A palaeogeographic reconstruction of the Dir Group: evidence for magmatic arc migration within Kohistan, N. Pakistan

Sullivan, Morgan; Windley, Brian F.; Saunders, A. D.; Haynes, John R.; Rex, D. C.

doi:10.1144/gsl.sp.1993.074.01.11

Cited by 35 publications

(31 citation statements)

References 36 publications

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“…Remarkably, the batholith shows very limited large-scale structural disruption. Only toward the west exhumation was accompanied by a major fault zone, the Dir-Kalam fault mapped as a thrust by Sullivan et al (1993). However, pressures are 0.15 GPa lower in the NW-hanging wall of the fault, compared to the footwall, indicating that at some point in its history, the fault had some significant normal movements.…”

Section: Discussionmentioning

confidence: 99%

TTG-type plutonic rocks formed in a modern arc batholith by hydrous fractionation in the lower arc crust

Jagoutz¹,

Schmidt

Enggist

et al. 2013

Contrib Mineral Petrol

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We present the geochemistry and intrusion pressures of granitoids from the Kohistan batholith, which represents, together with the intruded volcanic and sedimentary units, the middle and upper arc crust of the Kohistan paleo-island arc. Based on Al-in-hornblende barometry, the batholith records intrusion pressures from *0.2 GPa in the north (where the volcano-sedimentary cover is intruded) to max. *0.9 GPa in the southeast. The Al-in-hornblende barometry demonstrates that the Kohistan batholith represents a complete cross section across an arc batholith, reaching from the top at *8-9 km depth (north) to its bottom at 25-35 km (south-central to southeast). Despite the complete outcropping and accessibility of the entire batholith, there is no observable compositional stratification across the batholith. The geochemical characteristics of the granitoids define three groups. Group

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Section: Discussionmentioning

confidence: 99%

TTG-type plutonic rocks formed in a modern arc batholith by hydrous fractionation in the lower arc crust

Jagoutz¹,

Schmidt

Enggist

et al. 2013

Contrib Mineral Petrol

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“…Stratigraphically, the western part of the Kohistan arc, which is the studied area, is divided in two groups: Kalam and Dir (Sullivan et al, 1993) (Fig. 2).…”

Section: Geology and Samplingmentioning

confidence: 99%

“…These volcanics are andesites, rhyolites, and dacites. These volcanics were accumulated in subaerial environment and represent typical continental marginal arc series volcanics (Sullivan et al, 1993). Latter this idea was contradicted on the basis of detail mapping and Treloar et al, 1996).…”

Section: Geology and Samplingmentioning

confidence: 99%

Paleomagnetic study of Utror Volcanic Formation: Remagnetizations and postfolding rotations in Utror area, Kohistan arc, northern Pakistan

Ahmad

Yoshida²,

Fujiwara

2014

Earth Planet Sp

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The Utror Volcanic Formation forms a NE-SW belt with in Kohistan island arc, which lies between the Indian and Eurasian continents in the western Himalayas of northern Pakistan. The Utror Volcanic Formation formed during Late Paleocene, when Kohistan existed as an Andean-type arc on the southern margin of Eurasia. Five to ten block samples were collected from 17 sites of the formation for paleomagnetic studies. Magnetic minerals that serve as remanent carriers are maghemite, magnetite, hematite and titanohematite. Magnetite, hematite, and titanohematite carry the characteristic remanent magnetization (ChRM). The declination values of ChRM are highly discordant before and after structural correction. While inclination values show uniformity in geographic coordinates. The ChRM carried by magnetite yields downward inclinations, whereas the ChRM carried by hematite or titanohematite have upward inclinations in geographic coordinates. The correlation between polarity state and magnetic mineralogy suggests that the acquisition of magnetization occurred during two distinct time intervals. An inclination only fold test of ChRM of these two mineral assemblages indicates that they are post-folding magnetizations. The calculated paleolatitudes for ChRM carried by magnetite and hematite or titanohematite are 9±4• N and 13±4• N respectively. A comparison of these paleolatitudes with the Indian apparent polar wander path (APWP) shows that the remagnetization likely happened between 55 to 45 Ma. Discordant declinations indicate that these volcanics suffered local rotations after remagnetization event.

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“…1, 2). According to Sullivan et al (1993) the Western volcanic rocks display petrographic and geochemical characterstics similar to the Shamran volcanics. Further, they interpreted that the Shamran volcanics and the Western volcanics are continental marginal cover of the Kohistan arc rather than part of the island arc basement.…”

Section: Introductionmentioning

confidence: 99%

“…Further, they interpreted that the Shamran volcanics and the Western volcanics are continental marginal cover of the Kohistan arc rather than part of the island arc basement. The 40 Ar-39 Ar hornblende radiometric age of the Shamran volcanics is 58±1 Ma (Treloar et al, 1989;Sullivan et al, 1993). Pudsey (1986) mentioned a third type of volcanics, which are part of Aptian/Albian Yasin Group, overlying a one-meter thick sedimentary sequence.…”

Section: Introductionmentioning

confidence: 99%

Remagnetization of igneous rocks in Gupis area of Kohistan arc, northern Pakistan

2014

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The Kohistan arc was formed due to subduction of neo-Tethyan oceanic crust beneath Asia. The arc is comprised of volcanic, plutonic and sedimentary rocks of Mesozoic to Tertiary age, formed prior and after the suturing of the Indian and Asian continents. Paleomagnetic investigations have been carried out on Paleocene volcanic and plutonic rocks exposed in the northern part of the arc. A total of 110 samples from 16 sites were drilled. According to rock-magnetic studies the main magnetic carrier is magnetite. Optical microscopy study reveals that low-grade metamorphism have effected all rocks. Magnetite is found as both a primary magmatic mineral and secondary alteration product in all samples. Samples of volcanics yield post tilting characteristic remanent magnetizations (ChRM). The in situ mean direction of the ChRMs of the intrusives is similar to the in situ mean direction of volcanics. The presence of secondary magnetite in plutons, the similarity of in situ mean ChRM of plutons with that of post-tilting ChRMs of similar age volcanics and dissimilarity of the mean ChRM of plutons from expected directions at the time of formation of plutons support a secondary origin for the ChRM of plutons. As the ChRM directions of the volcanics and intrusives are the same, it implies that both ChRMs were acquired during the same remagnetization event. Comparing the mean paleolatitude (25 ± 6• N) from Gupis area with those from Indian APWP and considering the fact that there was prevailing heating event in Lower Tertiary in the area, the acquisition age of this secondary remanent magnetization can be bracketed between 50 and 35 Ma.

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A palaeogeographic reconstruction of the Dir Group: evidence for magmatic arc migration within Kohistan, N. Pakistan

Cited by 35 publications

References 36 publications

TTG-type plutonic rocks formed in a modern arc batholith by hydrous fractionation in the lower arc crust

TTG-type plutonic rocks formed in a modern arc batholith by hydrous fractionation in the lower arc crust

Paleomagnetic study of Utror Volcanic Formation: Remagnetizations and postfolding rotations in Utror area, Kohistan arc, northern Pakistan

Remagnetization of igneous rocks in Gupis area of Kohistan arc, northern Pakistan

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