As the amount of available data has multiplied over the past ten years, the number of apparently distinct reservoirs has risen from two (primitive and depleted mantle, respectively) to five (PREMA, Depleted, HIMU = high U/Pb and Two types of EM or enriched mantle reservoirs). The depleted reservoir produces “normal” (N-type) MORB probably more than […]
Anorthosites are defined as plutonic rocks with over 90% plagioclase. They are highly felsic, felsic minerals, however is a Calcic plagioclase, which along with subordinate associated high temperature mafic minerals. The anorthosites can be classified as Archaean and Proterozoic – Archaean Anorthosites :- Most Archaean anorthosites cluster in the range 3.2 to 2.8 Ga. They
An oceanic core complex or magnalium is a seabed geological feature that forms a long ridge perpendicular to a mid-oceanic ridge. It contains smooth domes that are lined with transverse ridge like a corrugated roof. They can vary in size from 10 to 150km in length, 5 to 15 km in width, and 500 to
Oceanic Core Complex Read More »
An ancient landform or landscape that had been buried beneath younger rocks or sediment and that is exposed by their subsequent erosion. This process is called Exhumation. Exhumation refers to any geological mechanisms that brings the rocks from deeper crustal levels to shallower crustal levels. While erosion or denudation is fundamental in eventually exposing these
Exhumed Topography Read More »
Important minerals : Types of chromite deposits :- Indian deposits :- Stratiform or Layered Chromite Associated with mafic/ ultramafic layered intrusions formed in calm environment (Precambrian) Podiform chromite Irregular geometry, found in disturbed environment, Phanerozoic in age Sukinda ultramafic complex, Orissa Stratified beds inclosed in a sequence of Dunite-peridotite Sithampundi chromite, Tamilnadu Stratiform deposit in
Chromium (Cr) Deposits Read More »
Important minerals : Type of Deposits : Indian Deposits :- Andhra Pradesh Kodurite Kalahandi and Koraput Precambrian iron ore series
Manganese (Mn) Deposits Read More »
Pseudomorphism is the existence of a mineral that has the appearance of another mineral. Pseudomorph means false form. Pseudomorphism occurs when a mineral alters in such a way that its internal structure and chemical composition changed but its external form is preserved. These mechanism of pseudomorphisms can be explained as follows :-
Chemical weathering may be defined as the spontaneous and irreversible thermodynamic process that causes degradation of the mineral phases under the prevailing environmental conditions at the surface of the Earth. It is usually considered to be the solid/solution interactive process occurring in contact with the atmosphere. In other words chemical weathering may be defined as that set of processes
Chemical Weathering and its type Read More »
If composition (or physical properties) changes abruptly at some interface, then seismic wave will both reflect off the interface and refract (or bend) and they pass through the interface. Two cases of wave refraction and reflection can be recognized. Reflection : A seismic reflection is generated when a wave impinges on a change in rock
Reflection and Refraction of Seismic Waves Read More »
