TACONIC PLATE KINEMATICS AS REVEALED BY FOREDEEP STRATIGRAPHY.APP ALACmAN OROGEN
Abstract. Destruction of the Ordovician passive margin of eastern North America is recorded by an upward deepening succession of carbonates, shales, and flysch. A compilation of the age of shelf drowning (carbonate-to-shale transition) reveals the degree to which orogeny was diachronous both across...
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| Language: | English |
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| Online Access: | http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.588.6954 http://alaska.usgs.gov/staff/geology/bradley/pubs/1989_Taconic_plate_kinematics.pdf |
| Summary: | Abstract. Destruction of the Ordovician passive margin of eastern North America is recorded by an upward deepening succession of carbonates, shales, and flysch. A compilation of the age of shelf drowning (carbonate-to-shale transition) reveals the degree to which orogeny was diachronous both across and along strike. Shelf drowning occurred fIrSt at the northern end of the orogen in Newfoundland, then at the southern end of the orogen in Georgia, and fmally in Quebec. Diachronism is attributed to oblique collision between an irregular passive margin, that had a deep embayment in Quebec, and at least one east dipping subduction complex. The rate of plate convergence during collision is estimated at 1 to 2 cm/yr, and the minimum width of the ocean that closed is estimated at 500 to 900 kin. Far-traveled deepwater sequences in the thrust belt contain anomalously old Taconic flysch, related to early arrival of the continental slope/rise at a west advancing trench then located far to the east The drowning isochron map provides a new basis for estimating tectonic transport distances of four of these allochthons (about 165 to, 450 kin), results not readily obtained by conventional structural analysis. IN1RODUCflON Reconstruction ofpre-Jurassic plate motions is hindered both by the fragmentary nature of the rock record and by the complexity of plate tectonics. One approach to this vast problem is the construction of global continental drift maps, which are based largely on paleomagnetism, biogeography |
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