Isotopic and trace-element arguments for the lower-crustal origin of Hercynian granitoids and pre-Hercynian orthogneisses, Massif Central (France)

Downes, Hilary; Duthou, Jean-Louis

doi:10.1016/0009-2541(88)90027-7

Cited by 89 publications

(37 citation statements)

References 21 publications

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“…Nevertheless, meta-igneous rocks (or thogneisses) better approach isotope signatures of the granites than metasedimentary country rocks. This is consistent with the results obtained by other authors for the origin of peraluminous Hercynian batholiths in western Europe (Downes and Duthou, 1988;Turpin et aI, 1990) (5) Based on the data presented, the possibility of disequilibrium partial melting of lower crustal sources and/ or the lowering of the isotopic ratios during granulitization of the lower crust may better explain the isotopic data of the peralum inous granites than the involvement of an unsampled crustal protolith, as suggested m other peralum inous batholiths (Bernard-Griffiths et aI, 1985;Clarke et aI, 1988).…”

Section: Discussionsupporting

confidence: 83%

“…Both materials show much less variation in (S N d)300 values, which is a common feature of the Hercynian crust (Bickle et aI., 1988). The orthogneisses have (S N d)300 values between -4.3 to -7.3, whereas the metapelites have lower values from -9.1 to -12.5, as is also typical in the Hercynian Belt (Downes and Leyreloup, 1986;Downes and Duthou, 1988 (Aparicio et aI., 1986). The coincidence of isotopic ratios as well as the similarity in trace element geochemistry suggest a similar source for the origin of the various granite types of the Spanish Central Region.…”

Section: Sr-nd and Other Isotopic Datamentioning

confidence: 92%

“…In this way, granitic melts derived from a source at depth do not necessarily have to match the isotopic composition of the equivalent metamorphic rocks at the level of granite emplacement. The avail able data for acid-intennediate meta-igneous lower crustal rocks in several orogenic segments seem to indicate a shift in Sr-Nd compositions towards bulk earth values when compared to the same metamor phic rocks in upper crustal levels (e.g., French Mas sif Central, compare data for the meta-igneous lower crustal rocks of Downes and Duthou, 1988 with the data for the outcropping meta-igneous rocks of Turpin et aI., 1990). Granulite facies lower crustal or thogneisses tend to decrease their Sr isotopic ratios more markedly than their Nd isotopic ratios which are much less modified (Fig.…”

Section: The Role Of the Associated Basic Magmatismmentioning

confidence: 99%

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Crustal origin of Hercynian peraluminous granitic batholiths of Central Spain: petrological, geochemical and isotopic (Sr, Nd) constraints

Villaseca

Barbero

Rogers

1998

Lithos

162

159

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In Central Spain, it is possible to distinguish two main types of peraluminous late-Hercynian granites: the PI types and the PS types. The distinction between both types is made on the basis of differences in peraluminosity (PS types are more peraluminous than PI types) and also on the appearance of some characteristic mafic minerals; PS types have biotite, cordierite and monazite as the most typical accessory phase, whereas PI types have biotite, amphibole (in the less evolved facies) and allanite as the accessory mineral. Both granite types have similar trace element ratios and initial Sr, Nd and Pb isotopic signatures, Initial 87Sr/ 86Sr ratios of both types exhibit a large range from 0,7073 to 0,7193, whereas initial BN d varies in a restricted range from -5,4 to -6,6, The scarce associated basic rocks do not play a significant role in the chemical variability of these peraluminous granites which follow low pressure crystal fractionation trends from granodior ite/monzogranite parental magmas, Mixing and AFC modelling of Sr and Nd isotopic data reveal an unrealistically high mantle contribution, Based on major and trace element and isotopic data, an orthogneissic protolith for both granitic series is proposed, Nevertheless, none of the metamorphic country rocks of Central Spain has the appropriate Sr isotopic composition to satisfy the origin of these granitic rocks, and so, it is argued that progressive isotopic re-equilibration of crustal material during the granulization of the lower Hercynian crust, together with the possibility of isotopic disequilibrium during melting (as has been demonstrated in migmatitic terranes in nearby areas) may explain the isotopic differences between the granites and the high level metamorphic country rocks,

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Section: Discussionsupporting

confidence: 83%

Section: Sr-nd and Other Isotopic Datamentioning

confidence: 92%

Section: The Role Of the Associated Basic Magmatismmentioning

confidence: 99%

See 1 more Smart Citation

Crustal origin of Hercynian peraluminous granitic batholiths of Central Spain: petrological, geochemical and isotopic (Sr, Nd) constraints

Villaseca

Barbero

Rogers

1998

Lithos

162

159

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“…The emplacement of these granitic massifs has been variously interpreted as synorogenic, late tectonic, or post tectonic (Alabouvette 1988;Faure 1995). Their origin has also been the subject of several isotopic studies suggesting a mixed provenance from partial melting of lower crustal lithologies (metasedimentary and metaigneous rocks) and mantle-derived basic magmas (Duthou et al 1984;Downes and Duthou 1988;Pin and Duthou 1990;Turpin et al 1990;Montel et al 1992;Williamson et al 1992;Downes et al 1997).…”

Section: Introductionmentioning

confidence: 97%

New age constraints on emplacement of the Cévenol granitoids, South French Massif Central

Brichau

Respaut

Monié

2007

Int J Earth Sci (Geol Rundsch)

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During the development of the Variscan orogeny, large amounts of granitic melt were produced, giving rise to the intrusion of granitoids at different structural levels. Despite numerous studies, ages available from previous work on the Cévennes granites remain largely imprecise. In order to better constrain the age and emplacement mode of these granites, we have combined UPb dating on monazites and zircons and 40 Ar/ 39 Ar dating on biotites with petrological observations, major element chemical analysis and SEM zircon imaging on five samples from the Aigoual-St Guiral-Liron and Mont Lozère granitic massifs. The results revealed that granitic intrusions and cooling in Southern Cévennes occurred in a short time span at~306 Ma after the main episode of regional metamorphism. Petrological and chemical data suggest that they result from a mixing between mantle-derived basic magmas (lamprophyres) and lower crust acid magmas. At a regional scale the production of these melts occurred at the end of crustal thickening induced by nappe stacking, at the same time as the late anatectic events recorded further north in the Velay dome and the granulite facies metamorphism recorded in metasedimentary granulite enclaves brought up by Tertiary volcanoes of the Velay area (Bournac).

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“…The study of basement nature of the WQOB is a key for understanding tectonic evolution of the WQOB, whether the WQOB and the EQOB have a united basement and the WQOB basement relationship to its adjacent North China and Yangtze (South China) blocks. Geochemical probing from magma source of granitoids is an alternative method to reveal the crustal basement nature [4,5] . Granitoids are widespread in the WQOB.…”

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confidence: 99%

Geochemical and Pb-Sr-Nd isotopic compositions of granitoids from western Qinling belt: Constraints on basement nature and tectonic affinity

et al. 2007

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Geochemical and Pb-Sr-Nd isotopic compositions of five Indosinian granitoid intrusions from the western Qinling belt provide insights into basementnature and tectonic affinity. The results show that the western Qinling granitoids incline towards basic in their bulk chemical composition. The granitoids belong to high-K to shoshonitic series with K 2 O/Na 2 O=1.04-1.86 and are dominantly metaluminous with A/CNK=0.90-1.05 (most samples have A/CNK of <1.0). They have similar trace elemental compositional patterns. In Sr-Nd isotopic compositions, they display some extent heterogeneity with I sr =0.70682-0.70845, ε Nd (t)=−4.85 to −9.17 and T DM =1.26-1.66 Ga. They are characterized by high radiogenic Pb isotopic compositions. Their initial Pb isotopic ratios are 206 Pb/ 204 Pb=17.996-18.468, 207 Pb/ 204 Pb=15.565-15.677 and 208 Pb/ 204 Pb=38.082-38.587. Geochemical and Sr-Nd isotopic composi-tions reveal that magma for the granitoids was derived from partial melting of high-K (Rb) basaltic rocks, which might be formed in 900-1400 Ma. It is suggested that a large amount of the Proterozoic high-K (Rb) basaltic rocks, which underlie the Phanerozoic sedimentary cover, constitute the crustal basement of the western Qinling belt. Pb-Sr-Nd isotopic compositional comparison between the eastern Qinling and the western Qinling Indosinian granitoids indicates that the crustal basement of the western Qinling is distinct from that of the eastern Qinling. The Baoji-Chengdu railway close to south-north orientation can be taken as an approximate boundary between both basements. The Pb-Nd isotopic compositional characteristics of the western Qinling granitoids suggest that the basement of the western Qinling belt has an affinity with the Yangtze block. granitoid, geochemistry, basement nature, tectonic affinity, West QinlingThe Qinling orogenic belt can be divided into two segments: the eastern Qinling orogenic belt (EQOB) and the western Qinling orogenic belt (WQOB), bounded by the Baoji-Chengdu railway [1] . In the EQOB, multidiscipline studies including geology, geochemistry and geophysics revealed that both the South Qinling and North Qinling tectonic units have an affinity with the Yangtze block [1,2] . Crustal basements in both tectonic units are composed of exposed Precambrian crystalline series and the Neoproterozoic underplating mafic protolith [1][2][3] . In contrast, the study of the basement nature and its tectonic affinity in the WQOB is still in sufficient, largely because the WQOB has no exposure of Precambrian basement which is covered by the Phanerozoic

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Isotopic and trace-element arguments for the lower-crustal origin of Hercynian granitoids and pre-Hercynian orthogneisses, Massif Central (France)

Cited by 89 publications

References 21 publications

Crustal origin of Hercynian peraluminous granitic batholiths of Central Spain: petrological, geochemical and isotopic (Sr, Nd) constraints

Crustal origin of Hercynian peraluminous granitic batholiths of Central Spain: petrological, geochemical and isotopic (Sr, Nd) constraints

New age constraints on emplacement of the Cévenol granitoids, South French Massif Central

Geochemical and Pb-Sr-Nd isotopic compositions of granitoids from western Qinling belt: Constraints on basement nature and tectonic affinity

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