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1.
《Russian Geology and Geophysics》2014,55(8):929-940
Petrological and geochemical studies performed with invoking data on the compositions of clinopyroxenes have clarified the conditions of formation of Vendian-Cambrian basaltic complexes in the Dzhida zone of the Paleoasian Ocean (northern Mongolia and southwestern Transbaikalia). The research was based on a comparative analysis with reference igneous basaltic associations. Of special importance are our microprobe data on trace and rare-earth elements in clinopyroxenes from igneous rocks of different present-day geodynamic settings, namely, N-MORB (Mid-Atlantic Ridge, Central Atlantic), OIB (Bouvet Island, South Atlantic), WPB (within-plate tholeiitic plateau basalts of the Siberian Platform), and boninites of ensimatic arcs (Izu-Bonin island arc, Pacific). The studies have shown that the paleo-oceanic structures in the district of the Urgol guyot formed during geodynamic processes under the impact of mantle plumes on oceanic spreading crust, which resulted in oceanic basaltic plateaus and within-plate oceanic islands. All these structures were later superposed by typical island-arc structure-lithologic associations. Formation of basalt complexes in the Dzhidot guyot district proceeded with a stronger effect of enriched plume melts of within-plate oceanic islands as compared with the Urgol guyot. This is evidenced from petrochemical and geochemical data showing the development of OIB-type magmatic systems on the oceanic basement. Data on clinopyroxenes confirm the participation of mantle plume in this process, which led to the evolution of magmas from typical oceanic basalts (MORB) to plateau basalts and OIB. 相似文献
2.
Ophiolite complexes, formed in a suprasubduction zone environment during Neoproterozoic time, are widely distributed in the
Eastern Desert of Egypt. Their mantle sections provide important information on the origin and tectonic history of ocean basins
these complexes represent. The geochemistry and mineralogy of the mantle section of the Wizer ophiolite complex, represented
by serpentinites after harzburgite containing minor dunite bodies, are presented. Presence of antigorite together with the
incipient alteration of chromite and absence of chlorite suggests that serpentinization occurred in the mantle wedge above
a Neoproterozoic subduction zone. Wizer peridotites have a wide range of spinel compositions. Spinel Cr# [100Cr/(Cr + Al)]
decrease gradually from dunite bodies (Cr# = 81–87) and their host highly depleted harzburgites (Cr# = 67–79) to the less
depleted harzburgites (Cr# = 57–63). Such decreases in mantle refractory character are accompanied by higher Al and Ti contents
in bulk compositions. Estimated parental melt compositions point to an equilibration with melts of boninitic composition for
the dunite bodies (TiO2 = ~<0.07–0.22 wt%; Al2O3 = 9.4–10.6 wt%), boninitic-arc tholeiite for the highly depleted harzburgites (TiO2 = <0.09–0.28 wt%; Al2O3 = 11.2–14.1 wt%) and more MORB-like affinities for the less depleted harzburgites (TiO2 = ~<0.38–0.51 wt%; Al2O3 = 14.5–15.3 wt%). Estimated equilibrium melts are found in the overlying volcanic sequence, which shows a transitional MORB–island
arc geochemical signature with a few boninitic samples. Enrichment of some chromites in TiO2 and identification of sulfides in highly depleted peridotites imply interaction with an impregnating melt. A two-stage partial
melting/melt–rock reaction model is advocated, whereby, melting of a depleted mantle source by reaction with MORB-like melts
is followed by a second stage melting by interaction with melts of IAT–boninitic affinities in a suprasubduction zone environment
to generate the highly depleted harzburgites and dunite bodies. The shift from MORB to island arc/boninitic affinities within
the mantle lithosphere of the Wizer ophiolite sequence suggests generation in a protoarc-forearc environment. This, together
with the systematic latitudinal change in composition of ophiolitic lavas in the Central Eastern Desert (CED) of Egypt from
IAT–boninitic affinities to more MORB-like signature, implies that the CED could represent a disrupted forearc-arc-backarc
system above a southeast-dipping subduction zone. 相似文献
3.
The study of melt inclusions in Cr-spinels from melanocratic troctolites provided the first direct information on the physicochemical
parameters of enriched magmatic systems that produced high-Fe and high-Ti intrusive complexes in the Sierra-Leone region (Central
Atlantic, 6°N). These complexes are made up of predominating hornblende Fe-Ti oxide gabbronorites and gabbrodiorites with
subordinate amount of ultramafics, diorites, quartz diorites, and trondhjemites. The study of melt inclusions and rocks showed
that the majority of gabbroids of the Central Atlantic (Sierra Leone area and 15°20′ Fracture Zone) were derived from N-MORB-type
melts, whereas differentiated Fe-Ti-oxide rocks were crystallized from other melts, which were preserved as inclusions in
the Cr-spinels from the melanocratic troctolites of the Sierra Leone region. The ion-microprobe study of these inclusions
yield direct evidence on the elevated water content (up to 1.24–1.77 wt %) in the parental melts of Fe-Ti oxide rocks. Data
on trace and rare-earth element distribution together with high (La/Sm)N and (Ce/Yb)N ratios in the inclusions indicate the possible influence of deep plume source on the generation of these magmas. Simulation
based on melt inclusion data testifies that high-Fe intrusions of the Sierra Leone area were crystallized from the water-saturated
magmas at relatively low temperatures (1020–1240°C). It was shown that the geochemically enriched Fe-Ti melts were presumably
formed regardless of N-MORB-type magmatism predominant in Central Atlantic, under the influence of new mantle plume that caused
melting of hydrated oceanic lithosphere. 相似文献
4.
The U/Pb dating of ophiolite and arc complexes in the Caledonides of SW Norway has demonstrated that these spatially associated
rocks are also closely related in time. A sequence of tholeiitic island arc volcanics, and an unconformably overlying sequence
of calc-alkaline volcanics have been dated as 494 ± 2 Ma (2σ) and 473 ± 2 Ma respectively. Ophiolitic crust formed both prior
to, and during the first 10 Ma after the tholeiitic island arc volcanism. Boninitic and island arc tholeiitic dyke swarms
intruded the ophiolites soon after they formed and represent a second phase of spreading-related magmatism in the ca 20 Ma
period that separated the tholeiitic and the calc-alkaline island arc volcanism. The magmatism ended with the formation of
alkaline, ocean island basalt (OIB)-like magmas. Quartz dioritic and S-type granitic plutons, dated to 479 ± 5 Ma and 474 +3/−2 Ma
respectively, intruded into the base of the arc crust during and subsequent to the boninitic magmatism, and at the time when
calc-alkaline volcanic centres developed. The quartz dioritic and the granitic rocks contain inherited zircons of Precambrian
age which prove the involvement of a continental source. This together with the geology of the terrain and the geochemistry
of these plutons suggests that the granitic magmas were partly derived from subducted clastic sediments. The Sr and Nd isotope
systematics indicate that the same continental source was a component in the boninitic and the calc-alkaline magmas. While
the calc-alkaline magmas may have gained this continental component at a crustal level by assimilation, both geology and isotope
systematics suggest that the continental component in the boninitic rocks was introduced by source contamination – possibly
by a direct interaction between the mantle source and the S-type granitic magmas. A modified mid ocean ridge basalt-like mantle
source was the principal source during the earliest and the main crust forming stage. This source became replaced by an OIB-like
source during the later stages in the evolution of this ancient arc.
Received: 27 June 1994 / Accepted: 16 September 1996 相似文献
5.
Using various methods of melt inclusion investigation, including electron and ion microprobe techniques, we estimated the
composition, evolution, and formation conditions of melts producing the trachydacites and pantellerites of the Late Paleozoic
bimodal volcanic association of Dzarta-Khuduk, Central Mongolia. Primary crystalline and melt inclusions were detected in
anorthoclase from trachydacites and quartz from pantellerites and pantelleritic tuffs. Among the crystalline inclusions, we
identified hedenbergite, fluorapatite, and pyrrhotite in the trachydacites and F-arfvedsonite, fluorite, ilmenite, and the
rare REE diorthosilicate chevkinite in the pantellerites. Melt inclusions in anorthoclase from the trachydacites are composed
of glass, a gas phase, and daughter minerals (F-arfvedsonite, fluorite, villiaumite, and anorthoclase rim on the inclusion
wall). Melt inclusions in quartz from the pantellerites are composed of glass, a gas phase, and a fine-grained salt aggregate
consisting of Li, Na, and Ca fluorides (griceite, villiaumite, and fluorite). Melt inclusions in quartz crystalloclasts from
the pantelleritic tuffs are composed of homogeneous silicate glasses. The phenocrysts of the trachydacites and pantellerites
crystallized at temperatures of 1060–1000°C. During thermometric experiments with quartz-hosted melt inclusions from the pantellerites,
the formation of immiscible silicate and salt (fluoride) melts was observed at a temperature of 800°C. Homogeneous melt inclusions
in anorthoclase from the trachydacites have both trachydacite and rhyolite compositions (wt %): 68–70 SiO2, 12–13 Al2O3, 0.34–0.74 TiO2, 5–7 FeO, 0.4–0.9 CaO, and 9–12 Na2O + K2O. The agpaitic index ranges from 0.92 to 1.24. The glasses of homogenized melt inclusions in quartz from the pantellerites
and pantelleritic tuffs have rhyolitic compositions. Compared with the homogeneous glasses trapped in anorthoclase of the
trachydacites, quartz-hosted inclusions from the pantellerites show higher SiO2 (72–78 wt %) and lower Al2O3 contents (7.8–10.0 wt %). They also contain 0.14–0.26 wt % TiO2, 2.5–4.9 wt % FeO, 9–11 wt % Na2O + K2O, and 0.9–0.15 wt % CaO and show an agpaitic index of 1.2–2.05. Homogeneous melt inclusions in quartz from the pantelleritic
tuffs contain 69–72 wt % SiO2. The contents of other major components, including TiO2, Al2O3, FeO, and CaO, are close to those in the homogeneous glasses of quartzhosted melt inclusions in the pantellerites. The contents
of Na2O + K2O are 4–10 wt %, and the agpaitic index is 1.0–1.6. The glasses of melt inclusions from each rock group show distinctive volatile
compositions. The H2O content is up to 0.08 wt % in anorthoclase of the trachydacites, 0.4–1.4 wt % in quartz of the pantellerites, and up to
5 wt % in quartz of the pantelleritic tuffs. The content of F in the glasses of melt inclusions in the phenocrysts of the
trachydacites is no higher than 0.67 wt %, and up to 1.4–2.8 wt % in quartz from the pantellerites. The Cl content is up to
0.2 wt % in the glasses of melt inclusions in the minerals of the trachydacites and up to 0.5 wt % in the glasses of quartz-hosted
melt inclusions from the pantellerites. The investigation of trace elements in the homogenized glasses of melt inclusions
in minerals showed that the trachydacites and pantellerites were formed from strongly evolved rare-metal alkaline silicate
melts with high contents of Li, Zr, Rb, Y, Hf, Th, U, and REE. The analysis of the composition of homogeneous melt inclusions
in the minerals of the above rocks allowed us to distinguish magmatic processes resulting in the enrichment of these rocks
in trace and rare earth elements. The most important processes are the crystallization differentiation and immiscible separation
of silicate and fluoride salt melts. It was also shown that all the melts studied evolved in spatially separated magma chambers.
This caused the differences in the character of melt evolution between the trachydacites and pantellerites. During the final
stages of differentiation, when the magmatic system was saturated with respect to ore elements, Na-Ca fluoride melts were
separated and extracted considerable amounts of Li. 相似文献
6.
Alkaline-ultrabasic mantle-derived magmas, their sources, and crystallization features: Data of melt inclusion studies 总被引：2，自引：0，他引：2
To find out the reasons responsible for the diversity of igneous rocks forming the alkaline-ultrabasic carbonatite Krestovskiy massif (the Maimecha–Kotui province, Russia) we have studied melt inclusions in clinopyroxene of trachydolerites, porphyric melanephelinites, and tholeiites. It was established that the homogenization temperatures of inclusions in these rocks are rather close: 1140–1180 °C, 1190–1230 °C, and 1150–1210 °C, respectively. Compositions of melt inclusions in clinopyroxenes from different rocks are significantly different. The chemical composition of clinopyroxene of trachydolerites corresponds to that of trachybasalts and their derivatives. The inclusions are enriched in Sr, Ba, P, and S and their total sum of alkalies (at K ≥ Na) is never less than 5–6 wt.%. Inclusions from the rims of clinopyroxene phenocrysts in porphyric melanephelinites are similar in composition also to inclusions in trachydolerites. But in the cores of clinopyroxene phenocrysts the composition of inclusions corresponds to nephelinite melt. The composition of some melt inclusions in the intermediate and cores zones of clinopyroxene from porphyric melanephelinite has high SiO2 (53–55 wt.%), MgO (8–9 wt.%) and a low (1–2 wt.%) total sum of alkalies (at Na ≥ K) and is depleted in Al2O3 (6–7 wt.%), which is similar to the composition of basaltic komatiites. The composition of inclusions in tholeiites is also basic, highly magnesian, and low-alkaline, Sr and Ba are rare to absent. Compared to the inclusions of basaltic komatiite composition, the inclusions in tholeiites are enriched in Al and depleted in Ca, Ti, and P. The melts trapped in clinopyroxenes from different rocks contain low (0.014–0.018 wt.%) water but they are enriched in F: from 0.37 wt.% in nephelinite melts to 0.1–0.06 wt.% in tholeiite and basaltic komatiite melts. Inclusions in all the rocks under study, host clinopyroxene, and the rocks themselves are significantly enriched in incompatible elements (1–2 orders of magnitude relative to the mantle norm). In tholeiites, the partitioning of these elements is rather uniform, while in trachydolerites and especially in melanephelinites it is contrasting with a drastic depletion in HREE relative to LREE, MREE, and HFSE. A conclusion is made that the Krestovskiy massif was formed by no less than three mantle-derived magmas: melanephelinite, tholeiite and basaltic komatiite. Magmas were generated in different magma sources at different depths with various degrees of enrichment in incompatible elements. These magmas were, most likely, dominated by melanephelinite magma. In intermediate chambers this magma differentiated to form derivative melts of nephelinite, trachydolerite–trachyandesite–trachyte compositions. Komatiite-basalt melts were, most likely, derivatives of primitive meimechite magmas. 相似文献
7.
Melt and fluid inclusions were investigated in six quartz phenocryst samples from the igneous rocks of the extrusive (ignimbrites
and rhyolites) and subvolcanic (granite porphyries) facies of the Lashkerek Depression in the Kurama mining district, Middle
Tien Shan. The method of inclusion homogenization was used, and glasses from more than 40 inclusions were analyzed on electron
and ion microprobes. The chemical characteristics of these inclusions are typical of silicic magmatic melts. The average composition
is the following (wt %): 72.4 SiO2, 0.06 TiO2, 13.3 Al2O3, 0.95 FeO, 0.03 MnO, 0.01 MgO, 0.46 CaO, 3.33 Na2O, 5.16K2O, 0.32 F, and 0.21 Cl. Potassium strongly prevails over sodium in all of the inclusions (K2O/Na2O averages 1.60). The average total of components in melt inclusions from five samples is 95.3 wt %, which indicates a possible
average water content in the melt of no less than 3–4 wt %. Water contents of 2.0 wt % and 6.6 wt % were determined in melt
inclusions from two samples using an ion microprobe. The analyses of ore elements in the melt inclusions revealed high contents
of Sn (up to 970 ppm), Th (19–62 ppm, 47 ppm on average), and U (9–26 ppm, 18 ppm on average), but very low Eu contents (0.01
ppm). Melt inclusions of two different compositions were detected in quartz from a granite porphyry sample: silicate and chloride,
the latter being more abundant. In addition to Na and K chlorides, the salt inclusions usually contain one or several anisotropic
crystals and an opaque phase. The homogenization temperatures of the salt inclusions are rather high, from 680 to 820°C. In
addition to silicate inclusions with homogenization temperatures of 820–850°C, a primary fluid inclusion of aqueous solution
with a concentration of 3.7 wt % NaCl eq. and a very high density of 0.93 g/cm3 was found in quartz from the ignimbrite. High fluid pressure values of 6.5–8.3 kbar were calculated for the temperature of
quartz formation. These estimates are comparable with values obtained by us previously for other regions of the world: 2.6–4.3
kbar for Italy, 3.7 kbar for Mongolia, 3.3–8.7 kbar for central Slovakia, and 3.3–9.6 kbar for eastern Slovakia. Unusual melt
inclusions were investigated in quartz from another ignimbrite sample. In addition to a gas phase and transparent glass, they
contain spherical Feoxide globules (81.2 wt % FeO) with high content of SiO2 (9.9 wt %). The globules were dissolved in the silicate melt within a narrow temperature range of 1050–1100°C, and the complete
homogenization of the inclusions was observed at temperatures of 1140°C or higher. The combined analysis of the results of
the investigation of these inclusions allowed us to conclude that immiscible liquids were formed in the high-temperature silicic
magma with the separation of iron oxide-dominated droplets. 相似文献
8.
E.S. Farahat 《Lithos》2010,120(3-4):293-308
Ophiolites are widely distributed in the Central Eastern Desert (CED) of Egypt, occurring as clusters in the northern (NCEDO) and southern (SCEDO) segments. Mineralogical and geochemical data on the volcanic sections of Wizer (WZO) and Abu Meriewa (AMO) ophiolites as representatives of the NCEDO and SCEDO, respectively, are presented.The WZO volcanic sequence comprises massive metavolcanics of MORB-like compositions intruded by minor boninitic dykes and thrust over island-arc metavolcanic blocks in the mélange matrix. Such transitional MORB-IAT-boninitic magmatic affinities for the WZO metavolcanics suggest that they most likely formed in a protoarc–forearc setting. Chemical compositions of primary clinopyroxene and Cr-spinel relicts from the WZO volcanic section further confirm this interpretation. The compositional variability in the WZO volcanic sequence is comparable with the associated mantle rocks that vary from slightly depleted harzburgites to highly depleted harzburgites containing small dunite bodies, which are residues after MORB, IAT and boninite melt formation, respectively. Source characteristics of the different lava groups from the WZO indicate generation via partial melting of a MORB source which was progressively depleted by melt extraction and variably enriched by subduction zone fluids. MORB-like magma may have been derived from ~ 20% partial melting of an undepleted lherzolite source, leaving slightly depleted harzburgite as a residuum. The generation of island-arc magma can be accounted for by partial melting (~ 15%) of the latter harzburgitic mantle source, whereas boninites may have been derived from partial melting (~ 20%) of a more refractory mantle source previously depleted by melt extraction of MORB and IAT melts, leaving ultra-refractory dunite bodies as residuum.The AMO volcanic unit occurs as highly deformed pillowed metavolcanic rocks in a mélange matrix. They can be categorized geochemically into LREE-depleted (La/YbCN = 0.41–0.50) and LREE-enriched (La/YbCN = 4.7–4.9) lava types that show an island arc to MORB geochemical signature, respectively, signifying a back-arc basin setting. This is consistent, as well, with their mantle section. Source characteristics indicate depleted to slightly enriched mantle sources with overall slight subduction zone geochemical affinities as compared to the WZO.Generally, CED ophiolites show supra-subduction zone geochemical signature with prevalent island arc tholeiitic and minor boninitic affinities in the NCEDO and MORB/island-arc association in the SCEDO. Such differences in geochemical characteristics of the NCEDO and SCEDO, along with the abundance of mature island arc metavolcanics which are close in age (~ 750 Ma) to the ophiolitic rocks, general enrichment in HFSE of ophiolites from north to south, and lack of a crustal break and major shear zones, is best explained by a geotectonic model whereby the CED represents an arc–back-arc system above a southeast-dipping subduction zone. 相似文献
9.
Dmitri A. Ionov Antoine Bénard Pavel Y. Plechov 《Contributions to Mineralogy and Petrology》2011,162(6):1159-1174
Glass-bearing inclusions hosted by Cr-spinel in harzburgite xenoliths from Avacha are grouped based on homogenization temperatures
and daughter minerals into high-T (1,200°C; opx + cpx), intermediate (900–1,100°C; cpx ± amph), and low-T (900°C; amph) and
are commonly accompanied by larger “melt pockets”. Unlike previous work on unheated inclusions and interstitial glass in xenoliths
from Kamchatka, the homogenized glass compositions in this study are not affected by low-pressure melt fractionation during
transport and cooling or by interaction with host magma. Primary melt compositions constrained for each inclusion type differ
in major and trace element abundances and were formed by different events, but all are silica saturated, Ca-rich, and K-poor,
with enrichments in LREE, Sr, Rb, and Ba and negative Nb anomalies. These melts are inferred to have been formed with participation
of fluids produced by dehydration of slab materials. The high-T inclusions trapped liquids produced by ancient high-degree,
fluid-induced melting in the mantle wedge. The low-T inclusions are related to percolation of low-T melts or hydrous fluids
in arc mantle lithosphere. Melt pockets arise from localized heating and fluid-assisted melting induced by rising magmas shortly
before the entrapment of the xenoliths. The “high-T” melt inclusions in Avacha xenoliths are unique in preserving evidence
of ancient, high-T melting events in arc mantle, whereas the published data appear to characterize pre-eruption enrichment
events. 相似文献
10.
The paper presents data on naturally quenched melt inclusions in olivine (Fo 69–84) from Late Pleistocene pyroclastic rocks
of Zhupanovsky volcano in the frontal zone of the Eastern Volcanic Belt of Kamchatka. The composition of the melt inclusions
provides insight into the latest crystallization stages (∼70% crystallization) of the parental melt (∼46.4 wt % SiO2, ∼2.5 wt % H2O, ∼0.3 wt % S), which proceeded at decompression and started at a depth of approximately 10 km from the surface. The crystallization
temperature was estimated at 1100 ± 20°C at an oxygen fugacity of ΔFMQ = 0.9–1.7. The melts evolved due to the simultaneous
crystallization of olivine, plagioclase, pyroxene, chromite, and magnetite (Ol: Pl: Cpx: (Crt-Mt) ∼ 13: 54: 24: 4) along the tholeiite evolutionary trend and became progressively enriched in FeO, SiO2, Na2O, and K2O and depleted in MgO, CaO, and Al2O3. Melt crystallization was associated with the segregation of fluid rich in S-bearing compounds and, to a lesser extent, in
H2O and Cl. The primary melt of Zhupanovsky volcano (whose composition was estimated from data on the most primitive melt inclusions)
had a composition of low-Si (∼45 wt % SiO2) picrobasalt (∼14 wt % MgO), as is typical of parental melts in Kamchatka and other island arcs, and was different from MORB.
This primary melt could be derived by ∼8% melting of mantle peridotite of composition close to the MORB source, under pressures
of 1.5 ± 0.2 GPa and temperatures 20–30°C lower than the solidus temperature of “dry” peridotite (1230–1240°C). Melting was
induced by the interaction of the hot peridotite with a hydrous component that was brought to the mantle from the subducted
slab and was also responsible for the enrichment of the Zhupanovsky magmas in LREE, LILE, B, Cl, Th, U, and Pb. The hydrous
component in the magma source of Zhupanovsky volcano was produced by the partial slab melting under water-saturated conditions
at temperatures of 760–810°C and pressures of ∼3.5 GPa. As the depth of the subducted slab beneath Kamchatkan volcanoes varies
from 100 to 125 km, the composition of the hydrous component drastically changes from relatively low-temperature H2O-rich fluid to higher temperature H2O-bearing melt. The geothermal gradient at the surface of the slab within the depth range of 100–125 km beneath Kamchatka
was estimated at 4°C/km. 相似文献
11.
The data obtained on melt and fluid inclusions in minerals of granites, metasomatic rocks, and veins with tin ore mineralization
at the Industrial’noe deposit in the southern part of the Omsukchan trough, northeastern Russia, indicate that the melt from
which the quartz of the granites crystallized contained globules of salt melts. Silicate melt inclusions were used to determine
the principal parameters of the magmatic melts that formed the granites, which had temperatures at 760–1020°C, were under
pressures of 0.3–3.6 kbar, and had densities of 2.11–2.60 g/cm3 and water concentrations of 1.7–7.0 wt %. The results obtained on the fluid inclusions testify that the parameters of the
mineral-forming fluids broadly varied and corresponded to temperatures at 920–275°C, pressures 0.1–3.1 kbar, densities of
0.70–1.90 g/cm3, and salinities of 4.0–75.0 wt % equiv. NaCl. Electron microprobe analyses of the glasses of twelve homogenized inclusions
show concentrations of major components typical of an acid magmatic melt (wt %, average): 73.2% SiO2, 15.3% Al2O3, 1.3% FeO, 0.6% CaO, 3.1% Na2O, and 4.5% K2O at elevated concentrations of Cl (up to 0.51 wt %, average 0.31 wt %). The concentrations and distribution of some elements
(Cl, K, Ca, Mn, Fe, Cu, Zn, Pb, As, Br, Rb, Sr, and Sn) in polyphase salt globules in quartz from both the granites and a
mineralized miarolitic cavity in granite were assayed by micro-PIXE (proton-induced X-ray emission). Analyses of eight salt
globules in quartz from the granites point to high concentrations (average, wt %) of Cl (27.5), Fe (9.7), Cu (7.2), Mn (1.1),
Zn (0.66), Pb (0.37) and (average, ppm) As (2020), Rb (1850), Sr (1090), and Br (990). The salt globules in the miarolitic
quartz are rich in (average of 29 globules, wt %) Cl (25.0), Fe (5.4), Mn (1.0), Zn (0.50), Pb (0.24) and (ppm) Rb (810),
Sn (540), and Br (470). The synthesis of all data obtained on melt and fluid inclusions in minerals from the Industrial’noe
deposit suggest that the genesis of the tin ore mineralization was related to the crystallization of acid magmatic melts.
Original Russian Text@ V.B. Naumov, V.S. Kamenetsky, 2006, published in Geokhimiya, 2006, No. 12, pp. 1279–1289. 相似文献
12.
V. N. Sharapov A. A. Tomilenko S. Z. Smirnov V. V. Sharygin S. V. Kovyazin 《Petrology》2013,21(5):427-453
In this paper, we discuss the formation conditions of rhyolites and results of their interaction with later portions of basic magmas on the basis of the investigation of melt and fluid inclusions in minerals from a rhyolite xenolith and host neovolcanic basalts of the Cleft segment of the Juan de Fuca Ridge. In terms of bulk chemistry and the compositions of melt inclusions in pyroxene and olivine phenocrysts, the basic rocks of the southern part of this segment are typical MOR basalts. Their olivine, clinopyroxene, and plagioclase crystallized at temperatures of 1160–1280°C and a pressure range between 20 and 100 MPa. The xenolith is a leucocratic rock with negligible amounts of mafic minerals, which clearly distinguishes it from the known occurrences of silicic rocks in the rift valleys of MOR. The rhyolite melt crystallized at temperatures of 900–880°C. The final stages of rhyolite melt crystallization at temperatures of 780–800°C were accompanied by the release of a saline aqueous fluid with high chloride contents. Based on the geochemical characteristics of melt inclusions and melting products, it can be suggested that the magmatic melt was produced by melting of metamorphosed oceanic crust within the Cleft segment under the influence sof saline aqueous fluid trapped in the pores and interstices of the rock. The rock represented by the xenolith is a late differentiation product of such melts. The ultimate products of silicic melt fractionation show high volatile contents: H2O > 3.0 wt %, Cl ～ 2.0 wt %, and F ～ 0.1 wt %. The interaction of the xenolith with the host basaltic melt occurred at temperatures equal or slightly higher than those of ferrobasalt melts (1190–1180°C). During ascent the xenolith occurred for a few tens of hours in high-temperature basic magma, and diffusion exchange between the basaltic and silicic melts was very minor. 相似文献
13.
14.
D. M. Ruscitto P. J. Wallace A. J. R. Kent 《Contributions to Mineralogy and Petrology》2011,162(1):109-132
Primitive chemical characteristics of high-Mg andesites (HMA) suggest equilibration with mantle wedge peridotite, and they
may form through either shallow, wet partial melting of the mantle or re-equilibration of slab melts migrating through the
wedge. We have re-examined a well-studied example of HMA from near Mt. Shasta, CA, because petrographic evidence for magma
mixing has stimulated a recent debate over whether HMA magmas have a mantle origin. We examined naturally quenched, glassy,
olivine-hosted (Fo87–94) melt inclusions from this locality and analyzed the samples by FTIR, LA-ICPMS, and electron probe. Compositions (uncorrected
for post-entrapment modification) are highly variable and can be divided into high-CaO (>10 wt%) melts only found in Fo > 91
olivines and low-CaO (<10 wt%) melts in Fo 87–94 olivine hosts. There is evidence for extensive post-entrapment modification
in many inclusions. High-CaO inclusions experienced 1.4–3.5 wt% FeOT loss through diffusive re-equilibration with the host olivine and 13–28 wt% post-entrapment olivine crystallization. Low-CaO
inclusions experienced 1–16 wt% olivine crystallization with <2 wt% FeOT loss experienced by inclusions in Fo > 90 olivines. Restored low-CaO melt inclusions are HMAs (57–61 wt% SiO2; 4.9–10.9 wt% MgO), whereas high-CaO inclusions are primitive basaltic andesites (PBA) (51–56 wt% SiO2; 9.8–15.1 wt% MgO). HMA and PBA inclusions have distinct trace element characteristics. Importantly, both types of inclusions
are volatile-rich, with maximum values in HMA and PBA melt inclusions of 3.5 and 5.6 wt% H2O, 830 and 2,900 ppm S, 1,590 and 2,580 ppm Cl, and 500 and 820 ppm CO2, respectively. PBA melts are comparable to experimental hydrous melts in equilibrium with harzburgite. Two-component mixing
between PBA and dacitic magma (59:41) is able to produce a primitive HMA composition, but the predicted mixture shows some
small but significant major and trace element discrepancies from published whole-rock analyses from the Shasta locality. An
alternative model that involves incorporation of xenocrysts (high-Mg olivine from PBA and pyroxenes from dacite) into a primary
(mantle-derived) HMA magma can explain the phenocryst and melt inclusion compositions but is difficult to evaluate quantitatively
because of the complex crystal populations. Our results suggest that a spectrum of mantle-derived melts, including both PBA
and HMA, may be produced beneath the Shasta region. Compositional similarities between Shasta parental melts and boninites
imply similar magma generation processes related to the presence of refractory harzburgite in the shallow mantle. 相似文献
15.
The fidelity of melt inclusions as records of melt composition 总被引：5，自引：5，他引：0
Don R. Baker 《Contributions to Mineralogy and Petrology》2008,156(3):377-395
A series of experiments created melt inclusions in plagioclase and pyroxene crystals grown from a basaltic melt at 1,150°C,
1.0 GPa to investigate diffusive fractionation during melt inclusion formation; additionally, P diffusion in a basaltic melt
was measured at 1.0 GPa. Melt inclusions and melts within a few 100 microns of plagioclase–melt interfaces were analyzed for
comparison with melt compositions far from the crystals. Melt inclusions and melt compositions in the boundary layer close
to the crystal–melt interface were similar, but both differ significantly in incompatible element concentrations from melt
found greater than approximately 200 microns away from the crystals. The compositional profiles of S, Cl, P, Fe, and Al in
the boundary layers were successfully reproduced by a two-step model of rapid crystal growth followed by diffusive relaxation
toward equilibrium after termination of crystal growth. Applying this model to investigate possible incompatible element enrichment
in natural melt inclusions demonstrated that at growth rates high enough to create the conditions for melt inclusion formation,
∼10−9–10−8 m s−1, the concentration of water in the boundary layer near the crystal was similar to that of the bulk melt because of its high
diffusion coefficient, but sulfur, with a diffusivity similar to major elements and CO2, was somewhat enriched in the boundary layer melt, and phosphorus, with its low diffusion coefficient similar to other high-field
strength elements and rare earth elements, was significantly enriched. Thus, the concentrations of sulfur and phosphorus in
melt inclusions may over-estimate their values in the bulk melt, and other elements with similar diffusion coefficients may
also be enriched in melt inclusions relative to the bulk melt.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
16.
The investigation of melt inclusions in the minerals of volcanic rocks from the massive sulfide deposits of Siberia and the Urals revealed some specific features in the development of their magmatic ore systems. It was shown that the petrochemical and rare earth element compositions of melt inclusions reflect the geodynamic conditions of their formation: island arc conditions for the massive sulfide deposits of Rudny Altai, eastern Tuva, and the Salair Range and a back arc basin environment for the Yaman-Kasy deposit. The silicic melts of inclusions from the volcanic rocks of massive sulfide deposits show some specific features with respect to the contents of volatile components. In all of the ore deposits studied, fluorine content was always low (0.03–0.08 wt %), whereas chlorine content (0.13–0.28 wt %) was higher than the average value for silicic melts (0.17 wt %). There is a strong differentiation of water content in melt inclusions, both between deposits and between various volcanics from a single deposit. Ore-bearing melts show the highest water contents of 3.34–4.07 wt %. High Cu contents in the silicic melts of the Yubileinoe and Kyzyl-Tashtyg deposits (up to 7118 and 3228 ppm, respectively) may indicate the affinity of some ore components to particular silicic magmas. This is supported by the elevated contents of Cu in the porphyry Cu deposits of Romania (Valea Morii), Mongolia (Bayan Ula), and Bolivia. On the other hand, the silicic melts of inclusions from the molybdenum-uranium deposit of the Strel’tsovka ore field show high contents of another group of ore components (U and F). 相似文献
17.
Bali E.; Zajacz Z.; Kovacs I.; Szabo CS.; Halter W.; Vaselli O.; Torok K.; Bodnar R. J. 《Journal of Petrology》2008,49(3):421-439
An unusual quartz-bearing orthopyroxene-rich websterite xenolithhas been found in an alkali basaltic tuff at Szigliget, Bakony–BalatonHighland Volcanic Field (BBHVF), western Hungary. Ortho- andclinopyroxenes are enriched in light rare earth elements (LREE),middle REE and Ni, and depleted in Nb, Ta, Sr and Ti comparedwith ortho- and clinopyroxenes occurring in either peridotiteor lower crustal granulite xenoliths from the BBHVF. Both ortho-and clinopyroxenes in the xenolith contain primary and secondarysilicate melt inclusions, and needle-shaped or rounded quartzinclusions. The melt inclusions are rich in SiO2 and alkalisand poor in MgO, FeO and CaO. They are strongly enriched inLREE and large ion lithophile elements, and display negativeNb, Ta and Sr anomalies, and slightly positive Pb anomalies.The xenolith is interpreted to represent a fragment of an orthopyroxene-richbody that crystallized in the upper mantle from a hybrid meltthat formed by interaction of mantle peridotite with a quartz-saturatedsilicate melt that was released from a subducted oceanic slab.Although the exact composition of the slab melt cannot be determined,model calculations on major and trace elements suggest involvementof a metasedimentary component. KEY WORDS: quartz; mantle; silicate melt inclusion; SiO2-rich melt; subduction; Carpathian-Pannonian Region 相似文献
18.
GARRIDO CARLOS J.; BODINIER JEAN-LOUIS; BURG JEAN-PIERRE; ZEILINGER GEROLD; HUSSAIN S. SHAHID; DAWOOD HAMID; CHAUDHRY M. NAWAZ; GERVILLA FERNANDO 《Journal of Petrology》2006,47(10):1873-1914
We report the results of a geochemical study of the Jijal andSarangar complexes, which constitute the lower crust of theMesozoic Kohistan paleo-island arc (Northern Pakistan). TheJijal complex is composed of basal peridotites topped by a gabbroicsection made up of mafic garnet granulite with minor lensesof garnet hornblendite and granite, grading up-section to hornblendegabbronorite. The Sarangar complex is composed of metagabbro.The Sarangar gabbro and Jijal hornblende gabbronorite have melt-like,light rare earth element (LREE)-enriched REE patterns similarto those of island arc basalts. Together with the Jijal garnetgranulite, they define negative covariations of LaN, YbN and(La/Sm)N with Eu* [Eu* = 2 x EuN/(SmN + GdN), where N indicateschondrite normalized], and positive covariations of (Yb/Gd)Nwith Eu*. REE modeling indicates that these covariations cannotbe accounted for by high-pressure crystal fractionation of hydrousprimitive or derivative andesites. They are consistent withformation of the garnet granulites as plagioclase–garnetassemblages with variable trapped melt fractions via eitherhigh-pressure crystallization of primitive island arc basaltsor dehydration-melting of hornblende gabbronorite, providedthat the amount of segregated or restitic garnet was low (<5wt %). Field, petrographic, geochemical and experimental evidenceis more consistent with formation of the Jijal garnet granuliteby dehydration-melting of Jijal hornblende gabbronorite. Similarly,the Jijal garnet-bearing hornblendite lenses were probably generatedby coeval dehydration-melting of hornblendites. Melting modelsand geochronological data point to intrusive leucogranites inthe overlying metaplutonic complex as the melts generated bydehydration-melting of the plutonic protoliths of the Jijalgarnet-bearing restites. Consistent with the metamorphic evolutionof the Kohistan lower arc crust, dehydration-melting occurredat the mature stage of this island arc when shallower hornblende-bearingplutonic rocks were buried to depths exceeding 25–30 kmand heated to temperatures above c. 900°C. Available experimentaldata on dehydration-melting of amphibolitic sources imply thatthickening of oceanic arcs to depths >30 km (equivalent toc. 1·0 GPa), together with the hot geotherms now postulatedfor lower island arc crust, should cause dehydration-meltingof amphibole-bearing plutonic rocks generating dense garnetgranulitic roots in island arcs. Dehydration-melting of hornblende-bearingplutonic rocks may, hence, be a common intracrustal chemicaland physical differentiation process in island arcs and a naturalconsequence of their maturation, leading to the addition ofgranitic partial melts to the middle–upper arc crust andformation of dense, unstable garnet granulite roots in the lowerarc crust. Addition of LREE-enriched granitic melts producedby this process to the middle–upper island arc crust maydrive its basaltic composition toward that of andesite, affordinga plausible solution to the ‘arc paradox’ of formationof andesitic continental-like crust in island arc settings. KEY WORDS: island arc crust; Kohistan complex; Jijal complex; amphibole dehydration-melting; garnet granulite; continental crustal growth 相似文献
19.
V. P. Kovach V. V. Yarmolyuk V. I. Kovalenko A. M. Kozlovskyi A. B. Kotov L. B. Terent’eva 《Petrology》2011,19(4):399-425
Part II of this paper reports geochemical and Nd isotope characteristics of the volcanogenic and siliceous-terrigenous complexes
of the Lake zone of the Central Asian Caledonides and associating granitoids of various ages. Geological, geochronological,
geochemical, and isotopic data were synthesized with application to the problems of the sources and main mechanisms of continental
crust formation and evolution for the Caledonides of the Central Asian orogenic belt. It was found that the juvenile sialic
crust of the Lake zone was formed during the Vendian-Cambrian (approximately 570–490 Ma) in an environment of intraoceanic
island arcs and oceanic islands from depleted mantle sources with the entrainment of sedimentary crustal materials into subduction
zones and owing to the accretion processes of the amalgamation of paleoceanic and island arc complexes and Precambrian microcontinents,
which terminated by ∼490 Ma. The source of primary melts for the low-Ti basalts, andesites, and dacites of the Lake zone ophiolites
and island arc complexes was mainly the depleted mantle wedge above a subduction zone. In addition, an enriched plume source
contributed to the genesis of the high-Ti basalts and gabbroids of oceanic plateaus. The source of terrigenous rocks associating
with the volcanics was composed of materials similar in composition to the country rocks at a minor and varying role of ancient
crustal materials introduced into the ocean basin owing to the erosion of Precambrian microcontinents. The sedimentary rocks
of the accretionary prism were derived by the erosion of mainly juvenile island arc sources with a minor contribution of rocks
of the mature continental crust. The island arc and accretion stages of the development of the Lake zone (∼540–590 Ma) were
accompanied by the development of high- and low-alumina sodic granitoids through the melting at various depths of depleted
mantle reservoirs (metabasites of a subducted oceanic slab and a mantle wedge) and at the base of the island arc at the subordinate
role of ancient crustal rocks. The melts of the postaccretion granitoids of the Central Asian Caledonides were derived mainly
from the rocks of the juvenile Caledonian crust at an increasing input of an ancient crustal component owing to the tectonic
mixing of the rocks of ophiolitic and island arc complexes and microcontinents. The obtained results indicate that the Vendian-Early
Paleozoic stage of the evolution of the Central Asian orogenic belt was characterized by the extensive growth of juvenile
continental crust and allow us to distinguish a corresponding stage of juvenile crust formation. 相似文献
20.
S. Maaløe 《Mineralogy and Petrology》2005,85(3-4):163-204
Summary The investigated mantle section of the Leka ophiolite complex extends 1.4 km from and 1.1 km along the exposed Moho. The foliated
peridotite contains numerous tabular and elongated dunite bodies, orthopyroxenite dikes, websterite veins, and dikes. The
foliation of the peridotite is inclined by about 45° to the Moho. The dunite bodies and the dikes cut the foliation at low
angles. The dunite bodies vary in width from 0.1 to 50 m and in length from 10 m to more than 1 km. Wider dunite bodies are
commonly surrounded by 0 to 1.0 m wide margins of dunitized peridotite. Websterite veins may be present outside these margins.
Apart from sporadic chromite layers the dunite is very homogenous. The dunite bodies are considered to have formed by deposition
of olivine along the walls of dikes originally containing tholeiitic melt. The tholeiitic melt at first heated the peridotitic
sidewalls so that they became partially molten and dunitized. The ascending magma then eroded the sidewalls and removed olivine
as xenocrysts. When the ascent rate decreased, the temperature of the sidewalls decreased, so that olivine (Fo89–92) began to crystallize along the dike walls. There is also evidence for percolative melt migration along foliation planes,
however, the largest proportion of the melts intruded along dikes.
The websterite dikes are mostly 1 to 4 cm wide and 3 to 20 m long and dispersed with mutual distances of 20–50 m. The websterite
veins and dikes probably originated from melts that were generated along the heated sidewalls of the dunite bodies. The 0.02
to 10 m wide orthopyroxenite dikes have exceptionally high MgO contents for their SiO2 contents; about 36 wt.% MgO and 50 wt.% SiO2. They may have formed as segregates from a SiO2-rich magma, although the parent magma does not appear to have been boninitic. The parent magma may instead have formed by
second stage partial melting of depleted lherzolite. 相似文献