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History and Geology of Guaymas Basin
The Gulf of California, also called the Sea of Cortez, is the body of water
separating mainland Mexico from the peninsula of Baja California. The first
European to sail into the Gulf was the Spanish explorer Hernan Cortez in
1532. Cortez, however, mistook Baja California for a large island. Seven
years later, another Spanish explorer, Francisco de Ulloa, discovered that
Baja California was in fact part of North America.
Five million years ago, the Gulf of California did not exist. How did it form?
The answer lies in the piece of the Mid-Ocean Ridge called the East Pacific
Rise. The northernmost part of the East Pacific Rise runs along the Mexican
coast. About five million years ago, this segment of the East Pacific Rise
began to spread. As a result, a thin sliver of continental crust in western
Mexico started to rift apart. The shallow sea that formed is now the Gulf of
The Gulf of California seafloor is spreading at
a rate of five to six centimeters every year. Seafloor spreading
in the Gulf of California is unique. In most places, seafloor
spreading occurs along a continuous ridge. In the Gulf of California,
it takes place along short ridge segments. These segments are
separated by transform faults. One of these short spreading centers
is in the Guaymas Basin.
Why There Are No Eruptions in Guaymas Basin
If you dived down to most parts of the Mid-Ocean Ridge, you would see volcanoes
and evidence of big eruptions. However, you won’t see these things
in Guaymas Basin. That is because a huge layer of sediment smothers the
seafloor. This sediment layer is made of sand and mud that have washed
into the water from the shore at a rate of 1 to 3 meters every thousand
years. This layer of sediment is so thick (up to a kilometer) that magma
cannot penetrate it. Instead, magma moves part way up into this sediment
layers and forms a layer of volcanic rock that is a 1 to 20 meter thick.
Think of it as a layer cake. The sediment is the cake. The volcanic rock
(also called basalt) is the icing between the layers.
What’s Different About Guaymas Basin
Hydrothermal vents are common in Guaymas Basin. However, there are important
differences between the chemistry of these vents and the chemistry of vents
found on most other parts of the Mid-Ocean Ridge. These differences are caused
by the sediment layer. The heated seawater must move up through hundreds
of meters of sediment before reaching the seafloor and the lush communities
of creatures that thrive there. Over millions of years, this scalding hydrothermal
fluid has converted the organic matter in these sediments into petroleum
or oil products. This oil is toxic to almost all living things on earth.
Therefore, organisms that flourish at these vents not only must withstand
the heat, pressure, and toxic chemicals normally found in vents, they must
survive the oil as well.