Characteristic of magmatic complexes, hotspots of Priamurye as inferred from aerogamma spectrometry data
Yu.A. Kosygin Institute of Tectonics and Geophysics, FEB RAS, Khabarovsk, Russia
Based on the data of comprehensive geophysical studies the Maya-Selemdja plume was discriminated in the Siberian Platform and the Central Asian Fold Belt (CAFB) contact zone, Priamurye, which was localized in the Mongolo-Okhotsk and Pacific Belt intersection area (Malyshev et al., 2002; Tectonics…, 2005). A series of hotspots, local structures originating at depth of the first hundreds of kilometers, surround the Maya-Selemja plume. Practically, all the hotspots are controlled by extended continental rift and fault zones. One of the zones, linearly shaped, is striking by the CAFB margin, in the proximity of the South Tukuringra and Paukan Faults. This zone is transversing the other arcuate-shaped zone representing the marginal rift and fault zone of the Siberian Platform with arranged hotspots, of those a part was inferred from the geological data only. The Siberian Platform marginal zone, composed of the ancient rocks, is distinguished by chains of greenstone belts, in part by faults and extremely extended Uchur-Maya diaclase. It is traced by a chain of arranged one after another and equally-spaced hotspots, among these are the Zeya, Upper Zeya, Toko (Arbarastakh), Konder, Ingili ones. Location of the first of these hotspots, the Zeya one, in the CAFB marginal zone is a characteristic feature. Apparently, hotspots are evidence of the Siberian Platform displacements in the geologic past, and their equal-spaced arrangement can be explained by the mantle convection processes (Baryshev, 1999).
Principles of airborne geophysical data application for the study of plume magmatism and various geodynamic environments are developed in (Volodkova, 2007). The characteristics of Natural Radioactive Element (NRE) ratios – indicators of magmatic processes - are of prime importance. The average NRE ratios are calculated for the magmatic complexes of Priamurye, the Earth’s layers (the upper and lower crust) and enriched mantle reservoirs EM I, EM II, HIMU. To our knowledge, the enriched mantle reservoir origin is associated with plumes, and uranium-potassium ratio can act as a geodynamic criterion; which is used to determine the origin of the magmatic complexes and their geodynamic type (Volodkova, 2007; Volodkova, 2008). By all appearances, taking into consideration all the errors, the magmatic complexes of the following geodynamic types can be distinguished (their characteristics are given in the parenthesis): I1– type (subduction, U/K ≥ 1.75); I2 – type (transitional to the collisional, U/K = 1.5 – 1.75); S1 – type (syncollisional, U/K = 1.25-1.5); S2 – type (late collisional, U/K = 1.0 – 1.25); À1 – type (post-collisional, U/K = 0.75 – 1.0); À2 – type (anorogenic, U/K ≤ 0.75). These are preliminary results due to the lack of statistical data. For refinement of validity of the conclusions made, Table 1 compares the geodynamic types of the magmatic rocks, determined from the uranium-potassium criterion and based on the geological-petrochemical data (Tectonic map…, 2001).
Table 1. Geodynamic type of magmatic rocks of Priamurye.
Notes. *1. Magmatic complexes of volcano-plutonic and volcanic belts.
*2. Rifrogenic magmatic complexes.
*3. Magmatic complexes of the active continental margins
1. A quite good consistency of the determination results of geodynamic rock types is observed on the basis of tectonic constructions and the uranium-potassium criterion, which proves the correctness of its choice.
2. A more differentiated determination of geodynamic rock type is possible using the uranium-potassium criterion (it is especially clearly observed in the VPB structures).
3. The NRE ratio characteristics of riftogenic formations depend either on the lacking or appreciable influence of plume originated magmas. In the latter case it is observed either a relationship with the enriched mantle reservoirs or high intensity NRE ratio values (in the case of high alkalinity rocks).
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