Carbonate Petrography

Carbonate petrography is the study of limestones, dolomites and associated deposits under optical or electron microscopes greatly enhances field studies or core observations and can provide a frame of reference for geochemical studies.

25 strangest Geologic Formations on Earth

The strangest formations on Earth.

What causes Earthquake?

Of these various reasons, faulting related to plate movements is by far the most significant. In other words, most earthquakes are due to slip on faults.

The Geologic Column

As stated earlier, no one locality on Earth provides a complete record of our planet’s history, because stratigraphic columns can contain unconformities. But by correlating rocks from locality to locality at millions of places around the world, geologists have pieced together a composite stratigraphic column, called the geologic column, that represents the entirety of Earth history.

Folds and Foliations

Geometry of Folds Imagine a carpet lying flat on the floor. Push on one end of the carpet, and it will wrinkle or contort into a series of wavelike curves. Stresses developed during mountain building can similarly warp or bend bedding and foliation (or other planar features) in rock. The result a curve in the shape of a rock layer is called a fold.

Where Does Metamorphism Occur?

Where Does Metamorphism Occur? 

So far, we've discussed the nature of changes that occur during metamorphism, the agents of metamorphism (heat, pressure, compression and shear, and hydrothermal fluids), the rock types that form as a result of metamorphism, and the concepts of metamorphic grade and metamorphic facies. With this background, let’s now examine the geologic settings on Earth where metamorphism takes place, as viewed from the perspective of plate tectonics theory.
Because of the wide range of possible metamorphic environments, metamorphism occurs at a wide range of conditions in the Earth. You will see that the conditions under which metamorphism occurs are not the same in all geologic settings. That’s because the geothermal gradient (the relation between temperature and depth), the extent to which rocks endure compression and shear during metamorphism, and the extent to which rocks interact with hydrothermal fluids all depend on the geologic environment.

Types of Metamorphic Rocks

Types of Metamorphic Rocks 

Coming up with a way to classify and name the great variety of metamorphic rocks on Earth hasn't been easy. After decades of debate, geologists have found it most convenient to divide metamorphic rocks into two fundamental classes: foliated rocks and non-foliated rocks. Each class contains several rock types. We distinguish foliated rocks from each other partly by their component minerals and partly by the nature of their foliation, whereas we distinguish non-foliated rocks from each other primarily by their component minerals. 

Foliated Metamorphic Rocks 

To understand this class of rocks, we first need to discuss the nature of foliation in more detail. The word comes from the Latin folium, for leaf. Geologists use foliation to refer to the parallel surfaces and/or layers that can occur in a metamorphic rock. Foliation can give metamorphic rocks a striped or streaked appearance in an outcrop, and/or can give them the ability to split into thin sheets. A foliated metamorphic rock has foliation either because it contains inequant mineral crystals that are aligned parallel to one another, defining preferred mineral orientation, and/or because the rock has alternating dark-coloured and light-coloured layers.

Sedimentary Basins

Sedimentary Basins

The sedimentary veneer on the Earth’s surface varies greatly in thickness. If you stand in central Siberia or south-central Canada, you will find yourself on igneous and metamorphic basement rocks that are over a billion years old sedimentary rocks are nowhere in sight. Yet if you stand along the southern coast of Texas, you would have to drill through over 15 km of sedimentary beds before reaching igneous and metamorphic basement. Thick accumulations of sediment form only in special regions where the surface of the Earth’s lithosphere sinks, providing space in which sediment collects. Geologists use the term subsidence to refer to the process by which the surface of the lithosphere sinks, and the term sedimentary basin for the sediment-filled depression. In what geologic settings do sedimentary basins form? An understanding of plate tectonics theory provides the answers.

Relation of Volcanism to Plate Tectonics

Relation of Volcanism to Plate Tectonics 

A map showing the distribution of volcanoes around the world and the basic geologic settings in which volcanoes form, in the contact of plate tectonics theory.
Different styles of volcanism occur at different locations on Earth. Most eruptions occur along plate boundaries, but major eruptions also occur at hot spots (figure above). We’ll now look at the settings in which eruptions occur, in the context of plate tectonics theory and see why different kinds of volcanoes form in different settings.

How Do You Describe an Igneous Rock?

How Do You Describe an Igneous Rock? 

Different parameters are used to describe an igneous rock which are described in detail.

Characterizing Color and Texture 

If you wander around a city admiring building facades, you’ll find that many facades consist of igneous rock, for such rocks tend to be very durable. If you had to describe one of these rocks to a friend, what words might you use? You would  probably start by noting the rock’s colour. Overall, is the rock dark or light? More specifically, is it gray, pink, white, or black? Describing colour may not be easy, because some igneous rocks contain many visible mineral grains, each with a different colour; but even so, you’ll probably be able to characterize the overall hue of the rock. Generally, the colour reflects the rock’s composition, but it isn't always so simple, because colour may also be influenced by grain size and by the presence of trace amounts of impurities. (For example, the presence of a small amount of iron oxide gives rock a reddish tint.) Next, you would probably characterize the rock’s texture. A description of igneous texture indicates whether the rock consists of glass, crystals, or fragments. If the rock consists of crystals or fragments, a description of texture also specifies the grain size. Here are the common terms for defining texture: