Structural Geology and Tectonics Flashcards

What does the term 'vergence' describe in fold analysis?

Answer: The direction toward which a fold or thrust is overturned or displaced

Vergence indicates the direction of tectonic transport or overturning, typically toward the foreland in fold-and-thrust belts.

Which seismic discontinuity separates the mantle from the outer core?

Answer: Gutenberg discontinuity

The Gutenberg discontinuity at ~2,900 km depth marks the core-mantle boundary where P-wave velocity drops sharply.

Slickensides on a fault surface provide information about what?

Answer: Direction and sense of slip

Slickensides are polished striations on fault surfaces that record the direction and often the sense of most recent slip.

An ophiolite sequence, from bottom to top, begins with which unit?

Answer: Ultramafic peridotite

A complete ophiolite sequence begins with ultramafic peridotite (mantle rock) at the base, overlain by gabbro, sheeted dikes, pillow basalts, and sediments.

Isostasy explains which geological observation?

Answer: Mountain roots extend deep into the mantle to achieve gravitational equilibrium

Isostasy describes how crustal blocks 'float' on the mantle; mountain belts have deep crustal roots to compensate for their elevated topography.

What type of metamorphic foliation forms by rotation and alignment of platy minerals perpendicular to the maximum compressive stress?

Answer: Slaty cleavage

Slaty cleavage forms when phyllosilicate minerals rotate and recrystallize perpendicular to σ1, producing a smooth planar fabric.

In a strike-slip fault, which term describes the block that moves toward the right when you face the fault?

Answer: Dextral fault

A dextral (right-lateral) strike-slip fault causes the block on the opposite side to appear to move to the right when facing the fault.