SmNd garnet ages from the Uluguru granulite complex of Eastern Tanzania: further evidence for post-metamorphic slow cooling in the Mozambique belt

M. A H Maboko, Eizou Nakamura

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41 Citations (Scopus)

Abstract

Two samples from the Uluguru granulite complex yield garnet SmNd ages of 633 ± 7 and 618 ± 16 Ma, similar to previously published hornblende 40Ar39Ar and KAr ages. The similarity of the SmNd to the KAr age suggests that the closure temperature of garnet to Nd diffusion is similar to that of hornblende to Ar diffusion. Assuming that published zircon UPb ages of about 700 Ma date peak granulite-facies metamorphism, a mean post-metamorphic cooling rate of 2-3°C/Ma can be calculated for the time interval 700 to 630 Ma. Such slow cooling rates imply thermal relaxation with a thickness length-scale greater than the thickness of average continental crust. This, in turn, implies that the thermal perturbation responsible for metamorphism was preceded by regional crustal thickening probably in a collisional orogen.

Original languageEnglish
Pages (from-to)195-202
Number of pages8
JournalPrecambrian Research
Volume74
Issue number4
DOIs
Publication statusPublished - 1995

Fingerprint

Garnets
granulite
garnet
Cooling
cooling
hornblende
metamorphism
closure temperature
crustal thickening
granulite facies
continental crust
zircon
perturbation
Temperature
Hot Temperature
rate

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geology

Cite this

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abstract = "Two samples from the Uluguru granulite complex yield garnet SmNd ages of 633 ± 7 and 618 ± 16 Ma, similar to previously published hornblende 40Ar39Ar and KAr ages. The similarity of the SmNd to the KAr age suggests that the closure temperature of garnet to Nd diffusion is similar to that of hornblende to Ar diffusion. Assuming that published zircon UPb ages of about 700 Ma date peak granulite-facies metamorphism, a mean post-metamorphic cooling rate of 2-3°C/Ma can be calculated for the time interval 700 to 630 Ma. Such slow cooling rates imply thermal relaxation with a thickness length-scale greater than the thickness of average continental crust. This, in turn, implies that the thermal perturbation responsible for metamorphism was preceded by regional crustal thickening probably in a collisional orogen.",
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AU - Nakamura, Eizou

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