Chapter 4
Sea Floor Rocks
Abstract Sea floor rocks can reveal Earth’s history. Based on the various
sampling operations conducted by ocean going scientists, it is inferred that the
relative distribution of oceanic rocks includes about 50 % basalts/dolerites, 20 %
gabbros and 30 % peridotites. Basalt and dolerite are the main volcanic rocks of
the upper crust, gabbros are formed during the solidification of a magma chamber
or magma conduit, and peridotites are either the heavy mineral residues left within
the reservoirs after magma solidification or they could be the remains after a
partial melting of mantle material. Basalt is the most common type of volcanic
rock found on the sea floor. Basalt and other related rocks have been extruded after
partial melting of the Earth’s mantle material. Rocks from the sea floor differ from
those encountered on land due to their shape and their chemical composition. The
effect of seawater and the pressure it exercises on hot, outpouring lava will fashion
the shape of deep-sea volcanic rocks giving the sea floor a different appearance
than what we see in subaerial environments. Curved and spherical-shaped pillow
lavas are only found on the sea floor due to the fact that seawater pressure is
equally applied on all directions of the lava flows and their cooling surfaces.
Basalts consist of silicates of magnesium, plus iron and calcium oxides. Less
common silica-enriched rocks (SiO 2 [ 53 %) such as andesites (SiO 2 =
53–59 %), rhyolites ([70 %) and trachytes (SiO 2 = 59–64 %) are also found on
some undersea structures such as domes and seamounts.
The history of rocks is what the field of petrology, my specialization, is all about.
The word ‘‘petrology’’ comes from the Greek words: ‘‘petros’’ meaning stone and
‘‘logos’’ meaning ‘‘study of’’ or ‘‘learning about’’. The description and classification of volcanic rocks helps us to understand their origin, their subsequent
evolution, and the subsurface circulation of the magmas responsible for their
formation. Mineralogical and chemical composition will influence the rate of lava
extrusion, as well as the lava’s cooling rate and the shape of various lava flows.
The magmatic history of the various geological provinces under the sea is affected
by a process of partial melting of deep-seated mantle as well as by crystal-liquid
fractionation in shallow depths within a magma reservoir.
R. Hekinian, Sea Floor Exploration, Springer Oceanography,
DOI: 10.1007/978-3-319-03203-0_4,
Ó Springer International Publishing Switzerland 2014
75
Sea Floor Rocks
Abstract Sea floor rocks can reveal Earth’s history. Based on the various
sampling operations conducted by ocean going scientists, it is inferred that the
relative distribution of oceanic rocks includes about 50 % basalts/dolerites, 20 %
gabbros and 30 % peridotites. Basalt and dolerite are the main volcanic rocks of
the upper crust, gabbros are formed during the solidification of a magma chamber
or magma conduit, and peridotites are either the heavy mineral residues left within
the reservoirs after magma solidification or they could be the remains after a
partial melting of mantle material. Basalt is the most common type of volcanic
rock found on the sea floor. Basalt and other related rocks have been extruded after
partial melting of the Earth’s mantle material. Rocks from the sea floor differ from
those encountered on land due to their shape and their chemical composition. The
effect of seawater and the pressure it exercises on hot, outpouring lava will fashion
the shape of deep-sea volcanic rocks giving the sea floor a different appearance
than what we see in subaerial environments. Curved and spherical-shaped pillow
lavas are only found on the sea floor due to the fact that seawater pressure is
equally applied on all directions of the lava flows and their cooling surfaces.
Basalts consist of silicates of magnesium, plus iron and calcium oxides. Less
common silica-enriched rocks (SiO 2 [ 53 %) such as andesites (SiO 2 =
53–59 %), rhyolites ([70 %) and trachytes (SiO 2 = 59–64 %) are also found on
some undersea structures such as domes and seamounts.
The history of rocks is what the field of petrology, my specialization, is all about.
The word ‘‘petrology’’ comes from the Greek words: ‘‘petros’’ meaning stone and
‘‘logos’’ meaning ‘‘study of’’ or ‘‘learning about’’. The description and classification of volcanic rocks helps us to understand their origin, their subsequent
evolution, and the subsurface circulation of the magmas responsible for their
formation. Mineralogical and chemical composition will influence the rate of lava
extrusion, as well as the lava’s cooling rate and the shape of various lava flows.
The magmatic history of the various geological provinces under the sea is affected
by a process of partial melting of deep-seated mantle as well as by crystal-liquid
fractionation in shallow depths within a magma reservoir.
R. Hekinian, Sea Floor Exploration, Springer Oceanography,
DOI: 10.1007/978-3-319-03203-0_4,
Ó Springer International Publishing Switzerland 2014
75