Petrography and Mapping of the Gwal Melange of Khanozai Region, Balochistan, Pakistan

AbstractThe Gwal mélange is mapped on a large scale and is divided into the lithological units such as ultramafic, mafic, volcanic, volcanoclastic rocks, pelagic sediments and ophicarbonates. Petrographically, the mapped rocks are classified as harzburgite, dunite, wehrlite, serpentinite, gabbro, basalt, and andesite. These rocks are quite deformed and altered into the secondary minerals. Harzburgite is a layered mantle peridotite consists of olivine and orthopyroxene while dunite lacks the presence of any pyroxene. Serpentinite is the secondary product after peridotite is the product of post magmatic stages. The mesh structure is usually observed when olivine is completely altered to serpentine. The volcanic rocks are structurally sheeted and pillow type while the volcanoclastic rocks are essentially hyaloclastites associated with pelagic sediments. The Ophicarbonate is composed of serpentinite fragments and carbonate minerals, most probably calcite. Minor to trace amounts of opaque minerals are also present in association with major components. The gabbros may be a fragment of the main crustal rocks and have been formed in a magma chamber by fraction crystallization. The origin of ophicarbonate may be due to gas seeps originated by mantle or as the surficial process where ultramafic rocks and carbonates are mixed through processes of gravity, tectonic crushing and sedimentary reworking. The Gwal mélange may the southern extension of Bagh Complex found beneath the Muslim Bagh Ophiolite. The mantle peridotite of the mélange is much like that of the Khanozai peridotite and may represent its detached blocks. Volcanic and volcanoclastic rocks may be the representatives of the uppermost part of ophiolite crust which might have trimmed off from subducting slab and are, now, part of the Gwal accretionary wedge. The mélange may have tectonically emplacement over the Indian platform sediments along with overlying the ophiolite sheet during the Late Cretaceous.

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Early Cretaceous crust–mantle interaction linked to rollback of the Palaeo-Pacific flat-subducting slab: constraints from the intermediate–felsic volcanic rocks of the northern Great Xing’an Range, NE China

Geological Magazine ◽

10.1017/s0016756821000170 ◽

2021 ◽

pp. 1-22

Author(s):

Jia-Hao Jing ◽

Hao Yang ◽

Wen-Chun Ge ◽

Yu Dong ◽

Zheng Ji ◽

...

Keyword(s):

Early Cretaceous ◽

Volcanic Rocks ◽

Geochemical Data ◽

Calc Alkaline ◽

Ne China ◽

Asthenospheric Mantle ◽

High K ◽

Wide Range ◽

Great Xing’An Range ◽

Subducting Slab

Abstract Late Mesozoic igneous rocks are important for deciphering the Mesozoic tectonic setting of NE China. In this paper, we present whole-rock geochemical data, zircon U–Pb ages and Lu–Hf isotope data for Early Cretaceous volcanic rocks from the Tulihe area of the northern Great Xing’an Range (GXR), with the aim of evaluating the petrogenesis and genetic relationships of these rocks, inferring crust–mantle interactions and better constraining extension-related geodynamic processes in the GXR. Zircon U–Pb ages indicate that the rhyolites and trachytic volcanic rocks formed during late Early Cretaceous time (c. 130–126 Ma). Geochemically, the highly fractionated I-type rhyolites exhibit high-K calc-alkaline, metaluminous to weakly peraluminous characteristics. They are enriched in light rare earth elements (LREEs) and large-ion lithophile elements (LILEs) but depleted in high-field-strength elements (HFSEs), with their magmatic zircons ϵHf(t) values ranging from +4.1 to +9.0. These features suggest that the rhyolites were derived from the partial melting of a dominantly juvenile, K-rich basaltic lower crust. The trachytic volcanic rocks are high-K calc-alkaline series and exhibit metaluminous characteristics. They have a wide range of zircon ϵHf(t) values (−17.8 to +12.9), indicating that these trachytic volcanic rocks originated from a dominantly lithospheric-mantle source with the involvement of asthenospheric mantle materials, and subsequently underwent extensive assimilation and fractional crystallization processes. Combining our results and the spatiotemporal migration of the late Early Cretaceous magmatic events, we propose that intense Early Cretaceous crust–mantle interaction took place within the northern GXR, and possibly the whole of NE China, and that it was related to the upwelling of asthenospheric mantle induced by rollback of the Palaeo-Pacific flat-subducting slab.

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Two key switches in regional stress field during multi-stage deformation in the Carboniferous−Triassic southernmost Altaids (Beishan, NW China): Response to orocline-related roll-back processes

Geological Society of America Bulletin ◽

10.1130/b35898.1 ◽

2021 ◽

Author(s):

Zhonghua Tian ◽

Wenjiao Xiao ◽

Brian F. Windley ◽

Peng Huang ◽

Ji’en Zhang ◽

...

Keyword(s):

Stress Field ◽

Large Scale ◽

Electron Backscatter Diffraction ◽

Volcanic Rocks ◽

Structural Deformation ◽

Regional Stress ◽

Regional Stress Field ◽

Multi Stage ◽

Beishan Orogenic Collage ◽

Roll Back

The orogenic architecture of the Altaids of Central Asia was created by multiple large-scale slab roll-back and oroclinal bending. However, no regional structural deformation related to roll-back processes has been described. In this paper, we report a structural study of the Beishan orogenic collage in the southernmost Altaids, which is located in the southern wing of the Tuva-Mongol Orocline. Our new field mapping and structural analysis integrated with an electron backscatter diffraction study, paleontology, U-Pb dating, 39Ar-40Ar dating, together with published isotopic ages enables us to construct a detailed deformation-time sequence: During D1 times many thrusts were propagated northwards. In D2 there was ductile sinistral shearing at 336−326 Ma. In D3 times there was top-to-W/WNW ductile thrusting at 303−289 Ma. Two phases of folding were defined as D4 and D5. Three stages of extensional events (E1−E3) separately occurred during D1−D5. Two switches of the regional stress field were identified in the Carboniferous to Early Permian (D1-E1-D2-D3-E2) and Late Permian to Early Triassic (D4-E3-D5). These two switches in the stress field were associated with formation of bimodal volcanic rocks, and an extensional interarc basin with deposition of Permian-Triassic sediments, which can be related to two stages of roll-back of the subduction zone on the Paleo-Asian oceanic margin. We demonstrate for the first time that two key stress field switches were responses to the formation of the Tuva-Mongol Orocline.

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Nd isotopic characteristics of metamorphic and plutonic rocks of the Coast Mountains near Prince Rupert, British Columbia

Canadian Journal of Earth Sciences ◽

10.1139/e98-007 ◽

1998 ◽

Vol 35 (5) ◽

pp. 556-561 ◽

Cited By ~ 13

Author(s):

P J Patchett ◽

G E Gehrels ◽

C E Isachsen

Keyword(s):

British Columbia ◽

Volcanic Rocks ◽

Metamorphic Rocks ◽

Published Data ◽

Isotopic Data ◽

Crustal Component ◽

Coast Mountains ◽

Crustal Rocks ◽

Metasedimentary Rocks ◽

Plutonic Rocks

Nd isotopic data are presented for a suite of metamorphic and plutonic rocks from a traverse across the Coast Mountains between Terrace and Prince Rupert, British Columbia, and for three contrasting batholiths in the Omineca Belt of southern Yukon. A presumed metamorphic equivalent of Jurassic volcanic rocks of the Stikine terrane gives epsilon Nd = +6, and a number of other metaigneous and metasedimentary rocks in the core of the Coast Mountains give epsilon Nd values from +3 to +7. A single metasedimentary rock approximately 3 km east of the Work Channel shear zone gives a epsilon Nd value of -9. Coast Belt plutons in the traverse yield epsilon Nd from -1 to +2. The Omineca Belt plutons give epsilon Nd from -10 to -17. All results are consistent with published data in demonstrating that (i) juvenile origins for both igneous and metamorphic rocks are common in the Coast Belt; (ii) representatives of a continental-margin sedimentary sequence with Precambrian crustal Nd are tectonically interleaved in the Coast Mountains; (iii) Coast Mountains plutons can be interpreted as derived from a blend of metamorphic rocks like those seen at the surface, or as arc-type melts contaminated with the older crustal component; and (iv) Omineca Belt plutons are dominated by remelted Precambrian crustal rocks.

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Mapping Stress and Structure From Subducting Slab to Magmatic Rift: Crustal Seismic Anisotropy of the North Island, New Zealand

10.26686/wgtn.12309776.v1 ◽

2020 ◽

Author(s):

Finnigan Illsley-Kemp ◽

Martha Savage ◽

Colin Wilson ◽

S Bannister

Keyword(s):

New Zealand ◽

Stress Field ◽

Large Scale ◽

Seismic Anisotropy ◽

Taupo Volcanic Zone ◽

Volcanic Zone ◽

The North ◽

Magma Reservoirs ◽

Tectonic Forces ◽

Subducting Slab

© 2019. American Geophysical Union. All Rights Reserved. We use crustal seismic anisotropy measurements in the North Island, New Zealand, to examine structures and stress within the Taupō Volcanic Zone, the Taranaki Volcanic Lineament, the subducting Hikurangi slab, and the Hikurangi forearc. Results in the Taranaki region are consistent with NW-SE oriented extension yet suggest that the Taranaki volcanic lineament may be controlled by a deep-rooted, inherited crustal structure. In the central Taupō Volcanic Zone anisotropy fast orientations are predominantly controlled by continental rifting. However at Taupō and Okataina volcanoes, fast orientations are highly variable and radial to the calderas suggesting the influence of magma reservoirs in the seismogenic crust (≤15 km depth). The subducting Hikurangi slab has a predominant trench-parallel fast orientation, reflecting the pervasive presence of plate-bending faults, yet changing orientations at depths ≥120 km beneath the central North Island may be relics from previous subduction configurations. Finally, results from the southern Hikurangi forearc show that the orientation of stresses there is consistent with those in the underlying subducting slab. In contrast, the northern Hikurangi forearc is pervasively fractured and is undergoing E-W compression, oblique to the stress field in the subducting slab. The north-south variation in fore-arc stress is likely related to differing subduction-interface coupling. Across the varying tectonic regimes of the North Island our study highlights that large-scale tectonic forces tend to dictate the orientation of stress and structures within the crust, although more localized features (plate coupling, magma reservoirs, and inherited crustal structures) can strongly influence surface magmatism and the crustal stress field.

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HEAVY CLASTIC MINERALS AS AN INDICATOR OF GEODYNAMIC SETTINGS OF ACCUMULATION AND PROVENANCE OF CRETACEOUS SEDIMENTS OF THE WEST SAKHALIN TERRANE

Bulletin of Kamchatka Regional Association «Educational-Scientific Center» Earth Sciences ◽

10.31431/1816-5524-2021-1-49-68-86 ◽

2021 ◽

pp. 68-86

Author(s):

A.I. Malinovsky ◽

Keyword(s):

Large Scale ◽

Volcanic Rocks ◽

Source Area ◽

Heavy Minerals ◽

Clastic Material ◽

The West ◽

Geodynamic Settings ◽

Eurasian Continent ◽

Ocean Boundary ◽

By Products

The article discusses the results of studying heavy clastic minerals from the Cretaceous sandy rocks of the West Sakhalin Terrane, and also presents their paleogeodynamic interpretation. It is shown that in terms of mineralogical and petrographic parameters, the terrane sandstones correspond to typical graywackes and are petrogenic rocks formed mainly by destruction of igneous rocks of the source areas. The sediments were found to contain both sialic, granite-metamorphic association minerals, and femic, formed by products of the destruction of basic and ultrabasic volcanic rocks. The interpretation of the entire set of data on the content, distribution and microchemical composition of heavy minerals was carried out by comparing them with minerals from older rocks and modern sediments accumulated in known geodynamic settings. The results obtained indicate that during the Cretaceous, sedimentation occurred along the continent-ocean boundary in a basin associated with large-scale left-lateral transform movements of the Izanagi Plate relative to the Eurasian continent. The source area that supplied clastic material to that basin combined a sialic landmass composed of granite-metamorphic and sedimentary rocks, a mature deeply dissected ensialic island arc, and fragments of accretion prisms, in the structure of which involved ophiolites.

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Origin of the Tulameen ultramafic-gabbro complex, southern British Columbia

Canadian Journal of Earth Sciences ◽

10.1139/e69-040 ◽

1969 ◽

Vol 6 (3) ◽

pp. 399-425 ◽

Cited By ~ 28

Author(s):

D. C. Findlay

Keyword(s):

British Columbia ◽

Internal Structure ◽

Fractional Crystallization ◽

Volcanic Rocks ◽

Age Determination ◽

Upper Triassic ◽

Ultramafic Rocks ◽

Metasedimentary Rocks ◽

Gabbroic Intrusion

The Tulameen Complex is a composite ultramafic-gabbroic intrusion that outcrops over 22 sq. mi. (57 km2) in the Southern Cordillera of British Columbia. The complex intruded Upper Triassic metavolcanic and metasedimentary rocks of the Nicola Group, and on the basis of geologic relations and a K–Ar age determination (186 m.y.) is tentatively dated as Late Triassic.The principal ultramafic units — dunite, olivine clinopyroxenite, and hornblende clinopyroxenite — form an elongate, non-stratiform body whose irregular internal structure is best explained by deformation contemporaneous with crystallization of the rocks. The derivation of the ultramafic rocks is attributed to fractional crystallization of an ultrabasic magma. The gabbroic mass, which consists of syenogabbro and syenodiorite, partly borders and partly overlies the ultramafic body and was apparently intruded by it.The ultramafic and gabbroic parts of the complex probably formed from separate intrusions of different magmas, but the two suites have sufficient mineralogical and chemical features in common to indicate an ultimate petrogenic affinity of the magmas. Comparison of the Tulameen rocks with nearby intrusions of the same general age, in particular the Copper Mountain stock, suggests that they are members of a regional suite of alkalic intrusions. The possibility is also raised that these intrusions may be comagmatic with the Nicola volcanic rocks.

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Magnetite Redistribution during Multi-stage Serpentinization: Evidence from the Taishir massif, the Khantaishir Ophiolite, Western Mongolia

10.5194/egusphere-egu21-13773 ◽

2021 ◽

Author(s):

Otgonbayar Dandar ◽

Atsushi Okamoto ◽

Masaoki Uno ◽

Noriyoshi Tsuchiya

Keyword(s):

Hydrogen Generation ◽

Mantle Peridotite ◽

Oceanic Lithosphere ◽

Ultramafic Rocks ◽

Western Mongolia ◽

Fluid Infiltration ◽

Multi Stage ◽

Fe Content ◽

Coarse Grains ◽

Modal Abundance

Magnetite commonly forms during serpentinization of mantle peridotite, involving the hydrogen generation within the oceanic lithosphere. Although magnetite is concentrated in veins, the mobility of iron during serpentinization is still poorly understood. The completely serpentinized ultramafic rocks (originally dunite) within the Taishir massif in the Khantaishir ophiolite, western Mongolia, include abundant magnetite + antigorite veins, which manifest novel distribution of magnetite. The serpentinite records the multi-stage serpentinization, in order of (1) Al-rich antigorite + lizardite mixture with hourglass texture (Al2O3 = 0.46-0.69 wt%; Atg+Lz), (2) Al-poor antigorite composed of thick veins and their branches (Atg), and (3) chrysotile that cut all previous textures. The Mg# (= Mg/ (Mg + Fetotal)) of Atg+Lz (0.94-0.96) is lower than Atg (0.99) and chrysotile (0.98). In the region of Atg+Lz, magnetite occurs as the arrays of fine grains (<50 &#956;m) around the hourglass texture. In the Atg veins replacing Atg+Lz, magnetite disappears and re-precipitated as coarse grains (100-250 &#956;m) in the center of some veins. As the extent of replacement of Atg+Lz by Atg veins increases, both modal abundance of magnetite and the bulk Fe content decrease. These characteristics indicate that hydrogen generation mainly occurred at the stage of Atg+Lz formation, and magnetite distribution was largely modified via dissolution and precipitation in response to later fluid infiltration associated with the Atg veins. This also indicates the high iron mobility within the serpentinized peridotites even after the primary stage of magnetite formation.

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Isolation and Separation of Epidermal and Mesophyll Protoplasts from Rye Primary Leaves — Tissue-Specific Characteristics of Secondary Phenolic Product Accumulation

Zeitschrift für Naturforschung C ◽

10.1515/znc-1986-1-205 ◽

1986 ◽

Vol 41 (1-2) ◽

pp. 22-27 ◽

Cited By ~ 29

Author(s):

Margot Schulz ◽

Gottfried Weissenböck

Keyword(s):

Phenolic Compounds ◽

Large Scale ◽

Tissue Specificity ◽

Light Period ◽

Primary Leaf ◽

Secondary Product ◽

Tissue Specific ◽

Mesophyll Protoplasts ◽

Flavonoid Compounds ◽

Product Accumulation

Abstract We have develop ed a technique for the large-scale isolation of epidermal and mesophyll protoplasts, as well as the vascular strands, of rye primary leaf blades. Separation of the two types of protoplasts has been successful only from leaves harvested at the end of a 13-h light period, when chloroplasts were enriched in starch. The occurrence of different flavonoid compounds, and amounts, in epidermal and mesophyll protoplasts can be used as criteria for protoplast purity and viability since C-glucosylflavone O-glycosides are characteristic of epidermal protoplasts whereas flavone O-glucuronides and anthocyanins are typical of mesophyll protoplasts. Several non-flavonoid phenolic compounds are found only in the epidermal protoplast. These patterns of secondary product accumulation reflect the high tissue specificity of the rye leaf.

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Melt equilibration depths as sensors of lithospheric thickness during Eurasia-Arabia collision and the uplift of the Anatolian Plateau

Geology ◽

10.1130/g46420.1 ◽

2019 ◽

Vol 47 (10) ◽

pp. 943-947 ◽

Cited By ~ 3

Author(s):

M.R. Reid ◽

J.R. Delph ◽

M.A. Cosca ◽

W.K. Schleiffarth ◽

G. Gençalioğlu Kuşcu

Keyword(s):

Late Miocene ◽

Large Scale ◽

Middle Miocene ◽

Volcanic Rocks ◽

Suture Zone ◽

Arabian Plate ◽

Seismic Structure ◽

Eurasian Plate ◽

Lithospheric Thickness ◽

Anatolian Plateau

Abstract A co-investigation of mantle melting conditions and seismic structure revealed an evolutionary record of mantle dynamics accompanying the transition from subduction to collision along the Africa-Eurasia margin and the >1 km uplift of the Anatolian Plateau. New 40Ar/39Ar dates of volcanic rocks from the Eastern Taurides (southeast Turkey) considerably expand the known spatial extent of Miocene-aged mafic volcanism following a magmatic lull over much of Anatolia that ended at ca. 20 Ma. Mantle equilibration depths for these chemically diverse basalts are interpreted to indicate that early to middle Miocene lithospheric thickness in the region varied from ∼50 km or less near the Bitlis suture zone to ∼80 km near the Inner Tauride suture zone. This southward-tapering lithospheric base could be a vestige of the former interface between the subducted (and now detached) portion of the Arabian plate and the overriding Eurasian plate, and/or a reflection of mantle weakening associated with greater mantle hydration trenchward prior to collision. Asthenospheric upwelling driven by slab tearing and foundering along this former interface, possibly accompanied by convective removal of the lithosphere, could have led to renewed volcanic activity after 20 Ma. Melt equilibration depths for late Miocene and Pliocene basalts together with seismic imaging of the present lithosphere indicate that relatively invariant lithospheric thicknesses of 60–70 km have persisted since the middle Miocene. Thus, no evidence is found for large-scale (tens of kilometers) Miocene delamination of the lower lithosphere from the overriding plate, which has been proposed elsewhere to account for late Miocene and younger uplift of Anatolia.

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Structural evolution of Archean rocks in the western Wawa subprovince, Minnesota: refolding of precleavage nappes during D2 transpression

Canadian Journal of Earth Sciences ◽

10.1139/e92-170 ◽

1992 ◽

Vol 29 (10) ◽

pp. 2146-2155 ◽

Cited By ~ 18

Author(s):

M. A. Jirsa ◽

D. L. Southwick ◽

T. J. Boerboom

Keyword(s):

Field Data ◽

Large Scale ◽

Volcanic Rocks ◽

Structural Evolution ◽

Precise Form

Recent mapping in the western Wawa subprovince (the Vermilion district and its westward extensions in Minnesota) has identified a major, northeast-trending stratotectonic break, informally called the Leech Lake structural disconformity (LLSD), that separates two contrasting terranes. North of the LLSD are elongate, east-northeast-trending, fault-bounded panels of volcanic rocks, which are mostly north topping and homoclinal. South of the LLSD, large-scale, northwest-trending folds involve basaltic sequences that are stratigraphically overlain by thick sections of dacitic volcaniclastic and turbiditic rocks. However, the most prominent outcrop-scale deformational features are northeast-trending vertical folds and associated axial-planar cleavage related to transpression in D2. D1 minor folds and cleavage are rare.New field data indicate that the large folds in a predominantly sedimentary part of the southern terrane are early formed (D0–D1), and nappe-like. The precise form of the early folds is largely obscured by (i) superimposed folds and metamorphism contemporaneous with D2, (ii) faulting that began in D2 and outlasted folding, and (iii) emplacement of the Giants Range batholith and associated plutons. Nevertheless, the presence in the southern terrane of large areas of shallow-plunging, downward-facing rock sequences and the map pattern of rock units imply that a large south-verging, northwest-plunging thrust nappe (or nappes) antedated D2. Where the nappe lacked thick, rigid volcanic layers, accommodation to D2 transpression took the form of abundant Z folds. Much of the observed Z asymmetry of F2 folds may have resulted from compression and shear oblique to the trend of rock units. In contrast, early thrusts are inferred to have positioned volcanic units north of the LLSD such that their strike was nearly perpendicular to D2 compression, and therefore F2 folds did not develop extensively.

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