New data about age of granitoids of Kalba-Narym polychronal batholith
Kotler P.D.
V.S. Sobolev Institute of Geology and Mineralogy sb ras, Novosibirsk, Russia
Novosibirsk state university, Novosibirsk, Russia
pkotler@yandex.ru
Kalba-Narym granitoid batholith, located in EastKazakhstan, is one of the largest intrusions in the CIS. Batholith has polychronal structure and consists of rocks of several intrusive complexes, which differ in composition and formation time. This area is one of the oldest mining region of Kazakhstan therefore extent of its examination is very high. The first geological data of the Kalba-Narym batholith were obtained at the end of the XIX century. Up until the 80s of XX century this area became the subject of detailed geological and petrological studies.
During these works it was determined that a variety of granitoid magmatism brings difficulties in the dismemberment of rocks on the complexes and to determine volumes of complexes. By the end of the XX century it was make four correlation schemes of Kalbinsky polychronous batholith magmatism [1, 2, 3]. They are based on many years of geological, petrological and petrographic studies carried out by several teams of specialists. The sequence of formation and age of magmatic complexes was determined by direct geological observations, or data based on the correlation of mineralogical and petrochemical composition. As a result of the formation of the Kalbinsky batholith was estimated in the range of about 100 million years - from the Early Carboniferous (kushbarlyksky and babylonian complexes C1 [1, 2]) to the Triassic (mirolyubovsky complex T1 [1, 2, 3]). First determinations of absolute age 6y U-Pb dating were characterized by low accuracy and are not allowed to make significant refinements to the accepted scheme [4].
In recent years 24 Ar-Ar and 3 U-Pb isotopic datings received, that allow to make some additions to the understanding of granitoid magmatism in Kalba-Narym region. This paper presents results of isotopic dating in the central part of the Kalb-Narym batholith and ita generalization. The studies included data of 19 granitoid massifs. The studied rocks compose the 5 complexes, that common in this territory.
Kunushsky complex. We studied the rocks that form Tochkinsko-Medvedkinsky and Karagoin-Saryozeksky intrusive belt, rocks of Besterek massif, and dikes in the edging of Zhilandinsky massif. In Tochkinsko-Medvedkinsky intrusive belt rocks of the complex represented by leucocratic plagiogranite-porphyres consisted of zoned plagioclase phenocrysts (25-30%) andesine composition (An35-40) and the holocrystalline matrix consisting of the second generation small plagioclase (20-25%) oligoclase composition (An25-30), and quartz (30%), feldspar (1%), scaled biotite (~ 15%) and green amphibole (3%). In Zhilandinsky massif biotite plagiogranites have uniform granular granite structure and are composed of quartz (40%), shortprizmatic plagioclase (45%) and scaly biotite (15%). Age of plagiogranites was obtained using ion mass spectrometer SHRIMP-II (VSEGEI, St. Petersburg). Obtained data evidence of a close age of magmatic zircons from plagiogranites Zhilandinsky massif (306,7 ± 8,7 Ma) with 10 experimental points and the Tochka (299 ± 2,3 Ma) and 7 experimental points [5].
Kaltuginsky complex. As part of kaltuginsky granite-granodiorite complex were taken rocks of Irtysh and Chernovinsky massif edges and dike belt in the central part of the region. The structure of the complex is three phases: granodiorites, granites and dykes of granodiorite, granite-porphyries and aplites. Isotope dating was obtained using Ar-Ar method on the rocks of each phase. The first phase - a fine-grained granodiorite from the southern border of the Irtysh massif, the second phase - the granite from the southwest border Chernovinsky massif, and the third phase - the granite-porphyry dike near the Shuruq village, that break depositionof burobaysky formation. Ages obtained for each phase were 286 ± 1,278 ± 2,272 ± 1 Ma, respectively.
Kalbinsky complex. Granitoids of Kalbinsky complex are the most common in the Kalba-Narym batholith. The volume of rocks and number of phases for this complex is still a debatable problem. As objects for the Ar-Ar isotopic dating were selected Belogorskiy, Narymsky, Priirtyshstky, Peschansky, Podgornensky, Chernovinsky arrays and mica of spodumene pegmatites and greisen associated with deposits of rare metal deposit Asubulak (13 dating in all). 8 out of 13 the results indicate Early Permian age of the granitoids, the remaining three have a younger age, until the early Triassic. Age obtained for Belogorsky and Podgornensky massifs (257 ± 2 and 248 ± 3 Ma, respectively) is conditionally accepted as unreliable due to the large difference between the main group of results. A possible reason for this rejuvenation of ages was defective sampling or error at the stage of the isotope-geochronological analysis.
The main part of dating (10 pieces) of kalbinsky complex rocks may be divided into two: young, with an average age of 277 ± 4 Ma and older, with age, around 290 ± 3 Ma. The first group includes: biotite porphyritic granite Peschansky array (275 ± 3, 280 ± 3 Ma), Chernovinsky array (277 ± 1 Ma) and Narymsky array (275 ± 3 Ma). The second: biotite porphyritic granite Irtysh massif (fine-grained - 287 ± 1 million years old, medium - 287 ± 1 Ma), and micas from greisen - 294 ± 4, 292 ± 4 Ma and from spodumene pegmatite - 292 ± 4, 295 ± 4Ma of rare metal deposit Asubulak [6].
Monastyrsky complex. In the selected area to the monastyrsky complex presented by Monastyrsky and Sibinsky leucogranite arrays, Voylochevsky massif and small tabular bodies into endocontacts of Mirolyubovsky and Kaindinsky arrays [3]. On the rocks of this complex were obtained 4 dating by Ar-Ar method and one dating by U-Pb isotopic method. The oldest ages obtained by U-Pb method for the leucogranites Sibinsky array - 284 ± 4 Ma. For Voylochevsky array obtained two Ar-Ar dating - 272 ± 1 Ma (coarse-grained biotite leucogranites) and 277 ± 1 Ma (leucocratic granite). Age obtained for the tabular arrays in a frame of Mirolyubovsky and Kaindinsky array - 269 ± 3 and 272 ± 3 Ma, respectively. Data on the age of the Monastyrsky complex arrays are similar to data on age Kalbinsky complex.
Kaindinsky complex. This complex was first selected by V.S. Shulygin and O.V. Navozov [3], and included Kaindinsky, Mirolyubovsky, Chernovinsky arrays, the eastern part of Kurchumsky and northern part of Voylochevsky
Fig. The definitions of absolute age of rocks from central part of Kalba-Narym batholith. Gray background color shows previously accepted intervals of magmatic complexes forming. The inset shows the time intervals of the formation of intrusive complexes according to the obtained dating.
massifs. The complex is selected on the basis of cutting the aplite dikes of the Monastyrsky complex younger coarse-grained porphyritic granites. According to other authors, these geological observations were not confirmed and rock of these massifs assigned to Kalbinsky complex [2]. Thus, the selection of this complex is still controversial and requires additional investigation. By samples assigned to Kaindinsky complex was carried out four Ar-Ar age determination for Mirolyubovsky, Chernovinsky and Voylochevsky massifs. The oldest age obtained on biotite porphyritic granites Chernovinsky array - 285 ± 1 Ma. The dating of rocks Mirolyubovsky array shows the age of - 277 ± 3 Ma. For rocks of Voylochevsky array has two results of isotopic-geochronological dating of 277 ± 1 and 270 ± 1 Ma.
A generalization of the results of isotope-geochronological dating is shown in Fig. Analysis of data shows that the vast part of granitoids, forming Kalba-Narym polychronal batholith generated in a relatively narrow time period of about 25 million years (295-270 Ma).
The forming of plagiogranitoids of Kunushsky complex occurred separately in time with respect to the main part of the granites in the range from 315 to 300 million years.
The results of dating obtained for the of Kaindinsky complex rocks questioned the feasibility of separation of the complex. The data of age can be attributed to Kalbinsky (286-275 Ma) and Monastyrsky (271-269 Ma) complexes.
The obtained results show about the development of magmatic activity within the Kalba-Narym area from the Late Carboniferous to Early Permian, and cause the need for additional review and revise existing schemes of the correlation of magmatic complexes in the region.
The author thanks Vladimirov A.G., Navozov O.V., Travin A.V., Khromykh S.V., Kuibida M.L. for providing a database of isotopic dating of Kalba-Narym batholith.
This work was supported by the project of partnership investigations from SB RAS № 10.3.
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