Geochronology of Layered Intrusions

2015 ◽  
pp. 3-74 ◽  
Author(s):  
James S. Scoates ◽  
Corey J. Wall
Keyword(s):  
Layered Intrusions

Concentration of platinum-group elements by magmatic fluids in layered intrusions

1992 ◽  
Vol 87 (7) ◽  
pp. 1830-1848 ◽  
Author(s):  
A. E. Boudreau ◽  
I. S. McCallum
Keyword(s):  
Platinum Group Elements ◽  
Layered Intrusions ◽  
Magmatic Fluids ◽  
Platinum Group

Order of Abundant Crystal Nucleation in a Natural Magma

1967 ◽  
Vol 104 (5) ◽  
pp. 473-486 ◽  
Author(s):  
D. D. Hawkes
Keyword(s):  
Equilibrium Temperature ◽  
High Index ◽  
Crystal Nucleation ◽  
Layered Intrusions ◽  
Slight Amount ◽  
Primary Minerals

ABSTRACTRhythmic layering in the Freetown Complex and in some other layered intrusions may be due to the different powers of nucleation of the primary minerals from an undercooled magma. It is suggested that, in slowly cooled intrusions, the total number of crystals per cm3 in a rock (whole rock index) is a measure of the amount of undercooling; rocks with a low whole rock index crystallized at or near the equilibrium temperature while rocks with a high index crystallized under conditions of undercooling. If this is so, then it is possible to determine the order of abundant nucleation of the primary minerals by graphical means. Only a slight amount of undercooling, perhaps of the order of 4 or 5° C, is necessary to produce marked changes in the order of separation of the minerals from the magma.

The Formation of Stratiform PGE Deposits in Layered Intrusions

1987 ◽  
pp. 313-397 ◽  
Author(s):  
A. J. Naldrett ◽  
G. Cameron ◽  
G. Gruenewaldt ◽  
M. R. Sharpe
Keyword(s):  
Layered Intrusions

Misinterpretation of zircon ages in layered intrusions

2021 ◽  
Author(s):  
R. Latypov ◽  
S. Chistyakova
Keyword(s):  
Phase Equilibria ◽  
High Precision ◽  
Bushveld Complex ◽  
Classical Model ◽  
Layered Intrusions ◽  
Isotopic Data ◽  
Magma Chambers ◽  
Stratigraphic Position

Abstract A recent re-interpretation of the Bushveld Complex and other layered intrusions as stacks of randomly emplaced, amalgamated sills is mostly fuelled by finding of zircon ages that are not getting progressively younger from the base upwards, as expected from a classical model for the formation of layered intrusions. Rather, they display several reversals from older to younger ages and vice-versa with moving up-section through the layered intrusions. Here, we show that the reported zircon ages are at odds with the relative ages of rocks as defined by cross-cutting relations in potholes of the Bushveld Complex. This indicates that interpretation of the zircon isotopic data as the emplacement age of the studied rocks/units is incorrect, making a new emplacement model for layered intrusions baseless. This conclusion is further buttressed by the phase equilibria analysis showing that regular cumulate sequences of layered intrusions are not reconcilable with a model of randomly emplaced sills. In this model, the late sills are free to intrude at any stratigraphic position of the pre-existing rocks, producing magmatic bodies with chaotic crystallization sequences and mineral compositional trends that are never observed in layered intrusions. There are thus no valid justifications for the re-evaluation of the current petrological model of the Bushveld Complex and other layered intrusions as large, long-lived and largely molten magma chambers. A fundamental implication of this analysis is that the current high-precision U-Pb TIMS ages from layered intrusions are inherently unreliable on the scale of several million years and cannot therefore be used for rigorous estimations of the timing of crystallization, duration of magmatism, and cooling of these intrusions.

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