K / Rb ratios of rocks from island arcs
TL;DR: The abundances of K and Rb have been determined in andesites and shoshonitic rocks from island arcs, inclusions from calc-alkaline rocks and alkali basalts, and in mineral separates from these rocks as mentioned in this paper.
About: This article is published in Geochimica et Cosmochimica Acta.The article was published on 1970-08-01. It has received 83 citations till now. The article focuses on the topics: Magmatism & Biotite.
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TL;DR: In this paper, fine-grained, high-alumina olivine tholeiite with excess water was reacted in sealed platinum capsules in piston-cylinder apparatus between 10 and 35 kbar pressure.
Abstract: Crystalline, fine-grained, high-alumina olivine tholeiite with excess water was reacted in sealed platinum capsules in piston-cylinder apparatus between 10 and 35 kbar pressure. Runs were planned to determine the curve for the beginning of melting, but combining these with published results at lower pressures permitted delineation of the major features of the phase diagram through the melting interval. Amphibolite melts below 10 kbar; quartz eclogite melts above 25 kbar; between them is a melting interval dominated by the breakdown of amphibole and formation of garnet and jadeitic pyroxene. The results introduce two features for geological applications. The solidus changes slope at about 13.5 kbar; the amphibole maximum-stability curve changes slope in the interval 12.5-15 kbar to such an extent that the amphibole stability field is more restricted at high pressures than anticipated from previous studies. With free water, eclogite is Stable only at depths greater than about 70 km, and amphibolite is Stable in the deep crust. Amphibolite crust thickened in the depth range 40-60 km with aqueous pore fluid melts, forming a liquid enriched in silica and albitic plagioclase; this is a potential source of water-undersaturated liquids for batholiths. The upper boundary of the mantle low-velocity zone could be the boundary between rocks with interstitial amphibole and those with interstitial hydrous silicate liquid. In oceanic crust forming the upper part of a subducted lithosphere slab, it appears that most hydrous minerals dehydrate or melt before they reach 100 km depth. If so, dehydration of subducted oceanic crust does not supply water for andesitic magmatism beyond the arc-trench gap, nor contribute to the chemical variations recorded in andesites across arc complexes (K_2O, K/Rb).
300 citations
TL;DR: In this paper, the lower and middle Miocene were dominated by a calcalkaline volcanism associated with minor acid and basic volcanics, and the basic subcrustal volcanics consist mainly of alkali basalts and hawaiites (9.7-11.9 m.y., mean value87Sr/86Sr=0.7121).
Abstract: During the lower and middle Miocene the western Anatolia and the eastern Aegean Sea were dominated by a calcalkaline volcanism associated with minor acid and basic volcanics. The basic subcrustal volcanics consist mainly of alkali basalts and hawaiites (9.7–11.9 m.y.), nepheline hawaiites and nepheline trachyandesites (Kula area from 1.1 m.y. to the recent times). The rhyolitic volcanics (12.5 m.y.) derived by a partial melting process in the upper crust (87Sr/86Sr=0.7121). The calcalkaline suite (16.2–21.5 m.y., mean value87Sr/86Sr=0.708) shows a trend from latite-andesites to dacites and rhyodacites; a latite andesite system related to a sinking slab of lithosphere and constituted by a mixing of oceanic crust (tholeiite), oceanic sediments and/or tectonic fragments of sialic crust is envisaged.
203 citations
TL;DR: The authors found high-K calc-alkaline lavas over Benioff zone depths in excess of 300 km, where tholeiites were found in the normal island arc association.
Abstract: Since Mesozoic time, Java and Bali have formed part of an evolving system of island arcs comprising the Sunda arc of Indonesia. The present tectonic setting is relatively simple with subduction occurring at the Java Trench to the south. A north-dipping Benioff seismic zone delineates an underthrust lithospheric slab to depths of approximately 600 km beneath the Java Sea. Quaternary lavas of the ‘normal island arc association’ range from tholeiites to high-K calc-alkaline lavas over Benioff zone depths from 120–250 km, respectively. More abundant calc-alkaline lavas lie between these extremes. High-K alkaline lavas are found over Benioff zone depths in excess of 300 km.
202 citations
TL;DR: In this paper, chemical variations between the 15 larger volcanic islands of the Lesser Antilles island arc are examined in detail as type examples of this variation, i.e. Grenada (south), Dominica (centre), and St. Kitts (north).
193 citations
TL;DR: In this paper, the phase relationship of a muscovite-granite reaction with excess water was presented through the melting interval with no free water added, and with an isobar at 15 kbar showing the effect of varying water contents on the mineral phase boundaries.
Abstract: Muscovite-granite was reacted in cold-seal pressure vessels at 2 kbar and in pistoncylinder apparatus between 10 and 35 kbar, with just 0.6 weight per cent water structurally bound in 14 modal per cent muscovite, and with additional water contents varying to 50 weight per cent. Phase relationships are presented through the melting interval with excess water, and with no free water added. Selected reactions above 10 kbars have been successfully reversed. An isobar at 15 kbar shows the effect of varying water contents on the mineral phase boundaries for vapor-present and vapor-absent conditions. For the dry rock, temperatures for the solidus and liquidas (quartz-out) curves, respectively, are 10 kbar-760° C, 1160° C; 15 kbar-810° C, 1220° C; 25 kbar-880° C; 1340° C; 35 kbar-1040° C, 1460° C. The solidus curve corresponds to the melting of muscovite + quartz. With water vapor present, the solidus is considerably lower, 15 kbar-610° C, 25 kbar-665° C. Water solubility in the liquid at 15 kbar is 24±3 weight per cent. Maximum temperatures for quartz and feldspars in the vapor-absent region decrease considerably with increasing water content. Temperatures for the quartz-out curve at 15 kbars are 0.6 % H2O-1230° C; 24 % H2O-760° C. At 15 kbars for low water contents, water-undersaturated liquid coexists with quartz and feldspars through hundreds of degrees. Subducted pelagic sediments which metamorphosed to muscovitebearing quartzo-feldspathic rocks would undergo two episodes of melting, beginning at different depths: (1) the first liquid dissolves all pore fluid, and transports it away when it escapes from the crystalline host, (2) reaction of muscovite yields a second liquid, with less dissolved water. According to two published thermal models for a lithosphere slab dipping at 45°, the depths would be (a) 60 km and 92 km, or (b) 17 km and 21 km. Magmas generated by partial fusion in subducted oceanic crust are cooler than the overlying crustal layers and the mantle above the slab by as much as 200° C to 300° C. This must lead to intrusion of relatively cool magma into hot rock. Consequent heating of the magma increases its prospects of reaching high levels in the upper mantle or crust before it solidifies by crossing the solidus curve.
150 citations
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TL;DR: In this paper, the results of a detailed experimental investigation of fractionation of natural basaltic compositions under conditions of high pressure and high temperature were reported, where a single stage, pistoncylinder apparatus has been used in the pressure range up to 27 kb and at temperatures up to 1500° C to study the melting behaviour of several basaltics compositions.
Abstract: This paper reports the results of a detailed experimental investigation of fractionation of natural basaltic compositions under conditions of high pressure and high temperature. A single stage, piston-cylinder apparatus has been used in the pressure range up to 27 kb and at temperatures up to 1500° C to study the melting behaviour of several basaltic compositions. The compositions chosen are olivine-rich (20% or more normative olivine) and include olivine tholeiite (12% normative hypersthene), olivine basalt (1% normative hypersthene) alkali olivine basalt (2% normative nepheline) and picrite (3% normative hypersthene). The liquidus phases of the olivine tholeiite and olivine basalt are olivine at 1 Atmosphere, 4.5 kb and 9 kb, orthopyroxene at 13.5 and 18 kb, clinopyroxene at 22.5 kb and garnet at 27 kb. In the alkali olivine basalt composition, the liquidus phases are olivine at 1 Atmosphere and 9 kb, orthopyroxene with clinopyroxene at 13.5 kb, clinopyroxene at 18 kb and garnet at 27 kb. The sequence of appearance of phases below the liquidus has also been studied in detail. The electron probe micro-analyser has been used to make partial quantitative analyses of olivines, orthopyroxenes, clinopyroxenes and garnets which have crystallized at high pressure.
1,246 citations
TL;DR: In this article, it was shown that oceanic tholeiites are either complete melts of the upper mantle or are generated from a mix of this tholeite and a magnesium-rich peridotite or dunite in proportions up to perhaps 1:4.
Abstract: Tholeiitic basalts (oceanic tholeiites) that form most of the deeply submerged volcanic features in the oceans are characterized by extremely low amounts of Ba, K, P, Pb, Sr, Th, U, and Zr as well as Fe 2 O 3 /FeO 10 in unaltered samples. Oceanic tholeiites also have rare earth abundance-distribution patterns and ratios of K/Rb (1300) and Sr 87 /Sr 86 (0.702) similar to or overlapping those of calcium-rich (basaltic) achondritic meteorites. The close compositional similarities between the oceanic tholeiites and calcium-rich achondrites indicates the relatively primitive nature of the oceanic tholeiites. In contrast, the alkali-rich basalts that cap submarine and island volcanoes are relatively enriched in Ba, K, La, Nb, P, Pb, Pb 206 , Rb, Fe 2 O 3 , Sr, Sr 87 , Ti, Th, U, and Zr; i.e . in the same elements and isotopes that are concentrated in the sialic continental crusts by factors of 5 to 1000 more than the amounts readily inferred in the upper mantle. These analytical data coupled with the field relationships indicate that the alkali-rich basalts are derivative rocks, fractionated from the oceanic tholeiites by processes of magmatic differentiation, and that the oceanic tholeiites are the principal or only primary magma generated in the upper mantle under the oceans. Studies of the abundances and compositions of continental basalts show that essentially identical tholeiitic lavas, contaminated with Si, K, and the chemically coherent trace elements and radiogenic isotopes from the sial, also have been the predominant or only magma generated in the mantle under the continents. The chemical properties of oceanic tholeiites suggest that the upper mantle probably contains less than (in parts per million): Ba, 10; K, 1000; Pb, 0.4; Rb, 10; Th, 0.2; and U, 0.1. The Sr 87 /Sr 86 must be less than 0.7015; Th/U about 2; K/Rb about 1500–2000; and Fe 2 O 3 /FeO less than 0.1. The integration of field and petrochemical data with seismic, density, and shock-wave studies suggests that the oceanic tholeiites are either complete melts of the upper mantle or are generated from a mix of this tholeiite and a magnesium-rich peridotite or dunite in proportions up to perhaps 1:4. The Mohorovicic discontinuity under the oceans appears to mark the transition downward from a largely tholeiitic oceanic crust to either tholeiite reconstituted to blueschist or greenschist or to the ultramafic residue left after expulsion of oceanic tholeiite.
698 citations
TL;DR: In this article, a high pressure experimental study of the partial melting fields of synthetic high-alumina olivine tholeiite and quartz eclogite under dry and wet conditions has been conducted in order to investigate possible origins of the calc-alkaline series from the upper mantle.
Abstract: A high pressure experimental study of the partial melting fields of synthetic high-alumina olivine tholeiite, high-alumina quartz tholeiite, basaltic andesite, andesite, dacite and rhyodacite under dry and wet
$$\left( {P_{{\text{H}}_{\text{2}} {\text{O}}} < P_{{\text{LOAD }}} } \right)$$
conditions has been conducted in order to investigate possible origins of the calc-alkaline series from the upper mantle Detailed analyses of crystallizing phases using the electron microprobe has enabled calculation of the liquid line of descent in these compositions at various pressures At 27–36 kb garnet and clinopyroxene are the liquidus or near-liquidus phases in dry tholeiite, basaltic andesite and andesite, while quartz is the liquidus phases in dry dacite and rhyodacite Under wet conditions at 27 kb garnet, not quartz, is the liquidus phase in the dacite Qualitatively these results show that the low melting fraction of a quartz eclogite at 27–36 kb under dry conditions is of andesitic composition whereas under wet conditions it is rhyodacitic or granodioritic At these pressures under dry conditions the andesite liquidus lies in a marked low temperature trough between the more basic and more acid compositions Quantitatively, the calculated compositions of liquid fractionates for varying degrees of melting of the quartz eclogite bulk composition broadly follow the calc-alkaline trend At 9–10 kb under wet conditions
$$\left( {P_{{\text{H}}_{\text{2}} {\text{O}}} < P_{{\text{LOAD }}} } \right)$$
sub-silicic amphibole and pyroxenes are the near-liquidus phases in tholeiite and basaltic andesite compositions Calcic plagioclase and garnet occur nearer the solidus The calculated liquid fractionates follow the calc-alkaline trend and demonstrate that the calc-alkaline series may be derived by the partial melting of amphibolite at lower crustal depths under wet conditions
$$\left( {P_{{\text{H}}_{\text{2}} {\text{O}}} < P_{{\text{LOAD }}} } \right)$$
, Or by the fractional crystallization of a hydrous basalt magma at similar depths These experimental results support two complementary hypotheses for the derivation of the calc-alkaline igneous rock suite from the mantle by a two stage igneous process In the first stage of both hypotheses large piles of basalt are extruded on the earth's surface Subsequently this pile of basalt may, under dry conditions, transform to quartz eclogite, sink into the mantle and finally undergo partial melting at 100–150 kms depth This partial melting gives rise to the calc-alkaline magma series leaving a residuum of clinopyroxene and garnet Alternatively, if wet conditions prevail in the basalt pile and the geotherms remain high, partial melting of the basalt may take place near the base of the pile, at about 10 kb pressure
$$\left( {P_{{\text{H}}_{\text{2}} {\text{O}}} < P_{{\text{LOAD }}} } \right)$$
The liquids so formed constitute the calc-alkaline suite and the residuum consists of amphibole, pyroxenes and possibly minor garnet and calcic plagioclase Both models may be directly linked to the hypothesis of sea-floor spreading
564 citations
TL;DR: In this paper, the lateral variation of quaternary basalt magmas in the Circum-Pacific belt and island arcs and also in Indonesia change continuously from less alkalic and more siliceous type (tholeiite) on the oceanic side to more alkaloic and less silicerous type (alkali olivine basalt) on a continental side.
Abstract: Quaternary basalt magmas in the Circum-Pacific belt and island arcs and also in Indonesia change continuously from less alkalic and more siliceous type (tholeiite) on the oceanic side to more alkalic and less siliceous type (alkali olivine basalt) on the continental side. In the northeastern part of the Japanese Islands and in Kamchatka, zones of tholeiite, high-alumina basalt, and alkali olivine basalt are arranged parallel to the Pacific coast in the order just named, whereas in the southwestern part of the Japanese Islands, the Aleutian Islands, northwestern United States, New Zealand, and Indonesia, zones of high-alumina basalt and alkali olivine basalt are arranged parallel to the coast. In the Izu-Mariana, Kurile, South Sandwich and Tonga Islands, where deep oceans are present on both sides of the island arcs, only a zone of tholeiite is represented. Thus the lateral variation of magma type is characteristic of the transitional zone between the oceanic and continental structures. Because the variation is continuous, the physico-chemical process attending basalt magma production should also change continuously from the oceanic to continental mantle. Suggested explanations for the lateral variation assuming a homogeneous mantle are: 1) Close correspondence between the variations of depth of earthquake foci in the mantle and of basalt magma type in the Japanese Islands indicates that different magmas are produced at different depths where the earthquakes are generated by stress release: tholeiite at depths around 100 km, high-alumina basalt at depths around 200 km, and alkali olivine basalt at depths greater than 250 km. 2) Primary olivine tholeiite magma is produced at a uniform level of the mantle (100–150 km), and on the oceanic side of the continental margin, it leaves the source region immediately after its production and forms magma reservoirs at shallow depths, perhaps in the crust, where it undergoes fractionation to produce SiO2-oversaturated tholeiite magma, whereas on the continental side, the primary magma forms reservoirs near the source region and stays there long enough to be fractionated to produce alkali olivine basalt magma, and in the intermediate zone, the primary magma forms reservoirs at intermediate depths where it is fractionated to produce high-alumina basalt magma.
562 citations