U.S. Geological Survey Bulletin
Paul Kibler Sims · Richard W. Ojakangas · S. A. Nachatilo · S. R. Hemming · Theodore J. Bornhorst · Val W. Chandler · William J. Gregg · G. B. Morey · Gilbert N. Hanson · R. L. Bauer · Rodney C. Johnson · Warren C. Day · Scott M. McLennan
1983 оны 1-р сар · U.S. Government Printing Office
5.0star
1 шүүмжreport
Электрон ном
15
Хуудас
reportҮнэлгээ болон шүүмжийг баталгаажуулаагүй Нэмэлт мэдээлэл авах
Энэ электрон номын тухай
he Great Lakes tectonic zone (GLTZ) is a Late Archean crustal boundary (paleosuture) at least 1,200 kilometers long that juxtaposes a Late Archean greenstone-granite terrane (Wawa subprovince of Superior province) on the north and an Early to Late Archean gneiss terrane (Minnesota River Valley subprovince) on the south. Recent mapping of an exposed seg- ment in the Marquette, Michigan, area provides new data on the vergence of the structure. These data necessitate reexami- nation of the COCORP seismic-reflection profiling in central Minnesota, which has been the principal basis for past views on the vergence of the GLTZ. In the Marquette area, the GLTZ is a northwest-striking mylonite zone about 2.3 kilometers wide that is superposed on previously deformed rocks of both Archean terranes. Shear zone walls strike N. 55°-60° W., and foliation in mylonite within the GLTZ strikes (average) N. 70° W. and dips 75° SW. A stretching lineation plunges 42° in a S. 43° E. direction. Hinges of tight to open (sheath?) folds of both Z- and S-symmetries plunge parallel to the lineation. The attitude of the lineation (line of tectonic transport and X finite strain axis), together with asymmetric kinematic indicators, indicates that collision at this locality was oblique; the collision resulted in dextral- thrust shear along the boundary, northwestward vergence, and overriding of the greenstone-granite terrane by the gneiss terrane. In contrast, the seismic-reflection profiling in central Minnesota has been interpreted by several investigators to indicate that the GLTZ is a shallowly north dipping (=30°) structure, which implies southward vergence on a north-dipping subduction zone. We suggest, alternatively, that the shallow- dipping reflectors in the seismic profiles indicate lithologic contacts related to recumbent and gently inclined folds (D1), perhaps enhanced by ductile deformation zones, and that the Morris fault is indeed the GLTZ. The Morris fault strikes about N. 70° E., dips steeply southeastward, is transparent in seismic profiles, appears to be narrow, and coincides with the inferred position of the GLTZ as shown on earlier maps. The oblique collision along northwest-trending segments of the GLTZ would be expected to produce dextral transpression across a large region north of the GLTZ, and may have produced an early nappe-forming event (D1) as well as younger upright folds (D2), and as a later, more brittle event, the numerous dextral faults and conjugate sinistral faults that are widespread in the Wawa and adjacent subprovinces.
Үнэлгээ, сэтгэгдэл
5.0
1 шүүмж
Энэ электрон номыг үнэлэх
Санал бодлоо хэлнэ үү.
Унших мэдээлэл
Ухаалаг утас болон таблет
Андройд болон iPad/iPhone-д Google Ном Унших аппыг суулгана уу. Үүнийг таны бүртгэлд автоматаар синк хийх бөгөөд та хүссэн газраасаа онлайн эсвэл офлайнаар унших боломжтой.
Зөөврийн болон ердийн компьютер
Та компьютерийн веб хөтчөөр Google Play-с авсан аудио номыг сонсох боломжтой.
eReaders болон бусад төхөөрөмжүүд
Kobo Цахим ном уншигч гэх мэт e-ink төхөөрөмжүүд дээр уншихын тулд та файлыг татаад төхөөрөмж рүүгээ дамжуулах шаардлагатай болно. Файлуудаа дэмжигддэг Цахим ном уншигч руу шилжүүлэхийн тулд Тусламжийн төвийн дэлгэрэнгүй зааварчилгааг дагана уу.
