Geochemistry of Mesozoic Pacific mid-ocean ridge basalt; constraints on melt generation and the evolution of the Pacific upper mantle

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doi: 10.1029/96JB03810
Author(s): Janney, Philip E.; Castillo, Paterno R.
Author Affiliation(s): Primary:
University of California at San Diego, Scripps Institution of Oceanography, La Jolla, CA, United States
Volume Title: Journal of Geophysical Research
Source: Journal of Geophysical Research, 102(B3), p.5207-5229. Publisher: American Geophysical Union, Washington, DC, United States. ISSN: 0148-0227
Note: In English. 105 refs.; illus., incl. 5 tables, sketch map
Summary: We present major and trace element and Sr-Nd-Pb isotope results on Mesozoic (130-151 Ma) mid-ocean ridge basalt (MORB) recovered from five Deep Sea Drilling Project sites in the central and northwestern Pacific Ocean. Seawater alteration is responsible for much of the major element variability in these basalts, but magmatic variations are still discernible. Major element modeling of the least altered samples indicates that the basalts were generated by degrees and pressures of melting identical to those of modern Pacific MORB, and this, in addition to the similarity in spreading rates between the East Pacific Rise and Mesozoic Pacific ridges, suggests that the style of mantle upwelling and melting at spreading centers is spreading rate dependent. In general, the five Mesozoic MORB units, like Jurassic Pacific MORB from Ocean Drilling Program Site 801, are depleted in highly incompatible elements relative to average N-MORB and display a wide range in Nd and Pb isotopic ratios (εNd(T) = 8.4-11.6; 206pb/204Pbi = 17.9-18.6) but have a low and uniform Sr isotopic composition (87Sr/86Sri = 0.7023-0.7026). This isotopic variation can be explained by mixing a depleted mantle source with small amounts of recycled oceanic crust (HIMU). In contrast to the older MORB, mid-Cretaceous Pacific MORB (≈115-100 Ma) are moderately to strongly enriched in highly incompatible elements with an "enriched mantle" isotopic affinity. The shift in MORB composition coincides with the onset of effusive mid-Cretaceous intraplate volcanism in the Pacific and reflects widespread contamination of the Pacific upper mantle with materials derived from the plumes or plume heads responsible for mid-Cretaceous oceanic plateaus and seamount chains. Copyright 1997 by the American Geophysical Union.
Year of Publication: 1997
Research Program: DSDP Deep Sea Drilling Project
Key Words: 02 Geochemistry; 05 Petrology, Igneous and Metamorphic; Alkaline earth metals; Basalts; Central Pacific; Crust; Deep Sea Drilling Project; Geochemistry; Igneous rocks; Isotopes; Lead; Leg 17; Leg 20; Leg 32; Magma contamination; Magmas; Major elements; Mantle; Melting; Mesozoic; Metals; Mid-ocean ridge basalts; Mid-ocean ridges; North Pacific; Northwest Pacific; Ocean floors; Oceanic crust; Pacific Ocean; Pb-206/Pb-204; Radioactive isotopes; Spreading centers; Sr-87/Sr-86; Stable isotopes; Strontium; Trace elements; Upper mantle; Volcanic rocks; West Pacific
Coordinates: N120000 N340000 E1570000 E1460000
N200000 N410000 E1800000 E1540000
Record ID: 1998003905
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