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

Abstract

The Central Atlantic Magmatic Province (CAMP) is among the largest igneous provinces on Earth, emplaced synchronously with or just prior to the Triassic–Jurassic (T–J) boundary ca. 200 Ma. In great part due to the controversial connection between the occurrence of CAMP and the events of the T–J boundary, the demand for better constraints on the duration and eruptive chronology of this province has increased. More than 100 new ⁴⁰Ar/³⁹Ar ages have been published in the last 15 years, with more than half of these in the last 3 years. A careful review and selection of available ages, as well as the publication of 16 new ages from the Carolinas, Newark Basin (USA), French Guyana and Morocco are presented. Judicious selection yields a total of 58 accepted age determinations for CAMP magmatism, ranging from 202 to 190 Ma covering every part of the CAMP. A more complete picture develops with intrusive CAMP magmatism commencing as early as 202 Ma. Extrusive activity initiated abruptly ∼ 200 Ma, reaching peak volume and intensity around 199 Ma on the African margin. The main period of CAMP magmatism is confirmed as brief, but is suggested to consist of at least two phases over ∼ 1.5 Ma, with magmatism commencing along the Africa–North American margins and slightly later along the South American margin. Two volumetrically minor, but distinctive magmatic peaks centered at 195 and 192 Ma are mirrored in data from all three continents and highlighted by our statistical approach. Models describing rifting and thermal input and magma production on these timescales are explored. Despite significant advances in our understanding of the chronology of CAMP, more data of better quality and broader geographical coverage are needed to completely characterize the evolution of the CAMP and infer its geodynamic origin. In addition, lack of a well-defined T–J boundary age, as well as the absence of a relevant basis for comparison between U/Pb and ⁴⁰Ar/³⁹Ar data for this time period remain limiting factors to unambiguously linking CAMP in time with the events of the T–J boundary.

Introduction

Central Atlantic Magmatic Province (CAMP) magmatism at ∼ 200 ± 4 Ma (Marzoli et al., 1999) is preserved across four continents, covering an area approximately 5000 km in length and 2000 km in width (Fig. 1). While the ∼ 1 × 10⁷ km² area affected by CAMP is large compared with other large igneous provinces (LIPs), the preserved volume is only ∼ 1 × 10⁶ km³ (McHone, 2003); primarily represented by dikes and sills in northeastern Brazil, west and central Africa and the southeastern United States. Exceptional occurrences of lava flow successions reaching total thicknesses of 100–300 m are preserved in basins in Morocco, North America and South America (De Min et al., 2003). Preserved magmatism has been used to estimate an original magmatic volume in excess of 2.5 × 10⁶ km³ (McHone, 2003), easily comparable with the more voluminous LIPs such as the Siberian, Deccan Traps and Ontong Java Plateau. In the last 5 years, the understanding of this province has improved, driven by recent publication of new ⁴⁰Ar/³⁹Ar data (Knight et al., 2004, Marzoli et al., 2004, Beutel et al., 2005, Vérati et al., 2007-this volume), cyclostratigraphic data (Olsen et al., 2003), a magnetostratigraphic study (Knight et al., 2004) and geochemical data (De Min et al., 2003, Marzoli et al., 2004, Vérati et al., 2005). As our knowledge improves, we can begin to address the magmatic duration, migration, scope and extrusion rate of CAMP. Answers to these questions provide critical constraints to our understanding of LIP generation and serve to clarify potential relations between this event and Pangean rifting, as well as the Triassic–Jurassic (T–J) biotic crisis (i.e., Marzoli et al., 2004). Central to these questions is the quality (accuracy and precision) and geographic coverage of available geochronological data.

This article presents a set of new ⁴⁰Ar/³⁹Ar data from plagioclase separates spanning three continents and discusses these data in the context of a critical review of all available ⁴⁰Ar/³⁹Ar data across the CAMP. This compilation builds on the wealth of new data available, particularly for Africa and North America, since the compilation of Knight et al. (2004). The published data is reviewed for accuracy, precision and geographic scope and filtered in order to limit problematic artifacts such as the presence of non-atmospheric ⁴⁰Ar (excess argon), significant sample disturbance or alteration, and monitor mineral calibration issues. We use the filtered published ages and our new data to discuss the duration of CAMP, presenting evidence for migration of magmatism. We then discuss the rifting of the Central Atlantic and the possible role of magmatism in the T–J boundary biotic crisis.