The Precambrian geochronology of Rajasthan and Bundelkhand, northern India

1970 ◽  
Vol 7 (1) ◽  
pp. 91-110 ◽  
Author(s):  
A. R. Crawford
Keyword(s):  
Field Studies ◽  
New Age ◽  
Peninsular India ◽  
Northern India ◽  
Gneiss Complex ◽  
Granitic Intrusion ◽  
Age Determinations

Many new age determinations are reported for the Precambrian of Rajasthan and Bundelkhand in northern peninsular India. All are by Rb–Sr and mostly from total-rock analyses. They show that the oldest rocks in the area are undated sediments intruded by the Bundelkhand and Berach Granites, dated at about 2550 m.y. The overlying Aravalli System was intruded by granites dated at between 1900 and 2100 m.y., and is succeeded by the Delhi System, which was intruded by granite dated at 1650 m.y. Other granitic intrusion at 950–1000 m.y. was followed by repeated pegmatitic intrusion. The Banded Gneiss Complex of Rajasthan contains components of ages varying from at least 2000 m.y. to less than 1000 m.y. Nepheline-syenites at Kishangarh have an age of 1490 ± 150 m.y., but a biotite in an inclusion gives 970 m.y., which is the age of the Newania carbonatite.These determinations show that the Precambrian sequence in Rajasthan is much older than previously suggested. They confirm the antiquity of the Bundelkhand–Berach craton suggested by field studies, denying its derivation from Aravalli System rocks by granitization.

Pre-Katangan geochronology of Zambia and adjacent parts of Central Africa

1968 ◽  
Vol 5 (3) ◽  
pp. 621-628 ◽  
Author(s):  
J. R. Vail ◽  
N. J. Snelling ◽  
D. C. Rex
Keyword(s):  
Lake Tanganyika ◽  
Central Africa ◽  
New Age ◽  
Orogenic Belt ◽  
Eastern Africa ◽  
Sedimentary Sequence ◽  
Precambrian Rocks ◽  
Late Precambrian ◽  
Orogenic Belts ◽  
Age Determinations

The significance of new age determinations on pre-Katangan (Late Precambrian) rocks and minerals from Zambia and adjacent parts of Tanzania and Rhodesia is discussed. In northwestern Rhodesia, the Lomagundi-Piriwiri sediments were deposited between 2500 and 2000 m.y. ago and were folded along meridional trends at circa 1940 m.y. A later episode of folding and metamorphism along similar trends occurred about 1700 m.y. ago, but only affected the western part of the sedimentary sequence (the Piriwiri Series). This latter date is comparable to that which appears to characterize the Tumbide trend, a N- to NE-trending fold system, in Zambia.In Zambia the Tumbide trend is the oldest tectonic episode preserved in the basement and is found only in isolated blocks and cores into which later tectonisms have not penetrated. The dominant pre-Katangan tectonism is represented by the NE to ENE Irumide trend. Such tectonic trends are particularly well developed in the Irumide Orogenic Belt of northern Zambia and adjacent Tanzania. Age determinations set a younger limit of circa 900 m.y. to this trend and the existence of an Irumide Cycle between about 1600 and 900 m.y. is suggested. The possibility that the relatively unmetamorphosed sediments of the Upper Plateau Series and Abercorn Sandstones at the southern end of Lake Tanganyika, the Mafingi Series of northern Malawi, and the Konse Series of Tanzania, represent near-contemporaneous platform deposition associated with the Irumide belt is considered.From this and other recent studies the distribution of orogenic belts in central and eastern Africa can be revised and a number of features of their pattern and inter-relationships noted.

Archean geochronological framework of the Bighorn Mountains, Wyoming

2006 ◽  
Vol 43 (10) ◽  
pp. 1399-1418 ◽  
Author(s):  
Carol D Frost ◽  
C Mark Fanning
Keyword(s):  
Ion Microprobe ◽  
Entire Area ◽  
Wind River Range ◽  
Gneiss Complex ◽  
Granitic Intrusion ◽  
Northern Portion ◽  
Tonalitic Gneiss ◽  
Archean Crust ◽  
Wyoming Province ◽  
Bighorn Mountains

The Bighorn Mountains of the central Wyoming Province expose a large tract of Archean crust that has been tectonically inactive and at relatively high crustal levels since ~2.7 Ga. Seven sensitive high-resolution ion microprobe (SHRIMP) U–Pb zircon and titanite age determinations on samples of the main lithologic units provide a geochronological framework for the evolution of this area. The oldest, precisely dated magmatic event occurred at 2950 ± 5 Ma, when diorite to granite dykes and sills intruded an older gneiss complex exposed in the central and southern Bighorn Mountains. Rocks as old as 3.25 Ga may be present in this gneissic basement, as indicated by the oldest dates obtained on areas of zircon grains that are interpreted as inherited cores. A tonalitic gneiss was intruded into the gneiss complex at 2886 ± 5 Ma. Deformation of the central and southern gneisses preceded the intrusion of the Bighorn batholith, a tonalitic to granitic intrusion that occupies the northern portion of the uplift. This composite batholith was intruded over the period 2.86–2.84 Ga. Ca. 3.0–2.8 Ga crust is also present in the Beartooth Mountains, the Washakie block of the northeastern Wind River Range, the Owl Creek Mountains, and the northern Granite Mountains, but late Archean deformation and plutonism has obscured much of the earlier history in the southern portion of this area. The entire area, referred to as the Beartooth–Bighorn Magmatic Zone, has been undeformed since 2.6 Ga. Proterozoic extension was focused in those parts of the Wyoming Province outside of this domain.

scholarly journals Taxonomy and palaeoecology of Ostracoda from the Middle to Late Pleistocene upper Karewa formation of Kashmir Valley, Northern India

2009 ◽  
Vol 28 (1) ◽  
pp. 25-36 ◽  
Author(s):  
Michael Kramer ◽  
Jonathan Holmes
Keyword(s):  
Late Pleistocene ◽  
Water Depth ◽  
Lake Water ◽  
Running Waters ◽  
Kashmir Valley ◽  
Intermontane Basin ◽  
Northern India ◽  
Kashmir Basin ◽  
Age Determinations

Abstract. Ostracoda from a 25 m thick exposure in sediments of the upper Karewa formation indicate lacustrine conditions in the Kashmir intermontane basin during the Middle to Late Pleistocene. The Middle to Late Pleistocene age is established on the basis of lithostratigraphy and confirmed by two thermoluminescence age determinations at the top of the section. The ostracod assemblages show that the lake water remained fresh or, at most, was very slightly saline, throughout the period represented by the section. Nearly all ostracod taxa identified from the sediments are cold stenothermal forms and they include inhabitants of the littoral and profundal domain as well as running waters and springs. The Ostracoda present within the section indicate that during deposition of the upper Karewa sediments a large, but fairly shallow, well-oxygenated open-basin freshwater lake existed in that central part of the Kashmir Basin. Although the sequences suggest changes in water depth may have occurred, lacustrine conditions were otherwise largely unchanged over the period represented by the section, up until the demise of the lake during the early part of the Late Pleistocene.

New age constraints on the Lan Sang gneiss complex, Thailand, and the timing of activity of the Mae Ping shear zone from in-situ and depth-profile zircon and monazite U-Th-Pb geochronology

2019 ◽  
Vol 181 ◽  
pp. 103886 ◽  
Author(s):  
Jürgen E. Österle ◽  
Urs Klötzli ◽  
Daniel F. Stockli ◽  
Markus Palzer-Khomenko ◽  
Pitsanupong Kanjanapayont
Keyword(s):  
Shear Zone ◽  
Depth Profile ◽  
New Age ◽  
Gneiss Complex ◽  
Age Constraints

NEW AGE DETERMINATIONS BY THE LEAD METHOD

1954 ◽  
Vol 60 (3) ◽  
pp. 511-520 ◽  
Author(s):  
J. Laurence Kulp ◽  
George L. Bate ◽  
Bruno J. Giletti
Keyword(s):  
New Age ◽  
Age Determinations

New Dates for the Solutrean and Magdalenian of Cantabrian Spain: El Miron and La Riera Caves

Radiocarbon ◽  
2018 ◽  
Vol 60 (3) ◽  
pp. 1013-1016 ◽  
Author(s):  
Lawrence G Straus ◽  
Manuel R González Morales
Keyword(s):  
New Age ◽  
Paleolithic Site ◽  
Rock Wall ◽  
Age Determinations

ABSTRACTThis sixth date list for the prehistoric site of El Mirón Cave (Cantabria, Spain) reports on new age determinations for the earliest and last Solutrean occupations (20.4 and 18.0 14C kyr BP) and for a Lower/Initial Magdalenian level with a possible rock wall (16.75 14C kyr BP). The site has now been dated by 92 radiocarbon (14C) assays. In addition, to help resolve inconsistencies in the 14C chronology of La Riera Cave (Asturias)—the first Paleolithic site in Spain to be extensively 14C-dated back in the 1970s—two AMS assays were done on bones from the Lower and Upper Magdalenian collections (15.1 and 13.5 14C kyr BP).

New age controls on the tephrochronology of the southernmost Andean Southern Volcanic Zone, Chile

2018 ◽  
Vol 91 (1) ◽  
pp. 250-264 ◽  
Author(s):  
DJ Weller ◽  
ME de Porras ◽  
A Maldonado ◽  
C Méndez ◽  
CR Stern
Keyword(s):  
Late Glacial ◽  
New Age ◽  
Explosive Eruptions ◽  
Volcanic Zone ◽  
Radiocarbon Age ◽  
Southern Volcanic Zone ◽  
Tephra Layers ◽  
Andean Southern Volcanic Zone ◽  
Lake Cores ◽  
Age Determinations

AbstractThe chronology of over 50 tephra layers preserved in a lake sediment core from Laguna La Trapananda (LLT) in the southern portion of the Andean Southern Volcanic Zone (SSVZ), Chile, is constrained by new radiocarbon age determinations, which span the period from late Pleistocene glacial retreat to the late Holocene. The tephra are correlative with tephra previously described from other lake cores in the region and are attributed to explosive eruptions of the SSVZ volcanoes Mentolat, Hudson, Macá, and potentially Cay. The new age determinations are used to estimate the ages of the >50 tephra in the LLT core, as well as those from the other previously described lake cores in the area, by a Bayesian statistical method. The results constrain the frequency of explosive eruptions of the volcanic centers in the southernmost SSVZ. They indicate that there was essentially no increase in the rate of eruptions from late-glacial to recent times due to deglaciation. They also provide isochrones used to constrain the depositional histories of the small lacustrine systems within which they were deposited and they provide a tephrochronologic tool for other paleoclimatic, paleoecologic, archaeologic and tephrochronologic studies in central Patagonia.

Unveiling ductile deformation during fast exhumation of a granitic pluton in a transfer zone

2021 ◽  
Author(s):  
Richard Spiess ◽  
Antonio Langone ◽  
Alfredo Caggianelli ◽  
Finlay M. Stuart ◽  
Martina Zucchi ◽  
...  
Keyword(s):  
Shear Zones ◽  
Integrated Approach ◽  
Field Studies ◽  
Ductile Deformation ◽  
Exhumation Rate ◽  
Pluton Emplacement ◽  
Ductile Shear Zones ◽  
Granitic Intrusion ◽  
Rheological Modeling ◽  
Extensional Setting

<p>Exhumation and cooling of upper crustal plutons is generally assumed to develop in the brittle domain, thus determining an abrupt passage from crystallization to faulting. To challenge this general statement, we have applied an integrated approach involving meso- and micro-structural studies, thermochronology, geochronology and rheological modeling. We have analyzed the Miocene syn-tectonic Porto Azzurro pluton on Elba (Tuscan archipelago – Italy), emplaced in an extensional setting, and have realized that its fast exhumation is accompanied by localized ductile shear zones, developing along dykes and veins, later affected by brittle deformation. This is unequivocally highlighted by field studies and the analysis of microstructures with EBSD. In order to constrain the emplacement and exhumation rate of the Porto Azzurro pluton we performed U-Pb zircon dating and (U+Th)/He apatite thermochronology. It results in a magma emplacement age of 6.4 ± 0.4 Ma and an exhumation rate of 3.4 to 3.9 mm/yr. By thermo-rheological modeling we were able to establish that localized ductile deformation occurred at two different time steps: within felsic dykes when the pluton first entered into the brittle field at 380 kyr, and along quartz-rich hydrothermal veins at c. 550 kyr after pluton emplacement. Hence, the major conclusion of our data is that ductile deformation can affect a granitic intrusion even when it is entered into the brittle domain in a fast exhuming extensional regime.</p>

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