40Ar/39Ar thermochronology constraints on jurassic tectonothermal event of nyainrong microcontinent

2014 ◽  
Vol 25 (1) ◽  
pp. 98-108 ◽  
Author(s):  
Chaoming Xie ◽  
Cai Li ◽  
Yanwang Wu ◽  
Ming Wang ◽  
Peiyuan Hu
Keyword(s):  
Tectonothermal Event

Field and isotopic evidence for a c. 750 Ma tectonothermal event in Moine rocks in the Central Highland region of the Scottish Caledonides

1983 ◽  
Vol 73 (3) ◽  
pp. 119-134 ◽  
Author(s):  
M. A. J. Piasecki ◽  
O. van Breemen
Keyword(s):  
Crustal Rocks ◽  
Highland Region ◽  
Ductile Shearing ◽  
Central Highland ◽  
Isotopic Studies ◽  
Previous Hypothesis ◽  
Moine Rocks ◽  
Early Palaeozoic ◽  
Similar Vein ◽  
Tectonothermal Event

ABSTRACTEvidence is presented for a late Proterozoic, tectonothermal event which affected the rocks of the Moine assemblage in the Central Highland region of the Scottish Caledonides c. 750 Ma ago. This is about 200 Ma before the early Palaeozoic Grampian orogeny, whose effects are superimposed on the Moine rocks as well as dominating the tectonism in the Dalradian Supergroup.Field and isotopic studies are integrated in zones of ductile thrusting (sliding) which are typified by belts of tectonic schists with related swarms of quartz and muscovite-bearing pegmatite veins. Of particular significance is a ductile thrust (the Grampian slide) which separates deeper crustal rocks (the Central Highland division), interpreted as showing the imprint of the Grenville orogeny, from shallower rocks (the Grampian division) representing a supracrustal assemblage formed between the Grenville and the c. 750 Ma events.The Grampian slide is the structurally highest member of a system of related, previously unrecorded slides affecting the Central Highland division. New structural, petrographic and Rb-Sr isotopic data, obtained largely from a recently recognised inlier of the Central Highland division at Laggan, bear out that the quartz and pegmatite veins are segregations formed during ductile shearing under amphibolite facies conditions. Muscovites from these veins yield ages between 780 and 730 Ma, and a regression analysis of tectonic schists and the muscovites gives an age of 740 ± 40 Ma. These data substantiate our previous hypothesis that the deeper-seated Moine rocks were affected by a distinct orogenic event at 750 ± 30 Ma.In the Northern Highlands, similar vein swarms are related to the Sgurr Beag slide and to belts of previously unrecorded tectonic schists in the Glenfinnan division of the Moine assemblage. A new, 755 ± 8 Ma age obtained from such a tectonic schist at Kinloch Hourn, combined with previous, similar age data from lensoid pegmatites, imply that the c. 750 Ma event may have also affected the Morar and Glenfinnan divisions.

scholarly journals Chapter 1 Introduction to the lithotectonic framework of Sweden and organization of this Memoir

2020 ◽  
Vol 50 (1) ◽  
pp. 1-15 ◽  
Author(s):  
Michael B. Stephens
Keyword(s):  
Principal Components ◽  
Solid Rock ◽  
Sedimentary Cover ◽  
Fennoscandian Shield ◽  
Mountain Building ◽  
Building Activity ◽  
Mountain Belts ◽  
Sveconorwegian Orogen ◽  
Tectonothermal Event

AbstractThe solid rock geology of Sweden comprises three principal components: (1) Proterozoic and (locally) Archean rocks belonging to the western part of the Fennoscandian Shield; (2) Phanerozoic and (locally) Neoproterozoic sedimentary cover rocks deposited on top of this ancient crust; and (3) the early to mid-Paleozoic (0.5–0.4 Ga) Caledonide orogen. Earlier compilations have applied different principles for the subdivision of the geology in the Fennoscandian Shield and the Caledonide orogen. A uniform lithotectonic framework has been developed here. Crustal segments affected by orogenesis have been identified and their ages determined by the youngest tectonothermal event. Four ancient mountain belts and six orogenies are preserved. Solid rocks outside the orogens have been assigned to different magmatic complexes or sedimentary successions based on their time of formation and tectonic affiliation. This approach allows relicts of older mountain-building activity to be preserved inside a younger orogen – for example, the effects of the Archean (2.8–2.6 Ga) orogeny inside the 2.0–1.8 Ga Svecokarelian orogen and Paleo–Mesoproterozoic (1.7–1.5 and 1.5–1.4 Ga) mountain-building processes inside the 1.1–0.9 Ga Sveconorwegian orogen. Sweden's five largest mineral districts are addressed in the context of this new lithotectonic framework, which forms the architecture to the contents of the chapters in this Memoir.

scholarly journals Depositional constraints and age of metamorphism in southern India: U–Pb chemical (EMPA) and isotopic (SIMS) ages from the Trivandrum Block

2005 ◽  
Vol 142 (3) ◽  
pp. 255-268 ◽  
Author(s):  
M. SANTOSH ◽  
A. S. COLLINS ◽  
T. MORIMOTO ◽  
K. YOKOYAMA
Keyword(s):  
Electron Microprobe ◽  
Secondary Ion Mass Spectrometry ◽  
Granulite Facies ◽  
Southern India ◽  
Biotite Gneiss ◽  
Metamorphic History ◽  
Gondwana Supercontinent ◽  
Late Neoproterozoic ◽  
Formed Part ◽  
Tectonothermal Event

We report U–Pb electron microprobe (zircon and monazite) and Secondary Ion Mass Spectrometry (SIMS) U–Pb (zircon) ages from a granulite-facies metapelite and a garnet–biotite gniess from Chittikara, a classic locality within the Trivandrum Block of southern India. The majority of the electron-microprobe data on zircons from the metapelite define apparent ages between 1500 and 2500 Ma with a prominent peak at 2109±22 Ma, although some of the cores are as old as 3070 Ma. Zircon grains with multiple age zoning are also detected with 2500–3700 Ma cores, 1380–1520 mantles and 530–600 Ma outer rims. Some homogeneous and rounded zircon cores yielded late Neoproterozoic ages that suggest that deposition within the Trivandrum Block belt was younger than 610 Ma. The outermost rims of these grains are characterized by early Cambrian ages suggesting metamorphic overgrowth at this time. The apparent ages of monazite grains from this locality reveal multiple provenance and polyphase metamorphic history, similar to those of the zircons. In a typical case, Palaeoproterozoic cores (1759–1967 Ma) are enveloped by late Neoproterozoic rims (562–563 Ma), which in turn are mantled by an outermost thin Cambrian rim (∼515 Ma). PbO v. ThO*2 plots for monazites define broad isochrons, with cores indicating a rather imprecise age of 1913±260 Ma (MSWD=0.80) and late Neoproterozoic/Cambrian cores as well as thin rims yielding a well-defined isochron with an age of 557±19 Ma (MSWD=0.82). SIMS U–Pb isotopic data on zircons from the garnet–biotite gneiss yield a combined core/rim imprecise discordia line between 2106±37 Ma and 524±150 Ma. The data indicate Palaeoproterozoic zircon formation with later partial or non-uniform Pb loss during the late Neoproterozoic/Cambrian tectonothermal event. The combined electron probe and SIMS data from the metapelite and garnet–biotite gneiss at Chittikara indicate that the older zircons preserved in the finer-grained metapelite protolith have heterogeneous detrital sources, whereas the more arenaceous protolith of the garnet–biotite gniess was sourced from a single-aged terrane. Our data suggest that the metasedimentary belts in southern India may have formed part of an extensive late Neoproterozoic sedimentary basin during the final amalgamation of the Gondwana supercontinent.

Mid-Jurassic Tectonothermal Event Superposed on a Paleozoic Geological Record in the Acatlán Complex of Southern Mexico: Hotspot Activity During the Breakup of Pangea

2004 ◽  
Vol 7 (1) ◽  
pp. 238-260 ◽  
Author(s):  
J. Duncan Keppie ◽  
R. Damian Nance ◽  
J. Dostal ◽  
A. Ortega-Rivera ◽  
Brent V. Miller ◽  
...  
Keyword(s):  
Southern Mexico ◽  
Geological Record ◽  
Tectonothermal Event ◽  
Acatlan Complex

A revised Archaean chronology for the Napier Complex, Enderby Land, from SHRIMP ion-microprobe studies

1997 ◽  
Vol 9 (1) ◽  
pp. 74-91 ◽  
Author(s):  
S.L. Harley ◽  
L.P. Black
Keyword(s):  
Time Interval ◽  
Minor Importance ◽  
High Grade ◽  
Bay Area ◽  
Igneous Activity ◽  
High Grade Metamorphism ◽  
Ancient Times ◽  
Tectonothermal Event ◽  
Very High ◽  
Napier Complex

The long and complex Archaean evolution of the Napier Complex of Enderby Land, characterized by high-grade metamorphism and several strong deformations, is reassessed in the light of new SHRIMPU–Pb zircon dating results bearing on the ages of protoliths and possible regional extents of distinct Archaean tectonothermal events. Initial felsic igneous activity occurred over a significant time interval c. 3800 Ma ago. An age of 2980±9 Ma for the emplacement of charnockite at Proclamation Island might date the oldest tectonothermal event to be recognized in the Napier Complex. An ensuing, very-high grade, previously imprecisely dated tectonothermal event occurred at 2837±15 Ma. U–Pb zircon ages ranging from 2456+8/−5 Ma to 2481±4 Ma date a subsequent, protracted high-grade tectonothermal event. Whereas the ~2840 Ma event is of regional importance in the Amundsen Bay-Casey Bay area, it is possible that the ~2980 Ma event was of only moderate grade, minor importance, or even absent, in that part of the Complex. If so, the apparent trend to very-high temperature metamorphism in the Tula and Scott mountains compared with the Napier Mountains may reflect two distinct metamorphic events rather than a simple baric and thermal gradient. The oldest crustal component in the Napier Complex appears to have been of igneous derivation. Zircon populations in paragneisses at Mount Sones are similar to those in the nearby orthogneisses, which therefore may have been basement. Another paragneiss, in the Casey Bay area, yields no zircons older than 2840 Ma, probably indicating that pre-3000 Ma crust, which is now located nearby, was not exposed at the time of sedimentation there. The isotopic data are quite complex, particularly in rocks that experienced postcrystallization metamorphic temperatures of 1000°C or more. It is postulated that this complexity, which was largely the product of migration of radiogenic Pb within the zircon grains in ancient times, and produced local excesses of this element with respect to its parent U, was caused by volume diffusion at these abnormally high regional crustal temperatures.

First report of Pan-African Sm—Nd and Rb—Sr mineral isochron ages from regional charnockites of southern India

1995 ◽  
Vol 132 (3) ◽  
pp. 253-260 ◽  
Author(s):  
C. Unnikrishnan-Warrier ◽  
M. Santosh ◽  
M. Yoshida
Keyword(s):  
Sri Lanka ◽  
Shear Zone ◽  
East Antarctica ◽  
Southern India ◽  
Peninsular India ◽  
Pan African ◽  
Mineral Isochron ◽  
Nd Model Age ◽  
Tectonothermal Event ◽  
Good Agreement

AbstractMineral and whole-rock isotope data for a massive charnockite from Kottaram in the Nagercoil Block at the southern tip of Peninsular India yield Sm—Nd and Rb—Sr ages of 517 ± 26 Ma and 484 ± 15 Ma respectively. The Nd model age calculated for the charnockite is c. 2100 Ma. Our study reports the first Pan-African mineral isochron ages from regional charnockites of Peninsular India, which are in good agreement with the recently obtained ages of incipient charnockites in the adjacent blocks, as well as alkaline plutons within the same block. Our results indicate that the Pan-African tectonothermal event in the granulite blocks south of the Palghat—Cauvery shear zone was regional, with terrain-wide rejuvenation. These results correlate with similar Pan-African tectono-thermal events reported from Sri Lanka and East Antarctica, and have an important bearing on Gondwana reconstructions.

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