Global Rift Research Articles

Carbon isotope evidence for the stepwise oxidation of the Proterozoic environment

The oxidation of the Earth's crust and the increase in atmospheric oxygen early in Earth history have been linked to the accumulation of reduced carbon in sedimentary rocks. Trends in the carbon isotope composition of sedimentary organic carbon and carbonate show that during the Proterozoic aeon (2.5-0.54 Gyr ago) the organic carbon reservoir grew in size, relative to the carbonate reservoir. This increase, and the concomitant release of oxidizing power in the environment, occurred mostly during episodes of global rifting and orogeny.

We Are Not the World

We are the world is a slogan with many possible interpretations. It may be interpreted as an updated version of the white man's burden, the globalization of late capitalism or the Americanization of the world. From a different, multicultural perspective the United States is seen as a microcosm of the world. Of course, these different interpretations have their common denominator in the dual process of global drift of capital and global rift of populations. In a special supplement to The New York Times, A World of Difference, the connection between commerce and diversity forms part of a celebration of multiculturalism that is really an advertisement for New York:

Wallerstein, World Systems Analysis, and Early Modern European History

TEXTS SUCH AS GLOBAL RIFT by L. S. Stavrianos or Daniel Chirot's Social Change in the Twentieth Century have acquainted many teachers of with the terminology, concepts and interpretations of worldsystems analysis, particularly as elaborated by Immanuel Wallerstein. A prolific writer and forceful polemicist on a wide range of topics from contemporary Africa to social theory, Wallerstein is best known for The Modern World-System: Capitalist Agriculture and the Origins of the European World-Economy in the Sixteenth Century (New York, 1974) and The Modern World-System II: Mercantilism and the Consolidation of the European World-Economy, 1600-1750 (New York, 1980), the first two volumes of a projected four-volume reinterpretation of post-medieval world history.1 Both volumes of The Modern World-System have been extensively discussed in this country and abroad and, as a glance at any recent issue of the Arts and Humanities Citation Index reveals, they continue to be referred to repeatedly. Reviews in sociological journals have acclaimed their author's unparalleled boldness of vision to raise all the important issues and his theoretical ambitions, while so eminent a scholar as Charles Tilly has praised Wallerstein's powerful contribution to sociological practice, notably his role in restoring time and history to the research agenda.2 In similar terms to their sociologist colleagues, and

History in the Grand Manner

Review of Global Rift: The Third World Comes of Age by L.S. Stavrianos.This article can also be found at the Monthly Review website, where most recent articles are published in full.Click here to purchase a PDF version of this article at the Monthly Review website.

Aeromagnetic Study of the Midcontinent Gravity High of Central United States

A composite map of detailed aeromagnetic surveys over the midcontinent gravity high provides coverage of the 600-mi-long buried belt of mafic rocks of the Keweenawan Series from their outcrop localities in Minnesota and Wisconsin through Iowa and Nebraska. A map of the subsurface extent of the mafic rocks, based on the intricate magnetic patterns, shows that the rocks form a long, semicontinuous block, averaging 40 mi wide and consisting mainly of a sequence of layered flows. This sequence is probably fault-bounded and has been tilted up along the margins, where the linearity of the anomalies indicates steeper dips. The associated clastic rocks, indicated by a smoother magnetic pattern, occur in basins along both sides of the mafic belt and in grabens and a series of axial basins on the upper surface of the block. The well-defined outliers of flows marginal to the main block and the truncation of some of the outermost flow units along a diagonal boundary striking at an angle to them suggest that the present boundaries of the block are postdepositional structural features. The basins and the edges of the block appear to have controlled later, largely vertical movement in the overlying Paleozoic and younger sedimentary cover. Calculated models based on coincident magnetic and detailed gravity profiles along typical cross sections of the midcontinent gravity high show that the block of mafic rocks is steep-sided and as much as several miles thick. The free-air gravity anomaly, which consists of a large positive maximum flanked by minima, averages very close to zero, indicating that this major crustal feature is regionally compensated, although locally each of its components shows a large departure from equilibrium. Remanent magnetization is a primary factor in the interpretation of the magnetic data. Magnetic property studies of Keweenawan mafic rocks in the Lake Superior region show that remanent magnetization may be five times the magnetization induced by the present Earth9s field and differs from it radically in direction. This magnetization was acquired before the flows were tilted into their present positions. A computed magnetic profile shows that a trough of flows with such a magnetization and inward-dipping limbs can account for the observed persistent lows along the western edge of the block, the relatively low magnetic values along the axis of the block, and the large positive anomaly along the eastern side of the block. Flows as much as 1 mi thick near the base of the sequence have a remanent magnetization with a nearly opposite polarity. This reverse polarity has been measured on both sides of Lake Superior and is probably also present farther south, particularly in Iowa where the outer units of the block in an area north of Des Moines give rise to a prominent magnetic low. The axis of this long belt of Keweenawan mafic rocks cuts discordantly through the prevailing east-west-trending fabric of the older Precambrian terrane from southern Kansas to Lake Superior. This belt has several major left-lateral offsets, one of which produces a complete hiatus in the vicinity of the 40th parallel where an east-west transcontinental rift or fracture zone has been proposed. The axial basins of clastic rocks are outlined by linear magnetic anomalies and show a concordant relation to the structure of the mafic flows. These basins are oriented at an angle to the main axis, suggesting that the entire feature originated as a major rift composed of a series of short, linear, en echelon segments with offsets similar to the transform faults characterizing the present mid-ocean rift system. This midcontinent rift may well have been part of a Keweenawan global rift system with initial offsets consisting of transform faults along pre-existing fractures, but apparently it never fully developed laterally into an ocean basin, and the upwelling mafic material was localized along a relatively narrow belt.