Petrofabric of the acid volcanic rocks from the Southern Paraná

Magmatic Province obtained via AMS: a contribution to the

understanding of their emplacement

Letícia Freitas Guimarães1; Maria Irene Bartolomeu Raposo1; Valdecir de Assis Janasi1; Edgardo

Cañón-Tapia2; Liza Angélica Polo1

1 Instituto de Geociências

leticia.guimaraes@usp.br; irene@usp.br; vajanasi@usp.br; lizapolo@gmail.com2 CICESE, Dept. of Geology

ecanon@cicese.mx

Extracted from

Renner (2010)

Paraná Magmatic Province

Extends over about 900,000 km²

Serra Geral Formation:

~90% (vol.) → basaltic rocks

~7% (vol.) → intermediate rocks

~3% (vol). → acid rocks

Subdivision and classification based on

geochemical criteria (Bellieni et al., 1984;

Mantovani et al., 1985; Peate et al., 1992;

Garland et al., 1995; Nardy et al., 2008;

Polo & Janasi, 2014)

Introduction AMS method Local Geology Sampling Results Conclusion

Paraná Magmatic Province – eruptive style of acid rocks

The best known and accepted

studies claim that these rocks are

the result of explosive events of

great magnitude , corresponding to

reoignimbrites (e.g. Milner et al.

1992; Bryan et al. 2010).

Recent studies in the Brazilian portion of the Province (e.g. Janasi et al., 2007; Luchetti,

2010; Nardy et al., 2011; Lima et al., 2012; Guimarães, 2014; Polo, 2014) → non-explosive

eruptive style predomine.

Introduction AMS method Local Geology Sampling Results Conclusion

Extracted from Bryan et al. (2010)

Why AMS methods?

• AMS is a physical property of rocks and depends on the preferential orientation of

magnetic mineral phases that constitute it (Tarling & Hrouda, 1993);

• It can be described by means of a second rank tensor defined by the correlation

between the applied magnetic field (HA) and the resulting induced magnetization (Mi)

(Tarling & Hrouda, 1993): Mi = Ki x HA.

• K1 > K2 > K3 = maximum, intermediate and minimum susceptibility

• The technique has been largely employed for igneous rocks as an auxiliary tool for the

reconstruction of magmatic flow directions, especially when rocks are characterized

texturally isotropic.

Introduction AMS method Local Geology Sampling Results Conclusion

Why AMS methods?

AMS in pyroclastic deposits

AMS in lavas and lava-domesAMS in dykes

• Good correlation with other flow direction

indicators in most cases

• K1 – magmatic flow direction

*imbrication effects

Knight & Walker (1988)

Variations within a single flow unit:

flow boundary effects!

Introduction AMS method Local Geology Sampling Results Conclusion

Závada et al. (2009)

Cañón-Tapia (2004)

Local Geology

Polo & Janasi (2014)

Santa Maria : SiO2 = 71 - 73%

Barros Cassal: SiO2 = 54 - 65%

Caxias do Sul: SiO2 = 68 - 69%

Introduction AMS method Local Geology Sampling Results Conclusion

AMS sampling

Sampling was carried out in the central and outer portions of the structures whose cooling

fractures are indicative of lobed flow (outcrop observations)..

NE SW

Introduction AMS method Local Geology Sampling Results Conclusion

AMS sampling

Santa Maria rhyolites: the sampling grid has been focused around a notable hill with

circular, dome-type structure, and along a quarry with a large rock exposure.

NE SW

Introduction AMS method Local Geology Sampling Results Conclusion

Magnetic mineralogy and rock magnetism studies

-200 0 200 400 600 800

Temperature (°C)

0

200

400

600

K T

ota

l

XG-28 Basalt

XG-10 Santa Maria

0 40 80 120 160 200

Alternating Field (mT)

0.0

0.2

0.4

0.6

0.8

1.0

No

rmalized

Mag

neti

zati

on

pARM

XG-17B1 Santa Maria

XG-13C1 Caxias do Sul

XG-34K4 Barros CassalXG-28I2 Basalt

1. Symmetric sigmoidal hysteresis curves,

narrow waisted = ferromagnetic grains

with low coercivity carry the bulk

magnetic susceptibilities.

2. Small Hopkinson peak + decrease in the

intensity of susceptibility around 550°C-

580°C (Curie Temperature) → Ti-

magnetite.

3. Partial anhysteretic remanence (pARM) -

Jackson et al., 1989:

Caxias do Sul – Ti-magnetite: 0.75 to 25 μm

Santa Maria – Ti-magnetite: 2 to 25 μm

Introduction AMS method Local Geology Sampling Results Conclusion

Magnetic fabric

Caxias do Sul dacites

Main flow direction: N

Introduction AMS method Local Geology Sampling Results Conclusion

Magnetic fabric

Caxias do Sul dacites

NE SW

Main flow direction: NE

Introduction AMS method Local Geology Sampling Results Conclusion

Magnetic fabric

NE SW

Santa Maria rhyolites

Introduction AMS method Local Geology Sampling Results Conclusion

Magnetic fabric

Santa Maria rhyolites

Introduction AMS method Local Geology Sampling Results Conclusion

Magnetic fabric

Introduction AMS method Local Geology Sampling Results Conclusion

Magnetic fabric

Santa Maria rhyolites

Introduction AMS method Local Geology Sampling Results Conclusion

Introduction AMS method Local Geology Sampling Results Conclusion

• Rock magnetic experiments allowed the recognition of “pseudo-single domain” of

magnetite (Mt) as the mean magnetic susceptibility carrier. Mt grain sizes range from

0.75 to 25 μm for the older dacitic unit (Caxias do Sul) and from 2 to 25 μm for the

younger rhyolitic unit (Santa Maria).

• AMS patterns from dacites: horizontal foliations on the central part and contrasting

opposite directions for foliations in the external parts of the structure. Magnetic

lineations suggest a main flow towards the NE. These results are consistent with

patterns expected for confined flows.

Conclusions

Conclusions

Introduction AMS method Local Geology Sampling Results Conclusion

• AMS patterns from rhyolites: existence of different flow units:

1º ) Magnetic lineation: frontal portion of lobed flows → flow main direction from NW to

SE + outer lateral sections → divergent flows to the SSW and NE.

2º ) Magnetic lineations obtained for the samples collected closer and around the domic

relief: divergent flow directions → define a major circular shaped structure. Its central

portion corresponds to the dome-type hills: a potential local emission center.

3º ) Extensive lava flows (quarry) from W to E.

Our data point towards dome to coulée structures with associated compound

lava flows (lobes). This type of volcanism implies in the existence of local

emission centers.

This work was carried out with the financial support of:

Process 2012/06082-6

“The Paraná-Etendeka Magmatic Province in Brazil: temporal

and petrologic relationships between the tholeiitic and alkaline magmatism

and geodynamic implications”

“A Província Magmática Paraná-Etendeka no Brasil: relações temporais e petrológicas entre o

magmatismo toleítico e alcalino e suas implicações geodinâmicas”

We thank Cristina de Campos for all help and reviews and Gustavo for

helping during the field work.

References

Bellieni, G., Brotzu, P., Comin-Chiaramonti, P., Ernesto, M., Melfi, A., Pacca, I.G., Piccirillo, E.M. (1984) – Flood basalt

to rhyolite suites in the southern Parana Plateau (Brazil): Palaeomagnetism, petrogenesis and geodynamic

implications. Journal of Petrology, 25(3): 579-618.

Bryan, S.E.; Peate, I.U.; Peate, D.W.; Self, S.; Jerram, D.A.; Mawby, M.R.; Marsh, J.S.; Miller, J.A. (2010) – The

largest volcanic eruptions on Earth. Earth-Science Reviews, 102: 207-229.

Cañón-Tapia, E. (2004) – ASM of lava flows and dykes a historial account. Geological Society, London, Special

Publications, 238; 205-225.

Garland, F.; Hawkesworth, C.J.; Mantovani, M.S.M. (1995) – Description and petrogenesis of the Paraná rhyolites,

southern Brazil. Journal of Petrology, 36(5): 1193-1227.

Guimarães, L.F. (2014) - Características físicas e químicas e modelo eruptivo para os riolitos tipo Santa Maria

(Província Magmática Paraná) na região de Gramado Xavier, RS. Dissertação de mestrado. Universidade de São

Paulo.

Jackson, M.; Gruber, W.; Marvin, J.; Banerjee, SK. (1989) – Partial anhysteretic remanence and its anisotropy:

application and grain-size dependence. Geophysical Research Letters, 15: 440-443.

Janasi, V.A.; Montanheiro, T.J.; Freitas, V.A.; Reis, P.M.; Negri, F.A.; Dantas, F.A. (2007) – Geology, petrography and

gechemistry of the acid volcanism of the Paraná Magmatic Province in the Piraju-Ourinhos region, SE Brazil.

Revista Brasileira de Geociências, 37(4): 745-759.

Knight, M.D.; Walker, G.P.L. (1988) – Magma flow directions in dikes of the Koolau Complex, Oahu, determined from

magnetic fabric studies. Journal of Geophysical Research, 93: 4301-4319.

Lima, E.F.; Philipp, R.P.; Rizzon, G.C.; Waichel, B.L.; Rossetti, L.M.M. (2012) – Sucessões vulcânicas, modelo de

alimentação e geração de domos de lava ácidos da Formação Serra Geral na região de São Marcos – Antônio Prado

(RS). Revista Geologia USP – Série Científica, 12(2): 49-64.

Lima, E.F.; Philipp, R.P.; Rizzon, G.C.; Waichel, B.L.; Rossetti, L.M.M. (2012) – Sucessões vulcânicas, modelo de

alimentação e geração de domos de lava ácidos da Formação Serra Geral na região de São Marcos – Antônio Prado

(RS). Revista Geologia USP – Série Científica, 12(2): 49-64.

Luchetti, A.C.F. (2010) – Aspectos vulcanológicos dos traquidacitos da região de Piraju - Ourinhos (SP). Dissertação de

Mestrado, Universidade de São Paulo, São Paulo.

Mantovani, M.S.M.; Marques, L.S.; Souza, M.A.; Atalla, L.; Civeta, L.; Innocenti, F. (1985) – Trace element and

strountium isotope constraints of the origin and evolution of Paraná Continental Flood Basalts of Santa Catarina

State (south Brazil). Journal of Petrology, 26: 187-209.

Milner, S.C., Duncan, A.R., Ewart, A. (1992) - Quartz latite rheoignimbrite flows of the Etendeka Formation, north

western Namibia. Bulletin of Volcanology, 54(3): 200-219.

Nardy, A.J.R.; Machado, F.B.; Oliveira, M.A.F. (2008) – As rochas vulcânicas mesozoicas ácidas da Bacia do Paraná:

litoestratigrafia e considerações geoquímico-estratigráficas. Revista Brasileira de Geociências, 38(1): 178-195.

Nardy, A.J.R.; Rosa, M.C.; Luchetti, A.C.F.; Ferreira, M.L.C.; Machado, F.B.; Oliveira, M.A.F. (2011) – Parâmetros

físicos pré-eruptivos do magmatismo ácido da Província Magmática do Paraná: resultados preliminares.

Geociências, UNESP, 30(4): 575-588.

Peate, D.W.; Hawkesworth , C.J., Mantovani, M.S.M. (1992) - Chemical stratigraphy of the Parand lavas (South

America): classification of magma types and their spatial distribution. Bulletin of Volcanology, 55: 119-139.

Polo, L.A. (2014) - O vulcanismo ácido da Província Magmática Paraná-Etendeka na região de Gramado Xavier, RS:

estratigrafia, estruturas, petrogênese e modelo eruptivo. Tese de doutoramento. Universidade de São Paulo.

Polo, L.A.; Janasi, V.A. (2014) – Volcanic stratigraphy of intermediate to acidic rocks in southern Paraná Magmatic

Province, Brazil. Geologia USP. Série Científica.

Tarling, D.H.; Hrouda, F. (1993) – The Magnetic Anisotropy of Rocks. Chapman and Hall, London, 217 pp.

Závada, P.; Kratinová, Z.; Kusbach, V.; Schulmann, K. (2009) – Internal fabric development in complex lava domes.

Tectonophysics, 466: 101–113.

References