Showing papers on "Partial melting published in 1971"
TL;DR: In this article, the authors present an internally consistent model of source composition, derived liquid compositions and residual mantle compositions, and the role of a small (0.1 %) content of water in the upper mantle.
Abstract: Basaltic magmas are formed by partial melting of a source rock of peridotitic composition (pyrolite) under upper mantle conditions. Experimental studies of the mineralogy of pyrolite and the melting relations of various basaltic magmas under high-pressure conditions are integrated in an attempt to present an internally consistent model of source composition, derived liquid compositions and residual mantle compositions. The role of a small (0.1 %) content of water in the upper mantle is treated in some detail. The presence of the low velocity zone in the upper mantle is attributed to a small ( 2 O, CO 2 and incompatible elements, occurs within the low-velocity zone. The evolution of continental and oceanic rift systems and of the Hawaiian volcanic province is discussed in relation to the depths and conditions of magma genesis derived from the models of magma genesis.
391 citations
TL;DR: In this paper, a systematic survey of rare-earth abundances in submarine tholeiitic basalts along mid-oceanic ridges has been made by neutron activation analysis.
Abstract: A systematic survey of rare-earth (r.e.) abundances in submarine tholeiitic basalts along mid-oceanic ridges has been made by neutron activation analysis. The r.e. fractionation patterns are remarkably uniform along each mid-oceanic ridge and from one ridge to another (Juan de Fuca Ridge, East Pacific and Chile Rise, Pacific-Antarctic, Mid-Indian and Carlsberg Ridge, Gulf of Aden, Red Sea Trough and Reykjanes Ridge). The patterns are all depleted in light r.e. except for three samples (Gulf of Aden and Mid-Indian Ridge) which are unfractionated relative to chondrites. They contrast markedly with tholeiitic plateau basalt which are shown to be related to the early volcanic phases associated with continental drift. Tholeiitic plateau basalts are light r.e. enriched as are most continental rocks. Mid-ocean ridge basalts are also distinguishable from spatially related oceanic shield volcanoes of tholeiitic composition (Red Sea Trough-Jebel Teir Is., East Pacific Rise-Culpepper Island). Thus on a r.e. basis there are tholeiites within tholeiites. The r.e. difference between mid-ocean ridge tholeiites and tholeiitic plateau basalts can be related to distinct thermal and tectonic regimes and consequently magmatic modes and rates of intrusions from the low velocity layer in the upper mantle. The difference between continental and oceanic volcanism appears to be triggered by: (1) presence or absence of a moving continental lithosphere over the low velocity layer, and (2) whether or not major rifts tap the low velocity layer through the lithosphere. Fractional crystallization during ascent of melts before eruption at the ridge crest does not affect appreciably the relative r.e. patterns. R.e. in mid-ocean ridge basalts appear to intrinsically reflect their distribution in the upper mantle source, i.e. the low velocity layer. Based on secondary order r.e. variation of mid-ocean ridge basalts: (1) If fractional crystallization is invoked for the small r.e. variations, up to approximately 50 % extraction of olivine and Ca-poor orthopyroxene in various combinations can be tolerated. However, only limited amount of plagioclase or Ca-rich clinopyroxene can be extracted, the former because of its effect on the abundance of Eu abundance and the latter because of its effect on the [La/Sm] e.f. ratio, alternatively. (2) If partial melting during ascent is invoked, and a minimum of 10% melting is assumed, the permissible degree of melting of originally a lherzolite upper mantle may vary between 10 and 30% . It is not possible to establish readily to what extent these two processes have been operative as they cannot be distinguished on the basis of r.e. data only. However, there is evidence indicating that both have been operative and are responsible for the small r.e. variations observed in mid-ocean ridge basalts. An attempt to correlate second order r.e. variations along or across mid-oceanic ridges with spreading rate, age, or distance from ridge crests has been made but the results are inconclusive. No r.e. secular variation of the oceanic crust is apparent. R.e. average ridge to ridge variations are attributed to small lateral inhomogeneities of the source of basalts in the low velocity layer, and to a certain extent, to its past history. The remarkable r.e. uniformity of mid-oceanic ridge tholeiites requires a unique and simple volcanic process to be operative. It calls for upward migration of melt or slush from a relatively homogeneous source in the mantle—the low velocity layer, followed by further partial melting during ascent. The model, although consistent with geophysics, may have to be reconciled with some evidence from experimental petrology. Models for r.e. composition of the upper mantle source of ridge basalt, formation of layers 2 and 3, and the moho-discontinuity, are also presented.
216 citations
TL;DR: In this article, major and trace element data from low-grade isochemically metamorphosed Archaean igneous suites in Transvaal, Rhodesia, Western Australia and Canada show consistent variations from those of corresponding younger volcanic suites.
105 citations
TL;DR: In this paper, a melting mechanism involving several stages and hypotheses concerning the possible composition of the depleted melting fractions are proposed, which have a bearing on the genesis of granitic materials.
93 citations
TL;DR: Island arc volcanism has contributed and is still contributing to continental growth, but the composition of island arcs differs from that of the upper continental crust in its lower abundance of Si, K, Rb, Ba, Sr and light rare earth elements as discussed by the authors.
88 citations
TL;DR: In this article, the authors indicate the outlines of a possible new extension from the plate tectonic theory to the study of the products of partial melting associated with global movements of plates.
Abstract: THE geological sciences have been advanced enormously by the philosophy of plate tectonics and it is appropriate now to apply data from igneous petrology to further this advance. This step is logical because magmatism is chiefly the study of the products of partial melting associated with global movements of plates. More needs to be done in this field, although the recent article by Baker and Wohlenberg1 is a valuable addition. In this letter I shall indicate the outlines of a possible new extension from the plate tectonic theory.
79 citations
TL;DR: In this article, the accretion hypothesis of Battey is supported and developed for the voluminous silicicic volcanics of the African rift system, which is not the products of fractionation, direct partial melting, or anatexis of continental crust.
Abstract: Volcanism on the Arabo-Ethiopian swell has accompanied the development of the three traversing spreading zones conjoining at Afar: the Red Sea, Gulf of Aden, and African rift systems. The Red Sea and Gulf of Aden floors are formed by oceanic tholeiites, but Afar and the main Ethiopian rift show a wider range of more alkaline volcanics. related to slower crustal spreading rates. The high plateaus between the rifts have had a strongly alkaline volcanism. The plateau basalts and especially the intermediate lavas are much more undersaturated than their rift equivalents, and are enriched in potash and Al/Fe. The silicic volcanics of the rift are soda-iron enriched relative to the plateau silicics. Magmatic composition can be equated with depth of melting, but the voluminous silicic volcanics are not the products of fractionation, direct partial melting, or anatexis of continental crust: the accretion hypothesis of Battey is supported and developed.
71 citations
TL;DR: This article showed that olivine becomes a liquidus phase at pressures above 8kb and the liquidus clinopyroxene becomes more Ca and Al-rich with increasing pressure, and that none of the observed olivines results from crystal accumulation.
54 citations
TL;DR: In this article, the authors examined the partial melting along appropriate geotherms, of a descending slab of oceanic crust, and suggested that magmas of the island arc tholeiitic series are produced by reactions involving the breakdown of amphibole at shallow depths.
48 citations
TL;DR: In this article, a suite of hornblende lherzolite xenoliths probably derived from the upper mantle are compared with clinopyroxenes from spinel lherzholite.
44 citations
TL;DR: The behavior of Rb, Sr, Eu, Zr and Ni in the Louis Lake batholith as a function of increasing fractionation from the granodiorite to the aplite stage is similar to the predicted and often observed behavior for these elements in calc-alkaline suites as mentioned in this paper.
TL;DR: In the Grand Canyon of the Rio Grande de Santiago of the Mexican Cordilleran Volcanic Province as discussed by the authors, a number of oriented cores of 2.5 cm diameter have been drilled from seven bodies comprising part of a sequence of ignimbrite sheets interdigitated with basalts and basaltic andesites.
Abstract: Seventy-two oriented cores of 2.5 cm diameter have been drilled from seven bodies comprising part of a sequence of ignimbrite sheets interdigitated with basalts and basaltic andesites, in the Grand Canyon of the Rio Grande de Santiago of the Mexican Cordilleran Volcanic Province. Field observations and whole-rock analyses reveal two groups: an olivine basalt-high alumina basalt-basaltic andesite series, and a sequence of rhyolitic ignimbrite sheets, with some rhyolitic and obsidian lava flows. Crystal separation, partial melting of oceanic tholeiite, and simple mixing of basalt and oceanic sediments or granodiorite cannot acceptably explain the observed fractionation trends. The favored origin is a partial melting of a second or third stage product, such as a basalt or amphibolite enriched in K, Rb, Th, and Pb, relative to oceanic tholeiite. The observed fractionation trends are parallel to those of the andesite-dacites of the Mexico City region, but the Rio Grande de Santiago rocks have a systematically higher K 2 O/SiO 2 ratio, which can be explained by a greater magma generation depth. The paleomagnetic polarity sequence with decreasing age is R,R,N,R,R,N,N, providing easily measurable markers of high potential stratigraphic value. The mean virtual geomagnetic pole is not significantly different from the present spin axis. The potassium-argon analyses show that the sampled section contains two distinct volcanic episodes, from approximately t = 4.6 to 5.5. m.y. and from approximately t = 8.7 to 9.5 m.y. The polarities recorded by the youngest volcanic cycle are consistent with the predicted polarity time scale of Heirtzler and others (1968), while the older cycle polarities can be explained by minor modification of the predicted polarity scale, to include a short period of reversed polarity between 9.0 and 9.5 m.y., within the normal polarity anomaly 5 (t = 8.79 to 9.94 m.y.) of the time scale.
TL;DR: In this article, the authors investigated the relationship between alkalies and silica for the two groups of volcanics and showed that a recent model of island-arc volcanism, involving partial melting of amphibolite and eclogite within a descending slab of oceanic crust, is broadly compatible with the observed characteristics of the Aegean lavas.
TL;DR: In this paper, the trace element abundances of lunar basalts are examined and the implications of the near-chondritic relative abundance of incompatible elements are discussed, and it is shown that with this distribution of trace elements in the source region, and under appropriate conditions of partial melting, most of the europium may be retained within the principal host mineral(s).
TL;DR: Strontium isotopic studies of kimberlites reveal no significant differences between the respective whole-rock Sr87/Sr86 ratios of fissure and pipe kimbersites as discussed by the authors.
Abstract: Strontium isotopic studies of kimberlites reveal no significant differences between the respective whole-rock Sr87/Sr86 ratios of fissure and pipe kimberlites. Kimberlites from the Swartruggens fissure (calcareous micaceous kimberlite) have Sr87/Sr86 ratios of from 0.709 to 0.716, whilst those from the Wesselton pipe have Sr87/Sr86 ratios of from 0.708 to 0.715. Other kimberlites range from 0.706 to 0.715. Samples are considered to be late Cretaceous to early Tertiary and thus the ratios are approximately initial ratios. The Sr87/Sr86 ratios bear no relation to the Rb or Sr content of individual kimberlite bodies. The high initial ratios are not due to bulk assimilation of granitic material in either a kimberlite or carbonatitic magma. Rb-Sr data for garnet peridotites and eclogite xenoliths in kimberlite are not compatible with production of kimberlite by eclogite fractionation from a melt derived from garnet lherzolite. The Sr isotopic composition of kimberlite is compatible with partial melting of garnet mica peridotite. The isotopic composition of liquids formed by partial melting of this rock can be modified by (i) gross contamination with material of low Sr87/Sr86 ratio or (ii) selective diffusion of material of high Sr87/Sr86 ratio into kimberlitic fluids.
TL;DR: In this paper, the rare earth elements (REE) La-Lu was analyzed for basaltic lava types and included xenoliths from the Comores Archipelago. But the results were limited to the basanite-phonolite series.
Abstract: Lavas and included xenoliths from the Comores Archipelago have been analysed for the rare earth elements (REE) La-Lu. Among basaltic lava types fractionation of REE rock/chondrite distribution patterns is more extreme with greater SiO2 undersaturation and contents of incompatible elements. Enrichment and slight fractionation of REE in the rock series basanite-phonolite is considered compatible with a model of fractional crystallisation at low pressures involving mainly olivine and clinopyroxene, and to a much lesser extent, plagioclase. Apatite is probably effective in curtailing further enrichment of REE. High level fractional crystallisation and eclogite fractionation at depth appear unlikely causes for the relative enrichment of light REE (La-Eu) in the undersaturated basalts. This effect is more probably due to mineralogical control during partial melting in the upper mantle. Lherzolite xenoliths are poor in REE, exhibiting a slight relative depletion in the light REE. These patterns are interpreted as those of possible mantle material subjected to small degrees of partial melting, although not necessarily related to those melts erupted as lava flows at the surface.
TL;DR: A palaeomagnetic map of south-western Iceland is presented in this article, which includes the neovolcanic zone and older lava successions on its east and west sides.
TL;DR: In this paper, the authors discussed the significance of the Deccan Traps and the opinions expressed on the genesis of the rocks are critically reviewed and the importance of their distribution is discussed.
Abstract: The acid rocks of the Deccan Traps including microgranites, felsites, rhyolites and related rocks are contined to tectonically weak zones in Western India. The significance of their distribution is discussed and the opinions expressed on the genesis of the rocks are critically reviewed. In their formation, fractional crystallization of tholeiitie basalt magma, which is supposed to be the parental one, was aided in certain localities by the melting of the sialic crust and assimilation or partial melting of the pre-Deccan Trap rocks. Evidence for the latter is found in the gradational contacts of the acid rocks with the earlier rocks, their association with cruptive centres or faulted zones and absence of any definite trend of variation in petrographical and chemical characters. Some of the rhyolitic rocks are also formed due to hydrothermal alteration of sedimentaries along the Narmada Valley.
TL;DR: In this article, a comparison between the average compositions of the granites in the Variscan, Caledonian, and Alpine orogenic belts of western Europe was made, showing that their respective compositions lie near the isobaric minima in the system Q-Or-Ab-H2O.
Abstract: A comparison has been made between the average compositions of the granites in the Variscan, Caledonian, and Alpine orogenic belts of western Europe. Their respective compositions lie near the isobaric minima in the system Q-Or-Ab-H2O for successively higher water pressures, whereas metamorphic facies series indicate that the three orogenic belts developed under successively lower geothermal gradients. These relationships are consistent with an origin of the granitic magmas by partial melting in the crust.
TL;DR: Partition coefficients of strontium between clinopyroxene and liquid were experimentally determined at 30, 40 and 52 kb in the system forsterite-diopside-anorthite-strontium feldspar.
TL;DR: In this article, two foliated metagabbros from the Mid-Atlantic Ridge near 30° N were analyzed for rare earth elements and the chondrite-normalized rare earth pattern for one of them is quite similar to those for abyssal tholeiites.
Abstract: Two foliated metagabbros from the Mid-Atlantic Ridge near 30° N were analyzed for rare earth elements. The chondrite-normalized rare earth pattern for one of them is quite similar to those for abyssal tholeiites. The pattern for another sample, however, is somewhat different from the above one. A new set of bulk partition coefficients for rare earth elements has been estimated correspondingly. This set throws a new light on the interpretation that many alkali olivine basalts were produced by a zone melting or partial melting of primary-liquid-type material. Also the same partition coefficients lead us to an inference that the high-temperature peridotite intrusion in the Lizard area, Cornwall, England, is a secondary-solid-type material which was once in equilibrium with a primary-solid-type material, whereas the pyroxenite, Canyon Mountain, Oregon, is a primary-solid-type material.
TL;DR: The existence of the low-velocity layer (or layers) in the uppermost parts of the mantle, at least in oceanic and tectogenic regions, is now accepted without any doubt as mentioned in this paper.
Abstract: The existence of the low-velocity layer (or layers) in the uppermost parts of the mantle, at least in oceanic and tectogenic regions, is now accepted without any doubt. Different explanations for the origin of the low-velocity layers have been suggested. One suggestion has been that partial melting is the principal cause; however, this suggestion presents two problems: (1) poor knowledge of the temperature at each respective depth, and (2) discovery in some areas of high-velocity layers that are situated just above the low-velocity zones. These two problems are discussed in this paper.
TL;DR: In this paper, the solidus of the lherzolite from Ichinomegata, Japan was determined at pressures between 1 atm and 50 kb, with a slope of about 7 °C/kb.
TL;DR: A potash trachyte (containing 13% K2O) crops out within the Malvernian (Pre-cambrian) calc-alkaline igneous complex as discussed by the authors.
Abstract: A potash trachyte (containing 13% K2O) crops out within the Malvernian (Pre-cambrian) calc-alkaline igneous complex. The chemical composition is similar to that of minor intrusions in areas of alkaline igneous activity. An origin by partial melting of biotite-rich basement rocks is proposed.
TL;DR: In this article, geochemical data for 13 samples of alkalic rocks from Nemuro Peninsula, Hokkaido, are presented and discussed, and it is shown that the Nemuro alkalics have distinctly higher concentrations of Ba, Zn, Cu, Pb, Y and Li, high ratios of K/Sr and Ca-Sr, and lower concentrations of Sr, Ni, Co, Cr, Sc, Sc and Zr.
Abstract: Geochemical data for 13 samples of alkalic rocks from Nemuro Peninsula, Hokkaido, are presented and discussed. Analyses for trace elements, Ni, Co, Cr, Sc, Cu, Zn, Ga, Zr, Y, Pb, Ba, Sr and Li in a differentiated sheet ranging from picritic dolerite to syenite and in an undifferentiated dolerite sheet showing pillow structure, are given. It is shown that the Nemuro alkalic rocks have distinctly higher concentrations of Ba, Zn, Cu, Pb, Y and Li, high ratios of K/Sr and Ca/Sr, and lower concentrations of Sr, Ni, Co, Cr, Sc and Zr than do alkali basaltic rocks from other districts in the world. The behavior of the major and trace elements suggests that the Nemuro alkalic rocks were modified chemically by deuteric alteration during the magmatic stage. The parental potash-rich olivine basalt magma of these alkalic rocks was formed probably by partial melting of phlogopite-peridotite in the upper mantle.