OPHIOLITE FORMATION AND OBDUCTION DURING THE PHANEROZOIC AND LATE PRECAMBRIAN

Ophiolites, tectono-stratigraphic assemblages of ancient oceanic crust are one of the key lines of evidence used to reconstruct ancient ocean basins and to constrain the timing of the collisional events that closed these ocean basins. We have assembled an ArcGIS (ESRI) database that describes the geographic and chronologic occurrences of more than 300 ophiolite localities, worldwide. The attributes of each ophiolite locality include: 1) the age of the formation of the ocean floor comprising the ophiolite, 2) the tectonic setting in which the ocean floor was formed (i.e., mid-ocean ridge vs. back-arc basin), 3) the age of obduction of the ophiolite, and 4) the tectonic setting of ophiolite obduction (e.g., continent-continent collision, back-arc basin collapse). A completeness score was also given for each ophiolite indicating how many of the seven classic ophiolite components were observed.

Using ArcMap, the ophiolite localities were plotted on a set of 40 plate tectonic reconstructions assembled by the PALEOMAP Project. These maps illustrate the changing location of ancient spreading centers, subduction zones, island arcs, seamounts, and oceanic plateaus since the late Precambrian. An attempt was made to show both the timing and location of ophiolite obduction, and a speculative estimate of where the oceanic crust comprising the ophiolite originally formed. This was done by “back-tracking” plate motions. An animated version of these maps will be presented.

In general, the data that we have compiled indicate that ophiolites did not form uniformly in space and time. Rather, there are times when ophiolite formation and emplacement were more likely. As other authors have proposed, 1) the oceanic crust that makes up most ophiolites often forms near subduction zones, probably in back arc basins and island arcs, 2) the age of oceanic crust formation usually precedes the time of ophiolite obduction by less than 20 million years of each other, and 3) it seems likely that most ophiolites form as a result of back-arc basin collapse, which may be a precursor of continent-continent collision.