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Mantle Plumes beneath the Baikal Rift Zone and Adjacent Areas: Geophysical Evidence
| Content Provider | Semantic Scholar |
|---|---|
| Author | Zorin, Yu A. Turutanov, E. Kh. Kozhevnikov, Vladimir |
| Copyright Year | 2003 |
| Abstract | Late Cenozoic alkaline basic volcanics in the Baikal Rift Zone and adjacent territories of eastern Siberia and central Mongolia are relatively small in volume. However, the geochemical and isotopic signatures indicate that these volcanics could be related to mantle plumes [1‐3]. At the same time, some researchers deem that the geochemical signature does not serve as critical evidence for the existence of plumes [4]. Geophysical methods may substantially help in the identification and localization of mantle plumes. The gravity and seismic evidence in favor of mantle plume development in the study region is discussed in this communication. A heated material of mantle plume should have lowered density and seismic velocity. Gravity measurements may be helpful in plume recognition. It is commonly noticed in the literature on plumes [2, 5, and others] that ascending material flows in plume conduits exert dynamic influence upon lithosphere, giving rise to positive gravity anomalies combined with topographic uplifts. The associated positive anomalies in free air are attributed to the domination of topographic masses influence. Moreover, theoretical estimates show that the influence of ascending flows on lithosphere is significant only for mantle models with uniform viscosity [6]. The models taking into account the existence of asthenosphere having a viscosity two orders of magnitude lower than the viscosity in a deeper mantle assume a marked weakening of the dynamic influence of an ascending flow on lithosphere [6]. Due to the damping effect of asthenosphere, the anomalous masses of plume conduit virtually do not participate in either dynamic or static equilibria. Since density is decreased, the above phenomenon should create a negative isostatic anomaly that should be rather wide (i.e., regional) owing to the deep localization of the attracting object. The relative gravity minimum above Iceland and the absolute minimum above the Galapagos Islands [7] are examples of such anomalies. Calculating the isostatic anomalies as guides for gravity effect of plume conduits, one should keep in mind that topographic uplifts above the plume may be equilibrated both by crust thickening caused by its magmatic underplating and by lithosphere thinning as a result of its replacement with a plume head [5]. In this work, we have calculated the isostatic anomalies taking into account that only 40% of topographic masses are compensated by variation of the Moho depth and the remainder (60%) is compensated by variation of lithosphere thickness. These relationships are based on the previously established correlation of topography and gravity field with seismic data on the crustal structure of eastern Siberia and central Mongolia [8, 9]. Gravity effects of isostatic compensation in plane zones with a radius of 222 km were attributed to the influence of deep-seated thin layers formed as a result of the condensation of topographic masses with opposite sign. The compensation masses related to variations of the Moho depth were condensed into a thin layer localized at the mean depth of this discontinuity (45 km), whereas the compensation masses related to the mantle were condensed into a thin layer at an average depth of the lithosphere‐asthenosphere boundary (120 km). The depths of these layers were estimated from seismic data on crust and lithosphere thickness in this region [8, 9]. The gravity compensation effects within the plane zones, 222 km in radius, were subtracted from the Bouguer anomalies. Topographic isostatic corrections for spherical zones (beyond the radius of 222 km) were determined using the correction map compiled by Artem’ev [10]. |
| Starting Page | 1302 |
| Ending Page | 1304 |
| Page Count | 3 |
| File Format | PDF HTM / HTML |
| Alternate Webpage(s) | http://www.mantleplumes.org/WebDocuments/ZorinBaikal.pdf |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
