Modern Continental Rifts: Characteristics and Applications to Recognition of Ancient Rifts: ABSTRACT

Characteristics of modern continental rifts can provide a checklist of expected features in ancient rift systems: (1) distinctive morphology and dimensions as long, linear, sinuous structures up to thousands of kilometers in length and tens of kilometers in width; (2) high heat flow, resulting in extrusive and intrusive igneous bodies and hot-spring deposits; (3) small volcanoes within and large volcanoes outside only certain parts of rift systems; (4) complex stress fields that combine elements of extension, compression, shear, and torsion; (5) complex internal faulting; (6) gravity highs over intrusive mafic rocks and gravity lows over sedimentary rocks; (7) high seismicity, which leaves a record of earthquake-induced sedimentary structures; (8) progressive basin abando ment because of rift-jumping; (9) reactivation through time; (10) individual basins within rift systems formed by complexes of tilted-fault blocks, grabens, and horsts; (11) interfingering sedimentary deposits from slope, riverine, valley-floor, and lacustrine environments; (12) large and small rift-valley lakes, only some of which exhibit high biological productivity and anoxic bottom waters depositing organic-rich muds; and (13) deposits of the precursors of coal, petroleum, gas, and minerals that bear such elements as copper, lead, zinc, phosphorus, barium, or uranium. The combination of these critical features helps to identify ancient rift systems. However, crust weakened by rift-forming processes may be overprinted by later tectonic events that tend to obscure important details in ancient rifts such as the Newark rift system of eastern North America. End_of_Article - Last_Page 1446------------