International Journal of Earth Sciences

, Volume 101, Issue 3, pp 773–786 | Cite as

Magnetic fabrics and their relationship with the emplacement of the Piracaia pluton, SE Brazil

  • M. Irene B. Raposo
  • Leonardo Frederico Pressi
  • Valdecir de Assis Janasi
Original Paper

Abstract

Magnetic fabric and rock-magnetism studies were performed on the four units of the 578 ± 3-Ma-old Piracaia pluton (NW of São Paulo State, southern Brazil). This intrusion is roughly elliptical (~32 km2), composed of (i) coarse-grained monzodiorite (MZD-c), (ii) fine-grained monzodiorite (MZD-f), which is predominant in the pluton, (iii) monzonite heterogeneous (MZN-het), and (iv) quartz syenite (Qz-Sy). Magnetic fabrics were determined by applying both anisotropy of low-field magnetic susceptibility (AMS) and anisotropy of anhysteretic remanent magnetization (AARM). The two fabrics are coaxial. The parallelism between AMS and AARM tensors excludes the presence of a single domain (SD) effect on the AMS fabric of the units. Several rock-magnetism experiments performed in one specimen from each sampled units show that for all of them, the magnetic susceptibility and magnetic fabrics are carried by magnetite grains, which was also observed in the thin sections. Foliations and lineations in the units were successfully determined by applying magnetic methods. Most of the magnetic foliations are steeply dipping or vertical in all units and are roughly parallel to the foliation measured in the field and in the country rocks. In contrast, the magnetic lineations present mostly low plunges for the whole pluton. However, for eight sites, they are steep up to vertical. Thin-section analyses show that rocks from the Piracaia pluton were affected by the regional strain during and after emplacement since magmatic foliation evolves to solid-state fabric in the north of the pluton, indicating that magnetic fabrics in this area of the pluton are related to this strain. Otherwise, the lack of solid-state deformation at outcrop scale and in thin sections precludes deformation in the SW of the pluton. This evidence allows us to interpret the observed magnetic fabrics as primary in origin (magmatic) acquired when the rocks were solidified as a result of magma flow, in which steeply plunging magnetic lineation suggests that a feeder zone could underlie this area.

Keywords

Magnetic fabric AMS AARM Granites Rock magnetism Piracaia pluton 

References

  1. Archanjo CJ, Hollanda MHBM, Rodrigues SWO, Neves BBB, Armtrong R (2008) Fabrics of pre- and syntectonic granite plutons and chronology of shear zone in the Eastern Borborema province, NE Brazil. J Struct Geol 30:310–326CrossRefGoogle Scholar
  2. Benn K, Paterson SR, Lund SP, Pignotta GS, Kruse S (2001) Magnetic fabrics in batholiths as markers of regional strains and plate kinematics: example of the Cretaceous Mt. Stuart Batholith. Phys Chem Earth A 26:343–354CrossRefGoogle Scholar
  3. Borradaile GJ, Werner T (1994) Magnetic anisotropy of some phyllosilicates. Tectonophysics 235:223–248CrossRefGoogle Scholar
  4. Bouchez JL (1997) Granite is never isotropic: an introduction to AMS studies of granitic rocks. In: Bouchez JL, Hutton DHW, Stephens WE (eds) Granite: from segregation of melt to emplacement fabrics. Kluwer Academic Publishers, pp 95–112Google Scholar
  5. Bouchez JL, Gleizes G, Djouadi T, Rochette P (1990) Microstructure and magnetic susceptibility applied to emplacement kinematics of granites: the example of the Foix pluton (French Pyrenees). Tectonophysics 184:157–171CrossRefGoogle Scholar
  6. Campos Neto MC (2000) Orogenic systems from Southwestern Gondwana: an approach to Brasiliano-Pan African cycle and orogenic collage in Southeastern Brazil. In: Cordani UG, Milani EJ, Thomaz Filho A, Campos DA (eds) Tectonic Evolution of South America. Rio de Janeiro, Brazil, pp 335–365Google Scholar
  7. Cañon-Tapia E (1996) Single-grain versus distribution: a simple three-dimensional model. Phys Earth Planet Inter 94:149–158CrossRefGoogle Scholar
  8. Clemens JD, Petford N, Mawer CK (1997) Ascent mechanism of granitic magmas: causes and consequences. In: Holness MB (ed) Deformation-enhanced fluid transport in the earth’s crust and mantle. Chapman and Hall, London, pp 144–171Google Scholar
  9. Constable C, Tauxe L (1990) The bootstrap for magnetic susceptibility tensor. J Geophys Res 95:8383–8395CrossRefGoogle Scholar
  10. Esmaeily D, Bouchez JL, Siqueira R (2007) Magnetic fabrics and microstructures of the Jurassic Shah-Kuh granite pluton (Lut Block, Eastern Iran) and geodynamic inference. Tectonophysics 439:149–170CrossRefGoogle Scholar
  11. Gaillot P, Saint-Blanquat M, Bouchez JL (2006) Effects on magnetic interactions in anisotropy of magnetic susceptibility: models, experiments and implications for igneous rock fabrics quantification. Tectonophysics 418:3–19CrossRefGoogle Scholar
  12. Hargraves RB, Johnson D, Chan CY (1991) Distribution anisotropy: the cause of AMS in igneous rocks? Geophys Res Lett 18:2193–2196CrossRefGoogle Scholar
  13. Hrouda F (1982) Magnetic anisotropy of rocks and its applications in geology and geophysics. Geophys Surv 5:37–82CrossRefGoogle Scholar
  14. Jackson M (1991) Anisotropy of magnetic remanence: a brief review of mineralogical sources, physical origins and geological applications, and comparison with susceptibility anisotropy. Pure Appl Geophys 136:1–28CrossRefGoogle Scholar
  15. Jackson M, Sprowl D, Ellwood BB (1989) Anisotropy of partial anhysteretic remanence and susceptibility in compact black shales: grain-size and composition-dependent magnetic fabric. Geophys Res Lett 16:1063–1066CrossRefGoogle Scholar
  16. Janasi VA, Vlach SRF, Ulbrich HHGJ (1993) Enriched-mantle contributions to the Itu granitoid belt, southeastern Brazil: evidence from K-rich diorites and syenites. Anais da Academia Brasileira de Ciências 65(Suppl 1):107–118Google Scholar
  17. Janasi VA, Salmoni B, Ulbrich HHGJ (2007) The role of enriched mantle in the petrogenesis of the post-orogenic Itu Granitic Province, SE Brazil: petrology of the Piracaia Monzodiorite. Geol Soc Am Abstr ProgramGoogle Scholar
  18. Janasi VA, Vlach SRF, Camos Neto M, Ulbrich HHGJ (2009) Associated A-type subalkaline and high-K calc-alkaline granites in the Itu Granite Province, Southeastern Brazil: petrological and tectonic significance. Canadian Mineral 47:1505–1526CrossRefGoogle Scholar
  19. Jelinek V (1981) Characterization of the magnetic fabric of rocks. Tectonophysics 79:T63–T67CrossRefGoogle Scholar
  20. Martins L, Vlach SRF, Janasi VA (2009) Reaction microtextures of monazite: correlation between chemical and age domains in the Nazaré Paulista migmatite, SE Brazil. Chem Geol 261(3–4):271–285CrossRefGoogle Scholar
  21. Njanko T, Nédélec A, Kwékam M, Siqueira R, Esteban L (2010) Emplacement and deformation of the Fomopéa pluton: implication for the Pan-African history of Western Cameroom. J Struct Geol 32:306–320CrossRefGoogle Scholar
  22. Paterson SR, Vernon RH, Tobisch OT (1989) A review of criteria for identification of magmatic and tectonic foliation in granitoids. J Struct Geol 11:349–363CrossRefGoogle Scholar
  23. Paterson SR, Fowler TK Jr, Schmidt KL, Yoshinobu AS, Yuan ES, Miller RB (1998) Interpreting magmatic fabric patterns in plutons. Lithos 44:53–82CrossRefGoogle Scholar
  24. Pignotta GS, Benn K (1999) Magnetic fabric of the Barrington Passage pluton, Meguma terrane, Nova Scotia: a two-stage fabric history of syntectonic emplacement. Tectonophysics 307:75–92CrossRefGoogle Scholar
  25. Raposo MIB, Gastal MCP (2009) Emplacement mechanism of the main granite pluton of the Lavras do Sul intrusive complex, South Brazil, determined by magnetic anisotropies. Tectonophysics 466:18–31CrossRefGoogle Scholar
  26. Stephenson A, Sadikum S, Potter DK (1986) A theoretical and experimental comparison of the anisotropies of magnetic susceptibility and remanence in rocks and minerals. Geophys J R Astro Soc 84:185–200CrossRefGoogle Scholar
  27. Tarling DH, Hrouda F (1993) The magnetic anisotropy of rocks. Chapman and Hall, LondonGoogle Scholar
  28. Trindade RIF, Raposo MIB, Ernesto M, Siqueira R (1999) Magnetic susceptibility and partial anhysteretic anisotropies in the magnetite-bearing granite pluton of Tourão, NE Brazil. Tectonophysics 314:443–468CrossRefGoogle Scholar
  29. Trubač J, Žák J, Chlupáčová M, Janoušek V (2009) Magnetic fabric of the Říčany granite, Bohemian Massif: a record of helical magma flow? J Volcan Geoth Res 181:25–34CrossRefGoogle Scholar
  30. Vauchez A, Tommasi A, Egydio-Silva M (1994) Self-indentation of a heterogeneous continental lithosphere. Geology 22:967–970CrossRefGoogle Scholar

Copyright information

© Springer-Verlag 2011

Authors and Affiliations

  • M. Irene B. Raposo
    • 1
  • Leonardo Frederico Pressi
    • 1
  • Valdecir de Assis Janasi
    • 1
  1. 1.Instituto de Geociências da Universidade de São PauloSão PauloBrazil

Personalised recommendations