Amphibolite is a metamorphic rock that contains amphibole, especially the species hornblende and actinolite, as well as plagioclase. A holocrystalline plutonic igneous rock composed primarily of hornblende amphibole is called a hornblendite, rocks with >90% amphiboles which have a feldspar groundmass may be a lamprophyre. Amphibolite is a grouping of rocks composed mainly of amphibole and plagioclase feldspars and it is typically dark-colored and heavy, with a weakly foliated or schistose structure. The small flakes of black and white in the rock often give it a salt-and-pepper appearance, amphibolites need not be derived from metamorphosed mafic rocks. Because metamorphism creates minerals based entirely upon the chemistry of the protolith, certain dirty marls, deposits containing dolomite and siderite readily yield amphibolites especially where there has been a certain amount of contact metamorphism by adjacent granitic masses. Metamorphosed basalts create ortho-amphibolites and other chemically appropriate lithologies create para-amphibolites, while it is a metamorphic amphibole, is derived most usually from highly metamorphosed ultramafic rocks, and thus tremolite-talc schists are not generally considered as amphibolites.
If the amphibolite appears to transgress apparent protolith bedding surfaces it is an ortho-amphibolite, picking a sill and thin metamorphosed lava flows may be more troublesome. Thereafter, whole rock geochemistry will suitably identify ortho- from para-amphibolites, the word metabasalt was thus coined, largely to avoid the confusion between ortho-amphibolites and para-amphibolites. While not a metamorphic rock name, as it infers an origin. Amphibolites define a set of temperature and pressure conditions known as the amphibolite facies. However, caution must be applied here before embarking on metamorphic mapping based on amphibolites alone. Firstly, for an amphibolite to be classed as a metamorphic amphibolite, it must be certain that the amphibole in the rock is a prograde metamorphic product, for instance, actinolite amphibole is a common product of retrograde metamorphism of basalts at greenschist facies conditions. Actinolite schists are often the result of alteration or metasomatism. Secondly, the microstructure and crystal size of the rock must be appropriate, amphibolite facies conditions are experienced at temperatures in excess of 500 °C and pressures less than 1.2 GPa, well within the ductile deformation field.
Gneissic texture may occur nearby, if not mylonite zones and ductile behaviour, while it is not impossible to have remnant protolith mineralogy, this is rare. More common is to find phenocrysts of pyroxene, olivine and even magmatic amphibole such as pargasite rhombohedra, original magmatic textures, especially crude magmatic layering in layered intrusions, is often preserved. Amphibolite facies is a result of continuing burial and thermal heating after greenschist facies is exceeded, in dry rocks, additional heat may result in granulite facies conditions. The texture is distinctive, the pyroxene altered to fuzzy, radially arranged actinolite pseudomorphically after pyroxene, the archaic term epidiorite is sometimes used to refer to a metamorphosed ortho-amphibolite with a protolith of diorite, gabbro or other mafic intrusive rock
The name Western Alps refers to the western part of the Alpine range. The term has different meanings according to the classification of the Alps in use, the peaks and mountain passes are higher compared to the Eastern Alps, while the range itself is not so broad and more arched. The Western Alps include the part of France, whole Monaco, the north-western part of Italy. While in the south-east the range is bound by the Italian Padan Plain, in the east the valley of the Rhone river separates it from the Massif Central. The northernmost part of Western Alps - in the meaning of the term - is formed by the Swiss Prealps sub-range. In this traditional subdivision the Western Alps start from the Bocchetta di Altare and end with the Col Ferret
Phyllite is a type of foliated metamorphic rock created from slate that is further metamorphosed so that very fine grained white mica achieves a preferred orientation. It is primarily composed of quartz, sericite mica, and chlorite, among foliated metamorphic rocks, it represents a gradation in the degree of metamorphism between slate and schist. The minute crystals of graphite, sericite, or chlorite, or the translucent fine-grained white mica, impart a silky, sometimes golden sheen to the surfaces of cleavage, the word comes from the Greek phyllon, meaning leaf. The protolith for phyllite is shale or pelite, or slate and its constituent platy minerals are larger than those in slate but are not visible with the naked eye. Phyllites are said to have a texture called phyllitic sheen, and are classified as having formed through low-grade metamorphic conditions through regional metamorphism metamorphic facies. Phyllites are usually black to gray or light gray in color. The foliation is commonly crinkled or wavy in appearance, phyllite is commonly found in the Dalradian metasediments of northwest Arran.
In north Cornwall, there are Tredorn phyllites and Woolgarden phyllites
Sedimentary rocks are types of rock that are formed by the deposition and subsequent cementation of that material at the Earths surface and within bodies of water. Sedimentation is the name for processes that cause mineral and/or organic particles to settle in place. The particles that form a rock by accumulating are called sediment. Sedimentation may occur as minerals precipitate from solution or shells of aquatic creatures settle out of suspension. The sedimentary rock cover of the continents of the Earths crust is extensive, sedimentary rocks are only a thin veneer over a crust consisting mainly of igneous and metamorphic rocks. Sedimentary rocks are deposited in layers as strata, forming a structure called bedding, sedimentary rocks are important sources of natural resources like coal, fossil fuels, drinking water or ores. The study of the sequence of rock strata is the main source for an understanding of the Earths history, including palaeogeography, paleoclimatology. The scientific discipline that studies the properties and origin of rocks is called sedimentology.
Sedimentology is part of both geology and physical geography and overlaps partly with other disciplines in the Earth sciences, such as pedology, geochemistry, sedimentary rocks have been found on Mars. Clastic sedimentary rocks are composed of rock fragments that were cemented by silicate minerals. Clastic rocks are composed largely of quartz, rock fragments, clay minerals, and mica, any type of mineral may be present, clastic sedimentary rocks, are subdivided according to the dominant particle size. Most geologists use the Udden-Wentworth grain size scale and divide unconsolidated sediment into three fractions, gravel and mud and this tripartite subdivision is mirrored by the broad categories of rudites and lutites, respectively, in older literature. The subdivision of these three categories is based on differences in clast shape and breccias), composition. Conglomerates are dominantly composed of rounded gravel, while breccias are composed of dominantly angular gravel, composition of framework grains The relative abundance of sand-sized framework grains determines the first word in a sandstone name.
Naming depends on the dominance of the three most abundant components quartz, feldspar, or the lithic fragments that originated from other rocks, all other minerals are considered accessories and not used in the naming of the rock, regardless of abundance. Clean sandstones with open space are called arenites. Muddy sandstones with abundant muddy matrix are called wackes, six sandstone names are possible using the descriptors for grain composition and the amount of matrix. Mudrocks are sedimentary rocks composed of at least 50% silt- and clay-sized particles and these relatively fine-grained particles are commonly transported by turbulent flow in water or air, and deposited as the flow calms and the particles settle out of suspension
The Helvetic zone, Helvetic system or the Helveticum is a geologic subdivision of the Alps. The Helvetic zone crops out mainly in Switzerland, hence the name, rocks in the Helvetic zone are sedimentary and were originally deposited at the southern margin of the European plate. The Helvetic zone correlates with the French Dauphinois zone, French geologists often prefer the French name, in Switzerland the Helvetic zone is found in outcrops on the northern side of the Alpine mountain ranges. The French Alps consist mainly of Helvetic material, in Germany and Austria the Helvetic nappes crop out as a narrow band. The Helvetic zone consists of a number of very different units. The Helvetic nappes are a stack that was thrusted over the molasse of the Molasse basin in the Alpine foreland. They are composed of Mesozoic marine limestone and shales, the Helvetic nappes are completely detached from their former basement. The Helvetic nappes are thrusted over the Infrahelvetic complex in eastern Switzerland, the Infrahelvetic complex is composed of autochthonous Mesozoic sediments on top of Hercynian basement rock.
The Mesozoic of this unit is contemporary with that of the Helvetic nappes, the Infrahelvetic is internally deformed by thrusting and folding that continues into the Hercynian basement. Because basement and cover were not detached, geologists do not call the Infrahelvetic units nappes, at places throughout the Alps the European basement was, after being detached of its cover rocks, tectonically uplifted in a late stage of the orogeny. Thus the external massivs were formed, places where the Hercynian basement rock crops out in large anticlinoria at the side of the Helvetic zone. Seen from the north the hard competent crystalline rocks of these external massivs form the first of the ranges of the Alps. These chains are, the Mercantour, the Massif des Écrins, the Belledonne, the Aiguilles Rouges and the Mont Blanc Massif, the Aarmassif, geology of the western and central Alps, website of S. M
An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. However, in places where the cover is removed through erosion or tectonic uplift. In Finland, glacial erosion during the last glacial maximum, followed by scouring by sea waves and superficial deposits may be exposed at the Earths surface due to human excavations such as quarrying and building of transport routes. Outcrops allow direct observation and sampling of the bedrock in situ for geologic analysis, in situ measurements are critical for proper analysis of geological history and outcrops are therefore extremely important for understanding the geologic time scale of earth history. Outcrops are important for understanding fossil assemblages, paleo-environment. An outcrop example in California is the Vasquez Rocks, familiar from location shooting use in many films, list of rock formations Geological formation Geologic time scale Media related to Outcrops at Wikimedia Commons
The term molasse refers to sandstones and conglomerates that form as terrestrial or shallow marine deposits in front of rising mountain chains. The molasse deposits accumulate in a basin, especially on top of flysch—like, for example. These deposits are typically the non-marine alluvial and fluvial sediments of lowlands, sedimentation stops when the orogeny stops, or when the mountains have eroded flat. The molasse can sometimes fill an foreland basin, creating a nearly flat depositional surface. Molasse can be very thick near the front, but usually thins out towards the interior of a craton, such massive
The Molasse basin is a foreland basin north of the Alps which formed during the Oligocene and Miocene epochs. The basin formed as a result of the flexure of the European plate under the weight of the wedge of the Alps that was forming to the south. In geology, the molasse basin is sometimes used in a general sense for a synorogenic foreland basin of the type north of the Alps. The Molasse basin stretches over a length of 1000 kilometers along the axis of the Alps, in France, Germany. The western end is at Lake Geneva, where the outcrop is just 20 km wide. Further to the northeast the basin becomes wider and it forms the subsurface of the Swiss Mittelland and reaches its largest width in the Bavarian foreland of the Alps. From Amstetten to Sankt Pölten the basin forms a narrow band, after that it widens again to the east. North of the Danube River it connects with the Vienna basin, the region where the molasse crops out is divided into two. The Subalpine Molasse zone along the Alps and the Foreland Molasse zone further into the foreland, in the Foreland Molasse zone the molasse sediments are relatively undisturbed, in the Subalpine Molasse zone the beds are often tilted and thrust over each other.
Before the development of the Molasse basin, in the Mesozoic era, the weight of the orogenic wedge made the European plate bend downward, resulting in the formation of a deep marine foredeep. In the Eocene epoch the basin became deeper until it formed a small oceanic trench north of the developing orogen, due to the huge amounts of sediments that were eroded from the forming mountain chain the basin was filled up and got shallower. During the Oligocene and Miocene epochs, undeep marine to continental molasse was deposited in the basin, around 10 to 5 million years ago, tectonic uplift had raised the basin to such a height that netto sedimentation stopped. From the south, the deposits were overthrust about 10 kilometers by the Helvetic nappes. The Jura mountains, a fold and thrust belt along the present Swiss-French border, in some places in the Jura mountains, molasse deposits were folded together with older Mesozoic limestones. Deformation instead localized further north, thus forming the relatively flat Swiss Mittelland between the Alps and the Jura Mountains, the Swiss part of the Molasse basin is now located in between the Alps and the Jura mountains, as a large piggy-back basin.
In the Eastern Alps an external mountain range such as the Jura Mountains never developed, the total thickness of molasse deposits in the basin can be up to 6 kilometers. Lithostratigraphically, this molasse is treated as a group that is divided into four formations and this division is made on whether the sedimentary facies is continental or marine. The lowermost formation is the Lower Marine Molasse and its age is Rupelian and it consists of shallow marine sand and marl
Geology of the Alps
The Alps form part of a Cenozoic orogenic belt of mountain chains, called the Alpide belt, that stretches through southern Europe and Asia from the Atlantic all the way to the Himalayas. This belt of mountain chains was formed during the Alpine orogeny, a gap in these mountain chains in central Europe separates the Alps from the Carpathians to the east. Orogeny took place continuously and tectonic subsidence has produced the gaps in between, the Alps arose as a result of the collision of the African and Eurasian tectonic plates, in which the Alpine Tethys, which was formerly in between these continents, disappeared. Most of this occurred during the Oligocene and Miocene epochs, crystalline basement rocks, which are exposed in the higher central regions, are the rocks forming Mont Blanc, the Matterhorn, and high peaks in the Pennine Alps and Hohe Tauern. The formation of the Mediterranean Sea is a recent development. The Alps form a convex arc around their southeastern foreland basin. Quaternary and Neogene sediments in this basin lie discordant over the southernmost thrust units, in the northeast, southward dipping and internally thrusted Cenozoic foreland deposits are found.
This Bavarian and Swiss foreland basin is called the Molasse basin, the foreland basin deposits are overthrusted from the south by the thrustfront of the Alpine nappes. In Switzerland the Molasse Basin is rimmed to the northwest by the Jura mountains, an external fold-and-thrust belt, the western part of the Molasse basin forms the plateau of the Mittelland between the Alps and Jura Mountains. The Jura Mountains location is still a topic for debate, a possible tectonic factor is the north-south extensional Upper Rhine Graben to the north. The Alps continue fairly smoothly into the following related Alpine mountain ranges, the Apennines to the southwest, the Dinarides to the southeast, in the east the Alps are bounded by the Viennese Basin and the Pannonian Basin, where east–west stretching of the crust takes place. The Alps have a geology, but the general structure is the same as for other mountain ranges formed by continental collision. The Alps are often divided into Eastern and Western Alps, the division between the Eastern and Central Alps is approximately the line between St.
Margrethen and Sondrio, the division between the Central and Western Alps is unclear. The main suture in the Alps is called the Periadriatic Seam and this is the boundary between materials from the European and Apulian plates. South of this line are folded and thrusted units of the Southern Alps, north of the Periadriatic seam, rocks from three main palaeogeographic domains are found, the Helvetic or Dauphinois, the Penninic and the Austroalpine domains. Folds and thrusts north of the Periadriatic seam are generally directed to the north, in the Southern Alps the thrusts are to the south so the vergence is dominantly southward. The rocks of the Austroalpine nappes form most of the outcrops in the Eastern Alps, while in the west these nappes are, with the exception of a few places, eroded away. In the Western Alps the Helvetic nappes can be found to the north and west, sometimes still under klippes of the Penninic nappes, as in the Préalpes du Sud south of Lake Geneva
The Pennine Alps, known as the Valais Alps, and formerly called Alpes Poeninae, are a mountain range in the western part of the Alps. They are located in Switzerland and Italy, the Italian side is drained by the rivers Dora Baltea and Toce, tributaries of the Po. The Swiss side is drained by the Rhône, the Great St Bernard Tunnel, under the Great St Bernard Pass, leads from Martigny, Switzerland to Aosta. The main chain runs from west to east on the border between Italy and Switzerland, from Mont Vélan, the first high summit east of St Bernard Pass, the chain rarely goes below 3000 metres and contains many four-thousanders such as Matterhorn or Monte Rosa. Unlike many other ranges, the higher peaks are often located outside the main chain
Intrusive rock is formed when magma crystallizes and solidifies underground to form intrusions, for example plutons, dikes, sills and volcanic necks. Intrusive rock forms within Earths crust from the crystallization of magma, magma slowly pushes up from deep within the earth into any cracks or spaces it can find, sometimes pushing existing country rock out of the way, a process that can take millions of years. As the magma slowly cools into a solid, the different parts of the magma crystallize into rocks, many mountain ranges, such as the Sierra Nevada in California, are formed mostly from large granite intrusions, see Sierra Nevada Batholith. Intrusions are one of the two ways igneous rock can form, the other is extrusive rock, that is, an eruption or similar event. Technically speaking, an intrusion is any formation of igneous rock, rock formed from magma that cools. In contrast, an extrusion consists of rock, rock formed above the surface of the crust. Large bodies of magma that solidify underground before they reach the surface of the crust are called plutons, plutonic rocks form 7% of the Earths current land surface.
Coarse-grained intrusive igneous rocks form at depth within the earth are called abyssal while those that form near the surface are called subvolcanic or hypabyssal. The term intrusive suite seems near synonymous, there is, however, a modest difference, An intrusive suite is a group of plutons related in time and space. Intrusions vary widely, from mountain-range-sized batholiths to thin veinlike fracture fillings of aplite or pegmatite, when exposed by erosion, such batholiths may occupy large areas. A well-known example of an intrusion is Devils Tower, another is Shiprock, New Mexico, USA. Be the pluton is large, it may be called a batholith or a stock, Intrusive rocks are characterized by large crystal sizes, and as the individual crystals are visible, the rock is called phaneritic. This is as the magma cools underground, and while cooling may be fast or slow, cooling is slower than on the surface, if it runs parallel to rock layers, it is called a sill. If an intrusion makes rocks above rise to form a dome, as heat dissipation is slow, and as the rock is under pressure, crystals form, and no vitreous rapidly chilled matter is present.
The intrusions did not flow while solidifying, hence do not show lines, contained gases could not escape through the thick strata, thus form cavities, which can often be observed. Because their crystals are of the rough equal size, these rocks are said to be equigranular, there is typically no distinction between a first generation of large well-shaped crystals and a fine-grained ground-mass. Earlier crystals originated at a time when most of the rock was still liquid and are more or less perfect, crystals are less regular in shape because they were compelled to occupy the spaces left between the already-formed crystals. The former case is said to be idiomorphic, the latter is xenomorphic, there are many other characteristics that serve to distinguish the members of these two groups