Abstract
The Vandfaldsdalen macrodike, which lies in the Skaergaard region of East Greenland, is a remarkably zoned fossil magma chamber, with a granophyric cap overlying cumulate gabboros. The intrusion is distinctly bimodal, with a large compositional discontinuity at the contact between the gabbro and granophyre. Although the exposed part of the macrodike is in contact with Tertiary basalts and sediments, the granophyre originated by assimilation of xenoliths derived from the underlying Archean basement. Sr and Nd isotopic ratios throughout the cumulate sequence are remarkably similar, indicating insignificant contamination of the gabbro by the granophyre. Modelling of the compositional effects of cooling and crystallization indicate that the cumulate pile resulted from fractional crystallization, with the complicating effects of trapped liquid and post-cumulus fractionation. The uppermost rocks in the mafic part, of the chamber (SiO2=62%; FeO*=12.4%) resulted from about 85% fractional crystallization. A transgressive sill of strongly fractionated magma (SiO2=67%; FeO*=8.8%) formed from extracted intercumulus liquid that was the result of 90% fractional crystallization of the original magma. Mass-balance indicates that typical granophyre is made up of about 75% dissolved xenoliths, by weight, and 25% mantle-derived basaltic magma. The magmas were not measurably affected by material exchange across the interface between the gabbro and granophyre. This magma chamber evolved by both assimilation and fractional crystallization, but the residual liquids formed by fractional crystallization were unaffected by assimilation. Heat exchange between were unaffected by assimilation. Heat exchange between the two parts of the chamber was obviously important, but there was insignificant material exchange. The inability of fractional crystallization and assimilation to affect the same liquid is related to the dynamic behavior of this particular magma chamber, particularly the buoyancy of granophyre relative to evolving tholeiitic magma.
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References
Baker DR (1989) Tracer versus trace element diffusion: diffusional decoupling of Sr concentrations from Sr isotope composition. Geochim Cosmochim Acta 53:3015–3023
Baker MB, Grove TL, Kinzler RJ, Donnelly-Nolan JM, Wandless GA (1991) Origin of compositional zonation (high-alumina basalt to basaltic andesite) in the Giant Crater lava field, Medicine Lake Volcano, California. J Geophys Res 96:21819–21842
Bergantz GW (1989) Underplating and partial melting: implications for mclt generation and extraction. Science 245:1093–1095
Bird DK, Rosing MT, Manning CE, Rose RM (1985) Geologic field studies of the Miki Fjord area, East Greenland. Bull Geol Soc Den 34:219–236
Bird DK, Manning CE, Rose NM (1988) Hydrothermal alteration of Tertiary layered gabbros, East Greenland. Am J Sci 288:405–457
Blichert-Toft J, Lesher CE, Rosing MT (1992) Selectively contaminated magmas of the Tertiary East Greenland macrodike complex. Contrib Mineral Petrol 110:154–172
Blundy JD, Wood BJ (1991) Crystal-chemical controls on the partitioning of Ba and Sr between plagioclase feldspar, silicate melts and hydrothermal solutions. Geochim Cosmochim Acta 55:193–209
Bowen NL (1928) The evolution of the igneous rocks. Princeton University Press, Princeton N.J.
Campbell IH (1986) Distribution of orthocumulate textures in the Jimberlana intrusion. J Geol 95:35–54
Campbell IH, Turner JS (1987) A laboratory investigation of assimilation at the top of a basaltic magma chamber. J Geol 95:155–172
Carmichael ISE (1964) The petrology of Thingmuli, a Tertiary volcano in eastern Iceland J Petrol 5:435–460
Condomines M, Gronvold K, Hooker PJ, Muehlenbachs K, O'Nions RK, Oskarsson N, Oxburgh ER (1983) Helium, oxygen, strontium and neodymium isotopic relationships in Icelandic volcanies. Earth Planet Sci Lett 66:125–136
Door WA (1976) Tertiary igneous rocks between Scoresby Sund and Kap Gustav Holm, East Greenland. In: Escher A, Watt WS (eds) Geology of Greenland. Geol Surv Greenland, Copenhagen, pp 404–429
DePaolo DJ (1981) Trace element and isotopic effects of combined wallrock assimilation and fractional crystallization. Earth Planet Sci Lett 53:189–202
Douglas JAV (1964) Geologic investigations in East Greenland: Part VII. The Basistoppen sheet, a differentiated basic intrusion into the upper part of the Skaergaard complex, East Greenland. Medd Groenl 164:1–66
Grove TL, Kinzler RJ, Baker MB, Donnelly-Nolan JM, Lesher CE (1988) Assimilation of granite by basaltic magma at Burnt lava flow, Medicine Lake volcano, northern California: decoupling of heat and mass transfer. Contrib Mineral Petrol 99:320–343
Himmelberg GR, Ford AB (1976) Pyroxenes of the Dufck intrusion, Antarctica. J Petrol 17:219–243
Hirschmann M (1992) Origin of transgressive granophyres from the Layered Series of the Skaergaard intrusion, East Greenland. J Volcanol Geotherm Res 52:185–208
Hooper PR, Johnston D (1989) Major and trace element analyses of rocks and minerals by automatic x-ray spectrometry. Geology Department, open-file report
Hoover JD (1989) The chilled marginal gabbro and other contact rocks of the Skaergaard intrusion. J Petrol 30:441–476
Hunter RH, Sparks RS (1987) The differentiation of the Skaergaard intrusion. Contrib Mineral Petrol 95:451–461
Huppert HE, Sparks RSJ (1988) The generation of granitic magmas by intrusion of basalt into continental crust. J Petrol 29:599–624
Kaczor SM, Hanson GN, Peterman Z (1988) Disequilibrium melting of granite at the contact with a basic plug: a geochemical and petrographic study. J Geol 96:61–78
Kay SM, Maksaev V, Moscoso R, Mpodozis C, Nasi C (1987) Probing the evolving Andean lithosphere: mid-late Tertiary magmatism in Chile (29°–30°30′S) over the modern zone of subhorizontal subduction. J Geophys Res 92:6173–6190
Kays MA, Goles GG, Grover TW (1989) Precambrian sequence bordering the Skaergaard intrusion. J Petrol 30:321–363
Komar PD (1972) Flow differentiation in igneous dikes and sills: profiles of velocity and phenocryst concentration. Geol Soc Am Bull 83:3443–3448
Langmuir CH (1989) Geochemical consequences of in situ crystallization. Nature 340:199–205
Lesher CE (1990) Decoupling of chemical and isotopic exchange during magma mixing. Nature 344:235–237
Marsh BD (1989) Magma chambers. Ann Rev Earth Planet Sci 17:439–474
McBirney AR (1989) The Skaergaard Layered Series: I structure and average compositions. J Petrol 30:363–399
McBirney AR, Taylor HP, Armstrong RL (1987) Paricutin re-examined: a classic example of crustal assimilation in cale-alkaline magma. Contrib Mineral Petrol 95:4–20
McBirney AR, White CM, Boudreau AR (1990) Spontaneous development of concentric layering in a solidified siliceous dike, East Greenland. Earth Sci Rev 29:321–330
Naslund HR (1989) Petrology of the basistoppen sill, East Greenland: a calculated magma differentiation trend. J Petrol 30:299–319
Nielsen RL (1990) Simulation of igneous differentiation processes. In: Nicholls J, Russell JK (eds) Modern methods of igenous petrology understanding magmatic processes (Reviews in Mineralogy vol 24). Mineralogical Society of America, Washington DC, pp 65–106
Nielsen TFD, Soper NJ, Brooks K, Faller AM, Higgins AC, Matthews DW (1981) The pre-basaltic sediments and the lower basalts at Kangerdlugssuaq, East Greenland: their stratigraphy, lithology, palaeomagnetism and petrology. Meddr Grønland Geoscience 6:3–25
Rosing MT, Lesher CE, Bird DK (1989) Chemical modification of East Greenland Tertiary magmas by two-liquid interdiffusion. Geology 17:626–629
Ross ME (1986) Flow differentiation, phenocryst alignment, and compositional trends within a dolerite dike at Rockport, Massachusetts. Geol Soc Am Bull 97:232–240
Shirley DN (1986) Compaction of igneous cumulates. J Geol 94:795–809
Stewart BW, DePaolo DJ (1990) Isotopic studies of processes in mafic magma chambers: II. The Skaergaard intrusion, East Greenland. Contrib Mineral Petrol 104:125–141
Taylor HP Jr, Forestcr RW (1979) An oxygen isotope study of the Skaergaard intrusion and its country rocks: a description of a 55-m.y. old fossil hydrothermal system. J Petrol 20:355–419
Vogel TA, Walker BM (1975) The Tichka Massif, Morocco: an example of contemporaneous acidic and basic plutonism. Lithos 8:29–38
von Cotta B (1858) Geologische Fragen. Freiberg
Walker KR, Ware NG, Lovering JF (1973) Compositional variations in the pyroxenes of the differentialed Palasades Sill, New Jersey. Geol Soc Am Bull 84:89–110
Watson EB (1982) Basalt contamination by continental crust: some experiments and models. Contrib Mineral Petrol 80:73–87
White CM, Geist DJ, Frost CD, Verwoerd WJ (1989) Petrology of the Vandfaldsdalen macrodike, Skaergaard region, E. Greenland. J Petrol 30:271–298
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Geist, D., White, C. Assimilation and fractionation in adjacent parts of the same magme chamber: Vandfaldsdalen macrodike, East Greenland. Contr. Mineral. and Petrol. 116, 92–107 (1994). https://doi.org/10.1007/BF00310692
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DOI: https://doi.org/10.1007/BF00310692