DOCSLIB.ORG

Magnetic Fabric and Deformation in Charnockitic Igneous Rocks of the Bjerkreim±Sokndal Layered Intrusion (Rogaland, Southwest Norway)

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Magnetic Fabric and Deformation in Charnockitic Igneous Rocks of the Bjerkreim±Sokndal Layered Intrusion (Rogaland, Southwest Norway) Journal of Structural Geology 22 (2000) 647±667 www.elsevier.nl/locate/jstrugeo Magnetic fabric and deformation in charnockitic igneous rocks of the Bjerkreim±Sokndal layered intrusion (Rogaland, Southwest Norway) Olivier Bolle a,*, Herve Diot b, Jean-Clair Duchesne a aL.A. GeÂologie, PeÂtrologie et GeÂochimie, Universite de LieÁge, Bd. du Rectorat, B20, B-4000 Sart Tilman, Belgium bC.L.D.G., PoÃle Sciences et Technologie, Universite de La Rochelle, Av. Marillac, F-17042 La Rochelle Cedex 01, France Received 2 December 1998; accepted 3 December 1999 Abstract The Bjerkreim±Sokndal intrusion (BKSK) belongs to the Proterozoic Rogaland igneous complex of Southwest Norway. The BKSK displays an anorthosite to mangerite cumulate series, folded into a syncline, in the core of which crop out massive acidic rocks of quartz mangerite to charnockite composition. We present a study which focuses on the acidic rocks, in which we use the low-®eld anisotropy of magnetic susceptibility (AMS) technique. Systematic microscope examination of the samples collected at 148 AMS stations, and considerations based on mineral intrinsic magnetic susceptibilities reveal magnetic mineralogy and anisotropy controlled by magnetite. Macro- to micro-scale petrofabrics and magnetic fabrics indicate that the acidic rocks, which intruded after deposition of the underlying cumulate series, were also aected by the syn- to post-magmatic folding event which gave rise to the BKSK syncline. In absence of any recognized plate-scale regional stress ®eld, it is suggested that this folding results from a gravity-induced subsidence linked to the ®nal stage of diapiric emplacement of huge neighbouring anorthosite plutons. This model is mainly supported by the structural pattern in the BKSK, which reveals a convergent ¯ow towards a central trough where lineations are sub-vertical. 7 2000 Elsevier Science Ltd. All rights reserved. 1. Introduction layered lower part of cumulative origin, here called the cumulate series, and an upper part made up of massive quartz mangerite and charnockite, here called acidic The Bjerkreim±Sokndal intrusion (BKSK) (Michot, rocks. This magma chamber, ¯anked by anorthosite 1960; Wilson et al., 1996; Duchesne and Wilmart, plutons, is folded. Field and petrological evidence 1997) is a layered magmatic body belonging to the (Duchesne et al., 1985; Duchesne and Maquil, 1987), Proterozoic Rogaland igneous complex of Southwest and a recent numerical modelling (Barnichon et al., Norway. It is a well-documented case of magmatic 1999) have shown that diapirism is a robust and con- complex of the AMCG suite (anorthosite±mangerite± sistent mechanical hypothesis for the emplacement of 1 charnockite±(rapakivi) granite) . The BKSK displays a these anorthosite bodies. A previous micro- to macro- scale structural study, conducted on a restricted por- tion of the cumulate series (Paludan et al., 1994), also * Corresponding author. ``Charge de Recherches du Fonds National Belge de la Recherche Scienti®que''. suggests that the BKSK has been aected by a gravity- E-mail address: [email protected] (O. Bolle). induced subsidence, coeval with the diapirism of the 1 Nomenclature of the AMCG rocks used in the present paper is neighbouring anorthosite plutons. as follows (Streckeisen, 1974): anorthosite=rock containing more This paper reports the results of a BKSK survey, than 90% of plagioclase; (leuco)norite=hypersthene (leuco)gabbro; using the low-®eld anisotropy of magnetic suscepti- jotunite (or monzonorite)=hypersthene monzogabbro; (quartz) man- gerite=hypersthene (quartz) monzonite; charnockite=hypersthene bility (AMS) technique (e.g. Rochette et al., 1992; granite. Borradaile and Henry, 1997), which allows rapid and 0191-8141/00/$ - see front matter 7 2000 Elsevier Science Ltd. All rights reserved. PII: S0191-8141(99)00183-2 648 O. Bolle et al. / Journal of Structural Geology 22 (2000) 647±667 b a BJERKREIM - SOKNDAL Oslo layered intrusion 6500 0 10 Km EGERSUND - OGNA anorthosite GARSAKNATT leuconorite HÅLAND - HELLEREN anorthosite ÅNA - SIRA anorthosite APOPHYSIS EIA - REKEFJORD jotunite HIDRA leuconorite 6490 BJERKREIM lobe N 0 5 Km MYDLAND lobe 6480 330000m E Granulitic gneisses Anorthosite - leuconorite (id. foliated) Jotunitic rocks The BKSK and the Apophysis: (Quartz) mangerite - charnockite (id. foliated) SOKNDAL Zone with jotunitic lenses 6470000m N lobe Cumulate series (anorthosite to mangerite) Fault AMS sampling stations (n = 148) 340 350 Fig. 1. Geological sketch map of (a) the Rogaland igneous complex; and (b) the BKSK and the Apophysis northern part (after Michot and Michot, 1969; Rietmeijer, 1979; Falkum, 1982; Krause et al., 1985; Duchesne and Maquil, 1987; Wilson et al., 1996; Bolle, 1998). In (a), lithology of the BKSK and the Apophysis is not detailed. In (b), dotted lines in the cumulate series ®gure the igneous layering and major lithological boundaries (in the Bjerkreim lobe, the stratigraphically lowest dotted line corresponds to the upper limit of major anorthosite occurrence; in the Bjerkreim and Sokndal lobes, the stratigraphically highest dotted line corresponds to the lower limit of the mangerite cumulates). Grid is the EURF89 kilometric UTM grid (32V zone, LK 100 km square). O. Bolle et al. / Journal of Structural Geology 22 (2000) 647±667 649 easy fabric characterization of weakly anisotropic the jotunitic kindred, cutting across the anorthosite rocks (e.g. Bouchez, 1997). The internal structure of plutons and the cumulate series, and forming dykes the massive acidic rocks which cap the cumulate series and small plutons (Duchesne et al., 1989). Among has been pictured. The study, which also deals with these jotunitic occurrences, the largest body is the Eia± petrofabric interpretation at micro- to macro-scales, Rekefjord intrusion (Michot, 1960; Wiebe, 1984), brings new arguments in favour of a gravity-induced which emplaced along the contact between the BKSK subsidence of the BKSK. and the Helleren and AÊ na±Sira anorthosites (Fig. 1a and b). Zircon and baddeleyite U±Pb ages, and whole rock 2. The Rogaland igneous complex Rb±Sr ages, obtained on various units of the Roga- land igneous complex, indicate an emplacement 2.1. Description around 930 Ma, in a very short time interval (SchaÈ rer et al., 1996 and references therein). The BKSK (Fig. 1a and b) (Michot, 1960; Wilson et al., 1996; Duchesne and Wilmart, 1997) occupies an 2.2. Geological setting area of 0230 km2. Its cumulate series is folded into a syncline, which branches into three lobes: a major one The Rogaland igneous complex belongs to the Pro- (the north-western Bjerkreim lobe) and two minor terozoic Sveconorwegian/Grenvillian orogenic belt. It ones (the southern Sokndal and south-eastern Myd- was emplaced in high-grade terrains, mainly made up land lobes). The axes of these lobes plunge towards of various ortho- and paragneiss complexes (e.g. the core of the structure, which is occupied by the Falkum and Petersen, 1980). The country rocks show acidic rocks. The Bjerkreim lobe displays the most a metamorphic gradient, from granulite-facies in the complete rock sequence in the cumulate series, more surroundings of the complex to amphibolite-facies than 7000 m thick in the axial zone of the syncline. further east, due to the cumulative eect of three meta- The acidic rocks lying above these cumulates are much morphic events (M1, M2, M3; Maijer, 1987). The most thinner (<2000±2500 m). The lowest rocks of the intense event, M2, is characterized by HT±LP unde- magma chamber crop out in the north-western part of formed mineral associations, and results from contact the Bjerkreim lobe, whereas the country rock roof, metamorphism induced by the intrusion of the Roga- capping the acidic rocks, has been completely eroded. land igneous complex (Bingen and van Breemen, The acidic rocks extend south-eastward in a thin sheet- 1998), at around 5.5 kbar and 800±8508C, as de®ned like intrusion (Fig. 1a and b), called the Apophysis by osumilite occurrence close to the contact (Holland (Demaie, 1972; Bolle, 1996, 1998). This intrusion is a et al., 1996). composite magmatic body, made up of acidic and jotu- In agreement with previous works (Michot, 1960; nitic rocks. Hermans et al., 1975; and references in Maijer, 1987), Beside the BKSK, the main units of the Rogaland Falkum (1998) has described six successive folding igneous complex are three large anorthosite plutons phases (F1±F6) to the east of the Rogaland igneous Ê (the Egersund±Ogna, HaÊ land±Helleren and Ana±Sira complex. F1 corresponds to intrafolial mesoscopic iso- bodies) (Fig. 1a). The Egersund±Ogna body (Michot, clinal folds. F2±F5 have produced folds with dominant 1960; Duchesne and Maquil, 1987) is dome-shaped N±S fold axes, gradually more tilted axial planes, and and shows a 1±3-km-thick inner margin of foliated decreasing amplitude (from pluri-kilometric-scale anorthosite±leuconorite and an anorthositic central recumbent isoclinal folds to small-scale tight folds). F6 part. The HaÊ land±Helleren body (Michot, 1961) is has led to large-scale, open to gentle folds with E±W made up of a foliated and folded anorthosite±leuco- axes and vertical axial planes. While the F1±F5 events norite (the HaÊ land pluton, similar to the Egersund± are coeval with regional metamorphism, F6 occurred Ogna margin) and of a massive anorthosite (the Helle- with only weak recrystallization. The F1±F6 detailed ren pluton, cutting across the Egersund±Ogna margin chronology and correlation with the M1, M2, M3 meta- and the HaÊ land pluton). Similar to the Egersund± morphic phases of Maijer (1987) are still uncertain. Ê Ogna body, the Ana±Sira anorthosite pluton is dome- The last regional-scale folding (F5) is, however, con- shaped, but without foliated margin (Krause and sidered to be 50±60 My older than the emplacement of Pedall, 1980; Krause et al., 1985). the 0930 Ma old Rogaland igneous complex (SchaÈ rer Two small leuconoritic intrusions crop out in the et al., 1996; Falkum, 1998). country rocks, along the eastern margin of the Roga- land igneous complex: the Garsaknatt and Hidra bodies (Michot and Michot, 1969; Demaie et al., 3.
Load more

Recommended publications
  • AN ABSTRACT of the THESIS of Federico Cernuschi Rodilosso For
    AN ABSTRACT OF THE THESIS OF Federico Cernuschi Rodilosso for the degree of Master of Science in Geology presented on February 11, 2011. Title: Geology of the Cretaceous Lascano-East Intrusive Complex: Magmatic Evolution and Mineralization Potential of the Merín Basin, Uruguay Abstract approved: John H. Dilles The Cretaceous Merín aborted-rift basin of eastern Uruguay is composed of sub- alkaline Paraná-Etendeka province basaltic flows and shallow intrusives (~133 to 131 Ma), rhyolitic ignimbrites (~130 to 128 Ma) and associated mildly alkaline to alkaline intrusions and volcanic rocks (~128 to 127 Ma). Four intrusive complexes from 20 to >30 kilometers wide are identified by circular positive gravity and cospatial magnetic anomalies and are aligned in a northeast-southwest trend. Whereas the outcropping Valle Chico complex is mainly composed by mildly alkaline syenites, drilling at Lascano East revealed mostly alkaline gabbros and trachytes. The Lascano-West and San Luis concealed complexes are inferred by the location of the aeromagnetic and gravity anomalies. Ten lithogeochemical units were identified and grouped into three rock associations. A sub-alkaline group composed of Treinta y Tres A basalts, Treinta y Tres B basalts and gabbros, Lavalleja rhyolitic ignimbries and San Miguel granodiorite granophyres; a mildly alkaline group including the Santa Lucía basalts and gabbros, Aiguá rhyolites, Valle Chico syenites and India Muerta rhyolites; and an alkaline group including the Lascano alkaline gabbro to trachyte series and the Arrayán olivine basalts. The only observed sedimentary rocks are conglomerates grouped as the Quebracho Formation. Melting of a shallow mantle source (depleted mantle) combined with abundant crustal assimilation likely produced the diversity of the sub-alkaline magmatic rocks.
    [Show full text]
  • On Charnockites ⁎ B
    Available online at www.sciencedirect.com Gondwana Research 13 (2008) 30–44 www.elsevier.com/locate/gr GR Focus On charnockites ⁎ B. Ronald Frost , Carol D. Frost Department of Geology and Geophysics, University of Wyoming, Laramie, WY 82071, USA Received 4 June 2007; received in revised form 20 July 2007; accepted 24 July 2007 Available online 7 August 2007 Abstract Charnockitic rocks form extensive orthogneiss plutons in many granulite terranes and are less commonly found in unmetamorphosed plutons, which have formed in various tectonic regimes. Geochemically, clearly igneous charnockites cover nearly the whole range of granite chemistry, from magnesian to ferroan and from calcic to alkalic. Pyroxenes from unmetamorphosed charnockitic rocks have compositions ranging from magnesian to very iron-rich and record temperatures as high as 1000 °C. Oxygen fugacities for these plutons range from below FMQ to Δ log FMQN+2, values that cover nearly the whole range found in other granitic rocks. This range in bulk chemistry and intensive parameters is a reflection of the many mechanisms that produce charnockites. They may form in rifting environments, where they are ferroan, alkali-calcic to alkalic and metaluminous. Many of these ferroan charnockites are isotopically primitive, suggesting that they have been derived largely or entirely from differentiation or melting of tholeiitic melts. Charnockites are also found in deeply eroded arcs, where they are magnesian, calcic to calc-alkalic and metaluminous. Some charnockitic magmas may form by crustal melting or have incorporated a large component of crustal melt; these plutons tend to be weakly to moderately peraluminous and to have intermediate values of FeO/(FeO+MgO).
    [Show full text]
  • The Genesis of the Gaborone Rapakivi Granite Complex in Southern Africa
    J. geof. Soc. London, Vol. 139. 1982, pp. 109-126, 16 figs, 2 tables. Printed in Northern Ireland. The genesis of the Gaborone rapakivi granite complex in southern Africa R. M. Key & E. P. Wrigbt SUMMARY: The Gaborone Granite is a mushroom-shaped intrusion with a surface area of over 5000 km’. Theintrusion is layered,consisting of a centralcore of rapakivigranite (ThamagaGranite) surrounded bysuccessive shells of anequigranular leucocratic granite (Kgale Granite), a porphyritic granophyre or microgranite (Ntlhantlhe Microgranite) and an outermostzone of massiveEelsite (Kanye Volcanics). Thewhole lithological sequence is deduced to have been derived from a single, highly viscous magma body emplaced into the crust at a high level. The genesis is proposed as follows. The outer felsitesrepresent quenched primary magma with the underlying porphyritic granophyreshaving formed during a subsequenttranquil period after emplacement. The rapakivi granite corewas also of early crystallization abovethe floor but with significant textural characters impressed during updoming in the late crystallization stage. Residual liquid rich in SiO,, K20 and volatiles migrated upwards to form the Kgale Granite. The Gaborone Granite was emplaced in the KaapvaalCraton at about 2400 Ma and its morphology was controlled by pre-existing structures in the crust. The countryrock consists of Archaean gneisses, Lobatse Volcanic Group supracrustals and locally Transvaal Supergroup strata. Chemically the Gaborone Granite is identical to other early Proterozoic non-orogenic granites of theKaapvaal Craton. It is also similar in manyrespects to the Fennoscandian rapakivi granites. The Gaborone Granite has a surface area exceeding al. (1974) reviewed the various hypotheses in the light 5000 km2 in SE Botswana and adjacent parts of South of results of a series of age determinations.
    [Show full text]
  • Basic Intrusion, Charnockite.Rapakivi Granite Plutonism Aod Crusta! Depletion, S
    RENolCONTI DELL,\ SOCIETA lTAUANA 01 MINERALOG IA E PETROLOGIA, 1988, \bI. 4}.2, pp. '4).,,4 Basic intrusion, charnockite.rapakivi granite plutonism aod crusta! depletion, S. W. Sweden FREDERIK H. HUBBARD Depanment of Geolosy, Dundee University, Dundee, Scotland AUSTRACT. - The southern segment of the South-West South-West Swedish Province by a series of Swedish Province (SWSP) of the Precambrian of the major thrust zones, it has characteristics Baltic Shield has features which distinguish it from the northern sesment of the same province and the peculiar to this region pf the Swedish Svecofennian sequences to the east. Repeated cycles of Precambrian. These include an abundance of syn and late·orogenic b..sic magma injection maimained meta-basic intrusions, the occurrence of high crusta! temperatures and led to progressive granulite fades assemblages within the general depletion of the rode! at, and adjacent to, the conduits. This is shown by the development of loc:::aI ~u1ile facies upper amphibolite facies terrain and zones in the seneral amphibolite facies terrain and the distinctive plutonic associations of alkaline occurrence of plutonic charnockite Jrulsses. granite and charnockite (e.g. QUENSEL P., The syn-orogenic: basic magmas caused depletion largely 1951; CALDENruS et al., 1966, MOHREN E., by the generation of hydrous solutions derived from dehydration of mafic minerals in the rountry rocks LARSSON W., 1968, HUBBARD F.H., 1975, ronsequent on the heat influx associated with the 1978). A Rb-Srisochron age of 1420Ma was intrusion. These hydrothermlll solutions metasomatised obtained by WELIN and GORBATSCHEV (1978) and migmatised the basic rocks, formed ap!ite from a composite charnock.ite and granite segregatioO$, or were exhausted to higher level.
    [Show full text]
  • Isotopic Evidence for the Origin of Proterozoic Massif-Type Anorthosites and Their Relation to Rapakivi Granites in Southern Finland and Northern Brazil
    Isotopic evidence for the origin of Proterozoic massif-type anorthosites and their relation to rapakivi granites in southern Finland and northern Brazil AKU HEINONEN ACADEMIC DISSERTATION Department of Geosciences and Geography To be presented, with the permission of the Faculty of Science of the University of Helsinki, for public examination in the Auditorium of the University Museum Arppeanum, on May 26th, 2012 at 12 o’clock noon. DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A18 / HELSINKI 2012 DEPARTMENT OF GEOSCIENCES AND GEOGRAPHY A18 © Aku Heinonen (synopsis and Paper III) © Oxford University Press (Paper I) © The Mineralogical Association of Canada (Paper II) © Elsevier B.V. (Paper IV) Cover photo: Outcrops of the Repartimento anorthosite of the Mucajaí complex along the Rio Repartimento, in Roraima, northern Brazil. Author’s address: Aku Heinonen Department of Geosciences and Geography P.O.Box 64 00014 University of Helsinki Finland [email protected] Supervised by: Professor Tapani Rämö Department of Geosciences and Geography University of Helsinki Co-supervised by: Dr. Irmeli Mänttäri Geological Survey of Finland Reviewed by: Professor Lewis Ashwal School of Geosciences University of Witwaterstrand South Africa Docent Hannu Huhma Geological Survey of Finland Discussed with: Professor James S. Scoates Department of Earth and Ocean Sciences University of British Columbia Canada Department of Geosciences and Geography A ISSN-L 1798-7911 ISSN 1798-7911 (print) ISBN 978-952-10-6319-0 (paperback) ISBN 978-952-10-6320-6 (PDF) http://ethesis.helsinki.fi Unigrafia Helsinki 2012 2 Heinonen, A., 2012. Origin of Proterozoic massif-type anorthosites Heinonen, A., 2012. Isotopic evidence for the origin of Proterozoic massif-type anorthosites and their relation to rapakivi granites in southern Finland and northern Brazil.
    [Show full text]
  • The Shahewan Rapakivi-Textured Granite – Quartz Monzonite Pluton, Qinling Orogen, Central China… 133
    The Shahewan rapakivi-textured granite – quartz monzonite pluton, Qinling orogen, central China… 133 THE SHAHEWAN RAPAKIVI-TEXTURED GRANITE - QUARTZ MONZONITE PLUTON, QINLING OROGEN, CENTRAL CHINA: MINERAL COMPOSITION AND PETROGENETIC SIGNIFICANCE XIAOXIA WANG, TAO WANG, ILMARI HAAPALA AND XINXIANG LU WANG, XIAOXIA, WANG, TAO, HAAPALA, ILMARI and LU, XINXIANG 2002. The Shahewan rapakivi-textured granite – quartz monzonite pluton, Qin- ling orogen, central China: mineral composition and petrogenetic significance. Bulletin of the Geological Society of Finland 74, Parts 1–2, 133–146. The Mesozoic Shahewan pluton consists of four texturally different types of biotite-hornblende quartz monzonite. In the porphyritic types alkali feldspar occurs as euhedral or ovoidal megacrysts that are often mantled by one or more plagioclase shells, and as smaller grains in the groundmass. Quartz, plagioclase (An20–28), biotite, and hornblende occur as inclusions in the alkali feldspar mega- crysts and, more abundantly, in the groundmass. Euhedral quartz crystals in the groundmass are not as common and well developed as in typical rapakivi gran- ite. Compared to typical rapakivi granites, the mafic minerals (biotite and horn- blende) are rich in Mg and poor in Fe, and the whole rock is low in Si, K, F, Ga, Zr, LREE, Fe/Mg, and K/Na. The rocks of the Shahewan pluton are thus regarded as rapakivi-textured quartz monzonites and granites but not true rapa- kivi granites. Key words: granites, rapakivi, quartz monzonite, alkali feldspar, phenocrysts, geochemistry, mineralogy, Mesozoic, Shahewan, Qinling, China Xiaoxia Wang: China University of Geosciences, Beijing 100083, China and Department of Natural Resources, Chang’an University, Xi’an 710054, China and Department of Geology, P.O.
    [Show full text]
  • Deciphering the Evolution of Rapakivi Magmas from Mineral Inclusions in Alkali Feldspar Megacrysts and Zircon
    Geophysical Research Abstracts Vol. 19, EGU2017-7447, 2017 EGU General Assembly 2017 © Author(s) 2017. CC Attribution 3.0 License. Deciphering the evolution of rapakivi magmas from mineral inclusions in alkali feldspar megacrysts and zircon Aku Heinonen (1), Irmeli Mänttäri (2), Tapani Rämö (3), and Kirsi Larjamo (3) (1) University of Helsinki, Institute of Seismology, Finland (aku.heinonen@helsinki.fi), (2) Geological Survey of Finland, (3) University of Helsinki, Department of Geosciences and Geography, Finland Rapakivi granites are ferroan (A-type) granites that are characterized by ovoid-shaped alkali feldspar megacrysts (diameter up to 15 cm) commonly mantled by plagioclase forming the namesake rapakivi texture. The ∼1.63 Ga Wiborg batholith in southeastern Finland is the type area of rapakivi granites. Recent studies into the chemistry and geochronology of the mineral inclusions within the Wiborg rapakivi granite ovoids have shown that the megacrysts may represent magmas that crystallized significantly earlier and either in different P/T conditions or from magmas with dissimilar compositions than the matrices of the respective granites. It is possible that the ovoids crystallized from magmas with more evolved geochemical characteristics than the matrices, including higher levels of REE and other incompatibe elements. All ovoids are perthitic and have concave and rod-shaped quartz, hypidiomorphic or slightly resorbed pla- gioclase (often with partial quartz rim), zircon, biotite, apatite, and ilmenite (and occasionally minor magnetite) inclusions. The ovoids of the mafic rapakivi granite types have also hornblende and sometimes olivine and clinopyroxene inclusions, whereas the more felsic types have abundant fluorite. In contrast to the ovoids, the groundmass feldspar grains have hardly any inclusions.
    [Show full text]
  • Paleomagnetism of the Amazonian Craton and Its Role in Paleocontinents Paleomagnetismo Do Cráton Amazônico E Sua Participação Em Paleocontinentes
    DOI: 10.1590/2317-4889201620160055 INVITED REVIEW Paleomagnetism of the Amazonian Craton and its role in paleocontinents Paleomagnetismo do Cráton Amazônico e sua participação em paleocontinentes Manoel Souza D’Agrella-Filho1*, Franklin Bispo-Santos1, Ricardo Ivan Ferreira Trindade1 , Paul Yves Jean Antonio1,2 ABSTRACT: In the last decade, the participation of the Amazonian RESUMO: Dados paleomagnéticos obtidos para o Cráton Amazôni- Craton on Precambrian supercontinents has been clarified thanks to co nos últimos anos têm contribuído significativamente para elucidar a a wealth of new paleomagnetic data. Paleo to Mesoproterozoic pale- participação desta unidade cratônica na paleogeografia dos superconti- omagnetic data favored that the Amazonian Craton joined the Co- nentes pré-cambrianos. Dados paleomagnéticos do Paleo-Mesoprotero- lumbia supercontinent at 1780 Ma ago, in a scenario that resembled zoico favoreceram a inserção do Cráton Amazônico no supercontinente the South AMerica and BAltica (SAMBA) configuration. Then, the Columbia há 1780 Ma, em um cenário que se assemelhava à config- mismatch of paleomagnetic poles within the Craton implied that ei- uração “South AMerica and BAltica” (SAMBA). Estes mesmos dados ther dextral transcurrent movements occurred between Guiana and também sugerem a ocorrência de movimentos transcorrentes dextrais Brazil-Central Shield after 1400 Ma or internal rotation movements entre os Escudos das Guianas e do Brasil-Central após 1400 Ma, ou of the Amazonia-West African block took place between 1780 and que movimentos de rotação do bloco Amazônia-Oeste África ocorreram 1400 Ma. The presently available late-Mesoproterozoic paleomagnetic dentro do Columbia entre 1780 e 1400 Ma. Os dados paleomagnéticos data are compatible with two different scenarios for the Amazonian atualmente disponíveis do final do Mesoproterozoico são compatíveis com Craton in the Rodinia supercontinent.
    [Show full text]
  • The Rıo De La Plata Craton
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Springer - Publisher Connector Int J Earth Sci (Geol Rundsch) (2011) 100:201–220 DOI 10.1007/s00531-010-0580-8 ORIGINAL PAPER The Rı´o de la Plata Craton: a review of units, boundaries, ages and isotopic signature Pedro Oyhantc¸abal • Siegfried Siegesmund • Klaus Wemmer Received: 22 March 2010 / Accepted: 8 July 2010 / Published online: 17 August 2010 Ó The Author(s) 2010. This article is published with open access at Springerlink.com Abstract A review of the lithostratigraphic units in the scenario can be observed. These differences together with Rı´o de la Plata Craton and of new and previously published contrasting geophysical signatures support the redefinition geochronological, isotopic and geophysical data is pre- of the Rı´o de la Plata Craton comprising only the Piedra sented. Sm–Nd TDM model ages between 2.6 and 2.2 Ga Alta Terrane and the Tandilia Belt. The Sarandı´ del Yı´ characterize the Piedra Alta Terrane of this craton. Crys- Shear Zone is regarded as the eastern margin of this tallization ages between 2.2 and 2.1 Ga for the metamor- Craton. phic protoliths and 2.1–2.0 Ga for the post-orogenic granitoids indicate juvenile crust, followed by a short Keywords Precambrian Á Transamazonian cycle Á South period of crustal recycling. Cratonization of this terrane American platform Á Rı´o de la Plata Craton occurred during the late Paleoproterozoic. Younger over- printing is not observed, suggesting it had a thick and strong lithosphere in the Neoproterozoic.
    [Show full text]
  • Age and Isotopic Fingerprints of Some Plutonic Rocks in the Wiborg Rapakivi Granite Batholith with Special Reference to the Dark Wiborgite of the Ristisaari Island
    Bulletin of the Geological Society of Finland, Vol. 86, 2014, pp 71–91 Age and isotopic fingerprints of some plutonic rocks in the Wiborg rapakivi granite batholith with special reference to the dark wiborgite of the Ristisaari Island O.T. RÄMÖ1)*, V. TURKKI2), I. MÄNTTÄRI3), A. HEINONEN1), K. LARJAMO1) AND Y. LAHAYE4) 1) Department of Geosciences and Geography, Division of Geology, P.O. Box 64, FI-00014 University of Helsinki, Finland 2) Rälssintie 12, FI-47200 Elimäki, Finland 3) Geological Survey of Finland, P.O. Box 96, FI-02150 Espoo, Finland 4) The National SGL Laboratory, c/o Geological Survey of Finland, P.O. Box 96, FI-02150 Espoo, Finland Abstract The mid-Proterozoic, locus classicus Wiborg rapakivi granite batholith of southeastern Finland and adjacent Russia comprises a varying, bimodal (silicic-basic) sequence of plutonic, subvol- canic, and volcanic rocks. At the current level of erosion silicic rocks are dominant, the most prominent of which are wiborgites and dark wiborgites (that have been considered to mark the main build-up stage of the batholith) and pyterlites. New observations and optical microscopy data from the dark wiborgite-dominated Ristisaari Island in the southern, off-shore part of the Wiborg batholith show that dark plagioclase megacrysts in dark wiborgite are calcic xenoc- rysts. They were probably incorporated into wiborgite magma from consanguineous massif- type anorthosite magmas in the course of the evolution of the bimodal magmatic system. Our new ID-TIMS U-Pb zircon age of the Ristisaari Island dark wiborgite, 1627±3 Ma, is the youn- gest isotopic age so far determined for the plutonic rocks of the Wiborg batholith.
    [Show full text]
  • The Vehmaa Rapakivi Granite Batholith – an Assemblage of Successive Intrusions Indicating a Piston-Type Collapsing Centre
    Bulletin of the Geological Society of Finland,Vol. 77, 2005, pp. 65–70 The Vehmaa rapakivi granite batholith – an assemblage of successive intrusions indicating a piston-type collapsing centre Olavi Selonen1)*, Carl Ehlers2) , Hannu Luodes1) and Jouni Lerssi1) 1) Geological Survey of Finland, FIN-70211 Kuopio, Finland 2) Åbo Akademi University, Department of Geology, FIN-20500 Turku, Finland Short Communication Key words: granites, rapakivi, batholiths, intrusions, magmatism, Paleoproterozoic,Vehmaa, Finland 1. Introduction The 700 km2 Vehmaa rapakivi granite batholith is lo- ite in the centre of the batholith is described in more cated in south-western Finland. It has a concentric detail than the other granite types. By careful map- structure and is composed of intrusions of five granite ping and by studying geophysical data, two succes- varieties (we use the terminology of the rock names ac- sive intrusion pulses of almost identical types of the cording to the published geological map sheet, Lind- medium-grained granite, in contact with each other, berg &Bergman, 1993): pyterlite, coarse-grained have been defined. The two intrusive phases have not porphyritic rapakivi granite, medium-grained por- previously been described. We think that the mode phyritic rapakivi granite, even-grained rapakivi gran- of intrusion of these granites is important for the un- ite, and porphyry aplite (Fig. 1). The granite types derstanding the emplacement of the whole batholith, yield a concordant monazite U-Pb age of 1573 ± 8 and suggests a more generally applicable model for Ma (even-grained granite of satellite intrusion) and other intrusions of rapakivi granite in Finland. a zircon U-Pb age of 1582 ± 4 Ma (pyterlite) (Lind- Recently, Haapala & Lukkari (2005) discussed the berg & Bergman 1993).
    [Show full text]
  • Magnetic Fabrics and Microstructures of Paleoproterozoic Intrusive Bodies of Piedra Alta Terrane, Río De La Plata Craton, Uruguay: a Reconnaissance Study
    SILEIR RA A D B E E G D E A O D L E O I G C I A O ARTICLE BJGEO S DOI: 10.1590/2317-4889202020200002 Brazilian Journal of Geology D ESDE 1946 Magnetic fabrics and microstructures of Paleoproterozoic intrusive bodies of Piedra Alta Terrane, Río de la Plata Craton, Uruguay: a reconnaissance study Pablo Reinaldo Franceschinis1,2* , Augusto Ernesto Rapalini1,2 , Leda Sánchez Bettucci3 , Carmen Martínez Dopico1,2 , Florencia Nidia Milanese1,2 Abstract Small to medium-sized intrusive bodies with ages between 2.1 and 2.0 Ga characterize Piedra Alta terrane and represent the final stabilization of Río de la Plata Craton. A reconnaissance study of petro- and magnetic fabrics based on microscopic observations, anisotropy of magnetic susceptibility and anhysteretic remanent magnetization, was carried out on 41 sites from 14 intrusive bodies, in order to obtain preliminary information on kinematics of their emplacement, degree of deformation, and regional stress regime during this magmatic event. The mag- netic fabrics coupled with the microstructural analysis are interpreted as generally reflecting magma kinematics near solidus temperature, although few cases of tectonically modified fabrics at local levels have been interpreted. Field evidence and magnetic fabrics in most plutons show subvertical to high angle E-W to NE-SW trending foliations and subvertical lineations. These data suggest that plutons were probably intruded under a regional extensional to transtensional regime, which controlled the magma ascent and distribution of the intrusions. Lack of metamorphism and low to null deformation shown by the study plutons suggest a late-orogenic character for this magmatism, which has been associated with crustal stabilization after accretionary processes that led to the formation of Río de la Plata Craton in the Orosirian.
    [Show full text]