Dike (geology)

A dike or dyke, in geological usage, is a sheet of rock, formed in a fracture of a pre-existing rock body. Dikes can be either magmatic or sedimentary in origin. Magmatic dikes form when magma flows into a crack solidifies as a sheet intrusion, either cutting across layers of rock or through a contiguous mass of rock. Clastic dikes are formed. An intrusive dike is an igneous body with a high aspect ratio, which means that its thickness is much smaller than the other two dimensions. Thickness can vary from sub-centimeter scale to many meters, the lateral dimensions can extend over many kilometres. A dike is an intrusion into an opening cross-cutting fissure, shouldering aside other pre-existing layers or bodies of rock. Dikes are high-angle to near-vertical in orientation, but subsequent tectonic deformation may rotate the sequence of strata through which the dike propagates so that the dike becomes horizontal. Near-horizontal, or conformable intrusions, along bedding planes between strata are called intrusive sills.

The term "sheet" is the general term for both sills. Sometimes dikes appear in swarms, consisting of several to hundreds of dikes emplaced more or less contemporaneously during a single intrusive event; the world's largest dike swarm is the Mackenzie dike swarm in Canada. Dikes form as either radial or concentric swarms around plutonic intrusives, volcanic necks or feeder vents in volcanic cones; the latter are known as ring dikes. Dikes can vary in texture and their composition can range from diabase or basaltic to granitic or rhyolitic, but on a global perspective the basaltic composition prevails, manifesting ascent of vast volumes of mantle-derived magmas through fractured lithosphere throughout Earth history. Pegmatite dikes comprise coarse crystalline granitic rocks - associated with late-stage granite intrusions or metamorphic segregations. Aplite dikes are sugary-textured intrusives of granitic composition; the term "feeder dike" is used for a dike. Magma flowed along out of the dike formed another feature.

In contrast to magmatic dikes, a sill is a magmatic sheet intrusion that forms within and parallel to the bedding of layered rock. Sedimentary dikes or clastic dikes are vertical bodies of sedimentary rock that cut off other rock layers, they can form in two ways: When a shallow unconsolidated sediment is composed of alternating coarse grained and impermeable clay layers the fluid pressure inside the coarser layers may reach a critical value due to lithostatic overburden. Driven by the fluid pressure the sediment forms a dike; when a soil is under permafrost conditions the pore water is frozen. When cracks are formed in such rocks, they may fill up with sediments; the result is a vertical body of sediment that cuts through a dike. Batholith Ring dike Fissure vent – Linear volcanic vent through which lava erupts Laccolith Runamo – A cracked dolerite dike in Sweden, for centuries held to be a runic inscription interpreted as a runic inscription. Dike swarm Sill

The Habitable Exoplanet Hunting Project

The Habitable Exoplanet Hunting Project is an international network of both professional and amateur astronomers created and coordinated by Alberto Caballero, an amateur astronomer and host of The Exoplanets Channel. As of December 2019, the network comprises 32 observatories located worldwide, including universities such as the University of South Africa, the University of Saskatchewan in Canada, the California Polytechnic State University; the participants are searching for new habitable exoplanets around non-flare G, K or M-type stars located within 100 light years. The initial list of targets consists of 10 stars that have known transiting exoplanets outside the habitable zone; the network is monitoring 24/7 each star at a time during several months. Despite G and K-type stars are the main targets of the project, the team is focusing on red dwarfs because it take less time to discard the existence of habitable exoplanets around these type of stars. Most of the observatories are able to detect transit depths as low as 0.1% and exoplanets with a radius of 0.7 Earth radii.

To search for new exoplanets, the team is using two different methods: transit photometry and transit duration variation. Overall, the project is a new approach to the quest for exoplanets in which a large network of astronomers located in the five continents have the time to continuously observe each star individually during long periods of time in the search for dips in brightness produced by transiting exoplanets; as of December 2019, the network has conducted observations on GJ 436 and GJ 1214, with a new campaign on GJ 3470 starting in January 2020. List of exoplanet search projects


Sicilians or the Sicilian people are a Romance ethnic group indigenous to the Italian island of Sicily, the largest island in the Mediterranean Sea as well as the largest and most populous of the autonomous regions of Italy. The Sicilian people are indigenous to the island of Sicily, first populated beginning in the Paleolithic and Neolithic periods; the aboriginal inhabitants of Sicily, long absorbed into the population, were tribes known to the ancient Greek writers as the Elymians, the Sicanians, the Sicels, the latter being an Indo-European-speaking people of Italic affiliation after whom the island was named. From the 11th century BC, Phoenicians began to settle in western Sicily, having started colonies on the nearby parts of North Africa. Sicily was colonized and settled by Greeks, beginning in the 8th century BC; this was restricted to the eastern and southern parts of the island. As the Greek and Phoenician communities grew more populous and more powerful, the Sicels and Sicanians were pushed further into the centre of the island.

By the 3rd century BC, Syracuse was the most populous Greek city in the world. Sicilian politics was intertwined with politics in Greece itself, leading Athens, for example, to mount the disastrous Sicilian Expedition in 415 BC during the Peloponnesian War; the constant warfare between Carthage and the Greek city-states opened the door to an emerging third power. In the 3rd century BC the Messanan Crisis motivated the intervention of the Roman Republic into Sicilian affairs, led to the First Punic War between Rome and Carthage. By the end of the war in 242 BC, with the death of Hiero II, all of Sicily except Syracuse was in Roman hands, becoming Rome's first province outside of the Italian peninsula. For the next 600 years, Sicily would be a province of the Roman Republic and Empire; as the Roman Empire was falling apart, a Germanic tribe known as the Vandals took over Sicily in 468 AD under the rule of their king Geiseric. However, they soon lost these newly acquired possessions, except one toehole in Lilybaeum, to Odoacer in 476 and to the Ostrogothic conquest of Sicily by Theodoric the Great which began in 488.

The Gothic War took place between the Ostrogoths and the Byzantine Empire, during the reign of Justinian I, Sicily was brought back under Greco-Roman rule, Greek language and religion were embraced by the majority of the population. It was Syracuse where the Byzantine Emperor Constans II desired to move his capital in 663 AD, a decision which led to his assassination. Sicily remained under Byzantine rule for several centuries, until an invasion by Arab Muslims in the 9th century; the Muslim conquest was a see-saw affair. Not until 965 was the island's conquest completed, with Syracuse in particular resisting to the end. In the 11th century, the mainland southern Italian powers were hiring Norman mercenaries, who were Christian descendants of the Vikings. In 1130, Roger II founded the Kingdom of Sicily as an independent state with its own Parliament and currency, while the Sicilian culture evolved distinct traditions and customs not found in mainland Italy; the Siculo-Norman rule of the Hauteville dynasty continued until 1198, when Frederick I of Sicily, the son of a Siculo-Norman queen and a German emperor ascended the throne.

His descendants governed Sicily until the Papacy invited a French prince to take the throne, which led to a decade-and-a-half of French rule under Charles I of Sicily. Their descendants ruled the Kingdom of Sicily until 1401. Following the Compromise of Caspe in 1412 the Sicilian throne passed to the Iberian monarchs from Aragon and Castille. After the Ottoman conquest of the Balkans, waves of Greek migrants fled to Sicily in sizable numbers between the 15th and 18th centuries to escape persecution. In 1735, the Spanish era ended. For the better part of the next century-and-a-half, Sicily was in personal union with the other Southern Italian Kingdom of Naples, with the official residence located in Naples. In 1861, Sicily became part of the Kingdom of Italy as a result of the Risorgimento. After the unification of Italy and the Fascist era, a wave of Sicilian nationalism led to the adoption of the Statute of Sicily, under which the island has become an autonomous region. Since 1946, the island enjoys the most advanced special status of all the autonomous regions, which allows the Sicilian residents to keep 100% of the revenue from all the taxes, without giving back any to the central government in Rome.

Sicily has experienced the presence of a number of different cultures and ethnicities in its history, including the original Italic peoples and Carthaginians, Romans, Byzantine Greeks, Normans, Swabians and Italians, Spaniards and Albanians. About five million people live in Sicily. However, in the first century after the Italian unification Sicily had one of the most negative net mig