Publishing House SB RAS:

Publishing House SB RAS:

Address of the Publishing House SB RAS:
Morskoy pr. 2, 630090 Novosibirsk, Russia

Log In   /  Register




Advanced Search

2007 year, number 2

1.
CHARACTER OF FORMATION OF THE ERDENET-OVOO PORPHYRY CU-MO MAGMATIC CENTER ( NORTHERN MONGOLIA ) IN THE ZONE OF INFLUENCE OF A PERMO-TRIASSIC PLUME

A.P. Berzina, V.I. Sotnikov
Institute of Geology and Mineralogy, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Porphyry Cu-Mo deposits; ore-bearing complex; granitoids; Permo-Triassic plume; trace elements in basic rocks and granitoids; Mongolia
Pages: 141-156

Abstract >>
The Erdenet-Ovoo magmatic center (EOMC) lies within the North Mongolian magmatic area formed through the interaction of a Permo-Triassic plume with the lithosphere in an environment of active continental margin. Two stages are recognized in the EOMC history: subduction stage with participation of basalt-andesite-dacite-rhyolite series and rifting stage with trachybasalt series. The granitoid magmatism (258-220 Ma) is expressed as the Selenge, Shivota, and ore-bearing porphyry complexes. The formation of the Selenge and Shivota granitoids was preceded by the intrusion of gabbroids. Trachybasalts formed during the granitoid magmatism after the Selenge complex, nearly synchronously with the Shivota and ore-bearing porphyry complexes. At the subduction stage of the EMC evolution, the plume influence is documented from the appearance of gabbros both depleted and enriched in lithophile trace elements similar to volcanic rocks of trachybasalt series and basaltoids of bimodal series in northern Mongolia. The Rb-Sr and Sm-Nd isotope characteristics of the enriched gabbros suggest the participation of a lower mantle source in their formation. The plume, as a heat carrier, led to a large-scale manifestation of volcanism and, obviously, a wide development of basic rocks of this stage at depth. The basic rocks were the source of granitoid magma that produced the Selenge granitoids. The protolith melted in the >50 km thick crust preventing the wide manifestation of basaltoid volcanism in that period. The increased plume influence, rifting, uplift of the region, and extension of the crust favored the basaltoid and granitoid (Shivota and ore-bearing porphyry) magmatism activity.



2.
GENESIS OF CENOZOIC BASALTS IN CENTRAL ASIA AND NORTHERN MONGOLIA ( from helium isotope and petrochemical data )

I.A. Zhukovaa, Yu.D. Litasova, A.D. Duchkovb, D.D. Novikovc
a Institute of Geology and Mineralogy, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
b Institute of Petroleum Geology and Geophysics, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
c Geological Institute, Kola Research Center of the RAS, 14 ul. Fersmana, Apatity, Murmansk Region, 184209, Russia
Keywords: Isotopes; helium; argon; geochemistry; basalts
Pages: 157-166

Abstract >>
Isotopic compositions of He (27 samples) and Ar (7 samples) as well as major and trace elements have been determined in Cenozoic effusive rocks and hosted olivine and pyroxene phenocrysts from northern and central Mongolia. The R = 3He/4He values are within (0.1-13) · 10-6. Abnormally high R value, 13 · 10-6, atypical of Cenozoic basaltic-volcanism areas in Mongolia, has been first revealed at one of the sites of the Hangayn upland. In composition the rocks under study correspond to tephrites, trachybasalts, and subalkalic andesite-basalts. Analysis of their REE patterns and spidergrams shows that the elements participating in the formation of basalt fields of the Hangayn upland were supplied from the enriched mantle (EM1). These patterns are similar to the OIB ones; (La/Yb) n = 9-53. The R values in the olivine phenocrysts are higher as compared with the pyroxene phenocrysts and the bulk rock compositions of the same samples. Based on the elemental composition of the rocks, their contents of radiogenic 4He and 3He were calculated. The rate of 3He formation is 5.65 · 10-2 at/(g · year). The calculated and measured R values in the rock samples point to the presence of trapped mantle helium.



3.
PERMIAN-TRIASSIC TRAP MAGMATISM IN BEL'KOV ISLAND ( NEW SIBERIAN ISLANDS )

A.B. Kuzmichev, A.E. Goldyrev
Geological Institute of the Russian Academy of Sciences, 7 per. Pyzhevsky, Moscow, 119017, Russia
Keywords: Siberian traps; within-plate basalts; Nb anomaly; Arctic tectonics; New Siberian Islands
Pages: 167-176

Abstract >>
The study was inspired by information on Paleozoic andesites, dacites, and diabases in Bel'kov Island in the 1974 geological survey reports used to reconstruct the tectonic evolution of the continental block comprising the New Siberian Islands and the bordering shelf. We did not find felsic volcanics or Middle Paleozoic intrusions in the studied area of the island. The igneous rocks are mafic subvolcanic intrusions, including dikes, randomly shaped bodies, explosion breccias, and peperites. They belong to the tholeiitic series and are similar to Siberian traps in petrography and trace-element compositions, with high LREE and LILE and prominent Nb negative anomalies. The island arc affinity is due to continental crust contamination of mantle magma and its long evolution in chambers at different depths. The 252±5 Ma K-Ar biotite age of magmatism indicates that it was coeval to the main stage of trap magmatism in the Siberian craton at the Permian-Triassic boundary. The terrane including the New Siberian Islands occurred on the periphery of the Siberian trap province where magmatism acted in a rifting environment. Magma intruded semiliquid wet sediments at shallow depths, shortly after their deposition. Therefore, the exposed Paleozoic section in Bel'kov Island may include Permian or possibly Lower Triassic sediments, of younger ages than it was believed earlier.



4.
PORPHYRY CU-MO-(AU) MINERALIZATION: THE AGE AND RELATIONSHIP WITH IGNEOUS ROCK COMPLEXES OF THE BORGULIKAN ORE FIELD ( UPPER-AMUR REGION )

V.I. Sotnikova, A.A. Sorokinb, V.A. Ponomarchuka, V.O. Gimona, A.P. Sorokinb
a Institute of Geology and Mineralogy, Siberian Branch of the RAS,
3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
b Institute of Geology and Nature Management, Far East Branch of the RAS,
2 ul. B. Khmel'nitskogo, Blagoveshchensk, 675000, Russia
Keywords: Porphyry Cu-Mo-(Au) mineralization; 40Ar/39Ar dating; Borgulikan ore field; Amur region
Pages: 177-184

Abstract >>
The Borgulikan ore field is localized in the west of the Umlekan-Ogodzha volcanoplutonic belt made up of various igneous (upper-Amur granite-granodiorite (140-134 Ma), Burunda monzodiorite-granodiorite (130-127 Ma), and Taldan andesite (127-123 Ma)) and superposed (Early Cretaceous Gal'ka trachybasalt-rhyolite (119-115 Ma) and Late Cretaceous trachybasalt-trachyandesite (97-94 Ma)) complexes. 40Ar/39Ar dating of porphyry intrusions breaking through the Taldan volcanic complex and associated with Cu-Mo-(Au) mineralization yielded the following ages: early (dark)



5.
PALEOMAGNETISM OF THE LATE CRETACEOUS INTRUSIONS FROM THE MINUSA TROUGH ( SOUTHERN SIBERIA )

D.V. Metelkina, A.Yu. Kazanskya, V.Yu. Bragina, V.A. Tsel'movichb, A.V. Lavrenchuka, L.V. Kungurtseva
a Institute of Geology and Mineralogy, Siberian Branch of the RAS, 3 prosp. Akad. Koptyuga, Novosibirsk, 630090, Russia
b Borok Geophysical Observatory of the Institute of Earth's Physics of the RAS,
Borok Village, Yaroslavl' Region, 152742, Russia
Keywords: Paleomagnetism; titanomagnetite; Late Cretaceous; explosion pipes; Minusa trough; intraplate strike-slip motions
Pages: 185-198

Abstract >>
The paper summarizes paleomagnetic and rock-magnetic data on the Late Cretaceous diatremes and associated dikes from the Minusa trough located within the southwestern Siberian Platform. It is shown that the stable characteristic component of magnetization is superimposed magnetization (in physical sense). It is linked to Fe-rich titanomagnetite produced by the decay and oxidation of Ti-rich titanomagnetite derived from a primary magma. This process, however, coincides in time with the intrusion cooling, which is supported by paleomagnetic tests. Correlation of magnetic polarity with 39Ar/40Ar ages suggests that the acquired stable characteristic component of magnetization corresponds to magnetic Chrons C33-C32 and characterizes the Middle Campanian magnetic field (74-82 Ma). The mean paleomagnetic pole for this span is located at 82.8



6.
MAIN TECTONIC FEATURES OF THE LITTLE QINLING GOLD BELT ( CENTRAL CHINA )

Li Youzhua, Xie Xing a , Gao Siyuan b , Xu Wenshic
a Chang'an University, 126 Yanta Road, Xi'an, 710054, China
b Group 712, Northwestern Geological Prospecting Nonferrous Metal Department, Ministry of Metallurgy,
12 Weiyang Road, Xianyang, 712000, China
c China Geological University, 29 Xiueyuan Road, Beijing, 710054, China
Keywords: Gold belt; anticlinorium; ore body; ore conduits; ductile-shear faults
Pages: 199-203

Abstract >>
We discuss main tectonic features of the Little Qinling gold belt in Central China, located along the northern border of the eastern Qinling E-W tectonic zone, which hosts hydrothermal lode gold deposits. The distribution of deposits and the strike of ore bodies are controlled by the Dayueping-Jinluoban anticlinorium and the related faults, namely large ductile-shear faults on its flanks striking parallel to the uplift axis and some large faults in the north and south. Mineralization is associated with smaller-scale mylonite zones of brittle-ductile deformation. The Dayueping-Jinluoban dome went through several stages of tectonic evolution (compression → folding → doming → strike-slip faulting → extensional faulting → reshearing) accompanied by regional deformation, metamorphism, migmatizition and mineralization.



7.
MOHO DEPTHS AND THREE-DIMENSIONAL VELOCITY STRUCTURE OF THE CRUST AND UPPER MANTLE BENEATH THE BAIKAL REGION, FROM LOCAL TOMOGRAPHY

A.V. Yakovlev, I.Yu. Koulakov, S.A. Tychkov
Institute of Geology and Mineralogy, Siberian Branch of the RAS, 3 prosp. Koptyuga, Novosibirsk, 630090, Russia
Keywords: Seismic tomography, earthquake location, Moho, Baikal Rift
Pages: 204-220

Abstract >>
We studied the 3D velocity structure of the crust and uppermost mantle beneath the Baikal region using tomographic inversion of ~25,000 P and S arrivals from more than 1200 events recorded by 86 stations of three local seismological networks. Simultaneous iterative inversion with a new source location algorithm yielded 3D images of P and S velocity anomalies in the crust and upper mantle, a 2D model of Moho depths, and corrections to source coordinates and origin times. The resolving power of the algorithm, its stability against variations in the starting model, and the reliability of the final results were checked in several tests. The 3D velocity structure shows a well-pronounced low-velocity zone in the crust and uppermost mantle beneath the southwestern flank of the Baikal rift which matches the area of Cenozoic volcanism and a high velocity zone beneath the Siberian craton. The Moho depth pattern fits the surface tectonic elements with thinner crust along Lake Baikal and under the Busiyngol and Tunka basins and thicker crust beneath the East Sayan and Transbaikalian mountains and under the Primorsky ridge on the southern craton border.



8.
ULTRAPOTASSIC BASITES IN THE CENTRAL CHUKCHI REGION AND THEIR ROLE IN GENESIS OF SN-BEARING GRANITES

S.V. Efremov, V.D. Kozlov
Institute of Geochemistry, Siberian Branch of the RAS, 1a ul. Favorskogo, Irkutsk, 664033, Russia
Keywords: Sn-bearing granites; ultrapotassic basites
Pages: 221-223

Abstract >>
Analysis of the genetic relationship of Sn-bearing granitoids with ultrapotassic basic magmatism showed that their metallogeny was determined by the geochemistry of a specific reservoir localized in the continental lithosphere mantle (metasomatized mantle). The granitoid formation is well explained by the binary model of mixing of primary melts (products of the metasomatized mantle) with the continental crustal material. Geochemical studies of basic magmatism of different ages showed that the specific lithosphere reservoir formed in the Middle-Late Jurassic and existed at least till the late Late Cretaceous, i.e., during both tin metallogenic epochs of the Chukchi region.