Granodiorite

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Sawn and polished specimen from Hauzenberg granodiorite ( Hauzenberg , eastern Lower Bavaria )
Granodiorite rocks in the route iron diagram
Granodiorite quarry in the Czech Republic
Freistadt granodiorite built as a brick ( Freistadt im Mühlviertel , Austria)
Relatively coarse-grained Piégut-Pluviers-Granodiorite (northwestern Massif Central , France )

Granodiorite is closely related to the granite related igneous rocks that are distributed worldwide and among the plutonic rocks of the earth's crust has a share of 34 percent. It occurs on every continent.

history

In Roman times, granodiorite marble was called Claudianus , which was mined in the Arabian desert at Gebel Fatireh ( Mons Claudianus ). The term "granodiorite" was used for the first time by G. F. Becker on maps of the Gold Belt in the Sierra Nevada towards the end of the 19th century . The first description of the rock comes from W. Lindgren in 1894.

Rock description

It is a mostly coarse and medium-grained, massive rock from white-gray to gray in color. Porphyry -like granodiorites with a non-uniform grain structure can reach grain sizes of several centimeters in the feldspars. The mineral grains appear to be arranged in a directionless manner, but on closer examination, a magmatic regulating structure can often be seen in the feldspars. Structures of tectonic origin are also by no means unusual.

Mineral inventory and composition

Of the granites to granodiorite hardly differs because it also feldspar , quartz and mica contains. In contrast to granite, granodiorite contains significantly more plagioclase than potassium feldspar , the plagioclase percentage in feldspars is between 65 and 90 percent by volume, the modal content of quartz fluctuates between 20 and 60 percent by volume. The content of mafic minerals is usually higher than that of granite. They usually consist of hornblende and biotite and therefore give the granodiorite a slightly darker color. With its higher iron and magnesium content , granodiorite forms the middle link between granite and diorite ( quartz diorite ), hence the name of the rock.

Accessories are mostly allanite , apatite , titanite and zircon , occasionally also epidote and zoisite . Ilmenite and magnetite act as opaque ore minerals .

If granodiorites have less than 5 percent dark minerals, especially biotite and hornblende , they are called leukogranodiorites, and if they are over 25 percent mela-granodiorites .

Modal mineral inventory

Granodiorites have the following modal mineral components (in percent by volume):

Anorthite content: from 30%

Accessories and ore minerals can account for up to 1.5%.

Chemical composition

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Granodiorites are chemically equivalent to dazites ; in the TAS diagram they therefore fall into the O 3 field . SiO 2 -rich granodiorites can also switch over to field R of the rhyolites . The average continental crust has the composition of granodiorite. Granodiorite also belongs to the tonalite-trondhjemite-granodiorite series (TTG).

Granodiorites are of SiO 2 supersaturated rocks and corundum - or diopside -normativ, their content of these minerals thus corresponds to the normative mineral constituents . Their SiO 2 content normally varies between 63 and 68 percent by weight, but can also be significantly higher (up to 73 percent by weight). The weight fraction of Na 2 O and K 2 O varies between 6 and 8 percent. Based on their K 2 O content, they belong to the medium, but mostly to the high K type (they are therefore calcareous ). Your magnesium number, Mg #, is around 0.52. Their aluminosity (A '/ F ratio, A' = Al 2 O 3 + Fe 2 O 3 - Na 2 O - K 2 O - CaO ; F = FeO + MnO + MgO ) is usually normal , even if the Half dome granodiorite e.g. B. is hypaluminous (A '/ F <0). Some varieties can be hyperaluminous (A '/ F> 0.33). The ratio of aluminum to the sum of the alkalis and calcium (Al / K + Na + Ca) is below 1.1, granodiorites therefore mainly belong to the intrusive I-type , but here too there are exceptions (metasedimentary S-type > 1, 1).

The following table shows the chemical composition and CIPW standard of an average granodiorite (average value from 885 analyzes), as well as the analyzes of the Half Dome granodiorite (low SiO 2 ) and the Cathedral Peak granodiorite (high SiO 2 ). The trace elements come from Cathedral Peak granodiorite and Deddick granodiorite on Mount Kosciuszko in southeastern Australia:

Oxide
wt.%		 Average
granodiorite		 Half
dome		 Cathedral
Peak		 CIPW norm
percent		 Average
granodiorite		 Half
dome		 Cathedral
Peak		 Trace elements
ppm		 Cathedral
Peak		 Deddick
SiO 2 66.91 63.47 69.60 Q 22.36 18.89 24.52 Pb 17.5 27-38
TiO 2 0.55 0.72 0.38 Or 16.11 19.14 21.67 Ni 3.0 17-23
Al 2 O 3 15.92 15.81 15.34 From 31.73 28.28 36.79 Cr 3.3 56-58
Fe 2 O 3 1.40 2.14 1.30 On 17.34 18.91 11.85 V 41.4 96-102
FeO 2.76 3.03 0.95 C. 0.26 Zr 135.9 168-184
MnO 0.08 0.09 0.06 Hy 7.40 6.28 1.63 Y 8.3 27-35
MgO 1.76 2.28 0.70 Mt 2.00 3.85 1.87 Sr 633.2 126-151
CaO 3.88 4.72 2.68 Il 1.03 1.37 0.73 Ba 748 528-553
Na 2 O 3.80 3.32 4.31 Ap 0.42 0.39 0.32 Rb 132.5 163-186
K 2 O 2.76 3.22 3.64 Tuesday 2.86 0.57 Nb 7.8 13-18
P 2 O 5 0.18 0.17 0.14
Mg # 0.52 0.56 0.55
A '/ F 0.06 −0.01 0.08
Al / K + Na + Ca 0.97 0.91 0.96

Varieties and types

The following varieties of granodiorite are known:

  • Biotite granodiorite
  • Hornblende granodiorite
  • Hornblende biotite granodiorite

As with granites, a distinction can also be made between I-type and S-type with granodiorites , with S-types having more than 1 percent normative corundum.

Crystallization

The presence of biotite and especially hornblende indicates a water content of 3 to 5 percent for granodioritic magmas . Crystallization experiments confirm the dominant position of plagioclase during the course of crystallization, which crystallizes together with biotite, hornblende, accessories and ore minerals over a wide temperature range. Only shortly before reaching the solidus then also quartz and alkali feldspar crystallize, mostly as a gusset filler between the relatively large, mostly isomorphic plagioclases.

Inclusions

Inclusions in the Švihov granodiorite

Granodiorites can occasionally contain inclusions or enclaves of mafic foreign rocks, mostly SiO 2- poor rocks such as diorite , quartz diorite or gabbro . Sometimes there are also xenocrystals and the so-called enclaves surmicacées , inclusions rich in biotite. Conversely, granodiorites can also be included in foreign rocks.

Occurrence

The deposits of granodiorite are worldwide. Like the equivalent dazites, they are mainly bound to subduction zones of active continental margins.

Larger granodiorite deposits can therefore be found in the Sierra Nevada in western North America and in the Peruvian coastal batholite.

Numerous granodiorites were formed in the Paleozoic in the Lachlan Fold Belt in Australia .

In Europe it occurs in Finland , France ( Massif Central and Pyrenees ), Italy ( Adamello , Elba , Giglio , Presanella , Rieserfernergruppe , Tuscany ), Slovakia and the Czech Republic . In Germany it can be found mainly in the Bavarian Forest , Ore Mountains , Fichtel Mountains , Harz , Lusatian Mountains (see Lusatian Granite ), Odenwald and Black Forest , in Austria near Freistadt in the Mühlviertel .

Physical Properties

Granodiorite is a relatively light rock, its density ranges between 2.64 and 2.70 g / cm 3 .

Thin sections

  • Granodiorite in linearly polarized light

  • Granodiorite with crossed polarizers

  • Granodiorite from Slovakia, crossed polarizers

use

The Rosette stone is probably the best-known cultural monument made of granodiorite
Man's head made of granodiorite, Old Kingdom , 4th Dynasty, around 2550 BC BC, Egyptian Museum Munich
City hall fountain at the New Dresden City Hall made of Lusatian granodiorite
(design: Georg Wrba , 1911)

Granodiorites have similar technical properties as granites. They can be processed in all ways and brought to the point of polishing.

Granodiorite has been processed since ancient times. In Roman times, granodiorite was a sought-after raw material and was mined , for example, in Mons Claudianus in Egypt . Because of their resilience, Granodiorite is well suited for floor and stair coverings, wall coverings on house facades and as a grain for road surfaces.

Colloquially, however, the term granodiorite is rarely used, as the difference between granite and granodiorite is generally not known. This is why granodiorite is known as granite in the natural stone industry and is therefore on the market.

Natural stone types

  • Stone patterns of granodiorites

  • Lausitz granodiorite, usually Lausitz granite called

  • Granodiorite from the Švihov deposit (Czech Republic)

  • Granodiorite from the Ctětín deposit (Czech Republic)

literature

  • MG Best, EH Christiansen: Igneous Petrology. Blackwell Science, 2001, ISBN 0-86542-541-8 .
  • RW Le Maitre: Igneous Rocks. A Classification and Glossary of Terms. Cambridge University Press 2002, ISBN 0-521-61948-3 .
  • W. Maresch, O. Medenbach: Steinbach's natural guide rocks. Munich 1996, ISBN 3-576-10699-5 .
  • Walter Maresch, Hans-Peter Schertl, Olaf Medenbach: Rocks. Systematics, determination, origin. 2., completely reworked. Edition. Schweizerbart, Stuttgart 2014, ISBN 978-3-510-65285-3 .
  • W. Wimmenauer: Petrography of igneous and metamorphic rocks. Ferdinand Enke Verlag, 1985, ISBN 3-432-94671-6 .

See also

Web links

Commons : Granodiorite  - collection of images, videos and audio files

Individual evidence

  1. ^ W. Maresch, O. Medenbach: Steinbach's natural guide rocks. 1996, p. 48.
  2. ^ Marc Waelkens, Norman Herz, Luc Moens: Ancient Stones. In: University Press, Leuven 1992, p. 167.
  3. ^ Deddick granodiorite