During the Cenozoic, the fragmentation of continental landmasses continued as the Earth's surface took on its present form. The major geologic events of the Cenozoic can be thought of as two basic processes. First, four different large fragments of the Gondwanan supercontinent moved north and became, to varying degrees, attached to the Laurasian landmass. This resulted in a number of spectacular mountain-building events which climaxed about the Early Miocene. Second, the north-south Atlantic spreading zone continued to widen the Atlantic, contributing to geologic strains in East Africa and the western parts of the Americas, as these continents were pushed into contiguous plates by the growing Atlantic Ocean.
Caribbean Plate at 60 & 45 Mya. Kerr et al. (1999)The defecting Gondwanan fragments were South America, Africa, India, and Australia. South America has not pushed far enough north to cause a the geological equivalent of a high speed collision with North America. Instead, the impact was cushioned by a sort of air bag of small plates in what is now the Caribbean Sea. In particular, the approach of the American continents pinched off part of the Pacific crust, a region containing the sea bottom south and west of Cuba. The cushioning effect of these intervening plates delayed the formation of a land bridge between the Americas until the Middle Pliocene (Piacenzian), and has confined the effects of continental collision to relatively mild and sporadic vulcanism around the Caribbean and its southern and western margins. See image from Kerr et al. (1999). Various other representations can be found at Prof. Manuel Iturralde's wonderful site on the Caribbean plate: Comparison of different opinions...
A similar, but less pneumatic, effect has softened the impact of Africa on Europe. The numerous microplates of the Mediterranean have been repeatedly rearranged and compressed as Africa approached from the south. Nevertheless, Africa's attempt to subduct under the European Plate has been a little like a hippopotamus trying to hide under a bed sheet -- there have been some inevitable little lumps and wrinkles. Some of these, like today's Alps, are difficult to overlook. Other, older ranges which run generally east to west across Europe are also products of this process. In addition, the approach of Africa squeezed shut the old Tethys Seaway, which played such a large part in Early Mesozoic tetrapod history, leaving only a few puddles, such as the Mediterranean Sea and the Black Sea.
Southern part of rift valley in East Africa. NASA.The impact of India doesn't seem to have been mitigated at all. A land bridge between India and the Asian mainland was not established until the Eocene. However, the continental shelves of Asia and India had been in contact for some time before this, and elevation of the Himalayas has been ongoing throughout the Cenozoic. Initially, most of the impact was in the East, as India attempted to subduct under Asia to become the basement level of Tibet. In the Miocene, the force of the collision was distributed further west, forming the high plateaus of Afghanistan and Iran, with collateral consequences as far west as Eastern Europe. Perhaps the same fate awaits Australia, the last of the Gondwanan refugees. However, Australia has been dawdling along in the Pacific and has only recently begun to interact with the outlying portions of the Indonesian plates.
While the northern and southern continents have been getting progressively cozier, the Mid-Atlantic spreading ridge has been busy separating east from west. In the north, after splitting Greenland from North America, the rift abruptly changed course in the Paleogene and began to separate Northern Europe from Greenland. As a result, the last land bridge between North America and Europe was broken in the Eocene. The westward pressure on the Americas may well have been responsible for the Laramide Orogeny in the Western United States during the Paleogene, and the seamless merger of the subduction zones of North and South America later on. It is less clear that it has had any role in the more recent events which raised the current complex set of north-south mountain ranges in North America.
On the other side, in East Africa, the eastward pressure of the Mid-Atlantic ridge, combined with the opposite forces generated by the impact of India, created enormous stresses. As a result, the Arabian peninsula was rotated and torn off the East coast of Africa, and a series of deep faults have begun to fracture the African plate. Late in the Cenozoic, the main rift valley running through Ethiopia, Kenya, and points south, became the home of several species of large, noisy, and nearly hairless apes.
Caribbean Plate at 60 & 45 Mya. Kerr et al. (1999)The defecting Gondwanan fragments were South America, Africa, India, and Australia. South America has not pushed far enough north to cause a the geological equivalent of a high speed collision with North America. Instead, the impact was cushioned by a sort of air bag of small plates in what is now the Caribbean Sea. In particular, the approach of the American continents pinched off part of the Pacific crust, a region containing the sea bottom south and west of Cuba. The cushioning effect of these intervening plates delayed the formation of a land bridge between the Americas until the Middle Pliocene (Piacenzian), and has confined the effects of continental collision to relatively mild and sporadic vulcanism around the Caribbean and its southern and western margins. See image from Kerr et al. (1999). Various other representations can be found at Prof. Manuel Iturralde's wonderful site on the Caribbean plate: Comparison of different opinions...
A similar, but less pneumatic, effect has softened the impact of Africa on Europe. The numerous microplates of the Mediterranean have been repeatedly rearranged and compressed as Africa approached from the south. Nevertheless, Africa's attempt to subduct under the European Plate has been a little like a hippopotamus trying to hide under a bed sheet -- there have been some inevitable little lumps and wrinkles. Some of these, like today's Alps, are difficult to overlook. Other, older ranges which run generally east to west across Europe are also products of this process. In addition, the approach of Africa squeezed shut the old Tethys Seaway, which played such a large part in Early Mesozoic tetrapod history, leaving only a few puddles, such as the Mediterranean Sea and the Black Sea.
Southern part of rift valley in East Africa. NASA.The impact of India doesn't seem to have been mitigated at all. A land bridge between India and the Asian mainland was not established until the Eocene. However, the continental shelves of Asia and India had been in contact for some time before this, and elevation of the Himalayas has been ongoing throughout the Cenozoic. Initially, most of the impact was in the East, as India attempted to subduct under Asia to become the basement level of Tibet. In the Miocene, the force of the collision was distributed further west, forming the high plateaus of Afghanistan and Iran, with collateral consequences as far west as Eastern Europe. Perhaps the same fate awaits Australia, the last of the Gondwanan refugees. However, Australia has been dawdling along in the Pacific and has only recently begun to interact with the outlying portions of the Indonesian plates.
While the northern and southern continents have been getting progressively cozier, the Mid-Atlantic spreading ridge has been busy separating east from west. In the north, after splitting Greenland from North America, the rift abruptly changed course in the Paleogene and began to separate Northern Europe from Greenland. As a result, the last land bridge between North America and Europe was broken in the Eocene. The westward pressure on the Americas may well have been responsible for the Laramide Orogeny in the Western United States during the Paleogene, and the seamless merger of the subduction zones of North and South America later on. It is less clear that it has had any role in the more recent events which raised the current complex set of north-south mountain ranges in North America.
On the other side, in East Africa, the eastward pressure of the Mid-Atlantic ridge, combined with the opposite forces generated by the impact of India, created enormous stresses. As a result, the Arabian peninsula was rotated and torn off the East coast of Africa, and a series of deep faults have begun to fracture the African plate. Late in the Cenozoic, the main rift valley running through Ethiopia, Kenya, and points south, became the home of several species of large, noisy, and nearly hairless apes.
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