ON THE PETROLOGY OF THE TYGERTYSH INTRUSIVE COMPLEX OF THE SAKSYR RANGE (Kuznetsk Alatau)

E. S. Edintsev

(Presented by Professor S. S. Ilyenok)

The rocks of the Tygertysh complex are widely distributed among the intrusive formations of the Saksyr Range and make up its central part. The formation of the complex took place in three intrusive phases: 1—“spotted” gabbro, gabbro-diorites, diorites, and quartz-bearing diorites; 2—porphyritic granites; 3—medium- to fine-crystalline leucocratic granites. The rocks of the first phase compose a belt of northeastern strike, 2–9 km wide, disrupted by bodies of granite. Rare measurements of the orientation of mafic minerals show that initially the diorite massif had a cupola-like form, with steep (60–80°) dips of the contacts beneath the enclosing rocks. The rocks of the second and third phases of the complex form bodies ranging in size from 0.5 × 1.0 to 8 × 9 km, which in plan have an isometric or slightly elongated form. The enclosing rocks are limestones, schists, and effusive rocks of the Martukhinskaya and Kulburtstogskaya suites of the Upper Proterozoic. In contact with the diorites and granites, the limestones have been transformed into marbles, and the schists and effusive rocks into hornfelses. The width of the belt of hornfelsed rocks is 50–100 m. In the southeastern part of the Saksyr Range, the diorites and granites of the Tygertysh intrusive complex are overlain by Middle Devonian deposits.

Diorites and quartz-bearing diorites are the most widespread rocks of the first phase. These are fine- to medium-crystalline rocks of gray color, with massive, sometimes weakly gneiss-like texture. Their quantitative mineralogical composition is as follows: plagioclase (58–71%), amphibole (27–28%), sodic feldspar (0–5%), quartz (2–4%), and ore and accessory minerals (2–3%). The structure of the rocks is hypidiomorphic-granular. Plagioclase (andesine No. 38–40) is represented by prismatic grains 0.1–5.0 mm in size. The mineral is strongly altered and replaced by sericite. Amphibole forms long-prismatic and irregularly shaped grains 0.1–1.5 mm in size. A distinct pleochroism is observed from green to greenish-yellow tones. Judging by its optical properties \((2V = -68^\circ,\ C:Ng = 17^\circ,\ Ng = 1.690 \pm 0.003,\ Np = 1.674 \pm 0.003,\ Ng - Np = 0.016)\), the mineral belongs to hornblende with an iron content of 55%. Potash feldspar is represented by grains of irregular form, 0.1–2.0 mm in size. In transmitted light the mineral is brown owing to pelitization. Quartz is observed in the form of irregularly shaped grains 0.1–0.5 mm in size. In the rock it is distributed unevenly. Ore and accessory minerals are represented by magnetite, apatite, sphene, and zircon.

Gabbro-diorites are very insignificant in extent and have gradual transitions with diorites. In contrast to the diorites, the amount of mafic minerals in them increases (to 34%); diopside appears ($N_g=1.712\pm0.003$; $N_p=1.688\pm0.003$; $N_g-N_p=0.024$); the plagioclase becomes somewhat more basic (andesine No. 45).

“Spotted gabbro” constitutes, on the southern slope of the Saksyr Range, two areas (250×600 and 300×700 m) among diorites, with which it has gradual transitions. Macroscopically, it is a medium-crystalline rock of dark-gray color with a taxitic texture, caused by the uneven distribution of mafic minerals. The quantitative mineral composition of the rock is as follows: plagioclase (56–58%), pyroxene (20–22%), amphibole (18–22%), ore and accessory minerals (1.0–1.5%).

Plagioclase is represented by isometric, more rarely prismatic grains 0.1–4.5 mm in size. The mineral is polysynthetically twinned and sharply zoned; the boundaries between the zones are comparatively distinct and clear. Refractive indices: core — $N_g=1.562\pm0.003$, $N_p=1.555\pm0.003$, $N_g-N_p=0.008$ (labrador No. 51); inner zone — $N_g=1.555\pm0.003$, $N_p=1.547\pm0.003$, $N_g-N_p=0.008$ (andesine No. 38–40); plagioclase of the outer zone corresponds to oligoclase-andesine No. 30. Monoclinic pyroxene forms isometric and irregular grains 0.1–1.0 mm in size. According to its optical constants ($N_g=1.714\pm0.003$; $N_p=1.690\pm0.003$; $N_g-N_p=0.024$; $2V=60^\circ$; $C:N_g=42^\circ$), the mineral belongs to diopside of the diopside-hedenbergite series, with a content of about 25% hedenbergite and 75% diopside molecule. Amphibole is observed as isometric prismatic grains 0.1–4.0 mm in size. According to its optical constants ($N_g=1.674\pm0.003$; $N_p=1.657\pm0.003$, $N_g-N_p=0.017$, $2V=-(74–80^\circ)$; $C:N_g=14^\circ$), the mineral is common hornblende. Accessory and ore minerals are represented by magnetite, apatite, and sphene.

Porphyritic granites are pinkish-gray medium-crystalline rocks with rare porphyritic segregations of potassic feldspar 5×7, 8×10 mm in size (sometimes porphyritic segregations are absent). The rock structure is porphyritic; the structure of the groundmass is hypidiomorphic-granular. The quantitative mineral composition of the porphyritic granites is as follows: sodium-potassium feldspar (16–26%), plagioclase (44–45%), quartz (28–33%), biotite (2–5%), amphibole (0–0.5), ore and accessory minerals (0.5–1.5%).

Sodium-potassium feldspar ($2V=-67^\circ$) is represented by tabular and irregular grains 0.1–3.5 to 5.0 mm in size. In transmitted light the mineral is brown owing to pelitization. Quartz is observed as irregular grains 0.1–4.0 mm in size. In the rock it is distributed more or less uniformly. Plagioclase (oligoclase No. 20–22) forms prismatic crystals 0.1–2.5 mm in size. Biotite ($N_g=1.674\pm0.003$, iron content 75%) is observed as flakes with ragged outlines 0.1–1.7 mm in size. Amphibole forms prismatic crystals 0.1–0.7 mm in size. In transmitted light the mineral is green with sharp pleochroism in green tones. According to optical constants ($2V=-70^\circ$; $C:N_g=17^\circ$; $N_g=1.674\pm0.003$; $N_p=1.658\pm0.003$; $N_g-N_p=0.016$), it is common hornblende with an iron content of 40%. Accessory and ore minerals are represented by apatite, zircon, sphene, and magnetite.

Leucocratic granites are a medium- to fine-crystalline rock of pinkish-gray and grayish-pink color. The percentage-mineral composition of the granites is as follows: sodium-potassium feldspar (30–35%), plagioclase (33–35%), quartz (28–30%), biotite (0.5–

1 — “spotted” gabbro; 4 and 6 — gabbro-diorites; 2, 3, 5 — diorites, quartz-bearing weakly porphyritic granites; 16, 17 — fine-crystalline leucocratic granites.

1.0%), ore and accessory minerals (0.5—1.0%). Plagioclase (oligoclase No. 15—25) is represented by tabular-prismatic polysynthetically twinned crystals 0.05—1.0 mm in size. Sodium-potassium feldspar forms prismatic or, more often, irregularly shaped crystals 0.05—1.0 mm in size. In transmitted light the mineral is brown owing to pelitization; it often contains poikilitic inclusions of quartz. Quartz is observed as isometric grains up to 1.0 mm in size. Biotite forms rare flakes of irregular shape. Among ore and accessory minerals the rock contains magnetite, zircon, apatite, and sphene. Molybdenum mineralization is genetically associated with the leucocratic granites.

In chemical composition (Table 1), the rocks of the first phase belong to the class of silica-saturated (analyses 2, 3, 5—8) and slightly silica-undersaturated (analyses 1, 4, 9) rocks, and, in alkalinity, to the group poor in alkalis

Table 1

…bearing diorites; 7, 8, 9—diorites and gabbro-diorites of the area of Ust-Bir station; 10–15—rocks ($Q = 1{,}5$–$8{,}4$; $a : c = 1{,}33$–$2{,}6$) (Chetverikov, 1956); the rocks of the second and third phases belong to the class of rocks supersaturated with silica and to the groups of rocks rich and moderately rich in alkalies ($Q = 16{,}6$–$33{,}4$; $a : c = 4{,}49$–$11{,}8$). From the more basic rocks to the more acid ones, alkalinity increases. In addition, a certain flattening of the vectors of the granites in the plane $csb$ on the diagram after A. N. Zavaritskii (Fig. 1) indicates that in this same direction the role of potassium in the sum of the alkalies increases.

The “spotted gabbro,” in chemical composition, is comparable with the average type of gabbro according to R. Daly (Chetverikov, 1956), differing from it by a somewhat greater content of the dark-colored component ($b = 28{,}2$ as against $27{,}0$) and a smaller amount of calcareous aluminosilicates ($c = 5{,}9$ as against $7{,}1$). The gabbro-diorites represented by analyses 4 and 9 are close to the average type of melaphyre (their constants differ by fractions of units). The figurative points of the diorites and quartz-bearing diorites on

Fig. 1. Diagram of the chemical composition of rocks of the Tygertysh intrusive complex (after A. N. Zavaritsky). 1 — variation line of the Tygertysh intrusive complex; 2 — representative points of average types along the Deli River (g — gabbro, m — melaphyre, d — diorite, pg — post-Cambrian granite, d — Precambrian granite, ga — granitic aplite).

in both planes of the diagram according to A. N. Zavaritsky are located near the point of the average type of diorite according to R. Daly. The most melanocratic of the porphyritic granites (analyses 10 and 11) are comparable with the average type of post-Cambrian granite according to R. Daly, differing from it in a higher content of alkali aluminosilicates ($a = 13.9$ and $14.2$ versus $12.7$) and a lower content of calcic aluminosilicates ($c = 1.4$–$1.9$ versus $2.6$). The porphyritic granites represented by analyses 12–15 are close in chemical composition to the average type of Precambrian granite according to R. Daly. As for the leucocratic granites, their figurative points occupy the uppermost position on the diagram according to A. N. Zavaritsky and are located near the point of the average type of granite aplite according to R. Daly.

According to the classification of Yu. A. Kuznetsov (Kuznetsov, 1964), the Tygertysh intrusive complex belongs to the formation of granitoid batholiths of variegated composition.

REFERENCES

1. Yu. A. Kuznetsov. Principal Types of Magmatic Formations. Nedra Publishing House, Moscow, 1964.

2. S. D. Chetverikov. A Manual of Petrochemical Calculations. State Scientific-Technical Publishing House of Literature on Geology and Mineral Protection, Moscow, 1956.