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1.
Recent pantelleritic lavas comprise the whole of the isolated and outlying volcano of Mayor Island. Mineralogically, they are characterised by phenocrystic anorthoclase-sodic27 sanidine, quartz, sodic ferrohedenbergite, and cossyrite. Nine new chemical analyses of the lavas are presented (including one residual glass), confirming their strongly sodic and peralkaline nature. One analysis is also given of trachybasalt, which occurs as common inclusions in the mantling pumice deposits. These inclusions are characterised by abundant feldspar phenocrysts. Detailed trace element data is presented for five of the lava samples, representing the mam volcanic phases and the trachybasalt inclusions. The following conclusions are presented:
- The lavas exhibit a marked enrichment (relative to “average” granitic compositions) of the alkalis; rare earths; highly charged cations (e.g. Nb, Zr, Hf, Mo, U, Th); Ga, Be, and Cl. In contrast, they show a spectacular depletion of Sr, Ba, and Mg, and a less intense depletion of Ca, Sc, V, and Cr.
- The pantelleritic rare earth patterns show a similar degree of fractionation to the sedimentary pattern, and are dominated by a very strong Eu depletion. This suggests feldspar subtraction. The trachybasalt pattern shows a similar degree of fractionation, but exhibits enrichment of Eu.
- The trachybasalt inclusions are characterised by a trace element assemblage comparable to alkali basalts, except for higher Ba and exceedingly high K/Rb and K/Cs ratios. The chemical and mineralogical data suggest that they represent partial feldspar accumulate rocks.
- There is a progressive enrichment of nearly all trace and minor elements in the youngest lavas. This includes those elements that show an overall depletion in the lavas. The younger lavas are also enriched in Na and Fe, but further depleted in Al.
2.
The Elzevir batholith belongs to a suite of trondhjemitic intrusions emplaced at ca. 1,240 Ma in the Grenville Province of eastern Ontario. New major and trace element data, including REE, combined with isotopic and petrographic data indicate that:
- the batholith has calc-alkalic affinities;
- the Elzevir parental magma is very similar to that of dacites in the nearby, coeval metavolcanic rocks; the magma formed by partial melting of crustal material at granulite grade;
- chemical differences between the plutonic and volcanic rocks can be best explained by accumulation of plagioclase in the plutonic environment;
- fractionation was dominated by plagioclase and quartz, with lesser biotite and epidote, and minor zircon and apatite.
3.
Aluminous, silica-deficient metasedimentary xenoliths in siliceous lavas of Mt. Amiata have preserved composite zoning-patterns indicative for complex processes of magma-rock interaction. Petrographic observations and small-scale mineralogical and chemical differences between up to five distinct zones (including the core and envelope of lava) provide evidence that:
- Partial melt formed in and extracted from the xenoliths was more mafic than the host magma and had a Mg/Fe ratio higher than that of the restite, at least during the peak of thermometamorphism.
- Liquid-state interdiffusion occurred at the interface between partial melt and the enclosing magma.
- Certain mineral phases in the restite (notably, hercynitic spinel) became unstable in the presence of a siliceous liquid.
4.
B. Lammerer I. Fruth D. D. Klemm E. Prosser K. Weber-Diefenbach 《International Journal of Earth Sciences》1976,65(1):436-459
Geologic, petrological and geochemical investigations have been carried out in the western part of the “Zillertaler Alpen”. Important results are:
- The premetamorphic material of the Greiner series consists of conglomerates, breccias, arcosic-sandstones or greywackes, bituminous shales, volcanic lavas and tuffs.
- The southern part of the “Zentralgneis” shows a differentiation trend from alkaline granite to quarzdiorite with predomination of granodiorite.
- Chemical relationships of granodiorite to its restitic inclusions allow the supposition of a palingenetic origin of the granitic rocks.
- At least two stages of metamorphism can be differentiated.
- Parts of the Greiner series, covered by triassic metasediments, are supposed to be of Permian age. A lower age boundary can not yet be given.
- Some vertical, northeast striking faults with throws of more than 1 or 2 kilometers produced southward verging drag folds.
- Geodynamic aspects, revealed from regional metamorphism and tectonics, are discussed.
5.
A comparative study of xenoliths from lavas and granitic rocks of central France indicates that:
- The evolution of the xenoliths is essentially the same in intermediate to acid lavas as in granites. The major factor in this evolution is the assimilation by the host magmas of the quartzofeldspathic components of the xenoliths, which then become Al, Fe, Mg-rich restites.
- Liquid immiscibility between melted xenoliths and host magmas can only be postulated for acid xenoliths in alkali basalts.
- The basic microgranular xenoliths in some granites do not show important compositional gaps with their host rocks, though they are regularly more basic. They can be considered as early segregations (cumulates).
6.
Six lithologic units in tectonic contact with each other have been defined during mapping of the Devonian in the Beaujolais area of the northeastern Massif Central. Five main igneous suites have been recognized:
- A transitional basaltic suite restricted to a single unit.
- An acid volcanic-plutonic suite the members of which are related by fractional crystallization and magma mixing.
- Low-TiO2 volcanic rocks with calc-alkaline affinities.
- A TiO2-rich tholeiitic suite related to an ophiolitic complex.
- A plutonic suite with close resemblances to Alaskantype intrusions.
7.
Prof. Dr. M. Weibel Dr. M. Frangipane-Gysel PD Dr. J. Hunziker 《International Journal of Earth Sciences》1978,67(1):243-252
The Nevado Coropuna (6400 m/19 500 ft) is the largest and highest volcano of Peru and is situated 150 km NW of the town of Arequipa at a distance of 110 km from the Pacific coast. Results of a thorough petrographic study are presented including microprobe and radiometric measurements.
- The constituent rocks building up the Coropuna volcano are lavas and rhyodacitic ash flows intercalated between older and younger lavas at the foot of the cone. The volcanic edifice rests on older ignimbrite sheets (14 m. y.) exposed only in the surrounding valleys.
- The lavas are typically latite-andesites which contain some normative quartz in the groundmass. Plagioclase has 37–47% An. The depth of the phenocryst crystallization is calculated at 8–12 km based on the equilibrium between plagioclase, clinopyroxene and groundmass.
- The Coropuna volcano has existed since the Late Miocene (5 m. y.). Approximately 2 m. y. ago a catastrophic explosion produced large rhyodacitic ignimbrite deposits around the foot of the mountain. Thereafter the effusion of lavas was dominant through Holocene times with the latest lavas becoming slightly more acidic (62% SiO2).
- 30–40 km to the W and SW of the Coropuna some outliers of the coastal batholites are exposed. Both their radiometric age (Cretaceous, 97 m. y.) and their chemical composition are in disagreement with the notion of these granodioritic to gabbroic rocks as the intrusive equivalents of the young volcanics.
8.
Dr. Heinz -Peter Jons 《International Journal of Earth Sciences》1986,75(2):461-493
The analysis of the martian relief leads to the conclusion that some of the most important relief elements are either concentrically or radially arranged with respect to a central structure and hence form aureoles. In this paper four different types of aureoles are identified and described:
- impact aureoles (as result of extradynamics),
- volcanic aureoeles (as result of lava flow through vents),
- tectonic aureoles (as result of isostatic adjustment and/or settlement),
- permafrost-related aureoles and mega-aureoles (as result of migration above thawing permafrost in areas with high relief).
9.
R. Catalano B. d'Argenio C. B. Gregor A. E. M. Nairn G. Nardi P. Renda 《International Journal of Earth Sciences》1984,73(2):577-598
The Mesozoic lavas and minor intrusions in the thrust sheets of western Sicily have the following characteristics:
- The lavas in the Triassic Mufara Formation in the north were broken into fragments which rotated independently within the incompetent strata that enclose them. This behavior is characteristic of igneous rocks found within the more internal (northerly) thrust units.
- The Jurassic lavas in the more external (southerly) units have consistent directions which agree with those of the Ammonitico Rosso limestones in the same zone and lie about 30° clockwise from those of coeval autochthonous formations in Tunisia.Schult's presumed Cretaceous directions from Custonaci on the north coast (similar to those found in the Cretaceous Scaglia Rossa at Terrasini to the east byChannel et al., 1980) are rotated still more (140°) with respect to those of the autochthonous Iblean platform of SE Sicily. These differences are believed to reflect rotation of the thrust sheets during tectonic transport in Cenozoic times, the internal units being the most strongly rotated.
- All the igneous rocks are highly altered: generally the original mineralogy cannot be completely determined. Relative abundances of some of the less mobile elements (Ti, Sr, Y) suggest that they are intraplate basalts.
10.
W. E. G. Taylor 《International Journal of Earth Sciences》1968,58(2):564-587
The paper presents novel information on the Caledonian orogeny in Ireland. A series of Dalradian (Upper Precambrian-Lower Cambrian) metasedimentary rocks occur as an envelope to a granitic igneous complex at Slieve Gamph, Western Ireland. These metasedimentary rocks have been deformed at several distinct times and evidence is shown for the following sequence of events:
- formation of major nappe structures and a tectonic slide. The axial-plane traces of the folds probably trended N. E.-S. W.
- formation of upright, gently plunging folds with axial-plane traces of the folds trending N. E.-S. W. Emplacement of the components of the Slieve Gamph igneous complex.
- formation of a conjugate set of folds:
- Open folds with N. N. E.-S. S. W. trending axial-planes which dip to the east,
- Open folds with E.W. trending axial-planes which dip to the north.
- formation of kink-bands, open and conjugate folds with an axialplane trace trending N. W.-S. E.
11.
Xueyuan Yu 《中国地球化学学报》1985,4(2):150-158
The Niutoushan basaltic cone, consisting of subalkali (quartz-tholeiite and olivine-tholeiite) and alkali basalts, is Late Tertiary in age. Its major characteristics are generalized as follows:
- Both early subalkali and late alkali bali basalts are formed under the same geological environment.
- The continuity in chemical composition from subalkali to alkali and the low FeO/MgO in alkali basalts show that they are the products of cognate magmatic differentiation.
- The change from low REE abundance and weak enrichment of LREE in subalkali to high REE abundance and strong enrichment of LREE in alkali basalts indicates obvious REE enrichment and fractionation during magmatic differentiation. Weak positive Eu anomalies in the REE patterns are indicative of their formation under low oxygen fugacity conditions.
- According to the calculated values, 70–75% of the primary olivine tholeiitic magma had been separated as subalkaline basaltic magma, the rest residual magma became alkaline basaltic magma. This result is consistent to the field observation that the outcrop area of subalkali basalts is four times as much as that of alkali basalts.
- The basaltic rocks of Niutoushan show an S-type distribution straddling the thermal barrier on Ol′-Ne′-Qu′ diagram and an evolution tendency for Ne to increase with increasing FeO/MgO. This is in agreement with the melting experimental data on olivine basalts at 10–20 kb.
- Mantle-derived inclusions (spinel lherzolite) in this area occur in both alkali olivine basalts and olivine tholeiites. The latter is of extremely rare occurrence. The formation temperature and pressure of the inclusions in alkalibasalts and olivine tholeiites have been calculated. The results show that the alkaline basaltic magma was separated from the subalkaline basaltic magma at about 20 kb.
12.
Biotite gneiss xenoliths included in a basanitic flow in the Causses region (France) show several kinds of partial melting. Rhyolitic glasses appear at the expense of the quartz + feldspar assemblage; initially undersaturated latitic glasses at the expense of biotite + feldspar (+ quartz); lastly hyperaluminous products derivating from large phenoblasts of alkali feldspar. The microprobe study of these glasses, of their contacts with the host lava, as well as that of the neogenic mineral phases, show that contamination occurs through, at least, four possible processes:
- Diffusion at the interface between two liquids of contrasted composition (rhyolitic and basanitic).
- Mechanical mixing of two liquids of less contrasted chemistry (latitic and basanitic).
- Progressive solution of a solid phase (quartz) into the magma.
- Vapour phase transfers.
13.
Dr. Hasso Schorin 《International Journal of Earth Sciences》1980,69(1):226-244
In the present phase of the volcanic activity on Nea Kameni / Santorini / Greece the calc-alkalic volcanic rocks are decomposed by H2O, CO2 and SO2 gases of about 100 °C. Using a method ofGresens (1967) for the determination of gains and losses of compounds five different processes could be distinguished:
- leaching of compounds
- enrichment of Ca as gypsum
- increase of Fe2O3 (6%–11%), TiO2 (0,8%–3%) and Zr
- enrichment of Al2O3 (15%–29%), TiO2 (0,8%–1,5%) and K
- increase of Al2O3 (15%–26%), Fe2O3 (6%–9%), TiO2 (0,8%–1,3%), Sr, Ba, Pb and Zr
14.
Alexander A. Godovikov George C. Kennedy 《Contributions to Mineralogy and Petrology》1968,19(2):169-176
Prior experimental work has shown that in the laboratory the mineralogy of eclogites is sensitive to the ratio of CaO ∶ MgO ∶ FeO and that the reaction pyroxene + kyanite?garnet + quartz proceeds to the right at high pressures in rocks rich in magnesium and to the left in rocks rich in calcium and iron. Typical basalts crystallized at high pressure never contain kyanite. The chemistry and mineralogy of a large number of naturally occurring eclogites show they belong to three classes.
- Kyanite-free magmatic eclogites, rich in magnesium, from:
- kimberlites
- dunites and serpentinites.
- Kyanite-bearing eclogites and grosspydites rich in CaO and low in FeO with intermediate MgO from:
- kimberlites
- gneisses.
- Kyanite-free eclogites of metamorphic origin rich in iron with low magnesium and intermediate amounts of calcium from:
- glaucophane schists
- gneisses.
15.
K-Ar dating on a suite of volcanic rocks from the island of Principe gives the following chronology.
- Basal palagonite breccia (30.6 ± 2.1 Ma).
- Older Lava Series (OLS) basalt (23.6±0.7 Ma) and hawaiite (19.1±0.5 Ma).
- Younger Lava Series (YLS) nephelinite (5.60±0.32 Ma) and basanite (3.51 ±0.15).
- Intrusive phonolite (5.32±0.17 Ma, 5.48±0.19 Ma), tristanite (4.89±0.15 Ma) and trachyphonolite (6.93±0.68 Ma) plugs.
16.
Dr. Barbara Theilen-Willige 《International Journal of Earth Sciences》1982,71(1):318-327
The following facts have supported the origin of the Araguainha circular structure in Central Brazil by a meteoritic impact:
- the almost circular contour
- the impact-morphologic sequence including a central uplift, ring walls and a basin rim of escarpments
- outcrops of suevites and mixed breccias
- the evidence of shock metamorphism
- the presence of shatter cones, and
- negative anomalies of the total intensity of the magnetic field at the center of the ring structure.
17.
According to Sakai-Ohmoto's theory regarding the evolution of sulfur isotopes in hydrothermal systems, in conjunction of new data on chemical resaction equilibrium constants and equilibrium isotopic fractionation factors as well as on individual ion activity coefficients of aqueous sulfur species, the following lgfo2.-pH diagrams are constructed:
- mole fractions of aqueous sulfur species (X i ),
- stability fields of some minerals in the Fe-S-O system,
- diagram depicting the oxidation-reduction-state ratio for aqueous sulfur species (R′)
- isotopic compositions of sulfur compounds ( \(\delta S_1 ^{34} \) ).
18.
- Xenoliths of ultrabasic, ultramafic, gabbroic or syenitic type occur in Teneriffe: dunites and clino-pyroxenites in the old alkalic basalt formations of Teno and Anaga peninsulas; gabbroic xenoliths in the Pedro Gil region; nepheline-syenite xenoliths in the Las Canadas and Vilaflor regions where intermediate and phonolitic lavas are abundant; ultramafic, clino-pyroxenite and syenitic xenoliths in the Anaga peninsula where there are many intrusions of nepheline-syenite and phonolitic syenite. Several xenoliths show signs of cataclasis, recrystallisation or reaction of their minerals with the host liquids.
- The ultrabasic, ultramafic and anorthoclase-rich xenoliths appear to be of cumulus origin, subtracted from basic to intermediate alkalic liquids. Major cumulus phases are: magnesium-rich olivine, sub-silicic, aluminous pyroxene, titanomagnetite, sub-silicic potassic kaersutite, and anorthoclase. It is suggested that the xenoliths formed at depths between 11 km and 30 km, largely under wet conditions that helped suppress formation of cumulus plagioclase.
- The subtraction of kaersutite from liquids of intermediate composition is thought to be a means of producing the gap in silica content between the Teneriffe trachybasalts and the more siliceous trachyphonolites and phonolites. It is also suggested that the subtraction of kaersutite and anorthoclase would considerably deplete residual liquids in alumina whilst enriching then in soda and this might be the means of producing peralkaline liquids.
- The presence of the xenoliths supports the geophysical data that indicated that Teneriffe has a sub-crustal structure of plutonic rocks. Correlation of the Teneriffe plutonic xenoliths with exposed plutonic basement rocks from other Canary Islands, which are believed to have similar sub-crustal structures, is considered necessary.
19.
Metagabbros from two widely separated areas in the Adirondacks show development of coronas. In the Southern Adirondacks, these are cored by olivine which is enclosed in a shell of orthopyroxene that is partially, or completely, rimmed by symplectites consisting of clinopyroxene and spinel. Compositions of the corona phases have been determined by electron probe and are consistent with a mechanism involving three partial reactions, thus:
- Olivine=Orthopyroxene+(Mg, Fe)++.
- Plagioclase+(Mg, Fe)+++Ca++=Clinopyroxene+Spinel+Na+.
- Plagioclase+(Mg, Fe)+++Na+=Spinel+more sodic plagioclase+Ca++.
- Olivine + Anorthite = Aluminous orthopyroxene + Aluminous Clinopyroxene + Spinel (Kushiro and Yoder, 1966).
- Orthopyroxene+Ca++=Clinopyroxene+(Mg, Fe)++.
- Clinopyroxene+Spinel+Plagioclase+(Mg, Fe)++=Garnet+Ca+++Na+.
- Plagioclase+(Mg, Fe)+++Na+=Spinel + more sodic plagioclase+Ca++.
- Orthopyroxene+Anorthite+Spinel=Garnet (Green and Ringwood, 1967).
20.
Analytical data are presented for the following elements: Cs, Rb, Ba, K, Sr, Ca, Na, Fe, Mg, Cu, Co, Ni, Li, Sc, V, Cr, Ga, Al, Si, La, Y, and Zr. Eight samples were analysed by the spark source method for rare earths, Tl, Pb, Hf, Sn, Nb, Mo, Bi, and In. In addition to data on rhyolitic volcanics, a small number of intermediate volcanics and eugeosynclinal sediments were analysed for comparative purposes. The following features are shown by the trace element data:
- The rhyolitic rocks have consistently lower concentrations of most trace and minor elements when compared with recent estimates of average concentrations in granites. None of the criteria for strong fractionation (e.g. low K/Rb, Ba/Rb and K/Cs ratios) are present.
- The data do not indicate any systematic differences between the rhyolitic lavas and ignimbrites, although the very young rhyolitic pumices are consistently more “basic” in their element concentrations compared to the other rhyolitic analyses.
- The residual glasses (and devitrified matrices) are depleted, relative to the total rock compositions, in Fe, Mg, Ca, Sr, V, Sc, and Al, and enriched in Cs, Rb, K, Ba, and Si. Zr is depleted in the residual glasses separated from rhyolites, but not in the andesitic residual matrices.
- The rare earth fractionation patterns of the rhyolitic and andesitic extrusives are very similar, being intermediate between chondritic and sedimentary patterns i.e., there is no evidence of strong fractionation. The rhyolitic patterns also indicate a slight Eu depletion.
- Comparable trace and minor element behaviour (with the possible exception of Zr) seems to exist through the rhyolite-andesite compositional range. This is supported by the whole rock-residual liquid trends for the various elements studied, which broadly coincide with the observed whole rock trends, both through the rhyolitic-andesitic compositonal range, and within the rhyolitic compositional range.