55 Ma, coincident with other events that occurred in the
Pacific at this time.
In the southern Pacific, spreading continued along the
Pacific–Antarctic ridge, extending eastward to connect
with the Pacific–Farallon and Farallon–Antarctic spreading ridges. At 67 Ma, a change in spreading direction is
recorded in the fracture zones of the South Pacific initiating the opening of the Aluk plate in the South Pacific. In
the Indian Ocean, spreading was occurring along the
Wharton ridge, SEIR, SWIR, and in the Mascarene Basin
(Figure 3h). Spreading in the Mascarene Basin ceased at
64 Ma jumping northward, isolating the Seychelles
microcontinent, and initiating spreading between India
and the Seychelles along the Carlsberg ridge. The SWIR
connected with spreading in the Malvinas plate until
66 Ma. After this, the SWIR connected directly with the
American–Antarctic and South Atlantic ridge. Seafloor
spreading propagated into the Eurasia–Greenland margin
along the Reykjanes ridge by 58 Ma, forming a triple junction between North America, Greenland, and Eurasia
(Figure 3h). The Jan Mayen microcontinent rifted off the
margin forming the fan-shaped Norway Basin along the
Aegir ridge. The Aegir ridge connected to the Mohns ridge
to the north and Reykjanes ridge to the south via a series of
transform faults. Spreading in the Eurasian Basin to the
north initiated around 55 Ma along the Gakkel/Nansen
ridge.
40 Ma
In the Pacific, spreading between the Kula–Pacific and
Kula–Farallon ceased at 42 Ma, leading to the Pacific
plate consisting of the Pacific, Vancouver, Farallon, Aluk,
and Antarctic plates (Figure 3i). The intersection of the
Murray transform fault with the North American subduction zone around 30 Ma led to the establishment of the
San Andreas Fault and corresponds to the establishment
of the Juan De Fuca plate at the expense of the Vancouver
plate.
In the western Pacific, spreading in the proto-South
China Sea ceased at 50 Ma coincident with the clockwise
rotation of the neighboring Philippine Sea plate. The dramatic change in motion of the Philippine Sea plate
reorganized the plate boundaries in the area leading to
the establishment of a subduction zone between Palawan
and the proto-South China Sea and the subduction of the
proto-South China Sea after 50 Ma (Figure 3i). Further
south, spreading initiated in the North Loyalty Basin
behind the proto-Tonga–Kermadec Trench. Spreading in
the West Philippine Basin ceased at 38 Ma, whereas
spreading continued in the Celebes Sea. The formation
of the Caroline Sea occurred behind a rapidly southward
migrating subduction zone. By 30 Ma, spreading initiated
in the Shikoku and Parece Vela Basins behind the westdipping Izu–Bonin–Mariana Arc. Spreading terminated
in the Celebes Sea. In the SW Pacific, spreading initiated
in the Solomon Sea at 40 Ma and in the South Fiji Basin
at 35 Ma.
The Indian Ocean was dominated by a series of
mid-ocean ridges such as the Wharton ridge, SEIR, SWIR,
and Carlsberg ridge (Figure 3i). Prior to 55 Ma, subduction was occurring along the Tethyan subduction zone,
consuming crust that formed during meso- and
neo-Tethys spreading. At 55 Ma, the northern tip of
Greater India marks the start of collision between India
and Eurasia and the uplift of the Himalayas. Closure of
the Tethys Ocean in this area occurred by about 43 Ma.
Full closure of the neo-Tethys between India and Eurasia
also corresponds to the cessation of spreading in the Wharton Basin, which describes Australia–India motion.
20 Ma to present day
In the Pacific, spreading continued along the Pacific–Juan
De Fuca, Pacific–Nazca, Pacific–Cocos, Cocos–Nazca,
Pacific–Antarctic, and Nazca–Antarctic ridges (Figure 3j,
k). The Bauer microplate formed along the East Pacific
Rise at 17 Ma and continued until 6 Ma. The locus of
spreading then jumped back to the East Pacific Rise
(between the Pacific and Nazca plates). The East Pacific
Rise is the fastest spreading ridge system (excluding
back-arc opening) and currently encompasses microplate
formation at the Easter, Juan Fernandez, and Galapagos
plates. Currently, the Juan De Fuca plate is limited at its
southern end by the Mendocino Fracture Zone and is
subducting slowly along the Cascadia subduction zone.
The western Pacific is dominated by the opening of a
series of back-arc basins due to the rollback of the subduction hinge of the Tonga–Kermadec and Izu–Bonin–
Mariana trenches (Figure 3j, k). Spreading in the Shikoku
and Parece Vela Basins and South China Sea ceased at
15 Ma. By 9 Ma, spreading initiated in the Mariana
Trough. We model complete closure of the proto-South
China Sea at around 10 Ma behind a subduction zone
located along Palawan and the North Borneo/Kalimantan
margin. In the SW Pacific, spreading in the Lau Basin initiated by 7 Ma with back-arc extension occurring in the
Havre Trough.
A further rupture of the Farallon plate occurred at
23 Ma leading to the establishment of the Cocos and
Nazca plates and initiation of the East Pacific Rise,
Galapagos Spreading Center, and Chile ridge. Cessation
of spreading in the South Fiji Basin occurred at 25 Ma.
In the Indian Ocean, spreading continued along the
SWIR, SEIR, CIR, and Carlsberg ridge (Figure 3j, k).
Extension along the East Africa rifts was established at
30 Ma leading to the breakup of Africa into Somalia plate.
Rifting along the Sheba ridge separating Arabia from
Africa/Somalia initiated at 30 Ma. A zone of diffuse deformation occurring in the middle of the Indo-Australian
plate led to the development of the Capricorn plate in the
central-east Indian Ocean at 20 Ma. Further west, spreading is initiated along the Sheba ridge at 20 Ma. The Sheba
ridge propagated into the Red Sea at 15 Ma.
Spreading in the South and North Atlantic continued
unabated, with the westward motion of the North
PALEOPHYSIOGRAPHY OF OCEAN BASINS
645
Pacific at this time.
In the southern Pacific, spreading continued along the
Pacific–Antarctic ridge, extending eastward to connect
with the Pacific–Farallon and Farallon–Antarctic spreading ridges. At 67 Ma, a change in spreading direction is
recorded in the fracture zones of the South Pacific initiating the opening of the Aluk plate in the South Pacific. In
the Indian Ocean, spreading was occurring along the
Wharton ridge, SEIR, SWIR, and in the Mascarene Basin
(Figure 3h). Spreading in the Mascarene Basin ceased at
64 Ma jumping northward, isolating the Seychelles
microcontinent, and initiating spreading between India
and the Seychelles along the Carlsberg ridge. The SWIR
connected with spreading in the Malvinas plate until
66 Ma. After this, the SWIR connected directly with the
American–Antarctic and South Atlantic ridge. Seafloor
spreading propagated into the Eurasia–Greenland margin
along the Reykjanes ridge by 58 Ma, forming a triple junction between North America, Greenland, and Eurasia
(Figure 3h). The Jan Mayen microcontinent rifted off the
margin forming the fan-shaped Norway Basin along the
Aegir ridge. The Aegir ridge connected to the Mohns ridge
to the north and Reykjanes ridge to the south via a series of
transform faults. Spreading in the Eurasian Basin to the
north initiated around 55 Ma along the Gakkel/Nansen
ridge.
40 Ma
In the Pacific, spreading between the Kula–Pacific and
Kula–Farallon ceased at 42 Ma, leading to the Pacific
plate consisting of the Pacific, Vancouver, Farallon, Aluk,
and Antarctic plates (Figure 3i). The intersection of the
Murray transform fault with the North American subduction zone around 30 Ma led to the establishment of the
San Andreas Fault and corresponds to the establishment
of the Juan De Fuca plate at the expense of the Vancouver
plate.
In the western Pacific, spreading in the proto-South
China Sea ceased at 50 Ma coincident with the clockwise
rotation of the neighboring Philippine Sea plate. The dramatic change in motion of the Philippine Sea plate
reorganized the plate boundaries in the area leading to
the establishment of a subduction zone between Palawan
and the proto-South China Sea and the subduction of the
proto-South China Sea after 50 Ma (Figure 3i). Further
south, spreading initiated in the North Loyalty Basin
behind the proto-Tonga–Kermadec Trench. Spreading in
the West Philippine Basin ceased at 38 Ma, whereas
spreading continued in the Celebes Sea. The formation
of the Caroline Sea occurred behind a rapidly southward
migrating subduction zone. By 30 Ma, spreading initiated
in the Shikoku and Parece Vela Basins behind the westdipping Izu–Bonin–Mariana Arc. Spreading terminated
in the Celebes Sea. In the SW Pacific, spreading initiated
in the Solomon Sea at 40 Ma and in the South Fiji Basin
at 35 Ma.
The Indian Ocean was dominated by a series of
mid-ocean ridges such as the Wharton ridge, SEIR, SWIR,
and Carlsberg ridge (Figure 3i). Prior to 55 Ma, subduction was occurring along the Tethyan subduction zone,
consuming crust that formed during meso- and
neo-Tethys spreading. At 55 Ma, the northern tip of
Greater India marks the start of collision between India
and Eurasia and the uplift of the Himalayas. Closure of
the Tethys Ocean in this area occurred by about 43 Ma.
Full closure of the neo-Tethys between India and Eurasia
also corresponds to the cessation of spreading in the Wharton Basin, which describes Australia–India motion.
20 Ma to present day
In the Pacific, spreading continued along the Pacific–Juan
De Fuca, Pacific–Nazca, Pacific–Cocos, Cocos–Nazca,
Pacific–Antarctic, and Nazca–Antarctic ridges (Figure 3j,
k). The Bauer microplate formed along the East Pacific
Rise at 17 Ma and continued until 6 Ma. The locus of
spreading then jumped back to the East Pacific Rise
(between the Pacific and Nazca plates). The East Pacific
Rise is the fastest spreading ridge system (excluding
back-arc opening) and currently encompasses microplate
formation at the Easter, Juan Fernandez, and Galapagos
plates. Currently, the Juan De Fuca plate is limited at its
southern end by the Mendocino Fracture Zone and is
subducting slowly along the Cascadia subduction zone.
The western Pacific is dominated by the opening of a
series of back-arc basins due to the rollback of the subduction hinge of the Tonga–Kermadec and Izu–Bonin–
Mariana trenches (Figure 3j, k). Spreading in the Shikoku
and Parece Vela Basins and South China Sea ceased at
15 Ma. By 9 Ma, spreading initiated in the Mariana
Trough. We model complete closure of the proto-South
China Sea at around 10 Ma behind a subduction zone
located along Palawan and the North Borneo/Kalimantan
margin. In the SW Pacific, spreading in the Lau Basin initiated by 7 Ma with back-arc extension occurring in the
Havre Trough.
A further rupture of the Farallon plate occurred at
23 Ma leading to the establishment of the Cocos and
Nazca plates and initiation of the East Pacific Rise,
Galapagos Spreading Center, and Chile ridge. Cessation
of spreading in the South Fiji Basin occurred at 25 Ma.
In the Indian Ocean, spreading continued along the
SWIR, SEIR, CIR, and Carlsberg ridge (Figure 3j, k).
Extension along the East Africa rifts was established at
30 Ma leading to the breakup of Africa into Somalia plate.
Rifting along the Sheba ridge separating Arabia from
Africa/Somalia initiated at 30 Ma. A zone of diffuse deformation occurring in the middle of the Indo-Australian
plate led to the development of the Capricorn plate in the
central-east Indian Ocean at 20 Ma. Further west, spreading is initiated along the Sheba ridge at 20 Ma. The Sheba
ridge propagated into the Red Sea at 15 Ma.
Spreading in the South and North Atlantic continued
unabated, with the westward motion of the North
PALEOPHYSIOGRAPHY OF OCEAN BASINS
645