Proceedings of the Ocean Drilling Program Volume 106/109 Scientific Results: Mid-Atlantic Ridge, Sites 395, 648–649, 669–670
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1990
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| author | Detrick, R. Honnorez, J. Bryan, W.B. Juteau, T. The Leg 106/109 Science Parties |
| author_facet | Detrick, R. Honnorez, J. Bryan, W.B. Juteau, T. The Leg 106/109 Science Parties |
| contents | <p>This Scientific Results volume covers Legs 106 and 109 of the cruises of the Drilling Vessel <em>JOIDES Resolution</em>, St. John's, Newfoundland, to Malaga, Spain, Sites 648–649, 27 October 1985–26 December 1985 (Leg 106) and Dakar, Senegal, to Bridgetown, Barbados, Sites 395, 648, 669, and 670, 17 April 1986–19 June 1986 (Leg 109).</p> <p>Understanding the complex and interrelated volcanic, tectonic, and hydrothermal processes occurring at oceanic spreading centers, where two thirds of the Earth's crust is created, is one of the highest priority scientific questions addressed by the Ocean Drilling Program (ODP). Although much has been learned about these spreading-center processes from detailed geological and geophysical investigations over the past decade, there are many fundamental questions regarding magma genesis, oceanic petrology, hydrothermal circulation, and crustal magnetization that can only be answered by direct sampling in deep crustal drill holes. Recent studies have shown that the accretionary zone where these geological processes are concentrated is remarkably narrow, averaging only a few kilometers in width. Thus, in order to study the formation of new oceanic lithosphere at mid-ocean ridges, drilling is required within the narrow, zero-age crust of the accretionary zone itself.</p> <p>Since Leg 37 of the Deep Sea Drilling Project (DSDP) first demonstrated the feasibility of drilling to substantial depths within the oceanic crust, numerous basement holes have been attempted on very young (< l-m.y.-old) seafloor, without notable success. In light of these problems and the importance of drilling at mid-ocean ridges, the COSOD report and the JOIDES Planning Committee recommended the development of new technology for drilling young, fresh volcanic rocks in areas with little or no sediment cover. A specially designed guidebase was constructed to provide lateral support for the drill string during bare-rock spud-in, and new drilling and coring techniques were developed for use in the hard, highly abrasive, fractured volcanic rocks found at mid-ocean ridges. It was considered essential to test and evaluate this new drilling technology early in the Ocean Drilling Program and establish one or more crustal drill holes at both fast- and slow-spreading centers. As a first step toward achieving this objective, Legs 106 and 109 were dedicated to establishing the first hole in zero-age crust in a well-studied portion of the Mid-Atlantic Ridge rift valley, south of the Kane Fracture Zone.</p> <p>Important scientific questions addressed by a drill hole in zero-age crust at a slow-spreading ridge include the following:<br>1. The composition and relative abundance of the parental magmas at a slow-spreading ridge and their relation to the "evolved" basalts erupted at the seafloor.<br>2. The variation in magma generation and crustal accretion rates in time and space and how these magmatic processes are linked to tectonic and hydrothermal activity within the rift valley.<br>3. The depth to the top of an axial magma chamber and the nature of the compositional variations within the chamber.<br>4. The effect of transforms on crustal accretion processes at a slow-spreading ridge.<br>5. The duration and extent of hydrothermal activity within the rift valley and the imprint of this activity on the alteration history of oceanic crust.<br>6. The nature of the root zone of an active hydrothermal system: the mineralogy and chemistry of vein filling and the nature and extent of alteration of adjacent basalts.<br>7. The nature of the earliest low-temperature alteration of zero-age basalts and its effects on crustal mineralogy.<br>8. The variation of crustal magnetization with depth in newly accreted crust and how it is affected by hydrothermal and tectonic processes in the rift valley.</p> <p>In addition to these specific questions, a crustal drill hole at a mid-ocean ridge offers a unique opportunity for a variety of downhole geophysical experiments and long-term monitoring of accretionary processes. This is a first step toward establishing a natural laboratory where geological processes at oceanic spreading centers can be studied using many different kinds of downhole instrumentation over an extended period of time.</p> |
| format | Recurso digital |
| id | zenodo_https___doi_org_10_5281_zenodo_18462905 |
| institution | Zenodo |
| language | |
| publishDate | 1990 |
| publisher | Zenodo |
| record_format | zenodo |
| spellingShingle | Proceedings of the Ocean Drilling Program Volume 106/109 Scientific Results: Mid-Atlantic Ridge, Sites 395, 648–649, 669–670 Detrick, R. Honnorez, J. Bryan, W.B. Juteau, T. The Leg 106/109 Science Parties Ocean Drilling Program ODP JOIDES Resolution Scientific Results Leg 106 Leg 109 Site 395 Site 648 Site 649 Site 669 Site 670 Mid-Atlantic Ridge <p>This Scientific Results volume covers Legs 106 and 109 of the cruises of the Drilling Vessel <em>JOIDES Resolution</em>, St. John's, Newfoundland, to Malaga, Spain, Sites 648–649, 27 October 1985–26 December 1985 (Leg 106) and Dakar, Senegal, to Bridgetown, Barbados, Sites 395, 648, 669, and 670, 17 April 1986–19 June 1986 (Leg 109).</p> <p>Understanding the complex and interrelated volcanic, tectonic, and hydrothermal processes occurring at oceanic spreading centers, where two thirds of the Earth's crust is created, is one of the highest priority scientific questions addressed by the Ocean Drilling Program (ODP). Although much has been learned about these spreading-center processes from detailed geological and geophysical investigations over the past decade, there are many fundamental questions regarding magma genesis, oceanic petrology, hydrothermal circulation, and crustal magnetization that can only be answered by direct sampling in deep crustal drill holes. Recent studies have shown that the accretionary zone where these geological processes are concentrated is remarkably narrow, averaging only a few kilometers in width. Thus, in order to study the formation of new oceanic lithosphere at mid-ocean ridges, drilling is required within the narrow, zero-age crust of the accretionary zone itself.</p> <p>Since Leg 37 of the Deep Sea Drilling Project (DSDP) first demonstrated the feasibility of drilling to substantial depths within the oceanic crust, numerous basement holes have been attempted on very young (< l-m.y.-old) seafloor, without notable success. In light of these problems and the importance of drilling at mid-ocean ridges, the COSOD report and the JOIDES Planning Committee recommended the development of new technology for drilling young, fresh volcanic rocks in areas with little or no sediment cover. A specially designed guidebase was constructed to provide lateral support for the drill string during bare-rock spud-in, and new drilling and coring techniques were developed for use in the hard, highly abrasive, fractured volcanic rocks found at mid-ocean ridges. It was considered essential to test and evaluate this new drilling technology early in the Ocean Drilling Program and establish one or more crustal drill holes at both fast- and slow-spreading centers. As a first step toward achieving this objective, Legs 106 and 109 were dedicated to establishing the first hole in zero-age crust in a well-studied portion of the Mid-Atlantic Ridge rift valley, south of the Kane Fracture Zone.</p> <p>Important scientific questions addressed by a drill hole in zero-age crust at a slow-spreading ridge include the following:<br>1. The composition and relative abundance of the parental magmas at a slow-spreading ridge and their relation to the "evolved" basalts erupted at the seafloor.<br>2. The variation in magma generation and crustal accretion rates in time and space and how these magmatic processes are linked to tectonic and hydrothermal activity within the rift valley.<br>3. The depth to the top of an axial magma chamber and the nature of the compositional variations within the chamber.<br>4. The effect of transforms on crustal accretion processes at a slow-spreading ridge.<br>5. The duration and extent of hydrothermal activity within the rift valley and the imprint of this activity on the alteration history of oceanic crust.<br>6. The nature of the root zone of an active hydrothermal system: the mineralogy and chemistry of vein filling and the nature and extent of alteration of adjacent basalts.<br>7. The nature of the earliest low-temperature alteration of zero-age basalts and its effects on crustal mineralogy.<br>8. The variation of crustal magnetization with depth in newly accreted crust and how it is affected by hydrothermal and tectonic processes in the rift valley.</p> <p>In addition to these specific questions, a crustal drill hole at a mid-ocean ridge offers a unique opportunity for a variety of downhole geophysical experiments and long-term monitoring of accretionary processes. This is a first step toward establishing a natural laboratory where geological processes at oceanic spreading centers can be studied using many different kinds of downhole instrumentation over an extended period of time.</p> |
| title | Proceedings of the Ocean Drilling Program Volume 106/109 Scientific Results: Mid-Atlantic Ridge, Sites 395, 648–649, 669–670 |
| topic | Ocean Drilling Program ODP JOIDES Resolution Scientific Results Leg 106 Leg 109 Site 395 Site 648 Site 649 Site 669 Site 670 Mid-Atlantic Ridge |
| url | https://doi.org/10.5281/zenodo.18462905 |