Central Atlantic magmatic province
The Central Atlantic magmatic province is the Earth's largest continental large igneous province, covering an area of roughly 11 million km2. It is composed mainly of basalt that formed before Pangaea broke up in the Mesozoic Era, near the end of the Triassic and the beginning of the Jurassic periods. The subsequent breakup of Pangaea created the Atlantic Ocean, but the massive igneous upwelling provided a legacy of basaltic dikes, sills, and lavas now spread over a vast area around the present central North Atlantic Ocean, including large deposits in northwest Africa, southwest Europe, as well as northeast South America and southeast North America. The name and CAMP acronym were proposed by Andrea Marzoli and adopted at a symposium held at the 1999 Spring Meeting of the American Geophysical Union.
The CAMP volcanic eruptions occurred about 201 million years ago and had four separate eruptive cycles. Each pulse lasted no more than 100 years each, spread out over ~600,000 years. The resulting large igneous province is, in area covered, the most extensive on Earth. The eruptive volume is between two and six million cubic kilometres, making it one of the most voluminous eruptions in Earth's history. Some research shows that mafic eruptions started as early as 100 kya prior to the main pulse eruptions began.
This geologic event is associated with the Triassic–Jurassic extinction event.
Formation of Pangea
Pangea was the most recent supercontinent that existed. It's formation and break up is a part of the larger Supercontinent cycle and the Wilson cycle. After the rifting and break up of the previous Supercontinent Rodinia, new oceans opened, which included the Iapetus Ocean and the Rheic Oceans. Around 600-550 Ma, these oceans began to close due to subduction zones which began the formation of Pangea.Pangea was assembled by the accretion of island arc terranes to the Laurentian margins. This was done by multiple subduction related volcanic island arcs which moved from Africa and collided with North and South America. This process played out between 600-320 Ma and would become a key component to the eventual eruptions of the CAMP basalts.
Break up of Pangea and lead up to CAMP volcanism
By ~300 Ma, Pangea was fully formed. The teconic and acadian orogenies were complete. The alleghanian orogeny was actively building up the Appalachian Mountains. However, like previous Supercontinent cycles before it, Pangea was destined to break up.252 Ma and the Siberian Traps
The process of Pangea's break up can loosely be traced back to ~252 Ma. As Pangea relaxed, magma was able to find its way to the surface in one of the largest eruptions in Earth's history known as the Siberian Traps. Similar to the later CAMP eruptions, the Siberian Traps erupted of lava. The cause of the Siberian Traps is still debated. While most scientists attribute the eruption as a deep Mantle plume, there is strong evidence against the plume theory and more towards a plate tectonic cause.Around 300 Ma, subduction initiation started in the Paleotethys Ocean. This caused extensional stress to be exerted onto Pangea due to slab pull. Couple this with ongoing strong slab pull around Pangea from subduction zones in the Panthalassa Ocean, a net extensional pull on Pangea began. The Siberian traps are thought to have been the first lithospheric failure due to subduction and slab pull.
Localized extension, rift valleys, and the lead up to CAMP volcanism
Shortly after the end of the Siberian traps eruption, rift valleys began to take shape around 247 Ma. Rift valley sediments, dating to 247 Ma, have been found in the Fundy basin and the Argana basins. By 230 Ma, new passive rift valleys formed, deepened, and filled with sediment. Large rift lakes were also established with their own Van Houten cycles. The CAMP rift valley basins, formed over old suture zones created by Rodina and Pangea. Later, magma would use these zones of weakness as an easy route to the surface.Between ~227-202 Ma, deep, half graben rift basins were well established and localized. This is also when Newark rift basins were deep with their own rift lake systems. By 201.635±0.029 Myr,, you have well established large mafic magma bodies.
Connected magma flows
Although some connections among these basalts had long been recognized, in 1988 they were linked as constituting a single major flood basalt province. The basaltic sills of similar age and composition which occur across the vast Amazon River basin of Brazil were linked to the province in 1999. Remnants of CAMP have been identified on four continents and consist of tholeiitic basalts formed during the opening of the Atlantic Ocean basin during the breakup of the Pangean supercontinent.Eruptions
Eruptions took place in a similar cycle across most rift valleys. A period prior to eruptions of sedimentation inside rift valleys, followed by a short but extremely high volume basaltic fissure eruptive phase,, followed by a few thousand years of sedimentation, followed by another high volume basaltic eruption lasting no more than 100 years, etc.Using the Culpeper Basin as an example, the sediment Midland Formation lies just above the initial pulse of volcanism,. The Midland Formation is 500–984 ft thick and dates ~40 kyrs between eruptive pulses. This was enough time to establish rift lakes and new ecosystems. The Van Houten lake cycles is the geological life cycle of a lake, which includes: lake transgression, high-stand, and regression
At the end of the sedimentation period, the second eruptive sequence began. This was another volumous, sub-~100 year eruptive cycle before ending.
The next sedimentation cycle is known as the Turkey Run Formation. This was a much longer sedimentation period lasting 550 kyrs. It consists of dark-red to greenish-gray ripple laminated, cross-bedded sandstone, siltstone, and shale. It's 0.5 to 1.5 km wide and 63 km long measuring 150 m to 330 m in thickness. There is evidence for rift lakes which is interpreted as a shallower, wave- reworked lake deposits that was intermittently sub-aerially exposed and desiccated.
The youngest eruption in the cycle is the Sander Basalt, which ages to 201.5±1.3Ma. There were at least 4 or more separate basaltic flows during this cycle, with thickness ranges from 140 to 600 m.
Connection with the Triassic-Jurassic boundary and the associated mass extinction event
In 2013 the CAMP's connection to the end-Triassic extinction, with major extinctions that enabled dinosaur domination of land, became more firmly established. Until 2013, the uncertainties in the geochronologic dates had been too coarse to confirm that the volcanic eruptions were correlated with major climate changes. The work by Blackburn et al. demonstrated a tight synchroneity between the earliest volcanism and extinction of large populations using zircon uranium-lead dating. They further demonstrated that the magmatic eruptions as well as the accompanying atmospheric changes were split into four pulses lasting for over ~600,000 years.Before that integration, two hypotheses were in debate. One hypothesis was based especially on studies on Triassic-Jurassic basins from Morocco where CAMP lava flows are outcropping, whereas the other was based on end-Triassic extinction data from eastern North American basins and lava flows showing an extremely large turnover in fossil pollen, spores, and vertebrates, respectively.
Geographical extent
The province has been described as extending within Pangaea from present-day central Brazil northeastward about across western Africa, Iberia, and northwestern France, and from the interior of western Africa westward for through eastern and southern North America. If not the largest province by volume, the CAMP certainly encompasses the greatest area known, roughly, 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 sills or sheets, small lopoliths, 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.
Morocco
The thickest lava flow sequences of the African CAMP are in Morocco, where there are basaltic lava piles more than 300 metres thick. 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 andesites, whereas the Upper and Recurrent units have basaltic composition. From Lower to Recurrent unit, we observe:
- a progressive decrease of eruption rate ;
- a trend going from intersertal to porphyritic texture;
- a progressive depletion of incompatible element contents in the basalts, possibly linked to a progressive depletion of their mantle source.