1
|
Kuppili VSC, Ball M, Batey D, Dodds K, Cipiccia S, Wanelik K, Fu R, Rau C, Harrison RJ. Nanoscale imaging of Fe-rich inclusions in single-crystal zircon using X-ray ptycho-tomography. Sci Rep 2024; 14:5139. [PMID: 38429500 PMCID: PMC10907758 DOI: 10.1038/s41598-024-55846-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2023] [Accepted: 02/28/2024] [Indexed: 03/03/2024] Open
Abstract
We apply X-ray ptycho-tomography to perform high-resolution, non-destructive, three-dimensional (3D) imaging of Fe-rich inclusions in paleomagnetically relevant materials (zircon single crystals from the Bishop Tuff ignimbrite). Correlative imaging using quantum diamond magnetic microscopy combined with X-ray fluorescence mapping was used to locate regions containing potential ferromagnetic remanence carriers. Ptycho-tomographic reconstructions with voxel sizes 85 nm and 21 nm were achievable across a field-of-view > 80 µm; voxel sizes as small as 5 nm were achievable over a limited field-of-view using local ptycho-tomography. Fe-rich inclusions 300 nm in size were clearly resolved. We estimate that particles as small as 100 nm-approaching single-domain threshold for magnetite-could be resolvable using this "dual-mode" methodology. Fe-rich inclusions (likely magnetite) are closely associated with apatite inclusions that have no visible connection to the exterior surface of the zircon (e.g., via intersecting cracks). There is no evidence of radiation damage, alteration, recrystallisation or deformation in the host zircon or apatite that could provide alternative pathways for Fe infiltration, indicating that magnetite and apatite grew separately as primary phases in the magma, that magnetite adhered to the surfaces of the apatite, and that the magnetite-coated apatite was then encapsulated as primary inclusions within the growing zircon. Rarer examples of Fe-rich inclusions entirely encapsulated by zircon are also observed. These observations support the presence of primary inclusions in relatively young and pristine zircon crystals. Combining magnetic and tomography results we deduce the presence of magnetic carriers that are in the optimal size range for carrying strong and stable paleomagnetic signals but that remain below the detection limits of even the highest-resolution X-ray tomography reconstructions. We recommend the use of focused ion beam nanotomography and/or correlative transmission electron microscopy to directly confirm the presence of primary magnetite in the sub 300 nm range as a necessary step in targeted paleomagnetic workflows.
Collapse
Affiliation(s)
- Venkata S C Kuppili
- Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK.
- Canadian Light Source, University of Saskatchewan, 44 Innovation Boulevard, Saskatoon, SK, S7N 2V3, Canada.
| | - Matthew Ball
- Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK
| | - Darren Batey
- Diamond Light Source, Harwell Campus, Didcot, OX11 0DE, UK
| | - Kathryn Dodds
- Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK
| | - Silvia Cipiccia
- Diamond Light Source, Harwell Campus, Didcot, OX11 0DE, UK
- Department of Medical Physics and Biomedical Engineering, University College London, Gower St, London, WC1E 6BT, UK
| | - Kaz Wanelik
- Diamond Light Source, Harwell Campus, Didcot, OX11 0DE, UK
| | - Roger Fu
- Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, 02138, USA
| | - Christoph Rau
- Diamond Light Source, Harwell Campus, Didcot, OX11 0DE, UK
| | - Richard J Harrison
- Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK
| |
Collapse
|
2
|
Tarduno JA, Cottrell RD, Bono RK, Rayner N, Davis WJ, Zhou T, Nimmo F, Hofmann A, Jodder J, Ibañez-Mejia M, Watkeys MK, Oda H, Mitra G. Hadaean to Palaeoarchaean stagnant-lid tectonics revealed by zircon magnetism. Nature 2023; 618:531-536. [PMID: 37316722 PMCID: PMC10266976 DOI: 10.1038/s41586-023-06024-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/08/2022] [Accepted: 03/27/2023] [Indexed: 06/16/2023]
Abstract
Plate tectonics is a fundamental factor in the sustained habitability of Earth, but its time of onset is unknown, with ages ranging from the Hadaean to Proterozoic eons1-3. Plate motion is a key diagnostic to distinguish between plate and stagnant-lid tectonics, but palaeomagnetic tests have been thwarted because the planet's oldest extant rocks have been metamorphosed and/or deformed4. Herein, we report palaeointensity data from Hadaean-age to Mesoarchaean-age single detrital zircons bearing primary magnetite inclusions from the Barberton Greenstone Belt of South Africa5. These reveal a pattern of palaeointensities from the Eoarchaean (about 3.9 billion years ago (Ga)) to Mesoarchaean (about 3.3 Ga) eras that is nearly identical to that defined by primary magnetizations from the Jack Hills (JH; Western Australia)6,7, further demonstrating the recording fidelity of select detrital zircons. Moreover, palaeofield values are nearly constant between about 3.9 Ga and about 3.4 Ga. This indicates unvarying latitudes, an observation distinct from plate tectonics of the past 600 million years (Myr) but predicted by stagnant-lid convection. If life originated by the Eoarchaean8, and persisted to the occurrence of stromatolites half a billion years later9, it did so when Earth was in a stagnant-lid regime, without plate-tectonics-driven geochemical cycling.
Collapse
Affiliation(s)
- John A Tarduno
- Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY, USA.
- Department of Physics and Astronomy, University of Rochester, Rochester, NY, USA.
- Laboratory for Laser Energetics, University of Rochester, Rochester, NY, USA.
- Geological Sciences, University of KwaZulu-Natal, Durban, South Africa.
| | - Rory D Cottrell
- Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY, USA
| | - Richard K Bono
- Geomagnetism Laboratory, University of Liverpool, Liverpool, UK
- Department of Earth, Ocean and Atmospheric Science, Florida State University, Tallahassee, FL, USA
| | - Nicole Rayner
- Natural Resources Canada, Geological Survey of Canada, Ottawa, Ontario, Canada
| | - William J Davis
- Natural Resources Canada, Geological Survey of Canada, Ottawa, Ontario, Canada
| | - Tinghong Zhou
- Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY, USA
| | - Francis Nimmo
- Department of Earth and Planetary Sciences, University of California, Santa Cruz, Santa Cruz, CA, USA
| | - Axel Hofmann
- Department of Geology, University of Johannesburg, Auckland Park, South Africa
| | - Jaganmoy Jodder
- Department of Geology, University of Johannesburg, Auckland Park, South Africa
- Evolutionary Studies Institute, University of the Witwatersrand, Wits, South Africa
| | | | - Michael K Watkeys
- Geological Sciences, University of KwaZulu-Natal, Durban, South Africa
| | - Hirokuni Oda
- Research Institute of Geology and Geoinformation, Geological Survey of Japan, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan
| | - Gautam Mitra
- Department of Earth and Environmental Sciences, University of Rochester, Rochester, NY, USA
| |
Collapse
|
3
|
Taylor RJ, Reddy SM, Saxey DW, Rickard WD, Tang F, Borlina CS, Fu RR, Weiss BP, Bagot P, Williams HM, Harrison RJ. Direct age constraints on the magnetism of Jack Hills zircon. SCIENCE ADVANCES 2023; 9:eadd1511. [PMID: 36608136 PMCID: PMC9821853 DOI: 10.1126/sciadv.add1511] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/25/2022] [Accepted: 12/06/2022] [Indexed: 06/16/2023]
Abstract
A potential record of Earth's magnetic field going back 4.2 billion years (Ga) ago is carried by magnetite inclusions in zircon grains from the Jack Hills. This magnetite may be secondary in nature, however, meaning that the magnetic record is much younger than the zircon crystallization age. Here, we use atom probe tomography to show that Pb-bearing nanoclusters in magnetite-bearing Jack Hills zircons formed during two discrete events at 3.4 and <2 Ga. The older population of clusters contains no detectable Fe, whereas roughly half of the younger population of clusters is Fe bearing. This result shows that the Fe required to form secondary magnetite entered the zircon sometime after 3.4 Ga and that remobilization of Pb and Fe during an annealing event occurred more than 1 Ga after deposition of the Jack Hills sediment at 3 Ga. The ability to date Fe mobility linked to secondary magnetite formation provides new possibilities to improve our knowledge of the Archean geodynamo.
Collapse
Affiliation(s)
- Richard J. M. Taylor
- Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
| | - Steven M. Reddy
- School of Earth and Planetary Sciences, Curtin University, Bentley, WA 6102, Australia
- Geoscience Atom Probe Facility, John de Laeter Centre, Curtin University, Bentley, WA 6102, Australia
| | - David W. Saxey
- School of Earth and Planetary Sciences, Curtin University, Bentley, WA 6102, Australia
- Geoscience Atom Probe Facility, John de Laeter Centre, Curtin University, Bentley, WA 6102, Australia
| | - William D. A. Rickard
- School of Earth and Planetary Sciences, Curtin University, Bentley, WA 6102, Australia
- Geoscience Atom Probe Facility, John de Laeter Centre, Curtin University, Bentley, WA 6102, Australia
| | - Fengzai Tang
- Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
| | - Cauê S. Borlina
- Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Roger R. Fu
- Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA
| | - Benjamin P. Weiss
- Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA
| | - Paul Bagot
- Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, UK
| | - Helen M. Williams
- Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
| | - Richard J. Harrison
- Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge CB2 3EQ, UK
| |
Collapse
|
4
|
Amor M, Wan J, Egli R, Carlut J, Gatel C, Andersen IM, Snoeck E, Komeili A. Key Signatures of Magnetofossils Elucidated by Mutant Magnetotactic Bacteria and Micromagnetic Calculations. JOURNAL OF GEOPHYSICAL RESEARCH. SOLID EARTH 2022; 127:e2021JB023239. [PMID: 35444924 PMCID: PMC9017866 DOI: 10.1029/2021jb023239] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 09/15/2021] [Revised: 11/30/2021] [Accepted: 12/14/2021] [Indexed: 06/14/2023]
Abstract
Magnetotactic bacteria (MTB) produce single-stranded or multi-stranded chains of magnetic nanoparticles that contribute to the magnetization of sediments and rocks. Their magnetic fingerprint can be detected in ancient geological samples and serve as a unique biosignature of microbial life. However, some fossilized assemblages bear contradictory signatures pointing to magnetic components that have distinct origin(s). Here, using micromagnetic simulations and mutant MTB producing looped magnetosome chains, we demonstrate that the observed magnetofossil fingerprints are produced by a mixture of single-stranded and multi-stranded chains, and that diagenetically induced chain collapse, if occurring, must preserve the strong uniaxial anisotropy of native chains. This anisotropy is the key factor for distinguishing magnetofossils from other populations of natural magnetite particles, including those with similar individual crystal characteristics. Furthermore, the detailed properties of magnetofossil signatures depend on the proportion of equant and elongated magnetosomes, as well as on the relative abundances of single-stranded and multi-stranded chains. This work has important paleoclimatic, paleontological, and phylogenetic implications, as it provides reference data to differentiate distinct MTB lineages according to their chain and magnetosome morphologies, which will enable the tracking of the evolution of some of the most ancient biomineralizing organisms in a time-resolved manner. It also enables a more accurate discrimination of different sources of magnetite particles, which is pivotal for gaining better environmental and relative paleointensity reconstructions from sedimentary records.
Collapse
Affiliation(s)
- Matthieu Amor
- Department of Plant and Microbial BiologyUniversity of CaliforniaBerkeleyCAUSA
- Aix‐Marseille Université, CEA, CNRS, BIAMSaint‐Paul‐lez‐DuranceFrance
| | - Juan Wan
- Department of Plant and Microbial BiologyUniversity of CaliforniaBerkeleyCAUSA
| | - Ramon Egli
- Zentralanstalt für Meteorologie und Geodynamik (ZAMG)ViennaAustria
- Université de Paris, Institut de Physique du Globe de Paris, CNRSParisFrance
| | - Julie Carlut
- Université de Paris, Institut de Physique du Globe de Paris, CNRSParisFrance
| | | | | | | | - Arash Komeili
- Department of Plant and Microbial BiologyUniversity of CaliforniaBerkeleyCAUSA
- Department of Molecular and Cell BiologyUniversity of CaliforniaBerkeleyCAUSA
| |
Collapse
|
5
|
Resonance in Chirogenesis and Photochirogenesis: Colloidal Polymers Meet Chiral Optofluidics. Symmetry (Basel) 2021. [DOI: 10.3390/sym13020199] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Metastable colloids made of crystalline and/or non-crystalline matters render abilities of photonic resonators susceptible to chiral chemical and circularly polarized light sources. By assuming that μm-size colloids and co-colloids consisting of π- and/or σ-conjugated polymers dispersed into an optofluidic medium are artificial models of open-flow, non-equilibrium coacervates, we showcase experimentally resonance effects in chirogenesis and photochirogenesis, revealed by gigantic boosted chiroptical signals as circular dichroism (CD), optical rotation dispersion, circularly polarized luminescence (CPL), and CPL excitation (CPLE) spectral datasets. The resonance in chirogenesis occurs at very specific refractive indices (RIs) of the surrounding medium. The chirogenesis is susceptible to the nature of the optically active optofluidic medium. Moreover, upon an excitation-wavelength-dependent circularly polarized (CP) light source, a fully controlled absolute photochirogenesis, which includes all chiroptical generation, inversion, erase, switching, and short-/long-lived memories, is possible when the colloidal non-photochromic and photochromic polymers are dispersed in an achiral optofluidic medium with a tuned RI. The hand of the CP light source is not a determining factor for the product chirality. These results are associated with my experience concerning amphiphilic polymerizable colloids, in which, four decades ago, allowed proposing a perspective that colloids are connectable to light, polymers, helix, coacervates, and panspermia hypotheses, nuclear physics, biology, radioisotopes, homochirality question, first life, and cosmology.
Collapse
|
6
|
Borlina CS, Weiss BP, Lima EA, Tang F, Taylor RJM, Einsle JF, Harrison RJ, Fu RR, Bell EA, Alexander EW, Kirkpatrick HM, Wielicki MM, Harrison TM, Ramezani J, Maloof AC. Reevaluating the evidence for a Hadean-Eoarchean dynamo. SCIENCE ADVANCES 2020; 6:eaav9634. [PMID: 32284988 PMCID: PMC7141829 DOI: 10.1126/sciadv.aav9634] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 11/05/2018] [Accepted: 12/19/2019] [Indexed: 06/11/2023]
Abstract
The time of origin of the geodynamo has important implications for the thermal evolution of the planetary interior and the habitability of early Earth. It has been proposed that detrital zircon grains from Jack Hills, Western Australia, provide evidence for an active geodynamo as early as 4.2 billion years (Ga) ago. However, our combined paleomagnetic, geochemical, and mineralogical studies on Jack Hills zircons indicate that most have poor magnetic recording properties and secondary magnetization carriers that postdate the formation of the zircons. Therefore, the existence of the geodynamo before 3.5 Ga ago remains unknown.
Collapse
Affiliation(s)
- Cauê S. Borlina
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology (MIT), Cambridge, MA, USA
| | - Benjamin P. Weiss
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology (MIT), Cambridge, MA, USA
| | - Eduardo A. Lima
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology (MIT), Cambridge, MA, USA
| | - Fengzai Tang
- Department of Earth Sciences, University of Cambridge, Cambridge, UK
| | | | - Joshua F. Einsle
- Department of Earth Sciences, University of Cambridge, Cambridge, UK
- Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, UK
- Department of Earth Science and Engineering, Imperial College London, London, UK
| | | | - Roger R. Fu
- Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA
| | - Elizabeth A. Bell
- Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, CA, USA
| | - Ellen W. Alexander
- Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, CA, USA
| | - Heather M. Kirkpatrick
- Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, CA, USA
| | - Matthew M. Wielicki
- Department of Geological Sciences, University of Alabama, Tuscaloosa, AL, USA
| | - T. Mark Harrison
- Department of Earth, Planetary, and Space Sciences, University of California, Los Angeles, Los Angeles, CA, USA
| | - Jahandar Ramezani
- Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology (MIT), Cambridge, MA, USA
| | - Adam C. Maloof
- Department of Geosciences, Princeton University, Princeton, NJ, USA
| |
Collapse
|
7
|
Abstract
The Earth’s magnetic field has operated for at least 3.4 billion years, yet how the ancient field was produced is still unknown. The core in the early Earth was surrounded by a molten silicate layer, a basal magma ocean that may have survived for more than one billion years. Here we use density functional theory-based molecular dynamics simulations to predict the electrical conductivity of silicate liquid at the conditions of the basal magma ocean: 100–140 GPa, and 4000–6000 K. We find that the electrical conductivity exceeds 10,000 S/m, more than 100 times that measured in silicate liquids at low pressure and temperature. The magnetic Reynolds number computed from our results exceeds the threshold for dynamo activity and the magnetic field strength is similar to that observed in the Archean paleomagnetic record. We therefore conclude that the Archean field was produced by the basal magma ocean. Cooling of the iron core in the early Earth may have been too slow to allow for the generation of a magnetic field. Based on quantum mechanical and geodynamical modelling approaches, the authors find that the electrical conductivity of silicate liquid at high pressure and temperature conditions could have been sufficient to generate a silicate dynamo and a magnetic field in the early Earth.
Collapse
|
8
|
Paleomagnetism indicates that primary magnetite in zircon records a strong Hadean geodynamo. Proc Natl Acad Sci U S A 2020; 117:2309-2318. [PMID: 31964848 PMCID: PMC7007582 DOI: 10.1073/pnas.1916553117] [Citation(s) in RCA: 31] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The age and early history of Earth’s geomagnetic field can provide insight into the evolution of the core and atmosphere. But measurement of Hadean zircons—the oldest known terrestrial materials—and the determination of the antiquity of their magnetizations are amongst the most challenging endeavors in paleomagnetism. New paleomagnetic, electron microscope, geochemical, and paleointensity data indicate the presence of primary magnetite inclusions in select zircons. These data support the presence of the geomagnetic field, and associated shielding of the atmosphere from the solar wind, ∼4.2 billion years ago. A relatively strong field recorded by these zircons at ∼4 billion years ago may be a signal that chemical precipitation in the core was powering the geodynamo. Determining the age of the geomagnetic field is of paramount importance for understanding the evolution of the planet because the field shields the atmosphere from erosion by the solar wind. The absence or presence of the geomagnetic field also provides a unique gauge of early core conditions. Evidence for a geomagnetic field 4.2 billion-year (Gy) old, just a few hundred million years after the lunar-forming giant impact, has come from paleomagnetic analyses of zircons of the Jack Hills (Western Australia). Herein, we provide new paleomagnetic and electron microscope analyses that attest to the presence of a primary magnetic remanence carried by magnetite in these zircons and new geochemical data indicating that select Hadean zircons have escaped magnetic resetting since their formation. New paleointensity and Pb-Pb radiometric age data from additional zircons meeting robust selection criteria provide further evidence for the fidelity of the magnetic record and suggest a period of high geomagnetic field strength at 4.1 to 4.0 billion years ago (Ga) that may represent efficient convection related to chemical precipitation in Earth’s Hadean liquid iron core.
Collapse
|
9
|
|
10
|
Zircon at the Nanoscale Records Metasomatic Processes Leading to Large Magmatic–Hydrothermal Ore Systems. MINERALS 2019. [DOI: 10.3390/min9060364] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The petrography and geochemistry of zircon offers an exciting opportunity to better understand the genesis of, as well as identify pathfinders for, large magmatic–hydrothermal ore systems. Electron probe microanalysis, laser ablation inductively coupled plasma mass spectrometry, high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) imaging, and energy-dispersive X-ray spectrometry STEM mapping/spot analysis were combined to characterize Proterozoic granitic zircon in the eastern Gawler Craton, South Australia. Granites from the ~1.85 Ga Donington Suite and ~1.6 Ga Hiltaba Suite were selected from locations that are either mineralized or not, with the same style of iron-oxide copper gold (IOCG) mineralization. Although Donington Suite granites are host to mineralization in several prospects, only Hiltaba Suite granites are considered “fertile” in that their emplacement at ~1.6 Ga is associated with generation of one of the best metal-endowed IOCG provinces on Earth. Crystal oscillatory zoning with respect to non-formula elements, notably Fe and Cl, are textural and chemical features preserved in zircon, with no evidence for U or Pb accumulation relating to amorphization effects. Bands with Fe and Ca show mottling with respect to chloro–hydroxy–zircon nanoprecipitates. Lattice defects occur along fractures crosscutting such nanoprecipitates indicating fluid infiltration post-mottling. Lattice stretching and screw dislocations leading to expansion of the zircon structure are the only nanoscale structures attributable to self-induced irradiation damage. These features increase in abundance in zircons from granites hosting IOCG mineralization, including from the world-class Olympic Dam Cu–U–Au–Ag deposit. The nano- to micron-scale features documented reflect interaction between magmatic zircon and corrosive Fe–Cl-bearing fluids in an initial metasomatic event that follows magmatic crystallization and immediately precedes deposition of IOCG mineralization. Quantification of α-decay damage that could relate zircon alteration to the first percolation point in zircon gives ~100 Ma, a time interval that cannot be reconciled with the 2–4 Ma period between magmatic crystallization and onset of hydrothermal fluid flow. Crystal oscillatory zoning and nanoprecipitate mottling in zircon intensify with proximity to mineralization and represent a potential pathfinder to locate fertile granites associated with Cu–Au mineralization.
Collapse
|