On the Question of Combining the Nordmarkite and Kolodzhul Intrusive Complexes of the Eastern Slope of the Kuznetsk Alatau

ON THE QUESTION OF UNITING THE NORDMARKITIC AND KOLODZHUUL INTRUSIVE COMPLEXES OF THE EASTERN SLOPE OF THE KUZNETSK ALATAU

B. D. VASIL'EV

(Presented by the scientific seminar of the Department of General Geology)

On the eastern slope of the Kuznetsk Alatau, in the basins of the Karysh, Tuim, and Sokhochul, there is a widespread association of distinctive alkaline syenites, nordmarkites, granosyenites, granites, and adamellites, the age position of which is still being debated. The rocks of this association compose a number of massifs which, as it seems to us, occupy a quite definite position in the structure of the region: they are located in a zone of northwestern (330–350°) strike about 40 km long and 10–15 km wide. The zone of occurrence of alkaline rocks, which hereafter we shall call the Sokhochul zone, is transverse with respect to the strike of the Salair structures of the Tuim structural-facies zone and cuts across the Ulen'-Tuim massif of batholithic granitoids at right angles to its strike (Fig. 1).

Within the Sokhochul zone, the massifs of alkaline rocks have for the most part a northeastern or sublatitudinal strike, i.e., transverse to the strike of the zone as a whole. A “staircase” structure of the zone is created, indicating an extensional setting at the time of formation of the bodies of the alkaline association.

In the south of the Sokhochul zone lies the largest massif—the Kilinpas-pakh massif, composed chiefly of alkaline syenites and nordmarkites. North of it is a smaller massif—the Tuim massif, in whose structure the principal role belongs to nordmarkites and alkaline granosyenites. Still farther north, in the Sokhochul basin, is the Sokhochul group of small, essentially granosyenitic fissure bodies of various strikes. Finally, in the north of the zone lies the isometric Kolodzhul adamellite stock, about 4 km in diameter, which is the petrotype of the Kolodzhul complex. Thus, in the Sokhochul zone there appear to be situated, as it were, two intrusive complexes: the Kolodzhul adamellite complex (whose sole representative is the Kolodzhul massif) and the Nordmarkitic complex, which unites bodies of alkaline syenites, nordmarkites, alkaline granosyenites, and granites from Sokhochul to Kilinpas-pakh. Let us examine the materials on these complexes.

The association of alkaline syenites, nordmarkites, and granosyenites of the region has been studied by many researchers. However, the geological age of the alkaline rocks has still not been reliably determined; therefore they were considered either as part of the young \((S_2—D_1)\) post-granitic gabbro-syenite complex (B. A. Timofeevsky), or were distinguished as

Fig. 1. Schematic geological structure of the Sokhozul zone. Compiled with consideration of materials by V. L. Khomichev, S. L. Khalfin, G. A. Ivankin, E. V. Vladimirova, V. N. Dovgal, and others: 1—Givetian and younger deposits of the North Minusinsk depression and the Ulen graben; 2—volcanogenic and terrigenous formations of the Byskar series; 3—Late Precambrian and Cambrian deposits of the Tuim structural-facies zone; 4—Late Precambrian and Cambrian of the Batenëvo zone; 5—11—Sokhozul complex; 5—adamellites; 6—granosyenites and two-feldspar granites; 7—nordmarkites and two-feldspar granosyenites; 8—alkaline syenites and nordmarkites; 9—nepheline syenites; 10—bodies of the “nordmarkite intrusion” without specification of composition; 11—ophiolitic gabbro of Kilinspasakh; 12—Koktazh gabbro; 13—granitoids of the Ulen–Tuim batholith; 14—biotite porphyritic gabbro-diorites; 15—disjunctive faults; 16—conventional boundaries of the Sokhozul zone. The numerals on the schematic denote massifs: 1—Kilinspasakh, 2—Tuim, 3—Pridorozhnyi, 4—Sokhozul, 5—Kolodzhul.

into an independent “nordmarkite intrusion” of the Upper Silurian (Yu. D. Skobelev, V. L. Khomichev), or were included in the composition of the ancient pre-granite Koktazh complex (S. L. Khalfin, V. N. Dovgal, and V. I. Besnibov). Finally, V. N. Dovgal describes them as part of the forma-

of Middle Paleozoic \((S_2—D_1)\) subvolcanic granites and syenites of the Kuznetsk Alatau, but notes that “alkaline syenites, nordmarkites, and granosyenites of the Tuim-Karysh type, or at least rocks analogous to them in composition, nowhere cut through the Middle and basic effusives of the Byskar series of the Lower Devonian on the eastern slope of the Kuznetsk Alatau” (V. N. Dovgal’, 1971, p. 124).

It should be noted that S. L. Khalfin and V. N. Dovgal’ studied the association of alkaline rocks on the Tuim-Karysh watershed, southeast of the Tuim mine, where Devonian deposits are absent and even the relationships of the alkaline rocks with the biotite granitoids of the Ulen’-Tuim complex are not clearly recorded. However, northwest of Tuim, in the Sokhoсhul area, the alkaline rocks clearly cut the granitoids of the Ulen’-Tuim complex and are in contact over a considerable distance (up to 8 km according to V. L. Khomichev) with Devonian volcanogenic-sedimentary formations of the North Minusinsk depression.

This contact was exposed by V. L. Khomichev in trenches in various sectors, but its character was not unambiguously determined, since on some of V. L. Khomichev’s maps this contact is shown throughout its entire extent as disjunctive (and then the age of the intrusion is not determined), while on others a disjunctive contact with a very complex outcrop pattern is replaced along strike by a stratigraphic one, which should indicate the clearly pre-Devonian age of the nordmarkite intrusion.

In order to clarify the age of the intrusion and the nature of the contact, this very interesting Sokhoсhul area was mapped by us with students of the TPI in 1969 and again in 1971 at a scale of 1 : 25,000, and the most important sectors were detailed to 1 : 5,000. The following results were obtained:

1. The Pridorozhny massif of granosyenites has an active intrusive contact with Devonian orthophyres and their tuffs, with diabases, felsites, and even paleobasalts of the Byskar series, which is clearly visible in the northernmost part of the massif, 1.5 km west of the Shira—Balakchino road (Fig. 2). Attention should be drawn to the western exocontact zone of the massif in this sector, where the host rocks are penetrated by numerous thin veinlets of granosyenites. In the trench of V. L. Khomichev, which exposed the northern contact of the Pridorozhny massif with the Devonian 0.8 km to the southeast, we also established thin veinlets of granosyenites in orthophyre tuffs.

2. The northeastern boundary of the Sokhoсhul massif with Devonian paleobasalts has not been reliably established because of poor exposure. It coincides with a scarp sharply expressed in the relief (the face of the Kuznetsk Alatau) and possibly is of tectonic nature.

Analyzing the materials obtained as a result of field work, as well as the data of V. L. Khomichev, S. L. Khalfin, G. A. Ivankin, and V. N. Dovgal’, we have arrived at the following conclusion.

Within the Sokhoсhul zone the composition of the rocks of the alkaline complex changes regularly: from southeast to northwest (as one approaches the Devonian), acidity gradually increases and alkalinity decreases in the rocks, which is reflected in changes in the mineralogical-petrographic composition of the rocks of the complex. In the same direction, the textures of the rocks change from coarse-grained to fine-grained porphyritic ones, reflecting facies zonation and different depths of emplacement of the intrusive bodies. From this standpoint, the Kolodzhul massif of adamelites occupies a quite definite position within the nordmarkite complex.

Thus, the southernmost and largest massif of the zone—the Kiliniaspakh massif—is composed chiefly of coarse-crystalline, substantially…

Fig. 2. Breakthrough of Devonian volcanogenic formations by granosyenites on the Sokhochul: 1—Quaternary proluvial deposits; 2—orthophyres and their tuffs; 3—paleobasalts; 4—felsites, albitophyres; 5—diabase porphyrites; 6—red fine-crystalline porphyritic granosyenites; 7—zone of small branching veinlets of granosyenite in the enclosing Devonian rocks.

...with kalishpatized alkaline syenites and nordmarkites, which in the southern part of the massif pass into nepheline syenites (40–50% nepheline) and syenite-diorites, and in the northern part into granosyenites. We emphasize that only in this massif are there nepheline syenites, while among the alkaline varieties olivine-pyroxene (10%) and pyroxene (20%) syenites are present; gastingsite (40%) and pyroxene-gastingsite (30%) alkaline syenites predominate. The content of mafic minerals and their assemblage indicate the increased basicity of the rocks of the massif: olivine up to 3–5%, pyroxene up to 10–15%, amphibole up to 25–30%; biotite is rare. Two-feldspar granosyenites appear here only in the dike facies. An association is observed of alkaline rocks with ophitic gabbros that preceded them (V. N. Dovgal, 1971).

The second massif from the south—the Tul’ma massif—is composed of more acidic rocks, chiefly two-feldspar riebeckite nordmarkites and granosyenites, which in the northern part of the massif pass into alkaline granites; at the same time, the quartz content in the rocks increases from south to north to 20–35%, while the riebeckite content correspondingly decreases from 8–10 to 2–3%. Alkaline quartz-free syenites (pyroxene-gastingsite and gastingsite) occur in this massif only in the south, at two points. The two-feldspar composition of the rocks of this massif indicates a lower temperature of their formation in comparison with the Kilinpaspaakh rocks.

The Pridorozhnyi massif is composed in its northern part of fine-grained red granites and granosyenites, and in its southern part of medium-grained, distinctly porphyritic, light-pink two-feldspar granosyenites, similar in appearance to the Kolodzhul granosyenites. Nordmarkites have been found only in the western part of the massif.

The Sokhochul massif is the most complex in composition and structure. Having a meridional strike, in its eastern half it is composed of coarse-crystalline nordmarkites analogous to the Tuim-Karysh ones; west of these, within the massif, flesh-red coarse- and medium-crystalline granosyenites and granites are successively situated and, finally, two-feldspar medium- and fine-crystalline porphyritic amphibole granosyenites and adamellites of the Kolodzhul type. In the latter there are relics and xenoliths of fine- and medium-grained gabbro-diorites, which make up the northwestern margin of the massif.

The Kolodzhul massif—the northernmost—is also not homogeneous in composition and structure: its large southern part is composed of full-crystalline two-feldspar light-pink adamellites, grading northward into red fine-crystalline granites. The quartz content in the adamellites and granites ranges from 22 to 32%; the mafic minerals (2–6%) are represented by biotite and single grains of amphibole.

Thus, it appears to us that, in the general series of variability in the composition and structural features of the rocks along the Sokhochul zone, the Kolodzhul adamellites and the Kilinpaspakh alkaline syenites are regular members of a single magmatic association, varying in space in connection with the different depth (and temperature) of formation of its various representatives. The present-day erosional section on Kilinpaspakh has exposed a deeper part of the intrusive massif in comparison with the apical parts of the bodies at Sokhochul and Kolodzhul.

The geological age of the Kolodzhul massif is disputed: V. L. Khomichev exposed, by trenching, the contact of the massif with the Devonian and defined it as disjunctive. G. A. Ivankin, having examined the same trench, concluded that the Devonian overlies it. The absolute age of the Kolodzhul adamellites by biotite is determined as 380 million years (V. L. Khomichev, 1966) and as 420 million years (G. A. Ivankin et al., 1969), which does not contradict their unification with the nordmarkites (430–438 million years according to V. L. Khomichev) into a single magmatic complex.

On the basis of the foregoing, it is proposed:

1. To unite the Nordmarkite and Kolodzhul complexes of the eastern slope of the Kuznetsk Alatau into one complex, including the ophitic gabbro, alkaline and nepheline syenites of Kilinpaspakh, nordmarkites, two-feldspar alkaline granosyenites, granites, and adamellites of Sokhochul and Kolodzhul.

2. To name the united complex the Sokhochul complex, after the name of the zone of its distribution, where its composition and geological age are determined.

The Sokhochul complex cuts through the volcanogenic formations of the Byskar Series at Sokhochul (the Pridorozhny massif), thereby defining the lower limit of its age. The most probable age of the complex is \(D_1^2—D_2^1\), pre-Givetian.

In composition, age, and structural position, the Sokhochul complex can be correlated with the Kiya complex of the northern part of the Kuznetsk Alatau.

REFERENCES

1. Dovgal V. N. Massifs of alkaline syenites and granosyenites of the Tuim-Karysh watershed (Khakassia). In: “Magmatic Formations of Siberia and the Far East.” Transactions of the Institute of Geology and Geophysics, Siberian Branch, Academy of Sciences of the USSR, issue 79, 1971.

2. Dovgal V. N., Bognibov V. I. Ancient gabbro-syenite complex

Kuznetsk Alatau. In: Magmatic Formations of the Altai–Sayan Folded Region. “Nauka,” 1965.

1. Ivankin G. A., Vladimirova E. V., Golyd R. M., Glazunova A. D. The Kolodzhul massif of adamellites (Khakassia). Izv. TPI, vol. 165, 1969.

2. Khafin S. L. Geology and petrography of the massif of quartz alkaline syenites on the watershed of the Tuim and Karysh rivers (Kuznetsk Alatau). In: Magmatic Complexes of the Altai–Sayan Folded Region. Tr. IGiG SO AN SSSR, issue 33, 1963.

3. Khomichev V. L. Intrusive magmatism of the Tuim district of Khakassia. In: New Data on the Geology of the South of Krasnoyarsk Krai. Krasnoyarsk, 1963.

4. Khomichev V. L. Intrusive magmatism of the Tuim district of Khakassia and certain questions of metallogeny associated with it. Author’s abstract of dissertation. Tomsk, 1966.