LATE CENOZOIC MAGMATISM OF THE NORTHWESTERN U.S. – THE ROLE OF SUB-CONTINENTAL LITHOSPHERIC MANTLE (SCLM)
These patterns suggest that the lithospheric plate strongly influences magmatic processes, with different influences between the craton to the east of the ID-OR border and accreted oceanic terranes to the west. Specifically, the thicker cratonic lithosphere precludes significant melt production from the Yellowstone plume, and favors infiltration of basaltic magmas within the crust/upper mantle and generation of voluminous silicic magmas in part due to remelting of early mafic inputs. Geochemistry of the mafic magmas is consistent with melting of ancient subcontinental lithospheric mantle (SCLM), rather than the plume, and this process can be attributed to decompressional melting of such domains in response to lithospheric extension that has propagated eastward across the region (and moreso in the Basin & Range province to the south).
Thinner lithosphere beneath the western accreted terranes may allow more efficient melting of upwelling sub-lithospheric mantle. However, geochemistry of basalts there implies that their sources (SCLM?) have been modified to varied extent by ancient(?) additions of subduction-like components, and this precludes their formation dominantly from a typical plume upwelling.