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1.
Stefanie S. Schmidberger Ernst Hegner 《Contributions to Mineralogy and Petrology》1999,135(4):373-385
Late Carboniferous (300–290 Ma) calc-alkaline basalts, andesites, and rhyolites typical of volcanic arc settings occur in
the intermontane Saar-Nahe basin (SW Germany) within the Variscan orogenic belt. The volcanic rock suite was emplaced under
a regime of tensional tectonics during orogenic collapse and its origin has been explained by melting of mantle and crust
in the course of limited lithospheric rifting. We report major, trace and rare-earth-element data (REE), and Nd-Pb-Sr-O isotope
ratios for a representative sample suite, which are fully consistent with an origin closely related to plate subduction. Major
and trace element data define continuous melt differentiation trends from a precursor basaltic magma involving fractional
crystallization of olivine, pyroxene, plagioclase, and magnetite typical of magma evolution in a volcanic arc. This finding
precludes an origin of the andesitic compositions by mixing of mafic and felsic melts as can be expected in anorogenic settings.
The mafic samples have high Mg numbers (Mg# = 65–73), and high Cr (up to 330 ppm) and Ni (up to 200 ppm) contents indicating
derivation from a primitive parental melt that was formed in equilibrium with mantle peridotite. We interpret the geochemical
characteristics of the near-primary basalts as reflecting their mantle source. The volcanic rocks are characterized by enrichment
in the large ion lithophile elements (LILE), negative Nb and Ti, and positive Pb anomalies relative to the neighboring REE,
suggesting melting of a subduction-modified mantle. Initial Nd values of −0.7 to −4.6, Pb, and 87Sr/86Sr(t) isotope ratios for mafic and felsic volcanics are similar and indicate partial melting of an isotopically heterogeneous and
enriched mantle reservoir. The enrichment in incompatible trace elements and radiogenic isotopes of a precursor depleted mantle
may be attributed to addition of an old sedimentary component. The geochemical characteristics of the Saar-Nahe volcanic rocks
are distinct from typical post-collisional rock suites and they may be interpreted as geochemical evidence for ongoing plate
subduction at the margin of the Variscan orogenic belt not obvious from the regional geologic context.
Received: 3 August 1998 / Accepted: 2 January 1999 相似文献
2.
The Abbott Unit (∼508 Ma) and the Vegetation Unit (∼475 Ma) of the Terra Nova Intrusive Complex (northern Victoria Land,
Antarctica) represent the latest magmatic events related to the Early Paleozoic Ross Orogeny. They show different emplacement
styles and depths, ranging from forcible at 0.4–0.5 GPa for the Abbott Unit to passive at ∼0.2 GPa for the Vegetation Unit.
Both units consist of mafic, felsic and intermediate facies which collectively define continuous chemical trends. The most
mafic rocks from both units show different enrichment in trace element and Sr-Nd isotopic signatures. Once the possible effects
of upper crustal assimilation-fractional crystallisation (AFC) and lower crustal coupled AFC and magma refilling processes
have been taken into account the following features are recognised: (1) the modelled primary Abbott Unit magma shows a slightly
enriched incompatible element distribution, similar to common continental arc basalts and (2) the modelled primary Vegetation
Unit magma displays highly enriched isotope ratios and incompatible element patterns. We interpreted these major changes in
magmatic affinity and emplacement style as linked to a major change in the tectonic setting affecting melt generation, rise
and emplacement of the magmas. The Abbott Unit mafic melts were derived from a mantle wedge above a subduction zone, with
subcontinental lithospheric mantle marginally involved in the melting column. The Vegetation Unit mafic melts are regarded
as products of a different source involving an old layer of subcontinental lithospheric mantle. The crustal evolution of both
types of mafic melts is marked by significant compositional contrasts in Sr and Nd isotopes between mafic and associated felsic
rocks. The crustal isotope signature showed an increase with felsic character. Geochemical variations for both units can be
accounted for by a similar two-stage hybridisation process. In the first stage, the most mafic magma evolved mainly by fractional
crystallisation coupled with assimilation of metasedimentary rocks having crustal time-integrated Sr and Nd compositions similar
to those of locally exposed metamorphic basement. The second stage involves contaminated products mixing with independently
generated crustal melts. Petrographic, geochemical and isotope data also provide evidence of significant compositional differences
in the felsic end-members, pointing to the involvement of metaigneous and metasedimentary source rocks for the Abbott granite
and Vegetation leucogranite, respectively.
Received: 31 March 1998 / Accepted: 3 May 1999 相似文献
3.
Geochemical variation within the northern Ryukyu Arc: magma source compositions and geodynamic implications 总被引:7,自引:0,他引:7
Ryuichi Shinjo Jon D. Woodhead Janet M. Hergt 《Contributions to Mineralogy and Petrology》2000,140(3):263-282
The major and trace element and Pb–Sr–Nd isotopic compositions of Quaternary mafic lavas from the northern Ryukyu arc provide
insights into the nature of the mantle wedge and its tectonic evolution. Beneath the volcanic front in the northern part of
the arc, the subducted slab of the Philippine Sea Plate bends sharply and steepens at a depth of ∼80 km. Lavas from the volcanic
front have high abundances of large ion lithophile elements and light rare earth elements relative to the high field strength
elements, consistent with the result of fluid enrichment processes related to dehydration of the subducting slab. New Pb isotopic
data identify two distinct asthenospheric domains in the mantle wedge beneath the south Kyushu and northern Ryukyu arc, which,
in a parallel with data from the Lau Basin, appear to reflect mantle with affinities to Indian and Pacific-type mid-ocean
ridge basalt (MORB). Indian Ocean MORB-type mantle, contaminated with subducted Ryukyu sediments can account for the variation
of lavas erupted on south Kyushu, and probably in the middle Okinawa Trough. In contrast, magmas of the northern Ryukyu volcanic
front appear to be derived from sources of Pacific MORB-type mantle contaminated with a sedimentary component. Along-arc variation
in the northern Ryukyus reflects increasing involvement of a sedimentary component to the south. Compositions of alkalic basalts
from the south Kyushu back-arc resemble intraplate-type basalts erupted in NW Kyushu since ∼12 Ma. We propose that the bending
of the subducted slab was either caused by or resulted in lateral migration of asthenospheric mantle, yielding Indian Ocean-type
characteristics from a mantle upwelling zone beneath NW Kyushu and the East China Sea. This model also accounts for (1) extensional
counter-clockwise crustal rotation (∼4–2 Ma), (2) voluminous andesite volcanism (∼2 Ma), and (3) the recent distinctive felsic
magmatism in the south Kyushu region.
Received: 30 November 1999 / Accepted: 20 July 2000 相似文献
4.
The aim of this study is to quantify the crustal differentiation processes and sources responsible for the origin of basaltic
to dacitic volcanic rocks present on Cordón El Guadal in the Tatara-San Pedro Complex (TSPC). This suite is important for
understanding the origin of evolved magmas in the southern Andes because it exhibits the widest compositional range of any
unconformity-bound sequence of lavas in the TSPC. Major element, trace element, and Sr-isotopic data for the Guadal volcanic
rocks provide evidence for complex crustal magmatic histories involving up to six differentiation mechanisms. The petrogenetic
processes for andesitic and dacitic lavas containing undercooled inclusions of basaltic andesitic and andesitic magma include:
(1) assimilation of garnet-bearing, possibly mafic lower continental crust by primary mantle-derived basaltic magmas; (2)
fractionation of olivine + clinopyroxene + Ca-rich plagioclase + Fe-oxides in present non-modal proportions from basaltic
magmas at ∼4–8 kbar to produce high-Al basalt and basaltic andesitic magmas; (3) vapor-undersaturated (i.e., P
H2O<P
TOTAL) partial melting of gabbroic crustal rocks at ∼3–7 kbar to produce dacitic magmas; (4) crystallization of plagioclase-rich
phenocryst assemblages from dacitic magmas in shallow reservoirs; (5) intrusion of basaltic andesitic magmas into shallow
reservoirs containing crystal-rich dacitic magmas and subsequent mixing to produce hybrid basaltic andesitic and andesitic
magmas; and (6)␣formation and disaggregation of undercooled basaltic andesitic and andesitic inclusions during eruption from
shallow chambers to form commingled, mafic inclusion-bearing andesitic and dacitic lavas flows. Collectively, the geochemical
and petrographic features of the Guadal volcanic rocks are interpreted to reflect the development of shallow silicic reservoirs
within a region characterized by high crustal temperatures due to focused basaltic activity and high magma supply rates. On
the periphery of the silicic system where magma supply rates and crustal temperatures were lower, cooling and crystallization
were more important than bulk crustal melting or assimilation.
Received: 2 July 1997 / Accepted: 25 November 1997 相似文献
5.
Generation of Deccan Trap magmas 总被引:1,自引:0,他引:1
Gautam Sen 《Journal of Earth System Science》2001,110(4):409-431
Deccan Trap magmas may have erupted through multiple centers, the most prominent of which may have been a shield volcano-like
structure in the Western Ghats area. The lavas are predominantly tholeiitic; alkalic mafic lavas and carbonatites are rare.
Radioisotope dating, magnetic chronology, and age constraints from paleontology indicate that although the eruption started
some 68 Ma, the bulk of lavas erupted at around 65–66 Ma. Paleomagnetic constraints indicate an uncertainty of ± 500,000 years
for peak volcanic activity at 65 m.y. in the type section of the Western Ghats. Maximum magma residence times were calculated
in this study based on growth rates of “giant plagioclase” crystals in lavas that marked the end phase of volcanic activity
of different magma chambers. These calculations suggest that the > 1.7 km thick Western Ghats section might have erupted within
a much shorter time interval of ∼ 55,000 years, implying phenomenal eruption rates that are orders of magnitude larger than
any present-day eruption rate from any tectonic environment. Other significant observations/conclusions are as follows: (1)
Deccan lavas can be grouped into stratigraphic subdivisions based on their geochemistry; (2) While some formations are relatively
uncontaminated others are strongly contaminated by the continental crust; (3) Deccan magmas were produced by 15–30% melting
of a Fe-rich lherzolitic source at ∼ 3–2 GPa; (4) Parent magmas of the relatively uncontaminated Ambenali formation had a
primitive composition with 16%MgO, 47%SiO2; (5) Deccan magmas were generated much deeper and by significantly more melting than other continental flood basalt provinces;
(6) The erupted Deccan tholeiitic lavas underwent fractionation and magma mixing at ∼ 0.2 GPa. The composition and origin
of the crust and crust/mantle boundary beneath the Deccan are discussed with respect to the influence of Deccan magmatic episode. 相似文献
6.
Melting of metasomatized subcontinental lithosphere: undersaturated mafic lavas from Rungwe,Tanzania 总被引:1,自引:0,他引:1
Tanya Furman 《Contributions to Mineralogy and Petrology》1995,122(1-2):97-115
This paper uses the geochemistry of primitive mafic lavas from the Rungwe volcanic province (southwestern Tanzania) to infer
the source mineralogy and melting history. Post-Miocene mafic lavas from Rungwe include alkali basalts, basanites, nephelinites
and picrites with up to 18.9 wt% MgO; nephelinites (>13.5% normative nepheline) are restricted to Kiejo volcano in the southern
portion of the province. Rungwe lavas differ from most Western Rift volcanics in that they are not unusually potassic (K2O/Na2O ca. 0.40). Sparsely phyric mafic lavas contain phenocrysts and xenocrysts of plagioclase (An82–90), clinopyroxene (4.5–9.5 wt% Al2O3), and olivine (Fo79–88); one basanite contains a 1 mm xenocryst of apatite included in magnesian clinopyroxene. All samples have high abundances
of incompatible elements (e.g., 0.7–2.2 wt% P2O5) and are enriched in REE relative to HFSE (Hf, Zr, Ti, Y), Cs, Ba, and K. Some incompatible element ratios are constant throughout
the Rungwe suite (e.g., Zr/Nb, Sr/Ce, K/Rb), but other ratios are extremely variable and exceed the range measured in global
Ocean Island Basalts (OIB) (e.g., Ba/Nb, Sm/Zr, La/Nb, Pb/Ce, Nb/U). The range in degree of silica saturation, and its excellent
correlation with P2O5/Al2O3, indicate that the Rungwe suite records variable degrees of melting. Variations of individual incompatible trace element
abundances in nephelinite and basanite samples suggest that the source contains metasomatic amphibole, ilmenite, apatite,
and zircon. The Rungwe suite is interpreted as a series of low-percentage melts of CO2-rich peridotite at pressures that span the garnet-spinel transition. A geochemical comparison of Rungwe samples to lavas
from other Western Rift volcanic centers requires that the source mineralogy varies along the rift axis, although each province
is underlain by metasomatized peridotite. The incompatible trace element signatures of Western Rift lavas indicate that the
source area is typically homogeneous on the scale of individual volcanoes, although lavas from each volcano reflect a range
in degree of melting. Significantly, volcanoes with distinct geochemistry are always separated by major rift faults, suggesting
that volcanic and tectonic surface features may correspond to metasomatic provinces within the subcontinental lithospheric
mantle.
Received: 30 May 1994 / Accepted: 5 April 1995 相似文献
7.
Ezz El Din Abdel Hakim Khalaf 《Arabian Journal of Geosciences》2012,5(4):663-695
Nugara volcanics are one of the northernmost outcrops of the Arabian?CNubian Shield. Two distinct volcanic successions are found in the Nugara basin: (1) old volcanic sequence composed of voluminous medium- to high-K calc-alkaline lavas and minor alkali basalt and (2) young volcanic sequence composed of subordinate tholeiitic mafic lavas. Their eruptions were punctuated by occasional volcaniclastic deposits that generated fall, flow, or reworked suites compositionally identical to the lava flows. These volcanics are a part of a post-subduction and extensional-related magmatic event in Northeastern Desert of Egypt. The volcanic rocks of the Nugara basin are characterized by strong enrichment in LILE relative to HESF, high LILE/HFSE ratios, and depletions of Nb on MORB-normalized multi-element diagrams. The geochemical features of the volcanic rocks suggest that they experienced fractional crystallization, along with mixing processes. Crustal contributions to the magma sources may also have occurred during magmatic evolution. These processes have resulted in scattered major and trace element variations with respect to increasing silica contents. The model proposed for their origin involves contrasting ascent paths and differentiation histories through crustal columns with different thermal and density gradients. The geochemical features of the most mafic samples suggest that the volcanic rocks in the region were derived from a mainly lithospheric mantle source that had been heterogeneously metasomatized by previous subduction events during convergence between the East and West Gondwanaland. The volcanic activity in the region is best explained by the delamination of lithospheric mantle slices that were heterogeneously enriched by previous subduction-related processes. 相似文献
8.
Cross-arc geochemical variations in volcanic fields in Honduras C.A.: progressive changes in source with distance from the volcanic front 总被引:1,自引:0,他引:1
Lina C. Patino Michael J. Carr Mark D. Feigenson 《Contributions to Mineralogy and Petrology》1997,129(4):341-351
A geochemical traverse across Honduras reveals the heterogeneity of the mantle underneath Central America. Alkali basalts
from Lake Yojoa (170 km behind the front) have low 87Sr/86Sr but high La/Yb, and elevated incompatible trace element abundances, consistent with derivation from a normal mid-ocean
ridge basalt source mantle via low degrees of melting. These lavas lack evidence for an enriched source thought to be intermingled
with normal mid-ocean ridge basalt source mantle beneath most of Central America. The amplitude of the subducted slab signature
decreases smoothly with distance from the volcanic front. Lavas from Zacate Grande, the area nearest to the volcanic front
(17 km behind the arc), display large ion lithophile element enrichment and high field strength element depletion indicating
the involvement of subducted material in magma genesis. Components of subducted material are not evident in lavas from Lake
Yojoa, the area furthest from the arc. Basalts and basaltic andesites from Tegucigalpa, 102 km behind the volcanic front,
are geochemically intermediate between those of Lake Yojoa and Zacate Grande. The lavas from Tegucigalpa show a decreased
influence of the subduction component, and are affected by assimilation-fractional crystallization processes at shallow depths.
The gradual decrease in the subducted component from the volcanic front to Zacate Grande, Tegucigalpa and finally Lake Yojoa
contrasts with the abrupt decrease documented for southeast Guatemala, the only other area in Central America where a cross-arc
transect has been studied.
Received: 1 July 1995 / Accepted: 16 July 1997 相似文献
9.
S. V. Rasskazov T. A. Yasnygina N. N. Fefelov E. V. Saranina 《Russian Journal of Pacific Geology》2010,4(1):13-40
Geochemical studies of the Middle—Late Cenozoic succession of volcanic rocks from the northern part of the Rio Grande Rift
were conducted. The initial activation of the rift structure was coeval with voluminous eruptions of lava and pyroclastic
material of mainly intermediate and acid compositions in the San Juan volcanic field 35–27 Ma. The composition of the volcanic
products after the rifting was dominated by basic and intermediate lavas. It is shown that the basanites and alkali basalts
of the territory had geochemical characteristics of sublithospheric slab and above–sl ab sources. The processes of the riftogenic
thinning of lithosphere are expressed by geochemical parameters that reflect the interaction between the liquids from the
sublithospheric mantle and the rocks from different levels of both the lithospheric mantle and lower crust. In the 35–18 Ma
interval, melts of different–depth sublithospheric and lithospheric sources erupted simultaneously in the northern part of
the rift. However, the products of interaction between the sublithospheric and lithospheric materials dominated later in the
past 15 Ma, although the sublithospheric magmatic liquids erupted at the northern structural termination of the rift within
the Yampa volcanic field at about 10 Ma. 相似文献
10.
Marjorie Wilson Aryeh E. Shimron Jeffrey M. Rosenbaum Jeremy Preston 《Contributions to Mineralogy and Petrology》2000,139(1):54-67
Early Cretaceous (146–115 Ma) magmatism in the region of Mt. Hermon, Northern Israel, is part of an extensive Mesozoic igneous
province within the Levant associated with the evolution of the Neotethyan passive margin of Gondwana. The initial stages
of activity were characterised by the emplacement of tholeiitic dykes (146–140 Ma) which were uplifted and eroded prior to
the eruption of a sequence of alkali basalts, basanites and more differentiated alkaline lavas and pyroclastics from 127 to
120 Ma. The latest stages of activity (120–115 Ma) were highly explosive, resulting in the emplacement of diatreme breccias.
Trace element and Sr-Nd-Pb isotope data for the most primitive Early Cretaceous mafic igneous rocks sampled suggest that they
were derived by mixing of melts derived by variable degrees of partial melting of both garnet- and spinel-peridotite-facies
mantle sources. Though isotopically heterogeneous, the source of the magmas has many similarities to that of HIMU oceanic
island basalts. Earlier Liassic (200 Ma) transitional basalts and Neogene–Quaternary (15–0 Ma) alkali basalts erupted within
northern Israel also have HIMU affinities. The petrogenesis of the Early Cretaceous and Cenozoic basalts is explained by partial
melting of a lithospheric mantle protolith metasomatically enriched during the Liassic volcanic phase, which may be plume-related.
Received: 23 July 1998 / Accepted: 6 December 1999 相似文献
11.
Giorgio Rivalenti Maurizio Mazzucchelli Vicente A.V. Girardi Riccardo Vannucci M. Adelaide Barbieri Alberto Zanetti Steve L. Goldstein 《Contributions to Mineralogy and Petrology》2000,138(4):308-325
Spinel–peridotite facies mantle xenoliths in Cenozoic alkali basalts of the Pico Cabuji volcano (Rio Grande do Norte State,
Northeast Brazil) and the adjacent South Atlantic oceanic island of Fernando de Noronha are studied for: (1) the information
they provide on the composition of the lithospheric component in the erupted basalt geochemistry, and (2) to check the effects
of the Fernando de Noronha plume track on the mantle lithosphere. Xenoliths from Pico Cabuji are protogranular lherzolites
and porphyroclastic harzburgites recording average equilibrium temperatures of 825 ± 116 and 1248 ± 19 °C, respectively. Pressure
in the porphyroclastic xenoliths ranges from 1.9 to 2.7 GPa (Ca-in-olivine geobarometer). Both groups show major element chemical
variation trends in whole-rock and Ti and HREE (Er, Yb) variations in clinopyroxene consistent with fractional melting and
basalt extraction. REE (rare earth element) profiles of clinopyroxenes vary from LREE (La, Ce) enriched (spoon shaped) to
LREE depleted in the protogranular group, whereas they are slightly convex upward in most porphyroclastic clinopyroxenes.
HFSE (Ti and Zr) negative anomalies are in general modest in the clinopyroxenes of both groups. Xenoliths from Fernando de
Noronha have textural variations similar to those of Pico Cabuji. Protogranular and porphyroclastic samples have similar temperature
(1035 ± 80 °C) and the pressure is 1–1.9 and 2.3 GPa, respectively. Whole-rock chemical variation trends overlap and extend
further than those of Pico Cabuji. The trace element profiles of the clinopyroxenes of the porphyroclastic xenoliths are enriched
in La up to 30 × PM and are smoothly fractionated from LREE to HREE, with deep, negative, Zr and Ti anomalies. The geochemical
heterogeneities of the xenoliths from both localities are interpreted in terms of reactive porous percolation. The porphyroclastic
xenoliths from Pico Cabuji represent the lower part of a mantle column (the head of a mantle diapir, at the transition conductive–adiabatic
mantle), where OIB infiltration triggers melting, and the protogranular xenoliths the top of the mantle column, chromatographically
enriched by percolation at a low melt/rock ratio. This interpretation may also apply for Fernando de Noronha, but the different
geochemical signature recorded by the clinopyroxenes requires a different composition of the infiltrated melt. Nd and Sr isotopes
of the Pico Cabuji porphyroclastic clinopyroxenes (143Nd/144Nd= 0.51339–0.51255, 87Sr/86Sr=0.70275–0.70319) and of Fernando de Noronha (143Nd/144Nd=0.51323–0.51285, 87Sr/86Sr=0.70323–0.70465) plot on distinct arrays originating from a similar, isotopically depleted composition and trending to
low Nd–low Sr (EMI) and low Nd–high Sr (EMII), respectively. Correlation of the isotope variation with geochemical parameters
indicates that the isotopic variation was induced by the metasomatic component, of EMI type at Pico Cabuji and of EMII type
at Fernando de Noronha. These different components enriched a lithosphere isotopically similar to DMM (depleted MORB mantle)
at both localities. At Fernando de Noronha, the isotopic signature of the metasomatic component is similar to that of the
∼ 8 Ma old lavas of the Remedios Formation, suggesting that this is the age of metasomatism. At Pico Cabuji, the mantle xenoliths
do not record the high 87Sr/86Sr component present in the basalts. We speculate that the EMII component derives from a lithospheric reservoir, which was
not thermally affected during mantle metasomatism at Pico Cabuji, but was mobilized by the hotspot thermal influence at Fernando
de Noronha. This interpretation provides a plausible explanation for the presence of distinct metasomatic components at the
two localities, which would be difficult to reconcile with their genetic relationship with the same plume.
Received: 12 June 1999 / Accepted: 13 December 1999 相似文献
12.
Five mafic lava flows located on the southern flank of Mount Baker are among the most primitive in the volcanic field. A comprehensive
dataset of whole rock and mineral chemistry reveals the diversity of these mafic lavas that come from distinct sources and
have been variably affected by ascent through the crust. Disequilibrium textures present in all of the lavas indicate that
crustal processes have affected the magmas. Despite this evidence, mantle source characteristics have been retained and three
primitive endmember lava types are represented. These include (1) modified low-K tholeiitic basalt (LKOT-like), (2) typical
calc-alkaline (CA) lavas, and (3) high-Mg basaltic andesite and andesite (HMBA and HMA). The Type 1 endmember, the basalt
of Park Butte (49.3–50.3 wt% SiO2, Mg# 64–65), has major element chemistry similar to LKOT found elsewhere in the Cascades. Park Butte also has the lowest
overall abundances of trace elements (with the exception of the HREE), indicating it is either derived from the most depleted
mantle source or has undergone the largest degree of partial melting. The Type 2 endmember is represented by the basalts of
Lake Shannon (50.7–52.6 wt% SiO2, Mg# 58–62) and Sulphur Creek (51.2–54.6 wt% SiO2, Mg# 56–57). These two lavas are comparable to calc-alkaline rocks found in arcs worldwide and have similar trace element
patterns; however, they differ from each other in abundances of REE, indicating variation in degree of partial melting or
fractionation. The Type 3 endmember is represented by the HMBA of Tarn Plateau (51.8–54.0 wt% SiO2, Mg# 68–70) and the HMA of Glacier Creek (58.3–58.7 wt% SiO2, Mg# 63–64). The strongly depleted HREE nature of these Type 3 units and their decreasing Mg# with increasing SiO2 suggests fractionation from a high-Mg basaltic parent derived from a source with residual garnet. Another basaltic andesite
unit, Cathedral Crag (52.2–52.6 wt% SiO2, Mg# 55–58), is an Mg-poor differentiate of the Type 3 endmember. The calc-alkaline lavas are least enriched in a subduction
component (lowest H2O, Sr/PN, and Ba/Nb), the LKOT-like lavas are intermediate (moderate Sr/PN and Ba/Nb), and the HMBA are most enriched (highest H2O, Sr/PN and Ba/Nb). The generation of the LKOT-like and calc-alkaline lavas can be successfully modeled by partial melting of a spinel
lherzolite with variability in composition of slab flux and/or mantle source depletion. The HMBA lavas can be successfully
modeled by partial melting of a garnet lherzolite with slab flux compositionally similar to the other lava types, or less
likely by partial melting of a spinel lherzolite with a distinctly different, HREE-depleted slab flux. 相似文献
13.
Fluid history of UHP metamorphism in Dabie Shan, China: a fluid inclusion and oxygen isotope study on the coesite-bearing eclogite from Bixiling 总被引:32,自引:1,他引:31
Yilin Xiao Jochen Hoefs Alfons M. van den Kerkhof Jens Fiebig Yongfei Zheng 《Contributions to Mineralogy and Petrology》2000,139(1):1-16
This paper characterizes late Holocene basalts and basaltic andesites at Medicine Lake volcano that contain high pre-eruptive
H2O contents inherited from a subduction related hydrous component in the mantle. The basaltic andesite of Paint Pot Crater
and the compositionally zoned basaltic to andesitic lavas of the Callahan flow erupted approximately 1000 14C years Before Present (14C years b.p.). Petrologic, geochemical and isotopic evidence indicates that this late Holocene mafic magmatism was characterized by H2O contents of 3 to 6 wt% H2O and elevated abundances of large ion lithophile elements (LILE). These hydrous mafic inputs contrast with the preceding
episodes of mafic magmatism (from 10,600 to ∼3000 14C years b.p.) that was characterized by the eruption of primitive high alumina olivine tholeiite (HAOT) with low H2O (<0.2 wt%), lower LILE abundance and different isotopic characteristics. Thus, the mantle-derived inputs into the Medicine
Lake system have not always been low H2O, primitive HAOT, but have alternated between HAOT and hydrous subduction related, calc-alkaline basalt. This influx of hydrous
mafic magma coincides temporally and spatially with rhyolite eruption at Glass Mountain and Little Glass Mountain. The rhyolites
contain quenched magmatic inclusions similar in character to the mafic lavas at Callahan and Paint Pot Crater. The influence
of H2O on fractional crystallization of hydrous mafic magma and melting of pre-existing granite crust beneath the volcano combined
to produce the rhyolite. Fractionation under hydrous conditions at upper crustal pressures leads to the early crystallization
of Fe-Mg silicates and the suppression of plagioclase as an early crystallizing phase. In addition, H2O lowers the saturation temperature of Fe and Mg silicates, and brings the temperature of oxide crystallization closer to
the liquidus. These combined effects generate SiO2-enrichment that leads to rhyodacitic differentiated lavas. In contrast, low H2O HAOT magmas at Medicine Lake differentiate to iron-rich basaltic liquids. When these Fe-enriched basalts mix with melted
granitic crust, the result is an andesitic magma. Since mid-Holocene time, mafic volcanism has been dominated primarily by
hydrous basaltic andesite and andesite at Medicine Lake Volcano. However, during the late Holocene, H2O-poor mafic magmas continued to be erupted along with hydrous mafic magmas, although in significantly smaller volumes.
Received: 4 January 1999 / Accepted: 30 August 1999 相似文献
14.
Ryuichi Shinjo Takele Chekol Daniel Meshesha Tetsumaru Itaya Yoshiyuki Tatsumi 《Contributions to Mineralogy and Petrology》2011,162(1):209-230
Major and trace element and isotopic ratios (Sr, Nd and Pb) are presented for mafic lavas (MgO > 4 wt%) from the southwestern
Yabello region (southern Ethiopia) in the vicinity of the East African Rift System (EARS). New K/Ar dating results confirm
three magmatic periods of activity in the region: (1) Miocene (12.3–10.5 Ma) alkali basalts and hawaiites, (2) Pliocene (4.7–3.6 Ma)
tholeiitic basalts, and (3) Recent (1.9–0.3 Ma) basanite-dominant alkaline lavas. Trace element and isotopic characteristics
of the Miocene and Quaternary lavas bear a close similarity to ocean island basalts that derived from HIMU-type sublithospheric
source. The Pliocene basalts have higher Ba/Nb, La/Nb, Zr/Nb and 87Sr/86Sr (0.70395–0.70417) and less radiogenic Pb isotopic ratios (206Pb/204Pb = 18.12–18.27) relative to the Miocene and Quaternary lavas, indicative of significant contribution from enriched subcontinental
lithospheric mantle in their sources. Intermittent upwelling of hot mantle plume in at least two cycles can explain the magmatic
evolution in the southern Ethiopian region. Although plumes have been originated from a common and deeper superplume extending
from the core–mantle boundary, the diversity of plume components during the Miocene and Quaternary reflects heterogeneity
of secondary plumes at shallower levels connected to the African superplume, which have evolved to more homogeneous source. 相似文献
15.
Martial Caroff René C. Maury Gérard Guille Joseph Cotten 《Contributions to Mineralogy and Petrology》1997,127(4):369-382
Process identification diagrams based on trace element data show that mafic lavas from Tubuai, including alkali basalts,
basanites, analcitites and nephelinites, result from different degrees of partial melting of an isotopically homogeneous mantle
source. Our fractionation-corrected data are consistent with a batch melting model or a dynamic melting model involving a
threshold value for melt separation close to 1% and degrees of melting ranging from 5–8% (alkali basalts) to 1.5–3% (nephelinites).
The relative source concentration pattern, calculated using an inverse numerical method, shows an enrichment in highly incompatible
elements. We propose that the Tubuai lava suite was derived from a two-stage partial melting process. Melting first affected
the plume material located within the transition zone between garnet and spinel domains, producing alkali basalts and basanites.
Then, the melting zone migrated upwards to the base of the overlying spinel-bearing lithospheric mantle, producing highly
silica-undersaturated lavas. The lower lithosphere had previously been enriched by intrusion of pyroxenite veins representing
plume-derived melts which percolated away from the main magma conduits.
Received: 11 June 1996 / Accepted: 8 January 1997 相似文献
16.
L. Beccaluva M. Coltorti P. Di Girolamo L. Melluso L. Milani V. Morra F. Siena 《Mineralogy and Petrology》2002,74(2-4):277-297
Summary The Late Pleistocene Mt. Vulture strato-volcano developed at the intersection of NE-SW and NW-SE lithospheric fault systems,
on the easternmost border of the Apennine compressional front overthrust onto the Apulian foreland. The initial phase of the
volcanic activity is represented by pyroclastic deposits, including lava blocks, and subordinate eccentric domes, mostly phonolitic
in composition. The later stages of activity formed the bulk of the strato-volcano (pyroclastic products and subordinate lavas),
mostly tephritic in composition, with minor intercalations of basanite, mela-foidite and melilitite lavas and dikes.
Variations in rock and mineral composition suggest that the volumetrically predominant basanite-tephrite (foidite)-phonotephrite-phonolite
series can be accounted for by fractional crystallization processes starting from basanitic parental magmas, in agreement
with the remarkably constant 87Sr/86Sr isotopes (0.70586–0.70581). Mass-balance calculations indicate that the variably differentiated magmas may have been produced
by removal of wehrlite, clinopyroxenite and syenite cumulates, some of which are occasionally found as cognate xenoliths in
the volcanics. Fractionation processes probably developed in multiple-zoned magma chambers, at depths of 3–5 km, corresponding
to the tectonic discontinuity between the allochthonous Apennine formations and the underlying Apulian platform. Highly differentiated
phonolitic magmas capping the magma chambers and their conduits thus appear to have fed the initial volcanic activity, whereas
dominantly tephritic products were erupted in later stages.
The least evolved mafic magmas, namely basanites, mela-foidites and melilitites, are characterized by diverse Na/K ratios
and critical SiO2-undersaturation, which indicate their derivation as independent melts generated from distinct, heterogeneously enriched mantle
sources and by variable partial melting degrees.
Primitive mantle-normalized incompatible element patterns of Vulture mafic lavas invariably share analogies with both orogenic
subduction-related magmas (high Low Field Strength Elements/High Field Strength Elements ratios, K, Rb and Th contents and
marked Ti and Nb negative anomalies) and alkaline lavas from within-plate and rift settings (high Light Rare Earth Elements,
P, Zr, Nb and Na). These geochemical features may be accounted for by magma generation from deep lithospheric mantle sources,
enriched in Na-alkali silicate/carbonatite anorogenic components, subsequently affected by orogenic subduction-related K-metasomatism,
analogous to that which modified magma sources of the Roman Magmatic Province along the internal Apennine Chain.
Received April 12, 2000; revised version accepted June 7, 2001 相似文献
17.
The geochemical variations of mid-Cretaceous lavas across western Shandong Province, China and their tectonic implications 总被引:1,自引:0,他引:1
Major and trace element as well as Sr–Nd isotopic compositions of mid-Cretaceous lavas across western Shandong Province, China
have been studied. These lavas can be generally divided into southern Shandong group (including Pingyi and Mengyin) and northern
Shandong group (including Laiwu and Zouping) based on their geochemistry. The southern group lavas are characterized by extreme
enrichment in LREE, large ion lithophile elements (LILE), and depletion in HFSE along with EMII-like Sr–Nd isotopic compositions,
suggesting that the crustal involvements play a significant role in their petrogenesis. Comparing studies with Fangcheng basalts
reveal that the Triassic continent–continent collision between the Yangtze craton (YC) and the North China craton (NCC), and
subsequent extensive modification of the sub-continental lithospheric mantle (SCLM) beneath the south part of the NCC by silicic
melts released from the subducted Yangtze lower crust, formed an enriched lithospheric mantle which was the source of the
southern Shandong group lavas. In contrast, the northern Shandong group lavas are mildly enriched in LREE and LILE relative
to those of the southern group lavas. The isotope compositions are also distinctive in that the Sr isotopic ratios are very
low. Available geochemical evidence and comparing studies with spatially closed related mafic intrusions suggest that the
SCLM feeding the northern group lavas seems to be linked to carbonatitic metasomatism and changed modal proportion of phlogopite
and clinopyroxene in the mantle rather than subduction-related modifications. The contrasting geochemical characters of the
mid-Cretaceous lavas across western Shangdong suggest that the SCLM of the NCC is spatially heterogeneous in Mesozoic. 相似文献
18.
In this study, we present Th–U disequilibria as well as radiogenic and trace element data for recent volcanic rocks from
the Nevados de Payachata volcano which erupted through ∼70 km of continental crust in the Central Volcanic Zone of the Andes
(18°S, 69°W). Both lavas and mineral separates were analyzed by mass spectrometry for 238U–230Th disequilibria. The lavas are characterized either by 230Th enrichment or depletion relative to its parent nuclide 238U. Mineral separates are used to derive U–Th isochron ages and these ages compare favorably with inferred stratigraphic ages
or K–Ar ages, although in one case the U–Th age is significantly older than the stratigraphic age. Despite relatively constant
Sr, Nd, and Pb isotope ratios, the lavas display inverse trends in 230Th/238U versus Ce/Yb or Ba/Hf diagrams. These trends cannot be interpreted by simple two-component mixing. Rather, there must be
three (and perhaps four components) involved in the genesis of the Parinacota lavas. A mantle wedge, a slab fluid, and a lower
crustal component can be identified. A sediment component is more difficult to detect as it is difficult to decipher its signature
because of the strong crustal influence. The existence of binary arrays can be explained by variable amounts of crustal material.
The process of crust–mantle interaction must have been short enough to preserve U–Th disequilibrium (<300 ka).
Received: 21 April 1999 / Accepted: 11 March 2000 相似文献
19.
Experimental study of the phase and melting relations of homogeneous basalt + peridotite mixtures and implications for the petrogenesis of flood basalts 总被引:20,自引:0,他引:20
Gregory M. Yaxley 《Contributions to Mineralogy and Petrology》2000,139(3):326-338
Flood basalt provinces may constitute some of the most catastrophic volcanic events in the Earth's history. A popular model
to explain them involves adiabatic ascent of plumes of anomalously hot peridotite from a thermal boundary layer deep in the
mantle, across the peridotite solidus. However, peridotitic plumes probably require unreasonably high potential temperatures
to generate sufficient volumes of magma and high enough melting rates to produce flood volcanism. This lead to the suggestion
that low melting eclogitic or pyroxenitic heterogeneities may be present in the source regions of the flood basalts. In order
to constrain petrogenetic models for flood basalts generated in this way, an experimental investigation of the melting relations
of homogeneous peridotite + oceanic basalt mixtures has been performed. Experiments were conducted at 3.5 GPa on a fertile
peridotite (MPY90)–oceanic basalt (GA1) compositional join. The hybrid basalt + peridotite compositions crystallised garnet
lherzolite at subsolidus temperatures plus quenched ne-normative picritic liquids at temperatures just above the solidus, over the compositional range MPY90 to GA150MPY9050. The solidus temperature decreased slightly from ∼1500 °C for MPY90 to ∼1450 °C for GA150MPY9050. Compositions similar to GA130MPY9070 have 100% melting compressed into a melting interval which is approximately 50–60% smaller than that for pure MPY90, due
to a liquidus minimum. During adiabatic ascent of hybrid source material containing a few tens of percent basalt in peridotite,
the lower solidus and compressed solidus–liquidus temperature interval may conspire to substantially enhance melt productivity.
Mixtures of recycled oceanic crust and peridotite in mantle plumes may therefore provide a viable source for some flood volcanics.
Evidence for this would include higher than normal Fe/Mg values in natural primary liquids, consistent with equilibration
with more Fe-rich olivine than normal pyrolitic olivine (i.e. <Fo89–92). Modelling of fractionation trends in West Greenland picrites is presented to demonstrate that melts parental to the Greenland
picrites were in equilibrium at mantle P–T conditions with olivine with Fo84–86, suggesting an Fe-enriched source compared with normal peridotite, and consistent with the presence of a basaltic component
in the source.
Received: 29 October 1999 / Accepted: 3 February 2000 相似文献
20.
Petrology and geochemistry of Camiguin Island, southern Philippines: insights to the source of adakites and other lavas in a complex arc setting 总被引:72,自引:1,他引:71
Paterno R. Castillo Philip E. Janney Renato U. Solidum 《Contributions to Mineralogy and Petrology》1999,134(1):33-51
Camiguin is a small volcanic island located 12 km north of Mindanao Island in southern Philippines. The island consists of
four volcanic centers which have erupted basaltic to rhyolitic calcalkaline lavas during the last ∼400 ka. Major element,
trace element and Sr, Nd and Pb isotopic data indicate that the volcanic centers have produced a single lava series from a
common mantle source. Modeling results indicate that Camiguin lavas were produced by periodic injection of a parental magma
into shallow magma chambers allowing assimilation and fractional crystallization (AFC) processes to take place. The chemical
and isotopic composition of Camiguin lavas bears strong resemblance to the majority of lavas from the central Mindanao volcanic
field confirming that Camiguin is an extension of the tectonically complex Central Mindanao Arc (CMA). The most likely source
of Camiguin and most CMA magmas is the mantle wedge metasomatized by fluids dehydrated from a subducted slab. Some Camiguin
high-silica lavas are similar to high-silica lavas from Mindanao, which have been identified as “adakites” derived from direct
melting of a subducted basaltic crust. More detailed comparison of Camiguin and Mindanao adakites with silicic slab-derived
melts and magnesian andesites from the western Aleutians, southernmost Chile and Batan Island in northern Philippines indicates
that the Mindanao adakites are not pure slab melts. Rather, the CMA adakites are similar to Camiguin high-silica lavas which
are products of an AFC process and have negligible connection to melting of subducted basaltic crust.
Received: 27 February 1998 / Accepted: 27 August 1998 相似文献