ResultsThis signature is found in Sulphur in the Archean before about 2.5 Ga ago. Farquhar’s discovery shows that there was a process taking place in the Archean which carried materials from earths surface to the mantle to the depth of diamond formation which is over 100 kilometers. One such process is subduction. (Rollinson, H.
, 2007. When did plate tectonics begin? Geology Today, 23(5), pp.190.) DiscussionThis theory is from stern who used evidence of former subduction as signs of former plate tectonic criteria is required to determine when plate tectonics had first begun. (Rollinson, H., 2007.
When did plate tectonics begin? Geology Today, 23(5), pp.191.) Blueschists analysis: electron microscope approachMethodThe mineral compositions were determined by electron microprobe on an ARL-EMX wavelength dispersive system along with a TN-2000 Tracor Northern energy dispersive system.
Isotopic analyses were carried out on a Varian-MAT GD150 mass spectrometer and the measurements were corrected for mass discrimination and sensitivity by using a calibrated argon pipette. (V.B Sisson and T.
C. Onstott, Dating blueschist Metamorphism: A combined Argon-40/Argon-39 and electron microprobe approach Pg. 1)ResultsThe crossite from the Iceberg lake schist yields a date of 176.6 Ma. For slab geometry, an initial age of 108 Ma was calculated. (V.B Sisson and T.
C. Onstott, Dating blueschist Metamorphism: A combined Argon-40/Argon-39 and electron microprobe approach Pg. 3)DiscussionThe potassium oxide content of the crossite was estimated from the amount of isotope Argon 39 was released, therefore this may have affected the results slightly. (V.B Sisson and T.C.
Onstott, Dating blueschist Metamorphism: A combined Argon-40/Argon-39 and electron microprobe approach Pg. 3) As blueschists were formed in low temperature and high-pressure conditions, it is indicative of a time on earth where cool crust was buried to great depth i.e. Indicates when plate tectonics may have begun.ConclusionEvidence from the Isua Accretionary complex suggest that plate tectonics had taken place 0.7-0.8 G. yr.
after the formation of Earth, signature Sulphur isotopes were more prominent 2.5 Ga ago, Blueschists were recorded to yield at an age of 176.6 Ma. These results are indicative that the beginning of plate tectonics was in fact in the Archean era, however, the ages of the different rocks and complexes differ, making it very difficult to determine a single age at which the tectonics started. Furthermore, it should be reiterated that these results were obtained from the oldest specimen of rock found, not the oldest rock available and uplift and subsidence make it harder to obtain older rock.
Moreover, in 2006 the Geologic society of America Penrose had a vote to decide when the scientists thought plate tectonics had begun. It was decided by the second vote that the median answer was that it took place 3.0 to 3.
5 Ga ago, however the key point here is that voting is not an accurate representation of the answer to the beginning of tectonics. This is clearly inaccurate and may have some bias which drastically changes the reliability of the answer to the topic at hand. This is indicative of the fact that currently geologists are depending on estimates of when tectonics had begun, rather than factual information, and raises the question: will we ever be sure of the exact age at which tectonics had started?References: (Komiya, T., Maruyama, S., Masuda, T., Nohda, S., Hayashi, M. and Okamoto, K.
, 1999. Plate tectonics at 3.8–3.7 Ga: field evidence from the Isua accretionary complex, southern West Greenland. The Journal of Geology, 107(5), pp.
515-554.)(Rollinson, H., 2007. When did plate tectonics begin? Geology Today, 23(5), pp.190.) (Rollinson, H.
, 2007. When did plate tectonics begin? Geology Today, 23(5), pp.191.) (Stern, R.J., 2007. When and how did plate tectonics begin? Theoretical and empirical considerations. Chinese Science Bulletin, 52(5), pp.
578-591.)(V.B Sisson and T.C. Onstott, Dating blueschist Metamorphism: A combined Argon-40/Argon-39 and electron microprobe approach Pg. 1)(V.
B Sisson and T.C. Onstott, Dating blueschist Metamorphism: A combined Argon-40/Argon-39 and electron microprobe approach Pg. 3)(Yuichiro Uenoa, b, Matthew S. Johnsonc,1, Sebastian O.
Danielacheb, c,d, Carsten Eskebjergc, Antra Pandeyb,d, and Naohiro Yoshidab,d-Geological sulfur isotopes indicate elevated OCS in the Archean atmosphere, solving faint young sun paradox, volume 106, No.35, Page 4)
