| dc.contributor.author | Chain, Deping. | en_US |
| dc.date.accessioned | 2014-10-21T12:35:32Z | |
| dc.date.available | 1994 | |
| dc.date.issued | 1994 | en_US |
| dc.identifier.other | AAINN05155 | en_US |
| dc.identifier.uri | http://hdl.handle.net/10222/55014 | |
| dc.description | When continental lithosphere is stretched, it thins, subsides, and ruptures, followed by formation of a new oceanic basin between the continental margins. The processes that govern the evolution of rifted continental margins have been controversially addressed, especially in the construction of rifting models (pure or simple shear) and in the interpretation of an anomalous high-velocity lower crustal layer that is commonly observed on both (conjugate) sides. | en_US |
| dc.description | This thesis presents the first conjugate margin studies based on crustal seismic velocity structure. The study area is the Labrador Sea conjugate margins: southwestern Greenland and Labrador margins. Data include wide-angle seismic records from two 230-km-long profiles along and across the southwestern Greenland margin, and a 150-km-long profile and a 350-km-long profile along and across the Labrador margin. Coincident deep multi-channel and single-channel reflection data are used during wide-angle modeling and final interpretations. Modeling of observed gravity and magnetic data is also performed and used in the interpretations. | en_US |
| dc.description | The results indicate three distinct zones across each margin. From the continent seaward, Zone I represents thinned continental crust, Zone II the transitional crust, and Zone III the true oceanic crust. The landward end of the cross-section in Zone I represents 27-30 km thick preexisting continental crust whose middle to lower crust has velocity of 6.2-6.9 km/s and whole upper crust has velocity of 5.5-5.6 km/s. This crust is thinned gradually seaward over a distance of $\sim$100 km in Zone I on the Labrador margin while on the SW Greenland margin it is thinned sharply over a distance of only 20 km. Zone II is characterized by a distinct lower crust with a high-velocity of 7.0-7.6 km/s. This layer is 4-5 km thick, extends for a horizontal distance of 70-80 km, and is located seaward of Chron 31 on both margins. Combined interpretation for this lower crustal block favors an origin of serpentinization rather than magmatic underplating. Comparison with the seafloor spreading magnetic anomaly data suggests that true oceanic crust started to form between Chrons 27 and 31, with the first clear magnetic anomaly occurring at Chron 27. | en_US |
| dc.description | The crustal cross-sections are used as a starting point in reconstruction of the rifting history. Results suggest that the initial continental stretching started symmetrically. At a later stage of stretching, more thinning occurred at the eastern side of the rift zone, leading to a lower crustal separation near the seaward end of the continental slope on western Greenland. A composite pure and simple shear model is favored in which all the lower crust in the rift zone moves with Labrador and most of the upper crust in the rift zone moves with Greenland. Serpentinization of upper mantle materials started after the crustal separation, forming undercrusting beneath the thinned upper crust on the southwestern Greenland margin and seaward of the lower crust on the Labrador margin. This proposed model explains all the new data presented in this thesis, as well as other observations that have been controversially addressed on similar margins. | en_US |
| dc.description | Thesis (Ph.D.)--Dalhousie University (Canada), 1994. | en_US |
| dc.language | eng | en_US |
| dc.publisher | Dalhousie University | en_US |
| dc.publisher | | en_US |
| dc.subject | Geophysics. | en_US |
| dc.title | The conjugate margins of the Labrador Sea: Crustal structure from refraction profiles and their tectonic implications. | en_US |
| dc.type | text | en_US |
| dc.contributor.degree | Ph.D. | en_US |
