georefid:2004-015870SEDIS Publication Catalogue

ana.macario@awi.de

http://sedis.iodp.org/pub-catalogue/informationpointOfContact2011-06-23T00:00:00Zhttp://sedis.iodp.org/pub-catalogue/index.php?id=2004-0158702002-01-01publicationgeorefid:2004-015870Harvey, P. K.University of Leicester, Department of Geology, Leicester, United KingdomauthorBrewer, T. S.Lamont-Doherty Earth Observatory, United StatesauthorGoldberg, D.authorHaggas, S.authorIturrino, G.authorAmerican Association of Petroleum Geologists, Tulsa, OK, United StatespublisherdocumentHardcopyIn: Lovell, Mike (editor), Parkinson, Neil (editor), Geological applications of well logs13199-211The structure and architecture of the oceanic crust, which underlies 70% of the earth's surface, are still virtually unknown. Slices of assumed oceanic crust obducted above sea level (ophiolites) provide a three-layer model for the oceanic crust, comprising a volcanic sequence (seismic Layers 2A/2B) underlain by sheeted dikes (seismic Layer 2C) that are underlain by gabbros (seismic Layer 3). The last are considered to constitute the frozen magma chambers from which the overlying basaltic sequence was derived. Beneath Layer 3, the model shows peridotites of the upper mantle, which represent the host from which the entire overlying sequence was derived by partial melting. We can validate this ophiolite model and understand the variation in crustal architecture only by drilling and studying active oceanic crust. In the past 20 years, the Deep Sea Drilling Program (DSDP) and Ocean Drilling Program (ODP) have drilled a few boreholes, with these objectives. Despite such efforts, no boreholes have penetrated the complete in-situ and assumed oceanic crustal sequence. Through studies of the few boreholes available, drilling has provided a wealth of information about the detailed lithologic architecture and its relationship to the gross permeability structure of active oceanic crust. With very poor core recoveries in basement holes (commonly less than 20%), much of the detailed information about the geologic sequence and physical properties can be derived only from wireline logs. This paper reviews the role of logging in the study of the oceanic basement, through discussion of these key boreholes where parts of the assumed oceanic model are represented. Holes 396A, 504B, and 896A provide a picture of volcanic layers 2A/2B at slow-and intermediate-spreading ridges. Hole 504B is the only significant section though Layer 2C and the seismic Layer 2/3 boundary, and Hole 735B provides an important section through Layer 3.completedSolid-earth geophysicsApplied geophysicsbasaltsboreholescorescrustDeep Sea Drilling ProjectdrillingDSDP Site 396DSDP Site 504gabbrosgeophysical methodsgeophysical surveysigneous rocksIPODLeg 148Ocean Drilling Programocean floorsoceanic crustODP Site 735ODP Site 896ophioliteperidotitesphysical propertiesplutonic rocksseismic methodsseismic stratigraphystratigraphic unitssurveysultramaficsvelocityvolcanic rockswell-loggingurn:org.iodp:exp:148urnlargerWorkCitationcampaignurn:org.iodp:exp:111:site:504urnlargerWorkCitationstudyurn:org.iodp:exp:111urnlargerWorkCitationcampaignurn:org.iodp:exp:137:site:504urnlargerWorkCitationstudyurn:org.iodp:exp:137urnlargerWorkCitationcampaignurn:org.iodp:exp:140:site:504urnlargerWorkCitationstudyurn:org.iodp:exp:140urnlargerWorkCitationcampaignurn:org.iodp:exp:148:site:504urnlargerWorkCitationstudyurn:org.iodp:exp:148urnlargerWorkCitationcampaignurn:org.iodp:exp:118:site:735urnlargerWorkCitationstudyurn:org.iodp:exp:118urnlargerWorkCitationcampaignurn:org.iodp:exp:176:site:735urnlargerWorkCitationstudyurn:org.iodp:exp:176urnlargerWorkCitationcampaignurn:org.iodp:exp:148:site:896urnlargerWorkCitationstudyurn:org.iodp:exp:148urnlargerWorkCitationcampaignEnglishgeoscientificInformation-83.435757.1618-32.432722.5853