Lithium isotopic composition of pore fluids and sediments in the Costa Rica subduction zone

Pore fluid and sediment Li concentrations and isotopic ratios provide important insights on the hydrology, sediment contribution to the arc volcanoes and fluid-sediment reactions at the dominantly non-accretionary Costa Rica subduction zone. Ocean Drilling Program Site 1039 in the trench axis provides a reference section of 400 m of the incoming sediments, and Site 1040, situated arcward from the trench, consists of a deformed sedimentary wedge and apron sediments, the décollement, and the partially dewatered underthrust sediment section. At the reference site, pore fluids show important isotopic variations (delta6Li=-21.7 to -37.8 per mil), reflecting the interplay of in situ alteration of volcanic material and ion exchange with clay minerals. In the basal section, a reversal of Li concentration and delta6Li toward seawater values is observed, providing supporting evidence for a lateral seawater flow system in the upper oceanic basement underlying this sediment section. At Site 1040, pore fluid of the lower deformed wedge sediments and within the décollement is enriched in Li and the isotopic compositions are relatively light, suggesting infiltration of a deep-seated fluid. The delta6Li value of -22 per mil of this Li-enriched fluid (261 µM), when compared with the delta6Li value of the subducted sediment section (-11 per mil), suggests that the deep source fluid originates from mineral fluid dehydration and transformation reactions at temperatures of 100 to 150°C, consistent with the temperature range of the up-dip seismogenic zone and of transformation of smectite to illite. The distribution of Li and its isotopes in the underthrust section are similar to those at the reference site, indicating near complete subduction of the incoming sediments and that early dewatering of the underthrust sediments occurs predominantly by lateral flow into the ocean. The hemipelagic clay-rich sediment section of the subducting plate carries most of the Li into this subduction zone, and the pelagic diatomaceous and nannofossil calcareous oozes contain little Li. The Li isotopes of both the clay-rich hemipelagic sediments and of the pelagic oozes are, however, similar, with delta6Li values of -9 to -12 per mil. The observations that (1) the delta6Li values of the underthrust sediments are distinctly lower than that of the mantle, and (2) the lavas of the Costa Rican volcanoes are enriched in Li and 7Li, provide an approximation of the contribution of the subducted sediments to the arc volcanoes. A first order mass balance calculation suggests that approximately half of the Li flux delivered by subducted sediments and altered oceanic crust into the Middle American Trench is recycled to the Costa Rican arc and at most a quarter of sedimentary Li is returned into the ocean through thrust faults, primarily the décollement thrust.

Literatura dominicana; comentarios crítico-históricos.

Mode of access: Internet.

The City school-tooth-clinic in Strassburg, Alsace and its activity : presented by the city of Strassburg to the visitors of the exposition ...

Also published in German as Die Städtische Schulzahnklinik in Strassburg im Elsass und ihre Tätigkeit : den Besuchern der Ausstellung überreicht von der Stadt Strassburg.

Development of an automated pre-sampling plan for construction projects. Final report.

Mode of access: Internet.

Highway maintenance simulation model. Final report.

Louisiana Department of Transportation and Development, Research and Development Section, Baton Rouge

Daily river stages at river gage stations on the principal rivers of the United States.

Mode of access: Internet.

The recognition policy of the United States since 1901,

Bibliography: p. 101-104.

Camp, court and siege; a narrative of personal adventure and observation during two wars: 1861-1865; 1870-1871.

The writer served successively on the staffs of Generals T. Williams, T.W. Sherman, and W.B. Franklin, 1862-1864 and E.R.S. Canby, 1865 in Louisiana and the lower Mississippi Valley; and was assistant secretary and secretary of the U.S. legation at Paris, 1866-1871.

Tribes and temples; a record of the expedition to middle America

Researches in southern Mexico and a short trip through Guatemala.

Annual report of the State Engineer ...

Latest issue consulted: 1848.

A comparison alcohol involvement in pedestrian and pedestrian casualties. Executive summary.

National Highway Traffic Safety Administration, Washington, D.C.

A comparison of alcohol involvement in pedestrians and pedestrian casualties. Final report.

National Highway Traffic Safety Administration, Washington, D.C.

The Atchafalaya River delta :

"January 1984."

1990 census of population and housing.

"Issued July 1991"

La. bulletin /

Title from cover.