Geology

Midcontinent Mineralization

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Science  29 Sep 2000:
Vol. 289, Issue 5488, pp. 2241
DOI: 10.1126/science.289.5488.2241d

Continental collisions do much more than just build mountains. As a consequence of the increased topography, large amounts of crustal fluid, which includes petroleum and metal-rich brines, are expelled thousands of kilometers underground toward continental interiors. These flows apparently were responsible for producing the Mississippi Valley-type zinc and lead sulfide ore deposits after the expelled fluids cooled and rose toward the surface. Previous dating of the ores had suggested that most of the fluids were supplied by formation of the Appalachian and Oachita Mountains about 250 million years ago (Ma) after the last collision of Europe and Africa with North America.

Coveney et al. provide additional dates and analysis of fluids from several major ore bodies that show a more complicated and much longer history. Although formation of the major ores is still coeval with formation of the Appalachian Mountains, some of the ores are younger and may be associated with fluid flow driven from the Laramide Orogeny in the Rocky Mountains, which occurred about 60 Ma. — BH

Geology28, 795 (2000).

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