Geochemistry and age of the Ontong Java Plateau

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doi: 10.1029/GM077p0233
Author(s): Mahoney, J. J.; Storey, M.; Duncan, R. A.; Spencer, K. J.; Pringle, M.
Author Affiliation(s): Primary:
University of Hawaii, School of Ocean and Earth Science and Technology, Honolulu, HI, United States
University of Keele, United Kingdom
Oregon State University, United States
U. S. Geological Survey, United States
Volume Title: Mesozoic Pacific; geology, tectonics, and volcanism
Volume Author(s): Pringle, Malcolm S., editor; Sager, William W.; Sliter, William V.; Stein, Seth
Source: The Mesozoic Pacific; geology, tectonics, and volcanism, edited by Malcolm S. Pringle, William W. Sager, William V. Sliter and Seth Stein. Geophysical Monograph, Vol.77, p.233-261. Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0065-8448. ISBN: 978-1-118-66389-9 CODEN: GPMGAD
Note: In English with English summary. 89 refs.; illus. incl. 5 tables, geol. sketch maps
Summary: Basement rocks from the Ontong Java Plateau are tholeiitic basalts which appear to record very high degrees of partial melting, much like those found today in the vicinity of Iceland. They display a limited range of incompatible element and isotopic variation, but small differences are apparent between sampled sites and between upper and lower groups of flows at Ocean Drilling Program Site 807. 40Ar-39Ar ages of lavas from Site 807, Deep Sea Drilling Project Site 289, and basement from the island of Malaita at the southern edge of the plateau are indistinguishable about a weighted mean of 122.4±0.8 Ma, indicating that plateau-building eruptions ended more or less simultaneously at widely separated locations. These data also provide the best minimum age available for magnetic reversal M0 and for the Aptian-Barremian boundary. Pb Nd-Sr isotopes for lavas from Sites 289, 803 and 807, as well as southern Malaita reflect a hotspot-like source with εNd(T) = +4.0 to +6.3, (87Sr/86Sr)T = 0.70423-0.70339, 206pb/204Pb = 18.245-18.709, and possessing consistently greater 208Pb/204Pb for a given 206Pb/204Pb than Pacific MORB. The combination of hotspot-like mantle source, very high degrees of melting, and lack of a discernible age progression is best explained if the bulk of the plateau was constructed rapidly above a surfacing plume head, possibly that of the infant Louisville hotspot. Basalt and feldspar separates indicate a substantially younger age of ∼90 Ma for basement at Site 803; in addition, volcaniclastic layers of mid-Cenomanian through Coniacian age occur at DSDP Site 288, and beds of late Aptian-Albian age are found at Site 289. Therefore, at least some volcanism continued on the plateau for 30 m.y. or more. The basalts at Site 803 are chemically and isotopically very similar to those at the ∼122 Ma sites, suggesting that the same hot plume-type mantle was present beneath the plateau for an extended period or at two different times. Surviving seamounts of the Louisville Ridge formed between 70 and 0 Ma have much higher 206pb/204Pb than any of the plateau basalts. Thus, assuming the Louisville hotspot was the source of the plateau lavas, a change in the hotspot's isotopic compositions may have occurred between roughly 70 and 90 Ma; such a change may have accompanied the plume-head to plume-tail transition. Similar shifts from early, lower 206Pb/204Pb to subsequent higher 206Pb/204Pb values are found in several other oceanic plateau-hotspot and continental flood basalt-hotspot systems, and could reflect either a reduction in the supply of low 206Pb/204Pb mantle or an inability of some off-ridge plume-tails to melt refractory low 206Pb/204Pb material.
Year of Publication: 1993
Research Program: DSDP Deep Sea Drilling Project
ODP Ocean Drilling Program
Key Words: 03 Geochronology; 05 Petrology, Igneous and Metamorphic; Age; Alkaline earth metals; Ar-40/Ar-39; Argon; DSDP Site 289; Deep Sea Drilling Project; Geochemistry; Interpretation; Isotopes; Lead; Leg 130; Leg 30; Magmas; Metals; Noble gases; Ocean Drilling Program; Ontong Java Plateau; Pacific Ocean; Partial melting; Pb-206/Pb-204; Radioactive isotopes; Sr-87/Sr-86; Stable isotopes; Strontium; West Pacific
Coordinates: S002956 S002955 E1583042 E1583041
N001906 N033626 E1613538 E1563728
Record ID: 1994007188
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