A hypabyssal kimberlite dike in southwestern Pennsylvania (USA), emplaced through Proterozoic basement and Phanerozic cover, contains a xenocryst and xenolith assemblage typical of material sampled within the subcontinental lithosphere, including xenocrysts of Cr-rich pyrope, magnesiochromite, Cr-rich diopside, and peridotite xenoliths. Temperatures and depths of equilibration of the clinopyroxene (840 °C and 130 km to 1350 °C and 170 km) indicate some sampling in the field of diamond stability. Diamonds have not been reported, however, and the chemistry of the garnet (lherzolite, Cr-poor megacryst, and Group II eclogite) and spinel (<56.0 wt.% Cr2O3) are consistent with diamond absence and the off-craton tectonic setting of the kimberlite. An unusual feature of this suite is that, unlike most mantle xenolith/xenocryst spinel, some of those from Masontown have an unusually high silica content (to 0.59 wt.% SiO2). The significance of the high silica content is unclear, but may be related to an ultrahigh-pressure precursor chromite polymorph with a calcium ferrite structure, which can accommodate Si in solid solution.
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Research Article|
July 01, 2015
Mantle Xenocrysts from the Masontown, Pennsylvania Kimberlite: an Ordinary Mantle with Si-enriched Spinel
Daniel J. Schulze;
Daniel J. Schulze
§
Department of Earth Sciences and Department of Chemical and Physical Sciences, University of Toronto, Mississauga, Ontario, Canada L5L 1C6
§Corresponding author e-mail address: [email protected]
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B. Carter Hearn, Jr.
B. Carter Hearn, Jr.
U.S. Geological Survey, Reston, Virginia, USA 22092 and Smithsonian Institution, Washington, D.C., USA
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Daniel J. Schulze
§
Department of Earth Sciences and Department of Chemical and Physical Sciences, University of Toronto, Mississauga, Ontario, Canada L5L 1C6
B. Carter Hearn, Jr.
U.S. Geological Survey, Reston, Virginia, USA 22092 and Smithsonian Institution, Washington, D.C., USA
§Corresponding author e-mail address: [email protected]
Publisher: Mineralogical Association of Canada
Received:
02 May 2015
Accepted:
19 May 2015
First Online:
16 Feb 2018
Online ISSN: 1499-1276
Print ISSN: 0008-4476
© 2015 Mineralogical Association of Canada
The Canadian Mineralogist (2015) 53 (4): 767–773.
Article history
Received:
02 May 2015
Accepted:
19 May 2015
First Online:
16 Feb 2018
Citation
Daniel J. Schulze, B. Carter Hearn; Mantle Xenocrysts from the Masontown, Pennsylvania Kimberlite: an Ordinary Mantle with Si-enriched Spinel. The Canadian Mineralogist 2015;; 53 (4): 767–773. doi: https://doi.org/10.3749/canmin.1500056
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Index Terms/Descriptors
- chain silicates
- chromite
- clinopyroxene
- diamond
- dikes
- diopside
- eclogite
- Fayette County Pennsylvania
- garnet group
- Grenvillian Orogeny
- igneous rocks
- inclusions
- intrusions
- kimberlite
- lherzolite
- mantle
- metamorphic rocks
- native elements
- nesosilicates
- orthosilicates
- oxides
- Pennsylvania
- peridotites
- plutonic rocks
- Precambrian
- pressure
- pyrope
- pyroxene group
- silicates
- silicon
- solid solution
- spinel
- ultrahigh pressure
- ultramafics
- United States
- upper mantle
- xenocrysts
- xenoliths
- magnesiochromite
- Masontown Pennsylvania
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