LOWER CAMBRIAN SPILITE-DIABASE FORMATION OF THE TALON-KAMZAS AREA IN THE SOUTHWESTERN PART OF THE KUZNETSK ALATAU

L. V. PESHEKHONOV

(Presented by Professor A. G. Sivov)

The least studied questions in the geology of the southwestern part of the Kuznetsk Alatau are those of the stratigraphy and material composition of the ancient volcanogenic sequences, which are widely distributed in the Talon-Kamzas area.

The first information on the effusive magmatism of the area is contained in the works of A. M. Kuzmin [5, 6], who regarded all the volcanogenic deposits of the area as Lower Paleozoic formations. In the works of G. V. Pinus [8], A. L. Dodin [2], I. T. Zhuravleva, L. N. Repina, V. V. Khomentovsky [3, 4], M. K. Vinkman, A. B. Gintsinger [1], A. A. Predtechensky, A. P. Shcheglov [9], and others, one can find only scattered and contradictory data, which, with varying degrees of detail, illuminate the stratigraphic position of the volcanogenic rocks and their material composition. The upper subdivisions of the formation, overlain unconformably by carbonate-terrigenous rocks of the Adiak suite, first described by K. V. Radugin [10], were at one time combined by A. G. Sivov into the Pyankov suite of the Lower Cambrian [11].

Without touching on the question of the stratigraphy of the ancient volcanogenic sequences of the area, information on which is contained in the author’s published work [7], the present article gives a structural-tectonic analysis of the conditions of formation and a characterization of the material composition of the volcanogenic rocks that we assign to the spilite-diabase formation of the Early Cambrian.

The rocks of the formation, together with carbonate deposits of the Late Proterozoic and Lower Cambrian, occupy large areas in the described part of the Kuznetsk Alatau in the vicinity of the settlements of Talon, Kamzas, and Taimet.

On the modern denudation surface, the rocks of the formation occupy elevated parts of the watershed area of the Pyzas, Kondoma, Kaurchak, and Kamzas rivers. Most often these are isolated fields of volcanogenic rocks 7–8 km long and 2–3 km wide. The effusive rocks of the spilite-diabase formation occupy their broadest area in the upper reaches of the Aryk and Kamzas rivers, where they form a belt of meridional strike up to 15 km long and 8–9 km wide.

Analysis of the factual material collected by us on effusive rocks, as well as of the works of previous researchers, makes it possible to judge that the initial stage in the development of the Salair geosyncline in our area, as in many other parts of the Kuznetsk Alatau, was accompanied by intensified volcanic activity, which followed the formati—

with the formation of thick carbonate sequences of the Late Precambrian. By this time, the manifestation of significant differential movements was associated with the formation, under submarine conditions, of sheets and flows of basic lavas of basaltic composition. The products of volcanism of this time have been preserved as a number of petrographic varieties of albitized porphyrites.

The spilite-diabase formation is represented in its fullest expression in the basin of the Kamzas and Aryk rivers, where we studied it in the greatest detail. From the sections presented (Fig. 1) it is evident that lava formations predominate in the composition of the formation; among them the following rock varieties are distinguished: spilites, albitized basaltic and hyalobasaltic porphyrites, albitized diabases, and diabase porphyrites.

Spilites are, in outward appearance, uniform, dense rocks of greenish-gray color, with aphyric and microporphyritic texture. Microscopically, they are rocks with devitrified mesostasis, in which small elongated laths of weakly altered acid plagioclase are immersed. In addition to acid plagioclase (albite No. 3–5), small grains of monoclinic pyroxene occur in minor amounts in the groundmass. The mesostasis of the groundmass is represented by an iron-chlorite or chlorite-epidote-carbonate aggregate, which accounts for the greenish-brown coloration. Along with secondary products of devitrification, fine disseminations of magnetite, ilmenite of acicular form, and earthy accumulations of leucoxene are often observed in the groundmass. Small amygdules filled with quartz, chlorite, calcite, and epidote are often observed in the groundmass. In the microporphyritic varieties of spilites, against the background of the groundmass characterized above, exclusively elongated laths of albite No. 3–6 are observed, whose length reaches 1.0–1.5 mm with a width of only 0.05–0.08 mm. Both in the microporphyritic segregations and in the groundmass, the albite is water-clear, with a small quantity of fine flakes of chlorite and sericite. The aphyric and microporphyritic varieties of spilites in most cases have spilite, more rarely intersertal hyalopilitic and pilotaxitic textures.

In addition to the small amygdules described above, which in the groundmass are usually of monomineralic filling, spilites contain macroamygdules (up to 5 mm) of concentric structure, filled with several minerals. The following mineral associations are most often observed in the amygdules: chlorite + calcite, chlorite + quartz, chlorite + epidote, or clinozoisite, quartz + epidote.

From the sections of the spilite-diabase formation presented above, it is evident that spilites play a minor role in the composition of the formation. They are closely connected by mutual transitions with albitized basaltic porphyrites, differing from the latter in material composition and, to some extent, in structural features, and are confined to the upper parts of the formation section. The described features of the material composition of the spilites allow us to regard them as albitized hyalobasalts formed under submarine conditions. The submarine conditions of formation of both spilites and other rock types of the formation are indicated by pillow or globular jointing, the interpillow space of which is filled with interbeds and nests of siliceous shales and jaspers.

Before proceeding to characterize the remaining petrographic varieties of lava formations, it should be noted that all of them may be assigned to the group of albitized to varying degrees...

Fig. 1. Structure of sections of the spilite–diabase formation of the Talon–Kamzas area: 1 — albitized diabases and diabase porphyrites; 2 — albitized basalt porphyrites; 3 — albitized hyalobasalt porphyrites; 4 — diabase porphyrites; 5 — albitized paleobasalts; 6 — spilites; 7 — spilites with lenses and nests of jasper in the interpillow space; 8 — tuff breccias of basic composition; 9 — lava breccias of basic composition; 10 — tuffs; 11 — lydite and jasper; 12 — light-gray reef limestones; 13 — black platy limestones; 14 — limestone sedimentary breccias; 15 — sandstones, tuffaceous sandstones; 16 — marls; 17 — carbonaceous-clayey and sandy-clayey shales; 18 — conglomerates; 19 — dolomites of the West Siberian Suite of the Late Precambrian; 20 — algae; 21 — archaeocyaths; 22 — disjunctive contact; 23 — boundary of hiatuses. I — right side of the middle course of the Aryk River; II — right side of the upper course of the Aryk River; III — basin of the Kommuzа rivulet; IV — basin of the Kamzas River (north of the settlement of Kamzas), right side of the Maly Khaюryuza rivulet; V — watershed of the Kommuzа and Bol. Khaюryuza rivulets; VI — left side of the upper course of the Kichik-Su rivulet.

rocks (Table 1). In albitized rocks the plagioclase is characterized by the presence of relics of decalcitized basic plagioclase.

The most widespread are albitized basalt porphyrites. As a result of intense albitization, varieties of basalt porphyrites are often encountered in which the plagioclase is represented by albite without relics of primary plagioclase and with only slight development of secondary minerals after it.

Albitized basalt porphyrites are the predominant effusive rocks in the sections along the Aryk, Kamzas, and Mal. Khairyuz rivers. In contrast to spilites, porphyritic segregations in the basalt porphyrites assume a more substantial quantitative role. Significant changes in the basalt porphyrites are observed also in the quantitative ratio of plagioclase and pyroxene. The amount of the latter increases both in the porphyritic segregations and in the groundmass and reaches 25–40%. Varieties of basalt porphyrites in which pyroxene predominates over plagioclase occur more rarely. In this connection, pyroxene-plagioclase and plagioclase-pyroxene albitized basalt porphyrites are distinguished.

Pyroxene in porphyritic segregations has the composition \(\mathrm{Ca}_{49}\mathrm{Mg}_{43}\mathrm{Fe}_{17}\) (determined from Hess’s diagram); \(Ng = 1.711\); \(Np = 1.681\); \(2V = +48–49^\circ\); \(CNg = 38–40^\circ\); \(Ng - Np = 0.028–0.030\).

Secondary minerals of the chlorite and actinolite groups develop in the pyroxenes mainly along fine cracks.

Plagioclase in the porphyritic segregations is represented both by pure albite No. 4–8 (\(Ng = 1.537–1.541\); \(Np = 1.527–1.531\); \(Ng - Np = 0.010\)), and by albite with relics of calcic plagioclase (No. 40–60). Basalt porphyrites that have undergone only a weak degree of albitization are characterized by broad development, among the secondary products, of fine-scaly chlorite, saussurite, epidote, and carbonates. Plagioclase, both in the porphyritic segregations and in the microlites of the groundmass, forms elongate, short-prismatic, tabular crystal forms.

The structure of the groundmass is in most cases intersertal. The spaces between chaotically arranged plagioclase microlites are filled with pyroxene, magnetite, more rarely acicular ilmenite and earthy leucoxene, as well as devitrified mesostasis. In appearance, the albitized basalt porphyrites are dense, grayish-gray rocks with an aphyric, porphyritic, more rarely glomeroporphyritic structure.

Albitized hyalobasalt porphyrites often occur together with albitized basalt porphyrites, composing the upper parts and the bases of flows of this composition. They are dark-green amygdaloidal rocks consisting of brown glass. Among the altered glass, which contains a small quantity of the finest microlites of acid plagioclase, rare porphyritic segregations of transparent albite No. 2–5 and monoclinic pyroxene are observed. The total amount of the primary crystalline phase does not exceed 5–20%. Numerous amygdules contain epidote, quartz, and chlorite of the delessite-diabantite group. The described albitized hyalobasalt porphyrites usually characterize the rapidly solidifying lower parts of a flow. The upper parts of a flow are usually characterized by a number of distinctive features. As a rule, they represent a devitrified glassy brown fractured crust, which, during the movement of the magma, was constantly broken up and carried along by a new portion of magma. During solidification, hyalobasalt porphyrites were formed that consist of a mass of quenched fragments of various shapes, resembling fragments of amygdules, cemen-

Table 1

Chemical composition of rocks of the spilite-diabase formation of the Talon-Kamzas area
(in percent)

vesicular brown basic groundmass containing rare idiomorphic crystals of fresh monoclinic pyroxene of composition \(\mathrm{Ca}_{46}\mathrm{Mg}_{46}\mathrm{Fe}_{14}\) (determined from the Hess diagram); \(Ng - Np = 0.030\); \(2V = +54—56^\circ\); \(CNg = 41—43^\circ\).

Albitized diabases and diabase porphyrites for the most part form flows in the northern part of the Talon–Kamzas area, where they almost entirely compose the Kubez, Pazyn, and other heights. At the indicated localities, diabases and diabase porphyrites predominate in comparison with the distribution of other effusive rocks. In places where albitized basalt porphyrites are predominantly developed, diabases and diabase porphyrites compose the central parts of flows. A gradual transition is clearly observed from albitized basalt porphyrites with a hyalo-ophitic structure, through diabases, to holocrystalline diabase varieties in the direction from the base and the roof toward the central part of the flow. They differ noticeably from the effusives characterized above in a number of features. Usually these are greenish-gray, dense, massive rocks with a clearly visible fine- and medium-grained fabric. Under the microscope the following mineral composition is established: plagioclase (40–55%), monoclinic pyroxene (35–40%), sulfides, ilmenite, magnetite (3–5%), quartz and apatite (2–1%), secondary minerals: epidote, chlorite, actinolite, leucoxene, calcite, quartz (5–15%). Thus, in material composition, albitized diabases and diabase porphyrites are very close to albitized basalt porphyrites, differing from them only in the character of the structure, which is usually diabasic, doleritic, more rarely hyalo-ophitic and tholeiitic. The plagioclase and pyroxene are analogous to these minerals described in the albitized basalt porphyrites. In the porphyritic segregations of diabase porphyrites there is usually only albite, in the form of single crystals or glomeroporphyritic aggregates with relics of primary basic plagioclase (No. 35–60).

Pyroclastic formations within the formation are less widespread. In significant quantities, clastic rocks of volcanogenic origin are observed on the watershed of the Kairyuz and Kommunza rivers. In their composition they correspond to the effusive formations characterized above, and by mode of formation they may be subdivided into tuffs, tuff breccias, and lava breccias.

Tuffs (especially crystalloclastic ones) are macroscopically difficult to distinguish from effusive formations. Under the microscope, tuffs show psammitic lithocrystalloclastic and vitrocrystalloclastic structures. The clastic material constitutes 50–80% of the total mass of the rock, with grain sizes no larger than 2 mm. The fragments include plagioclase, pyroxene, fragments of porphyrites, and brown weakly polarizing glass. The cement of the tuffs is almost entirely chloritized, intensely impregnated with iron hydroxides and the finest needles of actinolite and epidote.

Tuff breccias are recognized macroscopically much more easily by the presence of fragments in the cementing mass. The size of the fragments varies widely, from fractions of a centimeter to 3–5 cm. Under the microscope, the porphyritic composition of the fragments is established. The basal cement consists of finer, angular fragments of porphyrites, decomposed glass, plagioclase, pyroxene, and resembles the tuffs characterized above.

Lava breccias consist of fragments of spilites, albitized basalt porphyrites, and diabases. The size of the fragments is analogous to that indicated for the tuff breccias. The shape of the fragments is most often irregular.

with noticeable traces of melting. In composition and structure, the cementing mass corresponds to the hyalobasalt porphyrites of the flow tops.

Simultaneously with volcanic activity under submarine conditions, siliceous rocks—lydites and jaspers—were deposited at a distance from the centers of volcanism.

Lydites are essentially synchronous formations with the effusives and usually replace lavas along strike. These are black, dense, bedded or massive siliceous shales consisting of cryptocrystalline silica with an admixture of finely dispersed ore and carbonaceous matter. The bedded siliceous shales are a rhythmic alternation of brown, dark-gray, greenish-gray, and black interbeds of silica 1–4 cm thick. The coloration of this type of siliceous formation depends on the quantitative ratio of limonite, chlorite, and carbonaceous matter.

Jaspers occur directly within the belt of development of volcanogenic rocks. Their accumulation took place during pauses in the outpouring of effusives. Therefore, in sections they occur together with terrigenous and carbonate rocks, usually lying at the base of packets of sedimentary rocks. Such a combination of rocks can be observed in the upper part of the basin of the Kommunza River. The jaspers are composed mainly of cryptocrystalline chalcedony and are dense rocks with a conchoidal fracture and a banded texture. The color of the jaspers is characterized by dark-gray, light-gray, lilac, and raspberry-red tones.

Conclusions

Thus, the rock types of the spilite-diabase formation characterized above reflect its rather varied composition. Within the formation, alongside effusives, siliceous, terrigenous, and carbonate deposits are developed, which in certain areas attained considerable development relative to lava and tuffaceous formations.

Siliceous shales often replace lavas along strike. Among the volcanogenic formations, albitized basaltic and diabase porphyrites and their tuffs strongly predominate. Spilites, confined to the upper parts of the formation sections, are observed much more rarely. The assemblage of rocks and the nature of their combination in the sections make it possible to distinguish within the formation three zones replacing one another along strike: northern, central, and southern. The principal members of the northern zone are siliceous shales and albitized diabase porphyrites. The abundance of carbonaceous matter in the siliceous shales indicates that their formation proceeded under marine conditions at depths providing a reducing or weakly oxidizing environment.

In the central zone, effusives represented by albitized basaltic and diabase porphyrites, and more rarely by spilites and tuffaceous-sedimentary formations, predominate in the lower parts of the formation sections. In the lower parts of the upper half of the sections, jaspers, siliceous-clayey shales, and limestones predominate. The sections usually culminate in a unit of spilites and albitized diabases with a pillow type of texture. The accumulation of rocks in the lower half of the sections of this zone probably also took place under marine conditions at depths similar to those prevailing in the northern zone of the formation. It can be stated with greater confidence that the formation of rocks of the upper half of the sections of the central zone of the formation occurred under conditions of insignificant depths. This is evidenced by the presence in this part of the sections of reef limestones with archaeocyaths and algae and of coarse-clastic terrigenous rocks.

The southern zone is characterized by a considerable development of clastic rocks of volcanogenic origin, which are, in the main, products of eruptions of stratovolcanoes.

The constantly changing combination of the rocks of the formation in the horizontal and vertical directions may be explained by the heterogeneity of the internal structure of individual troughs of the Lower Cambrian geosyncline.

References

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