![]() ![]() The kinematic evolution may be related initially to changes in wedge strength, followed by response to overthickening of the wedge in an unbuttressed, obliquely convergent setting. The structures are consistent with orogen-normal shortening and vertical thickening followed by vertical thinning and along-strike extension. Sustained HP-LT conditions are possible only if structures formed in an accretionary prism during active subduction, which suggests that these brittle structures record internal wedge deformation at depth and early during uplift of the San Juan nappes. The presence of similar structures elsewhere indicates that the brittle structural sequence is typical of the San Juan nappes. High-pressure, low-temperature (HP-LT) minerals constrain the conditions for brittle deformation to ≥20 km and <250 ☌. ![]() Aragonite-bearing veins are associated with thrust and normal faults, but only rarely with strike-slip faults. After formation of regional ductile flattening and shear-related fabrics, the area was crosscut by brittle structures including: (1) southwest-vergent thrusts, (2) extension veins and normal faults related to northwest-southeast extension, and (3) conjugate strike-slip structures that record northwest-southeast extension and northeast-southwest shortening. Structural analysis of the Lopez Structural Complex, a major Late Cretaceous terrane-bounding fault zone in the San Juan thrust system, reveals a sequence of events that provides insight into accretionary wedge mechanics and regional tectonics.
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