Physics
Scientific paper
Dec 2006
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2006agufm.v31d0620p&link_type=abstract
American Geophysical Union, Fall Meeting 2006, abstract #V31D-0620
Physics
3600 Mineralogy And Petrology, 3614 Mid-Oceanic Ridge Processes (1032, 8416), 3621 Mantle Processes (1038)
Scientific paper
The Nova-Canton Trough (NCT) is an 8-km-deep abyss that merges with the far western trace of the Clipperton Fracture Zone north-northwest of the Manihiki Plateau. Ocean crust in this region formed during Cretaceous long magnetic normal Chron 34. Larson (Geology, 25, 779) argued that the NCT is part of an aborted rift system that formed between the Ontong Java and Manihiki plume heads, and terminated plateau construction around 120 Ma via drain-off of plume mantle to the region of rifting. Taylor (EPSL, 241, 372) instead proposed the two plateaus formed as one short-lived mega-plateau that broke apart, and that the NCT is part of the post-breakup transform system that separated a series of short spreading segments. Recently, the R.V. Kilo Moana dredged four sites along the prominent north-facing escarpment of the NCT between 168° 06' W and 168° 42' W at ~1° 24' S, and retrieved basalt, diabase, gabbro, pyroxenite, peridotite, serpentinite, breccias and sedimentary rocks. The diversity of rock types recovered demonstrates that a large cross-section through Cretaceous seafloor is exposed. The MgO content of the basalt and diabase samples varies from 8.9-4.3 wt.%. Incompatible element patterns display relative depletions in alteration- resistant large-ion lithophile elements, and most samples have a distinctive hump-shaped REE pattern, with chondrite-normalized (Sm/Yb)n >1.3 and (La/Sm)n <0.75, suggesting generation by high pressure, relatively low-degree melting of a MORB-type mantle source. One sample is less light-REE- depleted, with (La/Sm)n= 0.96. Age-adjusted (to 120 Ma) Nd-Pb isotope ratios plot within the high- 206Pb/204Pb portion of the Pacific MORB field at ɛNd values between +8.2 and +7.5. In contrast, data for the Ontong Java and Manihiki plateaus fall well below the Pacific MORB field at lower 206Pb/204Pb and ɛNd < +6.6. Thus, our data provide no evidence for Ontong Java or Manihiki mantle components in the NCT source.
Mahoney John J.
Pyle Douglas G.
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