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Geological map of the Kohistan arc. Numbers indicate pressure in kbar constrained by Al-in-Hbl barometry (brown) or net transfer reactions involving garnet (green) or pyx–plag–qtz (black) (see Table 1 for complete dataset and references). The isobars (dashed red line, number in kbar) illustrate the exhumation level of the Kohistan constrained by 67 pressure estimates that have been interpolated at unconstrained regions using geostatistical modeling as described in the text. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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... Kohistan arc, exposed in NE Pakistan, is the best-preserved complete arc section (Bard, 1983;Tahirkheli, 1979) in the geological record, with volcanic rocks and unmetamophosed sediments overlying a predominantly felsic plutonic upper crust in the northern exposures (Fig. 1). To the south, mafic and ultramafic plutons characterize the lower crust at the base of the arc section. The Cretaceous to Tertiary oceanic arc formed in the equatorial part of the Neotethyan ocean ( Khan et al., 2009;Zaman and Torii, 1999). It is composed of three main complexes from north to south ( Fig. 1): (1) the Gilgit Complex, ...
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... crust in the northern exposures (Fig. 1). To the south, mafic and ultramafic plutons characterize the lower crust at the base of the arc section. The Cretaceous to Tertiary oceanic arc formed in the equatorial part of the Neotethyan ocean ( Khan et al., 2009;Zaman and Torii, 1999). It is composed of three main complexes from north to south ( Fig. 1): (1) the Gilgit Complex, comprising the mid-to upperlevel of the arc, including the Kohistan Batholith composed of variable granitoids and its volcano-sedimentary cover sequences ( Khan et al., 2009;Petterson and Treloar, 2004;Windley, 1985, 1991); (2) the Chilas Complex maficultramafic, rift related mid-to lower-crustal intrusions ...
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... Kohistan Arc is separated in the north from the former southern Eurasian margin (the Karakoram) by the Shyok suture zone (or "the Northern-", or "Karakoram-Kohistan suture zone") and in the south is separated from India by the Indus suture zone (Fig. 1). The collision of the arc with India is well constrained at ∼50 Ma (Rowley, 1996). While the formation age of the Shyok suture zone has been discussed for decades (e.g., Bard, 1983;Brookfield and Reynolds, 1981;Petterson and Windley, 1985), it was recently shown to postdate the formation of the Indus suture by ∼10 Ma ( Bouilhol et al., ...
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... pressures of various plutons throughout Kohistan arc have been determined quantitatively ( Fig. 1) using existing Table 1 for complete dataset and references). The isobars (dashed red line, number in kbar) illustrate the exhumation level of the Kohistan constrained by 67 pressure estimates that have been interpolated at unconstrained regions using geostatistical modeling as described in the text. (For interpretation of the ...
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... in the Kohistan arc are complex and correlated to some degree with the subdivision into the three main complexes (Gilgit, Chilas and Southern Plutonic Complex). Importantly, the highest pressures recorded in the Gilgit Complex overlap and agree well with the lowest pressure recorded in the petrologically related Southern Plutonic Complexes (Fig. ...
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... general lack of major tectonic faults in the arc (with the exception of the faults in the Dir-Kalam area, Fig. 1), in accordance with the lack of significant jumps in emplacement depth over short distances (that could indicate undiscovered major fault zone), indicates that the Kohistan arc exposes a continuous crustal section without any significant gaps or repetitions due to tectonic faulting. Therefore it is possible to quantitatively model the ...
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... result of the geostatistical modeling is shown as isobars in Fig. 1. In Figs. 3-5, the emplacement depth is plotted against whole-rock geochemical data and is compared to the composition of a Kohistan primitive arc melt (Jagoutz, 2010). As discussed previously, no significant variation in pressure occurs in the Chilas Complex, and accordingly no parameters vary significantly with intrusion pressures ...
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... of all liquid-dominated plutonic rocks were calculated at their inferred intrusion pressure (assuming an H 2 O Fig. 6. P , T conditions in the Kohistan arc constrained by metamorphic exchange equilibrium (red symbols) and the near solidus temperature of felsic liquids determined by hbl-plag thermometry (yellow symbols, data source as cited in Fig. 1). Also shown (in black) are the liquidus temperatures of plutonic rocks with near liquid compositions (calculated using the MELTS program with 4 wt% H 2 O). The thermal conditions in Kohistan arc compared to predicted geotherms from thermal modeling (fine lines) as compiled by Kelemen et al. (2003) and different geotherms. The stippled ...
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... It has long been known that magmatic arcs are the main environment where continental crust is created on the post-Archean Earth; however, major questions remain relating to the geological processes that drive the growth and reworking of juvenile arc crusts (e.g., Hacker et al., 2011Hacker et al., , 2015Jagoutz, 2014;Ducea et al., 2015;Lee and Anderson, 2015). For example, how does juvenile basaltic arc crust evolve into mature andesitic continental crust, and over what time scales do these processes operate? ...
... Proposed mechanisms of transforming juvenile arc crust into continental crust include foundering of dense mafic rocks of lower arc crust (Arndt and Goldstein, 1989;Kay and Kay, 1991), crustal formation from primary mantlederived or subducted oceanic crust-derived andesitic magmas (Kelemen, 1995;Niu et al., 2013), or mixing of basaltic rock with silicic magma derived by partial melting of mafic, subducting crust (Martin, 1986), or relamination of buoyant, subducted silica-rich sediments that can increase the bulk-SiO 2 content of the lower crust as a whole (Hacker et al., 2011(Hacker et al., , 2015Kelemen and Behn, 2016). Fractional crystallization of mafic magma is commonly suggested to be a key mechanism of intracrustal differentiation and foundering of dense lower arc crustal rocks (Jagoutz, 2014;Keller et al., 2015;Jagoutz and Klein, 2018). However, partial melting within lower arc crust is likely necessary for juvenile arc crust to vertically differentiate and be refined into chemically mature continental crust (Kay and Kay, 1993;Brown and Rushmer, 2006;Garrido et al., 2006;Brown, 2007Brown, , 2010Stern and Scholl, 2010;Jagoutz and Behn, 2013;Ducea et al., 2015). ...
Magmatic arcs are the main environment where continental crust is created on the post-Archean Earth; however, how juvenile arc crust evolves into mature continental crust is still controversial. In this study, we report new bulk-rock major and trace elements, Sr-Nd isotopes, and zircon U-Pb ages and Hf isotopes from a large suite of granites collected from the eastern segment of the Gangdese arc, southern Tibetan Plateau, which record a complete history of arc crust evolution from Mesozoic subduction to Cenozoic collision. These new data show that Gangdese crust-derived granites generated during the subduction to collisional stages record significant geochemical changes with age, indicating that the bulk composition, lithological makeup, and thicknesses of the arc crust evolved over time. Here, we propose that the Gangdese arc had a thick juvenile crust with a small volume of ancient crustal components during late-stage subduction of the Neo-Tethys Ocean, a thin juvenile crust with heterogeneously distributed ancient crustal materials during early collision, and a thick juvenile crust with minor proportions of ancient rocks during late collision. This implies that the arc experienced episodes of crustal thickening during the Late Cretaceous and Eocene, interspersed by periods of thinning during the Paleocene and Miocene, and several discrete episodes of partial melting in the lower arc crust, and cycling or recycling of juvenile and ancient crustal materials within the arc crust and between the crust and mantle. We suggest that shallow subduction of the Neo-Tethys during the Late Cretaceous promoted tectonic thickening of the arc crust, partial melting of lower crust, and formation of high Sr/Y granites. After the onset of the Indo-Asian collision, breakoff of the subducted Neo-Tethyan oceanic slab during the Paleocene/early Eocene allowed thinning of the overlying arc crust and generation of granites derived from juvenile and ancient crustal sources. Continued underthrusting of the Indian continental crust and subsequent delamination of thickened lithospheric mantle led to thickening and thinning of the arc crust, respectively, and partial melting of thickened lower crust and generation of high Sr/Y granites during the Oligocene and Miocene. Using the Gangdese as an analogue for post-Archean continental margins, we suggest that the repeated thickening and thinning of arc crust, and associated multistage remelting of the lower arc crust, and material cycling or recycling within the crust and between the crust and mantle from subduction to collision are common processes that drive maturation of juvenile arc crust.
... Supplementary data to this article can be found online at https:// doi.org/10.1016/j.lithos.2023.107484. Bucholz et al., 2014Grove et al., 2012Jagoutz, 2014Jagoutz et al., 2011Liu et al., 2021Marxer and Ulmer, 2019Putirka, 2016Reubi and Müntener, 2022 Zhu et al. LITHOS xxx (xxxx) 107484 ...
Decoding the trans-crustal magmatic evolution processes from exposed paleo-depth that are otherwise inaccessible
above continental arc zone is instructive to understand the geochemical fractionation of arc magmatism
and geochemical stratification of continental crust. To unravel trans-crustal magmatic processes leading to the
formation of Neoproterozoic continental arc, we combined a comprehensive dataset of petrography, zircon
U–Pb geochronology, whole-rock major and trace elements, and Sr–Nd isotopes as well as zircon Lu–Hf isotopes
for the Neoproterozoic calc-alkaline Luding Intrusive Complex (LIC) in the western Yangtze Block, South
China. The LIC is composed of monzodiorites, gabbro-diorites, diorites, and granodiorites that formed at ca.
783–779 Ma. The LIC lithologies are calc-alkaline with highly variable Mg# values (40.8–70.6) and subductionrelated
trace elemental patterns. In combination with predominantly depleted and comparable whole-rock
Sr–Nd (initial 87Sr/86Sr = 0.703244–0.704248 and εNd(t) = +2.35 ~ +5.10) and zircon Hf isotopes (εHf(t)
= +4.47 ~ +9.99), the LIC originated from a common subduction fluids-metasomatized mantle source. The
hornblende geothermobarometry and whole-rock normative mineral trajectories as well as previously experimental
results collectively suggest that the crystallization of LIC occurred within the middle crustal level
(11.4–20.9 km) at various temperatures (776–875 ◦C) and pressures (2.50–5.50 kbar), and underwent different
degrees of fractional crystallization of predominant hornblende and plagioclase phases during the assemblage
and solidification of cogenetic and multiple batches magmatic pluming. The diorites-granodiorites result from
fractionation of early olivine + clinopyroxene phases followed by subsequent amphibole + plagioclase phases,
and the monzodiorites mainly represent accumulation residues of dominant hornblende + plagioclase phases
from more fractionated melts, while the gabbro-diorites underwent the fractionation from an isotopically homogeneous
mantle source, but differ in their elemental compositions. The LIC from Neoproterozoic continental
arc suggests that the cogenetic fractional crystallization of mantle-derived melts in intra-crustal magmatic system
can account for the petrochemical diversities of arc magmatic rocks during the construction of the Neoproterozoic
continental arc crust in the western Yangzte Block, South China.
... However, evidence from the Earth suggests that other factors modulate the influence of buoyancy on the ascent of magmas. For example, granitic magmas are buoyant relative to most of the arc crust, and yet can remain trapped in the lower and middle crust (Jagoutz, 2014;Vigneresse & Clemens, 2000). Water saturation has been proposed as a major control on the storage depth of arc magmas (Rasmussen et al., 2022). ...
... Water saturation has been proposed as a major control on the storage depth of arc magmas (Rasmussen et al., 2022). Magmas can freeze deeper than neutral buoyancy levels if they become viscous and immobile due to crystallization and/or degassing (Annen et al., 2006;Jagoutz, 2014), both processes influenced by volatile saturation. Ascent may also depend on the volume of the magma body (Burov et al., 2003). ...
Most of the Martian crust formed prior to ∼4 Ga, but the magmatic processes responsible for finalizing the structure and composition of the ancient crust remain enigmatic. Impacts can produce large volumes of melt under a wide range of melting pressures, temperatures, and degrees of melting. Hellas, Argyre, Isidis, and Utopia basins date to around 4 Ga, demonstrating that basin‐scale impacts helped to place the finishing touches on an already established crust. In this work, we focus on the ascent and intrusion of impact partial melts generated at mantle depths and the consequences for the petrology and structure of the Martian crust. Specifically, we show that the majority of impact partial melts are buoyant, favoring ascent to the surface or to neutral buoyancy levels in the crust, where magmas solidify as intrusive rocks. The composition of these polybaric melts overlaps with some ancient Martian igneous materials. We propose that the process of ascent of deep‐seated impact partial melts and intrusion at shallower levels may have contributed to the observed crustal stratification and ancient petrologic diversity on Mars.
... Zr (ppm) is plotted against (a) Nd (ppm), (b) Nb (ppm), (c) Sm (ppm), (d) La (ppm), (e) Yb (ppm) and (f) Gd (ppm) contents. The trace element contents of the Cretaceous Chilas Complex, Pakistan (Khan et al., 1989;Schaltegger et al., 2002;Jagoutz, 2006Jagoutz, , 2014Jagoutz et al., 2006Jagoutz et al., , 2009Jagoutz et al., , 2019Zafar et al., 2020;Lutfi et al., 2022), Cretaceous Bolivar Ultramafic Complex, Colombia (Kerr et al., 2004) and Freetown Layered Complex, Sierra Leone (Callegaro et al., 2017) are shown in the background for comparison. The symbols are the same as for those in Fig. 7. ...
The geochemistry of Archean anorthosite-bearing layered intrusions has major implications for the thermal and chemical state of the Archean crust/mantle system, as originally posited by Bowen (1917) as “the anorthosite problem” and expanded on by Ashwal (1993). Debates have centred on the nature of the parental magmas, emplacement mechanisms and geodynamic settings of Archean anorthosites, many of which have megacrystic textures. In this review, we have compiled whole-rock major and trace element and Nd isotope geochemical data
from Archean anorthosite-bearing layered intrusions worldwide to address the outstanding questions outlined above regarding the petrogenesis of anorthosites. Archean anorthosite-bearing layered intrusions were not significantly affected by hydrothermal alteration and were derived from depleted mantle sources and most (85%) were emplaced in oceanic settings. Some intrusions were intruded in continental settings or ocean-continent
transition zones, reflecting the emergence of continents in the Paleoarchean into the Neoarchean. Based on their petrography and major and trace element geochemistry, Archean anorthosite-bearing layered intrusions mostly crystallised from hydrous Ca- and Al-rich tholeiitic magmas that fractionated from more primitive tholeiitic parental magmas. Archean layered intrusions formed by shallow- and deep-level fractional crystallisation
of tholeiitic magmas and predominantly formed in back-arc suprasubduction zone and volcanic arc settings. Archean anorthosite-bearing layered intrusions started forming at ca. 3850 Ma, most of them representing relicts of dismembered Archean subduction-related ophiolites. Modern-style plate tectonic processes have operated at least since the earliest Archean and were the predominant contributor to Archean crustal growth.
... Sisson and Grove 1993;Blundy and Cashman 2008). These experimental constraints contrast with field observations of exposed paleo-oceanic island and continental arc crustal sections such as the Kohistan arc in Pakistan (Bard 1983;Jagoutz 2014), the Talkeetna arc in Alaska (Greene et al. 2006;Bucholz and Kelemen 2019), or the Famatinian arc in Argentina Walker et al. 2015;Rapela et al. 2018), where mafic to ultramafic cumulate rocks (the "residues" of crystallisation-driven magma differentiation) are predominantly observed in the lower crust and almost absent at upper-crustal levels. In addition, a significant amount of arc rocks exhibits geochemical evidence (e.g. ...
... For details on cumulate bulk composition calculations, see text cumulates (e.g. Bard 1983;Greene et al. 2006;Jagoutz 2014) and geochemical data point to an important role of high-pressure amphibole fractionation (e.g. Romick et al. 1992;Davidson et al. 2007;Larocque and Canil 2010). ...
Arc magmatism is fundamental to the generation of new continental or island arc crust. However, the mechanisms that add to the chemical complexity of natural calc-alkaline magmas ranging from basaltic to rhyolitic compositions are debated. Differentiation mechanisms currently discussed include magma mixing, assimilation, crustal melting, or (fractional) crystallisation. In this contribution, the differentiation of arc magmas by decompression-driven crystallisation is investigated. We performed a set of equilibrium crystallisation experiments at variable crustal pressures (200–800 MPa) on a hydrous high-Al basalt (3.5 wt.% of H2O in the starting material) with run temperatures varying from near-liquidus conditions (1110 °C) to 900 °C. Oxygen fugacity was buffered at moderately oxidising conditions close to the NNO equilibrium. Combining these novel experiments with previous polybaric fractional crystallisation experiments (Marxer et al., Contrib Mineral Petrol 177:3, 2022) we demonstrate the effects of pressure on the crystallisation behaviour of calc-alkaline magmas with respect to liquid and cumulate lines of descent, mineral chemistry, and phase proportions. Decompression shifts the olivine-clinopyroxene cotectic curve towards melt compositions with higher normative clinopyroxene and enlarges the stability field of plagioclase. This exerts a key control on the alumina saturation index of residual liquids. We argue that near-adiabatic (or near-isothermal) decompression accompanied by dissolution of clinopyroxene entrained during residual melt extraction in the lower crust keeps arc magmas metaluminous during crystallisation-driven differentiation thereby closely reproducing the compositional spread observed for natural arc rocks.
... The recognition of Kohistan-Ladakh as an island arc dates back to the 1970s and 80s including researchers such as, Bard et al. (1980), Bard (1983), Reuber (1986Reuber ( , 1989, Thakur (1981), Tahirkheli (1979), and Tahirkheli and Jan (1979). Researchers that built upon the island arc model and had a particular interest in geochemical, isotopic, magmatic, structural, and field-related studies of the Kohistan-Ladakh batholith include Ahmad et al. (1998), , Bignold and Treloar (2003), Bignold et al. (2006), , Clift et al. (2002Clift et al. ( , 2005, Coward et al. ( , b, 1986Coward et al. ( , 1987, George et al. (1993), Jagoutz (2009Jagoutz ( , 2010Jagoutz ( , 2014, Jagoutz and Schmidt (2012), Jagoutz and Keleman The full plutonic compositional suite from gabbro, gabbrodiorite, to granodiorite and granite is present within the batholith. In many parts of the batholith basic rocks are intruded by more silica rich rocks, although this trend can reverse in time also. ...
... Many workers report the presence of sericite and clay minerals, epidote, chlorite, and actinolite. Jagoutz (2014) and determined paleo-pressures across Kohistan of between > 10 and 2 kb. The highest pressures were determined from rocks close to the rapidly uplifted Nanga Parbat Syntaxis and the lowest pressures estimated from rocks in mid-northernmost Kohistan ( Fig. 1.1). ...
Magmatic activity within the Leh region is dated at 70–45 Ma, although this study predicts that this range does not reflect the full temporal spectrum of magmatism. Crustal depth pluton emplacement estimates range between 7 and 15 km. Low temperature geochronological studies indicate the batholith was uplifted to c. 3 km between 8 and 30 Ma. Zanskar structural studies indicate active cover-basement thrusting between 45 and 25 Ma with cover deformation in the Leh area to at least the Pliocene. Structural studies of the Nanga Parbat Syntaxis indicate Recent-present day active tectonics and the presence of the brittle–ductile transition zone at depths of c. 5 km, with an equivalent brittle–ductile transition zone depth of 12–6 km in the Leh area. Results from this study suggest a fractured basement crustal block deformation model with individual blocks exhibiting unique deformational histories, significant vertical and lateral movement, and variable depth exposure. Basement plutonic deformation contrasts with cover deformation in part due to the lack of pre-existing contiguous planar structures, the variable nature of stress transmission, and wide range and variable character of pre-existing fractures, weaknesses, and anisotropies. A tectonic-deformation model is presented exhibiting: (1) intrusive activity (Cretaceous–Eocene); (2) extensional rift deformation penetrating basement (Eocene–Oligocene); thrust-shear deformation within a fractured basement (Eocene–Miocene) and; (4) North-directed thrusting affecting cover and basement (Miocene–Pliocene).KeywordsCrustal blocksFractured basementBrittle–ductile transition zone
... The recognition of Kohistan-Ladakh as an island arc dates back to the 1970s and 80s including researchers such as, Bard et al. (1980), Bard (1983), Reuber (1986Reuber ( , 1989, Thakur (1981), Tahirkheli (1979), and Tahirkheli and Jan (1979). Researchers that built upon the island arc model and had a particular interest in geochemical, isotopic, magmatic, structural, and field-related studies of the Kohistan-Ladakh batholith include Ahmad et al. (1998), , Bignold and Treloar (2003), Bignold et al. (2006), , Clift et al. (2002Clift et al. ( , 2005, Coward et al. ( , b, 1986Coward et al. ( , 1987, George et al. (1993), Jagoutz (2009Jagoutz ( , 2010Jagoutz ( , 2014, Jagoutz and Schmidt (2012), Jagoutz and Keleman The full plutonic compositional suite from gabbro, gabbrodiorite, to granodiorite and granite is present within the batholith. In many parts of the batholith basic rocks are intruded by more silica rich rocks, although this trend can reverse in time also. ...
... Many workers report the presence of sericite and clay minerals, epidote, chlorite, and actinolite. Jagoutz (2014) and determined paleo-pressures across Kohistan of between > 10 and 2 kb. The highest pressures were determined from rocks close to the rapidly uplifted Nanga Parbat Syntaxis and the lowest pressures estimated from rocks in mid-northernmost Kohistan ( Fig. 1.1). ...
This chapter focuses on a NW–SE trending high strain zone (HSZ) within the southern part of the Ladakh batholith, extending some 40 km from Taroo in the NW to Stakmo in the SE. Results from detailed field observations and structural measurements accompanied by detailed analysis of photographs and photo-mosaics are presented. The HSZ is characterised by a high density of contiguously-fractured plutonics, an abundance of strongly foliated rocks, and high densities of brittle–ductile shear zones. These structures strongly influence the shape and overall geomorphic form of local topography producing isolated thrust-escarpment-ridges, and well-featured contiguous ridges. Thrust structures are present at a range of scales from micro to mountain. The overall thrust geometry is dendritic in form with concave-upwards branch secondary structures, rooted and asymptotic to basal sole thrusts, bending upwards towards and asymptotic to roof thrusts. This dendritic form, when mapped out clearly indicates kinematic thrust directions on the outcrop to mega-scale. Other classic thrust structural elements are present including, horses/discrete individual thrust units, ramps, pop-up structures, flower-structures, antiformal thrust stacks, and related synforms: many examples of these structures are presented. A combination of structural data and interpretations (field-outcrop, geological mapping, photographic interpretation) indicate thrust vergence to the NNE–NE and SSE–SW. In some areas the two vergence directions are pene-contemporaneous, whilst in others one direction dominates over the other and there is a clear time history to the thrust vergence. The overall regional structural architecture is presented via a series of structural cross sections and a klippen model, which is indicative of a highly fractured basement, with crustal blocks (klippen) varying in scale from c. 1–3 km2 to 7 km × 15 km. Individual klippen moved NNW to NW, and SW with additional strike-slip motions. Kinematic indicators close to klippen boundaries are complex indicating a range of rotational and translational klippen–tectonic-interactions.KeywordsThrusts and shearsStructural geologyFractured geological basement
... The recognition of Kohistan-Ladakh as an island arc dates back to the 1970s and 80s including researchers such as, Bard et al. (1980), Bard (1983), Reuber (1986Reuber ( , 1989, Thakur (1981), Tahirkheli (1979), and Tahirkheli and Jan (1979). Researchers that built upon the island arc model and had a particular interest in geochemical, isotopic, magmatic, structural, and field-related studies of the Kohistan-Ladakh batholith include Ahmad et al. (1998), , Bignold and Treloar (2003), Bignold et al. (2006), , Clift et al. (2002Clift et al. ( , 2005, Coward et al. ( , b, 1986Coward et al. ( , 1987, George et al. (1993), Jagoutz (2009Jagoutz ( , 2010Jagoutz ( , 2014, Jagoutz and Schmidt (2012), Jagoutz and Keleman The full plutonic compositional suite from gabbro, gabbrodiorite, to granodiorite and granite is present within the batholith. In many parts of the batholith basic rocks are intruded by more silica rich rocks, although this trend can reverse in time also. ...
... Many workers report the presence of sericite and clay minerals, epidote, chlorite, and actinolite. Jagoutz (2014) and determined paleo-pressures across Kohistan of between > 10 and 2 kb. The highest pressures were determined from rocks close to the rapidly uplifted Nanga Parbat Syntaxis and the lowest pressures estimated from rocks in mid-northernmost Kohistan ( Fig. 1.1). ...
The North–Northeastern zone of the Ladakh batholith, Leh–Ladakh Region is more heterogeneous in style, compared to the adjacent south High Strain Zone. It extends some 40 km NW–SE, and is up to 12 km wide NE–SW. This chapter reports the results of field-based observations and structural readings alongside detailed anlaysis of photographs and photomosaics. The N–NE Zone is characterised by a higher abundance of ductile deformation, which has produced a series of discrete shear zones that vary in scale from cm and metres to km wide. Shear zone-rich regions exhibit discrete zones of highly-sheared rock separated by low and lower strain zones. Other sub-zones are dominated by fold structures, particularly where meta-sediments crop out. More extensive lower strain zones are characterised by thrusts and high angle extensional faults. Shear zones produce strong gnieissic foliation, intense fracture and cleavage, extended xenoliths with long/sort axial ratios up to 20, and S–C fabrics. Brittle structures such as thrust zones have similar kinematic indicators to the High Strain Zone (NNW–NE vergence) reflecting a prevalent ENE–WSW structural grain. Shear zones mostly strike NW–SE to NNW–SSE. Fold axial planes vary in strike between NW–SE and NE–SW with the larger folds displaying a north–south axial planar strike. Structural data from the N–NNE zone support and extend the klippen-fractured basement model derived from structural analysis of the southern High Strain zone.KeywordsShear ZonesFractured basementFolds thrusts and extensional faults
... The recognition of Kohistan-Ladakh as an island arc dates back to the 1970s and 80s including researchers such as, Bard et al. (1980), Bard (1983), Reuber (1986Reuber ( , 1989, Thakur (1981), Tahirkheli (1979), and Tahirkheli and Jan (1979). Researchers that built upon the island arc model and had a particular interest in geochemical, isotopic, magmatic, structural, and field-related studies of the Kohistan-Ladakh batholith include Ahmad et al. (1998), , Bignold and Treloar (2003), Bignold et al. (2006), , Clift et al. (2002Clift et al. ( , 2005, Coward et al. ( , b, 1986Coward et al. ( , 1987, George et al. (1993), Jagoutz (2009Jagoutz ( , 2010Jagoutz ( , 2014, Jagoutz and Schmidt (2012), Jagoutz and Keleman The full plutonic compositional suite from gabbro, gabbrodiorite, to granodiorite and granite is present within the batholith. In many parts of the batholith basic rocks are intruded by more silica rich rocks, although this trend can reverse in time also. ...
... Many workers report the presence of sericite and clay minerals, epidote, chlorite, and actinolite. Jagoutz (2014) and determined paleo-pressures across Kohistan of between > 10 and 2 kb. The highest pressures were determined from rocks close to the rapidly uplifted Nanga Parbat Syntaxis and the lowest pressures estimated from rocks in mid-northernmost Kohistan ( Fig. 1.1). ...
The Kohistan–Ladakh batholith forms the most voluminous geological unit within the Kohistan–Ladakh island arc terrane, constituting c. 80% of the outcrop area in the Ladakh region. The batholith is up to 30 km thick, with emplacement depth estimates of various components of the batholith ranging between 10 and < 2 kb (c. 35–7 km depth): in Ladakh estimates are > 4 to c. 2 kb (c. 15–7 km depth). The Ladakh batholith is heterogeneous and complex, comprising plutons, stocks, dykes and sills that range in composition from hornblende cumulates to felsic rich leucogranites. The proportion of lithological compositions exposed in the batholith is c. 10–20% mafic/ultramafic, 20–30% intermediate, 50% acid, and 10% leucocratic-felsic acid sheets. Primary mineralogy is dominated by hbl-biot-plag-qz-alk feld-with minor px. Minor mineralogy comprises zirc-sph-ilm-mag-py-cp-xen. Batholith age estimates vary between 150 and < 30 Ma, although mostly 120 Ma or less, and 78–45 Ma in the Leh-Ladakh region. Metamorphic grade varies from very low to amphibolite grade, with sericite-lower greenschist grade being most common. Non-batholithic rocks in Ladakh comprise the Late Triassic–Cretaceous clastic-limestone marine Lamayuru Complex, the Jurassic–Cretaceous Dras Volcanics, the Palaeocene–Eocene marine-sedimentary Tar Formation, including the youngest marine Nummulitic limestone, and the Eocene-Upper Miocene Indus Suture molasse sequence. Deformation has produced central upright, southerly south-verging, and northerly north-verging thrusts and folds, with deformation from c. 70 Ma to the Pliocene, and modern active tectonics. Low temperature geothermometry suggests Ladakh uplifted through the 150 °C isotherm between 30 and 8 Ma (youngest ages in north Ladakh).KeywordsLadakh batholithIndus Suture molasseGeochronology and stratigraphic age
... The recognition of Kohistan-Ladakh as an island arc dates back to the 1970s and 80s including researchers such as, Bard et al. (1980), Bard (1983), Reuber (1986Reuber ( , 1989, Thakur (1981), Tahirkheli (1979), and Tahirkheli and Jan (1979). Researchers that built upon the island arc model and had a particular interest in geochemical, isotopic, magmatic, structural, and field-related studies of the Kohistan-Ladakh batholith include Ahmad et al. (1998), , Bignold and Treloar (2003), Bignold et al. (2006), , Clift et al. (2002Clift et al. ( , 2005, Coward et al. ( , b, 1986Coward et al. ( , 1987, George et al. (1993), Jagoutz (2009Jagoutz ( , 2010Jagoutz ( , 2014, Jagoutz and Schmidt (2012), Jagoutz and Keleman The full plutonic compositional suite from gabbro, gabbrodiorite, to granodiorite and granite is present within the batholith. In many parts of the batholith basic rocks are intruded by more silica rich rocks, although this trend can reverse in time also. ...
... Many workers report the presence of sericite and clay minerals, epidote, chlorite, and actinolite. Jagoutz (2014) and determined paleo-pressures across Kohistan of between > 10 and 2 kb. The highest pressures were determined from rocks close to the rapidly uplifted Nanga Parbat Syntaxis and the lowest pressures estimated from rocks in mid-northernmost Kohistan ( Fig. 1.1). ...
The Indus Suture Rocks crop-out south of the Kohistan batholith over a c. 40 km strike width from NW to SE. The Indus Suture Rocks are exceptionally well exposed, forming cliffs and mountains with a c. 2000 m + vertical relief in places. The unit is well bedded and contiguously bedded. Thrust and fault structures are clearly visible in mountainside outcrops. There is a wide variation in clastic lithological character from coarse conglomerates to shales. This stratigraphy constitutes a molasse sequence which, in part, onlaps unconformably onto the Ladakh batholith. Outcrops in the north-westernmost part of the study area are dominated by cyclical graded coarse sandstone/conglomerate—shale sequences akin to hemipelagic turbidites. Parallel bedded sequences of conglomerate, gritty sandstone, siltstone and shale predominate with individual beds varying in thickness between a few centimetres and 60 cm. The rocks are metamorphosed from very low grade to phyllite-low greenschist grade. Sedimentary structures include graded bedding, cross bedding, flute structures, soft sedimentary deformation structures, and erosive bases. A high abundance of mafic and feldspar minerals in some sandstones are indicative of volcanic and plutonic source rocks. Structural studies of the Indus Suture Rocks largely, from photo-mosaic interpretations, reveal complex thrust nappe/horse stacks, antiformal thrust-stacks, and related fold structures. Individual thrusts vary from 10s to 100s of m thick. Whilst there is a predominant NE-trending thrust vergence, back-thrusts verge towards the NW and SE, with local variations in thrust kinematics.KeywordsIndus Suture RocksTurbiditesPhoto-interpretation
