The Central Atlantic Magmatic Province extends into Bolivia
Introduction
Continental flood basalt (CFB) provinces are formed during major magmatic events punctuating the Earth's evolution. These are catastrophic episodes during which mantle dynamics cause the eruption of prodigious amounts of magma and result in serious disturbances of the atmosphere and biosphere, ultimately resulting, for some of them, in mass extinction events (Courtillot and Renne, 2003). Moreover, most CFB are associated with continental extension and break-up (White and Mckenzie, 1989). The Central Atlantic Magmatic Province (CAMP) is among the most recently recognized and probably the largest CFB on Earth, and consists of basaltic lava flows, sills and dyke swarms covering ~ 107 km2 (Marzoli et al., 1999, McHone et al., 2005). Its peak of activity at ~ 201 Ma was synchronous with, and thus probably triggered, the major mass extinction at the Triassic–Jurassic boundary (e.g., Hesselbo et al., 2002, Marzoli et al., 1999, Marzoli et al., 2004, Schaller et al., 2011). The emplacement of the CAMP was also linked to the initial break-up of the Pangea supercontinent and subsequent opening of the Central Atlantic Ocean, resulting in preserved outcrops now distributed over four circum-Atlantic continents (Fig. 1a). The lava-flow remnants are strictly associated with Triassic rift basins (in Portugal, Morocco, eastern North America, and Brazil) that formed during extensional tectonics prior to continental break-up.
Since the initial work on this event (e.g., Bertrand and Coffrant, 1977, May, 1971), the size of this huge CFB province has been progressively supplemented by identification of lava flows, sills and dyke swarms based on combined similarities in age (mainly 40Ar/39Ar dating) and geochemical composition. The resulting CAMP frontiers have been progressively pushed away as far as Brazil, southwards (Marzoli et al., 1999), Brittany (France), northwards (Jourdan et al., 2003), and Mali, eastwards (Verati et al., 2005). Some of these boundaries remain uncertain (e.g., eastwards in Africa and southwards in South America, Fig. 1a) but are yet crucial to define the size, geometry and volume of the erupted magmas because these parameters are needed to constrain the origin of the CAMP, which is still controversial. Indeed, several authors consider that the CAMP was formed by the impingement of a mantle plume head at the base of the lithosphere (Courtillot et al., 1999, Hill, 1991, May, 1971, Wilson, 1997), whereas others favor a non-plume origin (McHone, 2000, Pegram, 1990, Puffer, 2001) and propose alternative models such as plate boundary forces (Bott, 1982), edge-driven convection (Anderson, 1982, King and Anderson, 1998), or global warming of the mantle (Coltice et al., 2007, Coltice et al., 2009).
In this paper we investigate pre-Andean magmatism in southern Bolivia in order to assess whether it may represent a significant southward extension of the CAMP in South America. For this purpose, we combine geological, geochronological (40Ar/39Ar dating) and geochemical data, in comparison with those previously acquired and attributed to the CAMP in Brazil (De Min et al., 2003, Marzoli et al., 1999, Merle et al., 2011) and the Guianas (Deckart et al., 1997, Deckart et al., 2005), in order to discuss the geodynamic significance of this magmatism in the framework of Pangea breakup, and to constrain a petrogenetic model for the CAMP.
Section snippets
Geological framework
A rift system developed during the Triassic along what is now the axis of the Eastern Cordillera and the adjacent southeastern sub-Andean region of Bolivia (Sempere et al., 2002; Fig. 1b). Widespread coeval magmatism occurred in particular in the southeastern region of this rift system, and its remnants are documented in the areas of Tarabuco, Entre Ríos and Camiri (Fig. 2).
Petrographic notes
The lava-flows display textures varying from very fine-grained microlitic to fine- or medium-grained intersertal to intergranular. Some of them exhibit glomeroporphyritic clots of plagioclase or augite–plagioclase. The textures of the rocks from the sills evolve from fine- to medium-grained intersertal or intergranular (Camiri sill and bottom of Uyuni–Incapampa sill) to gabbroic and pegmatoid (core of Uyuni–Incapampa sill).
All the rocks are mafic except for a few differentiates observed towards
Electron microprobe analyses
Plagioclase and clinopyroxene major element compositions were analyzed at IGG-CNR Padova, Italy on a Cameca SX50 electron microprobe (EMP) using ZAF online data reduction and matrix correction procedures. At constant accelerating voltage, 15 kV, the beam's current as set at 15 nA (for plagioclase) and 20 nA (for clinopyroxene). Long counting times (1 min) were adopted for minor element analyses (K and Mg), in order to optimize analytical precision. Repeated analyses of standards indicate relative
Geochemistry
Major and some trace elements were analyzed by XRF spectrometry on seventeen samples from Entre Ríos lava-flows (n = 6), Tarabuco lava flows (n = 6), Uyuni–Incapampa sill (n = 3), and Camiri sill (n = 2). Twelve samples were also analyzed for trace elements (Rare Earth Elements and Pb, U, Th, Ta, Hf) by ICP-MS. The concentrations are reported in Table 1.
As a whole, the studied rocks share rather uniform chemical characteristics, whether they come from the Tarabuco, Entre Ríos or Camiri areas and
Comparison with CAMP occurrences in South America
Our combined stratigraphic, geochronological, and geochemical data demonstrate that the lava flows and sills from the Entre Ríos, Tarabuco and Camiri areas were erupted and emplaced during a single magmatic event, which we assign to the CAMP due to the 40Ar/39Ar ages obtained on the Tarabuco and Camiri basalts.
From a stratigraphic point of view, the studied lava flows occur at the transition between syn-rift Triassic (Ipaguazú Formation) and post-rift Jurassic (Tacurú Subgroup) sediments in the
Conclusions
Combined geological, 40Ar/39Ar and geochemical data obtained on tholeiitic lava flows and associated sills in the Tarabuco, Entre Ríos and Camiri areas of southern Bolivia allow us to assign this magmatism to the CAMP. The lava flows seal the syn-rift Triassic sedimentary infilling, in a stratigraphic position similar to that of CAMP lava flows preserved in other Triassic rift basins. Although no robust 40Ar/39Ar plateau ages could be obtained, our best estimates for the age of the Bolivian
Acknowledgments
We acknowledge P. Capiez for XRF analyses, R. Carampin for electron microprobe analyses, C. Douchet for ICP-MS analyses and C. Bassin for isotopes analyses. Support from the Institut de Recherche pour le Développement (IRD) for field work is gratefully acknowledged. We are grateful to M. Ducea for his constructive review and to D. Baker and A.C. Kerr for their editorial handling.
References (61)
A Sr–Nd isotope and REE study of late Triassic dolerites from the Pyrenees (France) and the Messejana dyke (Spain and Portugal)
Earth and Planetary Science Letters
(1985)- et al.
Mesozoic igneous activity in the Maranhão province, northern Brazil, 40Ar/39Ar evidence for separate episodes of basaltic magmatism
Earth and Planetary Science Letters
(1997) - et al.
Geochemistry of early Mesozoic tholeiites from Morocco
Earth and Planetary Science Letters
(1982) Cosmochemistry of rare earth elements: meteorite studies
- et al.
Implications of mantle plume structure for the evolution of flood basalts
Earth and Planetary Science Letters
(1990) - et al.
Global warming of the mantle beneath continents back to the Archean
Gondwana Research
(2009) - et al.
On the ages of flood basalt events
Comptes Rendus Geoscience
(2003) - et al.
On causal links between flood basalts and continental breakup
Earth and Planetary Science Letters
(1999) - et al.
Age of Jurassic continental tholeiites of French Guyana, Surinam and Guinea: implications for the initial opening of the Central Atlantic Ocean
Earth and Planetary Science Letters
(1997) - et al.
Geochemistry and Sr, Nd, Pb isotopic composition of the Central Atlantic Magmatic Province (CAMP) in Guyana and Guinea
Lithos
(2005)
Asthenospheric and lithospheric sources for Mesozoic dolerites from Liberia (Africa): trace element and isotopic evidence
Earth and Planetary Science Letters
Maximum size and distribution in time and space of mantle plumes: evidence from large igneous provinces
Journal of Geodynamics
Lithospheric sources of North Florida, USA tholeiites and implications for the origin of the Suwannee terrain
Lithos
Starting plumes and continental break-up
Earth and Planetary Science Letters
A plume head melting under a rifting margin
Earth and Planetary Science Letters
Timing and duration of the Central Atlantic Magmatic Province in the Newark and Culpeper basins, eastern USA
Lithos
The composition of the Earth
Chemical Geology
40Ar/39Ar ages and Sr–Nd–Pb–Os geochemistry of CAMP tholeiites from the western Maranhão basin (NE-Brazil)
Lithos
Chronology of the Central Atlantic Magmatic Province: implications for the Central Atlantic rifting processes and the Triassic–Jurassic biotic crisis
Palaeogeography, Palaeoclimatology, Palaeoecology
Development of continental lithospheric mantle as reflected in the chemistry of the Mesozoic Appalachian Tholeiites, U.S.A.
Earth and Planetary Science Letters
Concomitant separation of strontium and samarium-neodymium for isotopic analysis in silicate samples, based on specific extraction chromatography
Analitica Chimica Acta
Joint determination of 40K decay constants and 40Ar*/40K for the Fish Canyon sanidine standard, and improved accuracy for 40Ar/39Ar geochronology
Geochimica et Cosmochimica Acta
Late Permian–Middle Jurassic lithospheric thinning in Peru and Bolivia, and its bearing on Andean-age tectonics
Tectonophysics
Subcommission on geochronology: convention on the use of decay constants in geo and cosmochronology
Earth and Planetary Science Letters
40Ar/39Ar ages and cosmic ray exposures ages of Apollo 14 samples
Earth and Planetary Science Letters
The farthest record of the Central Atlantic Magmatic Province into West Africa craton: precise 40Ar/39Ar dating and geochemistry of Taoudenni basin intrusives (northern Mali)
Earth and Planetary Science Letters
Hotspots, polar wander, Mesozoic convection and the geoid
Nature
Geochemistry of tholeiites from north-east American margin; correlation with Morocco. A statistical approach
Contributions to Mineralogy and Petrolology
Origin of the lithospheric tension causing basin formation
Philosophical Transactions of the Royal Society of London
Enriched mantle source for the Central Atlantic magmatic province: new supporting evidence from Southwestern Europe
Lithos
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