Abstract
U-Pb titanite dates corroborate very slow exhumation of the north-east Greenland ultrahigh-pressure terrane from the Caledonian Orogen
Abstracts with programs - Geological Society of America, Vol.51(1)
Geological Society of America, Northeastern Section, 54th annual meeting
03/2019
Abstract
Quartzofeldspathic gneiss that hosts eclogite is the dominant lithology of the continental ultrahigh-pressure (UHP) terrane in the North-East Greenland Caledonides. Both lithologies contain coesite, indicating all the rocks reached mantle depths. The best-preserved gneiss is a clinopyroxene-bearing granulite with HP phases (kyanite, phengite, omphacite and rutile) included in garnet. Titanite is common in the retrogressed gneiss and shows a textural progression from overgrowths on matrix rutile to polycrystalline grains with no rutile to euhedral porphyroblasts. Titanite from 6 gneisses has been analyzed for U-Pb and trace elements by SHRIMP-RG using McClure Mountain titanite as a standard. Weighted mean 206Pb/238U dates, using data-defined common Pb values, range from 347+ or -6 to 321+ or -7 Ma. Regression of data from all samples defines an intercept of 331+ or -4 Ma (MSWD=2.6), which is taken as the age of rutile-to-titanite conversion. Four samples show concave-down trace element patterns, similar to igneous titanite, interpreted as formation in the presence of a melt; indeed, three of the samples contain thin, wispy leucosomes. Large (>600 mu m), zoned subhedral titanite from a metagranitoid gneiss preserves three distinct trace element patterns that can be related to melting, metamorphism and garnet breakdown. Zr-in-titanite temperatures, calculated at 0.5 GPa and aSiO2=aTiO2=1, range from 690-723 degrees C. The preservation of different trace element and age domains argues against simple cooling ages. UHP ages from coesite-bearing zircon in eclogite and gneiss are approximately 365-350 Ma, or approximately 35-20 m.y. earlier than titanite growth. Titanite from UHP gneiss in NE Greenland formed over a prolonged exhumation history also recorded by zircon: (1) Phengite decompression melting at the quartz-coesite transition starting at approximately 347 Ma; (2) Granulite to amphibolite facies metamorphism accompanied by pegmatite emplacement between 350 and 340 Ma; and (3) Continued amphibolite facies exhumation with titanite growth through 320 Ma. This contrasts with many UHP terranes where titanite grows within <4-15 million years of peak P. Slow exhumation agrees with a tectonic setting at the base of an overthickened, overriding plate where UHP occurs in intracontinental subduction zones, as has been proposed for present day Tibet.
Details
- Title: Subtitle
- U-Pb titanite dates corroborate very slow exhumation of the north-east Greenland ultrahigh-pressure terrane from the Caledonian Orogen
- Creators
- Jane A Gilotti - University of Iowa, Department of Earth and Environmental Sciences Iowa City, IA USA United StatesBill McClellandMatthew Coble
- Resource Type
- Abstract
- Publication Details
- Abstracts with programs - Geological Society of America, Vol.51(1)
- Conference
- Geological Society of America, Northeastern Section, 54th annual meeting
- Publisher
- Geological Society of America (GSA)
- ISSN
- 0016-7592
- Alternative title
- Geological Society of America, Northeastern Section, 54th annual meeting; abstracts
- Language
- English
- Date published
- 03/2019
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984240916502771
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