Chromian spinel as a petrogenetic indicator in abyssal and alpine-type peridotites and spatially associated lavas

1984 ◽  
Vol 86 (1) ◽  
pp. 54-76 ◽  
Author(s):  
Henry J. B. Dick ◽  
Thomas Bullen
Keyword(s):  
Chromian Spinel ◽  
Petrogenetic Indicator

CHROMIAN SPINEL AS A PETROGENETIC INDICATOR: PART 1. THEORY

1965 ◽  
Vol 2 (6) ◽  
pp. 648-672 ◽  
Author(s):  
T. N. Irvine
Keyword(s):  
General Formula ◽  
Cross Section ◽  
Solid Solutions ◽  
Chromian Spinel ◽  
Triangular Prism ◽  
Chemical Analyses ◽  
Calorimetric Data ◽  
Activity Ratios ◽  
Petrogenetic Indicator ◽  
Spinel Solid Solutions

Previous investigators have shown that natural chromium-bearing spinel solid solutions adhere closely to the general formula (Mg, Fe++) (Cr, Al, Fe+++)2O4 and may therefore be graphically portrayed in a triangular prism, the length of which represents the ratios MgO/FeO, and the cross section the relative proportions of Cr2O3, Al2O3, and Fe2O3. In this paper, theoretical expressions are derived whereby the prism may be "contoured" for conditions of isothermal–isobaric equilibrium according to (a) the spinel compositions that may coexist with olivine or pyroxene having specific MgO/FeO ratios; (b) the activity ratios of Cr/Al, Cr/Fe+++, or Al/Fe+++ that obtain in the environments in which the spinel solid solutions form, and (c) the oxygen fugacities that accompany formation of spinel in systems containing olivine (forsterite–fayalite) and orthopyroxene (enstatite–ferrosilite). Rough "working" values for the thermochemical coefficients involved are estimated from limited calorimetric data and chemical analyses of spinel–olivine and spinel–orthopyroxene pairs.

scholarly journals Cr-spinel records metasomatism not petrogenesis of mantle rocks

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Hamed Gamal El Dien ◽  
Shoji Arai ◽  
Luc-Serge Doucet ◽  
Zheng-Xiang Li ◽  
Youngwoo Kil ◽  
...  
Keyword(s):  
Subduction Zone ◽  
Plate Tectonics ◽  
Mantle Metasomatism ◽  
Mantle Melting ◽  
Ultramafic Rocks ◽  
Chromian Spinel ◽  
Core Composition ◽  
Mid Ocean Ridge ◽  
Ocean Ridge ◽  
Petrogenetic Indicator

Abstract Mantle melts provide a window on processes related to global plate tectonics. The composition of chromian spinel (Cr-spinel) from mafic-ultramafic rocks has been widely used for tracing the geotectonic environments, the degree of mantle melting and the rate of mid-ocean ridge spreading. The assumption is that Cr-spinel’s core composition (Cr# = Cr/(Cr + Al)) is homogenous, insensitive to post-formation modification and therefore a robust petrogenetic indicator. However, we demonstrate that the composition of Cr-spinel can be modified by fluid/melt-rock interactions in both sub-arc and sub-mid oceanic mantle. Metasomatism can produce Al-Cr heterogeneity in Cr-spinel that lowers the Cr/Al ratio, and therefore modifies the Cr#, making Cr# ineffective as a geotectonic and mantle melting indicator. Our analysis also demonstrates that Cr-spinel is a potential sink for fluid-mobile elements, especially in subduction zone environments. The heterogeneity of Cr# in Cr-spinel can, therefore, be used as an excellent tracer for metasomatic processes.

CHROMIAN SPINEL AS A PETROGENETIC INDICATOR: PART 2. PETROLOGIC APPLICATIONS

1967 ◽  
Vol 4 (1) ◽  
pp. 71-103 ◽  
Author(s):  
T. N. Irvine
Keyword(s):  
Oxygen Fugacity ◽  
Peritectic Reaction ◽  
High Pressures ◽  
Volcanic Rocks ◽  
Distribution Coefficients ◽  
Chromian Spinel ◽  
Low Oxygen ◽  
Petrogenetic Indicator

The crystallization of chromium-bearing spinel from silicate magmas is first examined, and then an attempt is made to apply the theory developed in Irvine (1965) to the principal occurrences of the mineral for which data are available. It is concluded that the chromium-rich varieties commonly known as chromite have generally formed simultaneously with olivine, and that their crystallization has in many occurrences been terminated by a peritectic (reaction) relation leading to formation of a pyroxene. The origin of the aluminium-rich varieties is more problematical and perhaps more varied; however, they evidently occur only in alpine-type peridotite bodies and peridotite "nodules" in basaltic volcanic rocks, and their formation may generally have involved high pressures. It is found that there is a rough correlation between the Mg/Fe++ ratios of chromian spinels, olivines, and pyroxenes occurring in the same rock bodies, and there is some evidence that the Mg–Fe++ distribution coefficients of spinel–silicate pairs may significantly be sensitive to temperature. The chromites of stratiform intrusions reflect an appreciable range of oxygen fugacities, whereas the spinels of alpine- type peridotite bodies seem generally to have formed at about the same relatively low oxygen fugacity. Chromites from ultra mafic bodies of the type common to southeastern Alaska have exceptionally high Fe+++/Cr + Al + Fe+++ ratios, probably because the bodies crystallized from magma that was extremely poor in silica.

Titanite as a petrogenetic indicator

Terra Nova ◽  
2021 ◽  
Author(s):  
E.A. Scibiorski ◽  
P.A. Cawood
Keyword(s):  
Petrogenetic Indicator

Sources of placer platinum in Yukon: provenance study from detrital minerals

2008 ◽  
Vol 45 (8) ◽  
pp. 879-896 ◽  
Author(s):  
Yana Fedortchouk ◽  
William LeBarge
Keyword(s):  
Unknown Origin ◽  
Heavy Mineral ◽  
Source Rocks ◽  
Ultramafic Rocks ◽  
Chromian Spinel ◽  
Mafic Intrusions ◽  
Platinum Group Minerals ◽  
Mineral Sample ◽  
Back Arc ◽  
Ocean Ridge

Source rocks for the platinum group minerals (PGM), historically reported in a number of Yukon placers, remain either unknown or poorly understood. A study of heavy-mineral samples from five creeks draining bedrock in west and central Yukon was undertaken to confirm the presence of placer platinum, to determine which mafic–ultramafic rock is the source of PGM in Kluane area, southern Yukon, and to explain platinum occurrences in Canadian and Florence creeks, central Yukon, where no known mafic–ultramafic rocks are present. Diverse composition of chromian spinel and clinopyroxenes from three creeks in the Kluane area indicate several sources of ultramafic rocks, including fragments of Alpine-type peridotites formed in back-arc basin and mid-ocean-ridge settings, and a source rock for zoned zinc-rich chromites of unknown origin. The Kluane ultramafic sills are the most likely source of PGM in this area. The heavy-mineral sample from Canadian Creek returned one PGM grain, no chromite, and abundant ilmenite and titanomagnetite. A group of chromium-rich magnesian ilmenites (∼4 wt.% MgO) closely match the composition of ilmenites from continental mafic intrusions produced during continental rift magmatism. This supports the continental rifting event recently proposed for this part of Yukon and indicates the economic potential of the Canadian Creek platinum occurrence. Composition of spinel from Florence Creek sample indicates an Alaskan-type intrusion as the source of PGM.

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