Tectonic setting of basic volcanic rocks determined using trace element analyses
TL;DR: In this paper, the results of analyses for Ti, Zr, Y, Nb and Sr in over 200 basaltic rocks from different tectonic settings have been used to construct diagrams in which these settings can usually be identified.
About: This article is published in Earth and Planetary Science Letters.The article was published on 1973-06-01. It has received 3403 citations till now. The article focuses on the topics: Volcanic rock & Basalt.
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TL;DR: In this article, the abundance and distribution of selected minor and trace elements (Ti, Zr, Y, Nb, Ce, Ga and Sc) in fresh volcanic rocks can be used to classify the differentiation products of subalkaline and alkaline magma series in a similar manner to methods using normative or major-element indices.
4,648 citations
TL;DR: A-type granites as mentioned in this paper were found to have high SiO2, Na2O+K2O, Fe/Mg, Ga/Al, Zr, Nb, Ga, Y and Ce, and low CaO and Sr.
Abstract: New analyses of 131 samples of A-type (alkaline or anorogenic) granites substantiate previously recognized chemical features, namely high SiO2, Na2O+K2O, Fe/Mg, Ga/Al, Zr, Nb, Ga, Y and Ce, and low CaO and Sr. Good discrimination can be obtained between A-type granites and most orogenic granites (M-, I and S-types) on plots employing Ga/Al, various major element ratios and Y, Ce, Nb and Zr. These discrimination diagrams are thought to be relatively insensitive to moderate degrees of alteration. A-type granites generally do not exhibit evidence of being strongly differentiated, and within individual suites can show a transition from strongly alkaline varieties toward subalkaline compositions. Highly fractionated, felsic I- and S-type granites can have Ga/Al ratios and some major and trace element values which overlap those of typical A-type granites. A-type granites probably result mainly from partial melting of F and/or Cl enriched dry, granulitic residue remaining in the lower crust after extraction of an orogenic granite. Such melts are only moderately and locally modified by metasomatism or crystal fractionation. A-type melts occurred world-wide throughout geological time in a variety of tectonic settings and do not necessarily indicate an anorogenic or rifting environment.
4,216 citations
TL;DR: In this paper, a table of mineral-liquid distribution coefficients for Ti, Zr, Y, and Nb for basic, intermediate and acid melt compositions were used to interpret variations of these elements, first in basalts and second during fractional crystallization from basic to acid magmas.
Abstract: Data from experimental runs, coexisting phases in ultramafic rocks and phenocryst-matrix pairs in volcanic rocks have been used to compile a table of mineral-liquid distribution coefficients for Ti, Zr, Y, and Nb for basic, intermediate and acid melt compositions. These values have then been used to interpret variations of these elements, first in basalts and second, during fractional crystallization from basic to acid magmas. For basalts, petrogenetic modelling of Zr/Y, Zr/Ti, and Zr/Nb ratios, when used in conjunction with REE, Cr and isotopic variations, suggests that: (1) the increase in Zr/Y ratio from mid-ocean ridge to within plate basalts and the low Zr/Nb ratios of alkalic basalts are due to (fluid controlled) source heterogeneities; (2) the low Zr and Zr/Y ratio of volcanic arc basalts results from high degree of partial melting of a depleted source; and (3) the high Zr and similar Zr/Y ratio of basalts from fast spreading relative to slow spreading ridges results from open-system fractional crystallization. Modelling of fractionation trends in more evolved rocks using Y-Zr, Ti-Zr and Nb-Zr diagrams highlights in particular the change in crystallizing mafic phases from island arcs (clinopyroxene-dominated) to Andean-type arcs (amphibole±biotite-dominated). These methods can be applied to altered lavas of unknown affinities to provide additional information on their genesis and eruptive environment.
2,680 citations
TL;DR: Two geochemical proxies are particularly important for the identification and classification of oceanic basalts: the Th-Nb proxy for crustal input and hence for demonstrating an oceanic, non-subduction setting; and the Ti-Yb proxy, for melting depth and hence indicating mantle temperature and thickness of the conductive lithosphere as mentioned in this paper.
2,487 citations
TL;DR: In this article, a large variation in trace element characteristics of graywackes of the Paleozoic turbidite sequences of eastern Australia show a large increase in light rare earth elements (La, Ce, Nd), Th, Nb and the Ba/Sr, Rb, Sr, La/Y and Ni/Co ratios.
Abstract: The graywackes of Paleozoic turbidite sequences of eastern Australia show a large variation in their trace element characteristics, which reflect distinct provenance types and tectonic settings for various suites. The tectonic settings recognised are oceanic island arc, continental island arc, active continental margin, and passive margins. Immobile trace elements, e.g. La, Ce, Nd, Th, Zr, Nb, Y, Sc and Co are very useful in tectonic setting discrimination. In general, there is a systematic increase in light rare earth elements (La, Ce, Nd), Th, Nb and the Ba/Sr, Rb/Sr, La/Y and Ni/Co ratios and a decrease in V, Sc and the Ba/Rb, K/Th and K/U ratios in graywackes from oceanic island arc to continental island arc to active continental margin to passive margin settings. On the basis of graywacke geochemistry, the optimum discrimination of the tectonic settings of sedimentary basins is achieved by La-Th, La-Th-Sc, Ti/Zr-La/Sc, La/Y-Sc/Cr, Th-Sc-Zr/10 and Th-Co-Zr/10 plots. The analysed oceanic island arc graywackes are characterised by extremely low abundances of La, Th, U, Zr, Nb; low Th/U and high La/Sc, La/Th, Ti/Zr, Zr/Th ratios. The studied graywackes of the continental island arc type setting are characterised by increased abundances of La, Th, U, Zr and Nb, and can be identified by the La-Th-Sc and La/Sc versus Ti/Zr plots. Active continental margin and passive margin graywackes are discriminated by the Th-Sc-Zr/10 and Th-Co-Zr/10 plots and associated parameters (e.g. Th/Zr, Th/Sc). The most important characteristic of the analysed passive margin type graywackes is the increased abundance of Zr, high Zr/Th and lower Ba, Rb, Sr and Ti/Zr ratio compared to the active continental margin graywackes.
2,133 citations
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...Pearce and Cann 1973; Winchester and Floyd 1977; Wood et al. 1979; Bailey 1981)....
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1,797 citations
TL;DR: In this paper, the existence of low density, high temperature upper mantle is indicated by the lack of a large gravity anomaly over the shallow oceanic crust of the inter-arc basin, by high heat flow there, and by anomalously high attenuation of shear waves passing through the upper mantle beneath the extensional zone.
Abstract: The semi-isolated basins and series of basins of intermediate to normal oceanic depths that lie behind island arc systems are termed marginal basins, and are believed to be of extensional origin. Marginal basins, although differing in size and amount of sediment fill, are all underlain by oceanic crust, and can be divided into actively spreading inter-arc basins and older inactive basins. The inactive basins are grouped on the basis of age as reflected by crustal heat flow; inactive basins with above-normal heat flow are apparently younger than those with normal heat flow. Volcano-tectonic rift zones with associated silicic tuffs are found in the tectonic position of inter-arc basins in some continental trench-arc systems and are thought to have been formed by similar extensional process. Large scale crustal extension and demonstratable trench migration imply displacement of the Benioff zone. However, the portion of the Benioff zone shallower than 150 km, and lying between the volcanic chain and the trench, remains relatively undeformed along the trend of arc systems in which the dip of the deeper segment of the Benioff zone changes markedly. Geometric relationships suggest that, as the inter-arc basin opens, the trench is forced to migrate and the Benioff zone is flattened, except in areas where crust can be consumed in a second trench behind the extensional zone. Active extension is restricted to arc systems with earthquakes deeper than about 350 km. The available data can be explained by a thermal diapir of shear-heated mantle material, bouyantly rising beneath the inter-arc basin from the upper surface of the under-thrust lithosphere. Hydrostatic forces associated with such a diapir are felt capable of over-coming the compressional forces in the mantle produced by shearing along the upper surface of the lithosphere and by the bending of the lithosphere. The existence of low density, high temperature upper mantle is indicated by the lack of a large gravity anomaly over the shallow oceanic crust of the inter-arc basin, by high heat flow there, and by anomalously high attenuation of shear waves passing through the upper mantle beneath the extensional zone.
961 citations
04 Feb 1971-Philosophical transactions - Royal Society. Mathematical, physical and engineering sciences
TL;DR: The Troodos Massif as discussed by the authors consists of a pseudostratiform mass of harzburgite, dunite, pyroxenite, gabbro, quartz diorite, diabase and pillow lava arranged in a dome-like manner.
Abstract: Many Alpine ophiolite complexes characteristically display a pseudostratiform sequence of ultramafics, gabbro, diabase, pillow lava and deep-sea sediments. These masses resemble the known rock suite from the ocean floor. They are either fragments of old oceanic crust and mantle caught up in deformed belts, or results of diapiric emplacement of partly molten mantle material on or near the sea bottom. Such complexes are widespread in the Tethyan mountain system and have been recognized also from the circumPacific region. The Troodos Massif, Cyprus, consists of a pseudostratiform mass of harzburgite, dunite, pyroxenite, gabbro, quartz diorite, diabase and pillow lava arranged in a dome-like manner. The diabase forms a remarkable dyke swarm, trending mostly north-south in which 100 km of extension is indicated over 100 km of exposure. Such a feature suggests formation by sea-floor spreading. Layering of pyroxenite, harzburgite and dunite generally is perpendicular to subhorizontal rock unit contacts. The harzburgite and dunite are tectonites and probably represent uppermost mantle. Pyroxenite, gabbro, quartz diorite and diabase may represent the products of partial fusion of mantle material or of fractional crystallization of such partial fusion products. Chemical compositions of mafic intrusive and extrusive rocks do not fit well with oceanic tholeiite compositions, but resemble greenstones and associated rocks recently reported from the oceans. The massif probably formed about an old Tethyan ridge. Some pillow lavas may be crust added after the main spreading episode. A fault zone active during emplacement of the lower units of the complex may represent a fossil transform fault. Complex chilled margins in the dyke swarms and mutually contradictory cross-cutting relations between dykes and plutonic mafic rock suggest formation of ocean crust by multiple intrusion of small portions of liquid. Uneven top surface of the dyke swarm and some conjugate dyke systems suggest independently varying rates of magma supply and extension. Other Tethyan ophiolites, particularly in Greece and Italy, exhibit internal structure parallel to, rather than perpendicular to, major rock units, and some show much less diversity in mafic rock type. If these masses are fragments of ocean floor and mantle, such differences in internal structure may be due to differences in spreading processes—perhaps differences in spreading rate.
704 citations
TL;DR: In this paper, the composition of island-arc volcanic rocks in relation to their geographic and stratigraphic relations is discussed and the differences in composition between volcanic rocks and those in continental margins are pointed out.
Abstract: The composition of recent island-arc volcanic rocks in relation to their geographic and stratigraphic relations is discussed. The differences in composition between volcanic rocks and those in continental margins are pointed out. Trace elements and major elements are shown to suggest a continuous gradational sequence from tholeiites through calc-alkaline rocks to shoshonites.
463 citations
TL;DR: The island arc tholeiitic series as mentioned in this paper is the most dominant in many western Pacific and Atlantic Island arcs and represents the earliest stages in arc evolution. But it is chemically inappropriate to call many of the rocks in island arcs calc-alkaline and they suggest they be known as the "island arc thoeitic series" and they differ from normal thoeiitic features by having a higher percentage of intermediate and acid members and too little normative olivine, for example, to have been in equilibrium with peridotite.
455 citations