Precambrian crustal evolution of Peninsular India: A 3.0 billion year odyssey

1891–1883 Ma Southern Bastar–Cuddapah mafic igneous events, India: A newly recognized large igneous province

Ion microprobe 207Pb/206Pb ages of zircons from the Bundelkhand massif, northern India: implications for crustal evolution of the Bundelkhand–Aravalli protocontinent

New U‐Pb zircon ages and Sm‐Nd and Rb‐Sr isotopic data are presented for orthogneisses from north‐central Madagascar, including Ile Sainte Marie, Alaotra‐Beforona, Maevatanana, and Ambatolampy‐Ambatomarina. A migmatite tonalite gneiss from Ile Sainte Marie is dated precisely at \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $3187\pm 2$ \end{document} Ma and has a Sm‐Nd model age (TDM) of 3204 Ma, thereby establishing a Middle Archean age for the oldest, juvenile gneisses in northeast Madagascar. Dated orthogneisses, int...

https://www.jstor.org/stable/10.1086/314337

U-Pb Geochronology and Isotope Geochemistry of the Archean and Proterozoic Rocks of North-Central Madagascar

207Pb/206Pb zircon ages and the evolution of the Singhbhum Craton, eastern India: an ion microprobe study1This paper is dedicated to Prof. A.K. Saha, one of the senior co-authors, who passed away after submission of the paper.1

https://www.prl.res.in/~library/Goswami_JN_325_96_abst.pdf

Stabilization of the Aravalli Craton of northwestern India at 2.5 Ga: An ion microprobe zircon study

We have lIsed an ion microprobe to measure 207 Pb/ 206 Pb ages on carefully selected ∼20 μm domains of single zircons from two samples of the Amet Granite. A sample of the Amet Granite, consisting of a strongly foliated augen gneiss, yields a minimum crystallization age of 1641±14 Ma (1σ). From a second sample, collected from an aplite dyke which cross-cuts the foliation of the augen gneiss, we calculate a minimum emplacement age of 1766±16 Ma; both these ages are based on a dynamic background correction of 0.01 c/s. As part of this study we conducted 30 analyses of an internal standard which has a published, concordant age of 2631±4 Ma. Our data suggest that a low intensity dynamic background (≤0.01 c/s), comparable to the 204 Pb count rate, is present within our system. This background could, in principle, lead to considerable uncertainties when calculating 206 Pb/ 204 Pb ages for young samples which have low radiogenic 206 Pb concentrations. We believe an inaccurate background correction is the most likely explanation why the cross-cutting dyke yields an apparent age which is older than that obtained from its host rock. Assuming that the dynamic background was negligible at the time of its analysis. we recalculate an age of 1646±19 Ma for the dyke sample which is statistically indistinguishable from the age of the augen gneiss. The use of small geometry ion microprobes for obtaining  207 Pb/ 206 Pb age is best suited for older and radiogenic Pb-rich zircon, when such a low intensity background becomes less significant. Our results indicate that the crystallization of the Amet porphyritic granite, the tectonic emplacement of the nearby mid-Proterozoic Sand Mata granulites and the subsequent deformation are the products of a single tectonic cycle which was completed by ∼ 1.64 Ga.

M. Wiedenbeck

Papers

Stabilization of the Aravalli Craton of northwestern India at 2.5 Ga: An ion microprobe zircon study

An Ion Microprobe Study of Single Zircons from the Amet Granite, Rajasthan