caa a22 4500 465791093 CHVBK 20180323112024.0 cr unu---uuuuu 170327e19900401xx s 000 0 eng 10.1007/BF00306664 doi (NATIONALLICENCE)springer-10.1007/BF00306664 Petrology, isotope characteristics, and K-Ar ages of the Maranhão, northern Brazil, Mesozoic basalt province [Elektronische Daten] [R. Fodor, A. Sial, S. Mukasa, E. McKee] 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% TiO2) in the western part that range about 160 to 190 Ma, and high-Ti basalts (3.4-4.4 wt% TiO2) 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 δ18O than the high-Ti basalts. Respectively, low- vs high-Ti: ɛSr26−54 vs 15−18; 206Pb/204Pb=18.25-.78 vs 18.22-.24; and δ18O 8.9-12.6 vs 6.5-8.6. Nd isotopes overlap: ɛNd−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. Springer-Verlag, 1990 Fodor R. Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, 27695, Raleigh, NC, USA aut Sial A. Departamento de Geologia, Universidade Federal de Pernambuco, Recife, PE, Brazil aut Mukasa S. Department of Geological Sciences, University of Michigan, 48109, Ann Arbor, MI, USA aut McKee E. U.S. Geological Survey, 94025, Menlo Park, CA, USA aut Contributions to Mineralogy and Petrology Springer-Verlag 104/5(1990-04-01), 555-567 0010-7999 104:5<555 1990 104 410 https://doi.org/10.1007/BF00306664 text/html Onlinezugriff via DOI 1 research-article jats NATIONALLICENCE 856 40 https://doi.org/10.1007/BF00306664 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Fodor R. Department of Marine, Earth, and Atmospheric Sciences, North Carolina State University, 27695, Raleigh, NC, USA aut NATIONALLICENCE 700 1- Sial A. Departamento de Geologia, Universidade Federal de Pernambuco, Recife, PE, Brazil aut NATIONALLICENCE 700 1- Mukasa S. Department of Geological Sciences, University of Michigan, 48109, Ann Arbor, MI, USA aut NATIONALLICENCE 700 1- McKee E. U.S. Geological Survey, 94025, Menlo Park, CA, USA aut NATIONALLICENCE 773 0- Contributions to Mineralogy and Petrology Springer-Verlag 104/5(1990-04-01), 555-567 0010-7999 104:5<555 1990 104 410 Metadata rights reserved Springer special CC-BY-NC licence nationallicence BK010053 XK010053 XK010000 NATIONALLICENCE NATIONALLICENCE NL-springer