Elsevier

Lithos

Volume 188, 1 February 2014, Pages 33-43
Lithos

The Central Atlantic Magmatic Province extends into Bolivia

https://doi.org/10.1016/j.lithos.2013.10.019Get rights and content

Highlights

  • Lava flows and associated sills from southern Bolivia seal Triassic syn-rift red beds.

  • New 40Ar/39Ar data on basalts in Bolivia give CAMP ages

  • Homogeneous low-Ti tholeiites from southern Bolivia have CAMP compositions.

  • Recognition of the Central Atlantic Magmatic Province in Bolivia

  • The Central Atlantic Magmatic Province extends over 8000 km from North to South.

Abstract

The Central Atlantic Magmatic Province (CAMP) is the largest continental flood basalt (CFB) province on Earth and was associated with the onset of fragmentation of the supercontinent Pangea at the Triassic–Jurassic boundary. In order to clarify the extent of the CAMP in South America, we investigate basaltic remnants in southern Bolivia (Tarabuco, Entre Ríos and Camiri areas) by combining stratigraphic, geochronological (40Ar/39Ar data) and geochemical (major and trace element, Nd–Sr isotopes) approaches. Lava-flows reaching a total thickness up to 150 m and associated sills overlie syn-rift red beds assigned to the Triassic. The magmatic rocks consist of low-Ti tholeiites that are remarkably homogeneous in composition. Notably, their trace element and Nd–Sr isotopic compositions closely match those of CAMP basalts particularly those of southwest Brazil. 40Ar/39Ar dating failed to yield robust plateau ages but the best estimates of the crystallization age at 198.1 ± 1.5 and 199.2 ± 2.2 Ma are similar to those of CAMP basalts throughout the province. These Bolivian basalts, which may have covered an initial surface of ~ 30,000 km2, represent the known southernmost occurrence of the CAMP. They were erupted as a single pulse, more than 8000 km away from the northern edge of the province. We discuss the implications of such a huge elongated CFB for the current plume models and we suggest, as an alternative, that large-scale melting beneath the Pangea supercontinent due to mantle global warming could have triggered the emplacement of the CAMP.

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)

  • C. Dupuy et al.

    Asthenospheric and lithospheric sources for Mesozoic dolerites from Liberia (Africa): trace element and isotopic evidence

    Earth and Planetary Science Letters

    (1988)
  • R.E. Ernst et al.

    Maximum size and distribution in time and space of mantle plumes: evidence from large igneous provinces

    Journal of Geodynamics

    (2002)
  • A.L. Heatherington et al.

    Lithospheric sources of North Florida, USA tholeiites and implications for the origin of the Suwannee terrain

    Lithos

    (1999)
  • R.I. Hill

    Starting plumes and continental break-up

    Earth and Planetary Science Letters

    (1991)
  • A.M. Leitch et al.

    A plume head melting under a rifting margin

    Earth and Planetary Science Letters

    (1998)
  • A. Marzoli et al.

    Timing and duration of the Central Atlantic Magmatic Province in the Newark and Culpeper basins, eastern USA

    Lithos

    (2011)
  • W.F. McDonough et al.

    The composition of the Earth

    Chemical Geology

    (1995)
  • R. Merle et al.

    40Ar/39Ar ages and Sr–Nd–Pb–Os geochemistry of CAMP tholeiites from the western Maranhão basin (NE-Brazil)

    Lithos

    (2011)
  • S. Nomade et al.

    Chronology of the Central Atlantic Magmatic Province: implications for the Central Atlantic rifting processes and the Triassic–Jurassic biotic crisis

    Palaeogeography, Palaeoclimatology, Palaeoecology

    (2007)
  • W.J. Pegram

    Development of continental lithospheric mantle as reflected in the chemistry of the Mesozoic Appalachian Tholeiites, U.S.A.

    Earth and Planetary Science Letters

    (1990)
  • C. Pin et al.

    Concomitant separation of strontium and samarium-neodymium for isotopic analysis in silicate samples, based on specific extraction chromatography

    Analitica Chimica Acta

    (1994)
  • P.R. Renne et al.

    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

    (2010)
  • T. Sempere et al.

    Late Permian–Middle Jurassic lithospheric thinning in Peru and Bolivia, and its bearing on Andean-age tectonics

    Tectonophysics

    (2002)
  • R.H. Steiger et al.

    Subcommission on geochronology: convention on the use of decay constants in geo and cosmochronology

    Earth and Planetary Science Letters

    (1977)
  • G. Turner et al.

    40Ar/39Ar ages and cosmic ray exposures ages of Apollo 14 samples

    Earth and Planetary Science Letters

    (1971)
  • C. Verati et al.

    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

    (2005)
  • D.L. Anderson

    Hotspots, polar wander, Mesozoic convection and the geoid

    Nature

    (1982)
  • H. Bertrand et al.

    Geochemistry of tholeiites from north-east American margin; correlation with Morocco. A statistical approach

    Contributions to Mineralogy and Petrolology

    (1977)
  • M.H.P. Bott

    Origin of the lithospheric tension causing basin formation

    Philosophical Transactions of the Royal Society of London

    (1982)
  • S. Callegaro et al.

    Enriched mantle source for the Central Atlantic magmatic province: new supporting evidence from Southwestern Europe

    Lithos

    (2013)
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