Sm–Nd and Rb–Sr dating of amphibolite from the Nellore–Khammam schist belt, SE India: constraints on the collision of the Eastern Ghats terrane and Dharwar–Bastar craton

2001 ◽  
Vol 138 (4) ◽  
pp. 495-498 ◽  
Author(s):  
T. OKUDAIRA ◽  
T. HAMAMOTO ◽  
B. HARI PRASAD ◽  
RAJNEESH KUMAR
Keyword(s):  
Eastern Ghats ◽  
Schist Belt ◽  
Bastar Craton ◽  
Pan African ◽  
Mineral Isochron ◽  
Peak Metamorphism ◽  
Thermal Overprint ◽  
Early Neoproterozoic

The Nellore–Khammam schist belt, SE India, is sandwiched in between the Proterozoic Eastern Ghats terrane and the Archaean Dharwar–Bastar craton. We report Sm–Nd and Rb–Sr mineral isochron ages of amphibolite from the schist belt. The Sm–Nd and Rb–Sr ages are 824±43 Ma and 481±16 Ma, respectively. The Sm–Nd age indicates the timing of peak metamorphism, whereas the Rb–Sr age indicates the Pan-African thermal overprint. The peak metamorphism was related to collision of the Eastern Ghats terrane with the Dharwar-Bastar craton, which occurred during early Neoproterozoic time.

Seismic imaging of the deep crustal structure beneath Eastern Ghats Mobile Belt (India): Crustal growth in the context of assembly of Rodinia and Gondwana supercontinents

2020 ◽  
Author(s):  
Arun Singh ◽  
Chandrani Singh
Keyword(s):  
Crustal Structure ◽  
High Elevation ◽  
Receiver Functions ◽  
Eastern Ghats ◽  
Mobile Belt ◽  
Seismic Profiles ◽  
Bastar Craton ◽  
Singhbhum Craton ◽  
Pan African ◽  
Eastern Ghats Mobile Belt

<p>We present the first high resolution seismic images illuminating the hitherto-elusive crustal architecture beneath the Eastern Ghats Mobile Belt (EGMB) using teleseismic receiver functions. Data were collected using 27 broadband seismic stations operated in a continuous mode covering two distinct seismic profiles (~550 km long) during 2015–2018. Several interesting observations and inferences are made through analysis of the receiver functions such as (a) a very thick crust (>40 km) with oppositely dipping Moho beneath the EGMB and Archean Bastar Craton, (b) EGMB formed from amalgamation of different crustal domains thrust over one another possibly during the Pan-African orogeny, (c) the Archean Bastar Craton crust extends (~75 km) eastward beneath the EGMB, from its surficial geological boundary, (d) there is a sharp contrast in the crustal structure (with ~20 km Moho offset) at the contact between the Rengali Province and Singhbhum Craton which does not support southward growth of the Singhbhum Craton through accretion, (e) anorthosite complexes may possibly be created by rising diapirs channeled through the weak zones in the crust, from the magma chambers developed by melting of frontal portion of the underthrusting lower crust. We report a significant change in the crustal architecture just east of the most elevated topography observed along the profile covering the Bastar Craton and the EGMB. It requires further careful petrological investigations to ascertain the relationship of high elevation and its linkages with the deep crust, forming a separate domain. Our results do not support or discard a Grenvillian age (~1 Ga) docking of the EGMB with Proto-India, though it is preferred to explain the present day crustal features with intense Pan-African (0.5–0.6 Ga) reorganization.</p>

Rb–Sr Geochronology of the Hida metamorphic belt, Japan

1970 ◽  
Vol 7 (6) ◽  
pp. 1383-1401 ◽  
Author(s):  
K. Shibata ◽  
T. Nozawa ◽  
R. K. Wanless
Keyword(s):  
Granitic Rocks ◽  
Metamorphic Event ◽  
Crystalline Schist ◽  
Metamorphic Rocks ◽  
Schist Belt ◽  
Metamorphic Belt ◽  
Early Mesozoic ◽  
Mineral Isochron ◽  
Middle Paleozoic ◽  
Later Phase

Rb–Sr whole-rock and mineral isochron ages have been determined for metamorphic and granitic rocks of the Hida metamorphic belt. The results indicate that an extensive metamorphic event together with plutonic activity took place within the belt during the latest Paleozoic – early Mesozoic period. The older ages of 220–250 m.y. represent an earlier phase of the metamorphism, whereas the younger ages of 170–180 m.y. represent a later phase. The Funatsu granitic rocks yielded a whole-rock isochron age of 176 m.y. with an initial 87Sr/86Sr ratio of 0.7056. This age is believed to indicate the time of original emplacement, and the rocks are considered to represent late-kinematic intrusion in the Hida belt.Some information on the middle Paleozoic metamorphism in the Hida Mountains was obtained from the isochron study. The whole-rock isochron age of 412 m.y. for the metamorphic rocks of the Fujibashi area may be considered, although not confirmed, to indicate the time of older metamorphism. The Omi Schist of the Circum–Hida crystalline schist belt, which belongs to the glaucophanitic type of metamorphism, gave a mineral isochron age of 350 m.y. thereby providing evidence of mid-Paleozoic metamorphism.The initial 87Sr/88Sr ratios for the whole-rock samples of the Hida metamorphic belt are found to be generally low, i.e. 0.705–0.708. This is especially so for the metamorphic rocks from the northern part of the belt where the lowest values were found.

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.

scholarly journals A New Interpretation of Geodynamic Context and Typology of Moroccan Anti-Atlas Silver Deposits

2017 ◽  
Vol 13 (12) ◽  
pp. 424
Author(s):  
Wafik Amina ◽  
Ramdani Abderahmane ◽  
El Aouad Nouaman ◽  
El Ghazali Mohamed
Keyword(s):  
Pressure Gradients ◽  
Metallogenic Province ◽  
Pan African ◽  
Silver Deposits ◽  
Peak Metamorphism ◽  
New Interpretation ◽  
Mega Event ◽  
Brine Pools ◽  
Metamorphic Facies ◽  
Volcanic Terrains

The argentiferous deposits in the Anti-Atlasic chain in Morocco are encased in the meta-sedimentary, volcanic-sedimentary and volcanic terrains of the Neoproterozoic, structured and schistosed during the Pan-African orogenesis. These deposits are associated with terminal Neoproterozoic rhyolites and granitoids. The deposits of Zgounder, Imiter and Bou Madine have similarities; Structurally are controlled and associated with faults; The source of the mineralization is generally magmatic or crustal. Precipitation of the mineralization would result from the mixing of mineralized fluids with meteoric waters or brine pools. The silver deposits in the Anti-Atlas are characterized by a number of criteria, which confirm their orogenic character. These deposits are associated with orogenic accretion events in relation to Pan-African orogenesis during the Neoproterozoic. Mineralization is syn- to post-peak metamorphism, controlled and associated faults, with veins that can have significant vertical extensions. The pressure gradients, and temperature metamorphism, indicating an orogenic environment, with metamorphic facies greenschist in general. These deposits can all be linked to an argentiferous mega-event during the Upper Neoproterozoic and thus define an argentiferous metallogenic province.

Reply to discussion on “From Pan-African transpression to Cadomian transtension at the West African margin: New U-Pb zircon ages from the Eastern Saghro Inlier (Anti-Atlas, Morocco)” by Ikenne et al. 2020 (GSL-SP, 503, 209-233)

2021 ◽  
pp. jgs2021-034
Author(s):  
Ezzoura Errami ◽  
Ulf Linnemann ◽  
Jamal El Kabouri ◽  
Mandy Hofmann ◽  
Andreas Gärtner ◽  
...  
Keyword(s):  
West African ◽  
Ultramafic Rocks ◽  
Geodynamic Evolution ◽  
The West ◽  
West African Craton ◽  
Zircon Age ◽  
Pan African ◽  
Stratigraphic Position ◽  
Age Constraints ◽  
Early Neoproterozoic

The comment of Ikenne et al. concerns recently described U-Pb baddeleyite ages, around 1.71 and 1.65 Ga, obtained on intrusive sills and dykes in the Taghdout-Lkest Group in the SW domain of the Anti-Atlas (AA). These authors suggest an independent geodynamic evolution of the eastern and western domains of the Anti-Atlas prior to the Ediacaran period. Furthermore, they state that we do not take this magmatic event into account when interpreting our data. We like to emphasize that this is beyond the scope of our paper and does not affect our interpretation of the AA evolution during the deposition of the Ediacaran sedimentary successions (Saghro, Mgouna, and Ouarzazate goups). We agree with the comment that we did not distinguish the Taghdout-Lkest from the Bleida-Tachdamt groups and now we separate them in the revised figure 2. The different geodynamic evolution of the SW and NE Anti-Atlas domains in pre-Ediacaran times sensu Ikenne et al., is not consistent with abundant inherited Paleoproterozoic zircon detritus and Nd model ages (0.80-1.82 Ga) from the northeastern Anti-Atlas and the Meseta. There is no doubt about Late Paleoproterozoic baddeleyite ages, but they do not have an analogue in the zircon age record of the West African Craton, which is expected from ultramafic rocks with few zircon grains. However, they locally allow assuming a Late Paleoproterozoic deposition of the lower Taghdout-Lkest Group. Any age constraints for the upper parts of this group are lacking, thus allowing a hypothetic deposition between ca. 1.65 Ga and 0.83 Ga (the assumed age of initial Bleida-Tachdamt Group deposition). Therefore, it is very important to close the gap in detailed stratigraphic studies that would allow differentiating between the different Late Paleoproterozoic and Early Neoproterozoic events including the stratigraphic position of the upper Taghdout-Lkest Group and Bleida-Tachdamt group.

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