The Central Atlantic Magmatic Province: Insights from Fragments of Pangea

269 Pages·2003·25.236 MB·English

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The Central Atlantic Magmatic Province
Insights from Fragments of Pangea
W. Hames
J. G. McHone
P. Renne
C. Ruppel
Editors
88 American Geophysical Union
Washington, DC
Published under the aegis of the AGU Books Board
Jean-Louis Bougeret, Chair, Gray E. Bebout, Carl T. Friedrichs, James L. Horwitz, Lisa A. Levin,
W. Berry Lyons, Kenneth R. Minschwaner, Darrell Strobel, and William R. Young, members.
Library of Congress Cataloging-in-Publication Data
The Central Atlantic magmatic province : insights from fragments of Pangea / W. Hames
... [et al.], editors.
p. cm. -- (Geophysical monograph ; 136)
Includes bibliographical references.
ISBN 0-87590-995-7
1. Rifts (Geology)--North Atlantic Ocean. 2. Continental margins-North Atlantic
Ocean. 3. Magmatism—North Atlantic Ocean. 4. Geology, Stratigraphic-Triassic. 5.
Geology, Stratigraphic--Jurassic. I. Hames, W. (Willis) 1960- II. Series
QE606.5.N724 C46 2003
551.872-dc21 2002038310
ISSN 0065-8448
ISBN 0-87590-995-7
Copyright 2003 by the American Geophysical Union
2000 Florida Avenue, N. W.
Washington, DC 20009
Cover photos depict volcanic and intrusive rocks of the Central Atlantic Magmatic Province.
From left to right: Cliffs of the Palisades sill basalts dominate the western shore of the Hudson
River near New York City (photo by Anthony G Taranto Jr.); Volcano-sedimentary sequence in
CAMP lavas from central Algarve (Portugal), where red clay sediments alternate with green pyro-
clastic layers (photo by Nasrrddine Youbi); Volcanic pile of CAMP basalt pahoehoe lava flows
overlying red clay sediments in Argana Basin, Morocco (photo by Nasrrddine Youbi).
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CONTENTS
Preface
Willis E. Hames, J. Gregory McHone, Paul R. Renne, and Carolyn Ruppel vii
Introduction
W. Hames, J. G. McHone, P. Renne, and C. Ruppel 1
Cyclo-, Magneto-, and Bio-Stratigraphic Constraints on the Duration of the CAMP Event and its
Relationship to the Triassic-Jurassic Boundary
Paul E. Olsen, Dennis V. Kent, Mohammed Et-Touhami, and John Puffer 7
Relative Timing of CAMP, Rifting, Continental Breakup, and Basin Inversion: Tectonic Significance
Roy W. Schlische, Martha Oliver With jack, and Paul E. Olsen 33
Age Estimates of the Seaward-Dipping Volcanic Wedge, Earliest Oceanic Crust, and Earliest
Drift-Stage Sediments Along the North American Atlantic Continental Margin
Richard N. Benson 61
Critical Evaluation of 40Ar/39Ar Ages for the Central Atlantic Magmatic Province: Timing,
Duration and Possible Migration of Magmatic Centers
Ajoy K. Baksi . 77
The Central Atlantic Magmatic Province (CAMP) in Brazil: Petrology, Geochemistry, 40Ar/39Ar Ages,
Paleomagnetism, and Geodynamic Implications
Angelo De Min, Enzo M. Piccirillo, Andrea Marzoli, Giuliano Bellieni, Paul R. Renne,
Marcia Ernesto, and Leila S. Marques 91
Paleomagnetic and Geochemical Constraints on the Timing and Duration of the
CAMP Activity in Northeastern Brazil
M. Ernesto, G. Bellieni, E. M. Piccirillo, I. S. Marques, A. De Min, I. G Pacca, G. Martins,
and). W. P. Macedo 129
A Reactivated Back-arc Source for CAMP Magma
John H. Puffer 151
Temporal Chemical Variations Within Lowermost Jurassic Tholeiitic Magmas
of the Central Atlantic Magmatic Province
Vincent J. M. Salters, P. C. Ragland, W. E. Hames, K. Milla, and C. Ruppel 163
The Late Triassic-Early Jurassic Volcanism of Morocco and Portugal in the Framework
of the Central Atlantic Magmatic Province: An Overview
Nasrrddine Youbi, Lfnia Tavares Martins, Jose Manuel Munha, Hassan Ibouh, Jose Madeira,
El Houssaine Ait Chayeb, and Abdelmajid El Boukhari 179
The Northernmost CAMP: 40Ar/39Ar Age, Petrology and Sr-Nd-Pb Isotope Geochemistry
of the Kerforne Dike, Brittany, France
Fred Jourdan, Andrea Marzoli, Herve Bertrand, Michael Cosca, and Denis Fontignie 209
CONTENTS
Magma Flow Pattern in the North Mountain Basalts of the 200 Ma CAMP Event:
Evidence From the Magnetic Fabric
Richard E. Ernst, Jelle Zeilinga de Boer, Peter Ludwig, and Taras Gapotchenko 227
Volatile Emissions From Central Atlantic Magmatic Province Basalts: Mass Assumptions
and Environmental Consequences
J. Gregory McHone 241
Volcanism of the Central Atlantic Magmatic Province as a Potential Driving Force
in the End-Triassic Mass Extinction
JozsefPalfy 255
PREFACE
A singular event in Earth's history occurred roughly 200 Some authors present syntheses of earlier work, and dis­
million years ago, as rifting of the largest and most recent cussions of models proposed for the CAMP, in combination
supercontinent was joined by basaltic volcanism that with new data and in a format that is more detailed than
formed the most extensive large igneous province (LIP) previously available. Stratigraphic relationships that define
known. A profound and widespread mass extinction of ter­ the relative timing of CAMP magmatism, and correlations
restrial and marine genera occurred at about the same time, to important biostratigraphic units are a major theme for
suggesting a causal link between the biological transitions some papers. Other papers draw inferences and correlations
of the Triassic-Jurassic boundary and massive volcanism. A to basaltic sub-provinces that may be members of the
series of stratigraphic, geochronologic, petrologic, tectonic, CAMP, such as the buried continental flood basalts and the
and geophysical studies have led to the identification of the seaward dipping reflector sequences (SDRs) of eastern
dispersed remnants of this Central Atlantic Magmatic North America. Detailed reviews and analysis of radioiso­
Province (CAMP) on the rifted margins of four continents. topic data for CAMP igneous rocks are an important com­
Current discoveries are generally interpreted to indicate ponent of some papers in this volume, with conclusions
that CAMP magmatism occurred in a relative and absolute that bear on the timing and duration of CAMP magmatic
interval of geologic time that was brief, and point to mech­ activity. Although consistent themes with respect to timing
anisms of origin and global environmental effects. Because and duration of magmatism emerge from these papers, vari­
many of these discoveries have occurred within the past ances in opinion are also evident, with some authors pre­
several years, in this monograph we summarize new obser­ ferring to view CAMP basalts as a temporal benchmark,
vations and provide an up-to-date review of the province. whereas others interpret the available age data to represent
Certainly several previous works support the current a measurable range of duration for CAMP magmatism.
monograph, and contain matter that is closely related and The basaltic remnants of the CAMP have been identified
relevant to the topic. However, while these volumes pro­ in North and South America, West Africa and Europe, over
vide important syntheses that emphasize stratigraphic and regions with a reconstructed total area of about 10 million
petrologic data of the North American portion of the square kilometers. Thus, reviews that report and synthesize
CAMP, more recent research in several areas has promoted observations for each of these regions constitute critical
recognition and definition of the CAMP in a circum- aspects of this volume. Papers here also provide new data
Atlantic context, including: (1) precise absolute and tectonic interpretations for the CAMP in South
geochronology of CAMP igneous rocks; (2) high-resolu­ America, where CAMP basalts have been identified rough­
tion stratigraphic studies that also may combine detailed ly 2000 km within the continent's interior. The deeply erod­
paleontology with magneto-stratigraphy and cyclo-stratig- ed plexus of basaltic dikes exposed in eastern North
raphy; (3) petrologic and paleomagnetic studies that char­ America, with their related sills and flows of Newark
acterize and relate distal portions of the CAMP; (4) geo- Supergroup basins, are a source for much of the petrologic
chemical and paleontologic studies that suggest global cli­ and geochemical data of the CAMP. New data and synthe­
mate change at the Triassic-Jurassic boundary; and (5) ses of previous studies of the North American CAMP pre­
recognition of the important role for LIPs in crustal devel­ sented in this volume suggest extensive involvement of the
opment and as a record of modes for mass and energy trans­ subcontinental lithosphere, and passive mechanisms for
fer throughout Earth's history. generation of CAMP magmas, as compared to models that
In this light, we conceived the present monograph to pro­ invoke deep mantle plumes. CAMP basaltic rocks in West
vide insights unique to a circum-Atlantic perspective of the Africa and Portugal constitute an eastern boundary of the
CAMP and its possible effects on Earth's climate and bio­ province. New data for this eastern part of the CAMP are
logical systems from an international group of authors. presented within the context of a regional synthesis.
vii
Identification of CAMP basalts in the Brittany region of This volume arose from discussions following a theme
France also emphasizes the northern extent of the province, session in the Fall 1999 meeting of the American
as reported with new data. Geophysical Union (The Earliest Magmatism of the
The results of other studies examine differing characteris­ Circum-Atlantic Large Igneous Province) and a workshop
tics of the CAMP that point to underlying causes and prob­ in the summer of 2000 (International Workshop for a
able effects of the province. The anisotropy of magnetic sus­ Climatic, Biotic, and Tectonic, Pole-to-Pole Coring
ceptibility in basaltic dikes and flows has proven very use­ Transect of Triassic-Jurassic Pangea). We gratefully
ful in analysis of magma transport directions and the loca­ acknowledge the inspiration and support from many col­
tion of magma sources, as reported in an analysis of dike leagues who participated in those meetings. We are partic­
and flow patterns from the Fundy basin. It is clear that the ularly grateful to the many reviewers of papers in this vol­
volatile emissions of the CAMP province were sufficient to ume (as indicated in the individual acknowledgements),
induce major, global environmental changes, as also who provided an exceptionally high level of professional
reviewed and considered here. The role of CAMP magma- peer review. We also acknowledge the editorial assistance
tism as a driving force behind global Triassic-Jurassic envi­ and oversight of the American Geophysical Union book
ronmental changes and mass extinctions is discussed and department staff.
carefully considered, with comparisons of terrestrial and
marine paleontologic records to the evolution of the CAMP
and other possible causative mechanisms.
The present volume provides definite advances in our Willis E. Hames
understanding of the CAMP that will be useful to scholars Auburn University
and researchers with interests in the magmatism of this
province, events associated with the Triassic-Jurassic J. Gregory McHone
boundary, the nature of mass extinctions, and large igneous University of Connecticut and Wesley an University
provinces in general. Although the availability of literature
for the CAMP has surged in the past few years, as this vol­
ume attests, we are still in a reconnaissance stage for under­ Paul R. Renne
standing the CAMP with new discoveries emerging on Berkeley Geochronology Center and
multiple research fronts. Thus, papers in this volume also University of California, Berkeley
direct the reader to areas for further research with a rich
potential for understanding one of Earth's most significant Carolyn Ruppel
magmatic episodes. Georgia Institute of Technology
viii
Introduction
W. Hames
Department of Geology and Geography, Auburn University, Auburn, Alabama
J. G. McHone
University of Connecticut, Department of Geology and Geophysics, Storrs, Connecticut
Wesleyan University, Department of Earth and Environmental Sciences, Middletown, Connecticut
P. Renne
Berkeley Geochronology Center, Berkeley, California
University of California, Department of Earth and Planetary Science, Berkeley, California
C. Ruppel
School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, Georgia
OVERVIEW OF RESEARCH ON THE CENTRAL and buried flood basalts that once covered large areas of
ATLANTIC MAGMATIC PROVINCE the land, and in the sedimentary strata that host the vol­
canic remnants. Scientists collect forensic evidence in
Large igneous provinces represent catastrophic out­
rock exposures from coastal Brittany to Brazilian rainfor­
pourings of immense quantities of basaltic lava, the origin
ests, in strata buried deeply beneath Texas and on plateaus
of processes that are hidden deep within Earth's interior
in sub-Saharan Mali in the effort to describe this province
and obscured by the movements of tectonic plates. Scien­
and determine its origin. Indeed, over the past several
tists from many different fields are combining their efforts
years we have learned through research that much of the
to understand the underlying mechanisms by which large
magmatism in this province was very sudden, although it
igneous provinces' form, the distribution and timing of
may have spread diachronously. The absolute age and
such provinces, and the effects and consequences of the
stratigraphic juxtaposition of this province seems coinci­
associated volcanism. This book presents a collection of
dent with the transition from the Triassic to the Jurassic
thirteen papers that delve into such fundamental questions
period. Many scientists are now studying this magmatic
for one of Earth's most calamitous events - the profound
province in an effort to understand how its effects may
and extensive magmatism that accompanied the breakup
relate to the global climate changes and profound mass
of Pangea.
extinction at the end of the Triassic (when perhaps 80% of
Dramatic relics of the magmatism that accompanied
Earth's terrestrial and marine faunas perished). And yet
breakup of Pangea are preserved on every continent of the
such a catastrophic distress for some may provide oppor­
circum-Atlantic region, in exposures of igneous intrusions
tunity to others, as the Jurassic rise of dinosaurs to domi­
that once provided magma conduits, as partially eroded
nate Earth may have begun with global climate changes
The Central Atlantic Magmatic Province: wrought by this large igneous province. Thus, the re­
Insights from Fragments of Pangea search on this individual magmatic province is part of a
Geophysical Monograph 136 broader and contentious scientific trial to determine
Copyright 2003 by the American Geophysical Union whether massive volcanic events, meteorite impact
10.1029/136GM01 events, or combinations of both are responsible for the
1
2 INTRODUCTION
major mass extinction events that have modulated the Relationships of the CAMP to the Seaward Dipping
course of life on Earth for the past 300 million years. Reflector Sequences of the Central Atlantic Basin
Recognition of the Central Atlantic Magmatic Province A seam that runs near the central axis of the CAMP,
along the plate boundary that would become the Atlantic
Although geologists first recognized the extent and sig­ basin, is defined by the seaward-dipping reflector se­
nificance of Triassic-Jurassic basalts around the Atlantic quences (SDRS, Figure 1). The SDRS are considered
region in the late nineteenth century (Russell, 1880), it is from seismic studies to represent thick, wedge-shaped ac­
only within the past few years that the timing and extent cumulations of basalt flows [Holbrook and Kelemen,
of magmatism was sufficiently constrained to define what 1993; Oh et al., 1995] that are deeply buried within the
we now refer to as the Central Atlantic Magmatic Prov­ continental margin. Extrusion of basalts in the SDRS
ince [CAMP; Marzoli et al., 1999]. The known distribu­ marks an end to CAMP magmatism in the continental
tion of CAMP dikes, sills and flows is represented in Fig­ realm and the birth of the central Atlantic basin. However,
ure 1 (adapted from McHone, 2000). Rifting of Pangea the timing of formation for SDRS in the central Atlantic,
and deposition of clastic sediments in intermontane basins and whether they should be considered as part of the
began by about 230 million years ago, reactivating more CAMP, is unclear. For comparison, the SDRS of the
ancient crustal boundaries and leading to a configuration North Atlantic Igneous Province seem to have formed
of incipient continental fragments as shown in Figure 1 by several years after the continent-based magmatism [Saun­
roughly 200 million years ago. CAMP basalts and associ­ ders et al., 1999]. Considering the CAMP, Benson [this
ated intrusions developed near the center of this evolving volume] reviews stratigraphic interpretations of the oldest
rift setting and close to an equatorial latitude [Olsen, drift-stage rocks of the North American margin and of
1997]. Much of the perimeter for the CAMP coincides early Atlantic sea-floor spreading rates suggestive of
with orogenic belts and deep boundaries in the continental much younger ages for the SDRS and earliest Atlantic sea
lithosphere, such as the western limit of the CAMP and floor. In contrast, Schlische et al. [this volume] present a
the Blue Ridge to Piedmont province boundary of the model for diachronous rift-drift CAMP magmatism, in
southeastern Appalachians. which the SDRS form in an earlier magmatic pulse with
the CAMP to the south and after the CAMP through a
Characteristics of the CAMP separate magmatic pulse to the north. Olsen et al. [this
volume] review and test earlier evidence for the age of the
The CAMP is dominated by tholeiitic basalts, with an CAMP and drilled units correlated with the SDRS, and
extent and major geochemical relationships that continue suggest they could be of the same age. Both Benson and
to be defined by new discoveries. CAMP dikes have been Olsen et al. [this volume] present discussions to highlight
identified in northwestern France [Jordan et al., this vol­ the need for drilling of basalts correlated with the SDRS
ume], that are similar in age and overall chemistry to in order to evaluate the alternate models for timing of the
CAMP basalts that are 2000 km within continental South SDRS in the Central Atlantic and their relationship to
America [De Min et al., this volume], although regional CAMP magmatism.
heterogeneities in basalt composition exist and seem re­
lated to differences in regional lithospheric composition. The CAMP as an Agent of Planetary Catastrophe
CAMP basalts in eastern Brazil are also more extensive
than previously recognized, where paleomagnetic data Through recorded human history we have come to un­
also suggest local basaltic magmatism significantly before derstand that volcanic events can cause catastrophes, but
and after a main stage at 200-190 Ma [Ernesto et al., this that the effects are generally local. The violent and explo­
volume]. The CAMP volcanics in Morocco and Portugal sive eruption of Mount Vesuvius was a catastrophe for the
comprise a significant proportion of subaerial lavas and citizens of Pompeii as recorded by Pliny the Younger
pyroclastics interbeded with shallow-water clastic se­ (and experienced by Pliny the Elder!), although this event
quences, and the geochemistry of dikes and flows in the was inconsequential for the climate and life of Earth be­
region is also compatible with a lithospheric mantle yond a small region of western Italy. It is difficult, there­
source [Youbi et al., this volume]. The broadly uniform fore, to imagine volcanic events, even the massive out­
composition of many CAMP basalts, the extent of CAMP pourings of basalt in large igneous provinces, as consti­
magmatism, the relationship to thickened lithosphere and tuting "planetary catastrophes" as posed by Courtillot
crustal boundaries of Pangea, and geochemical trends are [1999]. If we consider the scale of large igneous prov­
collectively most compatible with "passive" models in­ inces (Figure 2), however, the magnitude of their potential
volving upper mantle geodynamics [De Min et al., this effects is more readily understood.
volume; Jourdan et al., this volume; Puffer, this volume; The Columbia River Flood Basalt Province (Figure 2)
Salters et al., this volume]. is approximately one tenth the size of the other large ig-