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Tectonic, magmatic, hydrothermal and biological segmentation of mid-ocean ridges
TECTONOPHYSICS II
ELSEVIER
Tectonophysics 284 (1998) 175-177
Book Review Tectonic, Magmatic, Hydrothermal and Biological Segmentation of Mid-Ocean Ridges, by C.J. MacLeod, P.A. Tyler and C.L. Walker (Editors). Geological Society Special Publication No. 118, The Geological Society, London, UK, 1996. Hardbound, 258 pp. Price: £ 67.00 or U.S. $ 108.00. ISBN 1-897799-72-1. Solids loaded to failure in very heterogeneous stress fields often produce discontinuous fractures within single planes of observation. Materials scientists refer to this type of fracture behavior as mixed mode failure: a recognition that crack growth has both a tensile and a significant shear failure component. Newly formed oceanic crust of the mid-ocean ridges, of course, is such a 'solid', and the off-set planform geomorphology of the ridge crests is produced, in part, by discontinuous fractures providing the piecewise accommodation [via local resolution] to the heterogeneous ridge stress states. Part of this ridge stress field is external and tectonic: a lateral drag along the base of the new crust imparted by subhorizontally flowing asthenosphere. And part of the loading is internal and magmatic: upward and outward pressures exerted by picritic magmas within deep horizons of neutral buoyancy and the pressures exerted on the walls of newly formed vertical fractures by dike-forming laterally directed magma injections along the shallow horizon of neutral buoyancy. Together, both the tectonic and magmatic loading deform, fracture, and rearrange the new crust in ways that produce much of the observed segmentation. If the mid-ocean ridge magmatic system is characterized by segmented axis-parallel fracturing, then so too must the hydrothermal systems be similarly arranged along with the biological communities that are nourished within and above them. This volume on the geologic, geophysical, hy-
drothermal and biological aspects of segmentation comprises fifteen papers, and is an outgrowth of a meeting convened at Burlington House, London, by Lindsay Parson. The segmentation theme is a worthy focus for the organization of the book, and the inclusion of the biological section pleasantly compliments the geological and hydrothermal sections. J.C. Sempere, B.P. West and L. Geli, in "The Southeast Indian Ridge between 127° and 132°40' E, use SeaMarclI side-scan sonar to map the bathymetry of the Southeast Indian Ridge, placing emphasis on the 127 and 131 degrees East propagating ridge segments, and the morphology of the Australian-Antarctic Discordance. P. Blondel, in "Segmentation of the Mid-Atlantic Ridge south of the Azores, based on acoustic classification of TOBI data", treats towed ocean bottom instrument (TOBI) surveys of the Mid-Atlantic Ridge, just south of the Azores triple junction. The total information on the TOBI images is then related to the amount of returned acoustic energy, and has been statistically processed to extract yet additional information. E. McAllister and J.R. Cann, in "Initiation and evolution of boundary wall faults along the Mid-Atlantic Ridge, 25-29°N '', have used the results of TOBI surveys conducted between the Kane and Atlantis fracture zones to reconstruct the complex geometries of boundary wall faulting. Acoustic images paired with interpretive geometric sketch maps were then used to examine aspects of the faulting process that reveal sinuous, anastomosing fractures in various states of overlap and linkage. Low levels of volcanism throughout the study area enhanced tectonic features that were otherwise obscured. The developed model of boundary wall faulting compares the faulting kinematics to the sequential elevation of escalator steps as the sea floor spreading process continues. S. Allerton, R.C. Searle and B.J. Murton,
0040-1951/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved.
176
Book Review/ Tectonophysics 284 (1998) 175-177
in "Baythymetric segmentation and faulting on the Mid-Atlantic Ridge, 24°00'N to 24°40 ''', also studied and discussed the relationship between valley-wall faulting and bathymetry. K.A. Lawson, R.C. Searle and J.A. Pearce in "Detailed volcanic geology of the MARNOK area, Mid-Atlantic Ridge north of Kane transform", describe the geomorphology of the median valley floor, and document its structural features ]fractures, seamounts, small ridges] with TOBI sidescan sonar images. Electron microprobe analyses of ridge glasses reveals an intriguing along-axis variation in MgO content: high (--~8.50 wt.%) for segment centers, and low (-v6.5 wt.%) for segment ends. This type of geochemical variation is very consistent with relatively low pressure (<200 MPa) differentiation processes taking place within the shallow (tholeiitic) horizon of neutral buoyancy, and with the lateral injection of magma pulses along this level. These fundamental controls of mid-ocean ridge magma transport and storage have not been discussed by these authors, and thus represent a missed opportunity to understand the coupling between relatively isobaric intrusion, cooling and crystallization on the one hand, and the concomitant variations in residual melt chemistry on the other. R. Batiza, in "Magmatic segmentation of mid-ocean ridges: A review", discusses the segmentation continuum from the perspective of tectonics, magmatic processes and alongstrike variations in major element, trace element, and isotopic abundances, in light of the process of lateral intrusion at depth. C.J. Robinson, R.S. White, M.J. Bickle and T.A. Minshull, in "Restricted melting under the very slow spreading Southeast Indian Ridge", use major element chemistry from basaltic glasses to infer reduced degrees of partial melting beneath this very slow spreading ridge. S.J. Edwards, T.J. Falloon, J. Malpas and R.B. Pedersen, in "A review of the petrology of harzburgites at Hess Deep and Garrett Deep: Implications for mantle processes beneath segments of the East Pacific Rise", use texture, mineralogy, and major element chemistry of harzburgites to discuss the process of partial melt generation in upwelling mantle. R.M. Haymon, in "The response of ridge-crest hydrothermal systems to segmented episodic magma supply", discusses the importance of dike intrusion in the stimulation of hydrothermal circulation by both providing new sources of crustal heat, as well as by providing new permeable path-
ways above the dike. C.R. German, L.M. Parson, B.J. Murton and H.D. Needham, in "Hydrothermal activity and ridge segmentation on the Mid-Atlantic Ridge: A tale of two hot-spots", discuss segmentation along the Reykjanes Ridge, and use TOBI data to discuss the relationships between tectonism, magmatism, and hydrothermal activity. C.J. MacLeod and C.E. Manning, in "Influence of axial segmentation on hydrothermal circulation at fast-spreading ridges: insights from Hess Deep", study the nature of fluid-rock interactions in the root regions of a fast-spreading ridge hydrothermal system. V.V. Zaykov, V.V. Maslennikov, E.V. Zaykova and R.J Herrington present a discussion on the "Hydrothermal activity and segmentation in the Magnitogorsk-West Mugodjarian zone of the margins of the Urals paleo-ocean", that reviews the geology of basalt and basalt-rhyolite complexes of the Urals Paleozoic island arc and inter-arc, and links the development of massive sulfide deposits to the substructure of ancient hydrothermal vents. E.C. Southward, V. Tunnicliffe, M.B. Black, D.R. Dixon and L.R.J. Dixon, in "Ocean-ridge segmentation and vent tubeworms (Vestimentifera) in the NE Pacific", explore the geologic and geomorphic controls on the distribution of intra-species variations of Ridgeia piscesae and Lamellibrachia barhami along the Juan de Fuca and Gorda ridges, and the Cascadia subduction zone. Both rapid colonization (by R. piscesae) and attenuation have been observed, and correlate with close proximity and significant offset, respectively, between adjacent communities. Vestimentiferans appear to have significant dispersal and adaptation capability, and only encounter barriers to colonization at the "-~1000 km length scale of segmentation. V. Tunnicliffe, C.M.R. Fowler and A.G. McArthur discuss in "Plate tectonic history and hot vent biogeography" that, since ridge vent communities are also tied to the margins of plates, scientific avenues are then opened for looking back to past plate margins and their biological communities, as well as making predictions of the composition of vent communities in unexplored areas. Finally, E.G. Nisbet and C.M.R. Fowler, in "Hydrothermal imprint on life: Did heatshock proteins, metalloproteins and photosynthesis begin around hydrothermal vents?" hypothesize that ancient hydrothermal environments played key roles in the development of early life on Earth.
Book Review / Tectonophysics 284 (1998) 175-177
The book has been produced in a 17 by 25 cm format. The paperstock is of good quality, and pages are sewn in signatures, so that the book opens fiat for ease of reading. There are 129 black and white figures, of which 34 are half-tone plates, mostly illustrating marine bathymetry and volcanic landforms. Three colour plates are included. There is a combined subject and geographic index. [An author index would have enhanced accessibility]. The cover includes a colour image of the bathymetry of the Mid-Atlantic Ridge compiled using Sea Beam data. The volume abounds with half tone plates of TOBI marine bathymetry, and both the authors and the
177
publisher/printer have worked together to produce high resolution images. "Tectonic, Magmatic, Hydrothermal and Biological Segmentation of Mid-Ocean Ridges" is a book that geologists and biologists with an active interest in the mid-ocean ridge environment will want to have access to, and that libraries should consider acquiring for their earth science section. MICHAEL P. RYAN (Reston, VA, USA) PII S 0 0 4 0 - 1 9 5 1 ( 9 7 ) 0 0 1 7 4 - 1
ELSEVIER
Tectonophysics 284 (1998) 175-177
Book Review Tectonic, Magmatic, Hydrothermal and Biological Segmentation of Mid-Ocean Ridges, by C.J. MacLeod, P.A. Tyler and C.L. Walker (Editors). Geological Society Special Publication No. 118, The Geological Society, London, UK, 1996. Hardbound, 258 pp. Price: £ 67.00 or U.S. $ 108.00. ISBN 1-897799-72-1. Solids loaded to failure in very heterogeneous stress fields often produce discontinuous fractures within single planes of observation. Materials scientists refer to this type of fracture behavior as mixed mode failure: a recognition that crack growth has both a tensile and a significant shear failure component. Newly formed oceanic crust of the mid-ocean ridges, of course, is such a 'solid', and the off-set planform geomorphology of the ridge crests is produced, in part, by discontinuous fractures providing the piecewise accommodation [via local resolution] to the heterogeneous ridge stress states. Part of this ridge stress field is external and tectonic: a lateral drag along the base of the new crust imparted by subhorizontally flowing asthenosphere. And part of the loading is internal and magmatic: upward and outward pressures exerted by picritic magmas within deep horizons of neutral buoyancy and the pressures exerted on the walls of newly formed vertical fractures by dike-forming laterally directed magma injections along the shallow horizon of neutral buoyancy. Together, both the tectonic and magmatic loading deform, fracture, and rearrange the new crust in ways that produce much of the observed segmentation. If the mid-ocean ridge magmatic system is characterized by segmented axis-parallel fracturing, then so too must the hydrothermal systems be similarly arranged along with the biological communities that are nourished within and above them. This volume on the geologic, geophysical, hy-
drothermal and biological aspects of segmentation comprises fifteen papers, and is an outgrowth of a meeting convened at Burlington House, London, by Lindsay Parson. The segmentation theme is a worthy focus for the organization of the book, and the inclusion of the biological section pleasantly compliments the geological and hydrothermal sections. J.C. Sempere, B.P. West and L. Geli, in "The Southeast Indian Ridge between 127° and 132°40' E, use SeaMarclI side-scan sonar to map the bathymetry of the Southeast Indian Ridge, placing emphasis on the 127 and 131 degrees East propagating ridge segments, and the morphology of the Australian-Antarctic Discordance. P. Blondel, in "Segmentation of the Mid-Atlantic Ridge south of the Azores, based on acoustic classification of TOBI data", treats towed ocean bottom instrument (TOBI) surveys of the Mid-Atlantic Ridge, just south of the Azores triple junction. The total information on the TOBI images is then related to the amount of returned acoustic energy, and has been statistically processed to extract yet additional information. E. McAllister and J.R. Cann, in "Initiation and evolution of boundary wall faults along the Mid-Atlantic Ridge, 25-29°N '', have used the results of TOBI surveys conducted between the Kane and Atlantis fracture zones to reconstruct the complex geometries of boundary wall faulting. Acoustic images paired with interpretive geometric sketch maps were then used to examine aspects of the faulting process that reveal sinuous, anastomosing fractures in various states of overlap and linkage. Low levels of volcanism throughout the study area enhanced tectonic features that were otherwise obscured. The developed model of boundary wall faulting compares the faulting kinematics to the sequential elevation of escalator steps as the sea floor spreading process continues. S. Allerton, R.C. Searle and B.J. Murton,
0040-1951/98/$19.00 © 1998 Elsevier Science B.V. All rights reserved.
176
Book Review/ Tectonophysics 284 (1998) 175-177
in "Baythymetric segmentation and faulting on the Mid-Atlantic Ridge, 24°00'N to 24°40 ''', also studied and discussed the relationship between valley-wall faulting and bathymetry. K.A. Lawson, R.C. Searle and J.A. Pearce in "Detailed volcanic geology of the MARNOK area, Mid-Atlantic Ridge north of Kane transform", describe the geomorphology of the median valley floor, and document its structural features ]fractures, seamounts, small ridges] with TOBI sidescan sonar images. Electron microprobe analyses of ridge glasses reveals an intriguing along-axis variation in MgO content: high (--~8.50 wt.%) for segment centers, and low (-v6.5 wt.%) for segment ends. This type of geochemical variation is very consistent with relatively low pressure (<200 MPa) differentiation processes taking place within the shallow (tholeiitic) horizon of neutral buoyancy, and with the lateral injection of magma pulses along this level. These fundamental controls of mid-ocean ridge magma transport and storage have not been discussed by these authors, and thus represent a missed opportunity to understand the coupling between relatively isobaric intrusion, cooling and crystallization on the one hand, and the concomitant variations in residual melt chemistry on the other. R. Batiza, in "Magmatic segmentation of mid-ocean ridges: A review", discusses the segmentation continuum from the perspective of tectonics, magmatic processes and alongstrike variations in major element, trace element, and isotopic abundances, in light of the process of lateral intrusion at depth. C.J. Robinson, R.S. White, M.J. Bickle and T.A. Minshull, in "Restricted melting under the very slow spreading Southeast Indian Ridge", use major element chemistry from basaltic glasses to infer reduced degrees of partial melting beneath this very slow spreading ridge. S.J. Edwards, T.J. Falloon, J. Malpas and R.B. Pedersen, in "A review of the petrology of harzburgites at Hess Deep and Garrett Deep: Implications for mantle processes beneath segments of the East Pacific Rise", use texture, mineralogy, and major element chemistry of harzburgites to discuss the process of partial melt generation in upwelling mantle. R.M. Haymon, in "The response of ridge-crest hydrothermal systems to segmented episodic magma supply", discusses the importance of dike intrusion in the stimulation of hydrothermal circulation by both providing new sources of crustal heat, as well as by providing new permeable path-
ways above the dike. C.R. German, L.M. Parson, B.J. Murton and H.D. Needham, in "Hydrothermal activity and ridge segmentation on the Mid-Atlantic Ridge: A tale of two hot-spots", discuss segmentation along the Reykjanes Ridge, and use TOBI data to discuss the relationships between tectonism, magmatism, and hydrothermal activity. C.J. MacLeod and C.E. Manning, in "Influence of axial segmentation on hydrothermal circulation at fast-spreading ridges: insights from Hess Deep", study the nature of fluid-rock interactions in the root regions of a fast-spreading ridge hydrothermal system. V.V. Zaykov, V.V. Maslennikov, E.V. Zaykova and R.J Herrington present a discussion on the "Hydrothermal activity and segmentation in the Magnitogorsk-West Mugodjarian zone of the margins of the Urals paleo-ocean", that reviews the geology of basalt and basalt-rhyolite complexes of the Urals Paleozoic island arc and inter-arc, and links the development of massive sulfide deposits to the substructure of ancient hydrothermal vents. E.C. Southward, V. Tunnicliffe, M.B. Black, D.R. Dixon and L.R.J. Dixon, in "Ocean-ridge segmentation and vent tubeworms (Vestimentifera) in the NE Pacific", explore the geologic and geomorphic controls on the distribution of intra-species variations of Ridgeia piscesae and Lamellibrachia barhami along the Juan de Fuca and Gorda ridges, and the Cascadia subduction zone. Both rapid colonization (by R. piscesae) and attenuation have been observed, and correlate with close proximity and significant offset, respectively, between adjacent communities. Vestimentiferans appear to have significant dispersal and adaptation capability, and only encounter barriers to colonization at the "-~1000 km length scale of segmentation. V. Tunnicliffe, C.M.R. Fowler and A.G. McArthur discuss in "Plate tectonic history and hot vent biogeography" that, since ridge vent communities are also tied to the margins of plates, scientific avenues are then opened for looking back to past plate margins and their biological communities, as well as making predictions of the composition of vent communities in unexplored areas. Finally, E.G. Nisbet and C.M.R. Fowler, in "Hydrothermal imprint on life: Did heatshock proteins, metalloproteins and photosynthesis begin around hydrothermal vents?" hypothesize that ancient hydrothermal environments played key roles in the development of early life on Earth.
Book Review / Tectonophysics 284 (1998) 175-177
The book has been produced in a 17 by 25 cm format. The paperstock is of good quality, and pages are sewn in signatures, so that the book opens fiat for ease of reading. There are 129 black and white figures, of which 34 are half-tone plates, mostly illustrating marine bathymetry and volcanic landforms. Three colour plates are included. There is a combined subject and geographic index. [An author index would have enhanced accessibility]. The cover includes a colour image of the bathymetry of the Mid-Atlantic Ridge compiled using Sea Beam data. The volume abounds with half tone plates of TOBI marine bathymetry, and both the authors and the
177
publisher/printer have worked together to produce high resolution images. "Tectonic, Magmatic, Hydrothermal and Biological Segmentation of Mid-Ocean Ridges" is a book that geologists and biologists with an active interest in the mid-ocean ridge environment will want to have access to, and that libraries should consider acquiring for their earth science section. MICHAEL P. RYAN (Reston, VA, USA) PII S 0 0 4 0 - 1 9 5 1 ( 9 7 ) 0 0 1 7 4 - 1