User:Delaneyhopen/Galapagos Triple Junction

Galapagos Triple Junction

The Galapagos Triple Junction (GTJ) is located off the western coast of South America and has been studied for its unique geologic structure of a triple junction. Although this collision is not uniform in its entirety, Geologists and Scientists have used various forms of study in an attempt to understand it’s physical history. Overtime, it has been hypothesized that the Triple Junction of the Nazca, Cocos, and Pacific Plate was once colliding in various areas but now is a simple RRR, with all divergent spreading ridges. These plates have different directions and velocities of plate movement, which have all over time adjusted providing new tectonic formations like various spreading ridges and the Galapagos Micro-Plate . Collision of oceanic plates often cause specific landforms like volcanic arc systems, and divergent plates cause trenches and seafloor spreading patterns and both are secondary formations due to the greater tectonics of this area. These structures are seen in the GTJ area, implying that not only divergent boundaries are present but smaller convergent and transform as well. Determining relative ages of the geology in the area is challenging due to consistent volcanic activity along spreading ridges and trenches bordering each plate boundary.

Location (Google Earth)

Approximately 1300 miles West, off the coast of Ecuador, is where this tectonic activity is occurring in the middle of the Pacific Ocean. The Galapagos Micro-Plate is just East (about 600 miles from Darwin’s famous Galapagos Islands). Relative coordinates of the spreading zones are at 1.4°S, 99.8°W. This was estimated by earthquake data and locating via bathymetric imaging .

This image shows the location of each plate relative to one another, while also displaying the location of the Galapagos Micro Plate created form the Cocos, Nazca, and Pacific Plate Triple Junction

Geology

Triple Junctions occur when three plates are all moving in different directions while remaining next to one another. Typically form the shape of a ‘T’ with one plate along the top line of the ‘T’, and one on both sides of the vertical perpendicular stem of the ‘T’. All three of these plates are colliding at its intersection point of both the vertical and horizontal lines. Like plates all over the world, each plate moves with its own unique direction and speed. Each plate is moving with a different velocity which can change the outcome and shape of the whole triple junction .

In the Galapagos Triple Junction, the three corresponding plates don't collide perfectly but instead display differences in responses to individual velocities. The GTJ doesn’t form a typical Ridge-Ridge-Ridge Triple Junction. In plate collision, this would be the ‘perfect’ scenario. Divergent and convergent plate boundaries can form ridges, trenches, and/or faults. The shortened ‘R’ ‘T’ and ‘F’ are used to symbolize when put together what kind of structures are formed on the plate boundaries. In collisional plate movement such as these, geologist use these letter symbols to determine the kind of junction created from colliding plates, so the perfect scenario would be ‘RRR’, one for each edge of the colliding t-shape.

Since this these faults along each plate are not uniform or consistent, the Galapagos Microplate is being created via different velocities and directions of spreading that have changed over millions of years. In the GTJ, the Pacific Plate, Cocos Plate, Galapagos Microplate and Nazca Plate are all the present tectonics at work . This activity is causing 3 different rift areas, an extended volcanic ridge, and a large dominant spreading center . The Pacific plate is moving the fastest at 95 mm/yr NE, then the Cocos Plate moving relatively N-NW 67 mm/yr, and 40 mm/yr E –NE for the Nazca Plate . Differing border velocities that detect the rate of spreading as well as the lack of/slowing of spreading are also considered as well .

To detect these plate boundaries, landforms were identified using bathymetry and sample drilling. Drilling obtained data of rock compositions that make up this area along seafloor spreading ridges. Peridotite, Gabbro, Basalt, and Diabase are present . These are deep ocean rock forms that similarly make up ophiolites.

References

• Cox, A., & Hart, Robert Brian. (1986). Plate tectonics how it works. Boston: Blackwell Scientific Publications.
• Smith, D. K., Schouten, H., Zhu, W., Montési, L. G. J., & Cann, J. R. (2011). Distributed deformation ahead of the Cocos‐Nazca Rift at the Galapagos triple junction. Geochemistry, Geophysics, Geosystems, 12(11), n/a–n/a. https://doi.org/10.1029/2011GC00368
• Smith, Deborah K., and Hans Schouten. “Opening of Hess Deep Rift at the Galapagos Triple Junction.” Geophysical Research Letters, vol. 45, no. 9, 16 May 2018, pp. 3942–3950. Web of Science, doi:10.1029/2018gl077555.