We now journey to Oman, where we can examine the rocks within the Murri Anticline to help us understand an ancient oceanic-oceanic subduction complex. Oceanic-Oceanic Convergence: The Semail Ophiolite Complexįor our second stop, we will examine another convergent boundary situation, but this time it will be only oceanic lithosphere that was involved. You can learn more about California’s Coast Ranges and their accretionary wedge rocks in this case study. In addition to the serpentinite you see, if this is indeed a plate boundary where chunks of seafloor are being recycled, what other rock types might you expect to find contained as sheared-out chunks within the mélange? Large rounded chunks of seafloor are included within the serpentinite mélange. Serpentinite is a metamorphic rock that is created through the hydrous alteration of ultramafic rocks under great pressure. One type of rock that makes mélange in subduction zones is serpentinite. This is what is referred to with the French term “ mélange.” Translated, it means “mixture.” Mélange is a sheared-out mixture of heterogeneous seafloor scrapings. All of this is stirred up and mashed ocean floor sediment metamorphosed as one plate dove beneath another. The Franciscan Complex is a body of rock that, as you can see below, is in part made up of a metamorphic rock called serpentinite (formed under very intense pressures when mantle peridotite reacts with water), along with chunks of metamorphically altered ancient basaltic seafloor mixed with shelf and seafloor sediments such as cherts and mudstones. The accretionary prism units, including the mélange, are indicated in blue. The geologic setting of the Franciscan Complex. Consider what kinds of other rocks you might seek nearby if you wished to confirm your analysis of an outcrop of Franciscan Complex. In this case, the subduction was a classic situation of oceanic-continental convergence. The subduction zone is no longer active it shows us rocks that formed during the Mesozoic Era. This complex of rock is a part of the accretionary wedge, or mélange, associated with a subduction zone. The first image below is of an artist’s rendering of an idealized subduction zone displaying the “Franciscan Complex” in situ. Convergent Boundaries Continental-Oceanic Convergence: The Franciscan Complexįor a more in-depth geological analysis of this plate boundary, read this case study on the Franciscan Complex here. In this VFE, we will virtually travel to examples of all of the major types of plate boundaries, including:ġ) Convergent Boundary, Continental-Oceanic (Franciscan Complex, San Francisco, USA)Ģ) Convergent Boundary, Oceanic-Oceanic (Semail Ophiolite, Oman)ģ) Convergent Boundary, Continental-Continental (Himalayas)ĥ) Divergent Boundary, Continental (East African Rift)Ħ) Transform Boundary (San Andreas Fault)Īt each of these sites, you will be asked to use your powers of observation to explore some of the field geology produced at such locations. Plates and plate boundaries with a general sense of motion identified.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |