the word ‘‘beechen’’ means ‘‘hard’’ in Egyptian. The name basalt also could have
originated from the Hebrew word ‘‘barzel’’ meaning iron, since basalt is hard and
heavy, just like iron.
It was in the 1960’s that several scientists started to study sea floor rocks in
relation to their geological settings. For example, Engel and Engel in 1963, 1964,
and later Hekinian (1968) and Kay et al. (1970) emphasized the chemical and
mineralogical differences between the various basaltic lavas from the sea floor. In
addition to their differences from most subaerial rocks, basalt samples also show
compositional variation in relation to their geological locations. For example,
samples of basalt samples collected from seamounts and islands in oceanic basin
areas are seen to differ from the basalt lava erupted on accreting ridge systems.
These authors coined the term ‘‘alkali basalt’’ for the volcanic rocks from islands
and elevated seamounts and Mid-Ocean Ridge Basalt (MORB) to define the rocks
formed on spreading ridge systems.
One of the first comprehensive papers dealing with the terminology of basalt
and the inferred origin of these newly discovered oceanic rocks was published by
Engel and Engel (1963) in ‘‘Science’’. At about the same time, in 1964, I was a
student and also working on oceanic basalt samples at Colombia University. My
adviser and professor, Arie Poldervaart, was excited about some preserved glassy
samples that I had found in sediment cores from the Indian Ocean when I was
looking at the samples in the core-laboratory of the Lamont-Doherty Geological
Observatory. The pebble-sized glassy fragments, which had been quenched at
contact with seawater, represented a melt issued directly from the partial melting
of mantle material. It was on the basis of chemical analyses as well as on the basis
of mineralogical studies that the two major types of sea floor-generated basalt,
called MORBs (Mid-Ocean Ridge Basalt) and alkali basalts or Intraplate Oceanic
Basalt (IOB) were identified on a global scale.
Mid-Ocean Ridge Basalt (MORB)
Based on their mineralogy, chemistry and geological environments, a simplified
term, ‘‘Mid-Ocean Ridge Basalt’’ (MORB), was adopted by marine scientists to
define the exceptional character of these volcanic rocks and to distinguish them
from their land-based counterparts. The MORB is also called a tholeiite, named
after the German town of Tholey, where they were first collected and studied by
land geologists.
MORBs are subdivided into three types: the Normal (N-MORB), Transitional
(T-MORB) and Enriched (E-MORB). These classifications are based on their bulk
rock’s chemical composition in relation to their degree of enrichment in
‘‘incompatible compounds’’, such as the Large Ion Lithophile Elements (LILE),
for example, potassium (K), sodium (Na), zirconium (Zr), niobium (Nb) and
yttrium (Y), which do not easily enter into a mineral lattice.
Basaltic Rocks
79
originated from the Hebrew word ‘‘barzel’’ meaning iron, since basalt is hard and
heavy, just like iron.
It was in the 1960’s that several scientists started to study sea floor rocks in
relation to their geological settings. For example, Engel and Engel in 1963, 1964,
and later Hekinian (1968) and Kay et al. (1970) emphasized the chemical and
mineralogical differences between the various basaltic lavas from the sea floor. In
addition to their differences from most subaerial rocks, basalt samples also show
compositional variation in relation to their geological locations. For example,
samples of basalt samples collected from seamounts and islands in oceanic basin
areas are seen to differ from the basalt lava erupted on accreting ridge systems.
These authors coined the term ‘‘alkali basalt’’ for the volcanic rocks from islands
and elevated seamounts and Mid-Ocean Ridge Basalt (MORB) to define the rocks
formed on spreading ridge systems.
One of the first comprehensive papers dealing with the terminology of basalt
and the inferred origin of these newly discovered oceanic rocks was published by
Engel and Engel (1963) in ‘‘Science’’. At about the same time, in 1964, I was a
student and also working on oceanic basalt samples at Colombia University. My
adviser and professor, Arie Poldervaart, was excited about some preserved glassy
samples that I had found in sediment cores from the Indian Ocean when I was
looking at the samples in the core-laboratory of the Lamont-Doherty Geological
Observatory. The pebble-sized glassy fragments, which had been quenched at
contact with seawater, represented a melt issued directly from the partial melting
of mantle material. It was on the basis of chemical analyses as well as on the basis
of mineralogical studies that the two major types of sea floor-generated basalt,
called MORBs (Mid-Ocean Ridge Basalt) and alkali basalts or Intraplate Oceanic
Basalt (IOB) were identified on a global scale.
Mid-Ocean Ridge Basalt (MORB)
Based on their mineralogy, chemistry and geological environments, a simplified
term, ‘‘Mid-Ocean Ridge Basalt’’ (MORB), was adopted by marine scientists to
define the exceptional character of these volcanic rocks and to distinguish them
from their land-based counterparts. The MORB is also called a tholeiite, named
after the German town of Tholey, where they were first collected and studied by
land geologists.
MORBs are subdivided into three types: the Normal (N-MORB), Transitional
(T-MORB) and Enriched (E-MORB). These classifications are based on their bulk
rock’s chemical composition in relation to their degree of enrichment in
‘‘incompatible compounds’’, such as the Large Ion Lithophile Elements (LILE),
for example, potassium (K), sodium (Na), zirconium (Zr), niobium (Nb) and
yttrium (Y), which do not easily enter into a mineral lattice.
Basaltic Rocks
79