Stanowisko systematyczne granitoidów masywu Strzegom-Sobótka w międzynarodowej klasyfikacji skał plutonicznych

Alfred Majerowicz


The systematic position of the granitoid rocks of the Strzegom-Sobótka Massif in the international classification of plutonic rocks

Micrometric analyses of the granitoid rocks of the Strzegom-Sobótka massif canned out iby the present author (1972) and other investigators (H. Pendias 1956; M. Borkowska 1959; A. Majerowicz 1961, 1963, 1966, 1972; S. Kural, T. Morawski 1973; S. Maciejewski, T. Morawski 1975) have been presented so far on the diagram of K. Smulikowski (1929). On this diagram, the comers of the triangle assigned for rocks that do not contain feldspathoids are occupied by quartz, alkali feldspar comprising potassium feldspar and albite with the An content up to 12.5%, and plagioclase with mare than 12.5% An. According to K. Smulikowski’s classification scheme, three principal varieties of granitoid rocks which make up the bulk of intrusions were defined by the author (1972) as biotite granodiorite, alkali, and partly monzonitic, binary granite, and biotite (in places with hornblende) monzonitic granite. Two varieties older than the main intrusion were classified as fine-grained tonalité from Łazany and fine-grained imonizonite granite from Zimnik. The secondary leucocratized zone from Strzeblów was defined as alaskite metagranite. According to the new classification scheme, the three principal varieties are to be defined as: 1. biotite granodiorite (regional name: the Strzeblów granodiorite), 2. leucogranites or, more precisely, leucomonzogranites, in which biotitemuscovite and partly biotite leucogranites may be distinguished (regional name: the Wierzbno granite), 3. biotite, in places hornblendeibiotite, monzogranite (regional name: the Strzegom granite). Of the older varieties, the fine-grained granite from Zimnik is to be referred to as biotite or, in places, biotite-imuscovite leucogranite (more precisely, leucomonzognanite), and the fine grained granitoid rock from Łazany as augite-hornblende-biotite tonalite. The secondary leucocraitized variety from Strzeblów should be classified as alaskite or, to be precise, its former name, alaskite metagranite, may be retained. The regional distribution of the varieties discussed is shown in Fig. 2, into which an artificial division into regions denoted with numerals from I to VIII has also been introduced for practical reasons. The systematic position of the granitoid rocks in the new classification triangle Q A Pl is shown in figs. 3 and 1. In the triangle the areas of concentration of the analytical points of granodiorites and monzogranites are shown. The field of monzogranites comprises additionally the area in which leucogranites are concentrated. The Strzegom-Sobótka massif may be regarded (A. Majerowicz 1972) as an intrusion of palingenetic magma formed (by selective anatexis of the underlying .gneisses, similar to the gneisses of the Sowie Góry block. Consequently, the rocks may contain in places small, incompletely assimilated basic inclusions, as shown by the sample from Gola encroaching slightly upon the field of quartz monzodiorites (9'). The granitoid rocks also contain in places schlieric concentrations of biotite from the fluidal stage of magma, as well as cataclastic oriented structures from the post-consolidation stage and zones altered by postmagmatic processes. Those minor varieties, occurring only locally, are of great significance for elucidation of the genetic questions but cannot be taken into account when determining the systematic position of the principal varieties.

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