Petrology, isotope characteristics, and K-Ar ages of the Maranhão, northern Brazil, Mesozoic basalt province
dc.contributor.author | Fodor, R. V. | en_US |
dc.contributor.author | McKee, E. H. | en_US |
dc.contributor.author | Sial, A. N. | en_US |
dc.contributor.author | Mukasa, Samuel B. | en_US |
dc.date.accessioned | 2006-09-11T18:48:21Z | |
dc.date.available | 2006-09-11T18:48:21Z | |
dc.date.issued | 1990-04 | en_US |
dc.identifier.citation | Fodor, R. V.; Sial, A. N.; Mukasa, S. B.; McKee, E. H.; (1990). "Petrology, isotope characteristics, and K-Ar ages of the Maranhão, northern Brazil, Mesozoic basalt province." Contributions to Mineralogy and Petrology 104(5): 555-567. <http://hdl.handle.net/2027.42/47289> | en_US |
dc.identifier.issn | 1432-0967 | en_US |
dc.identifier.issn | 0010-7999 | en_US |
dc.identifier.uri | https://hdl.handle.net/2027.42/47289 | |
dc.description.abstract | Northern Brazil contains remnants of Mesozoic flood basalts and hypabyssal rocks that were apparently emplaced during tectonism related to opening of the Atlantic Ocean. Analyses and new K-Ar ages reveal that this ∼700x250 km Maranhão province (5°–8°S) has low-Ti basalts (∼1.1 wt% TiO 2 ) in the western part that range about 160 to 190 Ma, and high-Ti basalts (3.4–4.4 wt% TiO 2 ) in the eastern part about 115–122 Ma. Low-Ti basalt compositions are less evolved and have a smaller range, Mg# 62-56, than the high-Ti basalts, Mg# 44–33. General characteristics of the least evolved members of low- and high-Ti groups include, respectively, Zr 100 and 250 ppm, Sr 225 and 475 ppm, Ba 200 and 500 ppm, Nb 10 and 26 ppm, Y 29 and 36 ppm, La/Yb (n) 4.2 and 8.8, where La (n) is 30 and 90. Overall compositions resemble the low- and high-Ti basaltic rocks of the Mesozoic Serra Geral (Paraná) province in southern Brazil. The Maranhão low-Ti basalts have more radiogenic Sr and Pb and higher δ 18 O than the high-Ti basalts. Respectively, low- vs high-Ti: ɛ Sr 26−54 vs 15−18; 206 Pb/ 204 Pb=18.25–.78 vs 18.22–.24; and δ 18 O 8.9–12.6 vs 6.5–8.6. Nd isotopes overlap: ɛ Nd −1.6 to −3.8 vs −2.1 to −3. Ages, compositions, and isotopes indicate that the low- and high-Ti groups had independent parentages from enriched subcontinental mantle. However, both groups can be modeled from one source composition if low-Ti basalt isotopes reflect crustal contamination, and if the parentages for each group were picritic liquids that represent either higher (for low-Ti) or lower (for high-Ti) percentages of melting of that single source. When comparing Pb isotopes of Maranhão and Serra Geral high-Ti basalts (uncontaminated) to evaluate the DUPAL anomaly, Maranhão has Pb Δ7/4=4.6–11, and Pb Δ8/4=72–87; Serra Geral has Pb Δ7/4=10–13, and Pb Δ8/4=95–125. The small difference is not enough to conform to DUPAL contours, and is inconsistent with large-scale isotopic heterogeneity of mantle beneath Brazil prior to rifting of South America from Africa. Maranhão low-Ti magmas probably relate to the opening of central North Atlantic, and high-Ti magmas to the opening of equatorial Atlantic. The proposed greater percentage of source melting for low-Ti basalts may reflect a Triassic-Jurassic hotspot, while lesser melting for high-Ti magmas may relate to Cretaceous decompressional (rifting) melting. | en_US |
dc.format.extent | 1165810 bytes | |
dc.format.extent | 3115 bytes | |
dc.format.mimetype | application/pdf | |
dc.format.mimetype | text/plain | |
dc.language.iso | en_US | |
dc.publisher | Springer-Verlag | en_US |
dc.subject.other | Mineral Resources | en_US |
dc.subject.other | Geology | en_US |
dc.subject.other | Mineralogy | en_US |
dc.subject.other | Geosciences | en_US |
dc.title | Petrology, isotope characteristics, and K-Ar ages of the Maranhão, northern Brazil, Mesozoic basalt province | en_US |
dc.type | Article | en_US |
dc.subject.hlbsecondlevel | Geology and Earth Sciences | en_US |
dc.subject.hlbsecondlevel | Chemistry | en_US |
dc.subject.hlbtoplevel | Science | en_US |
dc.description.peerreviewed | Peer Reviewed | en_US |
dc.contributor.affiliationum | Department of Geological Sciences, University of Michigan, 48109, Ann Arbor, MI, USA | en_US |
dc.contributor.affiliationother | Departamento de Geologia, Universidade Federal de Pernambuco, Recife, PE, Brazil | en_US |
dc.contributor.affiliationother | Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, 27695, Raleigh, NC, USA | en_US |
dc.contributor.affiliationother | U.S. Geological Survey, 94025, Menlo Park, CA, USA | en_US |
dc.contributor.affiliationumcampus | Ann Arbor | en_US |
dc.description.bitstreamurl | http://deepblue.lib.umich.edu/bitstream/2027.42/47289/1/410_2004_Article_BF00306664.pdf | en_US |
dc.identifier.doi | http://dx.doi.org/10.1007/BF00306664 | en_US |
dc.identifier.source | Contributions to Mineralogy and Petrology | en_US |
dc.owningcollname | Interdisciplinary and Peer-Reviewed |
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