U-Pb dating of single zircon grains from a graywacke of the Point Lake area of the Archaean Slave Structural Province in Canada indicates that this sediment is derived from two sources: (1) the ancient shield (parts of which are at least 3100 Ma old), which is the basement of the Slave Province supracrustal rocks; and (2) younger rocks (about 2700 Ma old). This implies the creation of large amounts of acidic to intermediate rocks during the 2700 Ma event. It also indicates that magma generation and intracontinental sedimentary basin formation and deepening are strongly related.

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