Question
An igneous body with a flat top and a concave-upward base is known as a
The correct answer is
lopolith
To solve the question about the type of igneous body described, we need to understand the characteristics of each option provided: laccolith, lopolith, sill, and stock.
An igneous body is formed from magma that cools and solidifies beneath the Earth's surface. The shape and position of these intrusive bodies help define their classification.
- Laccolith: This is a dome-shaped intrusive body with a flat base and a convex (upward) top, caused by the pressure of magma lifting the overlying strata. It is not concave upward at the base.
- Lopolith: Characterized by a concave-upward base and a flat or basin-shaped top. This formation occurs when the weight of the overlying rock is sufficient to depress the central part of the body. The description fits well with the question prompt.
- Sill: This is a tabular intrusion that occurs parallel to the existing rock layers. It generally has flat tops and bases without significant changes in curvature.
- Stock: An igneous intrusion with an irregular shape that is less than 100 square kilometers in size. It is typically discordant and does not have the concave or flat characteristics mentioned in the question.
Based on this understanding, the only igneous body with a flat top and a concave-upward base is a lopolith.
Thus, the correct answer is lopolith.
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Important Questions from Igneous Petrology (Classification, Forms, Textures, Genesis)
- Match the rock types in Group-I with their most likely corresponding lithospheric / tectonic settings of formation in Group-II
Group-I Group-II P. Boninite 1. Continental anorogenic Q. Lamproite 2. Island-arc R. Phonolite 3. Continental collision S. Leucogranite 4. Intraplate oceanic - The mole percentages of SiO$_2$, Al$_2$O$_3$ and K$_2$O in a granitic rock are 84.21, 7.89 and 7.89, respectively. The molar proportion (in %) of K-feldspar in the rock is ________ [ round off to one decimal place]
- Which one of the following is a mafic volcanic rock?
Match the following igneous textures in Group-I with their definitions in Group-II.
Group-I
Group-II
P Vitrophyre 1 Alkali feldspar rimmed by plagioclase Q Rapakivi 2 Aggregate of radially arrayed, needle-like crystals of plagioclase with or without clinopyroxene R Ocelli 3 Sub-parallel skeletal, platy olivine and/or pyroxene S Spinifex 4 Large phenocrysts within a glassy matrix - Which one of the following statements about igneous rocks is CORRECT?
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