Abstract
Two different contamination processes have been identified as having been operative in the genesis of a plutonic suite: initial contamination of a mantle source, and subsequent crustal contamination of uprising partial melts from the mantle. These processes are indicated by a detailed analyses of Nd, Sr, and oxygen isotopes together with major-and trace-elements of the 32–30 Ma calc-alkaline Bergell intrusion. This intrusion is located at the suture of the Alpine continental collision zone and contains rock types capable of discriminating between mantle and intracrustal processes. A range from basaltic-andesitic dykes in the surrounding country rocks, cumulitic hornblendites, gabbros, tonalite, granodiorite and lamprophyres, to pegmatites and aplites, is exposed in this single intrusion. The results of REE modelling and isotopic compositions of the basic members suggest that the cumulates were fractionated from a picrobasaltic liquid originating by partial melting of enriched subcontinental mantle (εNd=+4). Increases in 87Sr/86Sr (0.7055) and δ18O(+6.7) in these samples relative to the mantle array and compositions of other Periadriatic intrusions are most likely the result of an initial contamination of the mantle source by dehydration or partial melting of altered subducted oceanic crust. Slight differentiation of such a picrobasaltic liquid produced the basaltic-andesitic dykes. Simultaneous fractional crystallization and contamination of the uprising magma by continental crust produced crustal isotopic signatures which increase with acidity to values of (εNd=-7.6), 87Sr/86Sr=0.716 and δ18O=+10. The crustal imprint and LREE enrichment in the dominating tonalite increase with decreasing crystallization depth which indicates that the tonalites were emplaced in several distinct batches with different degrees of contamination. Shoshonitic lamprophyres, which intruded into the partly solidified granodiorite, were generated in a deep, strongly contaminated mantle source. The posttectonic 26 Ma Novate leucogranite is not cogenetic with the main Bergell body, but rather formed from a predominantly crustal source. If the described features are indeed due to mantle source contamination processes, which are well known for volcanic arcs, it must be concluded that these may also play a significant role in the genesis of calcalkaline plutonic suites.
Article PDF
Similar content being viewed by others
Avoid common mistakes on your manuscript.
References
Arth JG, Barker F (1976) Rare-earth partitioning between hornblende and dacitic liquid and implications for the genesis of trondhjemitic-tonalitic magmas. Geology 4:534–536
Barth S, Oberli F, Meier M (1989) U-Th-Pb systematics of morphologically characterized zircon and allanite: a high-resolution isotopic study of the Alpine Rensen pluton (northern Italy). Earth Planet Sci Lett 95:235–254
Bernoulli D, Heitzmann P, Zingg A (1990) Central and southern Alps in southern Switzerland: tectonic evolution and first results of reflection seismics. In: Roure F, Heitzmann P, Polino R (eds) Deep structure of the Alps. Mém Soc géol France 156; Mém Soc géol suisse 1; Geol Soc Ital, Vol spec 1: 289–302
von Blanckenburg F (1990) Isotope geochemical and geochronological case studies of Alpine magmatism and metamorphism: the Bergell intrusion and Tauern Window. PhD dissertation ETH Zürich
Chen C-H, Shieh Y-N, Lee T, Chen C-H, Mertzman SA (1990) Nd-Sr-O isotopic evidence for source contamination and an unusual mantle component under Luzon Arc. Geochim Cosmochim Acta 54:2473–2483
Clondiffe E, Mottana A (1974) Studio sperimentale del «serizzo» a moderate pressioni. Soc It Mineral e Petrol 30:919–930
Davidson JP, Harmon RS (1989) Oxygen isotope constraints on the petrogenesis of volcanic arc magmas from Martinique, Lesser Antilles. Earth Planet Sci Lett 95:255–270
DePaolo DJ (1981) Trace element and isotopic effects of combined wallrock assimilation and fractional crystallization. Earth Planet Sci Letters 53:189–202
DePaolo DJ (1988) Neodymium isotope geochemistry. Springer, Berlin Heidelberg New York
Dickin AP, Exley RA, Smith BM (1980) Isotopic measurement of Sr and O exchange between metoric-hydrothermal fluid and the Coire Uaigneich granophyre, Isle of Skye, N.W. Scotland. Earth Planet Sci Lett 51:58–70
Diethelm K (1985) Hornblendite und Gabbros im östlichen Bergell (Val Sissone, Provinz Sondrio, Italien). Schweiz Mineral Petrogr Mitt 65:223–246
Diethelm K (1989) Petrographische und geochemische Untersuchungen an basischen Gesteinen der Bergeller Intrusion. PhD dissertation ETH-Zürich
Drescher-Kaden FK (1940) Beiträge zur Kenntnis der Migmatit-und Assimilationsbildungen, sowie der synantetischen Reaktionsformen. I. Über Schollenassimilation und Kristallisationsverlauf im Bergeller Granit. Chem Erde 12:157–238
Elderfield H, Hawkesworth CJ, Greaves MJ, Calvert SE (1981) Rare earth element geochemistry of oceanic ferromanganese nodules and associated sediments. Geochim Cosmochim Acta 45:513–528
England PC, Thompson AB (1986) Some thermal and tectonic models for crustal melting in continental collision zones. In: Coward MP, Ries AC (eds) Collision tectonics. Geol Soc London Spec Pub 19:83–94
Faure G (1986) Principles of isotope geology, 2nd edn. John Wiley & Sons, New York
Fowler MB, Harmon RS (1990) The oxygen isotope composition of lower crustal granulite xenoliths. In: Vielzeuf D, Vidal P (eds) Granulites and crustal evolution. Kluwer Academic Publishers, Dordrecht, pp 493–506
Gautschi A, Montrasio A (1978) Die andesitisch-basaltischen Gänge des Bergeller Ostrandes und ihre Beziehung zur Regional-und Kontaktmetamorphose. Schweiz Mineral Petrogr Mitt 58:329–343
Gulson BL (1973) Age relations in the Bergell region of the southeast Swiss Alps: with some geochemical comparisons. Eclogae Geol Helv 66:293–313
Gulson BL, Krogh TE (1973) Old lead components in the young Bergell massif, south-east Swiss Alps. Contrib Mineral Petrol 40:239–252
Halliday AN (1983) Crustal melting and the genesis of isotopically and chemically zoned plutons in the Southern Uplands of Scotland. In: Atherton MP, Gribble CD (eds) Migmatites, melting and metamorphism. Shiva publ ltd, Nautwich, pp 54–61
Hawkesworth CJ, O'Nions RK, Pankhurst PJ, Hamilton PJ, Evenson NM (1977) A geochemical study of island-arc and back-arc tholeiites from the Scotia Sea. Earth Planet Sci Lett 36:253–262
Henderson P (1982) Inorganic geochemistry. Pergamon, Oxford
Hill RI, Silver LT, Taylor HP (1986) Coupled Sr−O isotope variations as indicator of source heterogeneity for the Northern Peninsular Ranges batholith. Contrib Mineral Petrol 92:351–361
Hoernes S, Friedrichsen H (1980) Oxygen and hydrogen isotopic composition of Alpine and pre-Alpine minerals of the Swiss Central Alps. Contrib Mineral Petrol 72:19–32
James DE (1981) The combined use of oxygen and radiogenic isotopes as indicators of crustal contamination. Ann Rev Earth Planet Sci 9:311–344
Juteau M, Michard A, Albarede F (1986) The Pb−Sr−Nd isotope geochemistry of some recent circum-Mediterranean granites. Contrib Mineral Petrol 92:331–340
Kagami H, Fischer H, Steiger RH (1985) Nd and Sr isotope evidence for the crustal origin of the Periadriatic plutons (abstr). Terra Cognita 5:324
Kagami H, Ulmer P, Hansmann W, Dietrich V, Steiger RH (1991) Nd−Sr isotopic and geochemical characteristics of the southern Adamello (N Italy) intrusives: implications for crustal versus mantle origin. J Geoph Res 96:B14331–14346
Köppel V, Grünenfelder M (1975) Concordant U−Pb ages of monazite and xenotime from the Central Alps and the timing of the high temperature Alpine metamorphism, a preliminary report. Schweiz Mineral Petrogr Mitt 55:129–132
Krogh TE (1973) A low-contamination method for hydrothermal decomposition of zircon and extraction of U and Pb for isotopic age determinations. Geochim Cosmochim Acta 37:485–494
Kyser TK (1990) Stable isotopes in the continental lithospheric mantle. In: Menzies MA (ed) Continental Mantle. Clarendon Press, Oxford
Liew TC, Hoffmann AW (1988) Precambrian crustal components, plutonic associations, plate environment of the Hercynian Fold Belt of central Europe: Indications from a Nd and Sr isotopic study. Contrib Mineral Petrol 98:129–138
Mottana A, Morten L, Brunfelt AO (1978) Distribuzionc delle terre rare nel massiccio Val Masino-Val Bregaglia (Alpi Centrali). Rend Soc Ital Mineral Petrol 34:485–497
Nievergelt P, Dietrich V (1977) Die andesitisch-basaltischen Gänge des Piz Lizun (Bergell). Schweiz Mineral Petrogr Mitt 57:267–280
Reusser E (1987) Phasenbeziehungen im Tonalit der Bergeller Intrusion (Graubünden, Schweiz/Provinz Sondrio, Italien). PhD Dissertation, ETH-Zürich
Staub R (1918) Geologische Beobachtungen am Bergeller massiv. Vierteljahrssch Naturforsch Ges Zürich 63:1–18
Staub R (1921) Geologische Karte der Val Bregaglia (Bergell). Geologische Spezialkarten der Schweiz, Blatt 90
Stern CR, Frey FA, Futa K, Zartman RE, Peng Z, Kyser TK (1990) Trace-element and Sr, Nd, Pb, and O isotopic composition of Pliocene and Quarternary alkali basalts of the Patagonian Plateau lavas of southernmost South America. Contrib Mineral Petrol 104:294–308
Stille P (1987) Geochemische Aspekte der Krustenevolution im zentral-und südalpinen Raum. Habilitationsschrift, ETH Zürich
Stille P, Buletti M (1987) Nd−Sr isotopic characteristics of the Lugano volcanic rocks and constraints on the continental crust formation in the South Alpine domain (N-Italy-Switzerland). Contrib Mineral Petrol 96:140–150
Stille P, Fischer H (1990) Secular variation in the isotopic composition of Nd in Tethys seawater. Geochim Cosmochim Acta 54:3139–3145
Stille P, Steiger RH (1991) Hf isotope systematics in granitoids from the central and southern Alps. Contrib Mineral Petrol 107:273–278
Stille P, Oberhänsli R, Wenger-Schenk K (1989) Hf−Nd isotopic and trace element constraints on the genesis of alkaline and calc-alkaline lamprophyres. Earth Planet Sci Lett 96:209–219
Taylor HP Jr (1980) The effects of assimilation of country rocks by magmas on 18O/16O and 87Sr/86Sr systematics in igneous rocks. Earth Planet Sci Lett 47:243–254
Tilton GR, Schreyer W, Schertl H-P (1989) Pb−Sr−Nd isotopic behavior of deeply subducted crustal rocks from the Dora Maira Massif, Western Alps, Italy. Geochim Cosmochim Acta 53:1391–1400
Trommsdorff V, Nievergelt P (1983) The Bregaglia (Bergell) Iorio intrusive and its field relations. Mem Soc Geol Italy 26:55–68
Turpin L, Velde D, Pinte G (1988) Geochemical comparison between minettes and kersantites from the Western European Hercynian orogen: trace element and Pb−Sr−Nd isotope constraints on their origin. Earth Planet Sci Lett 87:73–86
Ulmer P (1988) High pressure phase equilibria of a calc-alkaline picro-basalt: Implications for the genesis of calc-alkaline magmas. Carnegie Inst Washington, Ann Rep of the Dir Geoph Lab 2102:28–35
Ulmer P, Callegari E, Sonderegger UC (1983) Genesis of the mafic and ultramafic rocks and their genetical relations to the tonalitic-trondhjemitic granitoids of the southern part of the Adamello batholith (Northern Italy). Mem Soc Geol Ital 26:171–222
Voshage H, Hofmann AW, Mazzucchelli M, Rivalenti G, Sinigoi S, Raczek I, Demarchi G (1990) Isotopic evidence from the Ivrca Zone for a hybrid lower crust formed by magmatic underplating. Nature 347:731–736
Wasserburg GJ, Jacobsen SB, DePaolo DJ, McCulloch MT, Wen T (1981) Precise determination of Sm/Nd ratios, Sm and Nd isotopic abundances in standard solutions. Geochim Cosmochim Acta 45:2311–2323
Weber J (1957) Petrographische und geologische Untersuchung des Tonalitzuges von Melirolo-Sorico zwischen Tessintal und Comersee. Schweiz Mineral Petrogr Mitt 37:267–397
Wedepohl KH (1978) Handbook of geochemistry, vol 2/4. Springer, Berlin Heidelberg New York
Wenk HR (1982) A geological history of Bergell granite and related rocks. In: Drescher-Kaden FK, Augustithis SS (eds) Transformists' Petrology. Theophrastus Publications, Athens, pp 113–148
Wenk HR, Cornelius SB (1977) Geologischer Atlas der Schweiz 1:25000, Blatt 70, Sciora, Schweiz Geol Komm
Wyllie PJ, Wuu-Liang Huang, Stern CR, Maaløe S (1976) Granitic magmas: possible and impossible sources, water contents, and crystallization sequences. Can J Earth Sci 13:1007–1019
Wilson M, Downes H (1991) Tertiary-Quaternary extension-related alkaline magmatism in Western and Central Europe. J Petrol 32:811–849
Ych H (1980) D/H ratios and late-stage dehydration of shales during burial. Geochim Cosmochim Acta 44:341–352
Author information
Authors and Affiliations
Rights and permissions
About this article
Cite this article
von Blanckenburg, F., Früh-Green, G., Diethelm, K. et al. Nd-, Sr-, O-isotopic and chemical evidence for a two-stage contamination history of mantle magma in the Central-Alpine Bergell intrusion. Contr. Mineral. and Petrol. 110, 33–45 (1992). https://doi.org/10.1007/BF00310880
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF00310880