Geology Definitions

Question 0

Terrane

Answer 0

A terrane in geology is a shorthand term for a tectonostratigraphic terrane, which is a fragment of crustal material formed on, or broken off from, one tectonic plate and accreted or “sutured” to crust lying on another plate. The crustal block or fragment preserves its own distinctive geologic history, which is different from that of the surrounding areas – hence the term “exotic” terrane. The suture zone between a terrane and the crust it attaches to is usually identifiable as a fault.

Question 1

Accretion

Answer 1

Accretion is a process by which material is added to a tectonic plate or a landmass. This material may be sediment, volcanic arcs, seamounts or other igneous features.

Question 2

Greenstone

Answer 2

Greenstone belts are zones of variably metamorphosed mafic to ultramafic volcanic sequences with associated sedimentary rocks that occur within Archaean and Proterozoic cratons between granite and gneiss bodies.

Question 3

Rhyolite

Answer 3

The fine-grained volcanic or extrusive rocks that are equivalent in composition to granite. Normally white, pink or gray in color.

Question 4

Ophiolite

Answer 4

The typical sequence of rocks in the oceanic crust: from bottom to top: ultrabasic rocks, gabbro, sheeted dikes, pillow basalts, and sea-floor sediments. Igneous rocks and deep-sea sediments associated with divergence zones and the sea-floor environment.

Question 5

Granitoid

Answer 5

A granitoid or granitic rock is a variety of coarse grained plutonic rock similar to granite which mineralogically are composed predominantly of feldspar and quartz.

Question 6

Klippe

Answer 6

A klippe is a geological feature of thrust fault terrains. The klippe is the remnant portion of a nappe after erosion has removed connecting portions of the nappe.

Question 7

Fenster

Answer 7

A tectonic window (or Fenster (lit. “window” in German)) is a geologic structure formed by erosion or normal faulting on a thrust system. In such a system the rock mass (hanging wall block) that has been transported by movement along the thrust is called a nappe. When erosion or normal faulting produces a hole in the nappe where the underlying autochthonous (i.e. un-transported) rocks crop out this is called a window.