Lead isotope evidence for crust-mantle interaction during magmagenesis in the South Sandwich Island arc and in the Andes of South America [microform]
- Bib ID:
- 3287435
- Format:
- Book and Microform
- Author:
- Barreiro, Barbara Anne
- Description:
- 185 p.
- Summary:
-
Lead isotopic compositions of volcanic and plutonic rocks can be used to trace the sources of intra-oceanic and continental-margin arc magmas. Lead isotope ratios have been measured in twelve volcanic rocks from the South Sandwich Islands, an intra-oceanic island arc. In Pb-Pb correlation diagrams, the data plot distinctly above the oceanic igneous rock regression line (ORL), and yield trends showing apparent mixing with 2-10% subducted sediment end member as given by South Atlantic pelagic sediments reported by Chow and Patterson (1962). Quaternary volcanic rocks of the Andes have passed through 30-70 km of continental crust, and their Pb isotopic compositions record varying amounts of interaction. The lavas from the Northern and Southern Andes are fairly homogeneous with respect to Pb isotopic composition. The isotope data can be accounted for by small amounts of contribution from subducted sediments or minor continental crustal contamination.
Volcanic rocks from the Central Andes, where continental crust reaches 70 km in thickness, are isotopically heterogeneous, even for samples from a single volcano. Lead in fifteen lavas from southern Peru contains a large component derived from 1.9 Ga old granulitic basement rocks, while part of the lead in eight volcanic rocks from northern Chile and the Cerro Galan volcanic center in Argentina is probably derived from Late Precambrian-Paleozoic basement. The fact that the volcanic rocks reflect the isotopic signatures of the local basement rocks implies that mixing occurs in upper crustal magma chambers during differentiation. A detailed study of the Pb isotopic compositions of 1.9 Ga old granulitic basement gneisses and Jurassic to Quaternary Andean igneous rocks have not experienced any significant interaction with the granulites. On the other hand, all of the Miocene to Quaternary volcanic rocks have been severely contaminated.
The sudden increase in the degree of crustal contamination in magmagenesis coincided with the beginning of the uplift of the Central Andes and the formation of a thick crustal root, suggesting a relationship between crustal thickness and crustal contamination in this region.
- Notes:
-
- (UnM)AAI8224634
- Source: Dissertation Abstracts International, Volume: 43-06, Section: B, page: 1769.
- Thesis (Ph.D.)--University of California, Santa Barbara, 1982.
- Reproduction:
- Microfiche. Ann Arbor, Mich.: University Microfilms International.
- Subject:
- Geochemistry
- Other authors/contributors:
- University of California, Santa Barbara
- Copyright:
-
In Copyright
Contact us for information about copying.
Copyright status was determined using the following information:
- Material type:
- Literary Dramatic Musical
- Published status:
- Unpublished
- Creation date:
- 1982
Copyright status may not be correct if data in the record is incomplete or inaccurate. Other access conditions may also apply. For more information please see: Copyright in library collections.
Request this item
Request this item to view in the Library’s reading room.
Feedback
Similar items
- South African aloes
- The role of the Bayswater South and Bayswater Primary German programs in language maintenance [microform] / Barbara Imberger
- The last waterfront : the people of South Street / Barbara Mensch
- The highway of the three kings: Arabia from south to north
- South West African imprints / a bibliography comp. by B.Voigts