Abstract

The Payson ophiolite (ca. 1.73 Ga), exposed within the Early Proterozoic orogenic belt of central Arizona, is a shallow-dipping, pseudostratigraphic sequence of gabbro, sheeted dikes, and submarine volcanic rocks, partly disjointed by later intrusion and deformation. An older basement complex occurs as roof pendants in the gabbro and screens in the sheeted dike complex and was tilted and eroded prior to development of the ophiolite. Gabbro-dike mingling and mutual intrusion in the transition from gabbro to sheeted dikes indicates that the dikes are rooted in the gabbro. Analysis of detailed measured sections of well-exposed sheeted dikes (600 m) reveals 90%–100% dikes with lateral variations in the proportions of tonalitic or dacitic dikes and basement screens. The transition from sheeted dikes to submarine basalts is abrupt and marked by a stratigraphically continuous zone of intensely altered rocks. The sheeted dike complex, pseudostratigraphic structure, and synmagmatic hydrothermal alteration of the Payson ophiolite are diagnostic of a crustal section formed by sea-floor spreading.

The Payson ophiolite intrudes, and is intruded by, arc granitoids and is overlain by arc-derived volcanic and sedimentary rocks. A model of an intra-arc basin formed along an arc parallel strike-slip fault is proposed to account for (1) screens of older arc crust, (2) inferred arc-parallel extension, and (3) juxtaposition of the ophiolite with a distinct arc terrane prior to regional convergent deformation and accretion of the arc to North America during the Yavapai orogeny (ca. 1.70 Ga).

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