HR: 1330h
AN: V42D-0388    [PDF]
TI: Global Pb Isotopic Signatures: Implications for Precambrian Mantle Reservoirs
AU: * Loewy, S L
EM: sloewy@mail.utexas.edu
AF: The University of Texas at Austin, Department of Geological Sciences, 1 University Station (C1100), Austin, TX 78712 United States
AU: Connelly, J N
EM: connelly@mail.utexas.edu
AF: The University of Texas at Austin, Department of Geological Sciences, 1 University Station (C1100), Austin, TX 78712 United States
AU: Dalziel, I W
EM: ian@utig.ig.utexas.edu
AF: The Institute for Geophysics, The University of Texas at Austin, 4412 Spicewood Springs Road, Bldg 600, Austin, TX 78759 United States
AB: Precambrian age-provinces have coherent Pb isotopic signatures that commonly differ from one craton to another. These distinctions have been exploited in paleogeographic reconstruction to test the affinities of potentially exotic terranes with host cratons or potential parent cratons. However, the global variability and distribution of these signatures was not well defined. Based on a compilation of whole-rock Pb isotopic compositions of Precambrian juvenile intrusions we conclude that; 1) Rocks in ca. 2.8-2.6 Ga, ca. 2.0-1.8 Ga, and ca. 1.3-1.0 Ga age-provinces in eastern Laurentia have coherent Pb isotopic signatures that vary systematically as if they were derived from the same homogeneous mantle reservoir that evolved with a constant $\mu$-value. 2) Signatures of ca. 1.3-1.0 Ga age provinces from Amazonia, Antarctica, Australia, Baltica, Kalahari, Oaxaca, and Laurentia overlap each other and define two global Pb isotopic signatures suggesting the presence of at least two large, isotopically-distinct mantle reservoirs during the Mesoproterozoic. Pb isotopic compositions of modern oceanic crust indicate the existence of two Mesozoic/Cenozoic, isotopically-distinct mantle reservoirs, referred to as "normal" mantle in the northern hemisphere and DUPAL mantle in the southern hemisphere. Compositions of Precambrian juvenile intrusions indicate that similar, long-lived reservoirs may have existed earlier in Earth's history.
DE: 1010 Chemical evolution
DE: 1020 Composition of the crust
DE: 1025 Composition of the mantle
DE: 1040 Isotopic composition/chemistry
DE: 9619 Precambrian
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting