently resides underneath Yellowstone National Park in the northwestern United States. The earliest-erupted basalts from this province aid in understanding and modeling plume impingement and the subsequent evolution of basaltic volcanism. We explore the Picture Gorge Basalt (PGB) formation of the CRBG, and discuss the location and geochemical significance in a temporal context of early CRBG magmatism. We report new ARGUS-VI multicollector 40Ar/39Ar incremental heating ages from known PGB localities and additional outcrops that we can geochemically classify as PGB. These 40Ar/39Ar ages range between 17.23 ± 0.04 Ma and 16.06 ± 0.14 Ma, indicating that PGB erupted earlier and for longer than other CRBG main-phase units. These ages illustrate that volcanism initiated over a broad area in the center of the province, and the geochemistry of these early lavas reflects a mantle source that is distinct both spatially and temporally. Combining ages with the strongest arc-like (but depleted) geochemical signal of PGB among CRBG units indicates that the shallowest metasomatized backarc-like mantle was tapped first and concurrently, with later units (Steens and Imnaha Basalts) showing increased influence of a plume-like source.

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McCONNELL, BRIAN, and JOHN MORRIS. "Initiation of Iapetus subduction under Irish Avalonia." Geological Magazine 134, no. 2 (March 1997): 213–18. http://dx.doi.org/10.1017/s0016756897006626.

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The Dowery Hill Member of metamorphosed basalt, dolerite and siltstone is here recognized as the oldest exposed volcanic unit of the Lower Ordovician Ribband Group, with a minimum age of early Arenig. Peperites and resedimented hydroclastic breccia demonstrate a volcanic origin for the basalts. The igneous rocks are tholeiitic, with a trace element geochemistry indicative of a subduction-modified fertile mantle source, which we interpret as recording an early stage of volcanic arc evolution. The member is therefore the oldest known component of the volcanic arc generated by subduction of Iapetus oceanic lithosphere under southeastern Ireland. Subduction started earlier than predicted by current plate tectonic models, and these should be re-evaluated.

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Ren, Qiubing, Mingchao Li, Shuai Han, Ye Zhang, Qi Zhang, and Jonathan Shi. "Basalt Tectonic Discrimination Using Combined Machine Learning Approach." Minerals 9, no. 6 (June 22, 2019): 376. http://dx.doi.org/10.3390/min9060376.

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Geochemical discrimination of basaltic magmatism from different tectonic settings remains an essential part of recognizing the magma generation process within the Earth’s mantle. Discriminating among mid-ocean ridge basalt (MORB), ocean island basalt (OIB) and island arc basalt (IAB) is that matters to geologists because they are the three most concerned basalts. Being a supplement to conventional discrimination diagrams, we attempt to utilize the machine learning algorithm (MLA) for basalt tectonic discrimination. A combined MLA termed swarm optimized neural fuzzy inference system (SONFIS) was presented based on neural fuzzy inference system and particle swarm optimization. Two geochemical datasets of basalts from GEOROC and PetDB served as to test the classification performance of SONFIS. Several typical discrimination diagrams and well-established MLAs were also used for performance comparisons with SONFIS. Results indicated that the classification accuracy of SONFIS for MORB, OIB and IAB in both datasets could reach over 90%, superior to other methods. It also turns out that MLAs had certain advantages in making full use of geochemical characteristics and dealing with datasets containing missing data. Therefore, MLAs provide new research tools other than discrimination diagrams for geologists, and the MLA-based technique is worth extending to tectonic discrimination of other volcanic rocks.

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Arai, Shoji. "Chemistry of chromian spinel in volcanic rocks as a potential guide to magma chemistry." Mineralogical Magazine 56, no. 383 (June 1992): 173–84. http://dx.doi.org/10.1180/minmag.1992.056.383.04.

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AbstractChromian spinel in volcanic rocks is a potential discriminant for magma chemistry. The TiO2 content of spinel, compared at similar Fe3+/(Cr + Al + Fe3+) ratios, can distinguish island arc basalts from intraplate basalts. MORB spinels are low in this ratio and are intermediate for the TiO2 level at comparable Fe3+ ratios. Spinels from back-arc basin basalts, although similar in TiO2/Fe3+ ratio, are more enriched in Fe3+ than the MORB spinels. Spinels in the oceanic plateau basalts are distinctly lower in TiO2 than other intraplate basalt spinels and even slightly lower in TiO2 than the MORB spinels. The data were successfully applied to estimate the kind of the magma from which spinelbearing cumulates, especially dunites, were formed. Original magma chemistry of altered or metamorphosed volcanics in which spinels survive can also be estimated by the chemistry of relict spinel alone. It is possible to estimate the magma type of source volcanics for detrital spinel particles of volcanic derivation.

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Monjoie, Philippe, Henriette Lapierre, Artan Tashko, Georges H. Mascle, Aline Dechamp, Bardhyl Muceku, and Pierre Brunet. "Nature and origin of the Triassic volcanism in Albania and Othrys: a key to understanding the Neotethys opening?" Bulletin de la Société Géologique de France 179, no. 4 (July 1, 2008): 411–25. http://dx.doi.org/10.2113/gssgfbull.179.4.411.

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AbstractTriassic volcanic rocks, stratigraphically associated with pelagic or reef limestones, are tectonically juxtaposed with Mesozoic ophiolites in the Tethyan realm. From the central (Dinarides, Hellenides) and eastern Mediterranean (Antalya, Troodos, Baër Bassit) to the Semail nappes (Oman), they occur either associated to the tectonic sole of the ophiolitic nappes or as a distinct tectonic pile intercalated between the ophiolites and other underthrust units. In the Dinaro-Hellenic belt, the Pelagonian units represent the lower plate, which is underthrust beneath the ophiolites. Middle to Late Triassic volcanic sequences are interpreted as the eastern flank of the Pelagonian platform and are therefore considered as a distal, deep-water part of the Pelagonian margin.The Triassic volcanics from Albania and Othrys are made up of basaltic pillowed and massive flows, associated locally with dolerites and trachytes. New elemental, Nd and Pb isotopic data allow to recognize four types of volcanic suites: (1) intra-oceanic alkaline and tholeiitic basalts, (2) intra-oceanic arc-tholeiites, (3) back-arc basin basalts, (4) calc-alkaline mafic to felsic rocks. Nd and Pb isotopic initial ratios suggest that the within-plate volcanic rocks were derived from an enriched oceanic island basalt type mantle source, devoid of any continental crustal component. The lower εNd value of the trachyte could be due to assimilation of oceanic altered crust or sediments in a shallow magma chamber. Island arc tholeiites and back-arc basin basalts have a similar wide range of εNd. The absence of Nb negative anomalies in the back-arc basin basalts suggests that the basin floored by these basalts was wide and mature. The high Th contents of the island arc tholeiites suggest that the arc volcanoes were located not far away from the continental margin.Albania and Othrys volcanics contrast with the Late Triassic volcanism from eastern Mediterranean (SW Cyprus, SW Turkey), which displays solely features of oceanic within plate suites. The presence of back-arc basin basalts associated with arc-related volcanics in Central Mediterranean indicates that they were close to a still active subduction during the Upper Triassic, while back-arc basins developed, associated with within-plate volcanism, leading to the NeoTethys opening.

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Macpherson, C. G., and R. Hall. "Deep differentiation of island arc basalt in Mindanao, Philippines: Implications for growth of arc lithosphere." Geochimica et Cosmochimica Acta 70, no. 18 (August 2006): A382. http://dx.doi.org/10.1016/j.gca.2006.06.772.

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Xun, YU, and CHEN LiHui. "Geochemical variation of back-arc basin basalt and its genesis." Acta Petrologica Sinica 36, no. 7 (2020): 1953–72. http://dx.doi.org/10.18654/1000-0569/2020.07.02.

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Kuritani, Takeshi, Takeyoshi Yoshida, Jun-Ichi Kimura, Yuka Hirahara, and Toshiro Takahashi. "Water content of primitive low-K tholeiitic basalt magma from Iwate Volcano, NE Japan arc: implications for differentiation mechanism of frontal-arc basalt magmas." Mineralogy and Petrology 108, no. 1 (March 2, 2013): 1–11. http://dx.doi.org/10.1007/s00710-013-0278-2.

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Staal, C. R. van. "Tectonic setting of the Tetagouche Group in northern New Brunswick: implications for plate tectonic models of the northern Appalachians." Canadian Journal of Earth Sciences 24, no. 7 (July 1, 1987): 1329–51. http://dx.doi.org/10.1139/e87-128.

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A regional compilation and reinterpretation of geochemical analyses of mafic igneous rocks from the Ordovician Tetagouche Group in northern New Brunswick indicates the presence of at least three mafic assemblages: two groups of basalts and gabbros and one group of gabbros only. The three groups can be separated on the basis of TiO2 and trace-element content. Group A basalts generally have mid-ocean-ridge basalt (MORB)-like compositions, whereas group B basalts indicate a "within-plate" setting (WPB). Group C gabbros intrude into silicic volcanics that underlie the basalts but are rare or absent in the areas underlain by group A and B basalts. The group C gabbros probably represent the earliest stages of mafic igneous activity and have MORB-like compositions or represent a transition between MORB and arc basalts.The association of group A and B basalts with abundant marine sediments, such as thinly bedded turbidites and black and red shales, and the fact that they erupted locally on top of continental-crust-derived silicic volcanics suggest that they represent a marginal-sea or back-arc-basin environment rather than true oceanic (Iapetus) eruptives as has been suggested.The proposed back-arc environment and existing structural data are inconsistent with previously proposed tectonic models and large-scale correlations. Evidence for penetrative pre-Late Ordovician (Taconic orogeny sensu stricto) deformation is lacking in the northern part of the Miramichi Zone. Instead the earliest folding and related thrusting (D1) is ascribed to deformation associated with closure of the back-arc basin in post-middle Caradocian times.

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McConnell, Brian J., Brian H. O'Brien, and Godfrey S. Nowlan. "Late Middle Ordovician olistostrome formation and magmatism along the Red Indian Line, the Laurentian arc Gondwanan arc boundary, at Sops Head, Newfoundland." Canadian Journal of Earth Sciences 39, no. 11 (November 1, 2002): 1625–33. http://dx.doi.org/10.1139/e02-084.

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The Sops Head Complex of Badger Bay, central Newfoundland, includes olistostromal and tectonized mélanges and marks the Red Indian Line, the boundary between the peri-Gondwanan Exploits and peri-Laurentian Notre Dame subzones of the oceanic Dunnage Zone. Basalts in the olistostromal mélange preserve peperitic contacts with mudstone and limestone within slumped sedimentary units, demonstrating that magmatism was coeval with olistostrome formation. Conodonts from the limestones date these events as late Darriwilian ("Llandeilian," Middle Ordovician) in age. The conodont fauna consists entirely of North Atlantic Faunal Realm elements, suggesting a peri-Gondwanan or mid-Iapetan provenance for limestone of the Sops Head Complex. Basalt geochemistry suggests magmatism in a mature volcanic-arc to back-arc setting. The Sops Head Complex shows similarities in age, provenance, and stratigraphic setting to the Dunnage Mélange, suggesting that the two units are correlative.

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Andrew, A., R. L. Armstrong, and D. Runkle. "Neodymium–strontium–lead isotopic study of Vancouver Island igneous rocks." Canadian Journal of Earth Sciences 28, no. 11 (November 1, 1991): 1744–52. http://dx.doi.org/10.1139/e91-156.

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Combined neodymium, strontium, and lead isotope measurements show that Vancouver Island is made up of Phanerozoic crustal material accreted to North America in the Mesozoic and early Cenozoic, but that there are differences in the relative proportions of depleted mantle and aged, enriched crustal components in the Phanerozoic magmatic episodes that contribute to this new crust.The Devonian Sicker Group volcanic arc has an isotopic signature that can be explained by mixing mantle material with subducted continentally derived sediments. The Early to Middle Jurassic Bonanza Volcanics and Island Intrusions magmatic arc isotopic signature indicates mixing of magma from a depleted mantle source with crustal material of Sicker arc-type, rather than of continental origin. This is consistent with large-scale assimilation of Sicker Group and Karmutsen rocks by Jurassic mantle-derived magmas, or introduction of arc-derived sediments into the Jurassic mantle by subduction. Eocene calc-alkaline Flores Volcanics – Catface Intrusions may be derived from reworked Vancouver Island crust with little addition of mantle material.Late Triassic Karmutsen Formation flood basalts are similar to the lower parts of the Columbia River Basalt in all three isotope systems and in petrochemistry. Radiogenic isotopic data are consistent with the interpretation that the Karmutsen basalts were extruded in a post-arc or back-arc setting, with mantle lithosphere and depleted mantle components, and perhaps some plume source input and crustal contamination, but the latter are not provable from the radiogenic isotopic data alone.Early Eocene Metchosin basalts show a depleted mantle source, consistent with their origin as ocean islands, before Middle to Late Eocene accretion to the rest of Vancouver Island.

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Landing, Ed, Georgia Pe-Piper, William SF Kidd, and Karem Azmy. "Tectonic setting of outer trench slope volcanism: pillow basalt and limestone in the Taconian orogen of eastern New York." Canadian Journal of Earth Sciences 40, no. 12 (December 1, 2003): 1773–87. http://dx.doi.org/10.1139/e03-076.

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The only pillow basalt in synorogenic sedimentary rocks at the exterior margin of the Taconic orogen in eastern North America is at Stark's Knob in eastern New York. Earlier reported as extrusive into allochthonous Ordovician slope and rise facies, this small lens (ca. 125+ m long, 39 m thick) is a fault-bounded block in Upper Ordovician melange under the Taconian frontal thrust. Its N-MORB (normal mid-ocean ridge basalt) basalt geochemistry and spinel composition are characteristic of oceanic ridge settings at a water depth of 2 km or more. Abundant limestone lenses on pillows and lava shelves within pillows yielded a middle Late Ordovician gastropod. The limestones are reconciled with this extrusion depth and with limited early Paleozoic pelagic carbonate production by lime mud transport from the Laurentian platform or abiotic carbonate precipitation with sea-water heating during basalt extrusion. A genetic relationship between the parautochthonous Stark's Knob basalts and the allochthonous Jonestown volcanics in slope and rise facies of the Hamburg klippe, eastern Pennsylvania, is likely. Both are Ordovician MORB basalts that reflect volcanism on the subducting outer trench slope prior to the Taconic arc Laurentia collision. Taconic orogenesis may have led to basalt production on the subducting plate by (1) the setting up of orogen-parallel, predominantly strike-slip motion on the subducting slab with MORB basalt generated at offsets in a setting analogous to the Gulf of California or (2) development of faults in a flexure-induced extensional regime. By either process, mafic volcanism appears to be a rare but tectonically significant process on outer trench slopes as continental margins or oceanic plates enter subduction zones.

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Kimura, Jun-Ichi, Bradley R. Hacker, Peter E. van Keken, Hiroshi Kawabata, Takeyoshi Yoshida, and Robert J. Stern. "Arc Basalt Simulator version 2, a simulation for slab dehydration and fluid-fluxed mantle melting for arc basalts: Modeling scheme and application." Geochemistry, Geophysics, Geosystems 10, no. 9 (September 2009): n/a. http://dx.doi.org/10.1029/2008gc002217.

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Mills, Andrea, and Hamish Sandeman. "Lithostratigraphy and lithogeochemistry of Ediacaran alkaline basaltic rocks of the Musgravetown Group, Bonavista Peninsula, northeastern Newfoundland, Canada: an extensional volcanogenic basin in the type-Avalon terrane." Atlantic Geology 57 (August 5, 2021): 207–34. http://dx.doi.org/10.4138/atlgeol.2021.010.

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Volcanic rocks of the Ediacaran Musgravetown Group on Bonavista Peninsula, Avalon terrane, Newfoundland, include basal ca. 600 Ma calc-alkaline basalt succeeded by continental tholeiite and alkaline rhyolite of the ca. 592 Ma Plate Cove volcanic belt (Bull Arm Formation), indicating a change from subduction-related to extensionrelated tectonic regimes during that interval. Alkalic basalts on northeastern (Dam Pond area) and southwestern (British Harbour area) Bonavista Peninsula occur below and above, respectively, the ca. 580 Ma glacial Trinity facies. Dam Pond basalt occurs in a structural dome intercalated with and flanked by fine-grained, siliciclastic deposits (Big Head Formation) overlain by Trinity facies. The British Harbour basalt occurs above the Trinity facies, in an upward- coarsening sandstone sequence (Rocky Harbour Formation) overlain by red beds of the Crown Hill Formation (uppermost Musgravetown Group). The Rocky Harbour and Big Head formations are likely stratigraphically interfingered proximal and distal deposits, respectively, derived from erosion of the Bull Arm Formation and older Avalonian assemblages.The Big Head basalts have lower SiO2, Zr, FeOT, P2O5, TiO2 and higher Mg#, Cr, V, Co and Ni contents, and are therefore more primitive than the more FeOT-, TiO2-, and P2O5-rich British Harbour basalts. Large-ionlithophile and rare-earth-element concentrations and ratios indicate that both suites originated from low degree partial melts of deep, weakly garnet-bearing, undepleted asthenospheric peridotite sources, with magma conduits likely focused along regional extensional faults. The protracted and episodic extension-related volcanic activity is consistent with a geodynamic setting that evolved from a mature arc into extensional basins with slowly waning magmatism, possibly involving slab rollback and delamination followed by magmatic underplating. The duration and variation of both volcanism and sedimentation indicate that the Musgravetown Group should be elevated to a Supergroup in order to facilitate future correlation of its constituent parts with other Avalonian basins.

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Arai, S., and N. Abe. "Podiform chromitite in the arc mantle: chromitite xenoliths from the Takashima alkali basalt, Southwest Japan arc." Mineralium Deposita 29, no. 5 (September 1994): 434–38. http://dx.doi.org/10.1007/bf01886963.

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LEAT, P. T., R. D. LARTER, and I. L. MILLAR. "Silicic magmas of Protector Shoal, South Sandwich arc: indicators of generation of primitive continental crust in an island arc." Geological Magazine 144, no. 1 (October 27, 2006): 179–90. http://dx.doi.org/10.1017/s0016756806002925.

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Protector Shoal, the northernmost and most silicic volcano of the South Sandwich arc, erupted dacite–rhyolite pumice in 1962. We report geochemical data for a new suite of samples dredged from the volcano. Geochemically, the dredge and 1962 samples form four distinct magma groups that cannot have been related to each other, and are unlikely to have been related to a single basaltic parent, by fractional crystallization. Instead, the silicic rocks are more likely to have been generated by partial melting of basaltic lower crust within the arc. Trace element and Sr–Nd isotope data indicate that the silicic volcanics have compositions that are more similar to the volcanic arc than the oceanic basement formed at a back-arc spreading centre, and volcanic arc basalts are considered to be the likely source for the silicic magmas. The South Sandwich Islands are one of several intra-oceanic arcs (Tonga–Kermadec, Izu–Bonin) that have: (1) significant amounts of compositionally bimodal mafic–silicic volcanic products and (2) 6.0–6.5 km s−1P-wave velocity layers in their mid-crusts that have been imaged by wide-angle seismic surveys and interpreted as intermediate-silicic plutons. Geochemical and volume considerations indicate that both the silicic volcanics and plutonic layers were generated by partial melting of basaltic arc crust, representing an early stage in the fractionation of oceanic basalt to form continental crust.

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McGoldrick, Siobhan, Alex Zagorevski, and Dante Canil. "Geochemistry of volcanic and plutonic rocks from the Nahlin ophiolite with implications for a Permo–Triassic arc in the Cache Creek terrane, northwestern British Columbia." Canadian Journal of Earth Sciences 54, no. 12 (December 2017): 1214–27. http://dx.doi.org/10.1139/cjes-2017-0069.

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In northwestern British Columbia, the Permian Nahlin ophiolite in the northern Cache Creek terrane comprises spinel harzburgite tectonite with minor lherzolite, lower crustal mafic and ultramafic cumulates, gabbroic rocks including dikes intruding mantle harzburgite, and basaltic volcanic and volcaniclastic rocks. New lithogeochemical data from the Menatatuline Range area confirm that plutonic and volcanic rocks of the ophiolite are tholeiitic and arc related, while only a minor component of volcanic rocks are alkaline intraplate basalts. Tholeiitic basalts of the Nahlin ophiolite represent the products of 2%–20% fractional melting, and their complementary residue may be peridotite from the ophiolite mantle section. Correlative tholeiitic volcanic sections can be found elsewhere in the northern Cache Creek terrane, and they may be linked to a regionally extensive (∼200 km) intraoceanic arc. The arc tholeiite geochemistry of the plutonic and volcanic rocks, and the highly depleted nature of the mantle residues, imply that the Nahlin ophiolite formed in a supra-subduction zone environment. The Nahlin ophiolite therefore occupied the upper plate during intraoceanic collision prior to emplacement of the Cache Creek terrane. The volumetrically minor ocean island basalt type volcanic rocks in the northern Cache Creek terrane are associated with carbonate successions bearing Tethyan fauna. These sequences are likely fragments of oceanic plateaux and their carbonate atolls sliced off of the subducting plate and are unrelated to the Nahlin ophiolite-arc system.

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Melzer, Stefan, and Bernd Wunder. "Island-arc basalt alkali ratios: Constraints from phengite-fluid partitioning experiments." Geology 28, no. 7 (July 2000): 583–86. http://dx.doi.org/10.1130/0091-7613(2000)028<0583:iabarc>2.3.co;2.

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Melzer, Stefan, and Bernd Wunder. "Island-arc basalt alkali ratios: Constraints from phengite-fluid partitioning experiments." Geology 28, no. 7 (2000): 583. http://dx.doi.org/10.1130/0091-7613(2000)28<583:ibarcf>2.0.co;2.

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Zelenski, Michael, Vadim S. Kamenetsky, Nikolai Nekrylov, and Alkiviadis Kontonikas-Charos. "High Sulfur in Primitive Arc Magmas, Its Origin and Implications." Minerals 12, no. 1 (December 26, 2021): 37. http://dx.doi.org/10.3390/min12010037.

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Sulfur contents in 98.5% of melt inclusions (MI) from calc-alkaline subduction basalts do not exceed 4000 ppm, whereas experimentally established limits of sulfur solubility in basaltic melts with high fO2 (characteristic of subduction zones, e.g., QFM + 2) surpass 14,000 ppm. Here we show that primitive (Mg# 62-64) subduction melts may contain high sulfur, approaching the experimental limit of sulfur solubility. Up to 11,700 ppm S was measured in olivine-hosted MI from primitive arc basalt from the 1941 eruption of the Tolbachik volcano, Kamchatka. These MI often contain magmatic sulfide globules (occasionally enriched in Cu, Ni, and platinum-group elements) and anhydrite enclosed within a brown, oxidized glass. We conclude that the ubiquitous low sulfur contents in MI may originate either from insufficient availability of sulfur in the magma generation zone or early magma degassing prior to inclusion entrapment. Our findings extend the measured range of sulfur concentrations in primitive calc-alkaline basaltic melts and demonstrate that no fundamental limit of 4000 ppm S exists for relatively oxidized subduction basalts, where the maximum sulfur content may approach the solubility limit determined by crystallization of magmatic anhydrite.

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Dusel-Bacon, Cynthia, and Kari M. Cooper. "Trace-element geochemistry of metabasaltic rocks from the Yukon-Tanana Upland and implications for the origin of tectonic assemblages in east-central Alaska." Canadian Journal of Earth Sciences 36, no. 10 (October 1, 1999): 1671–95. http://dx.doi.org/10.1139/e99-077.

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We present major- and trace- element geochemical data for 27 amphibolites and six greenstones from three structural packages in the Yukon-Tanana Upland of east-central Alaska: the Lake George assemblage (LG) of Devono-Mississippian augen gneiss, quartz-mica schist, quartzite, and amphibolite; the Taylor Mountain assemblage (TM) of mafic schist and gneiss, marble, quartzite, and metachert; and the Seventymile terrane of greenstone, serpentinized peridotite, and Mississippian to Late Triassic metasedimentary rocks. Most LG amphibolites have relatively high Nb, TiO2, Zr, and light rare earth element contents, indicative of an alkalic to tholeiitic, within-plate basalt origin. The within-plate affinities of the LG amphibolites suggest that their basaltic parent magmas developed in an extensional setting and support a correlation of these metamorphosed continental-margin rocks with less metamorphosed counterparts across the Tintina fault in the Selwyn Basin of the Canadian Cordillera. TM amphibolites have a tholeiitic or calc-alkalic composition, low normalized abundances of Nb and Ta relative to Th and La, and Ti/V values of <20, all indicative of a volcanic-arc origin. Limited results from Seventymile greenstones indicate a tholeiitic or calc-alkalic composition and intermediate to high Ti/V values (27-48), consistent with either a within-plate or an ocean-floor basalt origin. Y-La-Nb proportions in both TM and Seventymile metabasalts indicate the proximity of the arc and marginal basin to continental crust. The arc geochemistry of TM amphibolites is consistent with a model in which the TM assemblage includes arc rocks generated above a west-dipping subduction zone outboard of the North American continental margin in mid-Paleozoic through Triassic time. The ocean-floor or within-plate basalt geochemistry of the Seventymile greenstones supports the correlation of the Seventymile terrane with the Slide Mountain terrane in Canada and the hypothesis that these oceanic rocks originated in a basin between the continental margin and an arc to the west.

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Barresi, Tony, J. L. Nelson, J. Dostal, and R. Friedman. "Evolution of the Hazelton arc near Terrace, British Columbia: stratigraphic, geochronological, and geochemical constraints on a Late Triassic – Early Jurassic arc and Cu–Au porphyry belt." Canadian Journal of Earth Sciences 52, no. 7 (July 2015): 466–94. http://dx.doi.org/10.1139/cjes-2014-0155.

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Understanding the development of island arcs that accreted to the North American craton is critical to deciphering the complex geological history of the Canadian Cordillera. In the case of the Hazelton arc (part of the Stikine terrane, or Stikinia) in northwestern British Columbia, understanding arc evolution also bears on the formation of spatially associated porphyry Cu–Au, epithermal, and volcanogenic massive sulfide deposits. The Hazelton Group is a regionally extensive, long-lived, and exceptionally thick Upper Triassic to Middle Jurassic volcano-sedimentary succession considered to record a successor arc that was built upon the Paleozoic and Triassic Stikine and Stuhini arcs. In central Stikinia, near Terrace, British Columbia, the lower Hazelton Group (Telkwa Formation) comprises three volcanic-intrusive complexes (Mt. Henderson, Mt. O’Brien, and Kitselas) that, at their thickest, constitute almost 16 km of volcanic stratigraphy. Basal Telkwa Formation conglomerates and volcanic rocks were deposited unconformably on Triassic and Paleozoic arc-related basement. New U–Pb zircon ages indicate that volcanism initiated by ca. 204 Ma (latest Triassic). Detrital zircon populations from the basal conglomerate contain abundant 205–233 Ma zircons, derived from regional unroofing of older Triassic intrusions. Eleven kilometres higher in the section, ca. 194 Ma, rhyolites show that arc construction continued for >10 million years. Strata of the Nilkitkwa Formation (upper Hazelton Group) with a U–Pb zircon age of 178.90 ± 0.28 Ma represent waning island-arc volcanism. Telkwa Formation volcanic rocks have bimodal silica concentrations ranging from 48.1 to 62.8 wt.% and 72.3 to 79.0 wt.% and display characteristics of subduction-related magmatism (i.e., calc-alkaline differentiation with low Nb and Ti and high Th concentrations). Mafic to intermediate rocks form a differentiated suite that ranges from high-Al basalt to medium- to high-K andesite. They were derived from hydrous melting of isotopically juvenile spinel lherzolite in the mantle wedge and from subsequent fractional crystallization. Compared to basalts and andesites (εNd = +5 to +5.5), rhyolites have higher positive εNd values (+5.9 to +6.0) and overlapping incompatible element concentrations, indicating that they are not part of the same differentiation suite. Rather, the rhyolites formed from anatexis of arc crust, probably caused by magmatic underplating of the crust. This study documents a temporal and spatial co-occurrence of Hazelton Group volcanic rocks with a belt of economic Cu–Au porphyry deposits (ca. 205–195 Ma) throughout northwestern Stikinia. The coeval relationship is attributed to crustal underplating and intra-arc extension associated with slab rollback during renewed or reconfigured subduction beneath Stikinia, following the demise of the Stuhini arc in the Late Norian.

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Lapierre, H., M. Tardy, C. Coulon, E. Ortiz Hernandez, J. L. Bourdier, J. Martínez Reyes, and C. Freydier. "Caractérisation, genèse et évolution géodynamique du terrain de Guerrero (Mexique occidental)." Canadian Journal of Earth Sciences 29, no. 11 (November 1, 1992): 2478–89. http://dx.doi.org/10.1139/e92-194.

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The Guerrero terrane (western Mexico) is composed of Late Jurassic – Early Cretaceous plutono-volcanic and volcano-sedimentary sequences of the Alisitos–Teloloapan arc that accreted to the North American craton at the end of the Early Cretaceous. The geodynamic evolution of the Guerrero terrane is that of the Alisitos–Teloloapan intraoceanic arc, partly built on continental crust and partly on oceanic crust. The growth of the arc was likely linked to the subduction of the Arperos and Olvidada basins fringing the North American borderland. The subduction was dipping west-south-west.The continent-based segment of the arc, which is presently exposed mainly in northwestern Mexico, is composed of aerial and submarine K-rich calc-alkaline basalts, andesites, and rhyolites and of siliceous pyroclastic rocks interbedded with Aptian–Albian bioclastic carbonates or red beds bearing dinosaurus foot prints. The calc-alkaline basalts and andesites show light rare earth elements enriched patterns and high concentrations in large ion lithophile elements. The siliceous andesites and rhyodacites display low contents in Y and heavy rare earth elements, uncommon for such calc-alkaline SiO2-saturated rocks. This depletion is likely linked to amphibole fractionation and to the presence of sphene and zircon, minerals known to concentrate the heavy rare earth elements.In contrast, the magmatic arc sequences built on oceanic crust, that crops out in central-southern areas of the Guerrero terrane, show an evolution with time. The activity of the arc began with depleted tholeiitic igneous rocks, followed first by mature tholeiitic basalts, then by calc-alkaline olivine basalts interbedded with micritic limestones and radiolarian oozes of Early Cretaceous age (Neocomian). At the end of the arc development, in Late Aptian–Albian, calc-alkaline pillow basalts and andesites erupted at the volcanic front whereas shoshonitic basalts emitted backwards. In the late Early Cretaceous, the arc drifted towards the north and collided with the craton. Arc tholeiites are characterized by flat rare earth element patterns or slightly depleted in light rare earth elements and by high εNd ratios. The calc-alkaline plutonic and volcanic rocks show light rare earth elements enriched patterns and their εNd ratios decrease with time. This decrease of the εNd ratios suggests that either the mantle source of the calc-alkaline rocks was contaminated by subducted terrigenous sediments derived from an old continental crust (North American craton) or that these calc-alkaline rocks derive from the partial melt of an oceanic island basalt source present in the mantle wedge. The shoshonitic features of the basalts are marked by the presence of sanidine in the groundmass and the high levels of K2O, Ba, and Sr of the unaltered rocks.

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Dusel-Bacon, Cynthia, Warren C. Day, and John N. Aleinikoff. "Geochemistry, petrography, and zircon U–Pb geochronology of Paleozoic metaigneous rocks in the Mount Veta area of east-central Alaska: implications for the evolution of the westernmost part of the Yukon–Tanana terrane." Canadian Journal of Earth Sciences 50, no. 8 (August 2013): 826–46. http://dx.doi.org/10.1139/cjes-2013-0004.

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We report the results of new mapping, whole-rock major, minor, and trace-element geochemistry, and petrography for metaigneous rocks from the Mount Veta area in the westernmost part of the allochthonous Yukon–Tanana terrane (YTT) in east-central Alaska. These rocks include tonalitic mylonite gneiss and mafic metaigneous rocks from the Chicken metamorphic complex and the Nasina and Fortymile River assemblages. Whole-rock trace-element data from the tonalitic gneiss, whose igneous protolith was dated by SHRIMP U–Pb zircon geochronology at 332.6 ± 5.6 Ma, indicate derivation from tholeiitic arc basalt. Whole-rock analyses of the mafic rocks suggest that greenschist-facies rocks from the Chicken metamorphic complex, a mafic metavolcanic rock from the Nasina assemblage, and an amphibolite from the Fortymile River assemblage formed as island-arc tholeiite in a back-arc setting; another Nasina assemblage greenschist has MORB geochemical characteristics, and another mafic metaigneous rock from the Fortymile River assemblage has geochemical characteristics of calc-alkaline basalt. Our geochemical results imply derivation in an arc and back-arc spreading region within the allochthonous YTT crustal fragment, as previously proposed for correlative units in other parts of the terrane. We also describe the petrography and geochemistry of a newly discovered tectonic lens of Alpine-type metaharzburgite. The metaharzburgite is interpreted to be a sliver of lithospheric mantle from beneath the Seventymile ocean basin or from sub-continental mantle lithosphere of the allochthonous YTT or the western margin of Laurentia that was tectonically emplaced within crustal rocks during closure of the Seventymile ocean basin and subsequently displaced and fragmented by faults.

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Journal articles on the topic 'Arc basalt'

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