The Josephine ophiolite, northwestern California

Harper, Gregory D.

doi:10.1130/0016-7606(1984)95<1009:tjonc>2.0.co;2

Cited by 156 publications

(78 citation statements)

References 0 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…[9] The rock units mapped along the north wall of the Hess Deep Rift are broadly similar to those described from the upper crustal levels of ophiolites Harper, 1984a;Moores and Vine, 1971;Nicolas, 1989], some submarine escarpments [Auzende et al, 1989 [Alt et al, 1996]. However, the extent of our survey area and the combination of research tools we used has permitted us to document significant variations in the internal structure of these rock units and their contacts.…”

Section: Internal Structures Of Major Rock Unitsmentioning

confidence: 69%

“…Various features have been used to establish vertical or horizontal reference frames that are required to determine the original orientations of contacts between major rock units, unit thickness, and the orientations of structures in them. On this basis, many ophiolites show evidence of tectonic tilting of dikes in blocks bounded by riftrelated normal faults [Harper, 1984a;Hurst et al, 1994b;Varga and Moores, 1985]. However, in reconstructions of ophiolites, where major seafloor faulting is not evident, dikes are commonly assumed to define vertical reference planes.…”

Section: Implications For Structures In Ophiolitesmentioning

confidence: 99%

See 1 more Smart Citation

Structure of uppermost fast‐spread oceanic crust exposed at the Hess Deep Rift: Implications for subaxial processes at the East Pacific Rise

Karson

Klein

Hurst

et al. 2002

Geochem Geophys Geosyst

118

178

View full text Add to dashboard Cite

The uppermost 2 km of the oceanic crust created at the fast spreading (135 mm yr À1 , full rate) equatorial East Pacific Rise (EPR) is exposed for tens of kilometers along escarpments bounding the Hess Deep Rift. Mosaics of large-scale digital images from the remotely operated vehicle (ROV) Argo II and direct observations from the submersible Alvin document a degree of geological complexity and variability that is not evident from most studies of ophiolites or prevailing models of seafloor spreading. Dramatic variations in the thickness and internal structure are documented in both the basaltic volcanic and sheeted dike rock units. These rock units are characterized by extensive faulting, fine-scale fracturing, and rotations of coherent crustal blocks meters to tens of meters across. The uppermost basaltic lavas are essentially undeformed and have overall gently inclined flow surfaces. Through most of the basaltic lava unit, however, lava flow contacts dip (208-708W) toward the EPR and generally increase in dip downward in the section. Dikes cutting the lavas and in the underlying sheeted dike unit generally dip (908 -408E) away from the EPR. Deeper level gabbroic rocks show little evidence of the intense fracturing typical of the overlying units. We interpret this upper crustal structure as the result of subaxial subsidence within 1-2 km of the EPR that accommodated the thickening of the basaltic lava unit to $500 m. Variations in the thickness of lava and dike units and spatially related structures along the rift escarpments suggest temporal fluctuations in magma supply. These results indicate that substantial brittle deformation accompanied waxing and waning volcanism during the accretion of the crustal section exposed at the Hess Deep Rift. If this type of structure is typical of uppermost oceanic crust generated at the EPR, these processes may be common along fast spreading mid-ocean ridges.

show abstract

Section: Internal Structures Of Major Rock Unitsmentioning

confidence: 69%

Section: Implications For Structures In Ophiolitesmentioning

confidence: 99%

Structure of uppermost fast‐spread oceanic crust exposed at the Hess Deep Rift: Implications for subaxial processes at the East Pacific Rise

Karson

Klein

Hurst

et al. 2002

Geochem Geophys Geosyst

118

178

View full text Add to dashboard Cite

show abstract

“…Back arc basins are characterized by lithologic associations and geochemical systematics grossly similar to mid-ocean ridge basalts (MORB); ophiolites formed in this setting are for the most part indistinguishable from MORB geochemically and can only be associated with a back arc origin by careful study of the regional geologic setting [e.g., Harper, 1984;Harper et al, 1985]. I will focus here on those ophiolites thought to be associated with forearc rifting.…”

Section: Introductionmentioning

confidence: 99%

Birth, death, and resurrection: The life cycle of suprasubduction zone ophiolites

Shervais

2001

Geochem Geophys Geosyst

460

275

View full text Add to dashboard Cite

[1] Abstract: Suprasubduction zone (SSZ) ophiolites display a consistent sequence of events during their formation and evolution that suggests that they form in response to processes that are common to all such ophiolites. This sequence includes the following: (1) birth, which entails the formation of the ophiolite above a nascent or reconfigured subduction zone; this stage is typically characterized by the eruption of arc tholeiite lavas and the formation of layered gabbros and sheeted dike complex; (2) youth, during which is continued melting of refractory asthenosphere (depleted during birth) occurs in response to fluid flux from the subducting slab, with extensional deformation of the older plutonic suite, eruption of refractory lavas, and the intrusion of wehrlite-pyroxenite; (3) maturity, with the onset of semistable arc volcanism, typically calc-alkaline, as the subduction zone matures and stabilizes, and the intrusion of quartz diorite and eruption of silicic lavas; and (4) death, which is the sudden demise of active spreading and ophiolite-related volcanism, which in many cases is linked to collision with an active spreading center and the onset of shallow underthrusting of the buoyant spreading axis; expressed as dikes and lavas with oceanic basalt compositions that crosscut or overlie rocks of the older suites; (5) resurrection, with emplacement by obduction onto a passive margin or accretionary uplift with continued subduction. The early stages (1± 3) may be diachronous, and each stage may overlap in both time and space. The existence of this consistent progression implies that ophiolite formation is not a stochastic event but is a natural consequence of the SSZ tectonic setting.

show abstract

“…The low velocity just above the AMC has been interpreted to be due to a thermal anomaly, and the low velocity below the AMC is thought to represent a mush zone underlying the melt sill [Toomey et al, 1990;Vera et al, 1990]. Vera et al [Gudmundsson, 1995;Harper, 1984;Kidd, 1977;Oliver and McAlpine, 1998;Rosencrantz, 1983;Tryggvason, 1994;Umino et al, 2003]. However, Soule et al [2007] suggested that the dike fed the eruption over the whole 18-km-long section covered by the erupted lava flows on the seafloor, and using this length the calculated width of the dike is more reasonable 0.95 m. …”

Section: Melt Layer Thicknessmentioning

confidence: 99%

“…We can put constrains on the volume of magma involved in the eruption. The width of the AMC near 9°50'N is 500-700 m and the thickness is [Gudmundsson, 1995;Harper, 1984;Kidd, 1977;Oliver and McAlpine, 1998;Rosencrantz, 1983;Tryggvason, 1994;Umino et al, 2003]. However, Soule et al [2007] suggested that the dike fed the eruption over the whole 18-km-long section covered by the erupted lava flows on the seafloor, and using this length the calculated width of the dike is more reasonable 0.95 m. The second scenario suggests the 2005-06 eruption was fed from the accumulated southern and northern melt-rich sections.…”

Section: Relations Between the Physical State Of Amc Sill Pre-and Posmentioning

confidence: 99%

Advanced geophysical studies of accretion of oceanic lithosphere in Mid-Ocean Ridges characterized by contrasting tectono-magmatic settings

Xu¹

2012

View full text Add to dashboard Cite

The structure of the oceanic lithosphere results from magmatic and extensional processes taking place at mid-ocean ridges (MORs). The temporal and spatial scales of the variability of these two processes control the degree of heterogeneity of the oceanic lithosphere, represented by two end-member models: the classical Penrose Model exemplified by layered magmatic crust formed along fast-spreading MORs, e.g., East Pacific Rise (EPR); and the recently defined Chapman Model describing heterogeneous mafic and ultramafic lithosphere formed in settings of oceanic detachment faulting common along slow-spreading MORs, e.g., Mid-Atlantic Ridge (MAR). This thesis is using advanced marine geophysical methods (including finite-difference wave propagation modeling, 3D multi-channel seismic reflection imaging, waveform inversion, streamer tomography, and near-bottom magnetics) to study lithospheric accretion processes in MORs characterized by contrasting tectono-magmatic settings: the magmatically dominated EPR axis between 9°30'-10°00'N, and the Kane Oceanic Core Complex (KOCC), a section of MAR lithosphere (23°20'-23°38'N) formed by detachment faulting. At the EPR study area, I found that the axial magma chamber (AMC) melt sill is segmented into four prominent 2-4-km-long sections spaced every ~5-10 km along the ridge axis characterized by high melt content (>95%). In contrast, within the intervening sections, the AMC sill has a lower melt content (41-46%). The total magma volume extracted from the AMC sill was estimated of ~46 × 10 6 m 3 , with ~24 × 10 6 m 3 left unerupted in the upper crust as dikes after 2005-06 eruption. At the KOCC, I used streamer tomography to constrain the shallow seismic velocity structure. Lithological interpretation of the seismic tomographic models provides insights into the temporal and spatial evolution of the melt supply at the spreading axis as the KOCC formed and evolved. Investigation of a magnetic polarity reversal boundary in crosssection at the northern boundary of KOCC suggests that the boundary (representing both a frozen isotherm and an isochron) dips away from the ridge axis along the Kane transform fault scarp, with a west-dipping angle of ~45° in the shallow (<1 km) crust and <20° in the deeper crust. Many thanks to my project advisors and cooperators, Brian Tucholke, RalphStephen, and Maurice Tivey, who have worked with me during the past five and a half years. These research experiences have greatly broadened my horizons on marine geology and geophysics, synthetic seismology, and geomagnetism. Brian introduced me into the geological world of detachment fault system, and his patience and insightful comments on our scientific paper on Kane oceanic core complex are greatly appreciated.I am very thankful for Ralph who introduced me to the world of time-domain finite difference (TDFD) synthetic seismology and Tom Bolmer for setting up the workstation for my TDFD calculations. Ralph's encouragement, enthusiasm, and interactions with me have inspired me to dig out more intere...

show abstract

The Josephine ophiolite, northwestern California

Cited by 156 publications

References 0 publications

Structure of uppermost fast‐spread oceanic crust exposed at the Hess Deep Rift: Implications for subaxial processes at the East Pacific Rise

Structure of uppermost fast‐spread oceanic crust exposed at the Hess Deep Rift: Implications for subaxial processes at the East Pacific Rise

Birth, death, and resurrection: The life cycle of suprasubduction zone ophiolites

Advanced geophysical studies of accretion of oceanic lithosphere in Mid-Ocean Ridges characterized by contrasting tectono-magmatic settings

Contact Info

Product

Resources

About