Hydrothermal versus active margin sediment supply to the eastern equatorial Pacific over the past 23 million years traced by radiogenic Pb isotopes: Paleoceanographic and paleoclimatic implications

Höfig, Tobias W., Hoernle, Kaj, Hauff, Folkmar and Frank, Martin (2016) Hydrothermal versus active margin sediment supply to the eastern equatorial Pacific over the past 23 million years traced by radiogenic Pb isotopes: Paleoceanographic and paleoclimatic implications Geochimica et Cosmochimica Acta, 190 . pp. 213-238. DOI 10.1016/j.gca.2016.05.003.

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Abstract

We investigated the evolution of the Pb isotopic composition of bulk sediments on the Cocos Plate in sedimentary successions of Deep Sea Drilling Project (DSDP) Site 495 and Ocean Drilling Program (ODP) Site 1256 over the past 23 million years of depositional history. Our study addresses the relationship of the sediment Pb isotope record to plate tectonics, weathering inputs, and paleoceanography. It is the first effort to characterize the Pb isotopic evolution of eastern equatorial Pacific sedimentation covering the entire tectonic pathway of the Cocos Plate from its formation at the East Pacific Rise to its arrival at the Central American subduction zone. The Sites 495 and 1256 bulk sediment Pb isotope records are fully consistent over time despite distinct differences between the type of sediment deposited at both locations. A systematic and continuous trend from ∼23 to ∼6–4 Ma toward more radiogenic Pb isotopic compositions, e.g., 206Pb/204Pb ratios increase from 18.29 to 18.81, reflects a decrease in the contribution of hydrothermal particles from the East Pacific Rise and an increase in the predominantly eolian contribution of mixed weathering products from the continental arcs of the Northern and south Central Andes as well as from southern Mexico. Surprisingly, both the Pb isotopic composition of the detrital fraction and that of past seawater indicate that inputs from nearby Central America and the Galápagos Archipelago did not significantly contribute to the sediments of our core locations but were overwhelmed by other sediment sources. A systematic change to less radiogenic Pb isotope ratios in sediments younger than ∼4–3 Ma, reaching present-day 206Pb/204Pb values near 18.70, reflects a reduction of the continental input from the South Central Volcanic Zone of the Andean Arc and increased contributions from southern Mexican igneous complexes. This isotopic trend reversal took place as a consequence of changes in atmospheric circulation, when the studied sites crossed the Intertropical Convergence Zone due to tectonic drift and concurrent climate cooling. Eolian transport has played a major role in the supply of detrital material over the entire Neogene and Quaternary. The delivery of hydrothermal Pb originating from the East Pacific Rise to the easternmost tropical Pacific has been a persistent feature that is attributed to a remarkably stable central and eastern Pacific deep-water flow pattern over millions of years. Thus, deep ocean circulation did not change significantly as a consequence of either (1) the Early Miocene closure of the deep gateway between the Caribbean and eastern Central Pacific or (2) the Late Pliocene complete closure of the Central American Seaway.

Document Type: Article
Additional Information: WOS:000388802600013
Keywords: IODP Site 1256, DSDP Site 495, marine sediments, Pb isotopes, Cocos Plate, eastern equatorial Pacific
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-P-OZ Paleo-Oceanography
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS Magmatic and Hydrothermal Systems
Kiel University
Refereed: Yes
DOI etc.: 10.1016/j.gca.2016.05.003
ISSN: 0016-7037
Projects: DSDP, IODP/ODP, SPP 527
Date Deposited: 10 May 2016 08:40
Last Modified: 19 Dec 2017 12:50
URI: http://eprints.uni-kiel.de/id/eprint/32804

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