scholarly journals Titanium isotopes constrain a magmatic transition at the Hadean-Archean boundary in the Acasta Gneiss Complex

2020 ◽  
Vol 6 (50) ◽  
pp. eabc9959
Author(s):  
Sarah M. Aarons ◽  
Jesse R. Reimink ◽  
Nicolas D. Greber ◽  
Andy W. Heard ◽  
Zhe Zhang ◽  
...  
Keyword(s):  
Magmatic Differentiation ◽  
Calc Alkaline ◽  
Slave Craton ◽  
Isotopic Compositions ◽  
Gneiss Complex ◽  
Deep Interior ◽  
Alkaline Magmas ◽  
Granitoid Gneisses ◽  
Physical And Chemical ◽  
Plate Subduction

Plate subduction greatly influences the physical and chemical characteristics of Earth’s surface and deep interior, yet the timing of its initiation is debated because of the paucity of exposed rocks from Earth’s early history. We show that the titanium isotopic composition of orthogneisses from the Acasta Gneiss Complex spanning the Hadean to Eoarchean transition falls on two distinct magmatic differentiation trends. Hadean tonalitic gneisses show titanium isotopic compositions comparable to modern evolved tholeiitic magmas, formed by differentiation of dry parental magmas in plume settings. Younger Eoarchean granitoid gneisses have titanium isotopic compositions comparable to modern calc-alkaline magmas produced in convergent arcs. Our data therefore document a shift from tholeiitic- to calc-alkaline–style magmatism between 4.02 and 3.75 billion years (Ga) in the Slave craton.

Buffering of melt oxygen fugacity by sulphur redox reactions in calc-alkaline magmas

1994 ◽  
Vol 151 (5) ◽  
pp. 815-823 ◽  
Author(s):  
S. J. MATTHEWS ◽  
A. P. JONES ◽  
A. D. BEARD
Keyword(s):  
Oxygen Fugacity ◽  
Redox Reactions ◽  
Calc Alkaline ◽  
Alkaline Magmas

Isotope-abundance variations of selected elements (IUPAC Technical Report)

2002 ◽  
Vol 74 (10) ◽  
pp. 1987-2017 ◽  
Author(s):  
Tyler B. Coplen ◽  
John Karl Böhlke ◽  
P. De Bièvre ◽  
T. Ding ◽  
N. E. Holden ◽  
...  
Keyword(s):  
Chemical Elements ◽  
Radioactive Decay ◽  
Atomic Weight ◽  
Chemical Fractionation ◽  
Isotope Abundance ◽  
Isotopic Compositions ◽  
Technical Report ◽  
Isotopic Abundances ◽  
Calcium Iron ◽  
Physical And Chemical

Documented variations in the isotopic compositions of some chemical elements are responsible for expanded uncertainties in the standard atomic weights published by the Commission on Atomic Weights and Isotopic Abundances of the International Union of Pure and Applied Chemistry. This report summarizes reported variations in the isotopic compositions of 20 elements that are due to physical and chemical fractionation processes (not due to radioactive decay) and their effects on the standard atomic-weight uncertainties. For 11 of those elements (hydrogen, lithium, boron, carbon, nitrogen, oxygen, silicon, sulfur, chlorine, copper, and selenium), standard atomic-weight uncertainties have been assigned values that are substantially larger than analytical uncertainties because of common isotope-abundance variations in materials of natural terrestrial origin. For 2 elements (chromium and thallium), recently reported isotope-abundance variations potentially are large enough to result in future expansion of their atomic-weight uncertainties. For 7 elements (magnesium, calcium, iron, zinc, molybdenum, palladium, and tellurium), documented isotope variations in materials of natural ter- restrial origin are too small to have a significant effect on their standard atomic-weight uncertainties. This compilation indicates the extent to which the atomic weight of an element in a given material may differ from the standard atomic weight of the element. For most elements given above, data are graphically illustrated by a diagram in which the materials are specified in the ordinate and the compositional ranges are plotted along the abscissa in scales of (1) atomic weight, (2) mole fraction of a selected isotope, and (3) delta value of a selected isotope ratio.

Sign in / Sign up

Export Citation Format

Share Document