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1.
Rare-earth elements as source indicators of Pan-African granites from Obudu Plateau,Southeastern Nigeria 总被引:1,自引:1,他引:0
The rare-earth element (REE) concentrations of representative granite samples from the southeast of the Obudu Plateau, Nigeria, were analyzed with an attempt to determine the signatures of their source, evolutionary history and tectonic setting. Results indicated that the granites have high absolute REE concentrations (190×10^-6-1191×10^-6; av.=549×10^-6) with the chondrite-normalized REE patterns characterized by steep negative slopes and prominent to slight or no negative Eu anomalies. All the samples are also characterized by high and variable concentrations of the LREE (151×10^-6-1169×10^-6; av.= 466×10^-6), while the HREE show low abundance (4×10^-6-107×10^-6; av.=28×10^-6). These are consistent with the variable levels of REE fractionation, and differentiation of the granites. This is further supported by the range of REE contents, the chondrite-normalized patterns and the ratios of LaN/YbN (2.30-343.37), CeN/YbN (5.94-716.87), LaN/SmN (3.14-11.68) and TbN/YbN (0.58-1.65). The general parallelism of the REE patterns, suggest that all the granites were comagmatic in origin, while the high Eu/Eu* ratios (0.085-2.807; av.=0.9398) indicate high fo2 at the source. Similarly, irregular variations in LaN/YbN, CeN/YbN and Eu/Eu* ratios and REE abundances among the samples suggest behaviors that are related to mantle and crustal sources. 相似文献
2.
Christopher D. Wareham Ian L. Millar Alan P. M. Vaughan 《Contributions to Mineralogy and Petrology》1997,128(1):81-96
Subduction-related Mesozoic to Cainozoic granites s.l. in western Palmer Land, Antarctic Peninsula, have similar chemical compositions to Archean tonalite-trondhjemite-granodiorite
(TTG) suites, Phanerozoic slab-melts (adakites), and to experimental partial melts of basaltic material in equilibrium with
amphibole ± pyroxene ± garnet. They are predominantly sodic, metaluminous and most have Al2O3 > 15 wt% and Y < 18 ppm. All are light rare earth element (LREE)-enriched (2 < La/Ybn <30) and most have small Eu anomalies. They have a wide range of initial ɛNd(t) (−6.8 to +4.5) and ɛSr(t) (+293.4 to −3.7), but most Pb isotope compositions deviate by < 0.3% from their mean. The Pb isotope data indicate a crustal
component to all the granites, which Sr and Nd isotope variations suggest is pre-Triassic–Triassic. The 207Pb/204Pb(t) range from 15.602 to 15.666 and appear to preclude a significant Proterozoic, or older, crustal component. The granites have
chemical and isotopic compositions that suggest they are not partial melts of subducted oceanic lithosphere, as has been suggested
for some Archean and Phanerozoic TTG magmas. We conclude that they were produced by mixing between basaltic-andesitic arc
magmas, partial melts of juvenile basaltic lower crust and pre-Triassic crust. The low H(heavy)REE+Y content of some of the
granites requires that garnet was a residual phase in the crust during partial melting, indicating a crustal thickness of
>36 km. Between Triassic and Tertiary times the initial ɛNd(t) of the magmatism increased and ɛSr(t) decreased, suggesting that new continental crust was produced during this period. Underplating by mafic magma was an important
crustal growth mechanism in the arc: the generation of abnormally thick crust, and its subse quent fusion, is considered to
be a consequence of ca. ≥ 180 Ma of subduction and associated magmatism in the region. An implication of the model is that
dense garnet-amphibolite and eclogite residues from partial melting of the lower crust will accumulate. In theory, the setting
was appropriate for such residues to detach from the base of the crust and to sink into the convecting mantle. Such a process
would leave the rest of the crust enriched in large ion lithophile elements/LREE, but depleted in HREE+Y.
Received: 2 October 1995 / Accepted: 5 January 1997 相似文献
3.
J.-H. Yu S. Y. O’Reilly L. Zhao W. L. Griffin M. Zhang X. Zhou S.-Y. Jiang L.-J. Wang R.-C. Wang 《Mineralogy and Petrology》2007,90(3-4):271-300
Summary The F-rich Hongshan pluton in the eastern Nanling Range, southern China, is a topaz-bearing albite leucogranite. It is distinctive
from other topaz-bearing felsic rocks in South China with respect to age, size, geochemical evolution and topaz mode and morphology.
The Hongshan granites are highly peraluminous and characterized by high K2O/Na2O, Si, Rb, Cs, Nb, Ta and F, and low Ca, Ba, Sr, Zr, Hf, P, K/Rb, Zr/Hf and Eu/Eu*. The granites show significant trace-element variations with magma evolution, with increasing Rb, Cs, Nb, Ta, Sn, W and decreasing
Sr, Ba, Zr, Hf, Y, REE, Pb, Th, K/Rb, Zr/Hf, Th/U and Eu/Eu*. These changes dominantly reflect fractional crystallization of plagioclase, biotite and accessory minerals such as zircon
and monazite. The granites also exhibit a decrease in ɛNd(t = 225 Ma) from −7.9 to −11.7 with magma evolution. Modeling shows
that the Nd isotopic variation could result from assimilation of the Taoxi Group wall rocks during fractional crystallization.
The Hongshan pluton also shows spatial geochemical variations; the most evolved parts are located in the southeastern part
of the pluton, which would be the most likely target area for rare-metal mineralization commonly associated with other topaz-bearing
granites.
Zircon grains from two rock types in the Hongshan body were analyzed in situ for U–Pb ages and Hf isotopic values. The concordant zircon grains mostly range from 218 to 230 Ma with an average of 224.6
± 2.3 Ma (Indosinian). Some zircons with different internal structures and Hf isotope compositions, as well as monazite fragments,
yield U–Pb ages of ca. 280 to 240 Ma, suggesting older thermal events in the studied area. The ɛHf(t) of these older zircons
is strongly negative (−12.3), implying a crustal source with a Paleoproterozoic model age, similar to that for the Proterozoic
Zhoutan Group. The main (∼225 Ma) zircon population exhibits less negative ɛHf(t) (−3.0 to −7.6) and Mesoproterozoic model
ages, suggesting that the original magma of the Hongshan granite was generated from deeper Mesoproterozoic crust. 相似文献
4.
The Longwangzhuang granite pluton occurs on the southern margin of the North China Craton and consists mainly of biotite syenogranite with aegirine granite being locally distributed.The granites are characterized by high silicon and alkaline contents(SiO2=72.17%-76.82%,K2O+Na2O=8.28%-10.22%,K2O/Na2O>>1),AI(agpaitic index) =0.84-0.95,DI=95-97,ASI(aluminum saturation index)=0.96-1.13,and very high Fe* number(FeO*/(FeO*+Mg)=0.90-0.99),thus the granites are assigned to the metaluminous to weakly peraluminous,alkalic to calc-alkalic ferroan A-type granites.The granites are rich in large ion lithophile elements(LILE),especially high in REE concentrations(REE+Y=854×10-6-1572×10-6);whereas the enrichment of high strength field elements(Nb,Ta,Zr,Hf) is obviously less than that of LILEs,exhibiting mild depletions on trace element spider plots;and the rocks are significantly depleted in Ba,Sr,Ti,and Pb.The low εNd(t) values(-4.5--7.2) and high model ages(2.3-2.5 Ga) of the granites as well as the low εHf(t) values(-1.11--5.26) and high Hf model ages(THf1= 2.1-2.3 Ga,THf2=2.4-2.6 Ga) of zircons from the biotite syenogranite suggest that the granites were probably derived from an enriched mantle source.The zircons from the biotite syenogranite are mainly colorless transparent crystals exhibiting well-developed oscillatory zoning on the cathodoluminescence images with a LA-ICPMS zircon U-Pb age of 1602.1±6.6 Ma(MSWD=0.48).Petrochemical,trace elements,as well as Nd and Hf isotopic compositions of the rocks demonstrate that the granites were formed in a within-plate extensional tectonic regime possibly related to the breakup of the Columbia supercontinent.The granites were most likely formed through extreme fractional crystallization of alkali basaltic magma resulted from partial melting of the mantle,which was fertilized by recycling crustal rocks triggered by the delamination of lithospheric mantle and lower crust following the ~1.8 Ga collision and amalgamation of the North China Craton which is part of the Columbia supercontinent.However,contamination of neo-Archean to Paleoproterozoic crustal rocks during the ascent and emplacement of the magma could not be excluded.Being the youngest known anorogenic magmatism on the southern margin of the North China Craton related to Columbia breakup,it might represent the break off of the North China Craton from Columbia supercontinent at the end of Paleoproterozoic. 相似文献
5.
The paper presents results of petrochemical, geochemical, and isotope-geochemical study of the Patchemvarek and Severnyi gabbroanorthosite
massifs of the Kola Peninsula. It was shown that the rocks of these massifs differ from the gabbroanorthosite massifs of the
Neoarchean Keivy-Kolmozero Complex in the more calcic composition (70–85% An) of normative plagioclase, and low contents of
TiO2, FeO, and Fe2O3. In terms of chemical composition, the gabbroanorthosites of the studied massifs are close to the rocks of the Fisken?sset
Complex (Southwestern Greenland) and to the anorthosites of the Vermillion Lake Complex (Canada). U-Pb zircon dating established
Mesoarchean ages of 2925 ± 7 and 2935 ± 8 Ma for the gabbroan-orthosites of the Patchemvarek and Severnyi massifs, respectively.
It was shown that the gabbroanorthosites of the studied massifs have fairly low REE contents (Ce
n
= 2.2−4.2, Yb
n
= 1.6−2.6) and distinct positive Eu anomaly. Comagmatic ultrabasic differentiates have practically unfractionated REE pattern,
low total REE contents (Ce
n
= 1.2, Yb
n
= 1.1, La/Yb
n
= 1.3), and no Eu anomaly. The studied samples of the Archean gabbroanorthosites are characterized by positive εNd = +2.68 for the gabbroanorthosites of the Severnyi Massif and from + 2.77 to + 1.66 for the Patchemvarek Massif. Initial
strontium isotope ratios are 87Sr/86Sr
i
= 0.70204 ± 8 and 87Sr/86Sr
i
= 0.70258 ± 8 for the rocks of the Severnyi and Patchemvarek massifs, respectively. Our study showed that the obtained U-Pb
zircon ages for the gabbroanorthosites of the Patchemvarek and Severnyi massifs represent the oldest date for the Kola peninsula,
thus marking the oldest, Mesoarchean stage in the evolution of region. The differences in the initial 143Nd/144Nd ratios between the Neoarchean gabbroanorthosites of the Keivy-Kolmozero Complex and the Mesoarchean gabbroanorthosites
of the studied massifs suggest the existence of two mantle sources. One of them produced intrusions with an age of 2.67–2.66
Ga, while other was responsible for the formation of massifs with an age of 2.93–2.92 Ga. The composition and temperature
of “parental” melt of the gabbroanorthosites were simulated using COMAGMAT-3.5 program. According to the calculations, the
parental melt represented aluminous basalt, whose differentiation at T = 1280°C and P = 7 kbar at the crust-mantle boundary was accompanied by plagioclase floatation and formation of “crystal mesh” that produced
anorthosite complexes. The gabbroanorthosies of the Patchemvarek and Severnyi massifs were presumably derived from MORB-type
basalts of oceanic settings, while the Tsaga, Achinskii, and other anorthosite massifs of the Neoarchean age were generated
from subalkaline magma formed in within-plate anorogenic setting. Sm-Nd isotope data suggest the existence of several mantle
sources in the Kola region, which produced melts for different-age gabbroanorthosite massifs since Mesoarchean to the middle
Paleoproterozoic. The Archean-Early Proterozoic anorthosite magmatism of the Kola region records a complete cycle (∼ 800 Ma)
of the formation and consolidation of continental block. 相似文献
6.
The 1.86 Ga Liangtun-Kuangdonggou complex (LKC) is one of the oldest alkaline syenite bodies so far discovered in China. This syenite suite has elevated contents of total alkali (K2O Na2O), with an average of 10.50%, and a mean Rittmann Index (σ) of 6.48. The intrusions have slightly higher concentrations of K2O than those of Na2O on a weight percent basis, indicating the rocks belong to potassium-rich alkaline syenite series. Total rare-earth element concentrations (∑REE ) of the rocks are relatively high, ranging from 324×10 -6 to 1314×10 -6, with a mean value of 666×10 -6. The REE patterns are subparallel and rightward steep with (La/Yb)N >33, showing mild negative to positive Eu anomalies (δEu: 0.63-1.15). All samples exhibit strong LILE and LREE enrichments and TNT (Nb, Ta, Ti) and P depletions in multi-element spidergrams. On the εSr(t)-εNd(t) correlation diagram, most analytical data points plot within the enriched mantle field with low ( 87Sr/86Sr)i ratios (0.7045-0.7051) and negative εNd(t) values (-3.72--3.97), falling among those kimberlites from Fuxian County, Liaoning Provinve, from Mengyin County, Shandong Province and the Ⅱ-type kimberlites from South Africa. These characteristics imply that the LKC-rocks may have the same source as the above-mentioned kimberlites, i.e., they have close connections to the materials derived from enriched mantle reservoirs, further revealing that the upper mantle beneath the northeastern part of the North China Plate had been highly enriched before 1.86 Ga. Geodynamically, the LKC-rocks were formed in a within-plate environment with close genetic connections to rift-related alkaline magma activities possibly controlled by ancient mantle plumes. 相似文献
7.
M. Zhai A. B. Kampunzu M. P. Modisi Z. Bagai 《International Journal of Earth Sciences》2006,95(3):355-369
The Francistown plutonic rocks at the south-western margin of the Zimbabwe craton consist of three igneous suites: Sanukitoid, Tonalite–Trondhjemite–Granite (TTG) suites and High-K granites. The TTG suite is subdivided into High Aluminum-TTG (HA-TTG) and Low Aluminum-TTG (LA-TTG) sub-suites. Their Rb–Sr isotope systems were partially homogenized by post-crystallization thermo–tectonic events, in which hydrothermal solutions and migmatization played an important role. Therefore, the Rb–Sr isochron age of 2427±54 Ma can only be regarded as a lower limit to the Francistown plutonic rock age. The large errors in the Sm–Nd isochron dates of Francistown granitoids indicate that these dates are not really constrained. In this study we compared the rock types of Francistown and adjacent areas, adopting the precise U, Th–Pb single zircon SHRIMP ages from the Vumba area as references. For TTG and Sanukitoid suites, the age we adopted is ca. 2.7 Ga, which is close to their depleted-mantle Sm–Nd model ages (T
DM). For High-K granites, the age adopted is ca. 2.65 Ga, which is also close to their Sm–Nd isochron age. The highest ε
Nd
t
values of Sanukitoids and TTG are +2.1 and +2.3, respectively. The positive ε
Nd
t
values and trace element geochemistry support partial melting of a depleted mantle and young oceanic crust for the genesis of Sanukitoid and the TTG suites respectively. The lowest ε
Nd
t
values of Sanukitoids and TTGs are −1.0 and −1.1, respectively, indicating contamination by continental crust, up to 10 and 14%, respectively. The ε
Nd
t
values of TTG decrease with decreasing Al2O3 and Sr contents and increasing Eu negative anomalies (Eu*–Eu), suggesting that the TTG magmas underwent a coupled fractionation crystallization and crustal contamination, and that the LA-TTG was the product of the fractionation and contamination of the HA-TTG sub-suite. In contrast, negative ε
Nd
t
values for the High-K granites (from −0.4 to −3.5) indicate the involvement of LA-TTG and some materials from an old continental crust in their genesis. The products of partial melting of both oceanic and continental crusts at the south-western margin of the Zimbabwe craton occurred within a short time interval (from 2.7 to 2.65 Ga ago) suggesting that the Francistown plutonic rocks were formed in a active continental margin environment, where a young ocean plate (Limpopo oceanic plate) subducted underneath an old continental plate (Zimbabwe craton). 相似文献
8.
V. E. Strikha 《Geochemistry International》2006,44(8):791-807
Geochemical and isotopic data were used for a comparative analysis of Late Mesozoic (150–120 Ma) granitoids in various geological
structures of the upper Amur area. The granitoids are metaluminous high-potassic I-type rocks of the magnetite series. They
have variable alkalinity and consist of the monzonite-granite and granosyenite-granite associations. The monzonite-granite
association consists of calc-alkaline granitoids of normal alkalinity belonging to the Umlekan-Ogodzhinskaya volcanic-plutonic
zone and the Tynda-Bakaran Complex of the Stanovoy terrane. The rocks are characterized by negative anomalies of U, Ta, Nd,
Hf, and Ti (in patterns normalized to the primitive mantle), with Eu anomalies pronounced weakly in the granodiorites and
quartz and monzodiorites and more clearly in the granites: Eu/Eu* = 0.37–0.95, and (La/Yb)n = 7–24, Tbn/Ybn = 1.4–3.2. The granosyenite-granite association comprises of moderately alkaline rocks, which are subdivided into three groups
according to their geochemistry. The first group consists of phase-I granosyenites of the Uskalinskii Massif of the Umlekan-Ogodzhinskaya
zone with the highest concentrations of Sc, V, Cr, Co, Ni, Cu, Cs, Rb, Sr, Y, Zr, Yb, and Th; negative anomalies at Ba, Ta,
Sr, and Hf; Eu/Eu* = 0.50–0.58, (La/Yb)n = 15–16, and Tbn/Ybn = 1.8. The second group comprises of moderately alkaline granitoids of the Umlekan-Ogodzhinskaya zone and the Khaiktinskii
Complex of the Baikal-Vitim superterrane. Geochemically, the granitoids of this group are generally similar to the monzodiorite-granite
association and differ from it in having lower concentrations of REE and Y, Eu/Eu* = 6.2–1.0, (La/Yb)n = 28–63, and Tbn/Ybn = 2.1–4.5. The third group consists of granitoids of the Chubachinskii Complex of the Stanovoi terrane, which typically show
negative Cs, Rb, Th, U, Ta, Hf, and Ti anomalies; the lowest concentrations of V, Cr, Co, and Ni; and the highest contents
of Sr. The granosyenites of the first phase display clearly pronounced negative Eu anomalies (Eu/Eu* = 0.53–0.68), (La/Yb)n = 7–24, and Tbn/Ybn = 0.8–2.0. The granitoids of the second phase have (La/Yb)n = 51–84, no Eu anomalies, or very weak Eu anomalies (Eu/Eu* = 0.97–1.23). The silica-oversaturated leucogranites of the third
phase are characterized by elevated concentrations of REE, clearly pronounced Eu anomalies (Eu/Eu* = 0.48), and flat REE patterns
(Tbn/Ybn = 1.3). The diversity of the granitoids is demonstrated to have been caused largely by the composition of the Precambrian
source, which was isotopically heterogeneous. The rocks of the monzodiorite-granite association and first-group granosyenites
of the granosyenite-granite association of the Tynda-Bakaran Complex were supposedly derived from garnet-bearing biotite amphibolites.
In contrast to these rocks, the source of the second-group granites of the granosyenite-granite association was of mixed amphibolite-metagraywacke
composition. The third-group of granitoids were melted out of Early Proterozoic crustal feldspar-rich granulites of variable
basicity, with minor amounts of Archean crustal material. The granitoids were emplaced in a collisional environment, perhaps,
during the collision of the Amur superterrane and Siberian craton. This makes it possible to consider these rocks as components
of a single continental volcanic-plutonic belt.
Original Russian Text ? V.E. Strikha, 2006, published in Geokhimiya, 2006, No. 8, pp. 855–872. 相似文献
9.
The Duolanasayi gold deposit, 60 km NW of Habahe County, Xinjiang Uygur Autonomous Region, is a mid-large-scale gold deposit controlled by brittle-ductile shearing, and superimposed by albitite veins and late-stage magma hydrothermal solutions. There are four types of pyrite, which are contained in the light metamorphosed rocks (limestone, siltstone), altered-mineralized rocks (chlorite-schist, altered albite-granite, mineralized phyllite), quartz veins and carbonatite veinlets. The pyrite is the most common ore mineral. The Au-barren pyrite is present mainly in a simple form and gold-bearing pyrite is present mainly in a composite form. From the top downwards, the pyrite varies in crystal form from {100} and {210} {100} to {210} {100} {111} to {100} {111}. Geochemical studies indicate that the molecular contents of pyrite range from Fe1.057S2 to Fe0.941S2. Gold positively correlates with Mn, Sr, Zn, Te, Pb, Ba and Ag. There are four groups of trace elements: Fe-Cu-Sr-Ag, Au-Te-Co, As-Pb-Zn and Mn-V-Ti-Ba-Ni-Cr in pyrite. The REE characteristics show that the total amount of REE (ΣREE) ranges from 32.35×10 -6 to 132.18×10 -6; LREE/HREE, 4.466-9.142; (La/Yb)N, 3.719-11.133; (Eu/Sm)N, 0.553-1.656; (Sm/Nd)N, 0.602-0.717; La/Yb, 6.26-18.75; δEu, 0.628-2.309; δCe, 0.308-0.816. Sulfur isotopic compositions (δ 34S=-2.46‰--7.02‰) suggest that the sulfur associated with gold mineralization was derived from the upper mantle or lower crust. 相似文献
10.
Petrogenesis of isotopically unusual Pliocene olivine leucitites from Deep Springs Valley, California 总被引:2,自引:0,他引:2
High-K mafic alkalic lavas (5.4 to 3.2 wt% K2O) from Deep Springs Valley, California define good correlations of increasing incompatible element (e.g., Sr, Zr, Ba, LREE)
and compatible element contents (e.g., Ni, Cr) with increasing MgO. Strontium and Nd isotope compositions are also correlated
with MgO; 87Sr/86Sr ratios decrease and ɛNd values increase with decreasing MgO. The Sr and Nd isotope compositions of these lavas are extreme compared to most other
continental and oceanic rocks; 87Sr/86Sr ratios range from 0.7121 to 0.7105 and ɛNd values range from −16.9 to −15.4. Lead isotope ratios are relatively constant, 206Pb/204Pb ∼17.2, 207Pb/204Pb ∼15.5, and 208Pb/204Pb ∼38.6. Depleted mantle model ages calculated using Sr and Nd isotopes imply that the reservoir these lavas were derived
from has been distinct from the depleted mantle reservoir since the early Proterozoic. The Sr-Nd-Pb isotope variations of
the Deep Springs Valley lavas are unique because they do not plot along either the EM I or EM II arrays. For example, most
basalts that have low ɛNd values and unradiogenic 206Pb/204Pb ratios have relatively low 87Sr/86Sr ratios (the EM I array), whereas basalts with low ɛNd values and high 87Sr/86Sr ratios have radiogenic 206Pb/204Pb ratios (the EM II array). High-K lavas from Deep Springs Valley have EM II-like Sr and Nd isotope compositions, but EM
I-like Pb isotope compositions. A simple method for producing the range of isotopic and major- and trace-element variations
in the Deep Springs Valley lavas is by two-component mixing between this unusual K-rich mantle source and a more typical depleted
mantle basalt. We favor passage of MORB-like magmas that partially fused and were contaminated by potassic magmas derived
from melting high-K mantle veins that were stored in the lithospheric mantle. The origin of the anomalously high 87Sr/86Sr and 208Pb/204Pb ratios and low ɛNd values and 206Pb/204Pb ratios requires addition of an old component with high Rb/Sr and Th/Pb ratios but low Sm/Nd and U/Pb ratios into the mantle
source region from which these basalts were derived. This old component may be sediments that were introduced into the mantle,
either during Proterozoic subduction, or by foundering of Proterozoic age crust into the mantle at some time prior to eruption
of the lavas.
Received: 28 February 1997 / Accepted: 9 July 1998 相似文献
11.
Yanjun Li Junhao Wei Jun Tan Lebing Fu Xuntao Liu Lingjun Kong Yongjian Jiang Wenjie Shi 《中国地球化学学报》2011,30(2):165-174
The Liuyuan area,which is located on the southern margin of the Beishan orogenic belt,develops abundant Early Paleozic granitoids.SHRIMP zircon U-Pb dating yielded a weighted mean 206Pb/238U age of 421±8 Ma for the Liuyuan granodiorite(Zhao Zehui et al.,2007),implying its Late Silurian intrusion.Geochemical compositions showed that the Liuyuan granodiorite is characterized by high SiO2(65.01%-67.31%),A12O3(17.17%-18.05%) and Na2O(Na2O/K2O=1.67-1.87) but low Mg# contents calculated as 100×Mg2+/(Mg2++∑Fe2+) from 28.77 to 31.15,as well as being enriched in Sr(472×10-6-517×10-6) but depleted in Yb(1.2×10-6-1.42×10-6) and Y(12.8×10-6-14×10-6).The REEs are characterized by right-inclined patterns with LREE enrichment,HREE depletion and slightly negative Eu anomalies(Eu/Eu*=0.91-0.97).Major and trace elements indicate that the granodiorite is an adakite.The Nb/Ta values of the granodiorite vary from 10.80 to 18.01 and Nb/U from 6.32 to 10.09,both lying between the values of the crust and the mantle.The rock has low εNd(t) values(-2.5--0.8) and high ISr(0.706321-0.706495).Geochemical and Sr-Nd isotopic compositions indicate that the Liuyuan granodiorite is possibly derived from partial melting of thickening lower crust,related to mantle underplating.The Yb-Ta and Y+Nb-Rb discriminant diagrams imply the Liuyuan granodiorite intruded in a local extensional tectonic setting during late collision.Combined with previous studies on geochronology,geochemistry and tectonic setting of granitoids,we interprete that the constraint of this adakite in the Liuyuan area indicates that the tectonic setting may have transformed from collision to extension during the Early Devonian. 相似文献
12.
The metamorphic belt in central Jiangxi, located in the compound terrain within the Cathaysia, Yangtze Block and Caledonian fold zone of South China, is composed dominantly of meta-argillo-arenaceous rocks, with minor amphibolite. These rocks underwent amphibolite-facies metamorphism. The meta-argillo-arenaceous rocks show large variations in major element composition, but have similar REE patterns and trace element composition, incompatible element and LIE enrichments [ high Th/Sc (0.57-3.59) , La/Sc ( 1.46 - 12.4), La/Yb (5.84 - 19.0) ] and variable Th/U ratios, with ∑REE = 129-296μg/g, δEu =0.51 -0.86, and (La/Yb)N = 3.95 -12.9. The Nd isotopic model ages tDM of these rocks vary from 1597 to 2124 Ma. Their 143 Nd/144 Nd values are low [εNd (0) = - 11.4 to -- 15.8]. Some conclusions have been drawn as follows: (1) The metamorphic rocks in central Jiangxi Province are likely formed in a tectonic environment at the passive continental margin of the Cathaysia massif. (2) The metamorphosed argillo-arenaceous rocks are composed dominantly of upper crustal-source rocks (Al- and Krich granitic or/and sedimentary rocks of Early Proterozoic), which experienced good sorting, slow deposition and more intense chemical weathering. (3) According to the whole-rock Sm-Nd isochron ages (1113±49 to 1199 ± 26 Ma) of plagioclase-amphibole (schist) and Nd isotopic model age tDM ( 1597 - 2124Ma) of meta-argillo-arenaceous rocks, the metamorphic belt in central Jiangxi Province was formed during the Middle Proterozoic ( 1100 - 1600 Ma). 相似文献
13.
Yan-Jun Li Jun-Hao Wei Hua-Yong Chen Jun Tan Le-Bing Fu Gang Wu 《Mineralium Deposita》2012,47(7):763-780
The Maoduan Pb–Zn–Mo deposit is in hydrothermal veins with a pyrrhotite stage followed by a molybdenite and base metal stage. The Re–Os model ages of five molybdenite samples range from 138.6 ± 2.0 to 140.0 ± 1.9 Ma. Their isochron age is 137.7 ± 2.7 Ma. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb dating of the nearby exposed Linggen granite porphyry gave a 206Pb/238U age of 152.2 ± 2.2 Ma and the hidden Maoduan monzogranite yielded a mean of 140.0 ± 1.6 Ma. These results suggest that the intrusion of the Maoduan monzogranite and Pb–Zn–Mo mineralization are contemporaneous. δ 34S values of sulfide minerals range from 3.4‰ to 4.8‰, similar to magmatic sulfur. Four sulfide samples have 206Pb/204Pb = 18.252–18.432, 207Pb/204Pb = 15.609–15.779, and 208Pb/204Pb = 38.640–39.431, similar to the age-corrected data of the Maoduan monzogranite. These isotope data support a genetic relationship between the Pb–Zn–Mo mineralization and the Maoduan monzogranite and probably indicate a common deep source. The Maoduan monzogranite has geochemical features similar to highly fractionated I-type granites, such as high SiO2 (73.7–75.2 wt.%) and alkalis (K2O + Na2O = 7.8–8.9 wt.%) and low FeOt (0.8–1.3 wt.%), MgO (~0.3 wt.%), P2O5 (~0.03 wt.%), and TiO2 (~0.2 wt.%). The granitic rocks are enriched in Rb, Th, and U but depleted in Ba, Sr, Nb, Ta, P, and Ti. REE patterns are characterized by marked negative Eu anomalies (Eu/Eu* = 0.2–0.4). The Maoduan monzogranite, having (87Sr/86Sr) t = 0.7169 to 0.7170 and εNd(t) = −13.8 to −13.7, was probably derived from mixing of partial melts from enriched mantle and the Paleoproterozoic Badu group in an extensional tectonic setting. 相似文献
14.
Jiang-Feng Qin Shao-Cong Lai Chun-Rong Diwu Yin-Juan Ju Yong-Fei Li 《Contributions to Mineralogy and Petrology》2010,159(3):389-409
Petrogenesis of high Mg# adakitic rocks in intracontinental settings is still a matter of debate. This paper reports major
and trace element, whole-rock Sr–Nd isotope, zircon U–Pb and Hf isotope data for a suite of adakitic monzogranite and its
mafic microgranular enclaves (MMEs) at Yangba in the northwestern margin of the South China Block. These geochemical data
suggest that magma mixing between felsic adakitic magma derived from thickened lower continental crust and mafic magma derived
from subcontinental lithospheric mantle (SCLM) may account for the origin of high Mg# adakitic rocks in the intracontinental
setting. The host monzogranite and MMEs from the Yangba pluton have zircon U–Pb ages of 207 ± 2 and 208 ± 2 Ma, respectively.
The MMEs show igneous textures and contain abundant acicular apatite that suggests quenching process. Their trace element
and evolved Sr–Nd isotopic compositions [(87Sr/86Sr)i = 0.707069–0.707138, and εNd(t) = −6.5] indicate an origin from SCLM. Some zircon grains from the MMEs have positive εHf(t) values of 2.3–8.2 with single-stage Hf model ages of 531–764 Ma. Thus, the MMEs would be derived from partial melts of the
Neoproterozoic SCLM that formed during rift magmatism in response to breakup of supercontinent Rodinia, and experience subsequent
fractional crystallization and magma mixing process. The host monzogranite exhibits typical geochemical characteristics of
adakite, i.e., high La/Yb and Sr/Y ratios, low contents of Y (9.5–14.5 ppm) and Yb, no significant Eu anomalies (Eu/Eu* = 0.81–0.90),
suggesting that garnet was stable in their source during partial melting. Its evolved Sr–Nd isotopic compositions [(87Sr/86Sr)i = 0.7041–0.7061, and εNd(t) = −3.1 to −4.3] and high contents of K2O (3.22–3.84%) and Th (13.7–19.0 ppm) clearly indicate an origin from the continental crust. In addition, its high Mg# (51–55),
Cr and Ni contents may result from mixing with the SCLM-derived mafic magma. Most of the zircon grains from the adakitic monzogranite
show negative εHf(t) values of −9.4 to −0.1 with two-stage Hf model ages of 1,043–1,517 Ma; some zircon grains display positive εHf(t) of 0.1–3.9 with single-stage Hf ages of 704–856 Ma. These indicate that the source region of adakitic monzogranite contains
the Neoproterozoic juvenile crust that has the positive εHf(t) values in the Triassic. Thus, the high-Mg adakitic granites in the intracontinental setting would form by mixing between
the crustal-derived adakitic magma and the SCLM-derived mafic magma. The mafic and adakitic magmas were generated coevally
at Late Triassic, temporally consistent with the exhumation of deeply subducted continental crust in the northern margin of
the South China Block. This bimodal magmatism postdates slab breakoff at mantle depths and therefore is suggested as a geodynamic
response to lithospheric extension subsequent to the continental collision between the South China and North China Blocks. 相似文献
15.
Orhan Karsli Abdurrahman Dokuz İbrahim Uysal Faruk Aydin Bin Chen Raif Kandemir Jan Wijbrans 《Contributions to Mineralogy and Petrology》2010,160(4):467-487
We present elemental and Sr–Nd–Pb isotopic data for the magmatic suite (~79 Ma) of the Harşit pluton, from the Eastern Pontides
(NE Turkey), with the aim of determining its magma source and geodynamic evolution. The pluton comprises granite, granodiorite,
tonalite and minor diorite (SiO2 = 59.43–76.95 wt%), with only minor gabbroic diorite mafic microgranular enclaves in composition (SiO2 = 54.95–56.32 wt%), and exhibits low Mg# (<46). All samples show a high-K calc-alkaline differentiation trend and I-type
features. The chondrite-normalized REE patterns are fractionated [(La/Yb)
n
= 2.40–12.44] and display weak Eu anomalies (Eu/Eu* = 0.30–0.76). The rocks are characterized by enrichment of LILE and depletion
of HFSE. The Harşit host rocks have weak concave-upward REE patterns, suggesting that amphibole and garnet played a significant
role in their generation during magma segregation. The host rocks and their enclaves are isotopically indistinguishable. Sr–Nd
isotopic data for all of the samples display I
Sr = 0.70676–0.70708, ε
Nd(79 Ma) = −4.4 to −3.3, with T
DM = 1.09–1.36 Ga. The lead isotopic ratios are (206Pb/204Pb) = 18.79–18.87, (207Pb/204Pb) = 15.59–15.61 and (208Pb/204Pb) = 38.71–38.83. These geochemical data rule out pure crustal-derived magma genesis in a post-collision extensional stage
and suggest mixed-origin magma generation in a subduction setting. The melting that generated these high-K granitoidic rocks
may have resulted from the upper Cretaceous subduction of the Izmir–Ankara–Erzincan oceanic slab beneath the Eurasian block
in the region. The back-arc extensional events would have caused melting of the enriched subcontinental lithospheric mantle
and formed mafic magma. The underplating of the lower crust by mafic magmas would have played a significant role in the generation
of high-K magma. Thus, a thermal anomaly induced by underplated basic magma into a hot crust would have caused partial melting
in the lower part of the crust. In this scenario, the lithospheric mantle-derived basaltic melt first mixed with granitic
magma of crustal origin at depth. Then, the melts, which subsequently underwent a fractional crystallization and crustal assimilation
processes, could ascend to shallower crustal levels to generate a variety of rock types ranging from diorite to granite. Sr–Nd
isotope modeling shows that the generation of these magmas involved ~65–75% of the lower crustal-derived melt and ~25–35%
of subcontinental lithospheric mantle. Further, geochemical data and the Ar–Ar plateau age on hornblende, combined with regional
studies, imply that the Harşit pluton formed in a subduction setting and that the back-arc extensional period started by least
~79 Ma in the Eastern Pontides. 相似文献
16.
This paper is dedicated to the interpretation of isotope-geochemical data on high Sr-Ba granitoids exemplified by their typical
representatives—Late Miocene laccoliths of the Caucasian Mineral Waters (CMW). These massifs are made up of amphibole granites,
granosyenites, syenites, and leucogranites, which show particular behavior of Sr, Nd, and O isotope systems. The syenites
and granosyenites are characterized by δ18O variations from 8 to 10‰. As compared to them, the amphibole granites have lowered (up to 7‰), while leucogranites, elevated
(up to 12.5–13.7‰) oxygen isotope compositions. The (87Sr/86Sr)8.3 ratio in the granitoids accounts for 0.7083–0.7086, whereas σNd(T) varies from −4.2 to −2.1. 相似文献
17.
Kinwat crystalline inlier exposes Palaeoproterozoic granitoids belonging to the northern extensions of younger phase of Peninsular
gneissic complex (PGC) within Deccan Trap country in Eastern Dharwar Craton (EDC) and bounded in south by a major NW-SE trending
lineament (Kaddam fault). Geochemically, the Kinwat granitoids are similar to high-K, calc-alkaline to shoshonite magnesian
granitoids and subdivided into two major groups, i.e. felsic group (pink and grey granites) and intermediate to felsic group
(hybrid granitoids). The felsic group (∼67–74% SiO2) shares many features with Neoarchaean to Palaeoproterozoic high potassic granites of PGC such as higher LILE and LREE content
and marked depletion in Eu, P and HFSE, especially Nb, Ti, relative to LILE and LREE. The hybrid granitoids (∼58–67% SiO2) have comparatively higher Ca, Mg and Na contents and slightly lower REE content than the granitoids of felsic group. Both,
felsic and hybrid granitoids are metaluminous to weakly peraluminous and belong to highly fractionated I-type suite as evidenced
by negative correlation of SiO2 with MgO, FeOt, CaO, Na2O, Al2O3, whereas K2O, Rb and Ba show sympathetic relationship with SiO2. Moderate to strong fractionated REE patterns (Ce/YbN: ∼54–387) and strong negative Eu anomalies (Eu/Eu*: 0.13–0.41) are quite apparent in these granitoids. The geochemical characteristics
together with mineralogical features such as presence of biotite±hornblende as the dominant ferromagnesian mineral phases
point towards intracrustal magma source, i.e. derivation of magma by partial melting of probably tonalitic igneous protolith
at moderate crustal levels for felsic granites, whereas hybrid granitoids appear to be products of juvenile mantle-crust interaction,
in an active continental margin setting. 相似文献
18.
A. I. Grabezhev 《Geology of Ore Deposits》2010,52(2):138-153
The Early Devonian Gumeshevo deposit is one of the largest ore objects pertaining to the dioritic model of the porphyry copper
system paragenetically related to the low-K quartz diorite island-arc complex. The (87Sr/86Sr)t and (ɛNd)t of quartz diorite calculated for t = 390 Ma are 0.7038–0.7045 and 5.0–5.1, respectively, testifying to a large contribution of the mantle component to the composition
of this rock. The contents of typomorphic trace elements (ppm) are as follows: 30–48 REE sum, 5–10 Rb, 9–15 Y, and 1–2 Nb.
The REE pattern is devoid of Eu anomaly. Endoskarn of low-temperature and highly oxidized amphibole-epidote-garnet facies
is surrounded by the outer epidosite zone. Widespread retrograde metasomatism is expressed in replacement of exoskarn and
marble with silicate (chlorite, talc, tremolite)-magnetite-quartz-carbonate mineral assemblage. The 87Sr/86Sr ratios of epidote in endoskarn and carbonate in retrograde metasomatic rocks (0.7054–0.7058 and 0.7053–0.7065, respectively)
are intermediate between the Sr isotope ratios of quartz dioritic rocks and marble (87Sr/86Sr = 0.70784 ± 2). Isotopic parameters of the fluid equilibrated with silicates of skarn and retrograde metasomatic rocks
replacing exoskarn at 400°C are δ18O = +7.4 to +8.5‰ and δD = −49 to −61‰ (relative to SMOW). The δ13C and δ18O of carbonates in retrograde metasomatic rocks after marble are −5.3 to +0.6 (relative to PDB) and +13.0 to +20.2% (relative
to SMOW), respectively. Sulfidation completes metasomatism, nonuniformly superimposed on all metasomatic rocks and marbles
with formation of orebodies, including massive sulfide ore. The δ34S of sulfides is 0 to 2‰ (relative to CDT);87Sr/86Sr of calcite from the late calcite-pyrite assemblage replacing marble is 0.704134 ± 6. The δ13C and 87Sr/86Sr of postore veined carbonates correlate positively (r = 0.98; n = 6). The regression line extends to the marble field. Its opposite end corresponds to magmatic (in terms of Bowman, 1998b)
calcite with minimal δ13C, δ18O, and 87Sr/86Sr values (−6.9 ‰, +6.7‰, and 0.70378 ± 4, respectively). The aforementioned isotopic data show that magmatic fluid was supplied
during all stages of mineral formation and interacted with marble and other rocks, changing its Sr, C, and O isotopic compositions.
This confirms the earlier established redistribution of major elements and REE in the process of metasomatism. A contribution
of meteoric and metamorphic water is often established in quartz from postore veins. 相似文献
19.
G. Gruau J. Bernard-Griffiths C. Lécuyer O. Henin J. Macé M. Cannat 《Contributions to Mineralogy and Petrology》1995,121(4):337-350
Peridotites, dykes and gabbros from the 470–420 Ma Trinity Ophiolite Complex of northern California exhibit large geochemical
rare earth element (REE) and Nd isotopic variations on the small scales which are indicative of a complex history. The Trinity
Ophiolite, which covers an area of ≈1600 km2, consists of three distinct units: (1) a ∼2–4 km-thick sheet of plastically deformed peridotites, including various ultrabasic
lithologies (plagioclase and spinel lherzolite, harzburgite, wherlite and dunite); the peridotite unit is a fragment of mantle
lithosphere of oceanic affinity; (2) a series of small (∼1 km diameter) undeformed gabbroic massifs; (3) several generations
of basic dykes. The peridotites display the largest geochemical and isotopic variations, with ɛNd(T) values ranging from +10 down to 0. In the gabbroic massifs and intrusive dykes, the variation in model ɛNd(T) values is reduced to 7 ɛNd units: 0 to +7. As a general rule, peridotites, gabbros and dykes with ɛNd(T) values around 0 or +3 give less depleted L(light)REE patterns than do those with ɛNd(T) values in the range +7 to +10. In the peridotites, the Nd isotopic variations take place over very short distances, with
jumps as large as 7 ɛNd units occurring on scales of less than 20 m. Comparison with available age data indicates that the peridotites with ɛNd(T)≈+10 could be slightly older than the intrusive gabbro massifs and basic dykes (470 Ma vs. 420 Ma). Strontium isotopic data
used in connection with Sm-Nd results demonstrate that the 10 ɛNd units variation displayed by the Trinity Peridotite is a primary feature and not an artefact due to REE mobility during seawater
interaction. The variable Nd isotopic signatures and variable LREE patterns in the Trinity Peridotite cannot represent mantle
source characteristics as there is evidence that this unit was partially melted when it rose as part of the upwelling convecting
mantle. Field, petrographic, geochemical and isotopic data rather suggest that the observed heterogeneity is due to local
reactions between a 470 Ma proto-peridotite with ɛNd(T)=+10 and younger (420 Ma) basaltic melts with lower ɛNd(T) values (i.e. the gabbroic massifs and the dykes). The gabbros and basic dykes of the Trinity Complex have geochemical and
isotopic compositions similar to the arc basalts from the adjacent Copley Formation, so it is proposed that the younger melts
are related to arc magmatism.
Received: 13 January 1995/Accepted 5 May 1995 相似文献
20.
Summary The Salmi batholith is situated on the eastern edge of the EW-trending anorthositerapakivi granite belt of the Fennoscandian shield, at the contact between Proterozoic and Archean crustal domains. The tectonic setting and high K, Rb, Nb, Y, Zr, REE (except Eu), F, Sn, Be, and Li contents of.the Salmi batholith indicate that it represents typical subalkaline A-type and within plate granites. Gabbro-anorthosites of the batholith demonstrate a concordant U-Pb apatite age of 1563 ± 9 (2) Ma and a Sm-Nd internal isochron age of 1552 ± 69 Ma. Zircons from amphibole-biotite granites have an upper concordia intercept U-Pb age of 1543 ± 8 Ma. An older inherited zircon component with elevated Th/U ratio is found in zircons separated from K-feldspar ovoids. Rb-Sr internal errorchron for the granites yields an age of 1455 ± 17 Ma, probably the time of completion of postmagmatic processes within the batholith. The gabbro-anorthosites and granites show similar initial Nd, Sr, and feldspar Pb isotope compositions (
Nd = - 6.5 to - 8.2;
2 = 8.6 to 8.9;
2 = 3.9 to 4.0; ISr = 0.7052 to 0.7057 for the basic rocks, and
Nd = -6.2 to -8.9;
2 = 8.1 to 9.2;
2 = 4.0 to 4.4; ISr = 0.7050 to 0.7072 for the granites). Two-stage neodymium TDM model ages for both assemblages range from 2.60 to 2.80 Ga. Old LREE-enriched sources with low time-integrated U/Pb and Rb/Sr and elevated Th/U ratios were involved in the formation of both the gabbroanorthosites and the granites. Bulk contamination with crustal materials cannot explain the data for the basic rocks. Selective incorporation of Pb, Sr, and Nd from Archean lower crust is needed, or else, the gabbro-anorthosites may have been derived from an isotopically anomalous subcontinental mantle source. The ascent of a mantle diapir resulted in anatexis of the lower crust and formation of the parent magma for the rapakivi granites.
Pb-Nd-Sr Isotope, und geochemische Daten: Bedeutung für die Entstehung des 1,54–1,56 Salmi Rapakivi Granit-ANorthosit-Batholithen (Karelia, Rußland)
Zusammenfassung Der Salmi-Batholith ist am östlichen Rand des Ost-West streichenden Anorthosit Rapakivi-Granitgürtels des fennoskandischen Schildes am Kontakt zwischen proterozoischen und archaischen Krustenbereichen gelegen. Die tektonische Position und hohe K, Rb, Nb, Y, Zr, REE (mit Ausnahme von Eu), F, Sn, Be und Li-Gehalte des Salmi-Batholithen weisen darauf hin, daß es sich hier um einen typischen subalkalischen A-Typ und within plate Granit handelt. Gabbro-Anorthosite des Batholithen zeigen ein konkordantes U-Pb Apatit alter von 1563 ± 9 (2) Ma und ein internes Sm-Nd Isochronenalter von 1552 ± 69 Ma. Zirkone aus den Amphibolit-Biotitgraniten haben ein oberes Concordia U-Pb Alter von 1543 ± Ma. Ein ältere, ererbte Zirkonkom ponente mit erhöhtem Th/U Verhältnis kommt in Zirkonen, die von K-Feldspat Ovoi den abgetrennt wurden, vor. Eine interne Rb-Sr Errorchrone für die Granite ergibtein Alter von 1455 ± 7 Ma. Dies repräsentiert wahrscheinlich die Zeit des Abschlusses postmagmatischer Prozesse innerhalb des Batholithen. Die Gabbro-Anorthosite und Granite zeigen ähnliche Nd, Sr und Feldspat Pb Isotopenzusammensetzungen ( Nd = –6.5 to 8.2; 2 = 8.6 to 8.9; K2 = 3.9 to 4.0; ISr = 0.7052 to 0.7057 für die mafischen Gesteine, und Nd = –6.2 to -8.9; 2 = 8.1 to 9.2; K2 = 4.0 to 4.4; ISr = 0.7050 to 0.7072 für die Granite). Zweistufige Neodymium TDM Modellalter für beide Assoziationen liegen zwischen 2.60 und 2.80 Ga. Alte LREE-angereicherte Quellen mit niedrigen, zeitintegrierten U/Pb und Rb/Sr und erhöhten Th/U Verhältnissen waren bei der Bildung der Gabbro-Anorthosite und Granite involviert. Kontamination mit Krus tenmaterial kann die Daten für die basischen Gesteine nicht erklären. Entwederist dazu eine selektive Inkorporation von Pb, Sr und Nd aus der tieferen archaischen Kruste erforderlich oder man muß annehmen, daß die Gabbro-Anorthosite von einer isotopisch anomalen subkontinentalen Mantelquelle stammen. Der Aufstieg eines Mantel-Diapirs führt zu Anatexis der tieferen Kruste und zur Bildung der Ausgangsmagmen für die Rapakivi Granite.相似文献