chemical distinction of potassium alkaline rocks, kimberlites,
lamproites, and lamprophyres based on RHA information language
*, Burnaeva M.J. **
Using the traditional
approaches to a problem of classification of many magmatic rock types we
had shown that, e.g., the alkaline rich rocks, far not always allow
distinguishing and identifying them unequivocally. When chemical
composition of different groups of rocks is displayed on TAS diagrams,
their fields very often strongly overlap each other, and use of the
consecutive scheme for classification of magmatic rocks, according M. Le
Bas and A. Streckaisen (1991) and recommendations of IUGS and the
Petrographic Code approved by Russian IPC, also causes some questions.
So, it is not clear why some borders between groups of compositions are
appointed on some "round" figures (10, 50, 75, etc. %%) of
concentrations of any components (oxides,
minerals in modal, and sometimes normative volume %, or their
incorporated groups – e.g., foids – F, or mafic minerals – M). As other
classification principle, distinctions of rocks by their composition and
texture, agpaite factor are used also, etc. In existing classifications,
the general and uniform system of description, ordering, and also an
opportunity of comparison with known objects of new compositions have
not been incorporated.
Use of RHA
information language-method developed more than 40 years ago (Petrov,
1971) has allowed to begin drawing up on its basis of catalogues of
chemical composition of rocks (see file CollStart_En-2012 with data for
more than 5,650 inputs) and mineral composition in volumetric % (Vol. %)
according to calculation of normative contents of minerals (601 analyses
of lamprophyres + 475 of alkaline rocks) and modal compositions (457
analyses). All these datasets represented in Excel tables, are available
at web site:
further “Method RHA”. We shall remind that the first part of the
composition description – R – is a sequence of system components on
decreasing of their concentration in this system. As a result of such
ordering, the rank
formulas (Rmin) – sequences of minerals like
AlbtOrtcNeph are received, that
corresponds to volume mineral parts (Vol. %) in rock Albt> Ortc> Neph>.….
Sets of rank formulas are ordered under a certain "alphabet". As
the “alphabet”, the sequence of these
minerals received in their chemical R-classification of all minerals
(R-Min-Catalogue-2012.rar file at the same Internet address)
serves. The description of the method is
resulted both in the Internet, and in many publications (Petrov,
Krasnova, 2010; Petrov, Moshkin, 2012). Thus, the offered method allows
ordering unequivocally all compositions without any exception (see
table, the right column), that known classifications do not provide,
despite many attempts on there detailed elaboration and refinement.
data both on chemical and mineral compositions of the same rock samples
are given extremely rarely, that complicates correct comparison of the
received rank formulas (Rmin).
Based on revision of Rmin
sets received on recalculation of normative and modal mineral
composition of different rock groups using
program, it is
possible to draw the following conclusions.
1) For the majority of magmatic rocks, even on their normative
compositions it is possible to define more or less authentically their
classification group. An exception is made with rocks, the main
components of which are water-bearing or other minerals, that are not
involved in the program of CIPW recalculation (for example, micas,
amphiboles, melilite, etc.). 2) At calculation of norms, in many cases
virtual components, such as K2SiO3, Na2CO3,
corundum in granites, larnite in ultrabasic and basic rocks, etc. (in
the table they are italicized) are obtained. 3) Modal compositions allow
to define unequivocally not only a group of rocks, but also to allocate
in their limits the varieties differing in the content of minor and/or
accessory minerals (their symbols are in the right column of the table
on 3-4 ranks).
computer program used by us for data processing, composing of various
diagrams (including traditional, such as TAS) is also rather convenient.
The more informativeness of the dependences made for chemical rock
compositions on ratios of elements, instead of oxides, has been
revealed. Therefore, on the diagram reflecting the composition of
potassium-bearing rocks in coordinates of atomic % K/Al relation, fields
of points for different rock types are allocated individually enough.
The majority of compositions of dikes from the Kola Peninsula and
picrites from Spitsbergen correspond on these diagrams to composition of
lamprophyres and gabbroids.
critical revision of such full collections of RHAmin data for different
rock groups from different regions of the world, it will be possible to
develop a rational nomenclature for them.
specification of the
composition description in the form
of a rank formula,
values of complexity
(H or En) and
purity (A or
An) of the composition,
taking into account the degree of
rock monominerality can be used.
Creation of a
representative RHA-catalogue of such full data for all rocks will
provide an opportunity of their unequivocal identification on the real
mineral composition, opened for addition of new, previously unknown
types. In the future, such classifications on RHA method can become a
perspective task for different groups of geologists all over the world.
Le Bas M., Streckeisen A.L.
The IUGS Systematics of igneous rocks.
// J. Geol. Soc. London.
1991. 148, 825-833.
Petrov T.G. Substantiation of a variant of the general classification of
geochemical systems. //
Vestnik LGU. 1971. Ser. 18.
No 3. 30-38. (In Russian).
Petrov T.G., Krasnova N.I.
R-dictionary-catalogue of chemical compositions of minerals.
S.-Petersburg: Nauka Press. 150 p. (In Russian).
Petrov Tomas G., Moshkin
Sergey V. RHA – System for Coding of Discrete Distributions and Their
Alteration Processes. // Proc. The 3rd International Multi-Conference on
Complexity, Informatics and Cybernetics IMCIC 2012.2012 pp. 12-16.