Morphology and structure of the Galapagos Rise

Johnson, G. Leonard; Vogt, Peter R.; Hey, R. N.; Campsie, J.; Lowrie, Allen

doi:10.1016/0025-3227(76)90052-9

Cited by 43 publications

(11 citation statements)

References 37 publications

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“…On the basis of their orientations and position, faults are categorized into three populations: ridge‐parallel faults (270–290°), transform‐parallel faults (338°–348°), and transform‐oblique faults (290°–335°) (Figure 4). Ridge‐ and transform‐parallel fault populations are consistent with gross seafloor morphology identified in some of the earliest regional studies of the GSC [e.g., Johnson et al , 1976]. The transform‐oblique fault population has not been previously described, but the presence of a transtensional regional stress field was predicted because of the oblique orientation of the GTF relative to both the ridge axes and the spreading direction [e.g., Harpp and Geist , 2002; Harpp et al , 2003].…”

Section: Resultsmentioning

confidence: 99%

Multiple expressions of plume‐ridge interaction in the Galápagos: Volcanic lineaments and ridge jumps

Mittelstaedt¹,

Soule²,

Harpp³

et al. 2012

Geochem Geophys Geosyst

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[1] Anomalous volcanism and tectonics between near-ridge mantle plumes and mid-ocean ridges provide important insights into the mechanics of plume-lithosphere interaction. We present new observations and analysis of multibeam, side scan sonar, sub-bottom chirp, and total magnetic field data collected during the R/V Melville FLAMINGO cruise (MV1007; May-June, 2010) to the Northern Galápagos Volcanic Province (NGVP), the region between the Galápagos Archipelago and the Galápagos Spreading Center (GSC) on the Nazca Plate, and to the region east of the Galápagos Transform Fault (GTF) on the Cocos Plate. The NGVP exhibits pervasive off-axis volcanism related to the nearby Galápagos hot spot, which has dominated the tectonic evolution of the region. Observations indicate that $94% of the excess volcanism in our Copyright 2012 by the American Geophysical Union 1 of 31 survey area occurs on the Nazca Plate in three volcanic lineaments. Identified faults in the NGVP are consistent with normal ridge spreading except for those within a $60 km wide swath of transform-oblique faults centered on the GTF. These transform-oblique faults are sub-parallel to the elongation direction of larger lineament volcanoes, suggesting that lineament formation is influenced by the lithospheric stress field.We evaluate current models for lineament formation using existing and new observations as well as numerical models of mantle upwelling and melting. The data support a model where the lithospheric stress field controls the location of volcanism along the lineaments while several processes likely supply melt to these eruptions. Synthetic magnetic models and an inversion for crustal magnetization are used to determine the tectonic history of the study area. Results are consistent with creation of the GTF by two southward ridge jumps, part of a series of jumps that have maintained a plume-ridge separation distance of 145 km to 215 km since $5 Ma.

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Section: Resultsmentioning

confidence: 99%

Multiple expressions of plume‐ridge interaction in the Galápagos: Volcanic lineaments and ridge jumps

Mittelstaedt¹,

Soule²,

Harpp³

et al. 2012

Geochem Geophys Geosyst

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“…Significant offsets of this conduit at transform faults may act as dams and impede the flow, resulting in mass accumulations (shallow axial depths) on the upflow side of the offsets (Vogt and Johnson, 1975). These concepts have been utilized to explain topographic gradients and offsets along the spreading center away from Iceland, the Azores, the central Juan de Fuca Ridge (Vogt and Johnson, 1975), and the Galapagos Islands (Vogt, 1976;Johnson and others, 1976).…”

Section: Topographic Profile Along the Epr Crestmentioning

confidence: 99%

Tectonics of the Nazca-Pacific divergent plate boundary

Rea¹

1981

Geological Society of America Memoirs

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Five regions along the Nazca-Pacific plate boundary are the sites of detailed surveys completed during the Nazca Plate Project, four in relatively typical axial regions and one in the area of the tectonically complex Easter plate. Deep tow surveys have also been conducted on the spreading center and in a fracture zone. I n addition to the survey data, many tracklines of a reconnaissance nature cross the spreading center. Sea-floor spreading occurs at about 160 mm/ yr (whole rate) along this part of the East Pacific Rise. South of the Garret Fracture Zone at 13.5° S spreading is asymmetrical, being faster to the east than to the west. The lithosphere near fast-spreading rises is quite thin and therefore more susceptible to deformation than along slow-spreading ridges. The effects of a weak lithosphere take several forms: a long oblique ridge in the active portion of the Wilkes Fracture Zone at 9°S; twinned spreading centers surrounding the small Easter plate; and small, 10 to 15 km, offsets of the spreading center that can be formed or healed rapidly. These offsets are all formed within a time span of 0.5 m.y. or less and may involve segments of the rise axis up to 200 km long. Apparently they are the result of small, discrete axis jumps facilitated by the unusually thin lithosphere. Reconnaissance data between the 13.5°S and 4.5°S fracture zones are adequate to decipher the history of formation of the East Pacific Rise in this region. Spreading activity shifted 600 to 850 km westward from the old Galapagos Rise, now in the center of the Nazca plate, to its present location by three large jumps. Each of these jumps resulted in the formation of a fracture zone-bound section of the new rise; the jumping process covered about 2.5 m.y., from 8.2 to 5.7 m.y. ago. on July 14, 2015 memoirs.gsapubs.org Downloaded from on July 14, 2015 memoirs.gsapubs.org Downloaded from DIVERGENT BOUNDARY 31have provided the best bathymétrie maps of the Nazca plate and adjacent regions (Mammerickx and others, 1975;Mammerickx and Smith, 1978). DATA FROM THE RISE CREST 9° to 12° S RegionThe development of the EPR axis in the region between about 9° and 12°S is the simplest of the areas surveyed. Data in this region (Rea, 1976a) consist of a detailed survey area centered on the rise crest at about 10.5°S and several reconnaissance lines that cross the east flank and crest of the rise. A bathymetric contour map of the 10.5°S survey area (Fig. 2) depicts the typical features of the EPR crest. The precise axis of the EPR is a low ridge about 300 m high and 15 to 20 km wide (Figs. 2,3). The shallowest depth of this feature is 2,600 to 2,700 m, and the 3,000-m contour line (Fig. 2) generally defines its lateral extent. The axis is aligned along a trend of 018° in the northern two-thirds of the area, but changes trend at 11 ° S to 012° in the southern part of the survey area. Low ridges commonly occur along the flanks of the axial ridge and where well developed (Fig. 3, lines 4 and 5) divide the axial block into three peaks of subequal width; the ...

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“…The GSC passes to the north of the Galapagos Islands and roughly bisects the area between the Cocos Ridge, an aseismic ridge trending northeast, and the Carnegie Ridge, an aseismic ridge trending southeast from the islands. Two recent reviews have been made of the tectonic and geophysical setting of the Galapagos region [Hey, 1977;Johnson et al, 1976]. The following summary relies heavily on these two sources.Paper number 80B0388.…”

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The nature of differentiation trends in some volcanic rocks from the Galapagos Spreading Center

Byerly¹

1980

J. Geophys. Res.

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The Galapagos spreading center has produced a suite of volcanic rocks which include (1) typical ocean floor tholeiites, (2) iron‐ and titanium‐enriched tholeiites, (3) andesites, and (4) rhyodacites. Interpretation of major element compositions determined for these rocks, associated glassy selvedges, and mineral phases suggests that the entire suite can be produced by fractional crystallization of the observed low‐pressure phenocrysts. Early fractionation to extreme iron and titanium enrichment requires 50–75% crystallization of five parts plagioclase, three parts augite, and one part olivine. In the highly fractionated basalts, pigeonite replaces olivine as a phenocryst phase and is a minor phase in the fractionation. At extreme iron and titanium enrichment, titanomagnetite becomes a phenocryst phase, and fractionation produces a silica enrichment trend to andesite (79% total crystallization) and rhyodacite (87% total crystallization). Apatite occurs as a microphenocryst phase in the silicic rocks. This suite of iron‐ and titanium‐enriched basalt and low‐alumina andesite differs from the calc‐alkaline suite of island arcs and continental margins. It is similar to the suite of fractionated lavas of the Galapagos Islands and Iceland, though these rocks are generally more alkaline than the Galapagos spreading center suite, which is similar to other ocean floor basalt suites though more fractionated. Magma mixing is suggested by the presence of basaltic xenoliths in the silicic rocks; the presence of high‐silica glass inclusions in the glassy selvedges of the basalts, andesite, and rhyodacite; the common occurrence of reversely zoned phenocrysts in the silicic rocks; and the occurrence of some highly fractionated yet aphyric rocks. The unusual extent of fractionation for this region may be related to the size, morphology, and eruption and resupply rates of the magma chambers associated with the Galapagos spreading center. This and the regional distribution of these highly fractionated rocks suggest an important, though indirect, influence of the Galapagos hot spot.

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Morphology and structure of the Galapagos Rise

Cited by 43 publications

References 37 publications

Multiple expressions of plume‐ridge interaction in the Galápagos: Volcanic lineaments and ridge jumps

Multiple expressions of plume‐ridge interaction in the Galápagos: Volcanic lineaments and ridge jumps

Tectonics of the Nazca-Pacific divergent plate boundary

The nature of differentiation trends in some volcanic rocks from the Galapagos Spreading Center

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