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Geologists know that the Earth's crust isn't entirely stable. Solid material in the mantle below it undergoes convection as heat rises from Earth's core. The study of the crust's instabilities and the features they produce as the surface expression of this convection is called tectonics. In the 1960s, plate tectonics emerged as a revolutionary theory to explain a broad spectrum of geologic processes, including the occurrence of mountain belts, volcanic islands, ocean ridges, oceanic trenches, abyssal plains, and deep and shallow earthquakes. Thus a considerable proportion of the research at UTIG involves tectonics. One UTIG program that focuses specifically on tectonics is the industry-sponsored PLATES Project. For this, UTIG has compiled and continuously updates a digital database with global coverage of marine magnetic anomalies, bathymetry, satellite altimetry, and fracture zone data. The PLATES scientists have developed software that uses the data to produce regional models that describe the tectonic evolution of the Earth's plates and ocean basins. They have extended the database back so that today it produces a global, internally-consistent plate model that describes the tectonic evolution of the earth over the past 750 million years. In 1988, UTIG scientists began using the U.S. Global Positioning System (GPS) technology to study tectonic motions. Special ground-based stations monitor dedicated satellites, allowing the locations of GPS receivers to be determined very accurately. Indeed,with GPS one may measure the distance between sites hundreds of kilometers apart with a degree of precision less than one centimeter. By repeating such measurements over time, it ispossible to calculate the horizontal motions of tectonic plates and deformation within crustal blocks. Ongoing programs at UTIG focus on monitoring crustal motions in the southwest Pacific and Antarctica. As the theory of plate tectonics evolved, geoscientists realized that Earth has been characterized by different tectonic styles over its geologic history. The episodic production of large igneous provinces offers a dramatic example. |
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Large igneous provinces (LIPs) are the products of a significant type of planetary volcanism found on Earth, the Moon, Venus, and Mars. On Earth, LIPs occur in many geologic settings, including every ocean basin. The two largest LIPs are enormous: the Ontong Java Plateau in the Pacific Ocean, with an area of 1.86 million square kilometers, is nearly three times the size of Texas; the Kerguelen Plateau in the Indian ocean is almost as large at 1.78 million square kilometers. Both lie mostly below sea level. Such LIPs provide information about mantle composition and dynamics that is not reflected by volcanism at spreading ridges
The production of oceanic plateaus and other LIPs is associated with major transfers of heat and material to Earth's surface, possibly associated with decompression melting of an ascending hot mantle plume. LIPs currently account for only 5 to 10% of the heat and magma expelled from the Earth's mantle. By contrast, in Early Cretaceous time (145 to 85 million years ago) giant LIPs apparently accounted for as much as 50%. Since LIPs punctuate the oceanic crust, which is produced steadily at seafloorspreading centers, the magma eruptions that create the LIPs must occur sporadically. The episodic nature of LIP production documented in the geologic record, especially between 150 and 50 million years ago, is evidence that a more dynamic, unpredictable mode of mantle circulation existed during Earth's past.
The study of LIPs is important for several other reasons, as well. The intense igneous activity associated with their production profoundly affects oceanic and atmospheric temperatures. The resulting global environmental changes influence biological evolution and species diversity. Moreover, because oceanic LIPs appear to resist subduction, they may serve as future building blocks of continental crust.
Despite their huge size and distinctive morphology, oceanic LIPs remain among the least understood features in the ocean basins. UTIG scientists have collectively participated in a series of international research cruises to acquire marine geophysical data with which to better characterize thedimensions and structure of the Ontong Java and Kerguelen plateaus. In addition, they have particpated on three ODP cruises to drill into both plateaus.
