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1.
Uniformly mantle-like δ<Superscript>18</Superscript>O in zircons from oceanic plagiogranites and gabbros 总被引:1,自引:1,他引:0
Craig B. Grimes Takayuki Ushikubo Barbara E. John John W. Valley 《Contributions to Mineralogy and Petrology》2011,161(1):13-33
Lower ocean crust is primarily gabbroic, although 1–2% felsic igneous rocks that are referred to collectively as plagiogranites
occur locally. Recent experimental evidence suggests that plagiogranite magmas can form by hydrous partial melting of gabbro
triggered by seawater-derived fluids, and thus they may indicate early, high-temperature hydrothermal fluid circulation. To
explore seawater–rock interaction prior to and during the genesis of plagiogranite and other late-stage magmas, oxygen-isotope
ratios preserved in igneous zircon have been measured by ion microprobe. A total of 197 zircons from 43 plagiogranite, evolved
gabbro, and hydrothermally altered fault rock samples have been analyzed. Samples originate primarily from drill core acquired
during Ocean Drilling Program and Integrated Ocean Drilling Program operations near the Mid-Atlantic and Southwest Indian
Ridges. With the exception of rare, distinctively luminescent rims, all zircons from ocean crust record remarkably uniform
δ18O with an average value of 5.2 ± 0.5‰ (2SD). The average δ18O(Zrc) would be in magmatic equilibrium with unaltered MORB [δ18O(WR) ~ 5.6–5.7‰], and is consistent with the previously determined value for equilibrium with the mantle. The narrow range
of measured δ18O values is predicted for zircon crystallization from variable parent melt compositions and temperatures in a closed system,
and provides no indication of any interactions between altered rocks or seawater and the evolved parent melts. If plagiogranite
forms by hydrous partial melting, the uniform mantle-like δ18O(Zrc) requires melting and zircon crystallization prior to significant amounts of water–rock interactions that alter the
protolith δ18O. Zircons from ocean crust have been proposed as a tectonic analog for >3.9 Ga detrital zircons from the earliest (Hadean)
Earth by multiple workers. However, zircons from ocean crust are readily distinguished geochemically from zircons formed in
continental crustal environments. Many of the >3.9 Ga zircons have mildly elevated δ18O (6.0–7.5‰), but such values have not been identified in any zircons from the large sample suite examined here. The difference
in δ18O, in combination with newly acquired lithium concentrations and published trace element data, clearly shows that the >3.9 Ga
detrital zircons did not originate by processes analogous to those in modern mid-ocean ridge settings. 相似文献
2.
Li isotopes and trace elements as a petrogenetic tracer in zircon: insights from Archean TTGs and sanukitoids 总被引:1,自引:0,他引:1
Anne-Sophie Bouvier Takayuki Ushikubo Noriko T. Kita Aaron J. Cavosie Reinhard Kozdon John W. Valley 《Contributions to Mineralogy and Petrology》2012,163(5):745-768
We report δ7Li, Li abundance ([Li]), and other trace elements measured by ion probe in igneous zircons from TTG (tonalite, trondhjemite,
and granodiorite) and sanukitoid plutons from the Superior Province (Canada) in order to characterize Li in zircons from typical
Archean continental crust. These data are compared with detrital zircons from the Jack Hills (Western Australia) with U–Pb
ages greater than 3.9 Ga for which parent rock type is not known. Most of the TTG and sanukitoid zircon domains preserve typical
igneous REE patterns and CL zoning. [Li] ranges from 0.5 to 79 ppm, typical of [Li] in continental zircons. Atomic ratios
of (Y + REE)/(Li + P) average 1.0 ± 0.7 (2SD) for zircons with magmatic composition preserved, supporting the hypothesis that
Li is interstitial and charge compensates substitution of trivalent cations. This substitution results in a relatively slow
rate of Li diffusion. The δ7Li and trace element data constrain the genesis of TTGs and sanukitoids. [Li] in zircons from granitoids is significantly
higher than from zircons in primitive magmas in oceanic crust. TTG zircons have δ7Li (3 ± 8‰) and δ18O in the range of primitive mantle-derived magmas. Sanukitoid zircons have average δ7Li (7 ± 8‰) and δ18O higher than those of TTGs supporting genesis by melting of fluid-metasomatized mantle wedge. The Li systematics in sanukitoid
and TTG zircons indicate that high [Li] in pre-3.9-Ga Jack Hills detrital zircons is a primary igneous composition and suggests
the growth in proto-continental crust in magmas similar to Archean granitoids. 相似文献
3.
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
4.
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
5.
We report the oxygen isotope composition of olivine and orthopyroxene phenocrysts in lavas from the main magma types at Mt
Shasta and Medicine Lake Volcanoes: primitive high-alumina olivine tholeiite (HAOT), basaltic andesites (BA), primitive magnesian
andesites (PMA), and dacites. The most primitive HAOT (MgO > 9 wt%) from Mt. Shasta has olivine δ18O (δ18OOl) values of 5.9–6.1‰, which are about 1‰ higher than those observed in olivine from normal mantle-derived magmas. In contrast,
HAOT lavas from Medicine Lake have δ18OOl values ranging from 4.7 to 5.5‰, which are similar to or lower than values for olivine in equilibrium with mantle-derived
magmas. Other magma types from both volcanoes show intermediate δ18OOl values. The oxygen isotope composition of the most magnesian lavas cannot be explained by crustal contamination and the trace
element composition of olivine phenocrysts precludes a pyroxenitic mantle source. Therefore, the high and variable δ18OOl signature of the most magnesian samples studied (HAOT and BA) comes from the peridotitic mantle wedge itself. As HAOT magma
is generated by anhydrous adiabatic partial melting of the shallow mantle, its 1.4‰ range in δ18OOl reflects a heterogeneous composition of the shallow mantle source that has been influenced by subduction fluids and/or melts
sometime in the past. Magmas generated in the mantle wedge by flux melting due to modern subduction fluids, as exemplified
by BA and probably PMA, display more homogeneous composition with only 0.5‰ variation. The high-δ18O values observed in magnesian lavas, and principally in the HAOT, are difficult to explain by a single-stage flux-melting
process in the mantle wedge above the modern subduction zone and require a mantle source enriched in 18O. It is here explained by flow of older, pre-enriched portions of the mantle through the slab window beneath the South Cascades. 相似文献
6.
John W. Valley Peter D. Kinny Daniel J. Schulze Michael J. Spicuzza 《Contributions to Mineralogy and Petrology》1998,133(1-2):1-11
The oxygen isotope ratios of Phanerozoic zircons from kimberlite pipes in the Kaapvaal Craton of southern Africa and the
Siberian Platform vary from 4.7 to 5.9‰ VSMOW. High precision, accurate analyses by laser reveal subtle pipe-to-pipe differences
not previously suspected. These zircons have distinctive chemical and physical characteristics identifying them as mantle-derived
megacrysts similar to zircons found associated with diamond, coesite, MARID xenoliths, Cr-diopside, K-richterite, or Mg-rich
ilmenite. Several lines of evidence indicate that these 18O values are unaltered by kimberlite magmas during eruption and represent compositions preserved since crystallization in
the mantle, including: U/Pb age, large crystal size, and the slow rate of oxygen exchange in non-metamict zircon. The average
18O of mantle zircons is 5.3‰, ∼0.1 higher and in equilibrium with values for olivine in peridotite xenoliths and oceanic basalts.
Zircon megacrysts from within 250 km of Kimberley, South Africa have average 18O=5.32±0.17 (n=28). Small, but significant, differences among other kimberlite pipes or groups of pipes may indicate isotopically distinct
reservoirs in the sub-continental lithosphere or asthenosphere, some of which are anomalous with respect to normal mantle
values of 5.3±0.3. Precambrian zircons (2.1–2.7 Ga) from Jwaneng, Botswana have the lowest values yet measured in a mantle
zircon, 18O=3.4 to 4.7‰. These zircon megacrysts originally crystallized in mafic or ultramafic rocks either through melting and metasomatism
associated with kimberlite magmatism or during metamorphism. The low 18O zircons are best explained by subduction of late Archean ocean crust that exchanged with heated seawater prior to underplating
as eclogite and to associated metasomatism of the mantle wedge. Smaller differences among other pipes and districts may result
from variable temperatures of equilibration, mafic versus ultramafic hosts, or variable underplating. The narrow range in
zircon compositions found in most pipes suggests magmatic homogenization. If this is correct, these zircons document the existence
of significant quantities of magma in the sub-continental mantle that was regionally variable in 18O and this information restricts theories about the nature of ancient subduction.
Received: 8 August 1997 / Accepted: 6 May 1998 相似文献
7.
Multiple origins of zircons in jadeitite 总被引:1,自引:1,他引:0
Bin Fu John W. Valley Noriko T. Kita Michael J. Spicuzza Chad Paton Tatsuki Tsujimori Michael Bröcker George E. Harlow 《Contributions to Mineralogy and Petrology》2010,159(6):769-780
Jadeitites form from hydrothermal fluids during high pressure metamorphism in subduction environments; however, the origin
of zircons in jadeitite is uncertain. We report ion microprobe analyses of δ18O and Ti in zircons, and bulk δ18O data for the jadeitite whole-rock from four terranes: Osayama serpentinite mélange, Japan; Syros mélange, Greece; the Motagua
Fault zone, Guatemala; and the Franciscan Complex, California. In the Osayama jadeitite, two texturally contrasting groups
of zircons are identified by cathodoluminescence and are distinct in δ18O: featureless or weakly zoned zircons with δ18O = 3.8 ± 0.6‰ (2 SD, VSMOW), and zircons with oscillatory or patchy zoning with higher δ18O = 5.0 ± 0.4‰. Zircons in phengite jadeitite from Guatemala and a jadeitite block from Syros have similar δ18O values to the latter from Osayama: Guatemala zircons are 4.8 ± 0.7‰, and the Syros zircons are 5.2 ± 0.5‰ in jadeitite and
5.2 ± 0.4‰ in associated omphacitite, glaucophanite and chlorite-actinolite rinds. The δ18O values for most zircons above fall within the range measured by ion microprobe in igneous zircons from oxide gabbros and
plagiogranites in modern ocean crust (5.3 ± 0.8‰) and measured in bulk by laser fluorination of zircons in equilibrium with
primitive magma compositions or the mantle (5.3 ± 0.6‰). Titanium concentrations in these zircons vary between 1 and 19 ppm,
within the range for igneous zircons worldwide. Values of δ18O (whole-rock) ≅ δ18O (jadeite) and vary from 6.3 to 10.1‰ in jadeitites in all four areas. 相似文献
8.
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
9.
Sara Auer Ilya Bindeman Paul Wallace Vera Ponomareva Maxim Portnyagin 《Contributions to Mineralogy and Petrology》2009,157(2):209-230
Klyuchevskoy volcano, in Kamchatka’s subduction zone, is one of the most active arc volcanoes in the world and contains some
of the highest δ18O values for olivines and basalts. We present an oxygen isotope and melt inclusion study of olivine phenocrysts in conjunction
with major and trace element analyses of 14C- and tephrochronologically-dated tephra layers and lavas spanning the eruptive history of Klyuchevskoy. Whole-rock and groundmass
analyses of tephra layers and lava samples demonstrate that both high-Mg (7–12.5 wt% MgO) and high-Al (17–19 wt% Al2O3, 3–6.5 wt% MgO) basalt and basaltic andesite erupted coevally from the central vent and flank cones. Individual and bulk
olivine δ18O range from normal MORB values of 5.1‰ to values as high as 7.6‰. Likewise, tephra and lava matrix glass have high-δ18O values of 5.8–8.1‰. High-Al basalts dominate volumetrically in Klyuchevskoy’s volcanic record and are mostly high in δ18O. High-δ18O olivines and more normal-δ18O olivines occur in both high-Mg and high-Al samples. Most olivines in either high-Al or high-Mg basalts are not in oxygen
isotopic equilibrium with their host glasses, and Δ18Oolivine–glass values are out of equilibrium by up to 1.5‰. Olivines are also out of Fe–Mg equilibrium with the host glasses, but to a lesser
extent. Water concentrations in olivine-hosted melt inclusions from five tephra samples range from 0.4 to 7.1 wt%. Melt inclusion
CO2 concentrations vary from below detection (<50 ppm) to 1,900 ppm. These values indicate depths of crystallization up to ~17
km (5 kbar). The variable H2O and CO2 concentrations likely reflect crystallization of olivine and entrapment of inclusions in ascending and degassing magma. Oxygen
isotope and Fe–Mg disequilibria together with melt inclusion data indicate that olivine was mixed and recycled between high-Al
and high-Mg basaltic melts and cumulates, and Fe–Mg and δ18O re-equilibration processes were incomplete. Major and trace elements in the variably high-δ18O olivines suggest a peridotite source for the parental magmas. Voluminous, highest in the world with respect to δ18O, and hydrous basic volcanism in Klyuchevskoy and other Central Kamchatka depression volcanoes is explained by a model in
which the ascending primitive melts that resulted from the hydrous melt fluxing of mantle wedge peridotite, interacted with
the shallow high-δ18O lithospheric mantle that had been extensively hydrated during earlier times when it was part of the Kamchatka forearc. Following
accretion of the Eastern Peninsula terrains several million years ago, a trench jump eastward caused the old forearc mantle
to be beneath the presently active arc. Variable interaction of ascending flux-melting-derived melts with this older, high-δ18O lithospheric mantle has produced mafic parental magmas with a spectrum of δ18O values. Differentiation of the higher δ18O parental magmas has created the volumetrically dominant high-Al basalt series. Both basalt types incessantly rise and mix
between themselves and with variable in δ18O cumulates within dynamic Klyuchevskoy magma plumbing system, causing biannual eruptions and heterogeneous magma products.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
10.
Alluvial and colluvial gem sapphires are common in the basaltic fields of the French Massif Central (FMC) but sapphire-bearing
xenoliths are very rare, found only in the Menet trachytic cone in Cantal. The O-isotope composition of the sapphires ranges
between 4.4 and 13.9‰. Two distinct groups have been defined: the first with a restricted isotopic range between 4.4 and 6.8‰
(n = 22; mean δ18O = 5.6 ± 0.7‰), falls within the worldwide range defined for blue-green-yellow sapphires related to basaltic gem fields (3.0 < δ18O < 8.2‰, n = 150), and overlaps the ranges defined for magmatic sapphires in syenite (4.4 < δ18O < 8.3‰, n = 29). A second group, with an isotopic range between 7.6 and 13.9‰ (n = 9), suggests a metamorphic sapphire source such as biotite schist in gneisses or skarns. The δ18O values of 4.4–4.5‰ for the blue sapphire-bearing anorthoclasite xenolith from Menet is lower than the δ18O values obtained for anorthoclase (7.7–7.9‰), but suggest that these sapphires were derived from an igneous reservoir in
the subcontinental spinel lherzolitic mantle of the FMC. The presence of inclusions of columbite-group minerals, pyrochlore,
Nb-bearing rutile, and thorite in these sapphires provides an additional argument for a magmatic origin. In the FMC lithospheric
mantle, felsic melts crystallized to form anorthoclasites, the most evolved peraluminous variant of the alkaline basaltic
melt. The O-isotopic compositions of the first group suggests that these sapphires crystallized from felsic magmas under upper
mantle conditions. The second group of isotopic values, typified for example by the Le Bras sapphire with a δ18O of 13.9‰, indicates that metamorphic sapphires from granulites were transported to the surface by basaltic magma. 相似文献
11.
Ilya N. Bindeman Axel K. Schmitt John W. Valley 《Contributions to Mineralogy and Petrology》2006,152(6):649-665
Large volumes of silicic magma were produced on a very short timescale in the nested caldera complex of the SW Nevada volcanic field (SWNVF). Voluminous ash flows erupted in two paired events: Topopah Spring (TS, >1,200 km3, 12.8 Ma)–Tiva Canyon (TC, 1,000 km3, 12.7 Ma) and Rainier Mesa (RM, 1,200 km3, 11.6 Ma)–Ammonia Tanks (AT, 900 km3, 11.45 Ma; all cited ages are previously published 40Ar/39Ar sanidine ages). Within each pair, eruptions are separated by only 0.1–0.15 My and produced tuffs with contrasting isotopic values. These events represent nearly complete evacuation of sheet-like magma chambers formed in the extensional Basin and Range environment. We present ion microprobe ages from zircons in the zoned ash-flow sheets of TS, TC, RM, and AT in conjunction with δ18O values of zircons and other phenocrysts, which differ dramatically among subsequently erupted units. Bulk zircons in the low-δ18O AT cycle were earlier determined to exhibit ∼1.5‰ core-to-rim oxygen isotope zoning; and high-spatial resolution zircon analyses by ion microprobe reveal the presence of older grains that are zoned by 0.5–2.5‰. The following U–Pb isochron ages were calculated after correcting for the initial U–Pb disequilibria: AT (zircon rims: 11.7 ± 0.2 Ma; cores: 12.0 ± 0.1 Ma); pre-AT rhyolite lava: (12.0 ± 0.3 Ma); RM: 12.4 ± 0.3); TC: (13.2 ± 0.15 Ma); TS: (13.5 ± 0.2). Average zircon crystallization ages calculated from weighted regression or cumulative averaging are older than the Ar–Ar stratigraphy, but preserve the comparably short time gaps within each of two major eruption cycles (TS/TC, RM/AT). Notably, every sample yields average zircon ages that are 0.70–0.35 Ma older than the respective Ar–Ar eruption ages. The Th/U ratio of SWNVF zircons are 0.4–4.7, higher than typically found in igneous zircons, which correlates with elevated Th/U of the whole rocks (5–16). High Th/U could be explained if uranium was preferentially removed by hydrothermal solutions or is retained in the protolith during partial melting. For low-δ18O AT-cycle magmas, rim ages from unpolished zircons overlap within analytical uncertainties with the 40Ar/39Ar eruption age compared to core ages that are on average ∼0.2–0.3 My older than even the age of the preceding caldera forming eruption of RM tuff. This age difference, the core-to-rim oxygen isotope zoning in AT zircons, and disequilibrium quartz–zircon and melt-zircon isotopic fractionations suggest that AT magma recycled older zircons derived from the RM and older eruptive cycles. These results suggest that the low-δ18O AT magmas were generated by melting a hydrothermally-altered protolith from the same nested complex that erupted high-δ18O magmas of the RM cycle only 0.15 My prior to the eruption of the AT, the largest volume low-δ18O magma presently known.Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. 相似文献
12.
M. A. Semikhatov A. B. Kuznetsov A. V. Maslov I. M. Gorokhov G. V. Ovchinnikova 《Stratigraphy and Geological Correlation》2009,17(6):574-601
The main objective of this work is the generalization of lithostratigraphic, biostratigraphic and isotopic-geochronological
data characterizing carbonate rocks from type succession of the broadly acknowledged chronostratigraphic subdivision of the
Lower Riphean, such as the Burzyan Group of the Southern Urals and its analogs. Using an original approach to investigation
of the Rb-Sr and Pb-Pb isotopic systems in carbonates and strict criteria of their retentivity, we studied the least altered
(“best”) samples of the Burzyan carbonates, which retain the 87Sr/86Sr ratio of the sedimentation environment. As long ago as 1550 ± 30 and 1430 ± 30 Ma, that ratio corresponded to 0.70460–0.70480
and 0.70456–0.70481. The results confirm the influx of the mantle material predominantly into the World Ocean of the Early
Riphean. The influence of meteoric diagenesis was likely responsible for local declines of δ18O in the Burzyan carbonates down to the values of −2.5 to −1.5‰ V-PDB. In the “best” samples, this parameter ranges from −0.7
to 0‰, which is consistent with the assumption that δ18O values (0 ± 1‰) characterized the stasis of the carbonate carbon isotopic composition in oceanic water 2.06–1.25 Ga ago.
C-isotopic data on carbonate from the Paleoproterozoic-Lower Riphean boundary formations of the Urals, India, North America
and Siberia suggest that the mentioned stasis ended by the commencement of the Early Riphean ca. 1.6–1.5 Ga ago. In the least
altered carbonates of the Early Riphean, the δ18O variation range corresponds to 4.0–4.5‰. 相似文献
13.
A. Roy A. Sarkar S. Jeyakumar S. K. Aggrawal M. Ebihara H. Satoh 《Journal of Earth System Science》2004,113(4):649-665
Trace, rare earth elements (REE), Rb-Sr, Sm-Nd and O isotope studies have been carried out on ultramafic (harzburgite and
lherzolite) dykes belonging to the newer dolerite dyke swarms of eastern Indian craton. The dyke swarms were earlier considered
to be the youngest mafic magmatic activity in this region having ages not older than middle to late Proterozoic. The study
indicates that the ultramafic members of these swarms are in fact of late Archaean age (Rb-Sr isochron age 2613 ± 177 Ma,
Sri ∼ 0.702 ± 0.004) which attests that out of all the cratonic blocks of India, eastern Indian craton experienced earliest
stabilization event. Primitive mantle normalized trace element plots of these dykes display enrichment in large ion lithophile
elements (LILE), pronounced Ba, Nb and Sr depletions but very high concentrations of Cr and Ni. Chondrite normalised REE plots
exhibit light REE (LREE) enrichment with nearly flat heavy REE (HREE; (ΣHREE)N ∼ 2–3 times chondrite, (Gd/Yb)N ∼ 1). The εNd(t) values vary from +1.23 to -3.27 whereas δ18O values vary from +3.16‰ to +5.29‰ (average +3.97‰±0.75‰) which is lighter than the average mantle value. Isotopic, trace
and REE data together indicate that during 2.6 Ga the nearly primitive mantle below the eastern Indian Craton was metasomatised
by the fluid (± silicate melt) coming out from the subducting early crust resulting in LILE and LREE enriched, Nb depleted,
variable εNd, low Sri(0.702) and low δ18O bearing EMI type mantle. Magmatic blobs of this metasomatised mantle were subsequently emplaced in deeper levels of the
granitic crust which possibly originated due to the same thermal pulse. 相似文献
14.
Whole rock oxygen isotope data are presented for the Panorama district, in the Archean Pilbara Craton of Western Australia,
where near-perfect exposure reveals a cross section through a complete volcanogenic massive sulfide (VMS) hydrothermal alteration
system. The δ18O values decrease with depth in the volcanic pile, across semi-conformable alteration zones, to values below 6‰ immediately
above a large (180 km2) subvolcanic intrusion. Altered rocks in the upper parts of the subvolcanic intrusion have lower δ18O values (6–8‰) than least altered granite (8‰), apart from sericite–quartz altered zones, which are slightly higher (8–10‰).
Corridors of low δ18O values crosscut this regional zonation, and are coincident with transgressive feldspar-destructive alteration zones, which
underlie VMS mineralization. The whole rock oxygen isotope distribution patterns are interpreted to represent alteration temperature,
where high δ18O values correspond to low temperature alteration and low δ18O values correspond to high temperature alteration. Alteration temperatures, which were calculated using modal alteration
mineral abundances and an assumed fluid δ18O, are consistent with this interpretation. Increasing temperatures with depth in the volcanic pile and high temperatures
in transgressive corridors leading up to VMS deposits, are consistent with a convective hydrothermal model, in which heat
from the subvolcanic intrusion drove seawater through the volcanic pile. Granite-hosted sericite–quartz alteration zones are
18O-enriched, and are tentatively interpreted to have formed from a mixed magmatic-evolved seawater fluid.
Received: 12 April 1999 / Accepted: 6 April 2000 相似文献
15.
James M. D. Day Colin G. Macpherson David Lowry D. Graham Pearson 《Contributions to Mineralogy and Petrology》2012,164(1):177-183
Gurenko et al. (Contrib Mineral Petrol 162:349–363, 2011) report laser-assisted fluorination (LF) and secondary ionization mass spectrometry (SIMS) 18O/16O datasets for olivine grains from the Canary Islands of Gran Canaria, Tenerife, La Gomera, La Palma and El Hierro. As with prior studies of oxygen isotopes in Canary Island lavas (e.g. Thirlwall et al. Chem Geol 135:233–262, 1997; Day et al. Geology 37:555–558, 2009, Geochim Cosmochim Acta 74:6565–6589, 2010), these authors find variations in δ18Ool (~4.6–6.0 ‰) beyond that measured for mantle peridotite olivine (Mattey et al. Earth Planet Sci Lett 128:231–241, 1994) and interpret this variation to reflect contributions from pyroxenite-peridotite mantle sources. Furthermore, Gurenko et al. (Contrib Mineral Petrol 162:349–363, 2011) speculate that δ18Ool values for La Palma olivine grains measured by LF (Day et al. Geology 37:555–558, 2009, Geochim Cosmochim Acta 74:6565–6589, 2010) may be biased to low values due to the presence of altered silicate, possibly serpentine. The range in δ18Ool values for Canary Island lavas are of importance for constraining their origin. Gurenko et al. (Contrib Mineral Petrol 162:349–363, 2011) took a subset (39 SIMS analyses from 13 grains from a single El Hierro lava; EH4) of a more extensive dataset (321 SIMS analyses from 110 grains from 16 Canary Island lavas) to suggest that δ18Ool is weakly correlated (R 2 = 0.291) with the parameter used by Gurenko et al. (Earth Planet Sci Lett 277:514–524, 2009) to describe the estimated weight fraction of pyroxenite-derived melt (Xpx). With this relationship, end-member δ18O values for HIMU-peridotite (δ18O = 5.3 ± 0.3 ‰) and depleted pyroxenite (δ18O = 5.9 ± 0.3 ‰) were defined. Although the model proposed by Gurenko et al. (Contrib Mineral Petrol 162:349–363, 2011) implicates similar pyroxenite-peridotite mantle sources to those proposed by Day et al. (Geology 37:555–558, 2009, Geochim Cosmochim Acta 74:6565–6589, 2010) and Day and Hilton (Earth Planet Sci Lett 305:226–234, 2011), there are significant differences in the predicted δ18O values of end member components in the two models. In particular, Day et al. (Geochim Cosmochim Acta 74:6565–6589, 2010) proposed a mantle source for La Palma lavas with low-δ18O (<5 ‰), rather than higher-δ18O (c.f. the HIMU-peridotite composition of Gurenko et al. in Contrib Mineral Petrol 162:349–363, 2011). Here we question the approach of using weakly correlated variations in δ18Ool and the Xpx parameter to define mantle source oxygen isotope compositions, and provide examples of why this approach appears flawed. We also provide reasons why the LF datasets previously published for Canary Island lavas remain robust and discuss why LF and SIMS data may provide complementary information on oxygen isotope variations in ocean island basalts (OIB), despite unresolved small-scale uncertainties associated with both techniques. 相似文献
16.
Edward M. Ripley Nur Iskandar Taib Chusi Li Craig H. Moore 《Contributions to Mineralogy and Petrology》2007,154(1):35-54
Copper–nickel sulfide mineralization in the Partridge River Intrusion of the 1.1 Ga Duluth Complex is restricted primarily
to a 100 m thick zone near the base of the intrusion, which is heterogeneous at meter scales in terms of both sulfide contents
and rock types, which include dunite, melatroctolite, troctolite, leucotroctolite, gabbro, olivine gabbro, gabbronorite, and
rare norite. Olivine-rich troctolites and melatroctolites appear to have required mineral accumulation on a substrate, whereas
augite troctolite and gabbros are thought to have formed via in situ crystallization of magmas ranging in composition from
high-Al olivine tholeiite to high-Ti tholeiite. δ18O values of orthopyroxene-poor rocks in the Partridge River Intrusion range from 5.2 to 6.7‰. δ18O values of 6.7‰ are consistent with less than 20% contamination by high-18O metasedimentary country rock, either via devolatilization or local partial melting. Rocks with greater than ∼15% orthopyroxene,
gabbronorites, and norites, are characterized by δ18O values in excess of 6.9‰, and required the assimilation of larger amounts of siliceous country rocks. Sulfur isotopic values
in leucotroctolitic rocks that contain less than ∼400 ppm S and that overlie the basal zone range between −1.5 and 2‰, values
that are consistent with those of mantle-derived sulfur. In contrast, δ34S values in the basal zone range from −1.4 to 10.5‰, where the 34S-enriched samples require an input of sulfur from metasedimentary country rocks. δ34S values of the rocks in the basal zone correlate with variations in olivine Fo content but not with S abundance. The wide
range in δ34S values of rocks in the basal zone strongly suggests that magmas interacted with layers in the sedimentary country rocks
that were themselves characterized by variable sulfide contents and δ34S values. The S isotopic data suggest that the heterogeneity observed in the basal zone results from the emplacement of relatively
thin sheets of compositionally distinct magma. All rock types present in the basal zone can be produced as a result of variable
degrees of fractionation of a parental high-Al olivine tholeiite, followed by varying degrees of contamination of derivative
liquids by country rocks. The S-contamination process was essential for the development of Cu–Ni mineralization, and was restricted
to the earliest stages in the development of the Duluth Complex at a time when volatile species such as S and H2O, and low-T partial melts of country rocks, were available to magmas.
Electronic supplementary material The online version of this article (doi: ) contains supplementary material, which is available to authorized users. 相似文献
17.
R. Altherr U. Henes-Klaiber E. Hegner M. Satir C. Langer 《International Journal of Earth Sciences》1999,88(3):422-443
Latest Devonian to early Carboniferous plutonic rocks from the Odenwald accretionary complex reflect the transition from
a subduction to a collisional setting. For ∼362 Ma old gabbroic rocks from the northern tectonometamorphic unit I, initial
isotopic compositions (εNd=+3.4 to +3.8;87Sr/86Sr =0.7035–0.7053;δ18O=6.8–8.0‰) and chemical signatures (e.g., low Nb/Th, Nb/U, Ce/Pb, Th/U, Rb/Cs) indicate a subduction-related origin by partial
melting of a shallow depleted mantle source metasomatized by water-rich, large ion lithophile element-loaded fluids. In the
central (unit II) and southern (unit III) Odenwald, syncollisional mafic to felsic granitoids were emplaced in a transtensional
setting at approximately 340–335 Ma B.P. Unit II comprises a mafic and a felsic suite that are genetically unrelated. Both
suites are intermediate between the medium-K and high-K series and have similar initial Nd and Sr signatures (εNd=0.0 to –2.5;87Sr/86Sr=0.7044–0.7056) but different oxygen isotopic compositions (δ18O=7.3–8.7‰ in mafic vs 9.3–9.5‰ in felsic rocks). These characteristics, in conjunction with the chemical signatures, suggest
an enriched mantle source for the mafic magmas and a shallow metaluminous crustal source for the felsic magmas. Younger intrusives
of unit II have higher Sr/Y, Zr/Y, and Tb/Yb ratios suggesting magma segregation at greater depths. Mafic high-K to shoshonitic
intrusives of the southern unit III have initial isotopic compositions (εNd=–1.1 to –1.8;87Sr/86Sr =0.7054–0.7062;δ18O=7.2–7.6‰) and chemical characteristics (e.g., high Sr/Y, Zr/Y, Tb/Yb) that are strongly indicative of a deep-seated enriched
mantle source. Spatially associated felsic high-K to shoshonitic rocks of unit III may be derived by dehydration melting of
garnet-rich metaluminous crustal source rocks or may represent hybrid magmas.
Received: 7 December 1998 / Accepted: 27 April 1999 相似文献
18.
Chris Harris H. Stuart Smith Anton P. le Roex 《Contributions to Mineralogy and Petrology》2000,138(2):164-175
We have measured the δ18O values of the major phenocrysts (olivine, clinopyroxene and plagioclase) present in lavas from Tristan da Cunha and Gough
Island. These islands, which result from the same mantle plume, have enriched radiogenic isotope ratios and are, therefore,
prime candidates for an oxygen isotope signature that is distinct from that of MORB. Consistent differences between the δ18O values of olivine, pyroxene and feldspar in the Gough lavas show that the phenocrysts in the mafic Gough Island lavas are
in oxygen isotope equilibrium. The olivines in lavas with SiO2 <50 wt% have a mean δ18O value of 5.19‰, consistent with crystallization from a magma having the same oxygen isotope composition as MORB. Phenocrysts
in all the Gough lavas show a systematic increase in δ18O value as silica content increases, which is consistent with closed-system fractional crystallization. The lack of enrichment
in δ18O of the Gough magmas suggests that the mantle source contained <2% recycled sediment. In contrast, the Tristan lavas with
SiO2 >48 wt% contain phenocrysts which have δ18O values that are systematically ∼0.3‰ lower than their counterparts from Gough. We suggest that the parental mafic Tristan
magmas were contaminated by material from the volcanic edifice that acquired low δ18O values by interaction with water at high temperatures. The highly porphyritic SiO2-poor lavas show a negative correlation between olivine δ18O value and whole-rock silica content rather than the expected positive correlation. The minimum δ18O value occurs at an SiO2 content of about 45 wt%. Below 45 wt% SiO2, magmas evolved via a combination of assimilation, fractionational crystallization and crystal accumulation; above 45 wt%
SiO2, magmas appeared to have evolved via closed-system fractional crystallization.
Received: 23 November 1998 / Accepted: 27 September 1999 相似文献
19.
Y. Be’eri-Shlevin Y. Katzir J. Blichert-Toft I. C. Kleinhanns M. J. Whitehouse 《Contributions to Mineralogy and Petrology》2010,160(2):181-201
Multi-isotope study including whole-rock Nd–Sr, single zircon Hf, and SIMS δ18O analyses of zircons sheds light on magma sources in the northernmost Arabian–Nubian Shield (ANS) during ~820–570 Ma. Reconnaissance
initial Nd and Sr isotope data for the older rocks (~820–740 Ma) reaffirms previous estimates that early crustal evolution
in this part of the shield involved some crustal contamination by pre-ANS material. Prominent isotope provinciality is displayed
by post-collisional calc-alkaline and alkaline igneous rocks of ~635–570 Ma across a NW-SE transect across basement of the
Sinai Peninsula (Egypt) and southern Israel. Silicic rocks of the NW-region are characterized by lower εNd(T)–εHf(T) and higher
Sri and δ18O compared with rocks of the SE-region, and the transition between the regions is gradual. Within each region isotope ratios
are independent of the extent of magma fractionation, and zircon cores and rims yield similar δ18O values. Comparison with southern segments of the ANS shows that the source for most ~635–570 Ma rocks can be modeled as
the isotopically aged lower-intermediate crust in the ANS core (SE-region) and its northern, more contaminated ANS margins
(NW-region). Nevertheless, Nd–Sr isotope enrichment of the lithospheric mantle is indicated by some basic magmas of the NW-region
displaying the most enriched Nd–Sr isotope compositions. Comparison of Nd and Hf depleted mantle model ages for rocks of the
SE-region may indicate that crustal formation events in the ANS geographical core took place at 1.1–1.2 Ga and were followed
by crustal differentiation starting at ~0.9 Ga. 相似文献
20.
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