Paper No. 29-3
Presentation Time: 2:10 PM
EVALUATING SUBDUCTION ACCRETIONARY COMPLEX ARCHITECTURE AND HISTORY: ACCRETIONARY UNIT TYPES FROM THE FRANCISCAN AND MIURA-BOSO COMPLEXES
Subduction accretionary complexes (SACs), such as the Franciscan Complex of California and southern Oregon, consist of major and minor structural, stratigraphic, and tectonostratigraphic units. These units comprise Accretionary Units (AUs), the major architectural units of SACs. AUs are bounded by major faults, but AUs differ from terranes in that unlike terranes, they may contain units stratigraphically correlative with units in other major architectural units. AUs occur in three kinds of basic format — (1) singular sheets of mélange, dismembered formation, or coherent stratigraphic layers; (2) extensively faulted stratigraphic masses (broken formations or broken groups); and (3) folded units composed of one or more stratigraphic or block-in-matrix units. Composite AUs with attributes of all three formats are known and multiple suites of deformation features may arise from progressive early deformation or from later superimposed deformational events. AUs may be subdivided into traditional and other sub-units such as fault blocks, mélanges, dismembered formations, broken formations, formations, and members. Each AU should be defined on the basis of a unique set of characters that derive from a thorough description of the AU, including its distinct rock types and character; and where possible, submarine fan facies; structures; metamorphic facies; and unit history. Descriptions of partially described AUs from the Franciscan Complex of California — including the Rodeo Cove Melange AU, Conzelman Circle AU, and Black Sand-Conzelman AU of the Marin Headlands, and from the Miura-Boso area of Japan —including the Southern Misaki AU,provide concrete examples of the varied characteristics of AUs and their subunits. Ideally, the architecture and history of SACs, including the Franciscan Complex, can be detailed by assembling text and detailed map descriptions of AUs and their 3D positions, relationships, and histories.