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1.
Mark E. Brandriss Richard J. Nevle Dennis K. Bird James R. O’Neil 《Contributions to Mineralogy and Petrology》1995,121(1):74-86
Hydrogen and oxygen isotope analyses have been made of hydrous minerals in gabbros and basaltic xenoliths from the Eocene
Kap Edvard Holm intrusive complex of East Greenland. The analyzed samples are of three types: (1) primary igneous hornblendes
and phlogopites that crystallized from partial melts of hydrothermally altered basaltic xenoliths, (2) primary igneous hornblendes
that formed during late–magmatic recrystallization of layered gabbroic cumulates, and (3) secondary actinolite, epidote and
chlorite that formed during subsolidus alteration of both xenoliths and gabbros. Secondary actinolite has a δ18O value of −5.8‰ and a δD value of −158‰. These low values reflect subsolidus alteration by low–δ18O, low–δD hydrothermal fluids of meteoric origin. The δD value is lower than the −146 to −112‰ values previously reported
for amphiboles from other early Tertiary meteoric–hydrothermal systems in East Greenland and Scotland, indicating that the
meteoric waters at Kap Edvard Holm were isotopically lighter than typical early Tertiary meteoric waters in the North Atlantic
region. This probably reflects local climatic variations caused by formation of a major topographic dome at about the time
of plutonism and hydrothermal activity. The calculated isotopic composition of the meteoric water is δD=−110 ± 10‰, δ18O ≈−15‰. Igneous hornblendes and phlogopites from pegmatitic pods in hornfelsed basaltic xenoliths have δ18O values between −6.0 and −3.8‰ and δD values between −155 and −140‰. These are both much lower than typical values of fresh
basalts. The oxygen isotope fractionations between pegmatitic hornblendes and surrounding hornfelsic minerals are close to
equilibrium fractionations for magmatic temperatures, indicating that the pegmatites crystallized from low–δ18O partial melts of xenoliths that had been hydrothermally altered and depleted in 18O prior to stoping. The pegmatitic minerals may have crystallized with low primary δD values inherited from the altered country
rocks, but these values were probably overprinted extensively by subsolidus isotopic exchange with low–δD meteoric–hydrothermal
fluids. This exchange was facilitated by rapid self–diffusion of hydrogen through the crystal structures. Primary igneous
hornblendes from the plutonic rocks have δ18O values between +2.0 and +3.2‰ and δD values between −166 and −146‰. The 18O fractionations between hornblendes and coexisting augites are close to equilibrium fractionations for magmatic temperatures,
indicating that the hornblendes crystallized directly from the magma and subsequently underwent little or no oxygen exchange.
The hornblendes may have crystallized with low primary δD values, due to contamination of the magma with altered xenolithic
material, but the final δD values were probably controlled largely by subsolidus isotopic exchange. This inference is based
partly on the observation that coexisting plagioclase has been extensively depleted in 18O via a mineral–fluid exchange reaction that is much slower than the hydrogen exchange reaction in hornblende. It is concluded
that all hydrous minerals in the study area, whether igneous or secondary, have δD values that reflect extensive subsolidus
isotopic equilibration with meteoric–hydrothermal fluids.
Received: 22 March 1994 / Accepted: 26 January 1995 相似文献
2.
I. J. Richards Theodore C. Labotka Robert T. Gregory 《Contributions to Mineralogy and Petrology》1996,123(2):202-221
Late Proterozoic to Cambrian carbonate rocks from Lone Mountain, west central Nevada, record multiple post-depositional events
including: (1) diagenesis, (2) Mesozoic regional metamorphism, (3) Late Cretaceous contact metamorphism, related to the emplacement
of the Lone Mountain granitic pluton and (4) Tertiary hydrothermal alteration associated with extension, uplift and intrusion
of silicic porphyry and lamprophyre dikes. Essentially pure calcite and dolomite marbles have stable isotopic compositions
that can be divided into two groups, one with positive δ13C values from+3.1 to +1.4 ‰ (PDB) and high δ18O values from +21.5 to +15.8 ‰ (SMOW), and the other with negative δ13C values from –3.3 to –3.6‰ and low δ18O values from +16.9 to +11.1‰. Marbles also contain minor amounts of quartz, muscovite and phlogopite. Brown and blue luminescent,
clear, smooth textured quartz grains from orange luminescent calcite marbles have high δ18O values from +23.9 to +18.1‰, while brown luminescent, opaque, rough textured quartz grains from red luminescent dolomite
marbles typically have low δ18O values from +2.0 to +9.3‰. The δ18O values of muscovite and phlogopite from marbles are typical of micas in metamorphic rocks, with values between +10.4 and
+14.4‰, whereas mica δD values are very depleted, varying from −102 to −156‰. No significant lowering of the δ18O values of Lone Mountain carbonates is inferred to have occurred during metamorphism as a result of devolatilization reactions
because of the essentially pure nature of the marbles. Bright luminescence along the edges of fractures, quartz cements and
quartz overgrowths in dolomite marbles, low δD values of micas, negative δ13C values and low δ18O values of calcite and dolomite, and depleted δ18O values of quartz from dolomite marbles all indicate that meteoric fluids interacted with Lone Mountain marbles during the
Tertiary. Partial oxygen isotopic exchange between calcite and low 18O meteoric fluids lowered the δ18O values of calcite, resulting in uniform quartz-calcite fractionations that define an apparent pseudoisotherm. These quartz-calcite
fractionations significantly underestimate both the temperature of metamorphism and the temperature of post-metamorphic alteration.
Partial oxygen isotopic exchange between quartz and meteoric fluids also resulted in 18O depletion of quartz from dolomite marbles. This partial exchange was facilitated by an increase in the surface area of the
quartz as a result of its dissolution by meteoric fluids. The negative δ13C values in carbonates result from the oxidation of organic material by meteoric fluids following metamorphism. Stable isotopic
data from Lone Mountain marbles are consistent with the extensive circulation of meteoric hydrothermal fluids throughout western
Nevada in Tertiary time.
Received: 1 February 1994/Accepted: 12 September 1995 相似文献
3.
T. A. Ikonnikova E. O. Dubinina M. R. Saroyan A. V. Chugaev 《Geology of Ore Deposits》2009,51(6):505-512
The relationships between the δ18O of quartz veins and veinlets pertaining to the main stage of gold mineralization at the Sukhoi Log deposit and metasomatically
altered host slates are estimated. The oxygen isotopic composition of veined quartz and host slates is not uniform. The δ18O of quartz veins from the Western, Central, and Sukhoi Log areas of the deposit vary from +16 to + 18 ‰. The δ18O range of metasomatically altered slates in the Western and Sukhoi Log areas attains 6 ‰. The δ18O of quartz veins are always higher than those of host slates by 3–7‰. The regular difference in the δ18O between quartz veins and host slates indicates that the oxygen isotopic composition of the ore-bearing fluid forming the
system of quartz veins and veinlets at the Sukhoi Log deposit could have formed as a result of interaction with silicate rocks,
for instance, terrigenous slates enriched in δ18O. Such interaction, however, took place at deeper levels of the Sukhoi Log deposit. It is suggested that the fluid phase
participating in the formation of the vein and veinlet system had initially high δ18O(>+10‰) due to interaction with the rocks enriched in δ18O at a low fluid/rock ratio. The oxygen isotope data indicate that the fluid participating in the formation of gold mineralization
at the Sukhoi Log deposit was not in equilibrium with igneous rocks at high temperatures. 相似文献
4.
Oxygen isotopic composition was studied in the altered host rocks of the Dal’negorsk borosilicate deposit in order to establish
a boron source and the origin of ore-forming fluids responsible for deposition of economic borosilicate ore. The relationships
between oxygen isotopic composition and geochemistry of the altered igneous rocks occupying various structural and temporal
positions in the ore zone were studied, including premineral high-potassium minor intrusions located in the zones of datolite
mineralization; alkali basalt, gabbro, and breccia from the sedimentary framework of the deposit; and postmineral basaltic
andesite, basalt, and dolerite dikes. It was suggested that interaction of aqueous fluid with host rocks brought about not
only variation in oxygen isotopic composition but also shifts in geochemistry of these rocks, especially as concerns the chemical
elements contained in ore-forming fluid. The disturbance of oxygen isotopic system is typical of all studied rocks: δ18O values sharply decrease indicating interaction with aqueous fluid at elevated temperatures. The lowest δ18O (from −2.9 to +0.1‰) is characteristic of the premineral high-potassium and ultrapotassium minor intrusions from skarn-datolite
zone. Igneous rocks from the sedimentary framework of the deposit have δ18O of +2 to −0.9‰ The δ18O of postmineral basaltic andesite, basalt, and dolerite dikes varies from 0 to +7‰ with increasing distance from the ore
zone. The oxygen isotopic composition of aqueous fluid evidences its exogenic origin. The geochemical and isotopic characteristics
of ore-forming fluid show that it could have been deep-seated subsurface water similar to the contemporary water of the Alpine
fold zone, which contain up to 700–1000 mg/l B and is distinguished by high K, Li, Rb, Cs contents and high K/Na ratio. Similar
geochemistry is characteristic of the fluid inclusions in quartz from ore zones. It cannot be ruled out that continental evaporites
were a source of boron as well. The relationships between δ18O, K-Ar age, and geochemical parameters of premineral and postmineral altered intrusive bodies allow us to suggest that the
subsurface B-bearing water discharged through narrow channels controlled by premineral basaltic bodies. The discharge was
probably initiated by emplacement of basalt and dolerite dikes. 相似文献
5.
Whole rock and mineral stable isotope and microprobe analyses are presented from granitoids of the North Chilean Precordillera.
The Cretaceous to Tertiary plutonic rocks contain important ore deposits and frequently display compositional and textural
evidence of hydrothermal alteration even in barren rocks. Deuteric alteration includes replacement of biotite and amphibole
by chlorite and epidote, sericitization and saussuritization of feldspars, and uralitization of clinopyroxene and/or amphibole.
While whole rock compositions are not significantly affected, compositional variations in amphiboles suggest two types of
hydrothermal alteration. Hornblende with actinolitic patches and rims and tight compositional trends from hornblende to Mg-rich
actinolite indicate increasing oxygen fugacity from magmatic to hydrothermal conditions. Uralitic amphiboles exhibiting irregular
Mg-Fe distribution and variable Al content are interpreted as reflecting subsolidus hydration reactions at low temperatures.
The δD values of hydrous silicates vary from −63 to −105‰. Most δ18O values of whole rocks are in the range of 5.7 to 7.7‰ and are considered normal for igneous rocks in the Andes. These δ18O values also coincide well with the oxygen isotope composition of geochemically similar recent volcanics from the Central
Andean Volcanic Zone (δ18O = 7.0–7.4‰). Only one sample in this study (δ18O = 3.0‰) appears to be depleted by isotope exchange with light meteoric water at high temperatures. The formation of secondary
minerals in all other intrusions is mainly the product of deuteric alteration. This also holds true for the sample from El
Abra, the only pluton associated with mineralization. This indicates the dominant role of a magmatic rather than a meteoric
fluid in the alteration of the Cretaceous and Tertiary granitoids in northern Chile.
Received: 8 July 1998 / Accepted: 15 April 1999 相似文献
6.
D. P. Krylov E. B. Sal’nikova A. M. Fedoseenko S. Z. Yakovleva Yu. V. Plotkina I. V. Anisimova 《Petrology》2011,19(1):79-86
The Chupa nappe of the Belomorian Complex contains aluminous silica-undersaturated rocks with corundum, which are characterized
by extremely low 18O/16O (whole-rock δ18O up to −21‰). Revealed isotopic anomalies are explained by the influence of meteoric waters that were modified through evaporation-precipitation
cycles (Rayleigh distillation) under cold climatic conditions. In order to estimate whether the decrease in δ18O occurred prior to metamorphism of the protoliths of the Chupa Sequence or during water percolation in the course of metamorphic
or postmetamorphic transformations, we studied oxygen composition in the rocks and minerals and conducted U-Pb dating on single
zircons from corundumbearing rocks of Khitostrov. 相似文献
7.
Oxygen isotope systematics of gem corundum deposits in Madagascar: relevance for their geological origin 总被引:1,自引:1,他引:1
Gaston Giuliani Anthony Fallick Michel Rakotondrazafy Daniel Ohnenstetter Alfred Andriamamonjy Théogène Ralantoarison Saholy Rakotosamizanany Marie Razanatseheno Yohann Offant Virginie Garnier Christian Dunaigre Dietmar Schwarz Alain Mercier Voahangy Ratrimo Bruno Ralison 《Mineralium Deposita》2007,42(3):251-270
The oxygen isotopic composition of gem corundum was measured from 22 deposits and occurrences in Madagascar to provide a gemstone
geological identification and characterization. Primary corundum deposits in Madagascar are hosted in magmatic (syenite and
alkali basalt) and metamorphic rocks (gneiss, cordieritite, mafic and ultramafic rocks, marble, and calc-silicate rocks).
In both domains the circulation of fluids, especially along shear zones for metamorphic deposits, provoked in situ transformation
of the corundum host rocks with the formation of metasomatites such as phlogopite, sakenite, and corundumite. Secondary deposits
(placers) are the most important economically and are contained in detrital basins and karsts. The oxygen isotopic ratios
(18O/16O) of ruby and sapphire from primary deposits are a good indicator of their geological origin and reveal a wide range of δ18O (Vienna Standard Mean Ocean Water) between 1.3 and 15.6‰. Metamorphic rubies are defined by two groups of δ18O values in the range of 1.7 to 2.9‰ (cordieritite) and 3.8 to 6.1‰ (amphibolite). “Magmatic” rubies from pyroxenitic xenoliths
contained in the alkali basalt of Soamiakatra have δ18O values ranging between 1.3 and 4.7‰. Sapphires are classified into two main groups with δ18O in the range of 4.7 to 9.0‰ (pyroxenite and feldspathic gneiss) and 10.7 to 15.6‰ (skarn in marble from Andranondambo).
The δ18O values for gem corundum from secondary deposits have a wide spread between −0.3 and 16.5‰. The ruby and sapphire found in
placers linked to alkali basalt environments in the northern and central regions of Madagascar have consistent δ18O values between 3.5 and 6.9‰. Ruby from the placers of Vatomandry and Andilamena has δ18O values of 5.9‰, and between 0.5 and 4.0‰, respectively. The placers of the Ilakaka area are characterized by a huge variety
of colored sapphires and rubies, with δ18O values between −0.3 and 16.5‰, and their origin is debated. A comparison with oxygen isotope data obtained on gem corundum
from Eastern Africa, India, and Sri Lanka is presented. Giant placer deposits from Sri Lanka, Madagascar, and Tanzania have
a large variety of colored sapphires and rubies with a large variation in δ18O due to mingling of corundum of different origin: mafic and ultramafic rocks for ruby, desilicated pegmatites for blue sapphire,
syenite for yellow, green, and blue sapphire, and skarn in marbles for blue sapphire. 相似文献
8.
Oxygen isotope constraints on the petrogenesis of the Sybille intrusion of the Proterozoic Laramie Anorthosite Complex 总被引:2,自引:0,他引:2
The origin of monzonitic intrusions that are associated with Proterozoic massif-type anorthosite complexes is controversial.
A detailed oxygen isotope study of the Sybille intrusion, a monzonitic intrusion of the Laramie Anorthosite Complex (Wyoming),
indicates that either derivation from a basaltic magma of mantle origin with a metasedimentary component (∼20%) incorporated
early in its magmatic history, or a partial melt of lower crustal rocks is consistent with the data. The oxygen isotope compositions
of plagioclase, pyroxene and zircon from the Sybille monzosyenite, the dominant rock type in the Sybille intrusion, were analyzed
in order to establish the isotopic composition of the source of the magma. Plagioclase δ18O values range from 6.77 to 9.17‰. We interpret the higher plagioclase δ18O values (average 8.69 ± 0.30‰, n = 19) to be magmatic in origin, lower plagioclase δ18O values (average 7.51 ± 0.44‰, n = 22) to be the result of variable subsolidus alteration, and pyroxene δ18O values (average 6.34 ± 0.38‰, n = 19) to be the result of closed-system diffusional exchange during cooling. Low magnetic zircons, which have been shown
to retain magmatic oxygen isotope values despite high grade metamorphism and extensive subsolidus hydrothermal alteration,
have δ18O values (7.40 ± 0.24‰, n = 11) which are consistent with our interpretation of the plagioclase and pyroxene results. Oxygen isotope data from all
three minerals indicate that the magmatic oxygen isotope composition of the Sybille intrusion is enriched in 18O relative to the composition of average or “normal” mantle-derived magmas. This enrichment is approximately twice the oxygen
isotope enrichment that could result from closed-system fractionation, rendering a closed-system, comag- matic petrogenetic
model between the Sybille intrusion and the mantle-derived anorthositic lithologies of the Laramie Anorthosite Complex improbable.
Received: 7 April 1998 / Accepted: 19 January 1999 相似文献
9.
George B. Perkins Zachary D. Sharp Jane Selverstone 《Contributions to Mineralogy and Petrology》2006,151(6):633-650
Spinel lherzolite and pyroxenite xenoliths from the Rio Puerco Volcanic Field, New Mexico, were analyzed for oxygen isotope ratios by laser fluorination. In lherzolites, olivine δ18O values are high (+5.5‰), whereas δ18O values for pyroxenes are low (cpx=+5.1‰; opx=+5.4‰) compared to average mantle values. Pyroxenite δ18O values (cpx=+5.0‰; opx=+5.3‰) are similar to those of the lherzolites and are also lower than typical mantle oxygen isotope compositions. Texturally and chemically primary calcite in pyroxenite xenoliths is far from isotopic equilibrium with other phases, with δ18O values of +21‰. The isotopic characteristics of the pyroxenite xenoliths are consistent with a petrogenetic origin from mixing of lherzolitic mantle with slab-derived silicate and carbonatite melts. The anomalously low δ18O in the pyroxenes reflects metasomatism by a silicate melt from subducted altered oceanic crust, and high δ18O calcite is interpreted to have crystallized from a high δ18O carbonatitic melt derived from subducted ophicarbonate. Similar isotopic signatures of metasomatism are seen throughout the Rio Puerco xenolith suite and at Kilbourne Hole in the southern Rio Grande rift. The discrete metasomatic components likely originated from the subducted Farallon slab but were not mobilized until heating associated with Rio Grande rifting occurred. Oxygen diffusion modeling requires that metasomatism leading to the isotopic disequilibrium between calcite and pyroxene in the pyroxenites occurred immediately prior to entrainment. Melt infiltration into spinel-facies mantle (xenoliths) prior to eruption was thus likely connected to garnet-facies melting that resulted in eruption of the host alkali basalt. 相似文献
10.
Jade Star Lackey John W. Valley Hans J. Hinke 《Contributions to Mineralogy and Petrology》2006,151(1):20-44
Peraluminous granitoids provide critical insight as to the amount and kinds of supracrustal material recycled in the central
Sierra Nevada batholith, California. Major element concentrations indicate Sierran peraluminous granitoids are high-SiO2 (68.9–76.9) and slightly peraluminous (average molar Al2O3/(CaO + Na2O + K2O)=1.06). Both major and trace element trends mimic those of other high-silica Sierran plutons. Garnet (Grt) in the peraluminous
plutons is almandine–spessartine-rich and of magmatic origin. Low grossular contents are consistent with shallow (<4 kbar)
depths of garnet crystallization. Metasediments of the Kings Sequence commonly occur as wallrocks associated with the plutons,
including biotite schists that are highly peraluminous (A/CNK=2.25) and have high whole rock (WR) δ18O values (9.6–21.8‰, average=14.5±2.9‰, n=26). Ultramafic wallrocks of the Kings–Kaweah ophiolite have lower average δ18O (7.1±1.3‰, n=9). The δ18O(WR) of the Kings Sequence is variable from west to east. Higher δ18O values occur in the west, where quartz in schists is derived from marine chert; values decrease eastward as the proportion
of quartz from igneous and metamorphic sources increases. Peraluminous plutons have high δ18O(WR) values (9.5–13‰) consistent with supracrustal enrichment of their sources. However, relatively low initial 87Sr/86Sr values (0.705–0.708) indicate that the supracrustal component in the source of peraluminous magmas was dominantly altered
ocean crust and/or greywacke. Also, plutons lack or have very low abundances (<1% of grains) of inherited zircon (Zrc) cores.
Average δ18O(Zrc) is 7.9‰ in peraluminous plutons, a higher value than in coeval metaluminous plutons (6–7‰). Diorites associated with
peraluminous plutons also have high δ18O(Zrc), 7.4–8.3‰, which is consistent with the diorites being derived from a similar source. Magmatic garnet has variable
δ18O (6.6–10.5‰, avg.=7.9‰) due to complex contamination and crystallization histories, evidenced by multiple garnet populations
in some rocks. Comparison of δ18O(Zrc) and δ18O(Grt) commonly reveals disequilibrium, which documents evolving magma composition. Minor (5–7%) contamination by high δ18O wallrocks occurred in the middle and upper crust in some cases, although low δ18O wallrock may have been a contaminant in one case. Overall, oxygen isotope analysis of minerals having slow oxygen diffusion
and different times of crystallization (e.g., zircon and garnet), together with detailed textural analysis, can be used to
monitor assimilation in peraluminous magmas. Moreover, oxygen isotope studies are a valuable way to identify magmatic versus
xenocrystic minerals in igneous rocks.
Electronic Supplementary Material Supplementary material is available for this article at 相似文献
11.
Early carbonate cements in the Yanchang Formation sandstones are composed mainly of calcite with relatively heavier carbon isotope (their δ^18O values range from -0.3‰- -0.1‰) and lighter oxygen isotope (their δ^18O values range from -22.1‰- -19.5‰). Generally, they are closely related to the direct precipitation of oversaturated calcium carbonate from alkaline lake water. This kind of cementation plays an important role in enhancing the anti-compaction ability of sandstones, preserving intragranular volume and providing the mass basis for later disso- lution caused by acidic fluid flow to produce secondary porosity. Ferriferous calcites are characterized by relatively light carbon isotope with δ^13C values ranging from -8.02‰ to -3.23‰, and lighter oxygen isotope with δ^18O values ranging from -22.9‰ to -19.7‰, which is obviously related to the decarboxylation of organic matter during the late period of early diagenesis to the early period of late diagenesis. As the mid-late diagenetic products, ferriferous cal- cites in the study area are considered as the characteristic authigenic minerals for indicating large-scaled hydrocarbon influx and migration within the clastic reservoir. The late ankerite is relatively heavy in carbon isotope with δ^13C values ranging from -1.92‰ to -0.84‰, and shows a wide range of variations in oxygen isotopic composition, with δ^18O values ranging from -20.5‰ to -12.6‰. They are believed to have nothing to do with decarboxylation, but the previously formed marine carbonate rock fragments may serve as the chief carbon source for their precipitation, and the alkaline diagenetic environment at the mid-late stage would promote this process. 相似文献
12.
The strata-bound Cu−Pb−Zn polymetallic sulfide deposits occur in metamorphic rocks of greenschist phase of the middle-upper
Proterozoic Langshan Group in central Inner Mongolia. δ34S values for sulfides range from −3.1‰ to +37.3‰, and an apparent difference is noticed between vein sulfides and those in
bedded rocks. For example, δ34S values for bedded pyrite range from +10.6‰ to +20.0‰, while those for vein pyrite vary from −3.1‰ to +14.1‰. δ34S of bedded pyrrhotite is in the range +7.9‰–+23.5‰ in comparison with +6.5‰–+17.1‰ for vein pyrrhotite. The wide scatter
of δ34S and the enrichment of heavier sulfur indicate that sulfur may have been derived from H2S as a result of bacterial reduction of sulfates in the sea water. Sulfur isotopic composition also differs from deposit to
deposit in this area because of the difference in environment in which they were formed. The mobilization of bedded sulfides
in response to regional metamorphism and magmatic intrusion led to the formation of vein sulfides.
δ18O and δ13C of ore-bearing rocks and wall rocks are within the range typical of ordinary marine facies, with the exception of lower
values for ore-bearing marble at Huogeqi probably due to diopsidization and tremalitization of carbonate rocks.
Pb isotopic composition is relatively stable and characterized by lower radio-genetic lead. The age of basement rocks was
calculated to be about 23.9 Ma and ore-forming age 7.8 Ma.207Pb/204Pb−206Pb/204Pb and208Pb/204Pb−206Pb/204Pb plots indicate that Pb may probably be derived from the lower crust or upper mantle.
It is believed that the deposits in this region are related to submarine volcanic exhalation superimposed by later regional
metamorphism and magmatic intrusion. 相似文献
13.
Oxygen and hydrogen isotope geochemistry of gneisses associated with ultrahigh pressure eclogites at Shuanghe in the Dabie Mountains 总被引:18,自引:0,他引:18
Bin Fu Yong-Fei Zheng Zhengrong Wang Yilin Xiao Bing Gong Shuguang Li 《Contributions to Mineralogy and Petrology》1999,134(1):52-66
The oxygen and hydrogen isotope compositions of minerals and whole rock were determined for two types of gneiss (biotite
gneiss and granitic gneiss) associated with ultrahigh pressure (UHP) eclogites in the Shuanghe district of the eastern Dabie
Mountains. There are significant differences in δ18O between the two gneisses: the UHP biotite gneiss varying from −4.3‰ to 10.6‰ similar to the associated eclogites, whereas
the non-UHP granitic gneiss ranges only from −3.8‰ to 1.2‰. The δD values are similar in the two gneisses with −37 to −64‰
for epidote/zoisite, −92 to −83‰ for amphibole, and −63 to −109‰ for biotite/phengite. Hydrogen isotope disequilibrium among
the coexisting hydroxyl-bearing minerals is ascribed to retrograde exchange subsequent to amphibolite-facies metamorphism.
Oxygen isotopic equilibrium has been preserved among various minerals in both gneisses regardless of the large variation in
rock δ18O. Oxygen isotopic geothermometers yield different but regular temperatures corresponding to the closure temperatures of oxygen
diffusion in the minerals. The metamorphic temperatures of both eclogite facies and amphibolite facies have been recovered
in mineral pairs from the biotite gneiss. The isotopic temperatures for the granitic gneiss are mostly in accordance with
amphibolite-facies metamorphism. However, high temperatures of 550 to 650 °C are obtained from those minerals resistant to
retrograde oxygen isotope exchange, implying that the granitic gneiss may have experienced higher temperature metamorphism
than expected from petrologic thermometers. The 18O-depletion of both gneisses is interpreted to result from meteoric-hydrothermal exchange before/during plate subduction.
Therefore, the measured δ18O values of the gneisses reflect the oxygen isotope compositions of their protoliths prior to the UHP metamorphism. It is
inferred that the UHP unit is in foreign contact with the non-UHP unit like a tectonic melange, but both of them experienced the two common stages of geodynamic evolution:
(1) 18O-depletion prior to the UHP metamorphism, (2) uplifting since the amphibolite-facies metamorphism.
Received: 5 May 1998 / Accepted: 27 August 1998 相似文献
14.
V. Yu. Prokof’ev N. S. Bortnikov V. A. Kovalenker S. F. Vinokurov L. D. Zorina A. D. Chernova S. G. Kryazhev A. N. Krasnov S. A. Gorbacheva 《Geology of Ore Deposits》2010,52(2):81-113
The chemistry, REE patterns, and carbon and oxygen isotopic compositions of carbonates from ore veins of the Darasun deposit
are discussed. In addition to the earlier described siderite, calcite, and carbonates of the dolomite-ankerite series, kutnahorite
is identified. The total REE content in Fe-Mg carbonates of the dolomite-ankerite series (2.8–73 ppm) is much lower than in
later calcite (18–390 ppm). δ13C of Fe-Mg carbonates and calcite varies from +1.1 to −6.7‰ and from −0.9 to −4.9‰, respectively. δ18O of Fe-Mg carbonates and calcite varies from +17.6 to 3.6‰ and from +15.7 to −0.5‰, respectively. The REE sum and carbon
and oxygen isotopic compositions reveal zonal distribution relative to the central granodiorite porphyry stock. The correlation
between the carbon and oxygen isotopic compositions and REE sum reflects variations in the physicochemical formation conditions
and composition of ore-forming fluid. The isotopic composition of fluid is calculated, and possible sources of its components
are considered. Earlier established evidence for a magmatic source of ore-forming fluid and participation of meteoric water
in ore formation is confirmed. Geochemical evidence for interaction of ore-forming fluid with host rocks is furnished. The
relationships between the REE sum, on the one hand, and carbon and oxygen isotopic compositions of hydrothermal ore-forming
fluid, on the other, are established. 相似文献
15.
Aaron J. Cavosie John W. Valley Noriko T. Kita Michael J. Spicuzza Takayuki Ushikubo Simon A. Wilde 《Contributions to Mineralogy and Petrology》2011,162(5):961-974
The oxygen isotope ratios (δ18O) of most igneous zircons range from 5 to 8‰, with 99% of published values from 1345 rocks below 10‰. Metamorphic zircons
from quartzite, metapelite, metabasite, and eclogite record δ18O values from 5 to 17‰, with 99% below 15‰. However, zircons with anomalously high δ18O, up to 23‰, have been reported in detrital suites; source rocks for these unusual zircons have not been identified. We report
data for zircons from Sri Lanka and Myanmar that constrain a metamorphic petrogenesis for anomalously high δ18O in zircon. A suite of 28 large detrital zircon megacrysts from Mogok (Myanmar) analyzed by laser fluorination yields δ18O from 9.4 to 25.5‰. The U–Pb standard, CZ3, a large detrital zircon megacryst from Sri Lanka, yields δ18O = 15.4 ± 0.1‰ (2 SE) by ion microprobe. A euhedral unzoned zircon in a thin section of Sri Lanka granulite facies calcite
marble yields δ18O = 19.4‰ by ion microprobe and confirms a metamorphic petrogenesis of zircon in marble. Small oxygen isotope fractionations
between zircon and most minerals require a high δ18O source for the high δ18O zircons. Predicted equilibrium values of Δ18O(calcite-zircon) = 2–3‰ from 800 to 600°C show that metamorphic zircon crystallizing in a high δ18O marble will have high δ18O. The high δ18O zircons (>15‰) from both Sri Lanka and Mogok overlap the values of primary marine carbonates, and marbles are known detrital
gemstone sources in both localities. The high δ18O zircons are thus metamorphic; the 15–25‰ zircon values are consistent with a marble origin in a rock-dominated system (i.e.,
low fluid(external)/rock); the lower δ18O zircon values (9–15‰) are consistent with an origin in an external fluid-dominated system, such as skarn derived from marble,
although many non-metasomatized marbles also fall in this range of δ18O. High δ18O (>15‰) and the absence of zoning can thus be used as a tracer to identify a marble source for high δ18O detrital zircons; this recognition can aid provenance studies in complex metamorphic terranes where age determinations alone
may not allow discrimination of coeval source rocks. Metamorphic zircon megacrysts have not been reported previously and appear
to be associated with high-grade marble. Identification of high δ18O zircons can also aid geochronology studies that seek to date high-grade metamorphic events due to the ability to distinguish
metamorphic from detrital zircons in marble. 相似文献
16.
B. A. Elliott W. H. Peck O. T. Rämö M. Vaasjoki M. Nironen 《Mineralogy and Petrology》2005,85(3-4):223-241
Summary Oxygen isotope ratios of igneous zircon from magmatic rocks in Finland provide insights into the evolution and growth of the
Precambrian crust during the Svecofennian orogeny. These data preserve magmatic δ18O values and correlate with major discontinuities in the lower crust. Oxygen isotope ratios of zircon across the 1.88–1.87 Ga
Central Finland granitoid complex (CFGC) range from 5.50‰ to 6.84‰, except for three plutons in contact with the adjacent
greenstone and metasedimentary belts (δ18O(Zrc) = 7.60‰–7.78‰). There is a systematic variation in δ18O(Zrc) with respect to geographic location in the CFGC, ranging from 6.60±0.23‰ (σ) in the northeast to 5.90±0.40‰ in the
west-southwest. These values correlate with a change in crustal thickness and shift in geochemical composition. The oxygen
isotope composition of the 1.65–1.54 Ga rapakivi granites and related rocks in southern Finland show a decreasing trend from
north to south, independent of their emplacement age. The southern anorogenic granite group has an average δ18O in zircon of 6.14±0.07‰ and the northern anorogenic group has an average δ18O in zircon of 8.14±0.59‰. This difference reflects the boundary between island arc terrains accreted during the Paleoproterozoic.
Deceased 相似文献
17.
Carbon and oxygen isotopic analyses of silicate and carbonate minerals indicate that isotopic compositions in metasediments
of the Wallace Formation (Belt Supergroup) exposed northwest of the Idaho batholith have been affected by both prograde and
retrograde fluid-rock interaction. Silicates retain isotopic fractionations that reflect equilibration at peak metamorphic
temperatures. In contrast, calcite oxygen isotopic compositions range from δ18O(Calcite)=+2.3 to +18.6‰ SMOW (standard mean oceanic water) and indicate that some calcites have exchanged with low-δ18O meteorichydrothermal fluids. Values of Δ18O (Quartz-Calcite) as large as +15.5 clearly indicate that the isotopic depletion of these calcites postdates the peak of
regional metamorphism. Carbon isotopic compositions of 18O-depleted calcites are not significantly shifted relative to δ13C values in undepleted calcites, suggesting that the retrograde fluid was carbon-poor. Petrographically, retrograde fluid-rock
interaction is associated with the occurrence of fine-grained, highly-luminescent calcite overgrowths on less-luminescent,
metamorphic calcites, slight to moderate argillic alteration, and pseudomorphing of scapolite porphyroblasts by fine-grained
albite. Retrograde isotopic depletions may be related to shallow meteoric-hydrothermal fluid flow developed around the Idaho
batholith after intrusion and rapid uplift of the terrane. Peak metamorphic isotopic compositions in the Wallace Formation
reflect mineralogically heterogeneous protolith compositions and isotopic fractionation due to devolatilization and/or infiltration.
Variability in oxygen isotopic compositions on the order of 4–6‰ within the same rock type can be attributed to the combined
effects of inherited isotopic compositions and isotopic shifts resulting from prograde devolatilization. Isotopic and compositional
heterogeneity on the scale of mm to m precludes generalization of isotopic gradients on a regional scale. The isotopic data
presented here, and metamorphic fluid compositions determined in previous studies, are best reconciled with heterogeneous
bulk compositions, dominantly channelized prograde and retrograde fluid flow, and locally low fluid-rock ratios. 相似文献
18.
J. W. Valley J. S. Lackey A. J. Cavosie C. C. Clechenko M. J. Spicuzza M. A. S. Basei I. N. Bindeman V. P. Ferreira A. N. Sial E. M. King W. H. Peck A. K. Sinha C. S. Wei 《Contributions to Mineralogy and Petrology》2005,150(6):561-580
Analysis of δ18O in igneous zircons of known age traces the evolution of intracrustal recycling and crust-mantle interaction through time.
This record is especially sensitive because oxygen isotope ratios of igneous rocks are strongly affected by incorporation
of supracrustal materials into melts, which commonly have δ18O values higher than in primitive mantle magmas. This study summarizes data for δ18O in zircons that have been analyzed from 1,200 dated rocks ranging over 96% of the age of Earth. Uniformly primitive to mildly
evolved magmatic δ18O values are found from the first half of Earth history, but much more varied values are seen for younger magmas. The similarity
of values throughout the Archean, and comparison to the composition of the “modern” mantle indicate that δ18O of primitive mantle melts have remained constant (±0.2‰) for the past 4.4 billion years. The range and variability of δ18O in all Archean zircon samples is subdued (δ18O(Zrc)=5–7.5‰) ranging from values in high temperature equilibrium with the mantle (5.3± 0.3‰) to slightly higher, more evolved
compositions (6.5–7.5‰) including samples from: the Jack Hills (4.4–3.3 Ga), the Beartooth Mountains (4.0–2.9 Ga), Barberton
(3.5–2.7 Ga), the Superior and Slave Provinces (3.0 to 2.7 Ga), and the Lewisian (2.7 Ga). No zircons from the Archean have
been analyzed with magmatic δ18O above 7.5‰. The mildly evolved, higher Archean values (6.5–7.5‰) are interpreted to result from exchange of protoliths with
surface waters at low temperature followed by melting or contamination to create mildly elevated magmas that host the zircons.
During the Proterozoic, the range of δ18O(Zrc) and the highest values gradually increased in a secular change that documents maturation of the crust. After ∼1.5 Ga,
high δ18O zircons (8 to >10‰) became common in many Proterozoic and Phanerozoic terranes reflecting δ18O(whole rock) values from 9 to over 12‰. The appearance of high δ18O magmas on Earth reflects nonuniformitarian changes in the composition of sediments, and rate and style of recycling of surface-derived
material into magmas within the crust.
Electronic Supplementary Material Supplementary material is available for this article at 相似文献
19.
Yilin Xiao Zeming Zhang Jochen Hoefs Alfons van den Kerkhof 《Contributions to Mineralogy and Petrology》2006,152(4):443-458
In order to reconstruct the formation and exhumation mechanisms of UHP metamorphic terrains, the Chinese Continental Scientific Drilling Program (CCSD) has been carried out in Donghai of the Dabie-Sulu ultrahigh-pressure (UHP) metamorphic belt, East China. Eclogite, gneiss, amphibolite (retrograded from eclogite), ultramafic rocks, and minor schist and quartzite have been drilled. Aiming to reveal the fluid behaviour in a vertical sequence of an UHP slab, we investigated fluid inclusion and oxygen isotope characteristics of selected drillcores from the main hole and the pilot-holes PP2 and ZK 703 of the CCSD. More than 540 laser-ablation oxygen isotope analyses on garnet, omphacite, quartz, kyanite, amphibole, phengite, rutile, epidote, amphibole, plagioclase, and biotite from various rocks in the depth range of 0–3,000 m (mainly eclogite and gneiss) show that the investigated rocks can be divided into two groups: 18O-depleted rocks (as low as δ18O = −7.4‰ for garnet) indicate interaction with cold climate meteoric waters, whereas 18O-normal rocks (with bulk δ18O > +5.6‰) have preserved the O-isotopic compositions of their protoliths. Meteoric water/rock interaction has reached depths of at least 2,700 m. Oxygen isotope equilibrium has generally been achieved. Isotopic compositions of mineral phases are homogeneous on a mm to cm scale regardless of lithology, but heterogeneous on the scale of a few metres. Oxygen isotope distributions in the vertical sections favour an “in situ” origin of the UHP metamorphic rocks. The very negative δ18O eclogites usually have higher hydroxyl-mineral contents than the normal δ18O rocks, indicating higher water content during UHP metamorphism. Fluid inclusion data suggest that rocks with depleted 18O compositions have had different fluid histories compared to those with normal δ18O values. Rocks with depleted 18O mainly have primary medium-to-high salinity inclusions in omphacite, kyanite and quartz, and abundant secondary low-salinity or pure water inclusions in quartz, indicating a high-salinity-brine-dominated fluid system during peak UHP metamorphism; no carbonic inclusions have been identified in these rocks. By contrast, primary very high-density CO2 inclusions are commonly found in the rocks with normal δ18O values. These observations suggest that fluid and oxygen isotope composition of minerals are related and reflect variable degrees of alterations of the Dabie-Sulu UHP metamorphic rocks. 相似文献
20.
L. Ya. Aranovich E. O. Dubinina A. S. Avdeenko Yu. M. Lebedeva S. A. Bushmin D. D. Dolivo-Dobrovol’skii 《Geochemistry International》2010,48(8):739-751
Hypersthene-garnet-sillimanite-quartz enclaves were studied in orthopyroxene-plagioclase and orthopyroxene-clinopyroxene crystalline
schists and gneisses from shear zones exposed in Palenyi Island in the Early Proterozoic Belomorian Mobile Belt. Qualitative
analysis of mineral assemblages indicates that these rocks were metamorphosed to the granulite facies (approximately 900°C
and 10–11 kbar). Oxygen isotopic composition was determined in rock-forming minerals composing zones of the enclaves of various
mineralogical and chemical composition. The closure temperatures of the isotopic systems obtained by methods of oxygen isotopic
thermometry are close to the values obtained with mineralogical geothermometers (Grt-Opx and Grt-Bt) and correspond to the high-temperature granulite facies (860–900°C). Identified systematic variations in the δ18O values were determined in the same minerals from zones of different mineral composition. Inasmuch as these zones are practically
in contact with one another, these variations in δ18O cannot be explained by the primary isotopic heterogeneity of the protolith. The model calculations of the extent and trend
of the δ18O variations in minerals suggest that the only mechanism able to generate the zoning was fluid-rock interaction at various
integral fluid/rock ratios in discrete zones. This demonstrates that a focused fluid flux could occur in lower crustal shear
zones. The preservation of high-temperature isotopic equilibria of minerals testifies that the episode of fluid activity at
the peak of metamorphism was very brief. 相似文献