August 9, 2011
Antarctica And Texas Were Once Neighbors
The Earth was a much different place 1.1 billion years ago.
Researchers are discovering strong evidence that parts of what are now Texas and Antarctica were connected, according to Staci Loewy, a geochemist at California State University, Bakersfield.
Long before the supercontinent Pangaea formed, there were other landforms bouncing around on the surface of the planet, one of which is named Rodinia.
Loewy and her colleagues discovered that rocks collected from both locations have the exact same composition of lead isotopes. Earlier analyses showed the rocks to be the exact same age and have the same chemical and geologic properties.
The approximately 1.1 billion year old North American Mid-continent Rift System extends across the continent from the Great Lakes to Texas. Volcanic rocks associated with the rift, which appears to represent an aborted tectonic attempt to split the ancestral North American continent of Laurentia, are well exposed in the Keweenaw Peninsula of the Upper Peninsula of Michigan from which they take their name, the Keweenawan large igneous province.
Loewy and her researchers use new lead (Pb) isotopic data from the 1.1-billion-year-old rocks from Coats Land, to constrain the positions of Laurentia (ancestral North America) and Kalahari (ancestral southern Africa) in the 1-billion-year-old supercontinent, Rodinia.
The Coats Land rocks are identical in age to both the Keweenawan large igneous province of the North American mid-continent rift and the contemporaneous Umkondo large igneous province of southern Africa.
The tiny Coats Land block of Antarctica is a "Ëtectonic tracer' providing critical clues to the geographic relationships between three of the major continents of the planet in the time interval 1.1 "“ 1.0 billion years ago, just prior to the opening of the Pacific Ocean basin, the hypothesized "ËSnowball Earth' glaciations, and the rise of multi-cellular life.
The work is published in the September issue of the journal Geology.
Image Caption: Coats Land with its only rock outcrops, Littlewood (L) and Bertrab (B) nunataks. Photo courtesy of Ian Dalziel
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