Batholite

Composition

The batholites generally consist of rocks felsic S or mediosilic rocks such as the Granite, quartzic monzonite or the Diorite (see also granite dome).

Geological formation

Although they seem rather homogeneous at first sight, the batholites are actually structures of which history and composition are relatively complex. They consist of multiple masses, or let us plutons (originally magma coming from a zone of fusion partial at the base of the earth's crust) which approached surface. When they are still in displacement, one will call these plutons rather light magma of the plutonic Diapir S . Thanks to their high temperature and their viscous consistency, these diapirs will rise by clearing a way through the surrounding rock which they contribute to dissolve with the passage. The majority of the diapirs does not arrive at surface in the form of Volcan, but see their progression generally slowing down as their temperature drops and that they are solidified, with a depth from 5 to 30 km, to form plutons (in reference to Pluton, Roman God of the underground hells).

One will speak about batholite when a certain number of plutons end up amalgamating to form a sufficiently important mass of plutonic rock.

Examples

Some batholites are of gigantic size, extending along zones from subductions last or present or other sources of heat from the continental crust on hundreds from kilometers. One could quote for example the batholite of the Sierra Nevada: it is a continuous granitic training which constitutes the major part of this assembly line in California. A batholite even more gigantic, of which the greatest part forms the mountains of the west coast of Canada, extends until south-east from the Alaska on 1800 kilometers.

Geography

Definition of the term in geography

The term of batholite is also used in geography when a mass of plutonic rocks is found exposed on the surface on more than 100 km ². These rocks were exhumed by the erosion, worsened by the process of rising of the continents on tens even of the hundreds of million of years. This process caused to pickle the cover of higher rocks on tens of kilometers, revealing the presence of batholites thus formerly deeply hidden under surface.

Erosion of the batholites

The batholites thus discovered are exposed to conditions completely different from those which they knew under ground. Their crystalline structure will dilate slightly with the wire of time, during their decompression. This causes an erosion of surface by a process of exfoliation. This erosion will detach from vast glares of convex rocks and enough ends of the surface of the batholites. This process is accelerated besides by bad weather such as freezing.

One of the most famous examples of this phenomenon is the half-dome of the famous valley of the Yosemite in the west of the United States.

See too

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