Collision zone between the Kohistan arc and the Asian plate in NW Pakistan

1985 ◽  
Vol 76 (4) ◽  
pp. 463-479 ◽  
Author(s):  
C. J. Pudsey ◽  
M. P. Coward ◽  
I. W. Luff ◽  
R. M. Shackleton ◽  
B. F. Windley ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Deep Levels ◽  
Suture Zone ◽  
Island Arc ◽  
Central Unit ◽  
Volcanic Group ◽  
Collision Zone ◽  
Structural History ◽  
History Of ◽  
Layered Complex

ABSTRACTThis paper describes the suture zone between the Asian plate and the accreted Kohistan island arc in the Chitral district of NW Pakistan.The southern part of the Asian plate consists of two tectonic units separated by the N-dipping Reshun fault. The northwestern unit comprises Devonian carbonates and quartzites overlain by Devonian to Permian shales and slates with some limestones (Lun shales). Its structure is complex with S-verging thrusts and isoclinal folds. Along the Reshun fault, the relatively undeformed Reshun Formation may represent molasse. The central unit includes N-dipping Upper Palaeozoic slates and quartzites (Darkot Group), probably faulted against an antiformal tract of slates, schists derived from a volcanic assemblage and Cretaceous limestones (Chitral slate, Koghozi greenschist, Krinj and Gahiret limestones). Asian plate sediments are intruded by granitic and granodioritic plutons, variably deformed and locally porphyritic.The Northern suture melange of volcanic, sedimentary and serpentinite blocks in a slate matrix separates the Asian plate from the southeastern unit, the Kohistan arc. This comprises Cretaceous volcanic rocks with some sediments (Shamran Volcanic Group, Drosh, Purit and Gawuch Formations) intruded by aphyric diorites, tonalites and granites. These intermediate plutonic rocks pass southwards into a mafic layered complex and amphibolites representing deep levels of the arc. The volcanic rocks and sediments dip to the N and have a horizontal lineation. The structural history of southern Asia and Kohistan is consistent with an originally curved Northern suture: motion of the arc was initially to the NE relative to Asia and subsequently to the NW.

Age of the Eycott Volcanic Group and its conformable relationship to the Skiddaw Slates in the English Lake District

1972 ◽  
Vol 109 (3) ◽  
pp. 259-268 ◽  
Author(s):  
C. Downie ◽  
N. J. Soper
Keyword(s):  
Volcanic Rocks ◽  
Island Arc ◽  
Lake District ◽  
Volcanic Group ◽  
Volcanic Sequence ◽  
Volcanic Formation ◽  
English Lake District

SummaryAn earliest Llanvirn age is established on micropalaeontological grounds for the interbedded lava–pelite sequence at the base of the Binsey Volcanic Formation in the northern Lake District. The northern volcanic sequence, here termed the Eycott Volcanic Group, is earlier than, and chemically distinct from, the main Borrowdale Volcanic Group. The evidence precludes a regional unconformity between the Skiddaw Slates and the overlying volcanic rocks, but is compatible with the hypothesis that the vulcanicity occurred in an island arc environment.

Crustal evolution of Archean rocks in the Kakagi Lake area, Wabigoon Subprovince, Ontario, as interpreted from high-precision U–Pb geochronology

1986 ◽  
Vol 23 (2) ◽  
pp. 182-192 ◽  
Author(s):  
D. W. Davis ◽  
G. R. Edwards
Keyword(s):  
Volcanic Rocks ◽  
Time Span ◽  
Time Interval ◽  
Lake Area ◽  
Volcanic Group ◽  
Regional Deformation ◽  
Felsic Volcanism ◽  
Plutonic Complex ◽  
Late Event ◽  
History Of

The evolution of the Archean volcanic–plutonic complex in the Kakagi Lake area occurred during a time interval of ca. 32 Ma. The earliest age is [Formula: see text] from analysis of zircon and baddeleyite in a gabbro intruding the lowermost Katimiagamak Volcanic Group. An age of 2723.2 ± 1.8 Ma on a tonalite gneiss from the interior of the underlying Sabaskong Batholith is indistinguishable from a previously dated massive border phase of the batholith and shows no evidence for inheritance from an older sialic component. An early tonalite phase from the adjacent Aulneau Batholith is dated at [Formula: see text], and the latest granodiorite phase is dated at [Formula: see text]. This defines a time span of about 7 Ma for intrusion of the bulk of the batholith and indicates that previously dated felsic volcanism from the uppermost sequence, above the Kakagi Lake Volcanic Group, is coeval with late plutonic activity in the Aulneau Batholith. The end of regional deformation in the area is given by the ages of two late-tectonic intrusions, the Heronry Lake pluton and the Stephen Lake pluton, dated at 2701.0 ± 1.2 and 2699.2 ± 1.9 Ma, respectively.U–Pb analyses of sphene were carried out on four of the samples in an effort to establish details of the post-folding thermal history of the area. Sphene is least reset in the Heronry Lake pluton (2699.2 ± 1.6 Ma), which is spatially most closely associated with the volcanic rocks and most reset in the Sabaskong gneiss (2673.7 ± 6.6 Ma), the sample most strongly affected by diapirism. The data indicate that regional deformation was a relatively late event, possibly caused by diapirism in the centres of the large batholiths and driven by a long-lived heat source in the mantle or lower crust.

Chapter 14: The Brucejack Au-Ag Deposit, Northwest British Columbia, Canada: Multistage Porphyry to Epithermal Alteration, Mineralization, and Deposit Formation in an Island-Arc Setting

2020 ◽  
pp. 289-311
Author(s):  
Warwick S. Board ◽  
Duncan F. McLeish ◽  
Charles J. Greig ◽  
Octavia E. Bath ◽  
Joel E. Ashburner ◽  
...  
Keyword(s):  
Volcanic Rocks ◽  
Lower Jurassic ◽  
Early Jurassic ◽  
Island Arc ◽  
Late Triassic ◽  
Low Grade ◽  
Coarse Aggregates ◽  
History Of ◽  
Arc Setting ◽  
Mineral District

Abstract The Brucejack intermediate-sulfidation epithermal Au-Ag deposit, located 65 km north of Stewart, BC, forms part of a well-mineralized, structurally controlled, north-south gossanous trend associated with Early Jurassic intrusions straddling the Late Triassic-Early Jurassic Stuhini-Hazelton Group unconformity in the Sulphurets mineral district. Mining of the deposit commenced in mid-2017 after a long history of exploration dating back to the 1880s. Mineralization is hosted in deformed Lower Jurassic island-arc volcanic rocks of the Hazelton Group exposed on the eastern limb of the Cretaceous McTagg anticlinorium. High-grade Au-Ag mineralization was formed from ~184 to 183 Ma in association with a telescoped, multipulsed magmatic-hydrothermal system beneath an active local volcanic center. Precious metal mineralization occurs as coarse aggregates of electrum and silver sulfosalts in steeply dipping, E- to SE-trending quartz-carbonate vein stockwork zones cutting low-grade intrusion-related phyllic alteration. Epithermal vein development is interpreted to have occurred during the waning stages of Early Jurassic sinistral transpression in a compressive arc environment, followed by a limited Cretaceous deformation overprint.

History of subduction erosion and accretion recorded in the Yarlung Suture Zone, southern Tibet

2019 ◽  
Vol 483 (1) ◽  
pp. 517-554 ◽  
Author(s):  
Kathryn Metcalf ◽  
Paul Kapp
Keyword(s):  
Volcanic Rocks ◽  
Suture Zone ◽  
Geological Mapping ◽  
Published Data ◽  
Southern Tibet ◽  
Slab Rollback ◽  
History Of ◽  
Subduction Erosion ◽  
Felsic Volcanic ◽  
Almost All

AbstractThe history of pre-Cretaceous subduction accretion and erosion along the Yarlung Suture Zone remains poorly constrained. We present new geological mapping along c. 200 km of the suture zone, 4881 detrital zircon U–Pb ages, and sandstone petrography for the subduction complex and Tethyan Himalayan strata. We provide the first documentation of the c. 158 Ma marine Xiazha Formation, which contains volcanic clasts of intermediate to felsic volcanic rocks and ooids with both calcareous and volcanic cores. Based on our new data and synthesis of published data, we present a model in which the Zedong arc represents the southwards migration of the Gangdese arc onto a forearc ophiolite that was generated proximal to the southern Asian margin during Neotethyan slab rollback at 160–150 Ma. This contrasts with previous suggestions that the Zedong arc, Yarlung ophiolites and subduction complex rocks developed above an intra-oceanic subduction zone thousands of kilometres south of Asia. Although Gangdese arc magmatism began in the Middle Triassic, the only forearc units preserved are 160 Ma until collision between the Xigaze forearc basin and Tethyan Himalaya at c. 59 Ma. This suggests that almost all pre-Cretaceous forearc assemblages have been removed by subduction erosion at the trench.

Stratigraphy, structure and evolution of the Tibetan–Tethys zone in Zanskar and the Indus suture zone in the Ladakh Himalaya

1983 ◽  
Vol 73 (4) ◽  
pp. 205-219 ◽  
Author(s):  
M. P. Searle
Keyword(s):  
Subduction Zone ◽  
Late Cretaceous ◽  
Volcanic Rocks ◽  
Ocean Basin ◽  
Suture Zone ◽  
Island Arc ◽  
Indian Plate ◽  
Northern Margin ◽  
Ladakh Himalaya ◽  
Late Tertiary

ABSTRACTThe Tibetan–Tethys zone of the Zanskar Himalaya shows a complete Mesozoic shelf carbonate sequence overlying metamorphic basement of the Central crystalline complex and Palaeozoic sedimentary rocks. Continental rifting in the Permian produced the alkaline and basaltic Panjal volcanic rocks and by Triassic time a small ocean basin was developed in the Indus-Tsangpo zone. Stable sedimentation continued until the Middle-Late Cretaceous when a thick sequence of tholeiitic to andesitic island arc lavas (Dras arc) were erupted in the basin above a N-dipping subduction zone. The Spontang ophiolite was emplaced southwards onto the Zanskar shelf edge during latest Cretaceous or earliest Tertiary times.Following emplacement of the Spontang ophiolite, deep-sea sedimentation ended abruptly with initial collision between the Indian plate and the Dras island arc. Emplacement of the massive Ladakh (Trans-Himalayan) batholith along the southern margin of Tibet in late Cretaceous-Eocene time occurred by crustal melting as a result of northward subduction of Mesozoic oceanic crust along the Indus subduction zone. Southward-directed thrusting in both Zanskar and Indus zones accompanied ocean closure during the late Cretaceous–Eocene. Late Tertiary compression caused intense folding, overturning and a phase of northward-directed thrusting along the Indus suture zone and the northern margin of the Tibetan–Tethys zone, resulting in a large amount of crustal shortening.

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