scholarly journals Himalayan and Trans Himalayan granitic rocks in and adjacent to Nepal and their mineral potential

1981 ◽  
Vol 1 (1) ◽  
Author(s):  
A. H. G. Mitchell
Keyword(s):  
Root Zone ◽  
Porphyry Copper ◽  
Tectonic Setting ◽  
Granitic Rocks ◽  
Main Central Thrust ◽  
Southern Tibet ◽  
Late Mesozoic ◽  
The North ◽  
Augen Gneiss ◽  
Host Rocks

Granitic rocks occupying eight distinct tectonic settings can be recognized in the Himalayas and   Transhimalayas.  In the Lower Himalayas geographical belt a few plutons of two-mica granite intrude the lowest unit of the Nawakot Complex or Midland Group. More extensive are sheet- like lies of augen gneiss intrusive within a possibly thrust bounded succession carbonates and graphitic schists beneath the Main Central Thrust to the north. The most abundant granites in the Lower Himalayas are the two- mica cordierite- bearing granite within klippen; minor tin and tungsten mineralization is associated with these plutons, which are of late Cambrian age. Within the Higher Himalayas above the Main Central Thrust, the ‘Central Crystallines’ or Central Gneisses include pegmatites and pegmatitic granites intrusive into gneisses of probable early Proterozoic age; these have same potential for ruby, sapphire, aquamarine and possibly spodumene. Further north within the Higher Himalayan succession a southern belt of anatectic two- mica granites and leucogranites of mid-Tertiary age is favorable for tin, tungsten and uranium mineralization; a northern belt of granites or gneisses is of uncertain age and origin. North of the Indus Suture in the Transhimalayas extensive batholiths of hornblende granodiorite representing the root zone of a late Mesozoic to early Eocene volcanic arc are associated with porphyry copper deposits. Further north in southern Tibet the tectonic, setting for reported granitic bodies of  Tertiary  age  is  uncertain; their location suggests that they could be favorable host rocks for tin, uranium and porphyry molybdenum mineralization.

Cambrian to early Silurian ophiolite and accretionary processes in the Beishan collage, NW China: implications for the architecture of the Southern Altaids

2011 ◽  
Vol 149 (4) ◽  
pp. 606-625 ◽  
Author(s):  
S. J. AO ◽  
W. J. XIAO ◽  
C. M. HAN ◽  
X. H. LI ◽  
J. F. QU ◽  
...  
Keyword(s):  
Tectonic Setting ◽  
Island Arc ◽  
Passive Margin ◽  
Granitic Rocks ◽  
Geochemical Data ◽  
Weighted Mean ◽  
Ophiolite Complex ◽  
The North ◽  
Ophiolitic Mélange ◽  
Continental Growth

AbstractThe mechanism of continental growth of the Altaids is currently under debate between models invoking continuous subduction-accretion or punctuated accretion by closure of multiple ocean basins. We use the Yueyashan–Xichangjing ophiolite belt of the Beishan collage (southern Altaids) to constrain the earliest oceanic crust in the southern Palaeo-Asian Ocean. Five lithotectonic units were identified from S to N: the Huaniushan block, a sedimentary passive margin, the structurally incoherent Yueyashan–Xichangjing ophiolite complex, a coherent sedimentary package and the Mazongshan island arc with granitic rocks. We present a structural analysis of the accretionary complex, which is composed of the incoherent ophiolitic melange and coherent sedimentary rocks, to work out the tectonic polarity. A new weighted mean206Pb–238U age of 533 ± 1.7 Ma from a plagiogranite in the Yueyashan–Xichangjing ophiolite indicates that the ocean floor formed in early Cambrian time. Furthermore, we present new geochemical data to constrain the tectonic setting of the Yueyashan–Xichangjing ophiolite. The Yueyashan–Xichangjing ophiolite was emplaced as a result of northward subduction of an oceanic plate beneath the Mazongshan island arc to the north in late Ordovician to early Silurian time. Together with data from the literature, our work demonstrates that multiple overlapping periods of accretion existed in the Palaeozoic in the northern and southern Altaids. Therefore, a model of multiple accretion by closure of several ocean basins is most viable.

scholarly journals Characteristics and field relation of Ulleri Augen Gneiss to country rocks in the Lesser Himalaya: A case study from Syaprubesi-Chhyamthali area, central Nepal

2019 ◽  
Vol 58 ◽  
pp. 89-96
Author(s):  
Jharendra K.C. ◽  
Kabi Raj Paudyal
Keyword(s):  
Geological Mapping ◽  
Lesser Himalaya ◽  
Main Central Thrust ◽  
Nepal Himalaya ◽  
Field Relation ◽  
Central Nepal ◽  
Thrust Zone ◽  
Augen Gneiss ◽  
Host Rocks

The distribution of Ulleri Augen Gneiss and its origin in the Lesser Nepal Himalaya adjacent to the Main Central Thrust zone is stilla debate among the geo-scientists. Geological mapping was carried out along the Syaprubesi-Chhyamthali area of central Nepal with the aim to study the field relation, distribution, deformation and metamorphism of the Ulleri Augen Gneiss. During mapping, close traverses were set to observe the field relation and a number of systematic samples were collected for analysis of composition and texture. Some preliminary findings were obtained related to its geological position and distribution. This gneiss is hosted within the Kuncha Formation, the oldest unit of the Nawakot Group in the Lesser Himalaya. It has been evolved within this unit as a tabular form in some places and lenses in other places. It shows both concordant (i.e., sill type) and discordant (i.e., dike type) relationship with the host rock. It is characterized by augen-shaped porphyroblasts of K-feldspar and S-C mylonitic texture showing top to the SW sense of shear. The S-C structures and lineated textures shown by the minerals are associated with the shearing caused by the movement along the MCT during the syn-MCT metamorphic deformation. It is characterized in different types of lithologies such as augen gneiss, banded gneiss and two-mica gneiss. An attempt is made to explain the petrological characteristics and field relation of the Ulleri Augen Gneiss with the host rocks along with structural aspects. Based on the field relation and texture analysis, the evolution of the protolith of this Ulleri Augun Gneiss can be interpreted as a multi-story emplacement within the host rocks during and immediately after the sedimentation.

scholarly journals Geology, geochemistry, and radiochronology of the Kathmandu and Gosainkund Crystalline nappes, central Nepal Himalaya

2001 ◽  
Vol 25 ◽  
Author(s):  
Santa Man Rai
Keyword(s):  
Granulite Facies ◽  
Tectonic Block ◽  
Lesser Himalaya ◽  
Main Central Thrust ◽  
Nepal Himalaya ◽  
Magmatic Origin ◽  
The North ◽  
Multidisciplinary Study ◽  
Central Nepal ◽  
Augen Gneiss

A multidisciplinary study was carried out in the Lesser Himalaya (LH), the Kathmandu Crystalline Nappe (KCN) and the Gosainkund Crystalline Nappe (GCN) in central Nepal Himalaya. Two principal deformations are recorded in both the crystalline nappes and the Lesser Himalaya: ductile, syn-MCTor syn-MT metamorphic deformation marked by microstructures (stretching lineation, S-C structures, and isoclinal folding) and post-MCT/or post-MT metamorphic deformation recorded by a major EW-directed Likhu Khola anticline and by NNE-SSW-directed folds. The Upper Lesser Himalayan rocks close to the Main Central Thrust (MCT) record syn-MCT metamorphic conditions at 750 MPa and 566 °C. The rocks of the KCN record P-T condition from 900 to 720 MPa and 700 to 484 °C, while the GCN rocks were equilibrated at upper amphibolite- to granulite-facies conditions from 890 to 583 MPa and 754 to 588 °C. The P-T conditions and field observations exhibit well-preserved inverted metamorphism between the Upper Lesser Himalaya and the Gosainkund Crystalline Nappe. The augen gneisses from the GCN yielding 486±9Ma U-Pb zircon age and the granites of similar age in the KCN bear similar petrographic and geochemical characteristics and suggest a similar magmatic origin although they belong to different tectonic units. The chemical analyses of the Proterozoic Ulleri augen gneiss of the LH and the granites of the KCN fall within the same compositional field, indicating a magmatic origin of these augen gneisses. 40Ar/39Ar datings on muscovite indicate cooling ages younging systematically from south to north: 22 to 14 Ma in the KCN, 16 to 5 Ma in the GCN, and 12 to 6 Ma in the LH. This systematic younging of muscovite ages does not have any correlation with the present elevation, lithology and tectonic unit and is interpreted as a result of the exhumation of the rock units on the Main Himalayan Thrust (MHT) ramp situated to the north of Kathmandu Valley. Both the KCN and the GCN record a late emplacement history, but the KCN was exhumed earlier than the GCN. The two crystalline nappes presently form a single tectonic block, and the combined uplift of the two nappes occurs on a ramp of a major decollement developed in the upper part of the Indian crust.

Granites in the tectonic evolution of the Himalaya, Karakoram and southern Tibet

1988 ◽  
Vol 326 (1589) ◽  
pp. 281-299 ◽  
Keyword(s):  
Small Volume ◽  
Tectonic Setting ◽  
Southern Tibet ◽  
The North ◽  
Anatectic Granite ◽  
Regional Tectonic ◽  
Lower Palaeozoic ◽  
Intracontinental Subduction ◽  
Tectonic Settings ◽  
The Himalaya

Four major plutonic belts are related to the Meso-Cainozoic orogenic evolution of the Himalaya—Transhimalaya—Karakoram realm: the Transhimalaya belt and its satellite Kohistan arc, the Karakoram batholith, the High Himalaya belt and the North Himalaya belt. A fifth one results from the lower Palaeozoic epirogenic events: the ‘Lesser Himalaya’ belt. The tectonic settings of their production and emplacement are successively reviewed. Among the first four, two result from oceanic subduction along an Andean margin locally branching into an island arc and two result from intracontinental subduction after closure of the oceanic realm. Both Andean belts are made up of very large quantities of highly diversified granitoids produced more or less continuously during 70 Ma at least, whereas the intracontinental ones are limited to a small volume of very uniform anatectic granite produced during a 10—15 Ma period. The production and emplacement in the Andean belts is partly controlled by the obliquity of the convergence between India and Eurasia. The emplacement of the intracontinental belts is even more dependent on the regional tectonic setting. These contrasting belts are case studies probing the depths and mechanisms of their production and giving adequate models for older geodynamic frames.

Late Mesozoic – Cenozoic evolution of the eastern Cyprus offshore

2021 ◽  
Author(s):  
Nicolò Bertone ◽  
Lorenzo Bonini ◽  
Anna Del Ben ◽  
Giuseppe Brancatelli ◽  
Angelo Camerlenghi ◽  
...  
Keyword(s):  
Mediterranean Sea ◽  
Eastern Mediterranean ◽  
Tectonic Setting ◽  
Structural Evolution ◽  
Late Mesozoic ◽  
The North ◽  
Levantine Basin ◽  
North Eastern ◽  
Seismic Reflection Profiles ◽  
Extensional Structures

<p>The present‐day tectonic setting of the Eastern Mediterranean Sea results from a long deformation history, characterized by an alternation of extensional and contractional phases: from Mesozoic rifting to Late Cretaceous-present-day compression. This study focused on the tectonic reconstruction of the north-eastern side of the Mediterranean Sea, on a sector located between the Turkish coast and the northern Levantine Basin, using seismic reflection profiles. Previous studies dealt with the recent (Neogene) evolution because they did not have enough depth of investigation to recognize deeper reflections. We used vintage data such as MS and Strakhov surveys to analyze the deeper part of the area. We interpreted and depth-converted these seismic data, and we developed a sequential restoration to reconstruct the stratigraphic and structural evolution of the study area. </p><p>In general, from north to south, we recognize the Cilicia Basin: a piggy-back basin bordered to the south by the offshore continuation of the Kyrenia Range. The Kyrenia Range is a positive flower structure generated during a transpressional phase because of the rotation of the Arabic plate. Southward, a secondary contractional system with an onlapping wedge is present in the area between the Kyrenia Range and another prominent ridge, i.e. the Larnaca Ridge. In the southern part, the same transpressional phase that generated the Kyrenia Range led to a positive inversion of an ancient extensional system, i.e. the Latakia Ridge. Beyond these positive flowers, the Levantine Basin is affected by extensional structures showing weak positive reactivation, including halokinetic features.</p><p>In summary, we found that the inherited extensional structures strongly impacted the following contractional ones affecting both their geometry and their kinematics.</p>

Palaeoproterozoic metasedimentary rocks of the Ji'an Group and their significance for the tectonic evolution of the northern segment of the Jiao–Liao–Ji Belt, North China Craton

2017 ◽  
Vol 155 (1) ◽  
pp. 149-173 ◽  
Author(s):  
EN MENG ◽  
CHAO-YANG WANG ◽  
ZHUANG LI ◽  
YAN-GUANG LI ◽  
HONG YANG ◽  
...  
Keyword(s):  
North China Craton ◽  
North China ◽  
Tectonic Setting ◽  
Active Continental Margin ◽  
Volcanic Rocks ◽  
Granitic Rocks ◽  
Geochemical Data ◽  
Metasedimentary Rocks ◽  
The North ◽  
Northern Segment

AbstractIn this paper we present new petrological and whole-rock geochemical data for the Palaeoproterozoic metasedimentary rocks in the upper part of the Ji'an Group within the Jiao–Liao–Ji Belt, China, as well as zircon U–Pb age dates andin situLu–Hf isotope data. The new data improve our understanding of the original nature of the metasedimentary rocks, further providing insights into their tectonic setting and the evolutionary history of the northern segment of the Jiao–Liao–Ji Belt. The zircons can be divided into two groups, viz., one of magmatic origin and the other of metamorphic origin. Zircon U–Pb dating gave mean or statistical peak ages for the magmatic zircons at 2035, 2082, 2178, 2343–2421, 2451–2545, 2643–2814 and 2923–3446 Ma, and mean peak ages for the metamorphic zircons at 1855 and 1912 Ma, which indicate a maximum depositional age of 2.03 Ga and two-stage metamorphic events atc. 1.91 and 1.85 Ga for the metasedimentary rocks. Geochemical data show that (1) the protoliths of these rocks were mainly sandstones, greywackes and claystones, together with some shales; (2) the main sources of the sedimentary material were Palaeoproterozoic granites and acid volcanic rocks, with minor contributions from Archaean granitic rocks; and (3) the sediments were deposited in an active continental margin setting. Moreover, along the northeastern margin of the Eastern Block of the North China Craton there is evidence of ancient crustal materials as old as 3.76 Ga, and multiple crustal growth events at 3.23–3.05, 2.80–2.65, 2.54–2.45 and 2.28–2.08 Ga.

Imbricate Subduction Zones and their Relationship with Upper Cretaceous to Tertiary Porphyry Deposits in the Canadian Cordillera

1975 ◽  
Vol 12 (8) ◽  
pp. 1362-1378 ◽  
Author(s):  
C. I. Godwin
Keyword(s):  
North America ◽  
Subduction Zones ◽  
Upper Cretaceous ◽  
Granitic Rocks ◽  
Benioff Zone ◽  
Canadian Cordillera ◽  
Porphyry Deposits ◽  
Late Mesozoic ◽  
Tectonic Model ◽  
The North

A plate-tectonic model relates the genesis of Upper Cretaceous-to-Tertiary porphyry-type deposits to the evolution of the western and central Canadian Cordillera. Existence of two Benioff zones is assumed from definition of two distinct younging trends of intrusive centers. The first Benioff zone, initiated west of the Queen Charlotte Islands near the Middle Triassic, continued activity until the early Tertiary, when 50 m.y.-old granitic rocks and associated porphyry deposits near the eastern boundary of the Coast Crystalline Belt were formed. The second Benioff zone, initiated near the earliest Cretaceous, extended under the western margin of the North America plate and produced intrusive stocks and associated porphyry deposits that become younger from west to east across the Intermontane Belt. Intrusive activity associated with both Benioff zones ceased at about the same time, 50 m.y. ago, implying that the Benioff zones became imbricated. As a result, the North America plate overrode the Insular plate. Doubling of these plates is reflected in the late Mesozoic and Tertiary uplift and erosion of the Coast Crystalline Belt.

scholarly journals A Downgoing Indian Lithosphere Control on Along-Strike Variability of Porphyry Mineralization in the Gangdese Belt of Southern Tibet

2020 ◽  
Vol 116 (1) ◽  
pp. 29-46 ◽  
Author(s):  
Xiang Sun ◽  
Yongjun Lu ◽  
Qiang Li ◽  
Ruyue Li
Keyword(s):  
Porphyry Copper ◽  
Tectonic Setting ◽  
Igneous Rocks ◽  
Crustal Thickening ◽  
Hf Isotopes ◽  
Porphyry Copper Deposits ◽  
Bulk Rock ◽  
Southern Tibet ◽  
Copper Deposits ◽  
Isotope Data

Abstract The E-trending Gangdese porphyry copper belt in southern Tibet is a classic example of porphyry mineralization in a continental collision zone. New zircon U-Pb geochronological, zircon Hf-O, and bulk-rock Sr-Nd isotope data for the Miocene mineralizing intrusions from the Qulong, Zhunuo, Jiru, Chongjiang, and Lakange porphyry copper deposits and Eocene igneous rocks from the western Gangdese belt, together with literature data, show that both Paleocene-Eocene igneous rocks and Miocene granitoids exhibit coupled along-arc isotopic variations, characterized by bulk-rock ɛNd(t) and zircon ɛHf(t) values increasing from ~84° to ~92°E and then decreasing toward ~95°E. These are interpreted to reflect increasing contributions of subducted Indian continental materials from ~92° to ~84°E and from ~92° to ~95°E, respectively. The Miocene mineralizing intrusions were derived from subduction-modified Tibetan lower crust represented isotopically by the Paleocene-Eocene intrusions, with contributions from Indian plate-released fluids and mafic melts derived from mantle metasomatized by subducted Indian continental materials. Involvement of isotopically ancient Indian continental materials increased from east (Qulong) to west (Zhunuo), which is interpreted to reflect an increasingly shallower angle of the downgoing Indian slab from east to west, consistent with geophysical imaging. Exploration of Gangdese Miocene porphyry copper deposits should focus on the Paleocene-Eocene arc where the subarc mantle was mainly enriched by fluids from the subducted Neo-Tethyan oceanic slab. Neodymium-Hf isotope data for mineralizing igneous rocks from porphyry copper deposits globally show no obvious correlations with Cu endowment. Although Nd-Hf isotopes are useful for imaging lithospheric architecture through time, caution must be taken when using Nd-Hf isotopes to evaluate the potential endowment of porphyry copper deposits, because other factors such as tectonic setting, crustal thickening, magma differentiation, fluid exsolution, and ore-forming processes all play roles in determining Cu endowments and grades.

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