Oceanic island arcs, such as the izuogasawaramariana, tongakermadec, or kurilealeutian arcs, are believed to develop from normal oceanic crust at plate subduction boundaries. Thermal histories derived from multi diffusion domain analyses of k. Oct 01, 2006 precollision tilt of crustal blocks in rifted island arcs. The arc and the chilas complex occupy an area of 36,000 km 2, bounded on the north and south by major sutures. The intraoceanic kohistan island arc was initiated during the cretaceous as a result of northward movement of the indian plate. Lower continental crust formation through focused flow in km. The aleutian islands, an island arc off the alaskan coast. Russia arccontinent collision 79 kohistan geochemical evolution of the dras kohistan arc 255 kunashir island tyatya volcano 236 kuril arc tyatya volcano 236 l large. Island arc definition of island arc by the free dictionary. Systematic sampling and mapping in the kohistan accreted arc terrane of northern pakistan has provided a sample suite representing the lithologic diversity of the section from its base along the main mantle thrust upward through several stacked intrusions and their metamorphosed equivalents into the kohistan batholith. The kohistan arc, situated in the pakistan himalaya, is a cretaceous intraoceanic island arc which was initiated during the northward movement of the indian plate.
The kohistan island arc was initiated offshore of asia during the cretaceous as a result of subduction of neo. The kamila amphibolite extends ew across the southern part of the arc and has been studied in detail in the swat and indus. A back arc basin occurs on the side of the overriding plate and a fore arc basin forms toward the subducted plate side. Download video the jo dar gaya samjho mar gaya 3 full movie.
Introduction the kohistan terrane in ne pakistan figure 1 is regarded as a fossil island arc. Based on alinhornblende barometry, the batholith records intrusion pressures from 0. Petrogenesis of mafic garnet granulite in the lower crust. The jijal complex in the roots of the kohistan island arc. The karakoramkohistan suture zone kksz marks the locus of the collision between the karakoram, to the north, and the kohistan paleoisland. Petrography and physicomechanical properties of the. Geochemical architecture of the lower to middlecrustal. Pdf did kohistanladakh island arc collide first with india. Kohistan has experienced a prolonged tectonomagmatic history extending from the early cretaceous through the tertiary. Formation and evolution of a complex collisional orogenthe kohistan arc terrane of the western transhimalaya exposes a remarkable crosssection through an island arc sequence which developed as a result. New geochemical analyses for one of them the kohistan arc in pakistan reveal a multistage process for arc evolution and more than one.
Changing sources of magma generation beneath intra. Backarc basin assemblages in kohistan, northern pakistan. Episodic unroofing of the kohistan batholith, pakistan. Lower continental crust formation through focused flow in. The conventional assertion that the arc was erected above a northdipping subduction zone has been challenged by an alternative hypothesis, which suggests that the arc was built above a. Northward subduction of the indian plate beneath the.
The conventional assertion that the arc was erected above a northdipping subduction zone has been challenged by an alternative hypothesis, which suggests that the arc was built above a southdipping subduction zone. The jijal complex in the roots of the kohistan island arc in the northwest himalaya of pakistan revisited. Pb mineral ages from plutonic rocks help constrain the thermal and tectonic evolution of the kohistan island arc terrane following its collision with india in early tertiary time. Pdf did kohistanladakh island arc collide first with.
In northern pakistan, the extraordinary 40kmthick kohistan sequence of metamorphosed mafic, ultramafic and calcalkaline layered plutonic and volcanic. The chilas complex is related to extension within an island arc. Outline 4 the kohistan arc originated during jurassic cretaceous times through north dipping subduction in the. Sep 20, 2007 new geochemical analyses for one of them the kohistan arc in pakistan reveal a multistage process for arc evolution and more than one source of magma, suggesting that island arc formation. Geochemical parameters used to specify the tectonomagmatic regime suggest affinities of both island arc and morblike backarc basin basalts. Oct, 2011 different phases of remanent magnetizations have been identified in the cretaceoustertiary rocks collected from the northern margin of the kohistan island arc, northern pakistan. The kohistan island arc the kohistan sequence separates a structurally coherent section of an island arc terrane, comprising of a 30 to 40 km thick section of metamorphosed, plutonic, volcanic and sedimentary rocks. Isotopic compositions indicate that the great bulk of igneous rocks have an ultimate sub arc mantle source. Structural evolution of a crustal section in the western.
Kiyoshi suyehiro, kimihiro mochizuki, in international geophysics, 2002. Structural evidence from the kohistan arc jeanpierre burg,1 oliver jagoutz,1,2 hamid dawood,3 and s. The arc formed close to the margin of eurasia in response to the northward subduction. The kohistan island arc terrane and adjacent rocks of the. Changing sources of magma generation beneath intraoceanic. An island arc is a unique type of island chain, mostly made up of clusters of volcanoes through an arcshaped arrangement, situated close and parallel to. Available experimental data on dehydrationmelting of amphibolitic. Petrography and physicomechanical properties of the granitic. Kohistan island arc is formed as a result of intra oceanic subduction of neo tethys beneath eurasian plate in late jurassic to early cretaceous times and covering an. Pdf occurrences of nummulites fossil in limestone in. Kohistan can be divided into three tectonic zones, i the southern kamila zone comprises amphibolitized basalts, and mafic and ultramafic rocks, ii the central chilas complex, and iii the northern.
Petrogenesis of mafic garnet granulite in the lower crust of. The processes active in the deep crust above an oceanic subduction zone during its evolution have been constrained through a detailed geochemical study major and trace elements and sr, nd and pb isotopes of representative samples through an. They also possess a distinct curved form, a chain of active or recently extinct volcanoes, a deepsea trench, and a large negative bouguer anomaly on the convex side of the volcanic arc. May 08, 2014 jeanpierre burg, swiss federal institute of technology in zurich, switzerland. Island arcs can either be active or inactive based on their seismicity and presence of volcanoes. Five to ten block samples were collected from 17 sites of the formation for. It then be came an andeantype magmatic arc in paleoceneearly eocene times. An insight from the juvenile kohistan island arc, pakistan himalaya. Download limit exceeded you have exceeded your daily download allowance. A petrologic record of the collision between the kohistan islandarc and indian plate, northwest himalaya, tectonics of the western himalayas, lawrence. Consistent with the metamorphic evolution of the kohistan lower arc crust, dehydrationmelting occurred at the mature stage of this island arc when shallower hornblendebearing plutonic rocks were buried to depths exceeding 2530 km and heated to temperatures above c.
Upb and hf isotopic evidence from the kohistan arc complex, pakistan. Different phases of remanent magnetizations have been identified in the cretaceoustertiary rocks collected from the northern margin of the kohistan island arc, northern pakistan. The scale of an oceanic arc is typically a few hundred kilometers across, with only a small portion rising above. Pdf the kohistan ladakh block occupies the northwestern corner of the himalayan mountains and has long been recognized to represent an island arc. Issn print 00092541 full text not available from this archive. Mar 24, 2015 geochemical parameters used to specify the tectonomagmatic regime suggest affinities of both island arc and morblike back arc basin basalts. Multiple mantle sources during island arc magmatism. The utror volcanic formation formed during late paleocene, when kohistan existedas an andeantype arc on the southern margin of eurasia. To the east of the island arc, the 4000mdeep andaman sea figs. Download fulltext pdf occurrences of nummulites fossil in limestone in kohistan island arc an igneous and metamorphic zone article pdf available april 2018 with 260 reads.
An insight from the juvenile kohistan island arc, pakist core. Pdf on feb 11, 2008, m qasim jan and others published the jijal complex in the roots of the kohistan island arc in the northwest himalaya of pakistan revisited find, read and cite all the. The utror volcanic formation forms a nesw belt with in kohistan island arc, which lies between the indian and eurasian continents in the western himalayas of northern pakistan. The kohistan arc formed within the neotethys during the mesozoic and accreted to the karakoram likely in the midcretaceous. The southern part of the asian plate consists of two tectonic units separated by the ndipping reshun fault. The kohistan island arc terrane and adjacent rocks of the subjacent indian plate, nw pakistan. However, for kohistan, which is the last accreted fragment, it should be resolvable. Ttgtype plutonic rocks formed in a modern arc batholith. Northward subduction of the indian plate beneath the kohistan. The evolution of the kamila shear zone, kohistan, pakistan.
The kohistan island arc in pakistan was formed from more than one source of magma and in multiple stages. Pdf the kohistanladakh block occupies the northwestern corner of the himalayan mountains and has long been recognized to represent an island arc. Structural evidence from the kohistan arc precollision tilt of crustal blocks in rifted island arcs. The jijal and chilas complexes have been interpreted previously as the lower levels of the layered kohistan island arc, in pakistan. Jeanpierre burg, swiss federal institute of technology in zurich, switzerland. Ttgtype plutonic rocks formed in a modern arc batholith by. Among them, a magnetiterelated component is recognized as the most useful one because of its relatively stable behaviour and widespread presence in the volcanics and red beds. Precollision tilt of crustal blocks in rifted island arcs. Structural evolution of a crustal section in the western himalaya. Pdf the jijal complex in the roots of the kohistan island arc in the.
Kohistan arc form a volumetrically minor part of a compositionally diverse sequence in the northern part of the arc. Structural evidence from the kohistan arc burg, jean. This paper describes the suture zone between the asian plate and the accreted kohistan island arc in the chitral district of nw pakistan. It was during the earlier parts of stage 3 from the late 1970s into the 1980s that brian windley.
Introduction the kohistan terrane in ne pakistan figure 1 is regarded as a fossil island arc obducted between the collided indian and asian plates. A petrologic record of the collision between the kohistan island arc and indian plate, northwest himalaya, tectonics of the western himalayas, lawrence l. The great bulk of kohistan represents growth and crustal accretion during the cretaceous at an intraoceanic island arc dating from c. Jurassiccretaceous intraoceanic island arc, the zedong terrane, have been identi. In broad terms the kohistan terrane represents a juvenile mantle extract addition to the phanerozoic. Active arcs are ridges of recent volcanoes with an associated deep seismic zone. New paleomagnetic results from the northern margin of the.
Seismic signature and geochemistry of an island arc. Changing sources of magma generation beneath intraoceanic island arcs. The chilas complex is a 40 wide and 300 long composite plutonic body exposed in the central part of kohistan island arc. Prime examples of this form of geologic feature include the aleutianalaska arc and the kurilkamchatka arc. The kohistan island arc was initiated offshore of asia during the cretaceous as a result of subduction of neotethyan oceanic crust during the northward movement of the indian plate. A petrologic record of the collision between the kohistan. The new results indicate, in conjunction with literature data, that granitoid formation in the kohistan arc was a continuous rather than punctuated process. It was subsequently tilted northward when underplated by indian continental crust during the early stages of indiaasia collision. May 01, 2003 the intraoceanic kohistan island arc was initiated during the cretaceous as a result of northward movement of the indian plate.
An island arc is a type of archipelago comprising of a chain of islands usually near the convergent boundary of two tectonic plates. The kohistan arc terrane of the western transhimalaya exposes a remarkable crosssection through an island arc sequence which developed as a result of the northward subduction of neotethyan oceanic crust beneath asia during late jurassic and early cretaceous times. The kohistan complex correlates eastwards with the ladakh arcbatholith in northwestern india and the continental karakoram batholith correlates with the. Island arc, long, curved chain of oceanic islands associated with intense volcanic and seismic activity and orogenic mountainbuilding processes. Jul 09, 2016 the rock body are present along this thick melange are limestones, quartz, volcanic greenstones and altered rocks like serpentine in a slates matrix. The chilas complex is a large maficultramafic body closely associated with the kohistan arc sequence in the western himalaya of northern pakistan. Owing to the admirable quality of exposures, the kohistan offers an unrivalled. Dec 01, 2002 subject index subject index 20021201 00. Model for the origin of lower continental crust within the kohistan arc. Three magmatic pulses tapping geochemically different reservoirs are distinguished. Survival of an island arc in continental collision. A backarc basin occurs on the side of the overriding plate and a forearc basin forms toward the subducted plate side.
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