Tyrrell, T., and Zeebe, R. E., 2004. History of carbonate ion concentration over the last 100 million years. Geochimica et
Cosmochimica Acta, 68(17), 3521–3530.
Cross-references
Foraminifers (Benthic)
Foraminifers (Planktonic)
Paleoceanographic Proxies
Paleoceanography
Reefs (Biogenic)
MID-OCEAN RIDGE MAGMATISM AND VOLCANISM
Ken H. Rubin
Department of Geology & Geophysics, SOEST,
University of Hawaii, Honolulu, HI, USA
Definition
Mid-Ocean Ridge: A linear, narrow volcanic and tectonic
region which marks the constructive boundary between
two tectonic plates. It is divided into segments by transform faults and other offsets. The global ridge system cuts
through every major ocean basin and comes ashore in a
few places like Iceland. It forms an approximately
65,000 km long, globe-encircling, largely submarine
mountain chain.
Magmatism: Magmatism is the production and migration of magma, which is molten rock produced from the
partial or complete melting of solid materials within a
planetary body. When magma erupts on the surface, it is
known as lava.
Volcanism: Volcanism is the eruption of molten rock,
hot gases, or solidified rock fragments from an opening
(“vent”) in the Earth’s crust. Volcanism occurs on Earth
and other planets and moons. Most of the volcanism on
Earth occurs at mid-ocean ridges, almost always sight
unseen.
Mid-Ocean Ridge Magmatism: By far, the dominant
type of lava resulting from magmatic activity at
mid-ocean ridges is basalt, also called mid-ocean ridge
basalt (MORB). However, small amounts of other extrusive magma types (predominantly andesite, dacite, and
picrite) also erupt there. Variations in the rate and style
of magma production, volcanism, and faulting result from
variations in upper mantle temperature, upper mantle
composition, and seafloor spreading rate through the ridge
system, causing differences in igneous ocean crustal thickness, structure, and composition.
Mid-Ocean Ridge Volcanism: Volcanic eruptions at
ocean ridges vary in style, intensity, and duration around
the globe as a function of parameters such as magma
chamber depth, magma supply rate, and eruption depth
beneath sea-level. Nevertheless, the dominant eruption
styles either produce fissure-fed lava flows or pointsource, single vent volcanic lava mounds. Nearly all
volcanic products at ridges exhibit rapid quench textures,
formed by the freezing of molten magma upon contact
with cold seawater.
Introduction and history
Magmatism at mid-ocean ridges is one of our planet’s
most important geological processes, forming a dense,
low-lying, igneous crust that floors the vast ocean basins,
making up the solid rocks over nearly two-thirds of the
Earth’s surface. For most of geological history, the
greatest number and volume of volcanic eruptions on
Earth has occurred in the ocean, along mid-ocean ridges.
Earth’s globe-encircling volcanic system is a truly colossal geological structure (Figure 1). Yet it is one that many
people are not aware of because the global mid-ocean
ridge system mostly lies beneath the sea (except in rare
occurrences, such as in Iceland, where the mid-ocean
ridge is exposed on land due to an anomalously thickened
crust from the effects of the colocated Iceland Hotspot).
Viewed from space and with the world’s oceans stripped
away, the mid-ocean ridge system would stand out as
one of our planet’s most prominent surface geological features. The ridge system generally produces a layered crust,
with volcanic rocks on top, coarse-grained intrusive rocks
at depth, and an intervening layer of dikes. Together, these
layers form the igneous basement of the oceanic crust.
Mid-ocean ridges are segmented at various length
scales into volcano-scale units as well as longer coherent
segments that are separated by major offsets and discontinuities (e.g., Macdonald, 1982). Although at their upper
surface mid-ocean ridges are dominated by volcanic
rocks, the number and frequency of volcanic eruptions
that formed them is not well known (e.g., Rubin et al.,
2012). Compared to eruptions on land, we know less
about submarine eruptions and the magmas that drive
them, especially those that occur in the deep sea (here
defined as below 500 m depth) because eruptions in the
deep ocean are much more difficult to detect and observe
(Figure 1). Our first knowledge of submarine volcanic
rocks from mid-ocean ridges probably comes from reports
by deep-sea cable repair ships (Hall, 1876) and the Challenger Expedition (Murray and Renard, 1891), both of
which recovered volcanic rocks from the seafloor in the
1870s. Thus, while geologists working on land have had
thousands of years to develop an understanding of the
magmatic processes that drive subaerial volcanism,
marine geologists have had only a century or
so. Still, concerted multinational efforts in the last 35–40
years have accelerated the pace of learning, with several
marine expeditions to map, sample, and observe
mid-ocean ridges occurring around the globe each year.
Sampling campaigns over the past several decades have
resulted in greatly increased, but highly uneven, sampling
of the global ridge system. Some areas have few to
no known rocks recovered from them, and at the
other extreme, several locations have sampling
density equivalent to the best-studied volcanoes on land
(with 10–100 samples taken per km of ridge; Figure 1).
MID-OCEAN RIDGE MAGMATISM AND VOLCANISM
501
Cosmochimica Acta, 68(17), 3521–3530.
Cross-references
Foraminifers (Benthic)
Foraminifers (Planktonic)
Paleoceanographic Proxies
Paleoceanography
Reefs (Biogenic)
MID-OCEAN RIDGE MAGMATISM AND VOLCANISM
Ken H. Rubin
Department of Geology & Geophysics, SOEST,
University of Hawaii, Honolulu, HI, USA
Definition
Mid-Ocean Ridge: A linear, narrow volcanic and tectonic
region which marks the constructive boundary between
two tectonic plates. It is divided into segments by transform faults and other offsets. The global ridge system cuts
through every major ocean basin and comes ashore in a
few places like Iceland. It forms an approximately
65,000 km long, globe-encircling, largely submarine
mountain chain.
Magmatism: Magmatism is the production and migration of magma, which is molten rock produced from the
partial or complete melting of solid materials within a
planetary body. When magma erupts on the surface, it is
known as lava.
Volcanism: Volcanism is the eruption of molten rock,
hot gases, or solidified rock fragments from an opening
(“vent”) in the Earth’s crust. Volcanism occurs on Earth
and other planets and moons. Most of the volcanism on
Earth occurs at mid-ocean ridges, almost always sight
unseen.
Mid-Ocean Ridge Magmatism: By far, the dominant
type of lava resulting from magmatic activity at
mid-ocean ridges is basalt, also called mid-ocean ridge
basalt (MORB). However, small amounts of other extrusive magma types (predominantly andesite, dacite, and
picrite) also erupt there. Variations in the rate and style
of magma production, volcanism, and faulting result from
variations in upper mantle temperature, upper mantle
composition, and seafloor spreading rate through the ridge
system, causing differences in igneous ocean crustal thickness, structure, and composition.
Mid-Ocean Ridge Volcanism: Volcanic eruptions at
ocean ridges vary in style, intensity, and duration around
the globe as a function of parameters such as magma
chamber depth, magma supply rate, and eruption depth
beneath sea-level. Nevertheless, the dominant eruption
styles either produce fissure-fed lava flows or pointsource, single vent volcanic lava mounds. Nearly all
volcanic products at ridges exhibit rapid quench textures,
formed by the freezing of molten magma upon contact
with cold seawater.
Introduction and history
Magmatism at mid-ocean ridges is one of our planet’s
most important geological processes, forming a dense,
low-lying, igneous crust that floors the vast ocean basins,
making up the solid rocks over nearly two-thirds of the
Earth’s surface. For most of geological history, the
greatest number and volume of volcanic eruptions on
Earth has occurred in the ocean, along mid-ocean ridges.
Earth’s globe-encircling volcanic system is a truly colossal geological structure (Figure 1). Yet it is one that many
people are not aware of because the global mid-ocean
ridge system mostly lies beneath the sea (except in rare
occurrences, such as in Iceland, where the mid-ocean
ridge is exposed on land due to an anomalously thickened
crust from the effects of the colocated Iceland Hotspot).
Viewed from space and with the world’s oceans stripped
away, the mid-ocean ridge system would stand out as
one of our planet’s most prominent surface geological features. The ridge system generally produces a layered crust,
with volcanic rocks on top, coarse-grained intrusive rocks
at depth, and an intervening layer of dikes. Together, these
layers form the igneous basement of the oceanic crust.
Mid-ocean ridges are segmented at various length
scales into volcano-scale units as well as longer coherent
segments that are separated by major offsets and discontinuities (e.g., Macdonald, 1982). Although at their upper
surface mid-ocean ridges are dominated by volcanic
rocks, the number and frequency of volcanic eruptions
that formed them is not well known (e.g., Rubin et al.,
2012). Compared to eruptions on land, we know less
about submarine eruptions and the magmas that drive
them, especially those that occur in the deep sea (here
defined as below 500 m depth) because eruptions in the
deep ocean are much more difficult to detect and observe
(Figure 1). Our first knowledge of submarine volcanic
rocks from mid-ocean ridges probably comes from reports
by deep-sea cable repair ships (Hall, 1876) and the Challenger Expedition (Murray and Renard, 1891), both of
which recovered volcanic rocks from the seafloor in the
1870s. Thus, while geologists working on land have had
thousands of years to develop an understanding of the
magmatic processes that drive subaerial volcanism,
marine geologists have had only a century or
so. Still, concerted multinational efforts in the last 35–40
years have accelerated the pace of learning, with several
marine expeditions to map, sample, and observe
mid-ocean ridges occurring around the globe each year.
Sampling campaigns over the past several decades have
resulted in greatly increased, but highly uneven, sampling
of the global ridge system. Some areas have few to
no known rocks recovered from them, and at the
other extreme, several locations have sampling
density equivalent to the best-studied volcanoes on land
(with 10–100 samples taken per km of ridge; Figure 1).
MID-OCEAN RIDGE MAGMATISM AND VOLCANISM
501