Genesis of chromite deposits by dynamic upgrading of Fe ± Ti oxide xenocrysts

Lesher, C. Michael; Carson, Heather; Houlé, M G

doi:10.1130/g45448.1

Cited by 12 publications

(10 citation statements)

References 34 publications

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“…Furthermore, the natural sample contains a significant proportion of isolated or nearly isolated grains with coordination numbers of 0, 1 or 2; these are absent in the simulation. We conclude that (a) the low packing density, (b) the presence of isolated individual grains not supported by contact with any other chromite grains, and (c) the relationship between coordination number and crystal size in the UG1 chromitite are not consistent with random mechanical accumulation of non-interacting chromite grains, be it crystal settling in a melt [35][36][37][38] or kinetic sieving in a crystal mush 39,40 .…”

Section: Three-dimensional Framework Of Chromite Crystalsmentioning

confidence: 82%

“…This field observation strongly argues against the formation of the UG1 chromitite, both on the planar and overhanging portions of the chamber floor, by processes involving gravity-induced settling of chromite through either the resident melt [35][36][37][38] or a crystal-rich mush 39,40 . The simplest alternative mechanism is in situ growth of chromite directly at the chamber floor from a chromite-only-saturated melt 28,30 .…”

Section: Field and Textural Evidence For In Situ Growth Of Chromitementioning

confidence: 97%

“…1c). The traditional interpretation of such layers in the frame of gravity settling models is that chromite was the first to settle on the chamber floor [35][36][37][38] followed, after some period of post-depositional cooling, by in situ growth of plagioclase oikocrysts from the interstitial melt in a mushy chromitite. An important point is that settling chromite grains have enough time to reach the chamber floor and start growing there.…”

Section: Field and Textural Evidence For In Situ Growth Of Chromitementioning

confidence: 99%

“…The realization that massive chromitites form by in situ growth of chromite directly in the chamber (Fig. 4a) -rather than from chromite phenocrysts brought into the chamber with externally-derived crystal-rich mushes 9,12,38,40 -logically brings us to a long-known Cr mass balance issue 32,52,53 . The stratiform chromitite layers in layered intrusions can be up to 2 m thick and contain 40-50 wt.% Cr2O3, yet have evidently crystallized from a basaltic melt that was unlikely to have contained more than 1000 ppm Cr 31 .…”

Section: Chromium Budget Requires a Large Magma Volumementioning

confidence: 99%

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Chromitite layers require the existence of large, long-lived, and entirely molten magma chambers

Latypov

Chistyakova

Barnes

et al. 2021

Preprint

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An emerging and increasingly pervasive school of thought is that large, long-lived and largely molten magma chambers are transient to non-existent in Earth’s history1–13. These ideas attempt to supplant the classical paradigm of the ‘big magma tank’ chambers in which the melt differentiates, is replenished, and occasionally feeds the overlying volcanoes14–23. The stratiform chromitites in the Bushveld Complex – the largest magmatic body in the Earth’s crust24 – however, offers strong contest to this shifting concept. Several chromitites in this complex occur as layers up to 2 metres in thickness and more than 400 kilometres in lateral extent, implying that chromitite-forming events were chamber-wide phenomena24–27. Field relations and microtextural data, specifically the relationship of 3D coordination number and grain size, indicate that the chromitites grew as a 3D framework of touching chromite grains directly at the chamber floor from a melt saturated in chromite only28–30. Mass-balance estimates dictate that a 1 to 4 km thick column of this melt26,31,32 is required to form each of these chromitite layers. Therefore, an enormous volume of melt (>1,00,000 km3)24,25 must have been involved in the generation of all the Bushveld chromitite layers, with half of this melt being expelled from the magma chamber24,26. We therefore argue that the very existence of thick and laterally extensive chromitite layers in the Bushveld and other layered intrusions strongly buttress the classical paradigm of ‘big magma tank’ chambers.

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Section: Three-dimensional Framework Of Chromite Crystalsmentioning

confidence: 82%

Section: Field and Textural Evidence For In Situ Growth Of Chromitementioning

confidence: 97%

Section: Field and Textural Evidence For In Situ Growth Of Chromitementioning

confidence: 99%

Section: Chromium Budget Requires a Large Magma Volumementioning

confidence: 99%

See 2 more Smart Citations

Chromitite layers require the existence of large, long-lived, and entirely molten magma chambers

Latypov

Chistyakova

Barnes

et al. 2021

Preprint

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“…What I would like to argue for here is some genetic link between the podiform chromitite produced in the mantle and the stratiform one in the crust; some of the chromite grains in the latter are possibly precipitated in the mantle prior to the entrainment by magma to the crust. Many factors for the formation of chromiteoversaturated magmas in the crust have been proposed, such as compression of magmas due to vesiculation [79], an increase in oxygen fugacity [8,80], assimilation of Fe-oxiderich rocks [81,82] and decompression of magmas [14], reflecting the various geologic and petrologic contexts of the host's layered intrusions.…”

Section: Discussionmentioning

confidence: 99%

Genetic Link between Podiform Chromitites in the Mantle and Stratiform Chromitites in the Crust: A Hypothesis

Arai¹

2021

Minerals

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No genetic link between the two main types of chromitite, stratiform and podiform chromitites, has ever been discussed. These two types of chromitite have very different geological contexts; the stratiform one is a member of layered intrusions, representing fossil magma chambers, in the crust, and the podiform one forms pod-like bodies, representing fossil magma conduits, in the upper mantle. Chromite grains contain peculiar polymineralic inclusions derived from Na-bearing hydrous melts, whose features are so similar between the two types that they may form in a similar fashion. The origin of the chromite-hosted inclusions in chromitites has been controversial but left unclear. The chromite-hosted inclusions also characterize the products of the peridotite–melt reaction or melt-assisted partial melting, such as dunites, troctolites and even mantle harzburgites. I propose a common origin for the inclusion-bearing chromites, i.e., a reaction between the mantle peridotite and magma. Some of the chromite grains in the stratiform chromitite originally formed in the mantle through the peridotite–magma reaction, possibly as loose-packed young podiform chromitites, and were subsequently disintegrated and transported to a crustal magma chamber as suspended grains. It is noted, however, that the podiform chromitites left in the mantle beneath the layered intrusions are different from most of the podiform chromitites now exposed in the ophiolites.

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Layered intrusions: Fundamentals, novel observations and concepts, and controversial issues

Latypov,

Namur,

Bai

et al. 2024

Earth-Science Reviews

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Genesis of chromite deposits by dynamic upgrading of Fe ± Ti oxide xenocrysts

Cited by 12 publications

References 34 publications

Chromitite layers require the existence of large, long-lived, and entirely molten magma chambers

Chromitite layers require the existence of large, long-lived, and entirely molten magma chambers

Genetic Link between Podiform Chromitites in the Mantle and Stratiform Chromitites in the Crust: A Hypothesis

Layered intrusions: Fundamentals, novel observations and concepts, and controversial issues

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