cool enough to permit the evolution of life on Earth. In fact, life has been traced
back to the Archean period, 3.5 billion years ago. Probably the early appearance of
continental crustal nuclei as ‘‘blobs’’ of solid plates is comparable to what has been
observed on ancient terrains exposed on all the larger continents, which are more
than 3.5 billion years old (Fig. 2.5).
Large Igneous Provinces (LIP) as a Nucleus for Continent
Accretion
It is likely that ancient rocky outcrops existed at the early stage of the Earth’s
formation when the ‘‘magma mantle’’ started to solidify and convective heat
currents began to move matter from one part of the mantle to another (Fig. 2.5).
These convective currents were the driving mechanism to bring lighter material to
the surface and form crustal embryos of ‘‘continental islands’’. The early conditions for the formation of silica-rich continental rocks took place about 4 billion
years ago (4000 Ma) and were probably comparable to the more recent
(63–200 Ma) mechanisms giving rise to the Large Igneous Provinces (LIPs)
observed on the Earth’s surface.
LIPs are due to the upwelling of lava from large, hot mantle plumes. From
geological records it is known that these LIP must have been the result of huge
amounts of volcanism associated with the emission of deadly gases such as sulfur
dioxide (SO 2 ) and carbon dioxide (CO 2 ) and coinciding with long periods of acid
rain. Even if the toxic gases were eventually lost or consumed during rock
weathering over the next few thousand years, nevertheless significant environmental damage must have occurred because of the large quantity of toxic elements
emitted over a relatively short period of time during the closely spaced periods of
volcanic eruptions.
These LIP are found today in the Kuroo volcanic region of South Africa
(190 Ma), in the Deccan Trapp in India (63 Ma), in Uruanu in Japan (26 million
years), in the Yellowstone area in northwestern USA (2.2 Ma), on the Kerguelen
Plateau in the southern Indian Ocean (110 million years), and in the Parana region
(128 Ma) on the South American continent as well as in the Edenteka trap in
Namibia (Southwest Africa). All these continental Large Igneous Provinces are
covered by flood basalts accompanied by large amounts of silica-rich volcanic
rocks forming great volumes ([10
4 km
3 ) of eruptive material, which was later
uplifted at the tectonic (lithospheric) plate margins to form continental crust.
Other, even older continental crust can be found in the Finno-Scadinavian
provinces of Pechenga (2500 Ma), in South America (Uruguay) in the Rio de la
Plata Craton (1790 Ma), and in Siberia (250 Ma). In today’s ocean, Cretaceous
(70–120 millions years old) and Jurassic (up to 168 Ma old) Large Oceanic Plateaus covered by extensive amounts of flood basalts, are found in today’s submarine environments such as near Ontong, Java, and in the Maniki and Hikurangi
Formation of Continents
39
back to the Archean period, 3.5 billion years ago. Probably the early appearance of
continental crustal nuclei as ‘‘blobs’’ of solid plates is comparable to what has been
observed on ancient terrains exposed on all the larger continents, which are more
than 3.5 billion years old (Fig. 2.5).
Large Igneous Provinces (LIP) as a Nucleus for Continent
Accretion
It is likely that ancient rocky outcrops existed at the early stage of the Earth’s
formation when the ‘‘magma mantle’’ started to solidify and convective heat
currents began to move matter from one part of the mantle to another (Fig. 2.5).
These convective currents were the driving mechanism to bring lighter material to
the surface and form crustal embryos of ‘‘continental islands’’. The early conditions for the formation of silica-rich continental rocks took place about 4 billion
years ago (4000 Ma) and were probably comparable to the more recent
(63–200 Ma) mechanisms giving rise to the Large Igneous Provinces (LIPs)
observed on the Earth’s surface.
LIPs are due to the upwelling of lava from large, hot mantle plumes. From
geological records it is known that these LIP must have been the result of huge
amounts of volcanism associated with the emission of deadly gases such as sulfur
dioxide (SO 2 ) and carbon dioxide (CO 2 ) and coinciding with long periods of acid
rain. Even if the toxic gases were eventually lost or consumed during rock
weathering over the next few thousand years, nevertheless significant environmental damage must have occurred because of the large quantity of toxic elements
emitted over a relatively short period of time during the closely spaced periods of
volcanic eruptions.
These LIP are found today in the Kuroo volcanic region of South Africa
(190 Ma), in the Deccan Trapp in India (63 Ma), in Uruanu in Japan (26 million
years), in the Yellowstone area in northwestern USA (2.2 Ma), on the Kerguelen
Plateau in the southern Indian Ocean (110 million years), and in the Parana region
(128 Ma) on the South American continent as well as in the Edenteka trap in
Namibia (Southwest Africa). All these continental Large Igneous Provinces are
covered by flood basalts accompanied by large amounts of silica-rich volcanic
rocks forming great volumes ([10
4 km
3 ) of eruptive material, which was later
uplifted at the tectonic (lithospheric) plate margins to form continental crust.
Other, even older continental crust can be found in the Finno-Scadinavian
provinces of Pechenga (2500 Ma), in South America (Uruguay) in the Rio de la
Plata Craton (1790 Ma), and in Siberia (250 Ma). In today’s ocean, Cretaceous
(70–120 millions years old) and Jurassic (up to 168 Ma old) Large Oceanic Plateaus covered by extensive amounts of flood basalts, are found in today’s submarine environments such as near Ontong, Java, and in the Maniki and Hikurangi
Formation of Continents
39