Gravity anomalies of the ridge-transform system in the South Atlantic between 31 and 34.5� S: Upwelling centers and variations in crustal thickness

Kuo, Ban‐Yuan; Forsyth, Donald W.

doi:10.1007/bf00310065

Cited by 385 publications

(382 citation statements)

References 42 publications

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“…We calculated the magnetic anomaly by subtracting the appropriate International Geomagnetic Reference Field models, and then estimated the equivalent magnetization using the three-dimensional inversion method of (Parker and Huestis 1974;Macdonald et al 1980), assuming a 500-m-thick magnetized layer. We also calculated the free-air gravity anomaly, and then estimated the Mantle Bouguer anomaly by subtracting the predicted gravity effects of the seafloor relief and a 6-kmthick crust from the free-air gravity anomaly (Kuo and Forsyth 1988). Rock samples were also collected along the neo-volcanic zones within the axial valley and on some anomalous off-axis topographic highs, using dredge hauls and submersible dives.…”

Section: Rodriguez Triple Junction (Rtj) Areamentioning

confidence: 99%

Tectonic Background of Four Hydrothermal Fields Along the Central Indian Ridge

Okino

Nakamura

Sato

2014

Subseafloor Biosphere Linked to Hydrothermal Systems

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Since the discovery of the Kairei hydrothermal field at the southernmost end of the Central Indian Ridge (CIR) in 2000, only four active hydrothermal vent fields have subsequently been discovered. These four hydrothermal fields show remarkable diversity in the chemical compositions of fluids and associated ecosystems. Focused geophysical mapping and rock sampling indicate that different tectonic setting constrains the different hydrothermal activity for each field. Two hydrothermal fields in the southern CIR are located on the axial rift-valley wall. The hydrogen-rich Kairei hydrothermal field at 25 19 0 S is constrained by both basaltic magmatism and detachment faulting that exhume ultramafic rocks on a shallow subsurface, whereas no evidence of ultramafic exposure is recognized in the typical mid-ocean ridge type Edmond hydrothermal field at 23 52 0 S. Two other hydrothermal fields have been newly discovered in the central CIR. The Solitaire field at 19 33 0 S is located about 2.6 km away from the neo-volcanic zone and is likely influenced by intra-plate volcanism. The Dodo field at 18 20 0 S is located at the center of the axial valley floor, where a basaltic sheet-lava flow buries the seafloor. The lava morphology and the existence of an adjacent large off-axis seamount support the idea that excess melt is supplied in this segment. The anomalous magmatism is likely influenced by mantle plume components or by a large-offset transform fault just north of the segment. The large diversity found in the four hydrothermal fields along the CIR provides important insights on the tectonic control of global hydrothermal systems.

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Section: Rodriguez Triple Junction (Rtj) Areamentioning

confidence: 99%

Tectonic Background of Four Hydrothermal Fields Along the Central Indian Ridge

Okino

Nakamura

Sato

2014

Subseafloor Biosphere Linked to Hydrothermal Systems

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“…Theoretical models [e.g., Sparks et al, 1993] and observational geophysics [Kuo and Forsyth, 1988;Lin et al, 1990; Tolstoy et al, 1993] indicate that the least magmatic portions of slow spreading ridge segments are at segment ends where the ocean crust tends to be thin, the lithosphere is thick, and brittle deformation and fault throw are maximized [Shaw and Lin, 1993;Escartfn et al, 1997a]. Crustal morphology, gravity, and seafloor sampling also show that there is a consistent, strong asymmetry between inside-corner (IC) and outside-corner (OC) tectonic settings across the rift axis near segment ends [Tucholke and Lin, 1994].…”

Section: Geological Backgroundmentioning

confidence: 99%

Megamullions and mullion structure defining oceanic metamorphic core complexes on the Mid‐Atlantic Ridge

Tucholke¹,

Lin²,

Kleinrock³

1998

J. Geophys. Res.

497

539

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Abstract. In a study of geological and geophysical data from the Mid-Atlantic Ridge, we have identified 17 large, domed edifices (megamullions) that have surfaces corrugated by distinctive mullion structure and that are developed within inside-corner tectonic settings at ends of spreading segments. The edifices have elevated residual gravity anomalies, and limited sampling has recovered gabbros and serpentinites, suggesting that they expose extensive cross sections of the oceanic crust and upper mantle. Oceanic megamullions are comparable to continental metamorphic core complexes in scale and structure, and they may originate by similar processes. The megamullions are interpreted to be rotated footwall blocks of low-angle detachment faults, and they provide the best evidence to date for the common development and longevity (-1-2 m.y.) of such faults in ocean crust. Prolonged slip on a detachment fault probably occurs when a spreading segment experiences a lengthy phase of relatively amagmatic extension. During these periods it is easier to maintain slip on an existing fault at the segment end than it is to break a new fault in the strong rift-valley lithosphere; slip on the detachment fault probably is facilitated by fault weakening related to deep lithospheric changes in deformation mechanism and mantle serpentinization. At the segment center, minor, episodic magmatism may continue to weaken the axial lithosphere and thus sustain inward jumping of faults. A detachment fault will be terminated when magmatism becomes robust enough to reach the segment end, weaken the axial lithosphere, and promote inward fault jumps there. This mechanism may be generally important in controlling the longevity of normal faults at segment ends and thus in accounting for variable and intermittent development of inside-corner highs.

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“…To facilitate the observation of variations in crustal structure along the ridge axis, the free-air anomalies were corrected for the gravity effects of seafloor topography and relief on the crust-mantle boundary assuming a constant crustal thickness and a constant density crust yielding mantle Bouguer anomalies (MBA) [Kuo and Forsyth, 1988 Figure 2d for location), show strong differences in amplitude for both data sets, but the great majority of the points fall along a straight line with a slope close to one, in the 95 These results suggest that we could use the MBA computed from satellite data to an analysis of the along axis variation in gravity along the MAR, and these results allow us to investigate variations at wavelengths greater than those possible using individual surveys. …”

Section: Gravity Datamentioning

confidence: 99%

A systematic analysis of the Mid‐Atlantic Ridge morphology and gravity between 15°N and 40°N: Constraints of the thermal structure

Thibaud¹,

Gente²,

Maia³

1998

J. Geophys. Res.

105

163

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(2) "colder segments" which present a rough axial morphology with a deep, wide and well-defined rift valley, a low AMBA and a small length. For "hotter segments" the formation of the abyssal hills is mainly due to a magmato-tectonic cycle over periods of 0.3 to 1 Myr, whereas on "colder segments" the axial morphology is mainly controlled by a tectonic rift valley formation. We propose that these different segment types correspond to a temporal evolution of the rift valley morphology over periods of several million years.

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Gravity anomalies of the ridge-transform system in the South Atlantic between 31 and 34.5� S: Upwelling centers and variations in crustal thickness

Cited by 385 publications

References 42 publications

Tectonic Background of Four Hydrothermal Fields Along the Central Indian Ridge

Tectonic Background of Four Hydrothermal Fields Along the Central Indian Ridge

Megamullions and mullion structure defining oceanic metamorphic core complexes on the Mid‐Atlantic Ridge

A systematic analysis of the Mid‐Atlantic Ridge morphology and gravity between 15°N and 40°N: Constraints of the thermal structure

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