Basite magmatism preceding the intrusion of large volumes of felsic magmas takes place only during powerful tectonic rearrangements, which span both the continental crust and lithospheric mantle. The study of this magmatism makes it possible to solve many genetic problems and obtain important geological information on the sources and processes that are responsible for granitoid magmatism. This paper reports the results of the geochemical study of potassic and ultrapotassic magmatic rocks that predate the intrusion of the granitoid complex and belong to it. In terms of geochemistry, the studied magmatic rocks of Chukotka correspond to the derivatives of potassic and ultrapotassic magmas, which allows us to use the models of formation of ultrapotassic magmas for interpreting the genetic features of tin-bearing granites, in particular, for explaining the anomalous contents of incompatible elements in these rocks. Using modern genetic models in combination with geological, geophysical, and geochemical data, it is established that the source of this specialization was the lithospheric mantle domain. The domain was formed within a convergent geologic boundary owing to the metasomatic reworking of the mantle wedge by fluids that were released during dehydration of the oceanic lithosphere. Based on the obtained results, a new model was proposed for the formation of tin-bearing granitoids in the collisional orogens. This model is underlain by the concept of a particular lithospheric source, which acquired its geochemical and metallogenic signatures during intense tectonic transformation that involved the lithospheric mantle. These signatures were inherited by magmas formed during melting within this domain.
