Central Atlantic Magmatic Province
Encyclopedia
The Central Atlantic magmatic province (CAMP) is a large connected magma flow formed during the breakup of Pangaea
during the Mesozoic
Era. The initial breakup of Pangaea in early Jurassic
time provided a legacy of basalt
ic dikes
, sills
, and lava
s over a vast area around the present central North Atlantic Ocean
.
province
. The basaltic sills of similar age (near 200 Ma, or earliest Jurassic) and composition (intermediate-Ti quartz tholeiite) which occur across the vast Amazon River
basin of Brazil
were linked to the province in 1999 .
, Iberia
, and northwestern France
, and from the interior of western Africa westward for 2500 km through eastern and southern North America
. If not the largest Province by volume, the CAMP certainly encompasses the greatest area known, roughly 11 million km², of any continental large igneous province
.
Nearly all CAMP rocks are tholeiitic
in composition, with widely separated areas where basalt flows are preserved, as well as large groups of diabase
(dolerite) sills or sheets, small lopolith
s, and dikes throughout the province. Dikes occur in very large individual swarms with particular compositions and orientations. CAMP activity is apparently related to the rifting and breakup of Pangaea during the Late Triassic
through Early Jurassic periods, and the enormous province size, varieties of basalt, and brief time span of CAMP magmatism invite speculation about mantle processes that could produce such a magmatic event as well as rift a supercontinent
. ,
where CAMP lava flows
are outcropping (e.g.), whereas the other is based on data from eastern North America
n basins and lava flows , respectively.
The thickest lava flow sequences of the African CAMP are situated in Morocco, where we can find more than 300 metres thick basaltic lava piles. The most studied area is Central High Atlas
, where the best preserved and most complete basaltic lava piles are exposed. According to geochemical, petrographic and isotopic data four distinct tholeiitic basaltic units were recognized and can be placed throughout the Central High Atlas: Lower, Intermediate, Upper and Recurrent basalts.
The Lower and Intermediate units are constituted by basaltic andesite
s, whereas the Upper and Recurrent units have basalt
ic composition. From Lower to Recurrent unit, we observe:
, , . These data show indistinguishable ages (199.5±0.5 Ma) from Lower to Upper lava flows, from central to northern Morocco. Therefore the CAMP is an intense and short magmatic event. Basalts of the Recurrent unit are slightly younger (mean age: 197±1 Ma) and represent a late event. Consistently, the Upper and Recurrent basalts are separated by a sedimentary layer that locally reaches a thickness of circa 80 m.
data, the Moroccan CAMP were divided into five groups, differing in p-mag directions (declination and inclination) . Each group is composed by a smaller number of lava flows (i.e., a lower volume) than the preceding one.
These data suggest that the CAMP were created by five short magma pulses and eruption events, each one possibly <400 (?) years long.
All lava flow sequences are characterized by normal polarity, except for a brief paleomagnetic
reversal yielded by one lava flow and by a localized interlayered limestone in two distinct section of the High Atlas CAMP.
data from sedimentary layers samples at the base of four lava flow sequences constrain the onset of the CAMP, since there is no evidence of depositional hiatus or tectonic deformation at the bottom of the lava flow piles . The palynological assemblage observed in these basal layers is typical of Late Triassic
age, similar to that of the uppermost Triassic sedimentary rocks of eastern North America .
Samples from interlayered limestone in lava flows provided unreliable palynological data. In fact only one limestone bed from the top to the central High Atlas upper basalts yielded a Late Triassic palynological assemblage. However, the observed sporomorphs in this sample are rare and poorly preserved.
-J
boundary. Thus, it is well possible that there is a connection between this magmatic event and the Tr-J boundary climatic and biotic crisis that led to the mass-extinction.
The North American portion of the CAMP lava flows crop out in various sections in the basins of Newark, Culpeper, Hartford, Deerfield, i.e. the Newark Supergroup in New England (USA), and in the Fundy Basin
in Nova Scotia (Canada). The CAMP is here constituted by rare olivine
- and common quartz-normative basalts showing a great lateral extension and a maximum thickness up to 1 km. The basaltic flows occur on top of continental fluvial and lacustrine sedimentary units of Triassic age. 40Ar/39Ar data (on plagioclase) indicate for these basaltic units an absolute age of 198-200 Ma bringing this magmatic event undoubtedly close to the Triassic-Jurassic (Tr-J) boundary. Thus it is necessary to determine whether it straddles the boundary or not: if not, then the CAMP couldn’t be a cause of the Triassic#Late Triassic extinction event. For example, according to there are palynological, geochemical, and magnetostratigraphic evidences that the CAMP postdates the Tr-J boundary.
(Fundy basin, Nova Scotia) which are poorly sampled even if previous magnetostratigraphy analysis in this sequence showed only normal polarity, or in the Scots Bay Member of the Fundy basin which have never been sampled. There is only one outcrop in the CAMP of America where reverse polarity is observable: a CAMP–related (about 200 Ma) dike in North Carolina. suggest that reverse polarity intervals in this dike could be of post Triassic age and correlated with the same events in Morocco.
planorbis. In the Newark basin the palynological turnover event (hence the Tr-J boundary mass extinction) occurs below the oldest CAMP lava flows. The same can be said for the Fundy, Hartford and Deerfield Basins. In the investigated Moroccan CAMP sections (Central High Atlas Basin), sedimentary layers sampled immediately below the oldest basaltic lava flows, apparently contain Triassic taxa (e.g., P. densus), and were thus defined as Triassic in age as at least the lowest lava flows . Still, a different interpretation is suggested by : the sampled sedimentary strata are quite deformed and this can mean that some sedimentary units could be lacking (eroded or structurally omitted). With respect to the Triassic pollens found in some sedimentary units above the Upper Unit basalts, they could have been reworked, so they don’t represent a completely reliable constrain.
quartz
normative
(HTQ) basalts (TiO2 = 1.0-1.3 wt%); these are followed by lava flows classified as low titanium quartz normative (LTQ) basalts (TiO2 = ca. 0.8-1.3 wt%); and then by the youngest lava flow unit classified as high titanium iron quartz normative (HTIQ) basalts (TiO2 = 1.4-1.6 wt%). According to , geochemical analyses based upon titanium, magnesium and silicon contents show a certain correlation between the lower North American lava flows and the Lower Unit of the Moroccan CAMP, thus reinforcing the conclusion that the Moroccan basalts postdate the Tr-J boundary.
Therefore, according to these data, CAMP basalts shouldn’t be included among the direct causes of the Tr-J mass extinction.
Pangaea
Pangaea, Pangæa, or Pangea is hypothesized as a supercontinent that existed during the Paleozoic and Mesozoic eras about 250 million years ago, before the component continents were separated into their current configuration....
during the Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
Era. The initial breakup of Pangaea in early Jurassic
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
time provided a legacy of basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
ic dikes
Dike (geology)
A dike or dyke in geology is a type of sheet intrusion referring to any geologic body that cuts discordantly across* planar wall rock structures, such as bedding or foliation...
, sills
Sill (geology)
In geology, a sill is a tabular sheet intrusion that has intruded between older layers of sedimentary rock, beds of volcanic lava or tuff, or even along the direction of foliation in metamorphic rock. The term sill is synonymous with concordant intrusive sheet...
, and lava
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...
s over a vast area around the present central North Atlantic Ocean
Atlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
.
Connected magma flows
Although some connections among these basalts had long been recognized, in 1988 they were linked as constituting a single major flood basaltFlood basalt
A flood basalt or trap basalt is the result of a giant volcanic eruption or series of eruptions that coats large stretches of land or the ocean floor with basalt lava. Flood basalts have occurred on continental scales in prehistory, creating great plateaus and mountain ranges...
province
Large igneous province
A Large Igneous Province is an extremely large accumulation of igneous rocks—intrusive, extrusive, or both—in the earth's crust...
. The basaltic sills of similar age (near 200 Ma, or earliest Jurassic) and composition (intermediate-Ti quartz tholeiite) which occur across the vast Amazon River
Amazon River
The Amazon of South America is the second longest river in the world and by far the largest by waterflow with an average discharge greater than the next seven largest rivers combined...
basin of Brazil
Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...
were linked to the province in 1999 .
Geographical extent
The province has been described as extending within Pangaea from present-day central Brazil northeastward about 5000 km across western AfricaAfrica
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
, Iberia
Iberian Peninsula
The Iberian Peninsula , sometimes called Iberia, is located in the extreme southwest of Europe and includes the modern-day sovereign states of Spain, Portugal and Andorra, as well as the British Overseas Territory of Gibraltar...
, and northwestern France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
, and from the interior of western Africa westward for 2500 km through eastern and southern North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
. If not the largest Province by volume, the CAMP certainly encompasses the greatest area known, roughly 11 million km², of any continental large igneous province
Large igneous province
A Large Igneous Province is an extremely large accumulation of igneous rocks—intrusive, extrusive, or both—in the earth's crust...
.
Nearly all CAMP rocks are tholeiitic
Tholeiite
The tholeiitic magma series is one of two main magma series in igneous rocks, the other magma series being the calc–alkaline. A magma series is a series of compositions that describes the evolution of a mafic magma, which is high in magnesium and iron and produces basalt or gabbro, as it...
in composition, with widely separated areas where basalt flows are preserved, as well as large groups of diabase
Diabase
Diabase or dolerite is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. In North American usage, the term diabase refers to the fresh rock, whilst elsewhere the term dolerite is used for the fresh rock and diabase refers to altered material...
(dolerite) sills or sheets, small lopolith
Lopolith
A lopolith is a large igneous intrusion which is lenticular in shape with a depressed central region. Lopoliths are generally concordant with the intruded strata with dike or funnel-shaped feeder bodies below the body...
s, and dikes throughout the province. Dikes occur in very large individual swarms with particular compositions and orientations. CAMP activity is apparently related to the rifting and breakup of Pangaea during the Late Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
through Early Jurassic periods, and the enormous province size, varieties of basalt, and brief time span of CAMP magmatism invite speculation about mantle processes that could produce such a magmatic event as well as rift a supercontinent
Supercontinent
In geology, a supercontinent is a landmass comprising more than one continental core, or craton. The assembly of cratons and accreted terranes that form Eurasia qualifies as a supercontinent today.-History:...
. ,
Connection with the Triassic-Jurassic boundary and the associated mass-extinction event
Two hypotheses are in debate. One hypothesis is based especially on studies on Triassic-Jurassic basins from MoroccoMorocco
Morocco , officially the Kingdom of Morocco , is a country located in North Africa. It has a population of more than 32 million and an area of 710,850 km², and also primarily administers the disputed region of the Western Sahara...
where CAMP lava flows
Lava
Lava refers both to molten rock expelled by a volcano during an eruption and the resulting rock after solidification and cooling. This molten rock is formed in the interior of some planets, including Earth, and some of their satellites. When first erupted from a volcanic vent, lava is a liquid at...
are outcropping (e.g.), whereas the other is based on data from eastern North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
n basins and lava flows , respectively.
Morocco
High Atlas
High Atlas, also called the Grand Atlas Mountains is a mountain range in central Morocco in Northern Africa.The High Atlas rises in the west at the Atlantic Ocean and stretches in an eastern direction to the Moroccan-Algerian border. At the Atlantic and to the southwest the range drops abruptly...
, where the best preserved and most complete basaltic lava piles are exposed. According to geochemical, petrographic and isotopic data four distinct tholeiitic basaltic units were recognized and can be placed throughout the Central High Atlas: Lower, Intermediate, Upper and Recurrent basalts.
The Lower and Intermediate units are constituted by basaltic andesite
Basaltic andesite
Basaltic andesite is a black volcanic rock containing about 55% silica. Minerals in basaltic andesite include olivine, augite and plagioclase. Basaltic andesite can be found in volcanoes around the world, including in Central America and the Andes of South America. Basaltic andesite is common in...
s, whereas the Upper and Recurrent units have basalt
Basalt
Basalt is a common extrusive volcanic rock. It is usually grey to black and fine-grained due to rapid cooling of lava at the surface of a planet. It may be porphyritic containing larger crystals in a fine matrix, or vesicular, or frothy scoria. Unweathered basalt is black or grey...
ic composition. From Lower to Recurrent unit, we observe:
- a progressive decrease of eruption rate (the Lower and the Intermediate units represent over 80 % of preserved lava volume);
- a trend going from intersertal to porphyriticPorphyry (geology)Porphyry is a variety of igneous rock consisting of large-grained crystals, such as feldspar or quartz, dispersed in a fine-grained feldspathic matrix or groundmass. The larger crystals are called phenocrysts...
texture; - a progressive depletion of incompatible element contents in the basalts, possibly linked to a progressive depletion of their mantle source.
Isotopic analyses
Ages were determined by 40Ar/39Ar analysis on plagioclasePlagioclase
Plagioclase is an important series of tectosilicate minerals within the feldspar family. Rather than referring to a particular mineral with a specific chemical composition, plagioclase is a solid solution series, more properly known as the plagioclase feldspar series...
, , . These data show indistinguishable ages (199.5±0.5 Ma) from Lower to Upper lava flows, from central to northern Morocco. Therefore the CAMP is an intense and short magmatic event. Basalts of the Recurrent unit are slightly younger (mean age: 197±1 Ma) and represent a late event. Consistently, the Upper and Recurrent basalts are separated by a sedimentary layer that locally reaches a thickness of circa 80 m.
Magnetostratigraphy
According to magnetostratigraphicMagnetostratigraphy
Magnetostratigraphy is a geophysical correlation technique used to date sedimentary and volcanic sequences. The method works by collecting oriented samples at measured intervals throughout the section. The samples are analyzed to determine their characteristic remanent magnetization , that is, the...
data, the Moroccan CAMP were divided into five groups, differing in p-mag directions (declination and inclination) . Each group is composed by a smaller number of lava flows (i.e., a lower volume) than the preceding one.
These data suggest that the CAMP were created by five short magma pulses and eruption events, each one possibly <400 (?) years long.
All lava flow sequences are characterized by normal polarity, except for a brief paleomagnetic
Paleomagnetism
Paleomagnetism is the study of the record of the Earth's magnetic field in rocks. Certain minerals in rocks lock-in a record of the direction and intensity of the magnetic field when they form. This record provides information on the past behavior of Earth's magnetic field and the past location of...
reversal yielded by one lava flow and by a localized interlayered limestone in two distinct section of the High Atlas CAMP.
Palynological analyses
PalynologicalPalynology
Palynology is the science that studies contemporary and fossil palynomorphs, including pollen, spores, orbicules, dinoflagellate cysts, acritarchs, chitinozoans and scolecodonts, together with particulate organic matter and kerogen found in sedimentary rocks and sediments...
data from sedimentary layers samples at the base of four lava flow sequences constrain the onset of the CAMP, since there is no evidence of depositional hiatus or tectonic deformation at the bottom of the lava flow piles . The palynological assemblage observed in these basal layers is typical of Late Triassic
Triassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
age, similar to that of the uppermost Triassic sedimentary rocks of eastern North America .
Samples from interlayered limestone in lava flows provided unreliable palynological data. In fact only one limestone bed from the top to the central High Atlas upper basalts yielded a Late Triassic palynological assemblage. However, the observed sporomorphs in this sample are rare and poorly preserved.
Conclusions
All of these data indicate that the basaltic lava flows of the Central Atlantic magmatic province in Morocco were erupted at c. 200 Ma and spanned the TrTriassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
-J
Jurassic
The Jurassic is a geologic period and system that extends from about Mya to Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...
boundary. Thus, it is well possible that there is a connection between this magmatic event and the Tr-J boundary climatic and biotic crisis that led to the mass-extinction.
Eastern North America
Fundy Basin
The Fundy Basin is a sediment-filled rift basin on the Atlantic coast of southeastern Canada. It contains three sub-basins; the Fundy sub-basin, the Minas Basin and the Chignecto Basin. These arms meet at the Bay of Fundy, which is contained within the rift valley. From the Bay of Fundy, the Minas...
in Nova Scotia (Canada). The CAMP is here constituted by rare olivine
Olivine
The mineral olivine is a magnesium iron silicate with the formula 2SiO4. It is a common mineral in the Earth's subsurface but weathers quickly on the surface....
- and common quartz-normative basalts showing a great lateral extension and a maximum thickness up to 1 km. The basaltic flows occur on top of continental fluvial and lacustrine sedimentary units of Triassic age. 40Ar/39Ar data (on plagioclase) indicate for these basaltic units an absolute age of 198-200 Ma bringing this magmatic event undoubtedly close to the Triassic-Jurassic (Tr-J) boundary. Thus it is necessary to determine whether it straddles the boundary or not: if not, then the CAMP couldn’t be a cause of the Triassic#Late Triassic extinction event. For example, according to there are palynological, geochemical, and magnetostratigraphic evidences that the CAMP postdates the Tr-J boundary.
Magnetostratigraphy
In the Newark basin a magnetic reversal (E23r) is observed just below the oldest basalts and more or less in the same position as a palynologic turnover, interpreted as the Tr-J boundary. In Morocco, two reversal have been detected in two lava flow sequences. Two distinct correlations between the Moroccan and the Newark magnetostratigraphy have been proposed. suggest that the Tr-J boundary is located above the lower reverse polarity level which is positioned more or less at the base of the Intermediate basalt unit of Morocco. These two levels can be correlated with chron E23r of the Newark Basin, therefore the North American CAMP Basalts postdate the Tr–J boundary whereas part of the Moroccan CAMP was erupted within the Triassic. Contrarily, propose that these two levels could be earliest Jurassic intervals of reverse polarity not sampled in the Newark Basin Sequence (many more lava flows are present in the Moroccan Succession than in the Newark Basin), but observed in Early Jurassic sedimentary sequences of the Paris Basin of France. Reverse polarity intervals in America could be present within North MountainNorth Mountain (Nova Scotia)
North Mountain is a narrow southwest-northeast trending volcanic mountain range on the mainland portion of southwestern Nova Scotia, stretching from Brier Island to Cape Split...
(Fundy basin, Nova Scotia) which are poorly sampled even if previous magnetostratigraphy analysis in this sequence showed only normal polarity, or in the Scots Bay Member of the Fundy basin which have never been sampled. There is only one outcrop in the CAMP of America where reverse polarity is observable: a CAMP–related (about 200 Ma) dike in North Carolina. suggest that reverse polarity intervals in this dike could be of post Triassic age and correlated with the same events in Morocco.
Palynological analyses
The Tr-J boundary is not officially defined, but most workers recognise it in continental strata by the last appearance index taxa such as Ovalipollis ovalis, Vallasporites ignatii and Patinasporites densus or, in marine sections, by the first appearance of the ammonite PsilocerasPsiloceras
Psiloceras is an extinct genus of cephalopod belonging to the ammonite subclass. Psiloceras fossils are commonly found at Lyme Regis, Dorset Coast, England. Here smooth-shelled Psiloceras planorbis are to be found as usually flattened fossils in the Blue Lias....
planorbis. In the Newark basin the palynological turnover event (hence the Tr-J boundary mass extinction) occurs below the oldest CAMP lava flows. The same can be said for the Fundy, Hartford and Deerfield Basins. In the investigated Moroccan CAMP sections (Central High Atlas Basin), sedimentary layers sampled immediately below the oldest basaltic lava flows, apparently contain Triassic taxa (e.g., P. densus), and were thus defined as Triassic in age as at least the lowest lava flows . Still, a different interpretation is suggested by : the sampled sedimentary strata are quite deformed and this can mean that some sedimentary units could be lacking (eroded or structurally omitted). With respect to the Triassic pollens found in some sedimentary units above the Upper Unit basalts, they could have been reworked, so they don’t represent a completely reliable constrain.
Geochemical analyses
CAMP lava flows of North America can be geochemically separated in three units: the older ones are classified as high titaniumTitanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....
quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
normative
Normative mineralogy
Normative mineralogy is a geochemical calculation of the whole rock geochemistry of a rock sample that estimates the idealised mineralogy of a rock according to the principles of geochemistry....
(HTQ) basalts (TiO2 = 1.0-1.3 wt%); these are followed by lava flows classified as low titanium quartz normative (LTQ) basalts (TiO2 = ca. 0.8-1.3 wt%); and then by the youngest lava flow unit classified as high titanium iron quartz normative (HTIQ) basalts (TiO2 = 1.4-1.6 wt%). According to , geochemical analyses based upon titanium, magnesium and silicon contents show a certain correlation between the lower North American lava flows and the Lower Unit of the Moroccan CAMP, thus reinforcing the conclusion that the Moroccan basalts postdate the Tr-J boundary.
Therefore, according to these data, CAMP basalts shouldn’t be included among the direct causes of the Tr-J mass extinction.
