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1.
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:
  1. A transitional basaltic suite restricted to a single unit.
  2. An acid volcanic-plutonic suite the members of which are related by fractional crystallization and magma mixing.
  3. Low-TiO2 volcanic rocks with calc-alkaline affinities.
  4. A TiO2-rich tholeiitic suite related to an ophiolitic complex.
  5. A plutonic suite with close resemblances to Alaskantype intrusions.
The transitional metabasalts (1) form the oldest igneous suite and could represent either an intraplate magmatic forerunner of rifting or tectonic slices of weakly metamorphosed rocks representing a pre-Acadian event. The next three suites may be related to a short-lived ensialic marginal basin that developed between the Acadian and Bretonian orogenies. The basin is asymmetric, with the ophiolite of the central part flanked by an acid ridge on one side and a passive continental margin on the other. Quartz-keratophyres (2) and calc-alkalic basic volcanic rocks (3) were intercalated in varying proportions to form a bimodal volcanic pile before the rifting event that led to the formation of the ophiolites (4). The acid ridge (2) may be due to the reactivation of a continental basement. Cumulate rocks with Alaskan-type affinities occur as olistoliths, emplaced before the formation of the rift basin, supporting a comparison of the Hercynian belt with accreted magmatic arc terranes.  相似文献   

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:
  1. the batholith has calc-alkalic affinities;
  2. 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;
  3. chemical differences between the plutonic and volcanic rocks can be best explained by accumulation of plagioclase in the plutonic environment;
  4. fractionation was dominated by plagioclase and quartz, with lesser biotite and epidote, and minor zircon and apatite.
It is suggested that melting of sialic crust took place during the ‘docking’ of a partly-evolved, originally ensimatic arc system against the main cratonic mass to the northwest.  相似文献   

3.
The data obtained can be summed up in 6 points:
  1. The sediment consists of varying amounts of quartz (14–23 weight percent, mean value 18%), aragonite, dolomite, Mg-rich calcite, Mg-poor calcite, Na-rich plagioclase (7–10%, m.v. 8%), chlorite (18–32%, m.v. 22%), kaolinite (4–29%, m.v. 13%), illite and mixedlayered illite-montmorillonite (20–42%, m.v. 34%) and organic matter (0.7–2.5%, m.v. 1.1%).
  2. The composition of the carbonate fraction suggests a detrital origin for the carbonates deposited along the Persian Coast.
  3. The clay mineral distribution follows gradients perpendicular to the long half-axis of the Persian Gulf. This favours detrital origin. The kaolinite distribution suggests an additional detritus from Euphrates and Tigris,
  4. Enrichments of trace elements with regard to mean values in clays (Turekian and Wedepohl, 1961) are estimated for Fe, Co, Mo, Ni, V, Zr and Br; impoverishments are recorded for Cu, Mn, K. The contents of Rb, Ti and Zn comply with mean values of clays. The enrichments distribute as follows: chlorite concentrates Mn and Fe, kaolinite Ti and Zr, illite and mixedlayered illite-montmorillonite Rb, V, M, Zn, Mo and Co.
  5. The high Br-contents (up to 420 ppm) in the sediment give positive correlations with the concentrations of organic carbon. The X-ray analysis of isolated kerogen confirms an enrichment of Br in this fraction of the organic matter.
  6. The distribution of elements in the sediment to a large extent is controlled by a) detritus of Euphrates and Tigris, b) influence of organic matter.
  相似文献   

4.
Complex multivariant reactions involving Fe-Ti oxide minerals, plagioclase and olivine have produced coronas of biotite, hornblende and garnet between ilmenite and plagioclase in Adirondack olivine metagabbros. Both the biotite (6–10% TiO2) and the hornblende (3–6% TiO2) are exceptionally Titanium-rich. The garnet is nearly identical in composition to the garnet in coronas around olivine in the same rocks. The coronas form in two stages:
  1. Plagioclase+Fe-Ti Oxides+Olivine+water =Hornblende+Spinel+Orthopyroxene±Biotite +more-sodic Plagioclase
  2. Hornblende+Orthopyroxene±Spinel+Plagioclase =Garnet+Clinopyroxene+more-sodic Plagioclase
The Orthopyroxene and part of the clinopyroxene form adjacent to olivine. Both reactions are linked by exchange of Mg2+ and Fe2+ with the reactions forming pyroxene and garnet coronas around olivine in the same rocks. The reactions occur under granulite fades metamorphic conditions, either during isobaric cooling or with increasing pressure at high temperature.  相似文献   

5.
Scapolite at Mary Kathleen (North-Western Queensland) occurs in calcareous and non-calcareous metapelites, acid and basic metavolcanics and metadolerites. Graphical treatment of the relationship between scapolite composition (Me%) and the host rock oxide ratios CaO/Na2O and Al2O3/(CaO + Na2O) reveals the following points:
  1. The calcareous metapelites are also very sodic.
  2. Scapolite in calcareous metapelites is more marialitic than that in low-calcium equivalents.
  3. In graphs of Me% against CaO/Na2O and Al2O3/(CaO + Na2O) the metasediments and the metaigneous rocks show markedly different trends.
It is concluded that scapolite in the metasediments originated by isochemical metamorphism of shales and marls containing evaporitic halite. The local abundance of halite was the main control on the composition and distribution of the scapolite, but the relative abundance of CaO and Na2O was a modifying factor. In the metaigneous rocks scapolite formed metasomatically during regional metamorphism by the introduction of volatile-rich fluids derived from the adjacent evaporitic sediments. The relative availability of CO2 and Cl2 again appears to have been the primary control on scapolite composition and may in turn have been controlled by bulk rock composition.  相似文献   

6.
P, T, \(X_{{\text{CO}}_{\text{2}} }\) relations of gehlenite, anorthite, grossularite, wollastonite, corundum and calcite have been determined experimentally at P f =1 and 4 kb. Using synthetic starting minerals the following reactions have been demonstrated reversibly
  1. 2 anorthite+3 calcite=gehlenite+grossularite+3 CO2.
  2. anorthite+corundum+3 calcite=2 gehlenite+3 CO2.
  3. 3anorthite+3 calcite=2 grossularite+corundum+3CO2.
  4. grossularite+2 corundum+3 calcite=3 gehlenite+3 CO2.
  5. anorthite+2 calcite=gehlenite+wollastonite+2CO2.
  6. anorthite+wollastonite+calcite=grossularite+CO2.
  7. grossularite+calcite=gehlenite+2 wollastonite+CO2.
In the T, \(X_{{\text{CO}}_{\text{2}} }\) diagram at P f =1 kb two isobaric invariant points have been located at 770±10°C, \(X_{{\text{CO}}_{\text{2}} }\) =0.27 and at 840±10°C, \(X_{{\text{CO}}_{\text{2}} }\) =0.55. Formation of gehlenite from low temperature assemblages according to (4) and (2) takes place at 1 kb and 715–855° C, \(X_{{\text{CO}}_{\text{2}} }\) =0.1–1.0. In agreement with experimental results the formation of gehlenite in natural metamorphic rocks is restricted to shallow, high temperature contact aureoles.  相似文献   

7.
Samples of micaschists, gneisses, and migmatites from a sequence of metamorphic subfacies of the Gévennes Médianes (Dép. Ardèche, France) are characterized chemically by
  1. a high and only slightly varying Al2O3 content (m.v.=17.57 wt.-%, stand, dev.=1.804, var. coeff.=0.103).
  2. a negligible variation of the molar MgO/MgO+FeO ratio (m.v.=0.504, stand. dev.= 0.066, var. coeff.=0.130), and
  3. an insignificant variation of the molar CaO/CaO + Na2O ratio (m.v.=0.360, stand. dev.=0.014, var. coeff.=0.039).
The Na2O and K2O values of the migmatite samples are respectively 14 and 30% higher than those of the samples of the neighbouring gneisses and schists. The concentrations of all other major elements of the migmatites are within the variation limits determined for the gneisses and schists. Samples displaying initial migmatization have the following petrography:
  1. The light-coloured portions of the migmatites (leueosome) contain alkalifeldspar, plagioclase, and quartz, the dark-coloured ones (melanosome) are always free of alkalifeldspar and contain, besides ferromagnesian constituents, both plagioclase and quartz.
  2. The plagioclase of the melanosome has a remarkably higher An-content (An30–40mol.-%) than that one of the leueosome (An 9–14 mol.-%).
These observations seem to represent petrographic evidence that leueosome and melanosome have been in a restite-melt-relation at a temperature that just reached or slightly exceeded the value necessary to produce the beginning of melting. In addition, major element analyses of separated leueosome portions of samples displaying the petrography mentioned above have been undertaken. Normative Qz ∶ Ab: Or-ratios calculated from these analyses vary within very narrow limits about the average value of Qz ∶ Ab ∶ Or=36 ∶ 31 ∶ 33. Using the diagrams of von Platen (1965) concerning the crystallization of granitic melts the petrographic findings can be verified from analytical results, i.e. the migmatites of the Beaume valley are considered to be products of minimum temperature melting of the gneisses which still occur unaltered in adjoining areas of lower metamorphic grade.  相似文献   

8.
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:
  1. impact aureoles (as result of extradynamics),
  2. volcanic aureoeles (as result of lava flow through vents),
  3. tectonic aureoles (as result of isostatic adjustment and/or settlement),
  4. permafrost-related aureoles and mega-aureoles (as result of migration above thawing permafrost in areas with high relief).
The spatial distribution of these different types of aureoles indicates the predominant type of relief-forming dynamics in the area of their distribution (impact-related aureoles occur predominantly in the area of the Southern Uplands; volcanic, tectonic and permafrost-related aureoles in the area of large-scale updomings-TaNoVa, Elysiumand their volcanic provinces).  相似文献   

9.
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.
  1. 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.
  2. 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.
  3. 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).
  4. 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.
  相似文献   

10.
The system MgO-Al2O3-SiO2(MAS) comprises 88–90% of the bulk composition of an average peridotite. The MAS ternary is thus a suitable starting point for exploring peridotite phase relations in multicomponent natural systems. The basic MAS phase relations may be treated in terms of the reactions (see list of symbols etc).
  1. py (in Gt)=en (in Opx)+mats (in Opx),
  2. en (in Opx)+sp (in Sp)=mats (in Opx)+fo (in Ol), and
  3. py (in Gt)+fo (in Ol)=en (in Opx)+sp (in Sp).
Extensive reversed phase equilibria data on these three reactions by Danckwerth and Newton (1978), Perkins et al. (1981), and Gasparik and Newton (1984) employing identical experimental methods in the same laboratory have been used by us to deduce the following internally consistent thermodynamic data applying the technique of linear programming:ΔH 298(1) 0 = 2536 J, ΔS 298(1) 0 =? 6.064 J/K;ΔH 298(2) 0 = 29435 J, ΔS 298(2) 0 = 8.323 J/K; andΔH 298(3) 0 =?26899 J, ΔS 298(3) 0 =?14.388 J/K.These data are also found to be consistent with results of calorimetry. Figure 2 shows the calculated phase relations based on our thermodynamic data; they are consistent with the phase equilibria experiments. Successful extension of the MAS phase relations to multicomponent peridotites pivots on the extent to which the effects of the “non-ternary” (i.e. other than MAS) components can be quantitatively handled. Particularly hazardous in this context is Cr2O3, although it barely makes up 0.2 to 0.5 wt% of such rocks. This is because Cr+3 fractionates extremely strongly into Sp. This study focuses on the peridotite phase relations in the MgO-Al2O3-SiO2-Cr2O3 (MASCr) quaternary. Thermodynamic calculations of the MASCr phase relations have been accomplished by using ΔH 298 0 and ΔS 298 0 values for the reactions (1) through (3) indicated above, in conjunction with data on thermodynamic mixing properties of
  1. binary Sp (sp-pc) crystalline solution (Oka et al. 1984),
  2. ternary Opx (en-mats-mcts) crystalline solution (this study), and
  3. binary Gt (py-kn) crystalline solution (this study).
The results are shown in P-T projections (Figs. 3a and b) and isobaric-isothermal sections of MASCr in a projection through the component fo onto the SiO2-Al2O3-Cr2O3 ternary (Figs. 4a and b). The most important results of this work may be summarized as follows:
  1. With increasing incorporation of Cr+3 into Sp and Gt, the X mats isopleths of the reactions (1) and (2) are shifted to higher temperatures (Fig. 3a); simultaneously, the spinel-peridotite to garnet-peridotite phase transition is moved to higher pressures (Fig. 3b).
  2. At identical P and T, the X mats values of Opx coexisting in equilibrium with Ol and Sp is strongly dependent upon the X pc value in the latter phase (Figs. 4a and b). Accurate correction for the composition of Sp is, therefore, a necessary precondition for geothermometry of the spinelperidotites.
  3. The discrepant temperatures reported by Sachtleben und Seck (1981, Fig. 5) from the spinel-peridotites of the Eifel area (systematically too high temperatures as a function of X pc in Sp) are demonstrated to be the result of ignoring the nonideality in the chromian spinels.
  相似文献   

11.
Laihuite reported in the present paper is a new iron silicate mineral found in China with the following characteristics:
  1. This mineral occurs in a metamorphic iron deposit, associated with fayalite, hypersthene, quartz, magnetitc, etc.
  2. The mineral is opaque, black in colour, thickly tabular in shape with luster metallic to sub-metallic, two perfect cleavages and specific gravity of 3.92.
  3. Its main chemical components are Fe and Si with Fe3+>Fe2+. The analysis gave the formula of Fe Fe 1.00 3+ ·Fe 0.58 2+ ·Mg 0.03 2+ ·Si0.96O4.
  4. Its DTA curve shows an exothermic peak at 713°C.
  5. The mineral has its own infrared spectrum distinctive from that of other minerals.
  6. This mineral is of orthorhombic system; space group:C 2h /5 ?P21/c; unit cell:α=5.813ű0.005,b=4.812ű0.005,c=10.211ű0.005,β=90.87°.
  7. The Mössbauer spectrum of this mineral is given, too.
  相似文献   

12.
In the southern Apennin (= northern part of the region dealt with) and the Coasta Chain (= southern part) there are metabasalts wich are classified in the northern part as:
  1. Glaucophane rocks of the albite-lawsonite-glaucophane-subfacies with the assemblage glaucophane + pumpellyite + lawsonite ±albite ±aragonite ±muscovite (7 rock analyses, 8 mineral analyses). These rocks are conceived as relics of an older burial metamorphism.
  2. Rocks with pumpellyite and chlorite or also chlorite alone, that are interpreted as reaction rims between the metastable glaucophane rocks and the country rock (phyllites, quartzites). The assemblages pumpellyite + chlorite and chlorite alone are to be found (2 rock analyses and 2 mineral analyses).
  3. Rocks with lawsonite and/or epidote belong to the same mineral facies as the country rock: a facies similar to the greenschist facies (called “lawsonite-albite-chlorite-subfacies”) which is characterized by the assemblages lawsonite + albite + chlorite ±calcite and also epidote ±lawsonite + albite + chlorite ± muscovite. These types are attributed to a younger dynamo-metamorphism (2 rock analyses).
In the southern part, the metabasalts can be found only as rocks with epidote and/or lawsonite, a metamorphism with more than one event cannot be proved petrologically (3 rock analyses). Equations of the observed mineral reactions are given. The transitions of one facies into another are represented in the pseudo-quaternary system Al2O3-CaO-Na2O · Al2O3-2 Fe2O3 + FeO + MnO + MgO-(H2O). The pressure-temperature conditions are estimated on the basis of published experimental data (300° C and 6–7 kb for the glaucophane rocks; 400° C and about 6 kb for the rocks with lawsonite and/or epidote) and are compared with geologic facts.  相似文献   

13.
First results obtained in the study of the Ca-Ba diadochic substitution in the several polymorphic modifications of BaAl2Si2O8 are reported:
  1. in the hexagonal modifications synthesized at 1200° C by a solid state reaction, Ca replaces Ba up to 37% (atomic fraction);
  2. in the hexagonal modifications obtained by crystallization of a melt, the replacement is limited to 25%;
  3. in the monoclinic modifications obtained by heating the above mentioned modifications to 1450° C, the replacement is limited to 25% again.
A remarkable feature of the low and high hexagonal modifications is that their unit-cell parameters show no variation with composition. These hexagonal phases, furthermore, seem identical irrespective of the method of synthesis. The unit-cell parameters of the monoclinic phases vary very little with composition.  相似文献   

14.
High-temperature plagioclases NaAlSi3O8(Ab)-CaAl2Si2O8(An) have been prepared by dry devitrification of glasses. X-ray powder photographs were taken to follow the time-temperature dependence of indicators of structural state and to determine the lattice parameters of the plagioclases as well as their K-exchanged equivalents. Transmission electron microscopy (TEM) has been used to study the anorthite-type antiphase domain textures. The results are as follows:
  1. TEM and X-ray powder data suggest to subdivide the high-temperature plagioclase series into three structural regions: (a) An0 to An30–40: monalbite/analbite to high albite-type structures, (b) An60–70 to An100: anorthite-type structures, (c) An30–40 to An60–70: transitional structures assumed to represent the early stages in the development of the structural complexities found in chemically intermediate low temperature plagioclases.
  2. b-Antiphase domains typical for the anorthite-type structure could be imaged in samples ranging between An100 and An67.5, whereas c-antiphase domains have only been found in An90 and An100. The b-domains developed during isothermal crystallization, rather than cooling. The transition from the anorthite-type structure (S.G.I \(\bar 1\) ) to an intermediate C \(\bar 1\) -type structure at An60–70 appears to be a gradual one.
  3. The relative contribution of various structural and chemical influences on the cell edges and angles is discussed in detail. It is shown that the nonlinear variation of γ with An content is due to incomplete Al,Si disorder in the high series.
  相似文献   

15.
Principe is one of the volcanic centres comprising the Cameroun line in West Africa. The volcanic rocks can be divided into two stratigraphic units:
  1. Younger lava series — basanite and nephelinite overlying.
  2. Older lava series — transitional to mildly alkaline basalt and hawaiite.
These units lie on a basement of palagonite breccias of tholeiitic affinities. The basic lavas are intruded by plugs ranging in composition from tristanite to phonolite and are overlain by phonolite lavas. These rocks form two chemically and mineralogically distinct suites:
  1. Phonolites which evolved by low pressure crystal fractionation of the younger lava series basanitic magma, and
  2. Tristanite — trachyte — trachyphonolite suite which may have evolved by high pressure crystal fractionation of the older lava series magma.
  相似文献   

16.
Geologic, petrological and geochemical investigations have been carried out in the western part of the “Zillertaler Alpen”. Important results are:
  1. The premetamorphic material of the Greiner series consists of conglomerates, breccias, arcosic-sandstones or greywackes, bituminous shales, volcanic lavas and tuffs.
  2. The southern part of the “Zentralgneis” shows a differentiation trend from alkaline granite to quarzdiorite with predomination of granodiorite.
  3. Chemical relationships of granodiorite to its restitic inclusions allow the supposition of a palingenetic origin of the granitic rocks.
  4. At least two stages of metamorphism can be differentiated.
  5. 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.
  6. Some vertical, northeast striking faults with throws of more than 1 or 2 kilometers produced southward verging drag folds.
  7. Geodynamic aspects, revealed from regional metamorphism and tectonics, are discussed.
  相似文献   

17.
According to their material sources, China’s pegmatities can be divided into two broad types: (1) the crust-source pegmatites derived mainly from the upper continental crust, which can be subdivided into metamorphic differentiated, mixed metasomatic and anatectic magmadifferentiated pegmatites, and (2) the mantle-source pegmatites generated from the mantle, including those related to late differentiates and carbonatites. In space, carbonatites are usually accompanied with alkaii syenite. The criteria of discriminating the two-source pegmatites of China are listed as follows:
  1. Rock-forming minerals (micas and feldspars);
  2. REE distribution patterns;
  3. Zr/Hf ratios in zircons; and
  4. Species of apatite and REE contents.
  相似文献   

18.
The Neoarchean Bundelkhand greenstone sequences at Mauranipur and Babina areas within the Bundelkhand Gneissic Complex preserve a variety of magmatic rocks such as komatiitic basalts, basalts,felsic volcanic rocks and high-Mg andesites belonging to the Baragaon, Raspahari and Koti Formations.The intrusive and extrusive komatiitic basalts are characterized by low SiO_2(39-53 wt.%), high MgO(18-25 wt.%).moderately high Fe_2O_3(7.1-11.6 wt.%), Al_2O_3(4.5-12.0 wt.%), and TiO_2(0.4-1.23 wt.%)with super to subchondritic(Gd/Yb)N ratios indicating garnet control on the melts. The intrusive komatiitic suite of Ti-enriched and Al-depleted type possesses predominant negative Eu and positive Nb, Ti and Y anomalies. The chemical composition of basalts classifies them into three types with varying SiO_2, TiO_2, MgO, Fe_2O_3, Al_2O_3 and CaO. At similar SiO_2 content of type Ⅰ and Ⅲ basalts, the type II basalts show slightly high Al_2O_3 and Fe_2O_3 contents. Significant negative anomalies of Nb, Zr, Hf and Ti, slightly enriched LREE with relatively flat HREE and low ∑REE contents are observed in type Ⅰ and Ⅱ basalts. TypeⅢ basalts show high Zr/Nb ratios(9.8-10.4), TiO_2(1.97-2.04 wt.%), but possess strikingly flat Zr, Hf, Y and Yb and are uncontaminated. Andesites from Agar and Koti have high SiO_2(55-64 wt.%), moderate TiO_2(0.4-0.7 wt.%), slightly low Al_2O_3(7-11.9 wt.%), medium to high MgO(3-8 wt.%) and CaO contents(10-17 wt.%). Anomalously high Cr, Co and Ni contents are observed in the Koti rhyolites. Tholeiitic to calc alkaline affinity of mafic-felsic volcanic rocks and basalt-andesite dacite-rhyolite differentiation indicate a mature arc and thickened crust during the advanced stage of the evolution of Neoarchean Bundelkhand greenstone belt in a convergent tectonic setting where the melts were derived from partial melting of thick basaltic crust metamorphosed to amphibolite-eclogite facies. The trace element systematics suggest the presence of arc-back arc association with varying magnitudes of crust-mantle interaction. La/Sm, La/Ta,Nb/Th, high MgO contents(20 wt.%), CaO/Al_2O_3 and(Gd/Yb)_N 1 along with the positive Nb anomalies of the komatiite basalts reflect a mantle plume source for their origin contaminated by subductionmetasomatized mantle lithosphere. The overall geochemical signatures of the ultramafic-mafic and felsic volcanic rocks endorse the Neoarchean plume-arc accretion tectonics in the Bundelkhand greenstone belt.  相似文献   

19.
The following facts have supported the origin of the Araguainha circular structure in Central Brazil by a meteoritic impact:
  1. the almost circular contour
  2. the impact-morphologic sequence including a central uplift, ring walls and a basin rim of escarpments
  3. outcrops of suevites and mixed breccias
  4. the evidence of shock metamorphism
  5. the presence of shatter cones, and
  6. negative anomalies of the total intensity of the magnetic field at the center of the ring structure.
  相似文献   

20.
Phase relations of pumpellyite, epidote, lawsonite, CaCO3, paragonite, actinolite, crossite and iron oxide are analysed on an Al-Ca-Fe3+ diagram in which all minerals are projected from quartz, albite or Jadeite, chlorite and fluid. Fe2+ and Mg are treated as a single component because variation in Fe2+/Mg has little effect on the stability of phases on the diagram. Comparison of assemblages in the Franciscan, Shuksan, Sanbagawa, New Caledonia, Southern Italian, and Otago metamorphic terranes reveals several reactions, useful for construction of a petrogenetic grid:
  1. lawsonite+crossite + paragonite = epidote+chlorite + albite + quartz + H2O
  2. lawsonite + crossite = pumpellyite + epidote + chlorite + albite+ quartz + H2O
  3. crossite + pumpellyite + quartz = epidote + actinolite + albite + chlorite + H2O
  4. crossite + epidote + quartz = actinolite + hematite + albite + chlorite + H2O
  5. calcite + epidote + chlorite + quartz = pumpellyite + actinolite + H2O + CO2
  6. pumpellyite + chlorite + quartz = epidote + actinolite + H2O
  相似文献   

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