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1.
~~Characteristics of the mantle source region of sodium lamprophyres and petrogenetic tectonic setting in northeastern Hunan,China~~  相似文献   

2.
Two groups of rhyolites have been recognized at San Vincenzo (Tuscany, Italy). Group A rhyolites are characterized by plagioclase, quartz, biotite, sanidine and cordierite mineral assemblages. They show constant MgO and variable CaO and Na2O contents. Initial87Sr/86Sr ratios in group A samples range between 0.71950 and 0.72535, whereas the Nd isotopic compositions are relatively constant (0.51215–0.51222). Group B rhyolites are characterized by orthopyroxene and clinopyroxene as additional minerals, and show textural, mineralogical and chemical evidence of interaction with more mafic magmas. The Sr and Nd isotopic ratios range between 0.71283–0.71542 and 0.51224–0.51227 respectively. Magmatic inclusions of variable size (1 mm to 10 cm) were found in groups B rhyolites. These inclusions consist mainly of diopsidic clinopyroxene and minor olivine and biotite. They are latitic in composition and represent blobs of hybrid intermediate magmas entrained in the rhyolitic melts. These magmatic inclusions have relatively high Sr contents (996–1529 ppm) and Sr and Nd isotope-ratios of 0.70807–0.70830 and 0.51245–0.51252 respectively.87Sr/87Sr data on minerals separated from both group A and B rhyolites and magmatic inclusions reveal strong isotopic disequilibria due to the presence of both restitic and newly crystallized phases in group A rhyolites and due to interaction of rhyolites with a mantle-de-rived magma in group B rhyolites. Isotopic data on whole rocks and minerals allow us to interpret the group A rhyolites as representative of different degrees of melting of an isotopically fairly homogeneous pelitic source; conversely, group B rhyolites underwent interactions with a mantle-derived magma. The crustal source as inferred from isotopic systematics would be characterized by87Sr/86Sr and143Nd/144Nd ratios close to 0.7194 and 0.51216 respectively. The sub-crustal magma would have Sr isotopic composition close to 0.7077 and a143Nd/144Nd ratio greater than or equal to 0.51252. These isotopic features are different from those reported for the parental magmas postulated for Vulsini and Alban Hills in the nearby Roman Magmatic Province, and are similar to those of the Vesuvius and Ischia magmas.  相似文献   

3.
Isotopic ratios and trace element abundances were measured on samples of Ir-enriched clay at the Cretaceous-Tertiary boundary, and in carbonate and marl from 5 cm below and 3 cm above the boundary. Samples were leached with acetic acid to remove carbonate, and with hydrochloric acid. Leachates and residues were measured. The Sr, Nd, O and H isotopic compositions of the boundary clay residues are distinct from those of the stratigraphically neighboring materials. The data indicate that most of the clay material was derived from a terrestrial source with relatively low87Sr/86Sr and high143Nd/144Nd ratios. The δ18O data suggest that the detritus has been modified by submarine weathering. K-Ca and Rb-Sr systematics, as well as O isotope ratios of K-feldspar spherules within the boundary clay, suggest that they are predominantly authigenic and may have formed after the time of deposition. However, Sm-Nd and Rb-Sr isotopic data indicate that the spherules contain relict material that provides information on the nature of the original detritus. The isotopic evidence for foreign terrestrial detritus in the boundary clay, the low rare earth element concentrations and high Ni concentration, support the hypothesis of a terminal Cretaceous asteroidal impact that produced a global layer of fallout. The data are most easily explained if the impact site was on oceanic crust rather than continental crust, and if a substantial fraction of the fallout was derived from relatively deep within the lithosphere (>3 km). This would probably require a single large impactor.  相似文献   

4.
Neodymium isotope and REE analyses of recent volcanic rocks and spinel lherzolite nodules from the Afar area are reported. The143Nd/144Nd ratios of the volcanic rocks range from 0.51286 to 0.51304, similar to the range recorded from Iceland. However, the87Sr/86Sr ratios display a distinctly greater range (0.70328–0.70410) than those reported from the primitive rocks of Iceland. Whole rock samples and mineral separates from the spinel lherzolite nodules exhibit uniform143Nd/144Nd ratios (ca. 0.5129) but varied87Sr/86Sr ratios in the range 0.70427–0.70528.The SrNd isotope variations suggest that the volcanic rocks may have been produced by mixing between two reservoirs with distinct isotopic compositions. Two possible magma reservoirs in this area are the source which produced the “MORB-type” volcanics in the Red Sea and Gulf of Aden and the anomalous source represented by the nodule suite. The isotopic composition of the volcanics is compatible with mixing between these two reservoirs.It is shown that the anomalous source with a high87Sr/86Sr ratio cannot have been produced by simple processes of partial melting and mixing within normal mantle. Instead the high87Sr/86Sr is equated with a fluid phase. A primitive cognate fluid, subducted seawater or altered oceanic lithosphere may have been responsible for the generation of the source with a high87Sr/86Sr ratio.  相似文献   

5.
A 200-m section of Koolau basalt was sampled in the 1.6-km Trans-Koolau (T–K) tunnel. The section includes 126 aa and pahoehoe lava flows, five dikes and ten thin ash units. This volcanic section and the physical characteristics of the lava flows indicate derivation from the nearby northwest rift zone of the Koolau shield. The top of the section is inferred to be 500–600 m below the pre-erosional surface of the Koolau shield. Therefore, compared with previously studied Koolau lavas, this section provides a deeper, presumably older, sampling of the shield. Shield lavas from Koolau Volcano define a geochemical end-member for Hawaiian shields. Most of the tunnel lavas have the distinctive major and trace element abundance features (e.g. relatively high SiO2 content and Zr/Nb abundance ratio) that characterize Koolau lavas. In addition, relative to the recent shield lavas erupted at Kilauea and Mauna Loa volcanoes, most Koolau lavas have lower abundances of Sc, Y and Yb at a given MgO content; this result is consistent with a more important role for residual garnet during the partial melting processes that created Koolau shield lavas. Koolau lavas with the strongest residual garnet signature have relatively high 87Sr/86Sr, 187Os/188Os, 18O/16O, and low 143Nd/144Nd. These isotopic characteristics have been previously interpreted to reflect a source component of recycled oceanic crust that was recrystallized to garnet pyroxenite. This component also has high La/Nb and relatively low 206Pb/204Pb, geochemical characteristics which are attributed to ancient pelagic sediment in the recycled crust. Although most Koolau lavas define a geochemical endmember for Hawaiian shield lavas, there is considerable intrashield geochemical variability that is inferred to reflect source characteristics. The oldest T–K tunnel lava flow is an example. It has the lowest 87Sr/86Sr, Zr/Nb and La/Nb, and the highest 143Nd/144Nd ratio found in Koolau lavas. In most respects it is similar to lavas from Kilauea Volcano. Therefore, the geochemical characteristics of the Koolau shield, which define an end member for Hawaiian shields, reflect an important role for recycled oceanic crust, but the proportion of this crust in the source varied during growth of the Koolau shield. Received: 1 June 1998 / Accepted: 30 August 1998  相似文献   

6.
87Sr/86Sr and143Nd/144Nd ratios, REE and selected minor and trace elements are presented and compared for present-day volcanic rocks in the Scotia Sea.Tholeiitic basalts from the South Sandwich Islands show widely ranging contents of some lithophile elements, e.g. K2O (0.09–0.55%) and Rb (1.55–14.2 ppm), but fairly constant Na2O and Sr. Total REE contents range from about 4–20 times chondritic abundances with significant light-REE depletion and both positive and negative Eu anomalies. The variations in minor and trace element abundances are consistent with low-pressure fractional crystallization of plagioclase and clinopyroxene but only minor amounts of olivine. The87Sr/86Sr and143Nd/144Nd ratios of the parental magmas are thought be 0.7038–0.7039 and 0.51301–0.51314 respectively, and indicate derivation of at least some87Sr from subducted ocean crust.The back-arc tholeiites in the Scotia Sea have lower87Sr/86Sr ratios (0.7028–0.7033), similar143Nd/144Nd ratios (0.51305) and are variably light-REE-enriched(CeN/YbN= 1.0–1.6). Total REE contents are comparable to those of the South Sandwich Islands tholeiites.  相似文献   

7.
Diverse87Sr/86Sr and143Nd/144Nd isotopic compositions among basalts from the Lau Basin (LBB), an active backarc basin in the southwest Pacific, indicate heterogeneity in the underlying mantle. Isotopic compositions display bimodal distributions which are related to geographic location. Type I LBB (87/Sr86Sr 0.70366;143Nd/144Nd 0.51297) include tholeiites from the central basin, Peggy Ridge, and Rochambeau Bank, while Type II basaltic and andesitic glasses from the northeastern portion of the basin, near Niua Fo'ou island, have higher87Sr/86Sr ( 0.7038) and lower 143Nd/144Nd ( 0.51288). Both depleted (e.g. N-MORB) and enriched (e.g. E-MORB) trace element abundances occur among Type I and Type II LBB.Covariation between trace element and isotopic ratios among Type I LBB is consistent with mixing between depleted mantle similar to the source for MORB and relatively enriched peridotite similar to the source for E-MORB. Relative to MORB, uniformly high87Sr/86Sr ( +0.0005) among all Type I LBB for given Nd isotopic compositions ( εNd = +8 to +12) may reflect a lithospheric component, such as ancient recycled altered ocean crust. Type II LBB have SrNd isotopic compositions which are gradational between enriched mantle similar to the source of OIB and a component with distinct Sr isotopic composition such as that observed in Samoan post-erosional basalts. Isotopic and geographic discontinuity between Type I and Type II LBB, and isotopic affinity of Type II and Niua Fo`ou island basalts with those from Samoa suggests that volcanism in the northeastern portion of the basin is tapping deeper mantle beneath the adjoining Pacific plate, as well as Indo-Australian mantle overlying the Pacific lithosphere that is subducted into the Tonga Trench.  相似文献   

8.
Sr and Nd isotope analyses are presented for Tertiary continental alkaline volcanics from Cantal, Massif Central, France. The volcanics belong to two main magma series, silica-saturated and silica-undersaturated (with rare nephelinites). Trace element and isotopic data indicate a common source for the basic parental magmas of both major series; the nephelinites in contrast must have been derived from a mantle source which is isotopically and chemically distinct from that which gave rise to the basalts and basanites.87Sr/86Sr initial ratios range from 0.7034 to 0.7056 in the main magma series (excluding rhyolites) and143Nd/144Nd ratios vary between 0.512927 and 0.512669; both are correlated with increasing SiO2 in the lavas. The data can be explained by a model of crustal contamination linked with fractional crystallisation. This indicates that crustal magma chambers are the sites of differentiation since only rarely do evolved magmas not show a crustal isotopic signature and conversely basic magmas have primitive isotopic ratios unless they contain obvious crustal-derived xenocrysts. Potential contaminants include lower crustal granulites or partial melts of upper crustal units. Equal amounts of contamination are required for both magma series, refuting hypotheses of selective contamination of the silica-saturated series.The isotopic characteristics of the apparently primary nephelinite lavas demonstrates widespread heterogeneity in the mantle beneath Cantal. Some rhyolites, previously thought to be extremely contaminated or to be crustally derived, are shown to have undergone post-emplacement hydrothermal alteration.  相似文献   

9.
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10.
Major element, trace element and Sr, Nd, Pb and O isotopic data for a Franciscan Mn-deposit suggest an origin by seafloor hydrothermal circulation. Based onQ-mode factor analysis the cherts and Mn-lenses of the Blue Jay mine formed from a combination of 4 components representing 1 biogenic, 1 hydrothermal, and 2 detrital sources. RbSr, UThPb and O isotopic systematics in the Mn-lenses were affected by input from the hydrothermal circulation of material leached from the underlying basalts. Nd isotopic compositions in both cherts and Mn-lenses are identical and within the range measured for Pacific Ocean water suggesting the REE were not mobilized by hydrothermal activity. Correlation of δ18O with SiO2 and MnO2 in the Mn-lenses implies the lenses formed by simple mixing of hydrothermally derived Mn-oxides with seawater and biogenic silica. δ18O of the cherts is both uniform and depleted relative to DSDP Jurassic cherts but similar to microquartz-bearing cherts of the Monterey Formation: this suggests that diagenetic activity exerted more control on oxygen isotope compositions then hydrothermal alteration or metamorphism. Finally, a well defined RbSr isochron of158 ± 5Myr was obtained for these cherts and opens the possibility of determining absolute radiometric ages for similar cherts throughout the geologic record.  相似文献   

11.
The Bishop Tuff represents a single eruption of chemically zoned rhyolitic magma. Six whole rock samples spanning the compositional and temperature range yield initial87Sr/86Sr of 0.7060–0.7092 andδ18O of 5.9–10.3‰. Six constituent sanidines yield smaller ranges of initial87Sr/86Sr of 0.7061–0.7069 andδ18O of 6.7–7.9. In contrast143Nd/144Nd ratios for the six whole rocks and two constituent magnetites exhibit negligible variation with a mean of0.51258 ± 1. These data are used to show that the phenocrysts were precipitated from an already chemically zoned liquid, that the zoning process involved negligible assimilation of, or exchange with, country rocks and that the extreme Sr and O isotopic disequilibria are probably the result of post-eruptive interaction with meteoric water. The parent magma had?Nd = ?0.9, ?Sr = +23 andδ18O = 7‰ and was formed from mantle-derived magmas and/or melts of lower crustal rocks isotopically similar to parts of the Sierra Nevada Batholith.  相似文献   

12.
The lavas produced by the Timanfaya eruption of 1730–1736 (Lanzarote, Canary Islands) contain a great many sedimentary and metamorphic (metasedimentary), and mafic and ultramafic plutonic xenoliths. Among the metamorphosed carbonate rocks (calc-silicate rocks [CSRs]) are monomineral rocks with forsterite or wollastonite, as well as rocks containing olivine ± orthopyroxene ± clinopyroxene ± plagioclase; their mineralogical compositions are identical to those of the mafic (gabbros) and ultramafic (dunite, wherlite and lherzolite) xenoliths. The 87Sr/86Sr (around 0.703) and 143Nd/144Nd (around 0.512) isotope ratios of the ultramafic and metasedimentary xenoliths are similar, while the 147Sm/144Nd ratios show crustal values (0.13–0.16) in the ultramafic xenoliths and mantle values (0.18–0.25) in some CSRs. The apparent isotopic anomaly of the metamorphic xenoliths can be explained in terms of the heat source (basaltic intrusion) inducing strong isotopic exchange (87Sr/86Sr and 143Nd/144Nd) between metasedimentary and basaltic rocks. Petrofabric analysis also showed a possible relationship between the ultramafic and metamorphic xenoliths.  相似文献   

13.
Nd and Sr isotopic data on pargasite Iherzolite inclusions, kaersutite megacrysts and their host alkali basalts are presented here to clarify some questions regarding isotopic equilibration during mantle metasomatism and the role of metasomatism in basalt genesis. Five alkali basalts from Nunivak Island within the Aleutian back-arc basin, have87Sr/86Sr ratios of 0.70251–0.70330 and143Nd/144Nd ratios of 0.51289–0.51304. On a Nd versus Sr isotope composition diagram the basalts overlap the fields of MORB and ocean island basalts. Pargasites and mica separated from hydrous nodules found in these basalts have a range in87Sr/86Sr of 0.70256–0.70337 but identical143Nd/144Nd ratios of 0.51302. The metasomatic fluid represented by the pargasite is in isotopic equilibrium, both for Sr and Nd, with the dry mantle as represented by diopside. Eight alkali basalts from the Ataq diatreme, South Yemen, have87Sr/86Sr range of 0.70335–0.70426 and143Nd/144Nd range of 0.51252–0.51305. On a Nd versus Sr isotope composition diagram the basalts from Ataq plot in two distinct fields, (1) within the field of ocean island basalts, and (2) within the range of continental rift basalts but to the left of the Nd-Sr correlation line, somewhat similar to the Skye and Oslo rift basalts. Diopside and pargasite separated from three nodules at Ataq have a more complex history than those at Nunivak. Two nodules contain pargasite and diopside with identical87Sr/86Sr ratios but different143Nd/144Nd ratios. A third nodule contains diopside with a143Nd/144Nd ratio similar to that of other diopsides.The Nunivak basalts are derived from a source with a time-integrated light-REE depletion, in contrast to the light-REE-enriched nature of the basanites. This is best explained by a recent metasomatic event in the source region which increased the LIL element content of the peridotite thus accommodating higher degrees of melting. The Ataq volcanic rocks seem to tap different sources characterized by both light-REE enrichment and depletion, in contrast to the uniform source of the Nunivak basanites. Production of the Ataq basanites is believed to involve anataxis of metasomatically veined continental mantle where local mantle heterogeneities survived the melting event.  相似文献   

14.
143Nd/144Nd,87Sr/86Sr and trace element results are reported for volcanic and plutonic rocks of the Aleutian island arc. The Nd and Sr isotopic compositions plot within the mantle array with εNd values of from 6.5 to 9.1 and87Sr/86Sr ratios of from 0.70289 to 0.70342. Basalts have mildly enriched light REE abundances but essentially unfractionated heavy REE abundances, while andesites exhibit a greater degree of light to heavy REE fractionation. Both the basalts and andesites have significant large ion lithophile element to light rare earth element (LILE/LREE) enrichments. Variations in the isotopic compositions of Nd and Sr are not related to the spatial distribution of volcanoes in the arc, nor are they related to temporal differences. εNd and87Sr/86Sr do not correlate with major element compositions but do, however, correlate with certain LILE/LREE ratios (e.g. BaN/LaN). Plutonic rocks have isotropic and trace element characteristics identical to some of the volcanic rocks. Rocks that make up the tholeiitic, calc-alkaline and alkaline series in the Aleutians do not come from isotopically distinct sources, but do exhibit some differing LILE characteristics.Given these elemental and isotopic constraints it is shown that the Aleutian arc magmas could not have been derived directly from homogeneous MORB-type mantle, or fresh or altered MORB subducted beneath the arc. Mixtures of partially altered MORB with deep-sea sediment can in principle account for the isotopic characteristics and most of the observed LILE/LREE enrichments. However, some samples have exceedingly high LILE/LREE enrichments which cannot be accounted for by sediment contamination alone. For these samples a more complex scenario is considered whereby dehydration and partial melting of the subducted slab, containing less than 8% sediment, produces a LILE-enriched (relative to REE) metasomatic fluid which interacts with the overlying depleted mantle wedge. The isotopic and LILE characteristics of the mantle are extremely sensitive to metasomatism by small percentages of added fluid, whereas major elements are not substantially effected, Major element compositions of Aleutian magmas are dominantly controlled by the partial melting of this mantle and subsequent crystal fractionation; whereas isotopic and LILE characteristics are determined by localized mantle heterogeneities.  相似文献   

15.
3He/4He ratios have been obtained for basaltic, intermediate and acid volcanic glasses from Iceland. Basaltic glasses exhibit a wide range of 3He/4He ratios (4 < R/Ra < 24), which is consistent with the previously recorded range for Icelandic geothermal systems. In contrast the glasses with intermediate and acid compositions have 3He/4He values close to the atmospheric value (Ra) with the exception of a 13-Ma sample which has R/Ra= 0.07. 87Sr/86Sr, 143Nd/144Nd ratios and δ18O values are reported for the same samples.3He/4He does not correlate with either 87Sr/86Sr or 143Nd/144Nd ratio and radiogenic components of He, Sr and Nd have apparently been decoupled. Interaction of Icelandic magmas with hydrothermally altered and older Icelandic crust is the preferred explanation for variable and often low δ18O values. It is suggested that primary 3He/4He ratios may have been modified by incorporation of radiogenic helium developed within the Icelandic crust to impose a larger range of 3He/4He ratios on the erupted products than was actually inherited from the mantle beneath Iceland. Intermediate and acid samples have all been severely contaminated by atmospheric helium, most probably at very shallow levels within the crust.  相似文献   

16.
The Shabogamo Intrusive Suite comprises numerous bodies of variably metamorphosed gabbro which intrude Archean and Proterozoic sequences at the junction of the Superior, Churchill, and Grenville structural provinces in western Labrador. Combined Sm-Nd and Rb-Sr systematics in two bodies, ranging from unmetamorphosed to lightly metamorphosed, document a crystallization age of about 1375 m.y., and suggest that both bodies crystallized from magmas with similar Nd and Sr isotopic compositions. This age is in accordance with the existence of a regional magmatic event in the Churchill Province at approximately 1400 m.y.Rb-Sr systematics in two bodies of amphibolite-grade gabbro suggest a regional metamorphic event at about 950 m.y., corresponding to the waning stages of Grenville activity. Sm-Nd systematics in these high-grade bodies are affected to a much lesser degree than Rb-Sr.Initial ratios for143Nd/144Nd and87Sr/86Sr are lower and higher, respectively, than bulk earth values at 1375 m.y. Both these displacements are in the direction of older crustal material at 1375 m.y., and a model is proposed to produce the Shabogamo magma by mixing a mantle-derived magma with a partial melt of crustal rocks (approximately 4: 1 by volume). Young volcanic rocks with anomalous Nd and Sr isotopic ratios, which have previously been taken as evidence for “enriched” mantle, may be interpreted similarly.  相似文献   

17.
K, Rb and Sr concentrations and Sr isotopic compositions were determined for the Dai granitic rocks of trondhjemitic composition occurring in a serpentinite mass in the Nagato tectonic zone formed in the Late Paleozoic era, and for the granitic rocks of quartz dioritic composition recently dredged from the seamount of the Kyushu-Palao Ridge. Both granitic rocks are characterized by low abundances of K and Rb, low K2O/Na2O ratios, high K/Rb ratios, low Rb/Sr ratios and low initial87Sr/86Sr ratios. These characteristics suggest that strong similarities may exist between the Dai granitic rocks and the dredged granitic rocks, and that the Dai granitic rocks may be classified as oceanic plagiogranite. These oceanic plagiogranites may plausibly represent single-stage mantle-derived granites, possibly from the suboceanic mantle.  相似文献   

18.
Neodymium isotopic analyses have been measured on nine ophiolites and four orogenic lherzolites. εNd varies from +12 to +3 in the ophiolites and from +18 to +2 in the orogenic lherzolites. The majority of the analyses plot on a εNd-εSr correlation line as defined by Nd and Sr isotopic analyses of oceanic basalts. However, certain ophiolitic and lherzolitic samples exhibit high87Sr/86Sr ratios and as such lie to the right of the correlation line towards seawater compositions.From these data one can postulate several origins for ophiolites including that of mid-ocean ridges and ocean islands. If the orogenic lherzolites are interpreted as representative of the mantle occurring below active ridges a more complex model is required involving mantle heterogeneity and multi-episodic chemical fractionation starting prior to 2 Ga ago.  相似文献   

19.
The annular (6–8 km diameter) Golda Zuelva and Mboutou anorogenic complexes of North Cameroun are composed of a suite of alkaline plutonic rocks ranging from olivine gabbro to amphibole and biotite granite. For the Mboutou complex there are two overlapping centres. In the Golda Zuelva complex the plutonic rocks are associated with a later hawaiite to rhyolite volcanic suite. A Rb/Sr whole rock isochron gives an age of 66±3 Ma for the Golda Zuelva granites, with initial87Sr/86Sr ratio of 0.7020, and demonstrates that plutonism and volcanism were essentially contemporaneous and probably cogenetic. For Golda Zuelva and the north Mboutou centre18O/16O (5.6–6.2),87Sr/86Sr (0.7030–0.7045) and Pb isotopic ratios (207Pb/204Pb: 15.60–15.64) support a mantle origin for the initial magmas. Unlike Sr isotopes, the O isotopic ratios of the granitic end members at Golda Zuelva (～7.5) indicate crustal contamination. Post-magmatic alteration was not significant.For the younger south Mboutou centre the O-, Sr- and Pb-isotopic data indicate more extensive magma-crust interaction and in a different (higher level?) crustal environment with δ18O granite=3.3‰,87Sr/86Sr ratios up to 0.706 and Pb isotopic ratios more markedly displaced from the oceanic volcanic field. The low-18O granites probably record, at least in part, a magmatic process with subsequent minor post-magmatic alteration effects. The major and trace element systematics between the north and south Mboutou centres are directly comparable. The evolution of the magmas were dominated by fractional crystallisation and progressive crustal contamination processes.  相似文献   

20.
Abstract We present chemical and Sr–Nd–Pb isotopic compositions of three Triassic (226–241 Ma) calc‐alkaline granitoids (the Yeongdeok granite, Yeonghae diorite and Cheongsong granodiorite) and basement rocks in the northern Gyeongsang basin, south‐eastern Korea. These plutons exhibit typical geochemical characteristics of I‐type granitoids generated in a continental magmatic arc. The Yeongdeok and Yeonghae plutons have similar initial Sr, Nd and Pb isotope ratios (87Sr/86Srinitial = 0.7041 ~ 0.7050, ?Nd(t) = 2.3 ~ 4.0, 206Pb/204Pbfeldspar = 18.22 ~ 18.34), but distinct rare earth element patterns, suggesting that the two plutons formed from partial melting of a similar source material at different depths. The Cheongsong pluton has slightly more enriched Sr–Nd–Pb isotopic compositions (87Sr/86Srinitial = 0.7047 ~ 0.7065, ?Nd(t) = 3.9 ~ 2.8, 206Pb/204Pbfeldspar = 18.24 ~ 18.37) than the other two plutons. The Nd model ages of the basement rocks (1.1 ~ 1.4 Ga) are slightly older than those of the plutons (0.6 ~ 1.0 Ga). The initial Sr and Nd isotopic ratios of the plutons can be modeled by the mixing between the mid‐oceanic ridge basalt‐like depleted mantle component and the crustal component represented by basement rocks, which is also supported by Pb isotope data. The Sr and Nd isotope data from granitoids and basement rocks suggest that the Gyeongsang basin, the Hida belt and the inner zone of south‐western Japan share relatively young basement histories (middle Proterozoic), compared with those (early Proterozoic to Archean) of the Gyeonggi and Yeongnam massifs and the Okcheon belt. The Nd isotope data of basement rocks suggest that the Hida belt might be better correlated with the basement of the Gyeongsang basin than the Gyeonggi massif, the Okcheon belt or the Yeongnam massif, although it may represent an older continental margin of East Asia than the Gyeongsang basin considering its slightly older Nd model ages.  相似文献   

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