I. INTRODUCTION A significant portion of New England was formed as a result of an accretionary orogen. Southeastern New England is marked by a series of terranes that accreted onto the Laurentian supercontinent during the Silurian and Devonian. The Terranes of Gander, Nashoba, Avalon, and Meguma are present from west to east in eastern Massachusetts and all of are Gondwanan provenance. Their modern-day juxtaposition suggests that the marginal Gondwanan micro-continents collided sequentially from west to east, expanding the Laurentian continent with each respective collision. As each subsequent plate collided, an intervening subduction zone died and a new subduction zone was created to the east. The oblique collision of the Avalon Terrane into Laurentia followed the accretions of the Gander and Nashoba Terranes and preceded the accretion of Meguma. The collision was marked by uplift, mylonitic metamorphism, and calc-alkaline Nashoba plutonism as the Iapetus Ocean subducted under the Nashoba and eventually the Avalon collided obliquely into the continental margin. The area composed of the Gander, Nashoba, Avalon, and Meguma Terranes has been extensively studied for many years. However, it was only recently that the terranes were recognized as distinct geologic entities with unique tectonic histories thus there is still much debate regarding the tectonic model which brought these terranes together (Hon et al., 2007). This paper will address the geology of the peri-Gondwanan terranes and propose a potential tectonic model for the accretional orogenic events. It will also primarily focus on the juxtaposition between the Nashoba and Avalon Terranes. II. TECTONIC SETTING Global Tectonics The most recent complete supercontinent cycl... ... middle of paper ... ...J.C. (2004) Mylonites and Brittle Shear Zones Along the Western Edge of the Avalon Terrane West of Boston, NEIGC Field Trip Guide. Marshak, S. (2009) Essentials of Geology, 3rd ed. New York: W.W. Norton & Company, ch. 11, p. 298-320. Skehan, J.W., Rast, N., Kohut, E., Hepburn, J.C., and Grimes, S.W. (1998) Precambrian and Paleozoic Mylonites of the Boston Avalon, NEIGC Field Trip Guide. Stroud, M.M., Markwort, R.J., and Hepburn, J.C. (2009) Refining Temporal Constraints on Metamorphism in the Nashoba Terrane, Southeastern New England, Through Monazite Dating. Lithosphere, vol. 1, p. 337-342. Van Staal, C.R., Whalen, J.B., Valverde-Vaquero, P., Zagorevski, A., and Rogers, N. (2009) Pre-Carboniferous, Episodic Accretion-Related, Orogenesis along the Laurentian Margin of the Northern Appalachians. Geological Society, London, Special Publications, vol. 327, p. 271-316.
The Starved Rock Member of the Saint Peter Sandstone is preserved as a northeast-southwest trending belt of strata that is ...
"NPS: Nature & Science» Geology Resources Division." Nature.nps.gov » Explore Nature. Web. 05 Dec. 2011. .
The coastal belt of the Franciscan Complex is composed of the youngest and least deformed units and makes up the western quarter of all Franciscan rocks. The rocks of the coastal belt are composed of arkosic sandstones, andesitic graywackes, and quartzofeldspathic graywackes interbedded with radiolarian chert (turbidite deposits) (Blake and Jones, 1981). These sedimentary rocks suggest a depositional environment of deep-sea fan systems with both oceanic and continental provenance. Parts of the belt show evidence of later metamorphism, principally due to subduction. Low-grade blueschist mineral facies are indicated by the presence of minerals such as laumonite and prehnite-pumpellyite (Blake and Jones, 1981). All rock units show evidence of thrust (imbricate) faulting due to the compressional forces of subduction. Ages of the coastal belt run from as little as 40 Ma (Eocene) to as old as 100 Ma (middle Cretaceous).
Plummer, C.C., McGeary, D., and Carlson, D.H., 2003, Physical geology (10th Ed.): McGraw-Hill, Boston, 580 p.
Ehlen, Judy, and R.C. Whisonant. 2008. "Military geology of Antietam battlefield, Maryland, USA—geology, terrain, and casualties." Geology Today 20-27.
The sharp differences in elevation between the Badwater Basin and the surrounding mountains that include the highest point in the continental US (Mt. Whitney at 14,494 feet) stand as a representation of the regions violent tectonic past. The mountains themselves are considered fault block mountain ranges meaning that they were formed when blocks of rocks were squeezed through the Earth's crust along parallel faults or were loosened from the crust when it separated at a fault. In the valley, both of these methods not only were the cause of the current mountains formation less than four million years ago, but also are causing the mountains to be uplifted while the valley floor drops even further. This phenomenon is one of the reasons why the lowest and highest points in the continental...
After the Laramide orogeny things were still happening, just as always with Earth. Something is always changing even if it is not detectable day by day. Due to the Farallon Plate subducting there was a suction like effect going on because of the water that was being taken in with it (Humphreys). This would cause the North American plate to become weak and unstable, because it was being hydrated. This eventually would result in large plateaus and large amounts of uplift (Humphreys). There are many things that have been going on through out this time period but it all turns around and creates and shapes the earth into what it is today as well as what it will be in the future.
The rest of this article spends time speculating through the advances in technology and the reanalyzation of old evidence to determine various cataclysmic events that happened millions of years ago. There are many sections in this article that discuss the methods used to determine the closet possible dates and the sequence in which they follow. There are also sections in this article which discuss methods used for the evidence of impact, eruption and how reading the environmental changes can help paleontologists determine conclusions and narrow the perspectives of paleontologists (scientists) and popular culture as a whole.
Kennedy, Martin J.; Runneger, Bruce; Prave, Anthony R.; Hoffmann, K -H. ; Arthur, Michael A. (1998) Two or four Neoproterozoic glaciations? Geology 1059-1063
System and the Basalts of the Newark Basic, New Jersey, U.S.A.: Journal of Geology, p.
... used to be a sea (Beaumont,1978). As mountain-building forces continued for several million years it created a big fold or anticline as it squeezed the rocks. These same pressures continued and overturned the fold which eventually caused them to break along a great low-angle fault (Beaumont,1978). The western limb of the fold was driven upward and eastern placing older layers of rock on top of younger ones. The younger layers of rock include cretaceous shales and sandstones. The slice of crust has been moved more than 15 miles toward the east, the surface it moved through is called the Lewis Overthrust. (Dyson,1957). Years of erosion finally exposed the fault which was buried throughout its early years. Erosion then separated several remnants, Chief Mountain is the best known which consists of Altyn limestone, exposed on its base is the Lewis Overthrust fault.
Anatolian is a region in Turkey where vast amount of tectonic activity which was followed by magmatism took place during the Cenozoic era. The Anatolian microplate is bound to the north by the Mediterranean Sea, to the east by the Red sea and, to the south by the Aegean Sea. Ophiolites and suture zones seperate different pieces of continental blocks that came together to form the Anatolian microplate (Altunkaynak et al. 2012). Chorowicz (1999) defines Anatolia as a product of the African and Eurasian plate collision which formed mainly from lithospheric magma. A widespread of magmatism accompanied plate tectonism experienced in this region during the Cenozoic era. The late Eocene (37.3 ± 4.6, measure through K-Ar radiometric dating) marks the initial period where this magmatism in took place. This essay will establish if whether an East-west spatial control on the chemistry of Anatolian volcanics exists.
Smithsonian National Museum of Natural History (2014). Burgess Shale Fossil Specimens. Retrieved May 2014, from http://paleobiology.si.edu/burgess/burgessSpecimens.html
Froede, Carl R. “Stone Mountain Georgia: A Creation Geologist's Perspective.” CRS Quartely 31, no. 4 (March 1995): 6.
With its abundance of genera, the Burgess Shale is one of the world’s most important fossil fields. It’s discovery in 1909 led to over 100 years of paleontological study in the Canadian Rockies, a majority of which has been carried out in two quarries known as the Walcott and Raymond quarries (Hagadorn, 2002). Though he was originally in search of trilobites in the Burgess Shale Formation, paleontologist Charles Walcott also discovered a diverse group of soft- and hard-bodied fossils, from algae and sponges to chordates and cirripeds (Hagadorn, 2002). Soft-bodied fossils are incredibly rare due to their delicate structure and susceptibility to decay, so it is hard-bodied fossils that more regularly occur in fossil findings. However over 75,000 soft-bodied specimens have been found in the Burgess Shale formation (Hagadorn, 2002). These specimens are preserved in layers of shale formed from deposits of fine mud. One of the most significant species discovered is the Pikaia gracilens. Believed to be an early chordate, the Pikaia gracilens existed very close to the beginning of the evolutionary path that ultimately lead to humans (McGraw-Hill Encyclopedia, 2006).