Middle Ordovician (Darriwilian) conodonts from southern Tibet, the Indian passive margin: implications for the age and correlation of the roof of the world

2020 ◽  
pp. 1-25
Author(s):  
Svend Stouge ◽  
David A. T. Harper ◽  
Renbin Zhan ◽  
Jianbo Liu ◽  
Lars Stemmerik
Keyword(s):  
Middle Part ◽  
Passive Margin ◽  
Continental Margins ◽  
Oceanic Circulation ◽  
Mount Everest ◽  
Southern Tibet ◽  
Middle Ordovician ◽  
The North ◽  
Carbon Isotope Excursion ◽  
Central Tibet

Abstract New occurrences of middle–late Darriwilian (Middle Ordovician) conodonts are reported from the Nyalam region, southern Tibet. The conodont-yielding strata, referred to the Chiatsun Group, accumulated on the north Indian continental margin of northern Gondwana. These Middle Ordovician conodonts include the informal species Histiodella sp. A in the middle part of the Lower Formation of the Chiatsun Group succeeded by a fauna of the Pygodus serra Zone in the upper part of that formation. Pygodus anserinus is recorded from the base of the Upper Formation of the Chiatsun Group. The Nyalam succession and its conodont taxa allow for precise correlation of the strata preserved on top of Mount Qomolangma (Mount Everest), eastern Tibet and the Peri-Gondwana Lhasa (north central Tibet), South China, North China, Tarim Basin and Thailand-Malaysia (Sibumasu Terrane) terranes and/or microcontinents. The middle Darriwilian positive increase in δ13Ccarb values (carbon isotope excursion, or MDICE) is recorded from most terranes, and can be related to a late middle Darriwilian global short-term cooling and sea-level drop. The cooling event prompted temperate- to warm-water taxa to migrate towards the palaeoequator and constrained the Australasian Province to locations near and at the palaeoequator. The intensified oceanic circulation and upwelling on continental margins probably caused some characteristic taxa to become extinct. The incoming fauna was mainly of cool-water taxa. The conodont specimens from southern Tibet are black to pale grey, corresponding to conodont colour index (CAI) values of 5 to 6, which demonstrates that the host sedimentary rocks were once heated to more than 360°C.

Definition of tectono-sedimentary elements for rifted continental margins of the Norwegian and Greenland seas

2021 ◽  
pp. M57-2021-31
Author(s):  
Harald Brekke ◽  
Halvor S. S. Bunkholt ◽  
Jan I. Faleide ◽  
Michael B. W. Fyhn
Keyword(s):  
Lower Jurassic ◽  
Passive Margin ◽  
Continental Margins ◽  
Axial Line ◽  
Continental Breakup ◽  
The North ◽  
Tectonic Development ◽  
Definition Of ◽  
Conjugate Margins ◽  
Greenland Margin

AbstractThe geology of the conjugate continental margins of the Norwegian and Greenland Seas reflects 400 Ma of post-Caledonian continental rifting, continental breakup between early Eocene and Miocene times, and subsequent passive margin conditions accompanying seafloor spreading. During Devonian-Carboniferous time, rifting and continental deposition prevailed, but from the mid-Carboniferous, rifting decreased and marine deposition commenced in the north culminating in a Late Permian open seaway as rifting resumed. The seaway became partly filled by Triassic and Lower Jurassic sediments causing mixed marine/non-marine deposition. A permanent, open seaway established by the end of the Early Jurassic and was followed by the development of an axial line of deep marine Cretaceous basins. The final, strong rift pulse of continental breakup occurred along a line oblique to the axis of these basins. The Jan Mayen Micro-Continent formed by resumed rifting in a part of the East Greenland margin in Eocene to Miocene times. This complex tectonic development is reflected in the sedimentary record in the two conjugate margins, which clearly shows their common pre-breakup geological development. The strong correlation between the two present margins is the basis for defining seven tectono-sedimentary elements (TSE) and establishing eight composite tectono-sedimentary elements (CTSE) in the region.

scholarly journals Geological perspectives of the -East Greenland continental margin

1980 ◽  
Vol 29 ◽  
pp. 77-101
Author(s):  
Hans Christian Larsen
Keyword(s):  
Continental Margin ◽  
Fracture Zone ◽  
Middle Part ◽  
Passive Margin ◽  
Active Part ◽  
East Greenland ◽  
The North ◽  
Plate Separation ◽  
Sea Floor Spreading ◽  
Greenland Margin

The East Greenland continental margin can be divided into a northern area showing evidence for plate separation and suturing of Hudsonian, Grenvillian and Caledonian ages followed by post-Late Caledonian molasse sedimentation and Mesozoic rifting, and a southern area which apparently formed a cratonic block from the Early Proterozoic to the Middle Cretaceous. The whole margin was finally separated from the NW European margin by sea floor spreading in the latest Paleocene to earliest Eocene and now forms a rifted passive margin. The Tertiary consists of thin pre-drift sediments overlain by 1-7 km of Late Paleocene basaltic lavas extruded immediately prior to active spreading. Subsequent subsidence of the shelf led to accumulation of 2--8 km of post-basaltic sediments offshore whereas the land area was uplifted 1-2 km. Initiation of spreading along the Kolbeinsey Ridge during the late Oligocene was accompanied by renewed tectonism within the middle part of the margin. Finally the shelf was characterized by strong progradation during the Miocene. Backwards rotation of the inferred ocean-to-continent transition, through the total pole of opening, favours a slightly modified Talwani and Eldholm pole which provides a pre-drift fit of the two margins with no major overlap or gaps between the southern tip of Greenland and the Greenland-Senja Fracture Zone. Comparison of the Greenland margin and the V0ring Plateau implies a genesis for the latter, different from that proposed by Talwani and Eldholm. Minor revisions of the spreading history are presented including repeated westward displacement of the southernmost part of Mohns Ridge between anomaly 24 and 21, commencement of spreading around Kolbeinsey Ridge not later than anomaly 6 and associated activation of the recent active part of Jan Mayen Fracture Zone (JMFZ), to the north of the previous active part. The area between the fossil part of JMFZ and the recent active part including the northern part of Jan Mayen Ridge is suggested to have formed around a southern extension of Mohns Ridge active until about anomaly 6 and the predicted position of the extinct axis correlates well with bathymetry.

scholarly journals Lateral propagation–induced subduction initiation at passive continental margins controlled by preexisting lithospheric weakness

2020 ◽  
Vol 6 (10) ◽  
pp. eaaz1048 ◽  
Author(s):  
Xin Zhou ◽  
Zhong-Hai Li ◽  
Taras V. Gerya ◽  
Robert J. Stern
Keyword(s):  
Subduction Zones ◽  
Plate Tectonics ◽  
Numerical Models ◽  
Three Dimensional ◽  
Passive Margin ◽  
Continental Margins ◽  
Subduction Initiation ◽  
Passive Margins ◽  
The North ◽  
Lateral Propagation

Understanding the conditions for forming new subduction zones at passive continental margins is important for understanding plate tectonics and the Wilson cycle. Previous models of subduction initiation (SI) at passive margins generally ignore effects due to the lateral transition from oceanic to continental lithosphere. Here, we use three-dimensional numerical models to study the possibility of propagating convergent plate margins from preexisting intraoceanic subduction zones along passive margins [subduction propagation (SP)]. Three possible regimes are achieved: (i) subducting slab tearing along a STEP fault, (ii) lateral propagation–induced SI at passive margin, and (iii) aborted SI with slab break-off. Passive margin SP requires a significant preexisting lithospheric weakness and a strong slab pull from neighboring subduction zones. The Atlantic passive margin to the north of Lesser Antilles could experience SP if it has a notable lithospheric weakness. In contrast, the Scotia subduction zone in the Southern Atlantic will most likely not propagate laterally.

Preliminary results of the study on the reasons of the Hai Hau erosion phenomenon

2007 ◽  
Vol 29 (3) ◽  
pp. 415-426
Author(s):  
Pham Van Ninh ◽  
Phan Ngoc Vinh ◽  
Nguyen Manh Hung ◽  
Dinh Van Manh
Keyword(s):  
Mathematical Modeling ◽  
Historical Data ◽  
Middle Part ◽  
Red River ◽  
Erosion Process ◽  
Red River Delta ◽  
The North ◽  
Severe Erosion ◽  
North And South ◽  
Very High

Overall the evolution process of the Red River Delta based on the maps and historical data resulted in a fact that before the 20th century all the Nam Dinh coastline was attributed to accumulation. Then started the erosion process at Xuan Thuydistrict and from the period of 1935 - 1965 the most severe erosion was contributed in the stretch from Ha Lan to Hai Trieu, 1965 - 1990 in Hai Chinh - Hai Hoa, 1990 - 2005 in the middle part of Hai Chinh - Hai Thinh (Hai Hau district). The adjoining stretches were suffered from not severe erosion. At the same time, the Ba Lat mouth is advanced to the sea and to the North and South direction by the time with a very high rate.The first task of the mathematical modeling of coastal line evolution of Hai Hau is to evaluate this important historical marked periods e. g. to model the coastal line at the periods before 1900, 1935 - 1965; 1965 - 1990; 1990 - 2005. The tasks is very complicated and time and working labors consuming.In the paper, the primarily results of the above mentioned simulations (as waves, currents, sediments transports and bottom - coastal lines evolution) has been shown. Based on the obtained results, there is a strong correlation between the protrusion magnitude and the southward moving of the erosion areas.

Preliminary detrital zircon U-Pb Geochronology of the Wasatch Formation, Powder River Basin, Wyoming

2019 ◽  
Vol 56 (3) ◽  
pp. 247-266
Author(s):  
Ian Anderson ◽  
David H. Malone ◽  
John Craddock
Keyword(s):  
River Basin ◽  
Detrital Zircon ◽  
Middle Part ◽  
Detrital Zircons ◽  
Powder River Basin ◽  
Zircon Age ◽  
Lower Eocene ◽  
The North ◽  
Mountain Front ◽  
Fluvial Sandstone

The lower Eocene Wasatch Formation is more than 1500 m thick in the Powder River Basin of Wyoming. The Wasatch is a Laramide synorgenic deposit that consists of paludal and lacustrine mudstone, fluvial sandstone, and coal. U-Pb geochronologic data on detrital zircons were gathered for a sandstone unit in the middle part of the succession. The Wasatch was collected along Interstate 90 just west of the Powder River, which is about 50 km east of the Bighorn Mountain front. The sandstone is lenticular in geometry and consists of arkosic arenite and wacke. The detrital zircon age spectrum ranged (n=99) from 1433-2957 Ma in age, and consisted of more than 95% Archean age grains, with an age peak of about 2900 Ma. Three populations of Archean ages are evident: 2886.6±10 Ma (24%), 2906.6±8.4 Ma (56%) and 2934.1±6.6 Ma (20%; all results 2 sigma). These ages are consistent with the age of Archean rocks exposed in the northern part of the range. The sparse Proterozoic grains were likely derived from the recycling of Cambrian and Carboniferous strata. These sands were transported to the Powder River Basin through the alluvial fans adjacent to the Piney Creek thrust. Drainage continued to the north through the basin and eventually into the Ancestral Missouri River and Gulf of Mexico. The provenance of the Wasatch is distinct from coeval Tatman and Willwood strata in the Bighorn and Absaroka basins, which were derived from distal source (>500 km) areas in the Sevier Highlands of Idaho and the Laramide Beartooth and Tobacco Root uplifts. Why the Bighorn Mountains shed abundant Eocene strata only to the east and not to the west remains enigmatic, and merits further study.

Between Kongpo and Xanadu

2018 ◽  
Author(s):  
Ruth Gamble
Keyword(s):  
Southern Tibet ◽  
Central Tibet

The final chapter begins with Rangjung Dorjé in retreat in Kongpo, southern Tibet. Because of his growing reputation, however, he is soon forced to return to central Tibet to mediate between a group of rebels and members of the ruling Mongol-Sakya alliance. In 1329, the Mongol emperor summonses him to the capitals. He eventually arrives in Dadu nearly two years later, during the short reign of Irinjibal (1326–1332, r. 1332), and witnesses the enthronement of the final Mongol emperor, Toghon Temür (1320–1370, r. 1333–1370), who becomes his student. Once at the young emperor’s court, he is only allowed to return to Tibet briefly in 1334. He dies in Xanadu in the summer of 1339. According to his biographers, his death was enacted to facilitate his escape from the emperor’s decree that he stay in the capital. It enabled him, through rebirth, to return to his beloved mountains.

Landscape development in western and central Dronning Maud Land, East Antarctica

2001 ◽  
Vol 13 (3) ◽  
pp. 302-311 ◽  
Author(s):  
Jens-Ove Näslund
Keyword(s):  
Large Scale ◽  
High Elevation ◽  
Continental Margins ◽  
Landscape Development ◽  
Ice Streams ◽  
The North ◽  
Ice Stream ◽  
Dronning Maud Land ◽  
Break Up

Large-scale bedrock morphology and relief of two key areas, the Jutulsessen Nunatak and the Jutulstraumen ice stream are used to discuss glascial history and landscape development in western and central Dronning Maud Land, Antarctica. Two main landform components were identified: well-defined summit plateau surfaces and a typical alpine glacial landscape. The flat, high-elevation plateau surfaces previously were part of one or several continuous regional planation surfaces. In western Dronning Maud Land, overlying cover rocks of late Palaeozoic age show that the planation surface(s) existed in the early Permian, prior to the break-up of Gondwana. A well-develoment escarpment, a mega landform typical for passive continental margins, bounds the palaeosurface remnants to the north for a distance of at least 700 km. The Cenozoic glacial landscape, incised in the palaeosurface and escarpment, is exemplified by Jutulsessen Nunatak, where a c. 1.2 km deep glacial valley system is developed. However, the prominent Penck-Jutul Trough represents some of the deepest dissection of the palaeosurface. This originally tectonic feature is today occupied by the Jutulstraumen ice stream. New topographic data show that the bed of the Penck-Jutul Trough is situated 1.9±1.1 km below sea level, and that the total landscape relief is at least 4.2 km. Today's relief is a result of several processes, including tectonic faulting, subaerial weathering, fluvial erosion, and glacial erosion. It is probable that erosion by ice streams has deepened the tectonic troughs of Dronning Maud Land since the onset of ice sheet glaciation in the Oligocene, and continues today. An attempt is made to identify major events in the long-term landscape development of Dronning Maud Land, since the break-up of the Gondwana continent.

New Faunal and Isotopic Evidence on the Late Weichselian—Holocene Oceanographic Changes in the Norwegian Sea

1984 ◽  
Vol 21 (1) ◽  
pp. 74-84 ◽  
Author(s):  
Hans Petter Sejrup ◽  
Eystein Jansen ◽  
Helmut Erlenkeuser ◽  
Hans Holtedahl
Keyword(s):  
Deep Water ◽  
Circulation Pattern ◽  
Oceanic Circulation ◽  
Surface Cooling ◽  
Norwegian Sea ◽  
Neogloboquadrina Pachyderma ◽  
The North ◽  
Lower Oxygen ◽  
Late Weichselian ◽  
Stage 1

Downcore studies of planktonic and benthonic foraminifera and δ18O and δ13C in the planktonic foraminifer Neogloboquadrina pachyderma (sin.) in two piston cores from the southern part of the Norwegian Sea suggest large changes in the oceanic circulation pattern at the end of oxygenisotope stage 2 and in the early part of stage 1. Prior to oxygen-isotope Termination IA (16,000–13,000 yr B.P.), an isolated watermass with lower oxygen content and temperature warmer than today existed below a low salinity ice-covered surface layer in the Norwegian Sea. Close to Termination IA, well-oxygenated deep water, probably with positive temperatures, was introduced. This deep water, which must have had physical and/or chemical parameters different from those of present deep water in the Norwegian Sea, could have been introduced from the North Atlantic or been formed within the basin by another mechanism than that which forms the present deep water of the Norwegian Sea. A seasonal ice cover in the southern part of the Norwegian Sea is proposed for the period between Termination IA and the beginning of IB (close to 10,000 yr B.P.). The present situation, with strong influx of warm Atlantic surface-water and deep-water formation by surface cooling, was established at Termination IB.

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.

scholarly journals South Anyui suture: tectono-stratigraphy, deformations, and principal tectonic events

2009 ◽  
Vol 4 ◽  
pp. 201-221 ◽  
Author(s):  
S. D. Sokolov ◽  
G. Ye. Bondarenko ◽  
P. W. Layer ◽  
I. R. Kravchenko-Berezhnoy
Keyword(s):  
Active Continental Margin ◽  
Strike Slip ◽  
Passive Margin ◽  
The South ◽  
Asian Continent ◽  
Oblique Collision ◽  
North Asian Craton ◽  
The North ◽  
Continental Block ◽  
South Anyui Suture

Abstract. Geochronologic and structural data from the terranes of the South Anyui suture zone record a protracted deformational history before, during and after an Early Cretaceous collision of the passive margin of the Chukotka-Arctic Alaska continental block with the active continental margin of the North Asian continent. Preceding this collision, the island arc complexes of the Yarakvaam terrane on the northern margin of the North Asian craton record Early Carboniferous to Neocomian ages in ophiolite, sedimentary, and volcanic rocks. Triassic to Jurassic amphibolites constrain the timing of subduction and intraoceanic deformation along this margin. The protracted (Neocomian to Aptian) collision of the Chukotka passive margin with the North Asian continent is preserved in a range of structural styles including first north verging folding, then south verging folding, and finally late collisional dextral strike slip motions which likely record a change from orthogonal collision to oblique collision. Due to this collision, the southern passive margin of Chukotka was overthrust by tectonic nappes composed of tectono-stratigraphic complexes of the South Anyui terrane. Greenschists with ages of 115–119 Ma are related to the last stages of this collision. The postcollisional orogenic stage (Albian to Cenomanian) is characterized by sinistral strike slip faults and an extensional environment.

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