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
Alkaline rocks occur in all tectonic environments, including the ocean basins. Alkaline rocks are generally considered to have more alkalis than can be accommodated by feldspars alone. The excess alkalis then appear in feldspathoids, sodic pyroxenes/amphiboles or other alkali-rich phases. Alkaline rocks generally occurs in three principal settings :- Some important igneous Alkaline rocks are
Flood basalt is formed by an eruption or series of eruptions of large volcanic episodes that cover vast stretches of land or ocean floor with flows of mafic igneous rocks (basalt lava flows). A flood-basalt province is popularly known as Trap (Deccan Traps in India). Some major flood basalts provinces are as follows – Name Approximate
Continental Flood Basalts Read More »
Feldspars are the abundant minerals that occurs in igneous rocks, and alumina is one of the most important element in the feldspars. Thus alumina saturation is based on weather there is an excess or lack of Al to make up the feldspars – Based on the relative amount of K2O, Na2O, CaO and Al2O3 the
Alumina Saturation Index Read More »
Separation of a liquid from the partially melted solid residue is a form of diversification because it involves partitioning and separation of chemical constituents, and it can produce a variety of melt compositions from a single source. When the interfacial energy (surface tension) of the melt is similar to that of the minerals, the dihedral
Partial melting of rocks Read More »
Ophiolites are considered to be masses of oceanic crust and upper mantle thrust onto the edge of a continental or incorporated in mountain belts, where they are tectonically disrupted and now exposed by erosion. A typical Ophiolite, in this case based primarily on the Semail Ophiolite in Oman on the Arabian peninsula, a particularly well
Ophiolites / oceanic crust & upper mantle Read More »
Here is the list and short description of important Igneous rocks. Detailed description of the particular rock is given in separate post.
Important Igneous Rocks Read More »
