Academic literature on the topic 'Post-subduction magmatism'

ABSTRACT The Franciscan Complex of California, the type example of an exhumed accretionary complex, records a protracted history of voluminous subduction accretion along the western margin of North America. Recent geochronological work has improved our knowledge of the timing of accretion, but the details of the accretionary history are disputed, in part, due to uncertainties in regional-scale correlations of different units. We present new detrital zircon U-Pb ages from two sites on opposite sides of San Francisco Bay in central California that confirm previously proposed correlations. Both sites are characterized by a structurally higher blueschist-facies unit (Angel Island unit) underlain by a prehnite-pumpellyite-facies unit (Alcatraz unit). The Angel Island unit yields maximum depositional ages (MDAs) ranging from 112 ± 1 Ma to 114 ± 1 Ma (±2σ), and the Alcatraz unit yields MDAs between 94 ± 2 Ma and 99 ± 1 Ma. Restoration of post-subduction dextral displacement suggests these sites were originally 44–78 km apart and much closer to other Franciscan units that are now exposed farther south in the Diablo Range. Comparison with detrital zircon dates from the Diablo Range supports correlations of the Bay Area units with certain units in the Diablo Range. In contrast, correlations with Franciscan units in the northern Coast Ranges of California are not robust: some units are clearly older than those in the Bay Area whereas others exhibit distinct differences in provenance. Integration of age data from throughout the Franciscan Complex indicates long-lived and episodic accretion from the Early Cretaceous to Paleogene. Although minor, sporadic accretion began earlier, significant accretion occurred during the interval 123–80 Ma and was followed by minor accretion at ca. 53–49 Ma. Periods of accretion and nonaccretion were associated with arc magmatism in the Sierra Nevada–Klamath region, cessation of arc activity, and reorganization of paleodrainage systems, which implicates plate dynamics and sediment availability as major controls on the development of the Franciscan Complex.

The Jurassic subduction of the Neo-Tethys oceanic crust under the western continental margin of the Iranian Block has led to the fragmentation of the Iranian Block in the back-arc basin, leading to the opening of three oceanic basins around it. The ophiolitic belts surrounding central Iran are the indicators of the closure of these basins. The Sabzevar-Nain Basin is one of these basins, which has been created between the micro-block of central Iran in the south and the Alborz Mountain Ranges in the north. This basin opened in the late Jurassic as a rift and then became a trough in the early Cretaceous. Finally, this basin developed into an oceanic basin in the early late Cretaceous. The sedimentation in this basin can be divided into pre-rift, syn-rift and oceanic environments. All of these sediments are strongly folded and faulted. The closure of this basin started during the Paleocene with a subduction under the southern margin of the Alborz Mountain Ranges. The collision event between the northern margin of the micro-block of central Iran and the southern margin of the Alborz Mountain Ranges occurred in the early Eocene. The result of this event was the creation of a wide collision zone, forming a volcanic arc and a back arc basin on the active of the Alborz Mountain Ranges, an ophiolitic belt, and post- collision intrusion masses that appear everywhere in the collision zone. In the point of lithology, these intrusion masses are composed of granite, diorite, and granodiorite. The magmatic activities that started in the Paleocene-early Eocene continued until early Quaternary.