Summary
The dyke-like 1.63 Ga Jaala-Iitti rapakivi complex forms a 25 km long and up to 2 km wide intrusive body at the northwestern margin of the Wiborg rapakivi batholith cutting both the granites of the batholith and the surrounding 1.9 Ga Svecofennian crust. The subvolcanic-epizonal Jaala-Iitti complex consists of silicic (quartz-feldspar porphyry) and basic (diabase) rocks as well as more abundant intermediate hornblende-bearing hybrid rocks.
The hybrid rocks are characterised by: 1) diabase pillows and enclaves that commonly contain quartz and feldspar xenocrysts, 2) quartz megacrysts mantled by amphibole coronas, and 3) large, (up to 10 cm) rounded alkali feldspar megacrysts mantled by shells of micrographic plagioclase-quartz intergrowths. The observed data indicate that hybridization is caused by: 1) mixing of basic and silicic magmas, 2) incorporation of megacrysts from one of the interacting magmas into the another, and 3) assimilation and disaggregation of xenoliths and xenocrysts. It is proposed that the hybridization took place mainly before eruption deep in the crust where basic mantle-derived magmas and silicic crust-derived magmas interacted.
Zusammenfassung
Der gangförmige, 1.63 Mia alte Jaala-Iitti Rapakivi Komplex stellt einen 25 km langen und bis zu 2 km breiten Intrusionskörper am Nordwestrand des Wiborg Rapakivi Batholithes dar, der sowohl die Granite des Batholithes, wie auch die umgebende 1.9 Mia alte svekofennische Kruste durchschneidet. Der subvulkanische, epizonale Jaalalitti Komplex besteht aus sauren (Quarz-Feldspat-Porphyr) und basischen (Diabase) Gesteinen und aus häufig vorkommenden, intermediären, hornblendeführenden, hybriden Gesteinen.
Die hybriden Gesteine sind durchfolgende Charakteristika gekennzeichnet: 1) Diabas-Pillows und Enklaven, die überwiegend aus Quarz- und FeldspatXenokristallen bestehen, 2) Quarz-Megakristalle, die einen kronenartigen Amphibolsaum zeigen, und 3) große (bis 10 cm), runde Alkalifeldspat-Megakristalle, die von mikrographisch verwachsenem Quarz-Feldspat umrandet sind. Die beobachteten Erscheinungen deuten an, daß die Hybridisierung durch 1) Mischung von basischen und sauren Magmen, 2) Inkorporation von Megakristallen von einem in das andere der beiden sich mischenden Magmen, und 3) Assimilation und Disaggregation von Xenolithen und Xenokristallen, verursacht ist. Es wird angenommen, daß die Hybridisierung tief in der Kruste, vor der Eruption entstanden ist, dort, wo basische, aus dem Mantel stammende mit sauren, aus der Kruste stammenden Magmen in Wechselwirkung getreten sind.
Similar content being viewed by others
References
Boyd WW Jr (1972) Diabase variation and genesis. Geol Soc Finland Bull 44: 21–34
— Rämö OT (1991) Miscegenation in the Proterozoic. In:Haapala I, Rämö OT (eds) Symposium Rapakivi Granites and Related Rocks. Geol Surv Finland Guide 34: 9 (Abstract)
Castro A, Moreno-Ventas I, De la Rosa JD (1991) Multistage crystallization of tonalitic enclaves in granitoid rocks (Hercynian belt, Spain): implications for magma mixing. Geol Rundschau 80(1): 109–120
Eklund O, Fröjdö, S, Lindberg B, Andersson UB (1991) The link between anorthositic suites and rapakivi granites. In:Haapala I, Rämö OT (eds) Symposium Rapakivi Granites and Related Rocks. Geol Surv Finland Guide 34:14 (Abstract)
Haapala I (1977) Petrography and geochemistry of the Eurajoki stock, a rapakivi-granite complex with greisen-type mineralization in southwestern Finland. Geol Surv Finland Bull 286: 128 pp
— (1988) Metallogeny of the Proterozoic rapakivi granites of Finland. In:Taylor RP, Strong DF (eds) Recent advances in the geology of granite-related mineral deposits. Can Inst Mining and Metallurgy Spec Vol 39: 124–132
— (1989) The Eurajoki stock. In:Ehlers C, Haapala I (eds) Symposium Precambrian Granitoids, petrogenesis, geochemistry and metallogeny, Excursion A1. Geol Surv Finland Guide 27: 35–38
—Rämö OT (1990) Petrogenesis of the Proterozoic rapakivi granites of Finland. In:Stein HJ, Hannah JL (eds) Ore-bearing granite systems; petrogenesis and mineralizing processes. Geol Soc Am Spec Pap 246: 275–286
Huppert HE, Sparks RSJ (1988) The generation of granitic magmas by intrusion of basalt into continental crust. J Petrol 29: 599–624
Johanson BS (1989) Monzodioritic rocks of the gabbro-anorthosite complex associated with the Ahvenisto rapakivi granite batholith, southern Finland. In:Haapala I, Kähkönen Y (eds) Symposium Precambrian Granitoids. Geol Surv Finland Spec Pap 8: 74 (Abstract)
Laitakari I (1969) On the set of olivine diabase dikes in Häme, Finland Bull Comm Géol Finlande 241: 65 pp
Lehijärvi M, Lonka A (1964) The hornblende rapakivi dike of Jaala-Iitti. Bull Comm Géol Finlande 215: 127–141
Lindberg B, Eklund O (1989) The rapakivi granite—diabase association in southwestern Finland. In:Haapala I, Kähkönen Y (eds) Symposium Precambrian Granitoids. Geol Surv Finland Spec Pap 8: 82 (Abstract)
Rämö OT (1989) Bimodal silicic-basic magmatism associated with rapakivi granites: petrography and petrology of composite diabase—quartz porphyry dykes and K-feldspar diabases in the Suomenniemi complex, southeastern Finland. In:Haapala I, Kähkönen Y (eds) Symposium Precambrian Granitoids. Geol Surv Finland Spec Pap 8: 105–106 (Abstract)
2 (1990) Diabase dyke swarms and silicic magmatism-Evidence from the Proterozoic of Finland. In:Parker AJ, Rickwood PC, Tucker DH (eds) Mafic dykes and emplacement mechanisms. Balkema, Rotterdam Brookfield, pp 185–199
— (1991) Petrogenesis of the Proterozoic rapakivi granites and related basic rocks of southeastern Fennoscandia: Nd and Pb isotopic and general geochemical constraints. Geol Surv Finland Bull 355: 161 pp
Salonsaari PT, Haapala I (1991) The Jaala-Iitti rapakivi complex: an example of bimodal magmatism and hybridization in the Wiborg rapakivi batholith, Finland. In:Haapala I, Rämö OT (eds) Symposium Rapakivi Granites and Related Rocks. Geol Surv Finland Guide 34: 45 (Abstract)
Sato H (1975) Diffusion coronas around quartz xenocrysts in andesite and basalt from Tertiarn volcanic region in NE Shikoku, Japan. Contrib Mineral Petrol 50: 49–64
Sparks RSJ, Marshall LA (1986) Thermal and mechanical constraints on mixing between mafic and silicic magmas. J Volcanol Geotherm Res 29: 99–124
Turner JS, Campbell IH (1986) Convection and mixing in magma chambers. Earth Sci Rev 23: 255–352
Vaasjoki M, Rämö OT (1989) The Wiborg rapakivi batholith and associated rocks in south-eastern Finland. Symposium Precambrian Granitoids, petrogenesis, geochemistry and metallogeny, Excursion A2. Geol Surv Finland Guide 30: 32 pp
——Sakko M (1991) New U-Pb ages from the Wiborg rapakivi area: constraints on the temporal evolution of the granite—anorthosite—diabase dyke association of southeastern Finland. In:Haapala I, Condie KC (eds) Precambrian Granitoids—petrogenesis, geochemistry and metallogeny. Precambrian Res 51: 227–243
Vorma A (1971) Alkali feldspars of the Wiborg rapakivi massif in southeastern Finland. Bull Comm Geol Finlande 246: 72 pp
Author information
Authors and Affiliations
Additional information
With 5 figures
Rights and permissions
About this article
Cite this article
Salonsaari, P.T., Haapala, I. The Jaala-Iitti rapakivi complex. An example of bimodal magmatism and hybridization in the Wiborg rapakivi batholith, southeastern Finland. Mineralogy and Petrology 50, 21–34 (1994). https://doi.org/10.1007/BF01160136
Received:
Accepted:
Issue Date:
DOI: https://doi.org/10.1007/BF01160136