Late Paleozoic and Early Mesozoic rare-metal magmatism of Central Asia: Stages, provinces, and formation settings

V V Yarmolyuk,M I Kuzmin

doi:10.1134/s1075701512050054

Abstract

Late Paleozoic and Early Mesozoic epochs in the formation history of the Central Asian Foldbelt are distinguished by high rare-metal productivity. A number of large REE, Ta, Nb, Zr, Be, Sn, Li, Mo, Re, and other deposits were formed at that time. As a rule, they are of the magmatic origin and related to the intrusions of highly evolved igneous rocks varying in composition from alkaline ultramafic with carbonatites to alkali and Li-F granites. In general, the occurrences of rare-metal magmatism are related to the rift zones of the Central Asian Rift System formed 310–190 Ma ago and conjugated with a consecutive series of the Barguzin, Hangay, and Hentiy zonal igneous provinces characterized by the large batholiths in their centers and rift zones in the framework. Such a structure indicates that these provinces were formed above isometric mantle sources or plumes with participation of large-scale crustal anatexis. The evident links of rare-metal deposits to occurrences of mantle magmatism within the zonal igneous provinces show that plume sources played an important role in their formation.

Highlights

Initial divisibility of the Earth protolithosphere, i.e. the cooling outer hard cover of the planet, and its transformation with time into lithospheric blocks have not been properly studied yet in terms of the geody‐ namics of faulting, and tectonic regularities in divisibi‐ lity of the lithospheric blocks of various ranks still need to be clarified
Equations 3, 5, 6 and 7 are similar, which suggests that the fragmentation of 'solid' rocks follows a physically uniform pattern, and, in more general terms, there is a tectonophysical law of the fault‐block divisibility of the lithosphere which is valid for litho‐ spheric blocks of a wide range of areas, from blocks which size is compatible with North and South America continents, i.e. nearly as big as lithospheric plates, to lump of rocks observed on small outcropped sites
This study is pioneering in tectonophysical recon‐ struction of initial divisibility of the protolithosphere as a result of convection in the cooling primitive mantle

Summary

INTRODUCTION

Initial divisibility of the Earth protolithosphere, i.e. the cooling outer hard cover of the planet, and its transformation with time into lithospheric blocks have not been properly studied yet in terms of the geody‐ namics of faulting, and tectonic regularities in divisibi‐ lity of the lithospheric blocks of various ranks still need to be clarified. In the majority of problems solved by geodynamics, it is assumed that convection cells occupy the entire mantle or partially occupy the layer or occur between the layers [Kirdyashkin, Dobretsov, 1991; Dobretsov et al, 2001; Trubitsyn V.P., Trubitsyn A.P., 2014] In such conditions, the main factor predetermining convection is viscosity of the medium, which is included in equations of interre‐ lated Rayleigh, Grashof and Prandtl numbers. The main factor predetermining convection is viscosity of the medium, which is included in equations of interre‐ lated Rayleigh, Grashof and Prandtl numbers It can sig‐ nificantly increase or decrease their values and change the stability of convection . The merger of the two descending cooling flows leads to further thickening of the emerging cap, and the partition between emerging blocks of the lithosphere is fixed

THE ORIGIN OF THE FIRST LARGEST LOCAL STRUCTURES

GENETIC SOURCES OF THE LITHOSPHERE

DISCUSSION

Findings

CONCLUSION

10. REFERENCES