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staygeologyThe terrain isCrustA fragment of matter, either in aplateFormed on the top, or fractured from one plate, and then proliferated (or "sutured") onto another plate.At this time, this crustal block or fragment still has its own unique geological history, which is different from the surrounding area (therefore, the term "alien terrane" is occasionally used).The suture line between the terrane and the crust to which it is attached is usually afault。
TerrainThe concept ofNorth AmericacomplexCordilleraOrogenic beltProposed in the study.Before the new concept of plate tectonics was developed, this orogenic belt always showed an obvious unexplainable“Irreducible complexity”。The theory of plate tectonics points out that the formation of this orogenic belt is actually the result of some crustal fragments that are far away from their birthplace, arrive at and collide with a foreign coast after "drifting" for thousands of miles.Such crustal fragments are named by geologists asAccretionary terrane。
"It was soon believed that these foreign crustal fragments actually originated in quite remote areas and became 'suspicious terranes'. These remote areas are often thousands of meters away from the orogenic belt where these terranes finally stopped. From this, we can infer that the current orogenic belt itself is an increasing collage, which originated from the ringthe pacific oceanA large number of terranes in the region are now 'welded' to each other through major faults.This concept was immediately applied to other older orogenic belts, such as those in North AmericaAppalachian orogenic belt。……This new hypothesis is supported not only by the study of tectonics and petrology, but also by the study of faunabio-diversityandPaleomagnetism"(Carneyet al.)
If a terrain reflects multiple repeated accretionary events, so it has a more complex geological history and structure, it can be calledSuperterrane。
Terrane movement
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stayPlate tectonicsDescriptivelithosphereIn the type, the terrain is not an independentMicroplate, but in a large area that contains other crustal materials - usuallyOceanic crustMaterial - the crustal block above the plate.When this plate collides with plates related to other types of crust, the terrain above it will proliferate onto this new plate.Typical accretionary terrane orContinental crustAs part oftectonic movementAnd split off from other plates;Or at a distanceSubtractive bandFormed ancientisland arcRemains of.In some occasional cases, a third plate will participate in the movement of the terrain, which is usually of oceanic type, and can carry the terrain over a long distance and splice it onto another plate.
The transfer of terrane from one plate to another usually occurs in the process of the plate carrying it is reduced to the plate to which it is attached later.When the current one is forced to insert into the crust of the latter one, the terrain will be separated from the former one whose density has increased due to the reduction, and driven by the force generated in this process, it will be transferred to the latter one, either passing over the crustal material already carried by the latter itself or squeezing with it.If the accepted plate is of oceanic type, this process occurs at the ocean floor, thus affecting the thinner ocean crust.If the receiving plate is continental, this process will occur on land, resulting in very complex landforms.However, generally speaking, some of the receiving plates are oceanic and some are continental.
It is not clear whether the movement of terrain will change the plate boundary.Since the terrain itself does not constitute a plate, if a plate boundary changes due to terrain accretion, it means that these accretionary terranes actually contain fragments of plates, or some unknown tectonic movements that create new plate materials have occurred beneath them;Another possibility is that after the old subduction zone stopped moving, the plate carrying the terrane created a new subduction zone under the terrane, and the original old subduction zone was originally located under the suture line between the terrane and the receiving plate.This last situation seems reasonable. In this case, not only the terrain, but also some "stranded" fragments of the subducted plate are stitched onto the receiving plate, although they are still underground.The related research continues.
Conceptual criticism
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ChinaThe continent has a much more complex geological history than North America.The research shows that it is composed of many small blocks, so the concept of terrane was put forward and soon used for the analysis of Chinese geology.However, some Chinese scholars have raised objections to this concept, believing that it is a redundant concept with little necessity for creation.If the bottom of an terrane isAsthenosphereThe low velocity and high conductivity layer, and part of the rock is melted, then it isMicroplate；If its bottom is not deep into the asthenosphereOverthrust fault, then it isNappe；If the nature of its bottom is not known, it can be called“massif”。These concepts have long been used by the geological community, so it is not necessary to add another "terrane" term.In recent years, the number of users of "Terrain" in the world has become less and less.
