| Paired half-graben, crestal collapse graben: examples
from the early Mesozoic of eastern North America |
Abstract--Standard balanced kinematic models for the development
of half-graben with listric or kinked normal faults do not account for
the geometry of rift basin fill in eastern North America. Younger strata
within the Newark basin show a progressive decrease in dip and also progressively
onlap the basement in the hanging wall (HW) block. [Note: We no longer
subscribe to the hypothesis advocated in the remainder of the abstract.
See Schlische (1993), Tectonics, for a more current view.] Inspired by
the sandbox modeling of McClay and Ellis (1987), we hypothesize that half-graben
formation and HW block rotation are geometrically required to fill the
void which develops between HW and footwall blocks as a result of slip
on faults which shallow with depth. Strata which fill the developing half-graben
are also rotated, the oldest strata being tilted the most. The rotation
of the HW block must be accommodated elsewhere in the HW through the development
of antithetic normal faults and crestal collapse graben. According to our
hypothesis, the Pomperaug basin and associated structures are the eroded
remnants of the crestal collapse graben for the Hartford basin, the New
York Bight basin for the Newark basin, and the Farmville basin and associated
structures for the Culpeper-Danville and Deep River basins.
A consequence of the rotation of the HW block is the uplift of basement
material adjacent to the developing graben. Erosion of this uplifted basement
block explains the west-directed paleocurrents and HW block provenance
of a majority of the sediments filling the Newark basin. The lag time between
erosion of the upturned HW basement block and the filling of the half-graben
explains the onlap relationships of the sedimentary strata. This model
also allows for in-basin loading to cause adjacent compensating uplift
of the HW basement block, which seems otherwise inexplicable.
Go back to list of publications
peo87.html-- Revised: 17 Nov. 1996
Copyright © 1996 Rutgers
University
SCHLISCH@RCI.RUTGERS.EDU