INVESTIGADORES
SPALLETTI Luis Antonio
congresos y reuniones científicas
Título:
The African provenance of southern South America terranes: a record from Rodinia break-up to Gondwanan assembly.
Autor/es:
RAPELA, C.W.; FANNING, C.M.; CASQUET, C.; PANKHURST, R.J.; SPALLETTI, L.A.; POIRÉ, D.G. Y BALDO, E.G.
Lugar:
Mar del Plata
Reunión:
Congreso; International Geological Congress on the Southern Hemisphere.; 2010
Resumen:
A remarkable characteristic of southern South America, is that the 2.26-2.02 Ga
Palaeoproterozoic sequences of the Río de la Plata craton that define the oldest southern
core of the continent, have not been affected by the widespread Neoproterozoic
deformation and magmatism associated with the assemblage of Gondwana. In
Uruguay, the Sarandí del Yi megashear separates the Paleoproterozoic basement
unaffected by Neoproterozoic events (Piedra Alta and Pando terranes), from the
complex Archean to Mesoproterozoic Nico Pérez terrane, which was reworked during
the Mesoproterozoic (Bossi & Cingolani 2009, Oyhantçabal et al., 2009 and references
therein), as well as the collage of terranes accreted during the Brasiliano-Panafrican
orogeny (e.g., Punta del Este terrane and Dom Feliciano belt). Further south in the
Tandilia belt in Argentina, SHRIMP analyses of the 2.23-2.06 Ga Paleoproterozoic
basement do not show a Neoproterozoic overprint (Hartmann et al., 2002b); the 2.19-
2.09 Ga samples recovered from deep drill cores in the western side of the craton also
show no such evidence (Rapela et al., 2007).
Another important piece of evidence comes from the zircon provenance patterns
of Neoproterozoic sedimentary and metasedimentary sequences located along the
western and southern sides of the Río de la Plata craton (i.e. the Pampean Belt and the
North Patagonian Massif). These sequences are dominated by a bimodal pattern, with
peaks at 1250-960 Ma and 680-570 Ma and a minor peak c. 1900 Ma, with scarce, if
any, Palaeoproterozoic zircons in the Río de la Plata craton range of ages (e.g. Basei et
al., 2005, 2008; Pankhurst et al., 2006; Rapela et al., 2007). To explain these bimodal
patterns, African (Namaqua-Natal) and Brazilian sources have been postulated
(e.g. Schwartz & Gromet, 2004; Basei et al., 2005; Rapela et al, 2007).
However, it is difficult to make a coherent scenario incorporating the several
geodynamic models recently proposed for the pre-Atlantic (Adamastor ocean), and
those for the western side of the Río de la Plata craton. Another important issue that
remains poorly explained is the relative position of the Kalahari, Congo and Río de la
Plata cratons during the early Neoproterozoic. This paper presents new U-Pb SHRIMP
results on drill core samples from close to the present Atlantic coast, at the tip of the
Tandilia belt on the eastern margin of the Río de la Plata craton (Punta Mogotes), as
well as from the Sierra Ancasti and Sierra Brava in the Pampean belt, on the western
side of the craton. Zircon provenance patterns on these critically located samples,
together with previous results, allow an interpretation of the Neoproterozoic riftingdrifting
of the Río de la Plata craton, and infer a close connection with similar
processes in southwestern Africa. This process covers the transition from Rodinia
dispersal to Gondwana assembly.
The analyses of 5 samples from the 504 m deep Punta Mogotes borehole
(Marchese & Di Paola, 1975) show the expected sharp contrast in zircon age pattern
between the Neoproterozoic low-grade metapelites of the Punta Mogotes Formation and
that of the overlying quartzites of the Balcarce Formation. The patterns of the two
samples of the Punta Mogotes Formation are complex but remarkably similar,
suggesting a similar source for at least the upper section of this sequence. Conspicuous
younger peaks at 760-790 Ma defined by concordant zircons are the most important
characteristic of these patterns, with significant populations in the Mesoproterozoic
(peaks at 1250 and 1270 Ma respectively), and Upper Paleoproterozoic (peaks at 1735
and 1835 Ma), and minor but concordant populations at 1420-1560 Ma, 2070-2200 Ma,
together with Early Palaeoproterozoic and Archaean zircons. This pattern and those
found in the metasedimentary rocks of the Pampean Belt, characterized by prominent
bi-modal peaks at 560-625 Ma and 1025-1110 Ma, with minor peaks at 730-760 Ma and
c. 1900 Ma, have been used to constraint a plate reconstruction for various time periods
involving the Río de la Plata, Congo and Kalahari cratons.
The conspicuous peaks at 760-780 Ma of the Punta Mogotes Formation are unique
among the Neoproterozoic successions, and these dominantly concordant detrital
zircons define a minimum age for the siliciclastic succession. There are no Brasiliano-
Panafrican ages (560-680 Ma) in the Punta Mogotes Formation, although this is a
widespread event in southwestern South America, suggesting that the sequence is older
than 680 Ma as well as younger than or coeval with the 760-780 Ma detrital peaks.
Major detrital peaks at 635-660 Ma are otherwise observed in all samples of the
overlying Balcarce Formatiom. Orthogneisses with U-Pb SHRIMP ages of 762 ± 8 and
776 ± 12 Ma have been described from the Punta del Este Terrane in eastern Uruguay,
and inferred to be a portion of the Coastal Terrane of the Kaoko Belt (Hartmann et al.,
2002a; Oyhantçabal et al., 2009). In southwestern Africa, this period is characterized by
the inception of a large alkaline igneous province associated with rifting that was
eventually superseded by drifting and finally by inversion of the basins (Jacobs et al.,
2008 and references therein). A comparison with the Neoproterozoic detrital patterns of
southwestern Africa and southeastern South America suggests that the most suitable
source for the Punta Mogotes Formation was the basement of the Kaoko belt, on the
southwestern edge of the Congo craton. The Piedras de Afilar Formation, a thick
siliciclastic and carbonate sequence located on the edge of the Río de la Plata craton in
Uruguay, shows a similar detrital pattern, which however lacks the 760-790 Ma peak
(Gaucher et al., 2008 ), indicating that both sequences were derived from similar
sources in the Congo craton.
These similarities in detrital patterns strongly suggest that the Río de la Plata
craton was a conjugate rift margin of the Congo craton at the time of the 760-830
Neoproterozoic rifting. The NW-SE branch of the aulacogenic triple point located at
the western end of the Damara orogen (Goscombe et al., 2005 and references therein), is
here considered as initiating separation of the Río de la Plata and the Congo cratons,
resulting in development of the northern Adamastor ocean at the time of Rodinia breakup.
It is also considered that discrete continental terranes might have rifted away from
the Congo craton. The Archaean to Mesoproterozoic Nico Pérez terrane in Uruguay
(Bossi & Cingolani, 2009) may have been produced during this episode.
A second NE-SW branch of the triple point runs along the western edge of the
Kalahari craton and faced an open ocean to the west. Discrete continental African
terranes may have also rifted away during the opening of the southern Adamastor ocean.
The continental terranes affected by rifting at the latitude of the Gariep Belt were mostly
composed of the Mesoproterozoic complexes of the Natal-Namaqua orogen (c. 1000-
1100 Ma), and secondly by the 1700-2000 Ma Eburnean age basement, such as the
Richtersveld terrane (Frimmel et al., 2001). Maximum expansion of the northern
Adamastor and Khomas oceans took place at c. 700 Ma, while ocean opening continued
in the southern Adamastor ocean. East-directed subduction started in the northern
Adamastor ocean (Gray et al., 2006) at c. 680 Ma, with the possible formation of intraoceanic
arcs. Closing of the northern branch took place at c. 640 Ma, involving
transpression, e.g. the Kaoko Belt(Goscombe et al., 2005; Gray et al., 2006) and Punta
del Este terrane (Oyhantçabal et al., 2009). West-directed subduction started in the
southern Adamastor ocean with development of 620-580 Brasiliano magmatic arcs
preserved in the African terranes , now located to the west and southwest of the Río
de la Plata craton (present coordinates). Southward displacement of the Río de la Plata
craton with the attached Nico Pérez terrane led to the highly oblique collision against
the southwestern Congo craton, developing sinistral transpression in the Kaoko and
Dom Feliciano belts in the 640-600 Ma time interval.
Protracted oblique subduction led to closure of the Adamastor ocean at ca. 545 Ma
involving collision between the Río de la Plata and the Kalahari cratons (Frimmel &
Frank, 1998). On the west and southwest, the Río de la Plata craton was involved at ca.
530-520 Ma into right-lateral collision with a large continental terrane, developing the
transpressional Pampean Belt.
References
Basei, M.A.S., Frimmel, H.E., Nutman, A.P., Preciozzi, F., Jacob, J., 2005. A
connection between the Neoproterozoic Dom Feliciano (Brazil/Uruguay) and
Gariep (Namibia/South Africa) orogenic belts evidence from a reconnaissance
provenance study. Precambrian Research 139, 195-221.
Bossi, J., Cingolani, C., 2009. Extension and general evolution of the Río de la Plata
craton. In: Gaucher, G., Sial, A.N., Halverson, G.P., Frimmel, H.E. (eds.)
Neoproterozoic-Cambrian Tectonics, Global Change and Evolution: A Focus on
Southwesten Gondwana. Developments in Precambrian Geology, 16, Elsevier,
pp.73-85.
Basei, M.A.S., Frimmel, H.E., Nutman, A.P., Preciozzi F., 2008. West Gondwana
amalgamation based on detrital zircon ages from Neoproterozoic Ribeira and
Dom Feliciano belts of South America and comparison with coeval sequences
from SW Africa. In: Pankhurst, R.J., Trouw, R.A., Brito Neves, B.B. and de Wit,
M.J. (eds.) West Gondwana: Pre-Cenozoic Correlations Across the South Atlantic
Region. Geological Society, London, Special Publications, 294, 239-256.
Frimmel, H.E., Frank, W., 1998. Neoproterozoic tectono-thermal evolution of the
Gariep Belt and its basement, Namibia/South Africa. Precambrian Research 90, 1-
28.
Frimmel, H.E., Zartman, R.E., Späth, A., 2001. The Richstersveld Igneous Complex,
South Africa: U-Pb zircon and geochemical evidence for the beginning of the
Neoproterozoic continental break-up. The Journal of Geology 109, 493-508.
Gaucher, C., Finney, S.C., Poiré, D.G., Valencia, V.A., Grove, M., Blanco, G.
Paamoukaghlian, K., Gómez Peral, L., 2008. Detrial zircon ages of
Neoproterozoic sedimentary successions in Uruguay and Argentina: insightsinto
the geological evolution of the Río de la Plata Craton. Precambrian Research 167,
150-170.
Goscombe, B., Gray, D., Armstrong, R., Foster, D.A., Vogl, J., 2005. Event
geochronology of the Pan-African Kaoko Belt, Namibia. Precambrian Research
140, 1-41.
Gray, D.R., Foster, D.A., Goscombe, B., Passchier, C.W., Trouw, R.A.J., 2006.
40Ar/39Ar thermochronology of the Pan-African Damara orogen, Namibia, with
implications for tectonothermal and geodynamic evolution. Precambrian Research
150, 49-72.
Hartmann, L.A., Santos, J.O.S., Bossi, J., Campal, N., Schipilov, A., McNaughton, N.J.,
2002a. Zircon and titanite UPb SHRIMP geochronology of Neoproterozoic felsic
magmatism on the eastern border of the Río de la Plata craton, Uruguay. Journal
of South American Earth Sciences 15, 229-236.
Hartmann, L.A., Santos, J.O.S., Cingolani, C.A., McNaughton, N.J., 2002b. Two
Palaeoproterozoic orogenies in the evolution of the Tandilia Belt, Buenos Aires,
as evidenced by zircon UPb SHRIMP geochronology. International Geology
Review 44, 528-543.
Marchese, H.G., Di Paola, E.C., 1975. Reinterpretación estratigráfica de la Perforación
Punta Mogotes Nº 1, Provincia de Buenos Aires, República Argentina. Revista de
la Asociación Geológica Argentina 30, 44-52.
Oyhantçabal, P., Siegesmund, S., Wemmer, K., Presnyacov, S., Layer, P., 2009.
Geochronological constraintson the evolution of the southern Dom Feliciano Belt
(Uruguay). Journal of the Geological Society, London, 166, 1075-1084.
Pankhurst, R.J., Rapela, C.W., Fanning, C.M., Márquez, M., 2006. Gondwanide
continental collision and the origin of Patagonia. Earth Science Reviews 76, 235-
257.
Rapela, C.W. , Pankhurst, R.J., Casquet, C., Fanning, C.M., Baldo, E.G., González-
Casado, J.M., Galindo, C., Dahlquist, J., 2007. The Río de la Plata craton and the
assembly of SW Gondwana. Earth Science Reviews 83, 49-82.
Schwartz, J.J., Gromet, L.P., 2004. Provenance of Late Proterozoic-early Cambrian
basin, Sierras de Córdoba, Argentina. Precambrian Research 129, 1-21.