Kogin da ke cikin kogin

Kogin da ke cikin kogin

A river anticline is a geologic structure that is formed by the focused uplift of rock caused by high erosion rates from large rivers relative to the surrounding areas. An anticline is a fold that is concave down, whose limbs are dipping away from its axis, and whose oldest units are in the middle of the fold. These features form in a number of structural settings. In the case of river anticlines, they form due to high erosion rates, usually in orogenic settings. In a mountain building setting, like that of the Himalaya or the Andes, erosion rates are high and the river anticline's fold axis will trend parallel to a major river. When river anticlines form, they have a zone of uplift between 50-80 kilometers wide along the rivers that form them.

Dalili da sakamako

Irin fasalin yanayin ƙasa wanda zai samo asali ne daga ikon rafi da tsananin sassauci na ɓawon burodi. Lokacin da wutar lantarki ta karu kuma tsananin sassauci ya ragu, wannan yana haifar da tsarin ya ci gaba daga tsakiya zuwa tsakiya na kogi, kuma a cikin matsanancin yanayi zuwa aneurysm na tectonic. Halin anticlines na gaba a cikin jagorancin da kuma samarwa a kusa da ƙananan koguna tare da ƙarfin ƙuƙwalwa. Kogin kogin ya samo asali ne a kusa da manyan koguna masu lalacewa sosai inda ƙarfin ɓawon burodi yake da ƙarancin gaske. Tectonic aneurysms zai samo asali ne lokacin da rushewa ya yi yawa kuma ɓawon burodi yana da rauni sosai, don samar da tsarin tsarin.

Hanyar da kogin kogin ya samo asali ta hanyar zurfin kogin da kuma raguwar da ke tattare da shi, ya haifar da duwatsu masu zurfi a cikin ɓawon burodi don a fi so a tono su tare da manyan koguna kamar Arun, Indus, Sutlej, da Yarlung Zangbo River. Exhumation mai warewa yana haifar da matsin lamba mai girma da kuma samfurin metamorphic mai matsin lamba don a kawo shi farfajiya a matsakaicin matsakaicin har zuwa 5mm a kowace shekara. Bincike da kwanan wata na radiometric na waɗannan matsin lamba da manyan duwatsun metamorphic na iya taimakawa sake gina juyin halitta na tectonic na belin orogenic wanda ya kafa su.

Tabbacin

A cikin Himalaya, farantin nahiyar Indiya yana fadowa cikin farantin nahiwar Eurasia tare da kusan motsi na arewa maso kudu. Sabili da haka, matsawar duwatsu a cikin Himalaya yana cikin arewa maso kudu. Don haka, ninkawa ya kamata ya faru a gabas zuwa yamma, kamar yadda aka lura. Koyaya, an kuma lura cewa ninkawa yana faruwa a arewa maso kudu. An lura cewa waɗannan tuddai suna bin sawun manyan koguna, kamar Arun da Indus. Asalin waɗannan folds an bayyana su ta hanyar zaton cewa koguna ba su samar da waɗannan anticlines ba, maimakon haka hanyar kogin ta kasance ta hanyar daidaituwa a saman waɗannan siffofin geologic, wanda ya samo asali ne ta hanyar lalacewa. An ba da shawarar ra'ayin isostatic rebound a matsayin mafi kyawun hanyar da ta dace da waɗannan nau'ikan arewa maso kudu kuma yanzu an yarda da shi sosai.

Tsarin samarwa

Fayil:River anticline by, Michael Stevens.pdf

kafa kogin anticline

Samun kogi na kogi ta hanyar Isostasis rebound an kwatanta shi a cikin adadi zuwa dama a cikin matakai masu kyau. Ka'idar Isostasy ta ce idan lithosphere yana da 'yanci don motsawa tsaye, to zai iyo a zurfin da ya dace a cikin asthenosphere bisa ga kauri da yawa na lithosphere. Kogin anticlines ya samo asali ne lokacin da aka cire abubuwa masu yawa ta hanyar rushewa kogi a wani yanki mai ƙarancin ƙuƙwalwa. Yankin ya sake dawowa musamman a gefen kogi, yayin da sauran yankin suka kasance daidai. Wannan zai karkatar da ɓawon burodi don samar da anticline, wanda zai iya ɗaukar shekaru dubu goma. Yayin da kogi ke gudana a cikin yankin, yana lalata adadi mai yawa na dutsen da ke sama, wanda ke haifar da raguwa a cikin nauyin lithosphere, wanda ke kaiwa ga amsawar isostatic. Ba tare da dutse ba, kayan da ke ƙasa suna sakewa, kamar cire nauyi daga raft. Yayin da kogin ke ci gaba da rushewa sabili da haka sakewa yana ci gaba, wanda zai samar da tsarin karami mai faɗi. Don wannan sake dawowa ya faru lalacewa daga kogi dole ne ya wuce matsakaicin lalacewa ga yankin kuma ya wuce hauhawar orogen. Matsakaicin lalacewar Himalaya kusan 1 mm ne a kowace shekara, yayin da yawan lalacewar Kogin Arun na gabashin Himalaya ya kai 8 mm a kowace shekara. don haka yana da ma'ana cewa za mu ga kogin kogin Arun.  

Anereysms na tectonic

A tectonic aneurysm is an isolated zone of extreme uplift and exhumation rates. This forms when uplift from local tectonics are combined with very weak crust and uplift from a river anticline. When a major river flows over an area of tectonic uplift, the erosion from the river will erode the uplifted material. This will cause extremely rapid exhumation along the major rivers, of up to 10 mm per year. Within the Himalaya there are two tectonic aneurysms, each on one of the two syntaxis of the orogenic belt: Nanga Parbat in the west and Namche Barwa in the east. These tectonic aneurysms form in similar ways to river anticlines, but with extreme erosion rates and very weak and ductile crust. The syntaxis mark the end of the Himalayan orogen on either side and define the location of two large rivers, the Indus and the Yarlung Tsangpo River. The syntaxis on either side of the Himalaya are dominated by a strike slip fault zone, instead of a compressional thrust faulting, as in the rest of the orogen. In the west the Indus River flows through the Nanga Parbat and in the east the Yarlung Tsangpo River flows through the Namche Barwa. The very high erosion rates of these two rivers is coupled with weak, hot, thin, dry, crust to form areas of extreme uplift and exhumation.

Fayil:Young Tectonic Aneurysm.pdf

Hoto na 1: Hoton wani matashi mai suna tectonic aneurysm. Isothermal gradient anticline wanda ya haifar da yankan tashar da ke haifar da ƙanƙara fiye da kewayen. Rashin yana mai da hankali ga rauni yana tilasta kayan dumi zuwa cikin yankin don haka yana ɗaga isotherms a cikin gida

Fayil:Mature tectonic aneurysm isothermal gradient.pdf

Hoto na 2: Ci gaba da tectonic aneurysm. Isothermal gradient ya zama mafi ci gaba fiye da matashi. Gudun kayan aiki yana haifar da hauhawar dutse mai ƙanƙanta a gefen gefen yankin rushewa. Hawan yana kawo duwatsu masu dumi marasa ƙarfi zuwa farfajiya kuma yana haifar da babban taimako. Wannan yana haifar da hanzarin lalacewar taro da sauƙin lalacewa don haka tilasta kyakkyawan ra'ayi

Hoto na 3: Wannan zane ya bambanta da ƙarfin ɓawon burodi na wuri mai faɗi tare da lalacewar ƙasa mai mahimmanci (Blue Dashed Line) idan aka kwatanta da wuri mai faɗi wanda ba a canza shi ba (Green Dashed Line). Bayanan ƙarfin da aka kwatanta a cikin zane yana cikin yanki mai laushi tare da ƙaruwa mai zurfi tare da ƙaruwar ƙaruwa tare da zurfin ƙaruwa tare le ƙaruwar matsin lamba.

Hanyar lalacewa

Rashin lalacewa wanda ya haifar da aneurysms na tectonic yayi kama da aneuryms a cikin jijiyoyin jini wanda raunanawar ƙarfin da ke ba da damar haɓaka ko haɓaka. Koyaya, a cikin yanayin ƙasa, lalacewa yana faruwa sama da miliyoyin shekaru tare da ƙarfin lalacewa mai ƙarfi wanda ya kasance daga dubban daruruwan kiloWatts a kowace mita. Yankewa ko raguwar ɓawon burodi na wani yanki a saman da ke da alaƙa da kauri na ɓawon burbushin baya yana haifar da abubuwa biyu da ke faruwa waɗanda ke ba da damar samar da aneurysm. Da farko, saboda yanayin lalacewar duwatsu da ƙarfin da ke dogara da matsin lamba, raguwar kayan da ke rufewa yana rage ƙarfin ɓawon burodi idan aka kwatanta da yankunan da ke kewaye. Wannan yana faruwa ne saboda cire ɓawon burodi yana rage nauyin da ke tattare da matsin lamba wanda ke tasiri ga ƙarfin. Abu na biyu, yanayin geothermal yana ƙaruwa a tsaye. Kwarin da ke da zurfi suna haifar da yankuna masu rauni waɗanda ke mai da hankali ga damuwa kuma ta haka ne motsi na kayan ductile mai zurfi.

By weakening the crust in a localized area, a preferential region of strain can develop concentrating the flow of material. Ductile rocks deeper in the crust will be able to move towards the potential gradient, whereas brittle rocks near the surface will fracture when subject to increased strain. The transition between brittle deformation and ductile deformation is determined by the temperature which is generally controlled by depth as well as rheology. Weak hot minerals, below the ductile transition, with significant partial melt move into the area underlying the thinned crust as a result of the pressure gradient being decreased in the thin area. At a certain point, the pressure will decrease substantially moving from convergent basement rock into thinned crust. This causes rapid decompression at relatively stable and raised isotherms. Decompression melting occurs, which increases the proportion of partial melt within the material and causes rapid heat advection towards the surface. Continued convergent plate movement focuses the flow of material into the syntaxial areas with the localized weakness permitting upward escape as an accommodation mechanism. This process solves the fundamental problem of material being forced into a confined space by creating an outlet. The result of which creates a positive feedback with erosion focusing uplift which transports more weak rock vertically enhancing erosive capabilities. Areas of consistent elevation in river valleys and mountains with relief can be maintained by high exhumation rates of relatively young weak rocks. The ages of minerals in the area will be younger than the surrounding crust due to cooling occurring in an area with a steeper thermal gradient at shallower depths. Mature tectonic aneurysm systems, such as the Nanga Parbat, can have very high local reliefs of young rocks due to consistent erosion maintaining the elevation in the erosive area and vertical strain forcing material up along the proximal edges.

Wuraren da aka yi

Tectonic aneurysms are found in areas with localized high relief of relatively young rocks when compared to their surroundings. Actively observed systems that have been studied the most are located in 2 main regions of the Himalaya, the Nanga Parbat–Haramosh Massif and Namche Barwa–Gyala Peri which occur on the Eastern and Western edges respectively. The Indus River is the mechanism responsible for crustal removal in the Nanga Parbat region, and the Tsangpo River is active in the Namche Barwa region.

Proposed tectonic aneurysms are located in the Saint Elias region of Alaska, the Kongur Shan and Muztagh Ata in China, and the Lepontine Dome in the Swiss Alps. These locations show incipient or similar, less significant characteristics to actively observed systems. Glacial mechanisms of erosion and transport are believed to be responsible in many alpine areas including the Saint Elias system.

Nanga Parbat-Haramosh Tectonic Aneurysm

FaNanga Parbat-Haramosh shine yankin da aka fi nazarin shi a cikin mahallin tectonic aneurysms. Yankin yana da matsanancin taimako a kan gajeren nesa tare da kwarin Indus River kimanin kilomita 7 ƙasa da tsawo fiye da saman dutsen. A cikin yankin binciken, shekarun sanyaya na Biotite (280 °C ± 40 °C) koyaushe ba su da shekaru miliyan 10 suna nuna saurin fitarwa a yankin. Nazarin abun da ke ciki da tsarin duwatsu a yankin sun ba da shawarar gano zurfin da ke ƙasa da kilomita 20. Yawan fitarwa daga massif da kwarin sun fi girma fiye da ƙimar baya. Ƙididdigar ƙididdigar yawan gawawwakin ya kasance daga 5 zuwa 12 mm a kowace shekara dangane da wurin. Dutsen saman yana da ƙarancin ƙimar fiye da ƙasan kwarin duk da haka duka biyun sun fi girma idan aka kwatanta da ƙimar baya a waje da haɗin kai. granulite da aka nuna a cikin yankin aneurysm na tsakiya yana wakiltar narkewar matsin lamba da advection yayin da kayan suka koma cikin yankuna tare da raguwar matsin. Har zuwa kilomita 20 na unroofing domal a cikin ɗan gajeren lokaci an ƙaddara bisa ga shekarun samfurin daga 1 zuwa 3 miliyan shekaru.

Namche Barwa-Gyala Peri

Namche Barwa-Gayla Peri tectonic aneurysm yana kan gefen Gabas na Himalaya tare da Kogin Tsangpo mai aiki yana gudana a kwarin tsakanin duwatsu. Yawancin masu bincike sun kammala cewa tsarin tectonic aneurysm shine mafi kyawun bayani game da tsarin da aka lura da kuma tsarin tectonian na yankin. Shekaru na Argon-argon biotite da zircon fission track shekarun duwatsu daga yankin suna da shekaru miliyan 10 ko ƙasa da haka, wanda yake matashi idan aka kwatanta da duwatsun da ke kewaye. Irin wannan tsaunuka masu tsawo da aka gani a cikin Nanga Parbat suna bayyane tare da yankin Namche Barwa, tare da kusan kilomita 4 na canjin tsawo a tsaye a kan ɗan gajeren nesa. Ana samun manyan duwatsu masu tasowa a yankin tare da shaidu don ba da shawarar bambancin aikin metamorphic tsakanin yankuna daga tsakiya da gefuna. Binciken yana faruwa ne a cikin wani yanki mai zagaye tare da matasa, masu tsayi masu tsayi da aka mayar da hankali a tsakiya. A waje na mayar da hankali rubidium zuwa strontium ratios yana ba da shawarar narkewa tare da ruwa. An tsara kasancewar ruwa a cikin narkewa don faruwa ne sakamakon ruwan sama mai yawa wanda ke ba da damar ruwa ya shiga cikin duwatsu masu zurfi na dogon lokaci. An yi amfani da shekaru da tsarin barometric na duwatsu don lissafin girman nauyin da aka cire, wanda aka yi amfani da shi don ƙayyade 3 millimeters na yankan shekara-shekara a cikin shekaru miliyan 10 da suka gabata.

Mai Tsarki Iliya

Tsarin tectonic aneurysm na shekaru miliyan huɗu da aka tsara a cikin tsaunukan Saint Elias a Alaska an kafa shi ne ta hanyar rushewar kankara a kan duwatsun da aka haɓaka ta hanyar rushiyar Yakutat microplate a ƙarƙashin gefen Arewacin Amurka. Aneurysm yana faruwa a kusurwar farantin Arewa wanda ke sauyawa daga motsi na dextral zuwa motsi na motsi don haka mai da hankali. Dangantakar da aka fassara tsakanin ci gaban dutsen rushewa yana da bambance-bambance tsakanin masu bincike fiye da tsarin Himalayan saboda shekarun tsarin da ƙuntatawa game da aikin filin saboda rufe kankara. A cikin St. Elias kewayon haɗuwa da underthrusting ya haifar da hauhawar ƙasa da ke samar da duwatsu. Tsarin karuwar yanayi ya ba da damar ci gaban kankara wanda ya haifar da matsanancin rushewar kankara. Tun lokacin da aka fara shi, rushewar kankara ta kai turɓaya a Yamma zuwa Tekun Pacific da kuma kan iyakar nahiyar. Bayan haka, kimanin shekaru miliyan biyu da suka gabata, samuwar raguwa ya haifar da yanayin damuwa ya yada kudu. Canjin da aka mayar da hankali ya haifar da ci gaban dutse a kudu wanda ya rushe tsarin yanayi don haka ya rage ruwan sama a yankunan Arewacin Dutsen Saint Elias . Rugujewar da kuma fitar da gawawwakin yanzu sun mayar da hankali a yankin kudancin tsaunuka wanda ke samar da shekarun sanyaya na matasa da ke da alaƙa da cibiyar aneurysm ta yanzu.

Young detrital zircon fission track dating (240 °C ± 40 °C) and apatite fission track and uranium -thorium/ helium (110 °C ± 10 °C) cooling ages of sediments in glacial catchment areas support the theory of erosive influence on the St. Elias tectonic system. Rates of exhumation were inferred by calculating the difference between detrital zircon and apatite ages in sediments. The smaller the difference between zircon and apatite ages represents a faster movement of material through the isotherms and faster cooling. In the northern corner of contact between the plates, the zircon and apatite ages do not differ significantly, thereby providing evidence of rapid exhumation. The proximity to the depositional environment along the coastal margin and within fjords preserves a record of sedimentation rate which is used to interpret exhumation rates of 0.3 mm year originally and approximately 1.3 mm/year for the last million years. The sediment age and thickness are used to track the movement of the focus of erosion from the north to the south.

Kasancewar tsarin aneurysm na tectonic a cikin yankin yana da rikici sosai tare da masu bincike da yawa waɗanda suka kammala cewa rashin isasshen mayar da hankali ga gawawwakin yana faruwa don tallafawa ra'ayi. Muhimmin murfin glacial yana iyakance yawan samfurori na filin da kuma lura da ilimin ƙasa wanda za'a iya yi kai tsaye a saman don haka ƙara rashin tabbas ga fassarori. Sauran ra'ayoyin suna jayayya da ikon sarrafawa na tectonic na exhumation tare da ƙaramin tasiri a kan tsarin gaba ɗaya. Ana bayyana shekarun matasa ta hanyar mayar da hankali ga wuraren da suka haifar da lalacewa.

Ayyukan gona a yankunan da aka tsara

Ta hanyar kwatanta zurfin duniya inda wasu ma'adanai ke yin kwalliya da tsawo inda aka samo su, ana iya amfani da shekarun ma'adinai don ƙayyade yawan abin da yankin damuwa ya motsa kayan tsaye. An yi amfani da hanyoyi daban-daban na kwanan wata a kan takamaiman ruwa da ma'adanai don samar da bayanan lokaci-lokaci na yawan fitar da duwatsu a yankin. An yi amfani da kwanakin shekaru don sake gina tarihin exhumation da tsarin zafi ta hanyar kwatanta su da matsin lamba da iyakar ƙarancin zafin jiki na ma'adanai. Uranium-Thorium da uranium-helium shekarun sanyaya na samfurori na apatite suna nuna lokacin sanyaya 70 ° C. An tsara Yanayin rufewa mafi girma ta amfani da hanyoyin kwanan wata na argon-argon don samfurori na Biotite (300 ° C) da hanyoyin zircon fission (230 ° C - 250 ° C) . Ta hanyar nazarin shekarun ma'adanai tare da Yanayin rufewa daban-daban, masu bincike na iya ƙaddamar da saurin da suka motsa ta hanyar isotherms. Lokacin da bambancin tsakanin shekarun ma'adinai wanda ya sanyaya a babban zafin jiki da wanda ya sanyara a ƙananan zafin jiki suna da kama da juna, to ana ganin fitarwa ta kasance mai sauri. Ana samun geothermobarometry ta amfani da garnet-Biotite plagioclase don ƙuntata tsarin metamorphic mafi girma. Rashin ƙarancin ƙwayoyin cuta (shekaru na sanyaya) shi kaɗai ba za a iya amfani da shi ba don bayyana aneurysms na tectonic kamar yadda canje-canje masu zurfi na isothermal bazai shafar zurfin zurfi ba. Bugu da ƙari, sanyaya mai zurfi na zafin jiki na iya kasancewa da alaƙa da lalacewar da aka mamaye maimakon tasowa mai tasowa. Shekaru na samfurin daga ma'adanai tare da yanayin sanyi mafi girma suna nuna fitar da kayan da suka fi zurfi wanda shine aikin da aka tsara na aneurysm na tectonic.    

Ana amfani da bayanan Saurin girgizar ƙasa a kan manyan wuraren binciken don gano yiwuwar rashin daidaito na isothermal. Bayanai masu saurin gudu suna nuna duwatsu masu zafi tare da digiri mafi girma na narkewar ɓangaren wanda ke jinkirta P-waves idan aka kwatanta da kewayen. Ana yin samfurin Magnetotelluric don gwada resistivity na duwatsu wanda ake amfani dashi don ƙaddara yawan ruwa a cikin duwatsu.