in Relation to Plate Tectonics
tectonics, like crustal evolution, provides a basis for understanding the
distribution and origin of mineral and energy deposits. The relationship of
plate tectonics and mineral deposits is significant on three counts:
requirements must be fulfilled in any tectonic setting for the production and
accumulation of minerals. A number of tectonic settings meet these requirements:
- Geological processes operating
due to energy released at plate boundaries control the process of mineral
- Mineral deposits form in
particular tectonic settings which are governed by plate tectonics.
- Reconstruction of fragmented
continents can provide a useful basis for exploration of new mineral
I. DEPOSITS AT OCEANIC
RIDGES (DIVERGENT PLATE MARGINS)
activity at the ridges gives rise to a) Sulfide deposits and b)
Metalliferous sediments on the flanks of ridges. Important metallic
deposits formed are Fe, Zn, Cu, Pb, Au and Ag. In the Red
Sea metalliferous sediments containing Fe, Zn and Cu are being
- Mn oxide deposits are
important at some ridges Eg the TAG Hydrothermal field on the Atlantic
- Ultramafic rocks in ophiolites
containing asbestos, chromite and nickel ores. These are generally
accessible in Phanerozoic orogenic belts to which sites they have been
transported due to plate movement.
- Podiform chromite deposits
associated with serpentinized ultramafic rocks.
- Cyprus Type massive
sulfide deposits (Cu-Fe rich) are also associated with ophiolites and
represent hydrothermal deposits formed at ocean
Several types of mineral
deposits appear to show a genetic relationship to either the hot
mantle plume itself or the tracks it produces.
II. DEPOSITS AT CONVERGENT
deposits are commonly found at both continental and arc convergent plate
margins. Along the Circum-Pacific Belt major metallic deposits occur in western
North and South America, Japan, Philippines, New Zealand and Indonesia. More
than half of the world's supply of copper comes from the Porphyry Copper
Deposits of this region. Important deposits associated with present and former
convergent margins are:
of mineral deposits forming at convergent margins is apparent Eg in the Andes,
going from west to east, the various zones encountered are:
- Base metals (Cu, Pb, Zn, Mo).
- Precious metals (Pt, Au, Ag).
- Other metals (Sn, W, Sb, Hg).
(Red Bed uranium deposits are also associated with convergent boundaries Eg
SW United States).
a) contact metasomatic Fe-
zones are caused due to progressive liberation of metals from the descending
slab, with Sn coming from a depth of 300 Km. The metals are derived from some
combination of the descending slab and the overlying mantle wedge. They move
upwards in magmas or fluids and are concentrated in late hydrothermal and
b) Cu-Ag and Ag veins;
c) Porphypy Cu-Mo deposits;
d) Pb-Zn-Ag veins and contact metasomatic deposits; and
e) Sn deposits.
occurs in the back-arc basins in arc convergent margins where organic matter is
trapped and there is a lack of free circulation so that its oxidation is
prevented. Geothermal heat facilitates conversion of organic matter to
petroleum, and accompanying deformation forms traps for accumulation of
geothermal fields also occur along convergent margins.
III. DEPOSITS AT COLLISION
of local tectonic settings exist along collision plate margins. Most of the
deposits that occur here have formed in diverse tectonic settings and have been
transported to the collision zones. Consequently, a variety of metallic deposits
are abundant here:
IV. DEPOSITS IN CRATONIC RIFT
- Deposits generally related
with oceanic ridges (ophiolites).
- Those associated with
convergent plate margins.
- Mineral deposits associated
with cratonic assemblages.
- Deposits associated with
- Deposits genetically related
to collision zones are hydrocarbons which may accumulate in foreland basins
associated with such zones, Eg the Persian Gulf SW of the Zagros Suture in
Regional uplift and doming usually result when a
continent comes to rest over a hotspot and huge volumes of magma rise to the
surface. Extensional failure of the lithopheric crust may occur with continued
doming, triggering the development of a triple junction - a three armed continental
rift system. Typically, one arm of the rift fails remaining a fissure in
the crust known as an aulacogen, while the remaining two arms open to form an
oceanic basin. The prevalence of three armed rifts is revealed by reassembling
the continents surrounding the Atlantic Ocean to their positions before Pangea
split up. In most cases two of the arms were incorporated into the Atlantic,
while the third remained as a blind rift extending into the continent.
follows crustal doming in response to hot-spot activity in the mantle.
- Granites intruded at this
stage have associated Sn and fluorite deposits.
- Evaporites accumulate in the
rifts during the more advanced stages, with Pb-Zn-Ag deposits in limestones
forming during the early and middle stages of rifting. These are followed by
oceanic metalliferous deposits.
- Aulacogens are characterized
by the presence of fluorite, barite, carbonatites (with Nb, P, REE, U, Th
etc) and Sn-bearing granites.
- Geothermal fields occur
along the rifts due to the upwelling of the asthenosphere.
(unusual igneous rock rich in calcite and other carbonate minerals which are
considered to be mantle derived), kimberlites,
and alkaline granites within or adjacent to rifts provide a major source of
metallic and other minerals.
V. DEPOSITS IN CRATONIC BASINS
and intracontinental cratonic basins provide a favourable setting for
accumulation of organic matter. During the opening of a cratonic
rift, seawater moves into the basin and evaporation exceeds inflow, giving
rise to the formation of evaporites. The environment is characterized by
restricted circulation and hence organic matter is preserved leading to the
accumulation of petroleum. With continued rifting, circulation becomes
unrestricted and deposition of evaporites and organic matter ceases.
geothermal gradients beneath the opening rift and increase in pressure due to
burial by sediments facilitates the conversion of organic matter to petroleum.
In the final stages of the opening of the basin, the salt beds may begin to rise
as salt domes forming traps for oil and gas. Oil and gas may also be trapped in
structural and stratigraphic traps as they move up due to increasing temperature
and pressure, Eg the Red Sea.
speculation is lent support by the fact that around the Atlantic there is a
close geographic and geologic relationship between hydrocarbons and salt