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within-plate basalt (WPB) Basalts which are generated within a continental or oceanic plate, rather than at a constructive or destructive plate margin. Continental flood basalts (e.g. the Columbia River Plateau in the western USA) and ocean island basalts are types of within plate basalts. Although each has its own particular geochemical characteristics, they have been identified as a coherent group using their Ti/100; Zr; Y × 3 ratios (against a standard). This effectively separates the WPB group from the mid-ocean-ridge basalt (MORB), low-potassium tholeiite, and calc-alkaline basalt groups.