Age constraints on the tectonic evolution of the Itremo region in Central Madagascar

The Itremo region in Central Madagascar comprises a deformed metasedimentary sequence (Itremo Group) that has undergone greenschist to lower amphibolite facies metamorphism. During a first phase of deformation (D1) Itremo Group sediments were deformed into a fold-and-thrust belt and transported toward the E to NE on top of migmatitic gneisses rocks of Anatananarivo block. A second phase of deformation (D2) affected both the fold-and-thrust belt and structurally underlying units, and formed large-scale N-S trending folds with steeply dipping axial planes. A Late Neoproterozoic Th–U–Pb XRF monazite age (565±17 Ma) dates the emplacement of a granite that truncates first-phase structures in the Itremo Group, and indicates that the fold-and-thrust belt formed prior to ≈565 Ma. Th–U–Pb electron microprobe dating was applied to elongated monazites that lie within the first-phase foliation of Itremo Group metapelites. The detrital cores of zoned monazites reveal two distinct age populations at ∼2000 and 1700 Ma, the latter age giving a maximum depositional age for the Itremo Group. Statistical analysis of ages determined from the rims of zoned monazites and from unzoned monazites indicates three Late Proterozoic–Early Paleozoic monazite growth events at about 565–540, 500 and 430 Ma. The oldest age population is contemporaneous within error, with the intrusion of the dated granite. The two younger age populations are found both in the Th–U–Pb and Ar–Ar data; together with the perturbation of the Rb–Sr system we interpret both ages as due to alteration related to fluid circulation events, possibly connected to the emplacement of pegmatite fields in Central Madagascar. Syn-D1 tectonic growth of contact metamorphism minerals such as andalusite has been observed locally in metapelites along the margin of Middle Neoproterozoic (≈800 Ma) granites, suggesting that D1 in the Itremo Group is contemporaneous with the intrusion of granites at ≈800 Ma. The N-S trending D2 folds are associated with ≈E-W shortening during the final assembly of Gondwana in Late Neoproterozoic–Early Cambrian times.

The Pleistocene of the middle region of North America and its vertebrated animals /

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The Upper Pima of San Cayetano del Tumacacori; an archaeohistorical reconstruction of the Ootam of Pimeria Alta.

Bibliography: p. [571]-589.

Methods and devices for the professional improvement of teachers of vocational agriculture; summary of a study of the professional improvement of teachers of vocational agriculture of the southern region

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Pollution prevention : meeting the environmental challenges of the 1990s : Region 5 FY91 accomplishments.

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TASSIM: a transportation and air shed simulation model. Volume 1, case study of the Boston region. Final report.

Transportation Department, Secretary of Transportation, Washington, D.C.

Petroleum resources and uranium possibilities of the Pucallpa region, Loreto Department, Peru /

In cooperation with the Junta de Control de Energía Atómica del Peru.

Birds of the Pymatuning region /

Includes index.

The geology of the upper region of the main Walker river, Nevada,

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Maps, &c. of the mineral region of Lake Superior.

Cover title.

Economic advantages of the Milan region.

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Farrar's illustrated guide book to Moosehead Lake and vicinity, the wilds of northern Maine, and the head-waters of the Kennebec, Penobscot, and St. John rivers : with a new and correct map of the lake region, drawn and printed expressly for this book : also contains the game and fish laws of Maine (as rev. by the last Legislature), railroad, steamboat, and stage routes, time tables, tables of fares, list of hotels, prices of board, and other valuable information for the sportsman, tourist, or pleasure-seeker /

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The anatomy of the phalangeal region /

Thesis (D.V.M.)--Cornell University, 1907.