It is assumed that the reader is familiar with the names of common rocks (e.g. basalt, granite, sandstone, etc.) and structures (e.g. fold, fault).
A
accretionary complex: an accumulation of terranes of varying nature (e.g. continental, oceanic, or volcanic-arc) added to a continental margin during the subduction process.
accretionary prism: an accumulation of sediments and volcanic debris occupying the ocean trench and continental slope at a subduction zone; these are often piled up in a series of folded and thrust slices (see Fig. 3.11).
active margin: (of a continent) characterised by a subduction zone.
allochthonous: of a tectonic unit (e.g. a thrust sheet), derived from elsewhere.
alkaline: magma or igneous rock characterised by relatively high proportions of alkalis compared with calcium.
andesite: fine-grained igneous rock, intermediate in composition between basalt and rhyolite; typical product of subduction-related magmas.
asthenosphere: the weak layer of the upper mantle, situated beneath the lithosphere, capable of solid-state flow, which enables the plates to move (see Figs 3.5, 3.8).
autochthonous: of a tectonic unit (e.g. a thrust sheet), derived locally.
B
back-arc basin: sedimentary basin situated on the upper plate of a subduction zone behind the volcanic arc (see Fig. 3.14).
batholith: a very large igneous body, typically composed predominantly of calc-alkaline rocks such as granodiorite, and consisting of many individual plutons intruded over a long period.
black smoker: active submarine volcanic vent: typically located on ocean ridges.
C
calc-alkaline: magma or igneous rock (e.g. basalt, andesite or granite) characterised by relatively high proportions of calcium compared with alkalis.
carbonate: sedimentary rock composed mainly of carbonates of calcium (limestone) and/or calcium-magnesium (dolostone).
channel flow: process of gravity-induced lateral flow of a layer of warm, ductile material within an orogen.
clastic: (of sediments) composed primarily of fragments of older rock.
continental drift: theory of the relative movements of the continents, popularised originally by Alfred Wegener and incorporated into the modern theory of plate tectonics.
core complex: see metamorphic core complex.
craton: stable part of a continent, not involved in contemporary orogenic activity.
crust: uppermost layer of the solid Earth, composed of a wide variety of rocks and varying in thickness from c.10km in the oceans to over 80km in orogenic belts; it rests on the much more uniform mantle (see Fig. 3.8).
D
décollement: process where a rock layer or tectonic unit becomes detached from its base and slides along a detachment surface.
dextral: (right-lateral): movement (e.g. along a fault) where the side opposite the observer moves to the right.
dyke: a sheet-like igneous body, typically with a vertical or steeply inclined attitude, generally discordant with the prevailing structure (e.g. bedding) of the host rock.
E
eugeosyncline: (obsolete): type of geosyncline characterised by deep-marine sediments and vulcanicity.
evaporite: sedimentary deposit formed by the evaporation of water containing soluble salts.
F
flysch: marine sediments (typically including turbidites) derived from an active mountain range or island arc.
fore-arc: region on the ocean-ward side of a volcanic arc (e.g. see Figs 9.3, 9.5).
foredeep basin: a sedimentary basin resulting from the depression of the continental crust due to the load of a rising orogenic belt; it contains a thick sequence of sediments derived from its erosion (e.g. see Fig. 4.9).
foreland: that part of the continental crust lying immediately adjacent to an orogenic belt, and which has not been significantly affected by it.
G
geosyncline: obsolete term used to describe a large elongate basin within the crust that gradually deepened and became filled with sediment.
Gondwana: (formerly Gondwanaland): a supercontinent that existed during Palaeozoic time, consisting of the continents of South America, Africa, India, Antarctica and Australia (see Figs 2.4, 2.5)
graben: fault-bounded depression, created by extension.
granodiorite: the calc-alkaline variety of granite; coarse-grained equivalent of andesite.
greywacke: type of poorly sorted clastic sediment composed of material of varying composition and size: typical of turbidites.
H
horst: uplifted fault-bounded block, created by compression.
I
imbricate: (structure, zone): where the same sequence of strata is repeated many times in successive thrust slices (e.g. see Fig. 14.8A).
isostasy: state of general gravitational equilibrium in which the extra weight of (e.g.) a mountain range is balanced by a deficiency of denser material beneath.
K
karst: type of terrain dominated by carbonate rocks characterised by distinctive landforms and drainage patterns caused by solution by rainwater.
klippe: outcrop of a thrust sheet that has been separated from the rest of the sheet by erosion (e.g. see Fig. 5.4B).
L
Laurasia: a supercontinent that existed during Upper Palaeozoic time, consisting of the greater parts of the continents of North America, Europe and Asia.
lherzolite: type of ultrabasic igneous rock capable of yielding basaltic magma on partial melting and thought to represent the composition of the upper mantle.
listric: (fault) where the fault angle becomes shallower at depth: typical of extensional structures.
lithosphere: the strong upper layer of the Earth, with an average thickness of about 100km, including the crust and part of the upper mantle; it consists of a number of plates that move over the weaker asthenosphere beneath.
M
mantle: that part of the Earth’s interior between the crust and the core, composed mainly of rock with an ultrabasic composition (see Fig. 3.8).
mélange: rock unit, either sedimentary or tectonic, containing a mixture of material of varying provenance.
metamorphic core complex: interior part of an orogenic belt containing rocks that have been brought up from a considerable depth and have been intensely deformed and metamorphosed under high temperature and pressure.
miogeosyncline: (obsolete): type of geosyncline characterised by shallow-marine or continental shelf sediments and lacking volcanics.
molasse: non-marine sedimentary deposits (often red) derived from an active mountain range and deposited on continental crust.
N
nappe: a displaced tectonic unit resting on a thrust: a thrust sheet.
Neptunism: (obsolete) theory held by some eighteenth-century thinkers that all rocks (including crystalline igneous rocks such as granite) were precipitated from the great biblical flood.
O
obduction: process where a terrane or rock unit is thrust over an opposing plate at a subduction zone: i.e. the opposite of subduction.
ophiolite: rock unit or sequence interpreted as part of the oceanic lithosphere, consisting of basic and ultrabasic igneous material and oceanic sediments. A typical ophiolite should include oceanic lavas (e.g. pillow basalts), and both basic and ultrabasic intrusions (e.g. see Fig. 3.8A).
orogen, orogenic belt: part of the Earth’s crust, typically linear, formed as a result of orogeny.
orogeny: the process of mountain building resulting from plate collision, involving crustal thickening, uplift and the formation of mountains.
P
palaeolatitude: the latitude of a rock or rock unit (e.g. a terrane) at a previous time period as determined by palaeomagnetism.
palaeolongitude: the longitude of a rock or rock unit (e.g. a terrane) at a previous time period (this cannot be determined by palaeomagnetism).
palaeomagnetism: the study of the magnetic properties of rocks: principally to determine the orientation of their inherited magnetic palaeolatitude and pole position.
Pangaea: the supercontinent, consisting of (almost) the whole continental landmass, which existed during much of Upper Palaeozoic time (see Fig. 14.1).
passive margin: (of a continent): lacking evidence of subduction.
pegmatite: very coarse-grained crystalline rock, typically granitic, of magmatic or metamorphic origin, often formed from volatile-rich fluids.
pericline: large-scale fold with an elongate oval outcrop pattern.
pillow basalt: basaltic lava flow exhibiting pillow-shaped or tubelike structures formed by rapid cooling in relatively shallow water.
plate: a relatively stable piece of the lithosphere that moves independently of adjoining plates; plate boundaries are where tectonic processes such as earthquakes and orogeny are concentrated.
plate tectonics: the theory that ascribes tectonic processes to the relative movement of the lithosphere plates.
plateau basalt: type of basalt forming voluminous flow sequences on the continents; typical of plume-related volcanism preceding continental separation.
plume (mantle): column of hot rising mantle material thought to be responsible for ‘hotspots’ in the crust.
pluton: large intrusive igneous body.
R
reverse fault: where the fault plane is inclined towards the upthrown side.
rhyolite: fine-grained igneous rock of granitic composition, found typically in the form of lava flows.
rift: extensional fault-bounded valley or trough.
S
sea-floor spreading: (obsolete) theory explaining continental drift by movements of the ocean crust.
seismogenic: (layer): part of the strong, brittle upper crust within which earthquakes originate.
shear zone: zone of ductile deformation, the deeper-level equivalent of a fault.
sill: a sheet-like igneous body, typically with a horizontal or gently inclined attitude, generally parallel to the prevailing structure (e.g. bedding) of the host rock.
sinistral: (left-lateral): of movement along a fault or shear zone etc., where the opposite side, as seen by an observer, moves to the left.
strike-slip: (fault, shear zone etc.) where the movement has taken place horizontally along the structure (see also wrench fault – Fig. 3.2).
subduction: the process whereby an oceanic plate descends into the mantle along a subduction zone; part of the subducted plate melts to give rise to a zone of volcanoes on the opposite (upper) plate (see Figs 3.5, 3.10, 3.11).
suture: line or surface along which separate crustal blocks, terranes or continents have been joined together as a result of the subduction of intervening oceanic material.
T
terrane: (micro-plate): piece of crust, smaller in scale than a plate, that has moved independently of adjoining crustal units and has experienced a different tectonic history from them.
thin-skinned: (deformation): where deformation, typically thrust-related, takes place within a relatively thin upper layer leaving the material beneath undisturbed.
tholeiite: type of calc-alkaline basalt characterised by relatively high proportions of silica; typical type of basalt forming the oceanic crust.
thrust: a (usually) gently inclined fault that has emplaced an older (or lower) rock unit above a younger (or upper) one (e.g. see Fig. 14.8A).
transform fault: a fault that forms part of a plate boundary where the plates on each side move in opposite directions, parallel to the trend of the fault.
transpression: combination of strike-slip and convergent (compressional) movement.
transtension: combination of strike-slip and divergent (extensional) movement.
trench roll-back: (also known as slab roll-back): process where the outcrop position of a subduction zone (i.e. the trench) moves backwards along the subducting plate over time, creating extensional conditions on the upper plate.
triple junction: where three plate boundaries meet.
turbidite: a deposit, formed by a turbidity current, and characterised by poorly sorted sediment of varying coarseness and composition.
turbidity current: a water current generated by gravity-induced flow, carrying large quantities of sediment in suspension.
W
window (tectonic): where erosion has created a gap in a nappe or thrust sheet exposing the rock sequence beneath (e.g. see Fig. 5.4).
wrench fault: a fault where the displacement is horizontal and parallel to the trend of the fault (see Fig. 3.2).