Advance of allochthonous salt sheets in passive margins and orogens
AAPG Bulletin, v. 90, no. 10 (October 2006), pp. 1535–1564
ABSTRACT
Allochthonous salt sheets advance in four ways: (1) extrusive advance,
(2) open-toed advance, (3) thrust advance, and (4) salt-wing
intrusion. These mechanisms are determined primarily by the geometry
and thickness of the roof that overlies the advancing sheet.
An extrusive sheet spreads without a roof or with a roof of negligible
mechanical strength. An open-toed sheet is partially covered by
a mechanically significant roof but has an extrusive toe. An overthrusting
sheet advances along a thrust fault at its leading edge,
carrying its roof with it. A salt wing intrudes from the flank of a
diapir into a shallower salt layer.
Extrusive, open-toed, and overthrusting salt sheets are found in
both passive margins and orogens. A sheet typically evolves through
two or more of these mechanisms. Three lineages, or evolutionary
paths, are common. Plug-fed extrusions emanate from the top of a
salt dome or salt wall. Plug-fed thrusts form the base of the hanging
wall of thrust faults that are rooted in the tops of salt domes or salt
walls. Finally, source-fed thrusts initiate as thrust faults rooted in the
autochthonous salt layer. Source-fed thrusts form the largest individual
salt sheets, some covering thousands of square kilometers.
Salt-wing intrusions form only under special circumstances, so they
are not part of the three major lineages. These intrusions are restricted
to compressionally inverted basins containing multiple salt
layers and are known only in the Zechstein salt basin.
[ 此贴被笑韵在2008-12-01 10:09重新编辑 ]
