The Brazilian Shield

Question: “The Brazilian Shield is quite interesting. Likely the Nephites/Lamanites either did not know about it's existence or it was likely of such a low elevation that it may not have been inhabitable. Do you have any information about when it was colonized? Since the Andes would have been higher in elevation it makes sense that this area would be inhabitable. Thanks for the great information” 
    Response: Before answering this, let me just say that over the past few years we have received numerous flippant comments about how impossible it would have been for mountains to have formed in South America and the continent to rise above the surface in a matter of such a short time as described by Nephi during the crucifixion. It always amazes me how people with no background or understanding of the geological principles involved in such matters can so easily dismiss such events they lack any understanding about except for hearing or reading mainstream geologists who claim the Earth is 4.55 billion years old and that it takes tens of millions of years for mountains to form.
    This question, however, is just the opposite. Looking for the means by which continents rise and mountains are created, and how the building blocks of the continent determine what growth and phases the continent goes through during its existence.

On the other hand, it is claimed by geologists that it has taken 50-million years for the Himalayan mountain range and Tibetan plateau to have formed, which has resulted from the colossal collision between the Indian Plate and Eurasian Plate and continues today

    As one geologist stated in answering the question asked of him: “how long does it take for a mountain to form?” he answered, “It seems that since mountain ranges are created through the collision of tectonic plates ("theoretically"!), the scale of mountain creation is somewhere on the scale of tens to hundreds of millions of years. This of course depends on the specifics of the mountain we are discussing. To take a specific case: the Appalachian mountains on the northeastern seaboard of North America, took about 100 million years to completely form before plates shifted in a different direction. Now, 300 million years after the climax of the orogeny, the appalachians are much nearer to their death via erosion and subduction than their genesis.”
    One parenthetical note is most important here, and that is “theoretically!” So let us take a     look at the queston asked us and the formation of some solid evidence in South America about mountain building and continent-rising.

Most of the entire North American continent is a Craton, that is, a long-standing area of little or no movement, i.e., a geologic stable area

    Another comment to make is that almost all of North America is a single Creton, that is, the brown area on the map above shows the part of the North American continent that has been stable for over 600 million years. This region is made up of a basement older Precambrian metamorphic and igneous rock that is mostly covered by a relatively thin cover of younger sedimentary rock—a long-stable continental core, a Credton. And with such stability, the credibility by Great Lakes theorists that there has been movement or change in the lifetimre of man is contrary to the geologic bases of the entire area.

As for South America, there are two shields or rock Cretons in the north and east of the continent—these are stable portions of the continental crust from regions that are more geologically active and unstable. Cratons can be described as shields, in which the basement rock crops out at the surface, and platforms, in which the basement [rock] is overlaid by sediments and sedimentary rock—Sedimentary rock is one of the three main rock groups, along with “igneous” and “metamorphic” rocks, and is formed in four main ways: first, by the deposition of the weathered remains of other rocks (known as clastic sedimentary rocks; second, by the accumulation and the consolidation of sediments; third by the deposition of the results of biogenic activity; and fourth by precipitation from solution. Thus, rock that develops atop a Craton is far less stable and “permanent” as the rock making up the Craton beneath.
    Sedimentary rocks include common types such as chalk, limestone, sandstone, clay and shale, all of which covers about 75% of the Earth's surface, and develop in one or a combination of four basic processes, such as 1) weathering (erosion) caused mainly 2) by friction of waves, 3) transportation where the sediment is carried along by a current, or 4) deposition and compaction where the sediment is squashed together to form a rock of this kind. Sedimentary rocks, then, are formed from overburden pressure as particles of sediment are deposited out of air, ice, or water flows carrying the particles in suspension.
    As sediment deposition builds up, the overburden (or 'lithostatic') pressure squeezes the sediment into layered solids in a process known as lithification (“rock formation”) and the original connate fluids are expelled.
    So, with the Cratons forming at or just beneath the surface, the sedimentary rocks formed on top, creating a taller or higher solid rock foundation, called a Craton, that is about as permanent as rock can get and is the stable portion of the continental crust, especially known in regions that are more geologically active and unstable—such as was and is the continent of South America.

The Continental Craton. Sitting beneath both oceanic and continental crust is rigid peridotitic mantle that, with the overlying crust, comprises the lithosphere. Note: the Mantle Keel hosts nearly all of the world’s gem diamonds, and thus it deserves more than passing attention when considering the geologic origin of diamonds, and how far it deepens beneath the Craton 

    In addition, Cratons have thick lithospheric roots. Mantle tomography (imaging the subsurface of the Earth with seismic waves produced by earthquakes or explosions) shows that cratons are underlain by anomalously cold mantle corresponding to lithosphere more than twice the typical 60-mile thickness of mature oceanic or non-cratonic, continental lithosphere. At that depth, craton roots extend into the asthenosphere, which is the upper mantle of earth. Craton lithosphere is distinctly different from oceanic lithosphere because cratons have a neutral or positive buoyancy, and a low intrinsic isopycnic density—which is the core of the continent. This low compactness offsets density increases due to geothermal contraction and prevents the Craton from sinking into the deep mantle. In geology, Cratonic lithosphere is much, much older than oceanic lithosphere.
    Rock fragment xenoliths, which is “foreign rock” that is carried up from the mantle by magmas containing peridotite (coarse-grained igneous rock) delivered to the surface as inclusions, that is, any material that is trapped inside a mineral during its formation in subvolcanic (an intrusive igneous rock emplaced at medium to shallow depths within the crust) pipes called kimberlites, a rock which sometimes contain diamonds. These inclusions have densities consistent with Craton composition and are composed of mantle material residual from high degrees of partial melt, and are strongly influenced by the inclusion of moisture, which produces a low moisture content, that leads to much greater strength. It also contains high percentages of low-weight magnesium instead of higher-weight calcium and iron.

Cratons, both old and strong. Cratons are pieces of continents that have been stable for a very, very long time. As earth’s plates drift along, mountains periodically rise and fall, plate boundaries appear and disappear. But cratons are like great-grandmothers at family gatherings, while younger crust moves excitedly around them, they sit quietly, occasionally remarking on how different things were when they were young

    As for the Shield, it is generally a large area of exposed Precambrian crystalline igneous and high-grade metamorphic rocks that form tectonically stable areas. In all cases, the age of these rocks is very old and have been little affected by tectonic events, and are relatively flat regions where mountain building, faulting, and other tectonic processes are greatly diminished compared with the activity that occurs at the margins of the shields and the boundaries between tectonic plates.
    The term Shield, used to describe this type of geographic region, appears in the 1901 English translation of Edward Suess’, Face of Earth by H. B. C. Sollas, and comes from the shape "not unlike a flat shield" of the which has an outline that "suggests the shape of the shields carried by soldiers during the days of hand-to-hand combat."
    The furthest north of the South American shields is that of the Guiana Shield, and you can go to our website blog: Wednesday, September 12, 2012 for information on that.