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1.
Yueqing Yang Yunxiang Ni Yongquan Guo Nianming Qiu Chenghu Chen Chaofa Cai Yaping Zhang Jiabin Liu Yuexian Chen Yaping Zhang 《中国地球化学学报》1988,7(2):120-135
The Xikeng pegmatite field lies on the eastern margin of the south China fold system in Fujian Province, and it is located
at the junction of three major tectonic units.
The distribution of pegmatites is obviously controlled by the fold system. There exists apparent injection relationship between
the pegmatites and the surrounding Sinian schist and granulitite. The granitoids extensively distributed in the field belong
either to the Variscan or to the Yenshanian cycle, and it is evident that the pegmatites are genetically related to Variscan
migmatitic granites.
The pegmatites can be grouped into four types: muscovite-orthoclase-albite pegmatite (I), muscovite albite-orthoclase pegmatite
(II), muscovite-orthoclase-albite pegmatite (III), and muscovite-albite-spodumene pegmatite (IV). Owing to strong metasomatism
and multi-stage emplacement of pegmatitic meltsolution, the sequence of interior assemblage zones in the pegmatites does not
always represent the sequence of original crystallization.
The mineral composition of the pegmatites is extremely complicated. 81 kinds of minerals have so far been found. From type
I to type IV, the mineral assemblage tend to get increasingly complex, together with the synchronous intensification of rare-metal
and Sn mineralizations. Most of the type-IV pegmatites are of economic value.
The features of fluid inclusions in the minerals are significantly different not only in different types of pegmatite, but
also in different parts of a single pegmatite vein. Theδ
18O values of migmatitic granite and pegmatites are comparatively low (9.3–10.4‰), and those of rock-forming fluids are higher
than 9.5‰.
Isotopic ages of the pegmatites range from 235 to 328 Ma with initial87Sr/86Sr ratios being 0.715–0.746.
According to the temporal and spatial relationships between the pegmatites and the migmatitic granite, combined with the features
of the pegmatites themselves, it can be concluded that the Xikeng pegmatites are the product of differentiation closely related
to the migmatitic granite. 相似文献
2.
Mineral chemistry of submarine lavas from Hilo Ridge, Hawaii: implications for magmatic processes within Hawaiian rift zones 总被引:10,自引:0,他引:10
Huai-Jen Yang Frederick A. Frey David A. Clague Michael O. Garcia 《Contributions to Mineralogy and Petrology》1999,135(4):355-372
The crustal history of volcanic rocks can be inferred from the mineralogy and compositions of their phenocrysts which record
episodes of magma mixing as well as the pressures and temperatures when magmas cooled. Submarine lavas erupted on the Hilo
Ridge, a rift zone directly east of Mauna Kea volcano, contain olivine, plagioclase, augite ±orthopyroxene phenocrysts. The
compositions of these phenocryst phases provide constraints on the magmatic processes beneath Hawaiian rift zones. In these
samples, olivine phenocrysts are normally zoned with homogeneous cores ranging from ∼ Fo81 to Fo91. In contrast, plagioclase, augite and orthopyroxene phenocrysts display more than one episode of reverse zoning. Within each
sample, plagioclase, augite and orthopyroxene phenocrysts have similar zoning profiles. However, there are significant differences
between samples. In three samples these phases exhibit large compositional contrasts, e.g., Mg# [100 × Mg/(Mg+Fe+2)] of augite varies from 71 in cores to 82 in rims. Some submarine lavas from the Puna Ridge (Kilauea volcano) contain phenocrysts
with similar reverse zonation.
The compositional variations of these phenocrysts can be explained by mixing of a multiphase (plagioclase, augite and orthopyroxene)
saturated, evolved magma with more mafic magma saturated only with olivine. The differences in the compositional ranges of
plagioclase, augite and orthopyroxene crystals between samples indicate that these samples were derived from isolated magma
chambers which had undergone distinct fractionation and mixing histories. The samples containing plagioclase and pyroxene
with small compositional variations reflect magmas that were buffered near the olivine + melt ⇒Low-Ca pyroxene + augite +
plagioclase reaction point by frequent intrusions of mafic olivine-bearing magmas. Samples containing plagioclase and pyroxene
phenocrysts with large compositional ranges reflect magmas that evolved beyond this reaction point when there was no replenishment
with olivine-saturated magma. Two of these samples contain augite cores with Mg# of ∼71, corresponding to Mg# of 36–40 in
equilibrium melts, and augite in another sample has Mg# of 63–65 which is in equilibrium with a very evolved melt with a Mg#
of ∼30. Such highly evolved magmas also exist beneath the Puna Ridge of Kilauea volcano. They are rarely erupted during the
shield building stage, but may commonly form in ephemeral magma pockets in the rift zones.
The compositions of clinopyroxene phenocryst rims and associated glass rinds indicate that most of the samples were last equilibrated
at 2–3 kbar and 1130–1160 °C. However, in one sample, augite and glass rind compositions reflect crystallization at higher
pressures (4–5 kbar). This sample provides evidence for magma mixing at relatively high pressures and perhaps transport of
magma from the summit conduits to the rift zone along the oceanic crust-mantle boundary.
Received: 8 July 1998 / Accepted: 2 January 1999 相似文献
3.
Micas of the muscovite-lepidolite series from the fregeneda pegmatites (Salamanca,Spain) 总被引:1,自引:0,他引:1
Summary In the Fregeneda area different types of pegmatites can be recognized by their mineralogy, morphology, internal structure and field relationships. The most common type corresponds to a simple pegmatite with homogeneous internal structure, but zoned Li-bearing pegmatites also are relatively widespread. Cassiterite-bearing pegmatites are subordinate. The pegmatites are spatially associated to the Lumbrales granite. This is a parautochthonous, fine- to medium-grained, two-mica granite, one of the syntectonic massifs which were deformed during the third phase of Hercynian deformation. Representative micas selected from the different groups of pegmatites were studied to determine wether the pegmatites can be related by a common fractionation path, and how different pegmatite types are related to the spatially associated Lumbrales granite. Compositional variations in the micas depend on the pegmatite type. Muscovite coexisting with Li-micas in the Li-bearing pegmatites is one of the richest in Al2O3 (35.4–37.7 wt%) and the poorest in FeO (0.2–1.5 wt%) and MgO (0–0.3 wt%), whereas muscovite of the simple discordant pegmatites shows the highest FeO (2.2–3.3 wt%) and that from the Lumbrales granite is the richest in MgO (0.5–0.7 wt%) and TiO2 (0.6–1.1 wt%). On the other hand, Sn (70–1168 ppm), Li (< 5–22253 ppm), F (880–21470 ppm), Cs (< 5–1696 ppm), Rb (800–9181 ppm) and other trace elements seem to increase with distance from the Lumbrales granite, and K/Rb decreases. According to this ratio, the exterior Li-bearing pegmatites are the more evolved, whereas the interior pegmatites are less evolved, and are richer in Cs, Li and Zn than other pegmatite types.
With 4 Figures 相似文献
Glimmerminerale der Muscovit-Lepidolith-Serie aus den Pegmatiten von Fregeneda, Salamanca, Spanien
Zusammenfassung Im Gebiet von Fregeneda sind auf Grund ihrer Mineralogie, Morphologie, Internstruktur und Geländebeziehungen verschiedene Pegmatittypen zu unterscheiden. Am häufigsten sind einfache homogen aufgebaute Pegmatite. Zonar gebaute Li-Pegmatite sind ebenfalls weit verbreitet, Zinnstein-führende Pegmatite treten hingegen zurück, Die Pegmatite sind räumlich mit dem Lumbrales Granit, einem paraautochtonen, fein- bis mittelkörnigen Zwei-Glimmergranit, assoziiert, Dieser gehört einem der syntektonischen Massive, die während der dritten Phase der hercynischen Deformation deformiert wurden, an. Repräsentative, aus den verschiedenen Pegmatittypen separierte Glimmerminerale wurden untersucht, um zu klären, inwieweit die Pegmatite über einen direkten Fraktionierungspfad zu verbinden sind und in welcher Beziehung sie zu dem Lumbrales Granit stehen. Die Variation der Zusammensetzung der Glimmer hängt vom Pegmatittyp ab. Muscovite, die mit Li-Glimmern koexistieren, sind die relativ Al2O3-reichsten (32–37.7 Gew.%) und Fe- (0.2–1.5 Gew.%.) und Mg-ärmsten (0–0.3 Gew.%). Jene aus dem Lumbrales Granit sind die reich an MgO (0.5–0.7) und TiO2 (0.6–1.1 Gew.%). Die Gehalte von Sn (70–1168 ppm), Li (< 5–22253 ppm). F (880-21470 ppm), Cs (< 5–1696 ppm), Rb (800–9181 ppm) und anderer Spurenelemente nehmen mit der Entfernung vom Lumbrales Granit zu, während K/Rb abnimmt. Auf Grund dieses Verhältnisses sind die externen Li-führenden Pegmatite höher, die internen Pegmatite hingegen geringfügiger entwickelt. Erstere sind daher auch reicher an Cs, Li und Zn.
With 4 Figures 相似文献
4.
Lukáš Ackerman Jiří Zachariáš Marta Pudilová 《International Journal of Earth Sciences》2007,96(4):623-638
Fluid inclusions, mineral thermometry and stable isotope data from two types of mineralogically and texturally contrasting
pegmatites, barren ones and lithium ones, from the Moldanubian Zone of the Bohemian Massif were studied in order to constrain
P–T conditions of their emplacement, subsolidus hydrothermal evolution and to estimate composition of the early exsolved fluid
and that of the parental melt. Despite the fact that the lithium pegmatites are abundant throughout the crystalline units
of the Bohemian Massif, data similar to this paper have not been published yet. The studied pegmatites are hosted by iron-rich
calcic skarn bodies. This specific setting allowed scavenging of calcium, fluorine and some other elements from the host rocks
into the pegmatitic melts and post-magmatic fluids. Such contamination process was important namely in the case of barren
pegmatites, as can be deduced from the variation in anorthite contents in plagioclase and from the presence of fluorite, hornblende
(with F content) or garnet in the contact zones of pegmatite dykes. Fluid inclusions were studied mostly in quartz, but also
in fluorite, titanite and apatite. Early aqueous–carbonic and late aqueous fluids were identified in both pegmatite types.
The P–T conditions of crystallization as well as the detailed composition of exsolved magmatic fluid, however, particularly differ.
The magmatic fluids associated with barren pegmatites correspond to H2O–CO2 low salinity fluids, composition of which evolved from 20 to 23 to <5 mol% CO2, and from 2 to 4–6 mol% NaCl eq. Sudden decrease in the CO2 content of the post-magmatic fluids (<5 mol% CO2) seems to coincide with the enrichment of the fluid in calcium (from the contamination process) and resulted in precipitation
of calcites (frequently found as trapped solid phases in fluid inclusions). The fluids associated with lithium pegmatites
are more complex (H2O–CO2/N2–H3BO3–NaCl). The CO2 content of early exsolved fluid is 26–20 mol% CO2 and remains the same in the next fluid generation. The main difference between the magmatic and the first post-magmatic fluids
is the presence of 7–9 wt% of H3BO3 (identified as daughter mineral sassolite) in the former. The second post-magmatic fluids are again CO2-poor (∼4 mol%) and more saline (∼4 mol% NaCl eq.). The composition of exsolved fluid was further used to constrain volatile
composition and content of the parental melts. Finally, P–T conditions of pegmatite crystallization are constrained: 600–640°C and 420–580 MPa for the barren pegmatites and 500–570°C
and 310–430 MPa for the lithium pegmatite. While the emplacement of the former occurred in thermal equilibrium with the Moldanubian
host rock environment, the emplacement of the later suggests substantial thermal disequilibrium. 相似文献
5.
Zoisite-bearing high-pressure pegmatites from the MünchbergMassif, Germany, provide an excellent example of the characteristicsof the onset of metabasite melting at eclogite-facies conditions.The pegmatites were derived by partial melting of a mid-oceanridge basalt (MORB)-like eclogite at T 680°C/2·3GPa to 750°C/3·1 GPa, which produced small amountsof tonalitic to trondhjemitic melt. The melt concentrated locallyin isolated, small melt pockets and crystallized primary zoisiteas liquidus phase at P 2·3 GPa/680°C to 2·1GPa/750°C. Compositional zoning of pegmatite zoisite recordsan ensuing multi-stage uplift history with successive, discretecrystallization events at 1·4 ± 0·2 GPa/650700°Cand 1·0 ± 0·1 GPa/620650°C.Resorption textures indicate reheating and thermal perturbationof the whole system prior to each successive crystallizationevent. Final solidification of zoisite-pegmatites occurred at0·9 ± 0·1 GPa/620650°C. Thedata suggest that isolated melt + zoisite crystal mush pocketsformed an integral part of the eclogite throughout uplift frommelt formation at T 680°C/2·3 GPa to 750°C/3·1GPa to final solidification at 0·9 GPa/620630°C;that is, over a depth range of 4560 km. The entire pegmatite-formingprocess was probably fluid conserving: fluid present duringmelt formation was trapped by fully or nearly water-saturatedsiliceous melts, whereas fluid liberated during pegmatite crystallizationinteracted with dehydrated eclogite-facies assemblages to formamphibolite-facies hydrous minerals. A set of empirical Dmelt/eclogitevalues based on mean zoisite-pegmatite and eclogite compositionwere used to model the onset of partial high-pressure meltingof metabasites. KEY WORDS: adakite; high-pressure melting; pegmatite; trondhjemite; zoisite 相似文献
6.
Summary Four types of pegmatites comprise the zoned pegmatite field in the eastern sector of the Albera Massif. Type I is represented by barren pegmatites with graphic textures; type II comprises transitional varieties with Li-Fe-Mn phosphates, Be (chrysoberyl) and scarce Nb-Ta and U oxide minerals; type III consists of pegmatites with significant zones of replacement containing Li-Fe-Mn phosphates, beryl and more abundant Nb-Ta oxide minerals; and type IV, muscovite-quartz-albite pegmatites are highly mineralized with Be, Nb-Ta and HREE. REE mineralization is strongly related to abundance of graphite in the late pegmatite units and in the host-rock. The individual pegmatite types are distributed within four subparallel zones concentric around anatectic muscovite-biotite leucogranites, with type I within the granites or close to the contact, and type IV pegmatites in the outermost areas. The zoning from type I to type IV could relate to fractionation processes which generated the pegmatites and is characterized by an enrichment of Mn, Ta, Na, Li, P, Be and REE. According to the pegmatite distribution and their fractionation trends, we propose an origin by differentiation of a granitic melt.
With 5 Figures 相似文献
Résumé On a établi quatre types de pegmatites dans le champ pegmatitique zoné du secteur est du Massif des Albères (Pyrénées Orientales, France). Celles de type I sont des pegmatites non minéralisées avec des textures graphiques, celles de type II sont des variétés intermediaires avec des phosphates à Li-Fe-Mn, Be (chrysobéryl) et des rares oxides à Nb-Ta et U; celles de type Ill sont des pegmatites avec des zones de réplacement bien dévéloppées et qui contiennent des phosphates à Li-Fe-Mn, du béryl et des oxides à Nb-Ta plus abondants; celles de type IV sont des pegmatites bien minéralisées à Be, Nb-Ta et des T.R. La minéralisation à T.R. est liée à des phénomènes de graphitisation répandus dans les unités tardives de la pegmatite et dans l'encaissant. La distribution de chaque type de pegmatite correspond à quatre zones à peu près parallèles et concentriques autour des granites anatectiques à muscovite-biotite, avec le type I dans les granites ou prochain au contact, et les pegmatites à type IV dans la bande plus externe. La zonation serait due à des processus de fractionnement qui auraient généré les pegmatites et qui sont caracterisés par un enrichissement en Mn, Ta, Na, Li, P, Be et T.R. dès les pegmatites de type I vers celles de type IV. On propose un origine par différentiation des granites en vue de la distribution des pegmatites.
With 5 Figures 相似文献
7.
Dirk Küster Rolf L. Romer Dandena Tolessa Desta Zerihun K. Bheemalingeswara Frank Melcher Thomas Oberthür 《Mineralium Deposita》2009,44(7):723-750
The Kenticha rare-element pegmatite, a globally important tantalite source in the Neoproterozoic Adola Belt of southern Ethiopia,
is a highly fractionated, huge (2,000 m long and up to 100 m thick), subhorizontal, sheet-like body, discordantly emplaced
in ultramafic host rock. It corresponds to the spodumene subtype of the rare-element pegmatite class and belongs to the lithium–cesium–tantalum
petrogenetic family. The Kenticha pegmatite is asymmetrically zoned from bottom to top into granitic lower zone, spodumene-free
intermediate zone, and spodumene-bearing upper zone. A monomineralic quartz unit is discontinuously developed within the upper
zone. Whole-rock data indicate an internal geochemical differentiation of the pegmatite sheet proceeding from the lower zone
(K/Rb ~36, K/Cs ~440, Al/Ga ~2,060, Nb/Ta ~2.6) to the upper zone (K/Rb ~19, K/Cs ~96, Al/Ga ~1,600, Nb/Ta ~0.7). The latter
one is strongly enriched in Li2O (up to 3.21%), Rb (up to 4,570 ppm), Cs (up to 730 ppm), Ga (up to 71 ppm), and Ta (up to 554 ppm). Similar trends of increasing
fractionation from lower zone to upper zone were obtained in muscovite (K/Rb 23–14, K/Cs 580–290, K/Tl 6,790–3,730, Fe/Mn
19–10, Nb/Ta 6.5–3.8) and columbite–tantalite (Mn/Mn + Fe 0.4–1, Ta/Ta + Nb 0.1–0.9). The bottom-to-top differentiation of
the Kenticha pegmatite and the Ta mineralization in its upper part are principally attributed to upward in situ fractionation
of a residual leucogranitic to pegmatitic melt, largely under closed system conditions. High MgO contents (up to 5.05%) in
parts of the upper zone are the result of postmagmatic hydrothermal alteration and contamination by hanging wall serpentinite.
U–Pb dating of Mn-tantalite from two zones of the Kenticha pegmatite gave ages of 530.2 ± 1.3 and 530.0 ± 2.3 Ma. Mn-tantalite
from the Bupo pegmatite, situated 9 km north of Kenticha, gave an age of 529.2 ± 4.1 Ma, indicating coeval emplacement of
the two pegmatites. The emplacement of the pegmatites is temporally related to postorogenic granite magmatism, producing slightly
peraluminous, I-type plutons in the area surrounding the Kenticha pegmatite field. Fractionated members of this suite might
be envisaged as potential parental magmas. 相似文献
8.
The 150 m thick late Miocene Graveyard Point sill (GPS) is situated at the Idaho-Oregon border near the southwestern edge
of the western Snake River Plain. It records from bottom to top continuous fractional crystallization of a tholeiitic parent
magma (lower chilled border, FeO/(FeO+MgO) = 0.59, Ni = 90 ppm) towards granophyres (late pods and dikes, FeO/(FeO+MgO) = 0.98,
78 wt% SiO2 3.5 wt% K2O, <4 ppm Ni) showing a typical trend of Fe and P enrichment. Fractionating minerals are olivine (Fo79-Fo2), augite (X
Fe = 0.18−0.95), feldspars (An80Or1-An1Or62), Fe-Ti oxides (Ti-rich magnetite and ilmenite), apatite and in two samples super-calcic pigeonite (Wo18–28 Fs41–54). The granophyres may bear some quartz. Compositionally zoned minerals record a large interval of the fractionation process
in every single sample, but this interval changes with stratigraphic height. In super-calcic pigeonite-bearing samples, olivine
is scarce or lacking and because super-calcic pigeonite occurs as characteristic overgrowths on augite, its formation is interpreted
to be related to the schematic reaction: augite + olivine (component in melt) + SiO2 (in melt) = pigeonite, that defines the cotectic between augite and pigeonite in olivine-saturated basaltic systems. Line
measurements with the electron microprobe reveal that the transition from augite to super-calcic pigeonite is continuous.
However, some crystals show an abrupt “reversal” towards augite after super-calcic pigeonite growth. Two processes compete
with each other in the GPS: fractional crystallization of the bulk liquid (the bulk melt separates from solids and interstitial
liquids in the solidification front) and fractional crystallization of interstitial melt in the solidification front itself.
Interplay between those two processes is proposed to account for the observed variations in mineral chemistry and mineral
textures.
Received: 25 November 1998 / Accepted: 14 June 1999 相似文献
9.
喜马拉雅琼嘉岗超大型伟晶岩锂矿的形成时代、源区特征及分异特征 总被引:1,自引:0,他引:1
喜马拉雅新生代淡色花岗岩带是近年来提出的与高度结晶分异、异地深成淡色花岗岩有关的稀有金属战略远景区,目前其金属组合以铍-铌-钽(-锡-钨)为主。秦克章等(2021a)报道了在高喜马拉雅带珠峰地区发现的琼嘉岗锂矿,是喜马拉雅首例具有工业价值的伟晶岩型锂矿。本次研究重点揭示喜马拉雅琼嘉岗伟晶岩型锂矿的成矿特征、形成时代和源区特征。琼嘉岗矿区矿石矿物主要为锂辉石、铌铁矿-铌锰矿、少量锡石和绿柱石,特征性长柱状锂辉石主要产于块体微斜长石+锂辉石带和分层细晶岩带内。琼嘉岗锂辉石伟晶岩各结构分带的K/Rb含量较为相似,锂含量从边部细粒钠长石带(~100×10-6)到分层细晶岩带(~1000×10-6),再到块体微斜长石+锂辉石带(>3000×10-6)逐渐升高,而Cs含量逐渐降低。独居石和铌钽铁矿族矿物LA-ICPMS定年结果显示,琼嘉岗锂辉石伟晶岩形成于新喜马拉雅阶段早期(25~24Ma),与高喜马拉雅地区淡色花岗岩时代相近。矿物化学和独居石Nd同位素结果显示该稀有金属伟晶岩结晶于高度演化的花岗伟晶岩熔体,源区特征与高喜马拉雅结晶岩系一致。本研究所揭示的琼嘉岗成矿特征、形成时代和源区特征将为高喜马拉雅其它地区找寻大型花岗伟晶岩型锂矿提供重要借鉴意义。 相似文献
10.
Lithospheric Mantle Evolution during Continental Break-Up: The West Iberia Non-Volcanic Passive Margin 总被引:6,自引:0,他引:6
CHAZOT GILLES; CHARPENTIER SOPHIE; KORNPROBST JACQUES; VANNUCCI RICCARDO; LUAIS BEATRICE 《Journal of Petrology》2005,46(12):2527-2568
Ultramafic (lherzolites, metasomatized peridotites, harzburgites,websterites and clinopyroxenites) and mafic igneous (basalts,dolerites, diorites and gabbros) rocks exposed at the sea-flooralong the West Iberia continental margin represent a rare opportunityto study the transition zone between continental and oceaniclithosphere. The igneous rocks are enriched in LREE, unlikeNorth Atlantic MORB. A correlation between their 143Nd/144Ndisotopic composition and Ce/Yb ratio suggests that they originatefrom mixing between partial melts of a depleted mantle sourcesimilar to DMM and of an enriched mantle source which may residewithin the continental lithosphere. Clinopyroxenes and amphibolesin the ultramafic rocks are LREE depleted and have flat HREEpatterns with concentrations higher than those of abyssal peridotites.Clinopyroxenes in the harzburgites are less LREE depleted buthave lower HREE concentrations. The clinopyroxenes in the GaliciaBank (GB) lherzolites have radiogenic Nd (143Nd/144Nd rangingfrom 0·512937 to 0·513402) and unradiogenic Sr(87Sr/86Sr ranging from 0·702100 to 0·702311)isotopic ratios similar to, or higher than, DMM (Depleted MORBMantle) whereas the clinopyroxenes in the Iberia Abyssal Plainwebsterites have low-Nd isotopic compositions (143Nd/144Nd rangingfrom 0·512283 to 0·512553) with high-Sr isotopicratios (87Sr/86Sr ranging from 0·704170 to 0·705919).Amphiboles in Galicia Bank lherzolites and diorites have NdSrisotopic compositions (143Nd/144Nd from 0·512804 to 0·512938and 87Sr/86Sr from 0·703243 to 0·703887) intermediatebetween those of the clinopyroxenes from the Galicia Bank andthe Iberia Abyssal Plain, but similar to the clinopyroxenesin the 5100 Hill harzburgite (143Nd/144Nd = 0·512865and 87Sr/86Sr = 0·703591) and to the igneous rocks (143Nd/144Ndranging from 0·512729 to 0·513121 and 87Sr/86Srranging from 0·702255 to 0·705109). The majorand trace element compositions of cpx in the Galicia Bank spinellherzolites provide evidence for large-scale refertilizationof the lithospheric upper mantle by MORB-like tholeiitic melts.The associated harzburgites did not undergo partial meltingduring the rifting stage, but, in earlier times, probably during,or even before, the Hercynian orogeny. Iberia Abyssal Plainwebsterites are interpreted as high-pressure cumulates formedin the mantle. Their high Sm/Nd ratios (from 0·43 to0·67) coupled with very low-Nd isotopic compositionsare best explained by a two-stage history: formation of thecumulates from the percolation of enriched melts long beforethe rifting, followed by low-degree partial melting of the pyroxenites,accounting for their LREE depletion. This last event probablyoccurs during the rifting episode, 122 Myr ago. The isotopicheterogeneities observed in the ultramafic rocks of the Iberiamargin were already present at the time of the rifting event.They reflect a long and complex history of depletion and enrichmentevents in an old part of the mantle, and provide strong argumentsfor a sub-continental origin of this part of the upper mantle. KEY WORDS: Iberia margin; mantle peridotites; igneous rocks; petrology; geochemistry 相似文献
11.
Western Altun in Xinjiang is an important area, where lithium(Li)-bearing pegmatites have been found in recent years. However, the complex terrain and harsh environment of western Altun exacerbates in prospecting for Li-bearing pegmatites. Therefore, remote-sensing techniques can be an effective means for prospecting Li-bearing pegmatites. In this study, the fault information and lithologyical information in the region were obtained using the median-resolution remotesensing image Landsat-8, the ... 相似文献
12.
Rainer Thomas Paul Davidson Dieter Rhede Michael Leh 《Contributions to Mineralogy and Petrology》2009,157(4):505-523
In this paper, we show that the crystallization of miarolitic pegmatites at K?nigshain started at about 700°C, in melts containing
up to 30 mass% water. Such high water concentration at low pressures (1–3 kbar) is only possible if the melts are peralkaline.
Such peralkaline melts are highly corrosive, and reacted with the wall rock—here the granite host—forming the graphic granite
zone, in part via a magmatic–metasomatic reaction. With cooling, the water concentration in some melt fractions increased
up to 50 mass% H2O. The melt-dominated system ends below 600°C and passes into a fluid-dominated system, the beginning of which is characterized
by strong pressure fluctuations, caused by the change of OH and CO3
2− in the melt, to molecular water and CO2. We note two generations of smoky quartz, one crystallized above the β–α-transition of quartz (≈573°C), and one below, both
of which contain melt inclusions. This indicates that some melt fraction remains during at least the higher-temperature portion
of the growth of minerals into the miarolitic cavity, contradicting the view that minerals growing into a pegmatite chamber
only do so from aqueous fluids. We show that the K?nigshain miarolitic pegmatites are part of the broad spectrum of pegmatite
types, and the processes active at K?nigshain are representative of processes found in most granitic pegmatites, and are thus
instructive in the understanding of pegmatite formation in general, and constraining the composition and characteristics of
pegmatite-forming melts.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
13.
This paper deals with inclusions, megacrysts, and nodules froma group of Stephanian and Permian vents and associated intrusiveson the Fife (Scotland) coast near Elie. The petrography andchemistry of inclusions of spinel Iherzolite, wehrlite, andclinopyroxenite are described. The Elie Ness vent contains coarse-grainedplutonic nodules (Elie type nodules) and megacrysts of pyrope,sub-calcic augite, kaersutite, and anorthoclase. Elie type nodulesare divisible into five groups: (1) kaersutite-olivine-pyroxenite,(2) type 1 +oligoclase, (3) biotite-pyroxenite, (4) sodic amphibole-biotite-albite,(5) biotite-albite. Experimental studies show that sub-calcic augite and pyropephenocrysts could have coprecipitated from an alkali basaltmagma at P > 25 kb, T = 13001450 ?C. It is proposedthat the primary alkali basalt liquid was formed by partialmelting of a vapour-free, mica-bearing garnet Iherzolite mantleat a depth of c. 100 km, with subsequent pyrope-augite phenocrystcrystallization at not less than 70 km depth. Geochemical studiesof clinopyroxenes from the Elie type nodules indicate crystallizationwithin the lower crust. It is proposed that types 1 and 2 nodulesare cumulates from the alkaline basaltic liquid, intercumuluskaersutite representing compositions of liquids intermediateon the Fife basalt trend. Type 3 nodules may represent basalticliquids at the basic end of the Fife trend, wholly crystallizedat pressure from 1015 kb. Experimental data on stabilityof anorthoclase in its host basanite show it to be present inthe basanite melting interval only at P < 9 kb (dry). Itis thought that crystallization of anorthoclase may be associatedwith formation of types 4 and 5 nodules, possibly from a trappedpocket of evolved alkaline liquid at upper crustal levels. TheElie Ness eruption must have been rapid enough to strip theaccumulated pyroxenites from the lower crust and carry unresorbedgarnet megacrysts from depths of over 70 km. Spinel-lherzoliteinclusions are found only in late stage basic sheets whose intrusionmay be unrelated to the initial violent tuff eruptions. 相似文献
14.
Hartmut Beurlen Marcelo R. R. Da Silva Rainer Thomas Dwight R. Soares Patrick Olivier 《Mineralium Deposita》2008,43(2):207-228
The Borborema Pegmatitic Province (BPP), northeastern Brazil, is historically important for tantalum mining and also famous
for top-quality specimens of exotic Nb–Ta oxides and, more recently, for the production of gem quality, turquoise blue, ‘Paraíba
Elbaite.’ With more than 750 registered mineralized rare-element granitic pegmatites, the BPP extends over an area of about
75 by 150 km in the eastern part of the Neoproterozoic Seridó Belt. The Late Cambrian pegmatites are mostly hosted by a sequence
of Neoproterozoic cordierite–sillimanite biotite schists of the Seridó Formation and quartzites and metaconglomerates of the
Equador Formation. The trace-element ratios in feldspar and micas allow to classify most pegmatites as belonging to the beryl–columbite
phosphate subtype. Electron microprobe analyses (EMPA) of columbite, tapiolite, niobian–tantalian rutile, ixiolite and wodginite
group minerals from 28 pegmatites in the BPP are used to evaluate the effectiveness of Nb–Ta oxide chemistry as a possible
exploration tool, to trace the degree of pegmatite fractionation and to classify the pegmatites. The columbite group mineral
composition allows to establish a compositional trend from manganoan ferrocolumbite to manganocolumbite and on to manganotantalite.
This trend is typical of complex spodumene- and/or lepidolite-subtype pegmatites. It clearly contrasts with another trend,
from ferrocolumbite through ferrotantalite to ferrowodginite and ferrotapiolite compositions, typical of pegmatites of the
beryl–columbite phosphate subtype. Large scatter and anomalous trends in zoned crystals partially overlap and conceal the
two main evolution patterns. This indicates that a large representative data set of heavy mineral concentrate samples, collected
systematically along cross-sections, would be necessary to predict the metallogenetic potential of individual pegmatites.
Other mineral species, e.g. garnets and/or tourmaline, with a more regular distribution than Nb–Ta oxides, would be more appropriate
and less expensive for routine exploration purposes. The currently available Nb–Ta oxide chemistry data suggest the potential
for highly fractionated Ta–Li–Cs pegmatites in the BPP, so far undiscovered, and encourages further, more detailed research. 相似文献
15.
《International Geology Review》2012,54(4):426-430
Pegmatites of several areas are described. It is contended that their properties and relationships support Fersman's idea that pegmatites are magmatic rather than hydrothermal or metasomatic. The principal arguments are as follows: 1) contacts of the pegmatite material are sharp where it occurs in the original bides or in xenolithic fragments; 2) later K-Na metasomatism affects pegmatites and enclosing granite the same way; 3) a pegmatite body contains the same minerals, including, accessories, whether the country rock is granite, diabase or limestone; 4) graphic texture occurs in some of the dikes; 5) there is strong differentiation in thick dikes; less, in thin ones (branches); 6) method of incorporation of xenoliths in pegmatites suggests viscous melt, not aqueous solution; 7) Xenoliths in pegmatite are'only slightly altered, if at all. -- E. Ingerson. 相似文献
16.
The Graveyard Point Intrusion: an Example of Extreme Differentiation of Snake River Plain Basalt in a Shallow Crustal Pluton 总被引:1,自引:0,他引:1
The Graveyard Point intrusion is the only known example of awell-exposed differentiated mafic pluton associated with thelate MiocenePleistocene magmatism of the western SnakeRiver Plain (SRP). It is exposed in a 6 km by 4 km area adjacentto the OregonIdaho border, and exposures range in thicknessfrom 20 to 160 m. The thicker parts of the intrusion are stronglydifferentiated and contain a 2560 m thick section ofwell-laminated cumulus-textured gabbros that grade upward intopegmatoidal ferrogabbro. Evolved liquids formed sheets of Fe-richsiliceous granophyre. At least two injections of magma are indicatedby abrupt discontinuities in the rock and mineral compositions,and by the lack of mass balance between the bulk intrusion andits chilled borders. The laminated gabbros are interpreted tohave formed from a tongue of augite and plagioclase crystalsthat were carried in with the second pulse of magma. Followingthe final emplacement of the intrusion, in situ differentiationproceeded through a two-stage process: the ferrogabbros areexplained as interstitial liquids forced out of the crystalmush by compaction, and the siliceous granophyres are interpretedto be residual liquids that migrated out of the partly crystallizedferrogabbros in response to the exsolution of volatiles. Becausethe geochemical trend inferred for the mafic to intermediatecomposition liquids in the Graveyard Point intrusion is similarto the trend for many western Snake River Plain lavas, the plutonmay be a good model for shallow sub-volcanic magma chamberselsewhere in the SRP. However, some western SRP lavas containanomalously high concentrations of P2O5 , which are best explainedby mixing within the active crustal mush column or with partialmelts of previously formed differentiated mafic intrusions. KEY WORDS: Snake River Plain; mafic intrusions; tholeiitic; sill; granophyre 相似文献
17.
Are Arc Basalts Dry, Wet, or Both? Evidence from the Sumisu Caldera Volcano, Izu-Bonin Arc, Japan 总被引:2,自引:0,他引:2
TAMURA Y.; TANI K.; ISHIZUKA O.; CHANG Q.; SHUKUNO H.; FISKE R. S. 《Journal of Petrology》2005,46(9):1769-1803
Basaltbasaltic andesite (<55 wt % SiO2) and daciterhyolite(6674 wt % SiO2) are the predominant eruptive productsin the Sumisu caldera volcano, IzuBonin arc, Japan. Themost magnesian basalt (8·5% MgO), as well as some ofthe other basalts, has a low Zr content (2025 ppm), andcannot yield basalts with higher Zr contents (2940 ppm)through fractionation and/or assimilation. The high- and low-Zrbasalts have different phenocryst assemblages, olivine, plagioclaseand pyroxene phenocryst chemistries, REE (rare earth element)patterns, and fluid-mobile element/immobile element ratios.Estimated primary olivine compositions are more magnesian (>Fo91)in the low-Zr basalts compared with those in high-Zr basalts(<Fo89). The low-Zr basalts contain up to 11 vol. % augite,but many high-Zr basalts are free of augite, which appears onlyin their more differentiated products. The low-Zr basalts areconsidered to be hydrous magmas in which olivine crystallizesfirst followed by augite and plagioclase, whereas the high-Zrbasalts are dry. The low-Zr basalts have higher U/Th ratiosthan the high-Zr basalts. We suggest that both dry and wet primarybasalts existed in the Sumisu magmatic system, each having differenttrace element concentrations, mineral assemblages and mineralchemistry. The lower contents of Zr and light REE and magnesianprimary olivines in the wet basalts could have resulted froma higher degree of partial melting (20%) of a hydrous sourcemantle compared with 10% melting of a dry source mantle. TheSr, Nd and Pb isotope compositions of the wet and dry basaltsare similar and are limited in range. These lines of evidenceindicate that a mantle diapir model might be applicable to satisfythe configuration of such a mantle source region beneath a singlevolcanic system such as Sumisu. KEY WORDS: degree of melting; hot fingers; isotopes; mantle diapir; mantle wedge 相似文献
18.
中国云南哀牢山含海蓝宝石伟晶岩的起源和成岩模拟实验研究 总被引:1,自引:0,他引:1
The Ailaoshan aquamarine-bearing pegmatites are associated with Proterozoic metamorphic rocks in the southern portion of the Ailaoshan fault-folded complex.The gem-bearing pegmatite mineralization zones of the region occur in areas generally consistent with the regional tectonic trend.The pegmatites are found in metamorphic rocks,migmatites and in the inner/outer contact zones of gneissoid granites. The Rb-Sr isochron drawn for the pegmatites is 26~31 Ma,(i.e.in Himalayan).The homogenization temperatures of melt and liquid inclusions in minerals vary from 185 to 920℃,which are comparable to the inclusions observed in banded migmatites and ptygmatic quartz veins in the surrounding metamorphic rocks. The mineralization fluids of the pegmatite were rich in HCO_3 and CO_2,and their compositional assemblages are comparable to metamorphic fluids.Results of H,O,C,Si etc.isotopic analyses and REE,and Be analyses indicates that the sources of mineralization components that formed the pegmatites are closely associated with metamorphic fluids and the enclosing metamorphic rocks. A pegmatite structure simulation experiment was conducted at high temperature and pressure(840℃and 1,500×105Pa.),with various metamorphic rock samples in a water-rich and volatile-rich environment.When the liquidus was reached,the temperature was gradually decreased at the rate of 5~10℃/day over a time period of three months.SEM energy-dispersive spectrum analyses were performed on the experimental products.A series of pegmatoid textures were observed including zonal texture,megacryst texture,drusy cavities,crystal druses,and vesicular texture along with more than ten types of minerals including plagioclase,microcline,quartz and biotite.Different metamorphic rock melts generated different mineral assemblages.Experiment results revealed that the partial melting of metamorphic rocks could form melts similar to pegmatite magmas. Based upon the geological characteristics,geochemistry,and pegmatite texture simulation experimental results,it is concluded that the mineralization components of Ailaoshan aquamarine-bearing pegmatites came from metamorphic rocks.The petrogenetic model for the origin of pegmatites is related to ultrametamorphism and metamorphic anatexis. 相似文献
19.
A 1500 m thick sheet-like body of ferroaugite syenite is divisiblemineralogically into an upper and lower series of syenites.The lower syenites are characterized by well developed igneouslayering defined by mafic cumulus minerals. The syenites aresaturated to oversaturated and contain as cumulus phases alkalifeldspar, olivine (Fa8393), ferroaugite (Di50Hd45Ac5Di5Hd90Ac5)and ilmeno-magnetite. Amphiboles which crystallized from theintercumulus liquid range in composition from ferrohastingsitichornblende to ferroedenitic hornblende to ferroactinolitic edenite.The upper series are coarse grained cumulates with poorly definedlayering and abundant patch pegmatites. Cumulus phases are alkalifeldspar, olivine (Fa93), and acmitic-hedenbergite (Di5Hd50Ac5Ac50Hd50).Intercumulus liquids are peralkaline and crystallized to aenigmatiteand amphiboles which range in composition from ferrorichteritickatophorite to ferrorichterite, Patch pegmatites are peralkalinerocks composed of ferrorichterite, ferroactinolite, alkali feldspar,aenigmatite, quartz and zircon. Extreme differentiation of ferroaugitesyenite magma generates residua which are ironrich, oversaturatedand peralkaline. Initial and final temperatures of crystallizationare estimated from mineral stability data to be 800900°C to 500550 °C respectively. Thermodynamic dataand mineral compositions indicate that during crystallizationthe oxygen fugacity of the magma decreased from approximately1015 to 10231024 bars. Ferroaugitesyenite pyroxene compositional trends are similar to those ofundersaturated peralkaline syenites (llimaussaq) and demonstratethat acmite enrichment trends are independent of silica activityand take place under decreasing oxygen fugacities. 相似文献
20.
An initial phase of an extensive geochemical study of pegmatites from the Black Hills, South Dakota, indicates potassium feldspar composition is useful in interpreting petrogenetic relationships among pegmatites and among pegmatite zones within a single pegmatite. The and ratios and Li and Cs contents of the feldspars within each zoned pegmatite, to a first approximation, are consistent with the simple fractional crystallization of the potassium feldspar from a silicate melt from the wall zone to the core of the pegmatites. Some trace element characteristics (i.e. Cs) have been modified by subsolidus reequilibration of the feldspars with late-stage residual fluid. ratios of the potassium feldspar appear to be diagnostic of the pegmatite mineral assemblage. The relationship between and mineralogy is as follows: Harney Peak Granite (barren pegmatites) > 180; Li-Fe-Mn phosphate-bearing pegmatites = 90?50; spodumene-bearing pegmatites = 60?40; pollucitebearing pegmatites < 30. Although the ratios suggest that the pegmatites studied are genetically related by fractional crystallization to each other and the Harney Peak Granite, overlapping ratios and the general increase in Sr and Ba with decreasing indicate the genetic relationship is much more complex and may also be dependent upon slight variations in source (chemistry and mineralogy) material composition and degrees of partial melting. 相似文献