Spatial and temporal evolution of magmatic systems beneath the Endeavor Segment, Juan de Fuca Ridge: Tectonic and petrologic constraints

Journal Article · Sat Nov 10 04:00:00 EST 1990 · Journal of Geophysical Research; (United States)

OSTI ID:5226823

Karsten, J L ^[1]; Delaney, J R ^[2]; Rhodes, J M; Liias, R A ^[3]

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1. Univ. of Hawaii, Honolulu (USA)
2. Univ. of Washington, Seattle (USA)
3. Univ. of Massachusetts, Amherst (USA)

Major and trace element data for a suite of lavas have been used to investigate the geometry and evolution of magmatic systems beneath the Endeavour Segment, Juan de Fuca Ridge. The morphology of the Endeavour Segment between the northward propagating Cobb Offset and the recently formed (<0.2 m.y.) Endeavour Offset is dominated by a shallow, rifted, elongate crestal volcano (Endeavour Ridge) that deepens along-strike into a broad, deep basin at each offset. Lavas from the current axis of the Endeavour Segment are moderately fractionated (MgO: 6-8.5 wt %) and have generally higher SiO{sub 2}, Al{sub 2}O{sub 3}, Na{sub 2}O, and K{sub 2}O, and lower FeO than lavas from south of the Cobb Offset (SOCO lavas). Incompatible trace element abundances and ratios indicate the Endeavour lavas are primarily enriched E-MORBs and T-MORBs in contrast with the SOCO lavas, which are more depleted in character. Thus, the 30-km wide Cobb Offset appears to mark a major geochemical boundary beneath the Juan de Fuca Ridge. In contrast with the Endeavour Segment axial lavas, samples from adjacent abyssal hills are more similar to the SOCO lavas in their major and trace element characteristics. These observations suggest that the parental magmas of the Endeavour Segment exhibit temporal variability, with more enriched material arriving only recently beneath the ridge axis. Pronounced compositional variability is observed at small spatial scales within the Endeavour Segment axial lavas, which does not correlate with axial morphology. Small scale heterogeneity along-strike seems incompatible with models of centralized upwelling of melts beneath the summit region of the ridge axis, with shallow lateral injection of melts to distal ends of the segment, unless these spatial variations actually reflect temporal variations in the source composition and collapse of the shallow magmatic systems toward the summit region as rift failure has progressed.

• OSTI ID: 5226823
• Journal Information: Journal of Geophysical Research; (United States), Journal Name: Journal of Geophysical Research; (United States) Vol. 95:B12; ISSN 0148-0227; ISSN JGREA
• Country of Publication: United States
• Language: English

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58 GEOSCIENCES
580000* -- Geosciences
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ALKALINE EARTH METAL COMPOUNDS
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ALUMINIUM OXIDES
BARIUM
CHALCOGENIDES
CHEMISTRY
ELEMENTS
ENRICHMENT
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