East Scotia Ridge unsecured

Glassy rim 03 cm aphyric 109ds 2 glass rimmed up to 05

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Unformatted text preview: ·702489 7 0·513113 4 17·999 5 15·477 4 37·515 9 E5 wx50 0·702540 8 0·513075 9 18·083 2 15·474 2 37·574 4 E6 106DS-1 0·702622 6 0·513129 7 17·832 3 15·463 3 37·399 7 E6 107DS-1 0·702498 9 0·513111 11 17·838 2 15·463 1 37·370 4 E6 107DS-3 0·702749 7 0·513112 7 17·904 3 15·476 2 37·517 6 E6 108DS-1 0·702824 7 0·513084 8 17·871 2 15·475 2 37·465 5 E7 wx54b 0·702649 8 0·513120 5 17·869 7 15·497 6 37·514 14 E7 109DS-1 0·702517 8 0·513143 4 17·869 4 15·450 3 37·391 8 E7 110DS-3 0·702829 7 0·513081 6 17·885 4 15·473 3 37·506 8 E8 wx56 0·702807 8 0·513105 8 17·946 2 15·484 2 37·619 5 E8 wx60 0·702911 9 0·513101 6 18·231 3 15·537 3 38·010 6 E8 wx62 0·702869 9 0·513072 5 18·276 2 15·535 2 38·035 4 E9 wx63 0·702982 8 0·513034 7 18·213 2 15·539 2 37·984 5 E9 wx64 0·703038 8 0·513031 7 18·091 5 15·517 4 37·821 10 E9 wx65 0·703039 9 0·513009 9 18·198 2 15·548 2 38·010 5 E9 wx67 0·703102 8 0·513001 9 17·992 3 15·505 2 37·675 6 E9 wx68 0·702940 10 0·513063 7 17·919 7 15·487 6 37·590 14 E9 wx69 0·703100 7 0·513016 8 17·935 2 15·513 2 37·659 4 Segment Sample E3 E3 87 Nd/144Nd ± ± 11 (n = 11) over the course of this study. The long-term reproducibility of NBS 981 (n = 63) in this laboratory is 206Pb/204Pb = 16·896 ± 5, 207Pb/204Pb = 15·437 ± 7 and 208Pb/204Pb = 36·524 ± 21. During the course of this study, NBS 981 analyses (n = 8) gave 206 Pb/204Pb = 16·893 ± 10, 207Pb/204Pb = 15·433 ± 13 and 208Pb/204Pb = 36·514 ± 41, and were corrected to the values of Todt et al. (1996). Total chemistry Pb blanks were <0·3 ng and thus negligible. In Table 2 we show the isotope analyses of selected East Scotia Ridge samples and the 2 standard deviations. RESULTS Petrography and mineral chemistry We present a general summary of the major petrographic features and mineralogical characteristics of the dredged 206 Pb/204Pb ± 208 15·475 3 37·578 8 15·482 2 37·581 5 2 15·487 2 37·652 4 1 15·512 1 37·886 3 Pb/204Pb Pb/204Pb ± lavas from segments E3–E7 in Table 3. Individual mineral analyses are not presented here, but can be downloaded from the Journal of Petrology Web site at http://www. petrology.oupjournals.org. The phenocrysts are dominated by plagioclase and olivine phenocrysts with subordinate clinopyroxene, chrome spinel and magnetite. The most visible differences between the samples are in both their phenocryst contents and their vesicularity. Samples from segment E3 (96DS, 97DS, 98DS) contain some plagioclase and olivine phenocrysts (5%) and few vesicles, whereas the lavas from segment E4 (99DS, 100DS) are highly vesicular, but have an almost aphyric groundmass and sparse olivine and plagioclase phenocrysts (<3%). Most of the samples from dredge locations in segments E5 (104DS), E6 (106DS, 107DS) and E7 (109DS, 110DS) are slightly vesicular and exhibit a far higher plagioclase phenocryst content (30%) than the other segments. 1447 JOURNAL OF PETROLOGY VOLUME 43 NUMBER 8 AUGUST 2002 Table 3: Petrographic description of the dredged samples Segment S...
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