Abstract

At Chelan Butte in central Washington the marginal granodiorite facies of a large batholith is irruptive into hornblende schist. Along the margin a broad zone of contact breccias and striped migmatites has been formed which occupies an area of many square miles. Field study, petrographic examination, and chemical analyses, all converge to show that the inclusions of schist caught up by the batholith were first thoroughly recrystallized, feldspathized, and silicified until they became fine-grained granoblastic rocks which megascopically resemble diorites, and then were differentially assimilated as a result of the liquefaction and running together of the felsic constituents allowing the remaining still-solid material which consisted chiefly of hornblende to pack together into clots of amphibolite. During this process the hornblende crystals of the zenoliths grew in size by precipitation of material upon them from the adjacent magma.

Such amphibolite clots are indistinguishable from the “basic schlieren” which occur throughout the batholith. Although definitive proof is lacking, it is suggested that the basic schlieren of this and other areas may represent similarly reconstituted foreign inclusions. A modification of Beger’s hypothesis of the origin of lamprophyres is suggested in view of this conception of the origin of schlieren.

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