| Summary: | Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 2001. CDROM contains entire thesis in PDF format. CDROM copy of thesis held by MIT Institute Archives only. Includes bibliographical references. This thesis addresses the complexity of both syn- and post-orogenic extension in the overriding plate during Caledonian continental collision through field and laboratory investigations in the central East Greenland Caledonides. During the course of this work, attempts were made to answer some of the outstanding regional and local questions in East Greenland geology. Structural, U-Pb and ⁴⁰Ar/³⁹Ar geochronologic, petrographic and thermobarometric data were combined to constrain and reconstruct a portion of the tectonic history of this orogen. Most extension was accommodated along a system of orogen-parallel, N-S striking normal faults known as the Fjord Region Detachment (FRD) system. The FRD system comprises two temporally distinct, but overlapping, splays just south of 73⁰ N. The lowermost splay is called the Hogedal detachment was active from ca. 417 to 380 Ma, and was active for a second time as recently as ca. 357 Ma. The uppermost splay is the Tindern detachment. This fault was active from ca. 425-423 Ma, exhuming material at rates as fast as 6.5 mm/year. Continued extension in the hanging-wall of this fault accounts for additional denudation at much slower rates over a 25 my time-period. In-between activity on these faults, there is evidence to suggest that middle-crustal thickening continued to occur. Thus, the East Greenland Caledonides preserve evidence for crustal thickening (minimum -16 km) and orogen parallel shear, followed by rapid upper-middle crustal thinning (-13 km), followed by coeval middle-crustal thickening (unknown amount) and upper-crustal thinning (5 km), and ending with crustal collapse (-16 km thinning). (cont.) This is the first time that an alternation between thrusting and normal faulting has been observed in an ...
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