RE-CRYSTALLIZATION IN GEOLOGY

Re-crystallization in Geology

Abstract

A geologic fold occurs when a flat surface is bent or contorted. For a rock or sediment to show its folds, it must have a set of parallel surfaces or different layers inside it. A very homogeneous rock mass with no internal variation would not show that any force had been applied to it to make it fold. Folds form in sediments and rocks generally from near the surface to as much as 45 km (kilometers) deep in the Earth, where elevated temperatures and the high rock overburden and fluid pressures cause the rocks to be ductile and change shape as they are subjected to tectonic or other forces from glaciers and surface processes. This allows their development in sediments and sedimentary rocks, in a full spectrum of metamorphic rocks, and even as primary flow structures in some igneous rocks.

Clastic sedimentary rocks constitute more than 75% of the total sedimentary rocks. These rocks are formed from cemented grains and particles derived from the breakdown of preexisting rocks of any type (e.g., igneous, sedimentary, or metamorphic). The classification of clastic sedimentary rocks is based mainly on the size of the grains. A clastic sedimentary rock formed by gravel (i.e., grains bigger than 2 mm [millimeters] in diameter: granules, pebbles, or boulders) is called conglomerate (if the grains are rounded) or breccia (if the grains are angular).

Re-crystallization in Geology

Introduction

In geology, re-crystallization refers to the metamorphic process, which occurs under different situations of high and intense temperature along with pressure where atoms and molecules of a mineral or rock are packed closer together, creating a new crystal structure. This process can be easily understood by taking the example of snow or glaciers.

Glacier

The term glacier originates from the Latin word glacies, meaning “ice,” and refers to anybody of perennial ice originating on land through the densification and re-crystallization of snow that is massive enough to be flowing under its own weight. Generally, glaciers form in areas where the annual accumulation of snow, through precipitation and deposition, is greater than the annual mass loss due to melting, sublimation, and the calving of icebergs at the glacier margin. Glaciers provide important stores of water to more than 40% of the world's population, maintain the temperature of the planet through a high albedo (they reflect sunlight back to space), and, in the case of the largest bodies of ice, even affect local and regional climate (Thomas, 1993).

Process of re-crystallization in glaciers

Glaciers form where the snow accumulates for hundreds to thousands of years. As the snow accumulates, older layers of snow are buried beneath more and more mass and are eventually compressed and re-crystallized into dense glacial ice (density = 917 kilograms per cubic meter). If enough mass accumulates, the ice begins to flow downhill and outward toward the margins, where mass is lost.

Mass loss on a glacier is known as ablation. Anywhere on the glacier or ice mass where annual ablation exceeds accumulation is included in the ablation ...