Dynamics of LIP-forming decompression melting zones in the upper mantle

This works covers dynamical problems of origin and evolution of decompression melting zones of more than 500km linear sizes within the upper mantle. For this we used the modified Boussinesq model with full phase diagram of the upper mantle and multilayered lithosphere. The length of our mantle system is 2400km; the at the upper-lower mantle boundary there are hot spots of 100km sizes with the gaps from 300 to 700km between them. There are also larger hot spots of 340-1600km sizes (which can be regarded as superplumes). Both uniform and asymmetric temperature distributions were used for hot spot chains and for separate spots, having temperature exceeding at the perovskite boundary up to 5-15%. For the hot spot system having the step ≤500km rearrangement of dissipative systems takes place: the formation of mutual melting zone above the neighboring spots is possible; in this case convection above distant spots is less intense. The total melting zone can reach 1500km. The zone system separated into two branches at the beginning of its evolution shows different development scenarios. The similar scheme is typical for the spot system having subsequent spot size increase up to 200km, as well as temperature increase. Within the convective cells cyclic upwelling tilt change takes place, with the change of configuration, sizes and intensity of decompression melting. For the neighboring cells these processes become synchronous. In some plumes the transfer of melting zones and their separation into individual sub-zones take place. As the whole, above the hot spot system, under the lithosphere plate, the zone of decompression melting evolves; there the periodic structure, melting zone sizes and decompression melting intensity change. The character of the mantle matter above hot spots of sizes ~300-800 km can be due to the popular-discussed scenario of the development of the asthenosphere zones adjacent to plumes, where the melting zone size depends on the starting size of heat anomaly at the upper-lower mantle boundary; above the larger hot spots the size of the asthenosphere zone can reach ~700-1000 km. Different evolution for the asthenosphere zones is typical for larger hot spots (more than 1000km). At the beginning of their evolution the system of convective cells develops above them; with time these cells degenerate into one super-cell of complex periodical structure. This restructurization is responsible for the complex evolution of morphology, sizes and melting degrees of the ashenosphere zones, which themselves can form periodic structures. The total length for the decompression melting zones can reach 1500km. This work was financially supported by the project 24.1.2, program of RAS 24.