The formation and rupturing of continents
- 出版日期：2004.
- 页数：1 v. :
- 第一责任说明：Donna J. Shillington.
- 分类号：a242.1
- ISBN：0496870459(ebk.) :
MARC全文
02h0029443 20120614111156.0 cr un||||||||| 120614s2004 xx ||||f|||d||||||||eng | 3139904 0496870459(ebk.) : CNY371.35 NGL NGL NGL a242.1 Shillington, Donna J. The formation and rupturing of continents [electronic resource] : seismic studies of the Aleutian island arc and the Newfoundland nonvolcanic rifted margin / Donna J. Shillington. 2004. 1 v. : digital, PDF file. Adviser: Holbrook, W. Steven. Thesis (Ph.D.)--University of Wyoming, 2004. Island arcs and rifted margins embody the creation and destruction of continental and oceanic crust. Subduction zones consume downgoing oceanic crust, and island arcs are the manifestation of the associated magmatism. At the other end of the spectrum, rifted margins record continental breakup and the inception of seafloor spreading in the resulting new ocean basins. Although island arc magmatism constitutes a source of significant magmatic addition and might serve as a primary continental-crustal building block, debate continues regarding the composition of the middle and lower crust of island arcs and their relationship to the compositions of lavas erupted at the surface. Crustal velocity structure along the central Aleutian island arc suggests that the middle crust is composed of plutons with andesitic to basaltic compositions, and the lower crust is composed of ultramafic-mafic cumulates. The bulk composition of this island arc estimated from velocity is significantly more mafic than average continental crust, thus requiring modifications to be a suitable building block for continental crust. Additionally, variations in crustal velocity show a first-order correspondence to trends in the major element geochemistry of lavas in the central Aleutians. Nonvolcanic rifted margins form by continental breakup accompanied by little synrift magmatism and thus are ideal places to image rifting structures that would otherwise be obscured by synrift magmatism. On many nonvolcanic margins, crust of uncertain affinity has been observed between unambiguous continental and oceanic crust. On the Iberia margin, "transitional" crust is denuded, subcontinental mantle, exposed during the final stages of rifting. Delineating crustal structure of Iberias conjugate margin, Newfoundland, can allow us to determine margin symmetry, which can be used to understand continental rupture and initial seafloor spreading. Pretack depth migrations of multichannel seismic reflection data on the Newfoundland margin, together with the work of Van Avendonk et al. [2003] and Nunes [2002], suggest that "transitional" crust on the Newfoundland margin is oceanic, which implies significant margin asymmetry and a complicated period of seafloor spreading following continental rupture. The "featureless" appearance of "transitional" crust on Newfoundland might be due to poor signal penetration beneath postrift sills encountered during Ocean Drilling Program Leg 210. Sea-floor spreading ; Subduction zones Newfoundland and Labrador. ; Alaska ; Aleutian Islands. Electronic dissertations. aeBook. aCN bNGL http://pqdt.bjzhongke.com.cn/Detail.aspx?pid=ThWa%2bO%2f1y%2fU%3d NGL Bs1503 rCNY371.35 ; h1 bs1204