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1.
2.
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
3.
N. A. Gnatus’ M. D. Khutorskoy V. K. Khmelevskoi 《Moscow University Geology Bulletin》2011,66(3):151-157
The geological-geophysical, methological, and economic aspects of extraction and utilization of petrothermal resources (“hot
dry rock thermal”) for thermal and electric energy production were considered. Heat collectors are hydraulic fracturing zones
of natural or artificially made cracks in the crystalline rocks of the basement; these rocks have higher temperature and can
be a kind of “thermal cauldron.” Detection of such “collectors” can be carried out by geophysical methods. When pumped out
of wells and warmed to 100–300°C, waters function as a heat transfer for thermal energy supply and electric energy generation.
If the technical problem of the rapid drilling of 6–10 km wells could be solved, then petrothermal energy will become competitive
with the traditional types of energy production and supply. 相似文献
4.
Petrology,geochemistry and genesis of Kuiqi granite batholith 总被引:1,自引:0,他引:1
The Kuiqi granite batholith outcrops in the vicinity of Fuzhou City, Fujian Province and constitutes one of the typical alkali
granitic complexes in the “Belt of Miarolitic Granites” extending along the southeast coast of China. The complex is believed
to have been emplaced at higher levels of the crust in a tensional fault environment. Petrographically it is composed mainly
of aegirine-arfvedsonite granites with early biotite granites scattered. Miarolitic structure and granophyric texture are
commonly observed. The Rb-Sr isochron age of the complex is 107.65 m.y. Both petrological and petrochemical studies show that
the Kuiqi granite is of A-type. Data on chemical composition, REE pattern and transition elements reveal that there is a close
genetic connection between granites and associated volcanic rocks. Thus, syntexistype (I-type) granite, A-type granite and
volcanic rocks form a cogenetic “trinity”, in which the A-type granite is usually the latest member of the volcanic-intrusive
series. 相似文献
5.
P. Antonini E. M. Piccirillo R. Petrini L. Civetta M. D'Antonio G. Orsi 《Contributions to Mineralogy and Petrology》1999,136(1-2):1-19
The major, trace (including rare earth) element abundances, and Sr-Nd-Pb isotopic compositions, have been analysed for andesitic
basalt and andesitic sills and lavas of the Jurassic Ferrar Magmatic Province, Prince Albert Mountains, Antarctica. The typical
“crustal signature” of the Ferrar magmatism, characterized by relatively high SiO2, LREE and LILE contents in these samples, is associated with high 87Sr/86Sr and low 143Nd/144Nd. Systematic correlations of major and trace elements indicate that fractional crystallization was important. However, increases
in incompatible elements are positively correlated with initial 87Sr/86Sr, suggestive of crustal assimilation processes. The observed correlations between initial 87Sr/86Sr and LREE enrichments have been modelled by an AFC process, starting from the least evolved sample and assuming the compositions
of the orthogranulites of Victoria Land as contaminants. The REE patterns of the least evolved Ferrar rocks approach those
of E-type MORB, differing only by higher LREE/IREE. The enrichment in LREE, accompanying high initial 87Sr/86Sr, 207Pb/204Pb and low 143Nd/144Nd compared with E-type MORB, can be explained by interaction of “primary Ferrar basalt” with crystalline basement. We propose
a petrological model whereby Ferrar magmas were generated through high degrees of melting of an E-type MORB mantle source,
and subsequently these “primary” melts underwent AFC processes inheriting a crustal signature. The Sr-Nd-Pb isotopic compositions
required by the AFC model for the primary Ferrar basalt are similar to those of the Dupal signature of the oceanic basalts
of the Southern Hemisphere (Hart 1984). Transantarctic Mountains would have been located inside the Dupal anomaly in pre-Gondwana
dispersion times.
Received: 21 April 1998 / Accepted: 25 January 1999 相似文献
6.
Kuznetsov N. B. Natapov L. M. Belousova E. A. Griffin U. L. O’Relly S. Y. Kulikova K. V. Soboleva A. A. Udoratina O. V. 《Doklady Earth Sciences》2010,435(2):1676-1683
This report presents the first results of U/Pb dating, isotope-geochemical, and geochemical studies of detrital zircons from
the Neoproterozoic clastic rocks of the Southern Timan. Sixty-one zircon grains were treated, including 51 from red-colored
sandstones and 10 grains from aleurosandstones of the Djejim Formation of the southern Chetlas-Djejim zone (Djejim-Parma Hill).
It was found that the U/Pb-ages of zircons from the rocks of the Djejim Formation, varied from ∼2.97 to ∼1.20 Ga. The studies
of microelement composition in 47 grains (of 61 U/Pb isotope ages obtained), on the basis of several empirical regularities
found formerly, show that the detrital zircons had originated from “granites” (22 grains), “diorites” (12 grains), or their
volcanic analogues, or more rarely, from “syenites” and “basites” (5 and 8 grains, respectively). The Lu/Hf isotope system
of zircons allows one to estimate the model ages (T
DMC) of the substrate magmatic rocks being parental to the zircons considered. In particular, Archean zircons are characterized
by ∼2.84–3.36 Ga model ages of magmaforming rocks. For some of the grains, their model ages (∼2.84 Ga) are close to those
of zircons as such (∼2.7–2.8 Ga), which points to the juvenile character of the substrate from which the parent magma of the
zircons treated was fused. For Proterozoic (to Middle Riphean) zircons, the Lu/Hf isotope system allows one to estimate the
model age of the substrate of their parental rocks within ∼2.00–3.36 Ga, which shows that these rocks were formed under the
recycling of the Archean and Early-Proterozoic crust. The ages obtained for detrital zircons, as well as model ages of the
substrate of the corresponding parental magmatic rocks, are quite comparable to the age of crystalline complexes of the ancient
framework of the East European Platform (EEP), formed in the course of the Archean, Early-Proterozoic, and Early-Middle Riphean
tectonomagmatic events. This permits us to conclude that the Neoproterozoic detrital complexes of the Timan were formed owing
to the erosion of earlier Neoproterozoic and Early Precambrian complexes constituting the Neoproterozoic Baltica continent,
presenting complexes of the passive margin of this continent. A variety of ages of detrital zircons from sandstones and aleurosandstones
from the Djejim Formation of Djejim-Parma Hill, and of the estimates of magmatic rocks parental to these zircons, may be characterized
as a Baltic Provenance signal. 相似文献
7.
O. V. Avchenko I. A. Aleksandrov V. O. Khudolozhkin M. A. Mishkin 《Russian Journal of Pacific Geology》2009,3(4):307-318
Chromatographic and electrochemical measurements, combined with computer simulation of the natural mineral parageneses and estimation of the stability field of muscovite-bearing assemblages, yielded a consistent model of the fluid regime for the amphibolite-facies metamorphism of the Dzhugdzhur-Stanovoy fold area (DSFA). The model allows the fluid differentiation into “internal” and “external” fluids. The “internal” fluid is formed by the volatiles of the rock, while the “external” fluid arrived from an outer source: the mantle or other reservoir. It is established that the chromatographic and electrochemical measurements refer to the “external” fluid, whereas the redox state estimated from the mineral equilibria is related to the “internal” fluid, whose composition is buffered by the equilibrium mineral assemblage. The “external” fluid trapped by rocks preserves its own redox state only at the regtrograde stage, when the solid-phase reactions slacken and the buffer role of the mineral assemblages is minimized. This aspect explains the contradiction between the wide variations in the oxidation state of the mineral equilibria (log fO2 from ?15 to ?20), on the one hand, and the persistent oxidation state of the external fluid established by the chromatographic and electrochemical methods, on the other hand. The main reason for the wide development of hornblende-bearing assemblages in the amphibolite-facies metamorphic rocks of the Dzhugdzhur-Stanovoy fold system is the high H2O pressure in the “external” fluid. According to the obtained data, the composition of the “external” fluid is determined by the conditions $ P_{H_2 O} Chromatographic and electrochemical measurements, combined with computer simulation of the natural mineral parageneses and
estimation of the stability field of muscovite-bearing assemblages, yielded a consistent model of the fluid regime for the
amphibolite-facies metamorphism of the Dzhugdzhur-Stanovoy fold area (DSFA).
The model allows the fluid differentiation into “internal” and “external” fluids. The “internal” fluid is formed by the volatiles
of the rock, while the “external” fluid arrived from an outer source: the mantle or other reservoir. It is established that
the chromatographic and electrochemical measurements refer to the “external” fluid, whereas the redox state estimated from
the mineral equilibria is related to the “internal” fluid, whose composition is buffered by the equilibrium mineral assemblage.
The “external” fluid trapped by rocks preserves its own redox state only at the regtrograde stage, when the solid-phase reactions
slacken and the buffer role of the mineral assemblages is minimized. This aspect explains the contradiction between the wide
variations in the oxidation state of the mineral equilibria (log fO2 from −15 to −20), on the one hand, and the persistent oxidation state of the external fluid established by the chromatographic
and electrochemical methods, on the other hand. The main reason for the wide development of hornblende-bearing assemblages
in the amphibolite-facies metamorphic rocks of the Dzhugdzhur-Stanovoy fold system is the high H2O pressure in the “external” fluid. According to the obtained data, the composition of the “external” fluid is determined
by the conditions ≥ 0.7 PS and = 0.01–0.3. The oxidation potential of the “external” fluid is close to that of the H2O-C system under carbon-saturated vapor conditions.
Original Russian Text ? O.V. Avchenko, I.A. Aleksandrov, V.O. Khudolozhkin, M.A. Mishkin, 2009, published in Tikhookeanskaya
Geologiya, 2009, Vol. 28, No. 4, pp. 3–15. 相似文献
8.
Strontium and oxygen isotopic variations in Mesozoic and Tertiary plutons of central Idaho 总被引:2,自引:0,他引:2
Regional variations in initial 87Sr/86Sr ratios (r
i) of Mesozoic plutons in central Idaho locate the edge of Precambrian continental crust at the boundary between the late Paleozoic-Mesozoic
accreted terranes and Precambrian sialic crust in western Idaho. The r
i values increase abruptly but continuously from less than 0.704 in the accreted terranes to greater than 0.708 across a narrow,
5 to 15 km zone, characterized by elongate, lens-shaped, highly deformed plutons and schistose metasedimentary and metavolcanic
units. The chemical and petrologic character of the plutons changes concomitantly from ocean-arc-type, diorite-tonalite-trondhjemite
units to a weakly peraluminous, calcic to calcalkalic tonalite-granodiorite-granite suite (the Idaho batholith). Plutons in
both suites yield Late Cretaceous ages, but Permian through Early Cretaceous bodies are confined to the accreted terranes
and early Tertiary intrusions are restricted to areas underlain by Precambrian crust. The two major terranes were juxtaposed
between 75 and 130 m.y. ago, probably between 80 and 95 m.y.
Oxygen and strontium isotopic ratios and Rb and Sr concentrations of the plutonic rocks document a significant upper-crustal
contribution to the magmas that intrude Precambrian crust. Magmas intruding the arc terranes were derived from the upper mantle/subducted
oceanic lithosphere and may have been modified by anatexis of earlier island-arc volcanic and sedimentary units.
Plutons near the edge of Precambrian sialic crust represent simple mixtures of the Precambrian wall-rocks with melts derived
from the upper mantle or subducted oceanic lithosphere with r
i of 0.7035. Rb/Sr varies linearly with r
i, producing “pseudoisochrons” with apparent “ages” close to the age of the wall rocks. Measured δ
18O values of the wall rocks are less than those required for the assimilated end-member by Sr-O covariation in the plutons,
however, indicating that wall-rock δ
18O was reduced significantly by exchange with circulating fluids. Metasedimentary rocks of the Belt Supergroup are similarly
affected near the batholith, documenting a systematic depletion in 18O as much as 50 km from the margin of the batholith.
Plutons of the Bitterroot lobe of the Idaho batholith are remote from the accreted terranes and represent mixtures of Precambrian
wall-rocks with melts dominated by continental lower crust (r
i>0.708) rather than mantle. “Pseudoisochrons” resulting from these data are actually mixing lines that yield apparent “ages”
less than the true age of the wall rocks and meaningless “ri”. Assimilation/ fractional-crystallization models permit only insignificant amounts of crystal fractionation during anatexis
and mixing for the majority of plutons of the region. 相似文献
9.
Experimental research on the chemical weathering of alkaline-olivine basalt from Huangyi Mountain,Kuandain County,Liaoning.Province and olivine basalt from Dayangke,Mingxi County,Fujian Province has shown that the acidity of the solution tends to become neutral regardless of what the acidity of the starting solution would be during basalt0-water interaction.We call this phenome-non“pH neutralized Effect”.The dissolved species in the solution were determined and unreacted and reacted sample-surface chemical components involved or uninvolved in reaction were analyzed using X-ray photoelectron spectroscopy(XPS).The results revealed two different mechanisms of dissolution of basalt in acidic and basic solutions. 相似文献
10.
L. Valenzuela-Vásquez J. Ramírez-Hernández J. Reyes-López A. Sol-Uribe O. Lázaro-Mancilla 《Environmental Geology》2006,51(1):17-27
Anomalous high fluoride concentration up to 7.59 mg/dm3 is found in groundwater from “La Victoria” area. This water is used to supply drinking water to Hermosillo City, Sonora. Geochemistry of groundwater, relationship between physicochemical parameters, hydrogeology and geologic setting were correlated to define the origin and the geochemical mechanisms of groundwater fluorine enrichment. High fluoride concentration is associated with high bicarbonates, pH and temperature, and it decreases toward the west and south of the area. Fluoride is in negative correlation to calcium concentration. Sodium sulphate facies of regional deep water flow are related to high fluoride concentration. High electric resistivity rocks associated with granites from the Sierra Bachoco basement might be the deep source of fluoride. Outcropping of Sierra Bachoco in the west causes upward regional flow. Groundwater of longer residence time can be pumped there. The anomalous area is restricted to “La Victoria” because calcareous paleozoic rocks outcrop to the south. 相似文献
11.
Eastern China is a Cenozoic composite volcanic rock province, where volcanic rocks of the tholeiite series, calc-alkali series,
Hy-norm-bearing olivine basalt series, Na-alkali series and K-alkali series coexist. Eastern China is separated into the northern
and southern volcanic rock regions by the Changzhou-Yueyang old deep fault. Magma generation and magmatic activities in the
northern region were controlled by the mantle uplift and old deep faults. These old deep faults were revived and some of them
were changed into a multiple rift system due to back-arc expansion. The Bohai Sea depression is situated at the intersection
of the Lujiang-Tancheng-Shenyang-Mishan and Zhangjiakou-Tianjin uplift belts of the upper mantle. Eogene (71.5-28.5 Ma) tholeiites
largely occur in the central part of the mantle uplift; the well developed Neogene (23.8-2.6 Ma) alkali olivine basalts are
distributed in the outer lane of the former and the Quaternary (1.48 Ma-recent) peralkali volcanic rocks are far away from
them. In the southern region magma generation and magmatic activities were controlled mainly by plate subduction and three
sets of old deep faults.
Studies of incompatible elements and REE show that the degree of enrichment of incompatible elements and LREE increases with
decreasing age, increasing source depth and decreasing degree of partial melting of the upper mantle. This presumably is an
indication of a rapid uplifting and then waning magmatic hearth with gradually decreasing temperature, accompanied with down-cutting
of the lithospheric faults. We call such a process “a reverse process of magma generation”. And the opposite process of the
magmatic evolution of the East African rift in Kenya can be called “a positive process of magma generation”. 相似文献
12.
黑龙江依兰地区变玄武岩及变堆晶辉长岩LA-ICP-MS锆石U-Pb年龄及其地质意义 总被引:2,自引:0,他引:2
对依兰地区黑龙江混杂岩中的变玄武岩、变枕状玄武岩及变堆晶辉长岩岩块中的锆石进行了LA-ICP-MS U-Pb同位素测定,结果表明,变玄武岩的锆石大量为捕获基底的锆石,其年龄范围大,从3172±24Ma到176±1Ma均有分布,其中具有基性岩典型的板状特征的锆石年龄为243±1Ma,代表了变玄武岩的原岩形成年龄;变枕状玄武岩及变堆晶辉长岩的年龄分别为251±1Ma和252±1Ma,分别代表各自原岩的形成年龄。本次锆石年龄的获得,证明晚二叠世佳木斯地块和松嫩-张广才岭地块之间存在古洋盆,为研究黑龙江杂岩的演化历史提供了重要的年代学依据。 相似文献
13.
Hydrochemistry and Classification of Groundwater Resources of Ishwardi Municipal Area,Pabna District,Bangladesh 总被引:2,自引:0,他引:2
Golzar Hossain M. Farhad Howladar Lutfun Nessa Syed Samsuddin Ahmed Chowdhury Quamruzzaman 《Geotechnical and Geological Engineering》2010,28(5):671-679
The chemical property of groundwater depends largely on the mineralogical composition of the rocks through which the water
has moved and the rate of movement and these characteristics of surface water depend on organic and inorganic reactions, industrial
effluents, rainfall and temperature etc. The underground water tends to contain more dissolved materials than those in surface
water because of their more intimate and longer contact with organic materials of soil and rock particles. The groundwater
of the studied area is dominant of alkaline earth’s (Ca2+ and Mg2+) and weak acids (HCO3
−) which may be classified as Magnesium-Bicarbonate and Calcium Carbonate types. Genetically, the groundwater of the area belongs
to both “Normal Chloride” “Normal Sulphate” and “Normal Carbonate” to “Super Carbonate” group. Based on EC, SAR and RC, the
groundwater of the area varies from good–excellent quality for irrigation purposes with low alkali hazard and medium salinity
hazard. 相似文献
14.
WANG Pengpeng HU Yuzhao LIU Lu JIANG Xiaojun LI Chao Chad Joseph Bartholomew ZHANG Guiquan 《《地质学报》英文版》2017,91(6):2153-2163
Abundant organic inclusions are present in the Qinglong antimony deposit. However, the source rocks of these organic matters have not been reliably identified. Recently, a paleo–oil reservoir was found in the Qinglong antimony deposit. In view of similar components of gaseous hydrocarbon, we propose that the organic matters observed in inclusions in Qinglong antimony deposit would come from this paleo–oil reservoir. We used the Re–Os dating method to determine the age of the bitumen from this paleo–oil reservoir, and obtained an isochron age of 254.3±2.8 Ma. The age indicates that the oilgeneration from source rock occurred in the early Late Permian, earlier than the Sb mineralization age(~148±8.5 Ma) in the Qinglong antimony deposit area. After oil generation from Devonian source rock, first and secondary migration, the crude oil have probably entered into the fractures and pores of volcanic rocks and limestone and formed a paleo–oil reservoir in the western wing of Dachang anticline. As burial process deepened, the crude oil has turned into natural gas, migrates into the core of Dachang anticline and formed a paleo–gas reservoir. The hydrocarbons(including CH_4) in the reservoirs can serve as reducing agent to provide the sulfur required for Sb mineralization through thermal chemical reduction of sulfates. Therefore, the formation of oil–gas in the area is a prerequisite for the Sb mineralization in the Qinglong antimony deposit. 相似文献
15.
The Karakaya Complex within the Early Mesozoic Cimmerian Orogeny in northern Turkey represents the remnants of the Palaeotethys.
It includes slivers and/or mega-blocks of slightly metamorphic basic volcanic rocks associated with fossiliferous sediments
as well as hypabyssal and intrusive rocks with basaltic-andesitic to ultramafic compositions. They display two distinct compositional
groups; namely alkaline and variably tholeiitic. The alkaline basalt samples are more akin to oceanic-island basalts (OIB)
with relatively enriched trace element characteristics together with strong partitioning in HREE ([La/Yb]N = 5.8–16.2), suggesting that garnet is present as a residual phase in the source of those basalts. The variably tholeiitic
samples apart from diabases display E-MORB characteristics; being relatively depleted compared to the alkaline counterparts
and less fractionated REE patterns ([La/Yb]N = 2.1–3.6). The diabases, on the other hand, are distinctively different with a significant negative Nb anomaly (Zr/Nb = 28.9–43.4)
and flat REE patterns ([La/Yb]N = 0.8–1.4), suggesting their generation above a supra-subduction zone, probably a back-arc basin. These results may suggest
that a mantle plume-related magmatism associated with extensional oceanic system should have been installed within Palaeotethys
during Middle-Late Triassic time, which was then incorporated into subduction–accretion prism forming the final picture, that
is, “the Karakaya Complex”. 相似文献
16.
17.
Surendra P. Verma 《Journal of Earth System Science》2000,109(1):79-88
This paper presents error propagation equations for modeling of radiogenic isotopes during mixing of two components or end-members.
These equations can be used to estimate errors on an isotopic ratio in the mixture of two components, as a function of the
analytical errors or the total errors of geological field sampling and analytical errors. Two typical cases (“Small errors”
and “Large errors”) are illustrated for mixing of Sr isotopes. Similar examples can be formulated for the other radiogenic
isotopic ratios. Actual isotopic data for sediment and basalt samples from the Cocos plate are also included to further illustrate
the use of these equations. The isotopic compositions of the predicted mixtures can be used to constrain the origin of magmas
in the central part of the Mexican Volcanic Belt. These examples show the need of high quality experimental data for them
to be useful in geochemical modeling of magmatic processes. 相似文献
18.
Li Zhaolin Qiu Zhili Qin Shecai Pang Xuebin Liang Dehua Teng Yunye Li Yang 《中国地球化学学报》1994,13(2):107-117
Volcanic rocks in seamounts of the South China Sea consist mainly of alkali basalt, tholeiitic basalt, trachyandesitic pumice,
dacite, etc. Inclusions in the minerals of the volcanic rocks are mainly amorphous melt inclusions, which reflects that the
volcanic rocks are characterized by submarine eruption and rapid cooling on the seafloor. Furthermore, fluid-melt inclusions
have been discovered for the first time in alkali basalts and mantle-derived xenoliths. indicating a process of differentiation
between magma and fluid in the course of mantle partial melting. Alkali basalts and inclusions may have been formed in this
nonhomogeneous system.
Rock-forming temperatures of four seamounts were estimated as follows: the Zhongnan seamount alkali basalt 1155 ∼ 1185 °C;
the Xianbei seamount alkali basalt 960 ∼ 1200 °C; tholeiitic basalt 1040 ∼ 1230 °C; the Daimao seamount tholeiitic basalt
1245 ∼ 1280 °C; and the Jianfeng seamount trachyandestic pumice 880 ∼ 1140 °C. Equilibrium pressures of alkali basalts in
the Zhongnan and Xianbei seamounts are 13.57 and 8.8 × 108 Pa, respectively. Pyroxene equilibrium temperatures of mantle xenoliths from the Xianbei seamount were estimated at 1073
∼ 1121 °C, and pressures at (15.58 ∼ 22.47)×108Pa, suggesting a deep-source (e.g. the asthenosphere) for the alkali basalts.
This project was financially supported by the National Natural Science Foundation of China and Guangzhou Marine Geology Survey. 相似文献
19.
O. A. Bogatikov E. V. Sharkov A. V. Vesselovskii V. B. Mescheryakova 《Doklady Earth Sciences》2009,427(2):907-911
A geographic information system (GIS “Volcanic belts”) was used for analyzing the spatial and temporal relationship between
tectono-magmatic cycles in the Cenozoic that took place at the convergent plate boundaries, mostly in volcanic arc-back-arc
systems. The onset of back-arc basins and subaerial arc volcanism and their main evolutionary stages are shown to have occurred
about the same time. These processes are still ongoing, which is indicated by today’s active volcanoes, high heat flows, and
high deep-focus seismicity. The crust underlying both tectonic structures undergoes transformation, which results in a significant
thinning of the “granite” layer within the volcanic belts, whereas crust within the back-arc basins changes its properties
to the transitional (suboceanic) and oceanic type crusts. All processes that occur at the convergent plate boundaries can
be described within the arc-back-arc system, the principal dynamic components of which are the asthenospheric plume upwelling
above the continent edge and the oceanward-spreading plume head. This was accompanied by a gradual crustal thinning in the
back-arc region and the formation of areas with oceanic crust, as well as by involvement of crustal material, together with
rocks of the subducting slab, into subduction processes. As a result, the continental crust is removed from the tectonosphere
and stored in the “slab cemetery.” Only a minor portion of the crustal materials is returned to the surface as subduction-related
magmatism. 相似文献
20.
The role of crustal fertility in the generation of large silicic magmatic systems triggered by intrusion of mantle magma in the deep crust 总被引:1,自引:0,他引:1
S. Sinigoi J. E. Quick G. Demarchi U. Klötzli 《Contributions to Mineralogy and Petrology》2011,162(4):691-707
The Sesia magmatic system of northwest Italy allows direct study of the links between silicic plutonism and volcanism in the
upper crust and the coeval interaction of mafic intrusions with the deep crust. In this paper, we focus on the chemical stratigraphy
of the pre-intrusion crust, which can be inferred from the compositions of crustal-contaminated mafic plutonic rocks, restitic
crustal material incorporated by the complex, and granitic rocks crystallized from anatectic melts. These data sources independently
indicate that the crust was compositionally stratified prior to the intrusion of an 8-km-thick gabbroic to dioritic body known
as the Mafic Complex, with mica and K-feldspar abundance decreasing with depth and increasing metamorphic grade. Reconsideration
of published zircon age data suggest that the igneous evolution initiated with sporadic pulses at around 295 Ma, when mafic
sills intruded deep granulites which provided a minor amount of depleted crustal contaminant, very poor in LIL elements. With
accelerated rates of the intrusion, between 292 and 286 m.y, mafic magmas invaded significantly more fertile, amphibolite-facies
paragneisses, resulting in increased contamination and generating hybrid rocks with distinct chemistry. At this point, increased
anatexis produced a large amount of silicic hybrid melts that fed the incremental growth of upper-crustal plutons and volcanic
activity, while the disaggregated restite was largely assimilated once ingested by the growing Mafic Complex. This “igneous
climax” was coincident with an increasing rate of intrusion, when the upper Mafic Complex began growing according to the “gabbro
glacier” model and, at about the same time, volcanic activity initiated. Cooling lasted millions of years. In the coupled
magmatic evolution of the deep and upper crust, the Mafic Complex should be considered more as a large reservoir of heat rather
than a source of upper-crustal magma, while the fertility of “under/intra-plated” crust plays a crucial role in governing
the generation of large volumes of continental silicic magmas. 相似文献