Leucogranite

The leucogranite is an igneous plutonic rock and is one of the granitoids. The rock is a variety of the granite leukokrate with more than 95 percent by volume of light mineral constituents.

History

Leucogranite was described scientifically for the first time by J. Lameyre in 1966, to use the term interchangeably for two- mica granite. The description was based on Leukograniten in the French Massif Central.

Rock description

Leukogranite are very pale to white rocks (old Greek λευκός leukos "white" ), in the weathered state they take slightly yellowish tones along. The grain sizes move usually 3-5 millimeters, but there are also fine-grained and porphyritic to pegmatitic varieties. The structure is usually equal grainy, but tectonically stressed rocks form a foliation, which is recognized by a regulation of the mica, muscovite particular, noticeable. The quartz aggregates contained may experience a flattening then as well.

The color index is defined as less than 5

Mineral content and composition

Leukogranite have the typical Granite minerals. They usually consist of about 70 weight percent SiO2.

Modal mineral constituents

• Quartz
• Orthoclase
• Plagioclase ( oligoclase )
• Biotite
• Mica

In addition, you may also have:

• Sillimanite
• Andalusite
• Cordierite

As accessory minerals occur:

• Apatite
• Tourmaline
• Zircon

Chemical composition

Led is the average composition of the Saint- Mathieu- leucogranite (14 analyzes) and from the Cognac -la- Forêt- leucogranite (25 analyzes ) - all from the north-western Massif Central:

Leukogranite are supersaturated in SiO2, their average SiO2 content is 73 %, with a variation range of 70 to 75 %. They are also korundnormativ and peraluminous. According to the alphabet soup classification of granitoids they belong to the S- type.

Formation and association

Leukogranite arise primarily by a very advanced anatexis of metasediments ( greywacke and metapelites ) in the continental crust area. They are mainly associated with the collision type with orogeny processes; in this context, they may be linked with significant flat-lying thrust faults or regionally significant, steeply dipping faults.

Occurrence and localities

Leukogranite are distributed worldwide. A very important and huge Leukogranitvorkommen is located in the Himalayas, which occurs along the Main Central Thrust and owes its genesis to the alpidischen major thrust in the Tertiary. Well-known examples are the Manaslu leucogranite and the Lhotse Nup - leucogranite.

Numerous examples of Leukogranite can also be found in the French Massif Central. They came here towards the end of the Variscan orogeny in the Upper Carboniferous and are linked to the shifting and folding and / or lateral displacements.

Locations in Europe are the Black Forest in Germany, the north-eastern Portugal, the north-eastern Sardinia, the province of Salamanca in Spain, the south-eastern Bulgaria and northwestern Turkey ( Pontic Mountains). An example of a leucogranite from the Proterozoic is the Hearney - leucogranite in the Black Hills, United States.

Raw materials

Leukogranite can greatly enrich Lithophile elements such as uranium and thorium. The latter are usually bound to pegmatites, granite micro - or Lamprophyrgänge.

• Plutonic rocks
• Petrology