Researchers have found evidence that
Researchers have discovered that dense rocks located beneath the Sierra Nevada mountain range are breaking loose and sliding downwards into the Earth's mantle.
Scientists at the University of Colorado have made a groundbreaking discovery that clarifies how the Earth's continental crust came into existence.
Researchers have long hypothesized that plate tectonics was responsible for the significant geological changes that occurred about four billion years ago, but a discovery in California has confirmed their theory.
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The new research confirms that sections of the Sierra Nevada separated several million years ago, and it's currently happening in the central area, whereas the process has not yet occurred in the northern region.
The researchers stated, 'We have thus captured snapshots of a fundamental continent-building process.'
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This imaging technique involves seismic waves that undergo changes as they cross under-surface structures. By analyzing these changes, researchers can develop a clear image of the conditions deep underground.
Schulte-Pelkum and Klib also examined earthquake data from the Advanced National Seismic System Comprehensive Earthquake Catalog, or ComCat.
This analysis revealed a series of seismic activity in the central Sierra Nevada consisting of small earthquakes measuring between magnitude 1.9 and 3.2 that occurred at unusually low depths, approximately 25 miles or deeper.
The presence of such deep earthquakes in this area is also attributed to the presence of a segment of colder lower continental crust which fractures rather than stretches and flows like the molten material usually found at such great depths, the researchers point out.
In fact, they did not find any evidence of this layer in the northern Sierra, which implies that this area has not yet been subjected to foundering.
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Based on these observations, Schulte-Pelkum and Klib concluded that foundering has been occurring beneath the Sierra Nevada mountains for at least three million years, and it could be advancing northward.
They have found evidence of a process called differentiation, which means the separation of different materials in the Earth's lithosphere, based on how heavy they are.
This may help confirm geologists' long-held suspicions that subduction facilitates the planet creating its lighter continental crust from the denser mix of minerals beneath.
The Earth's continental crust, the land where we reside, is composed of solid rock that contains a significant content of minerals, consisting primarily of silicates, aluminum and potassium.
In comparison, the oceanic crust, lying at the bottom of ocean basins, is denser due to its predominantly basaltic composition, a volcanic rock primarily consisting of magnesium and iron.
Both of these greatly varying crusts originated from the same source: the Earth's mantle. Yet, how did the continental crust end up so dissimilar to its parent material, while the oceanic crust maintained its high density and basaltic composition from the mantle?
One possible explanation could be differentiation through the process of fragmentation.
In other words, the heavier elements in the upper mantle, such as those found in basalt, separate themselves out of the mixture as they melt, making it possible for them to form distinct layers.
Because these plates are so dense, the lower layer might then "peel" away and slowly sink deeper into the molten part of the mantle.
The removal of these denser materials makes it possible for the lighter continental crust to develop and ascend above the denser oceanic crust, giving rise to the land we inhabit.
This explanation has been nothing more than a theory for years, but now, Schulte-Pelkum and Klib have uncovered evidence to suggest it is an actual process that happens all across the globe.
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