Evidence for evolved Hadean crust from Sr isotopes in apatite within Eoarchean zircon from the Acasta Gneiss Complex

Emo, Robert B.; Smit, Matthijs; Kielman‐Schmitt, Melanie; Kooijman, Ellen; Scherer, Erik E.; Sprung, P.; Bleeker, Wouter; Mezger, Klaus

doi:10.1016/j.gca.2018.05.028

Cited by 41 publications

(26 citation statements)

References 46 publications

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“…Wash-out and ablation times were both 45 s. The 87 Sr- 86 Sr ratios were corrected for potential isobaric interferences such as 87 Rb or doubly charged REEs through peak-stripping. A detailed description of the correction protocol, which is identical for the analysis of Sr in apatite, can be found in Emo et al [68]. The corrected 87 Sr/ 86 Sr values are normalized to an in-house brachiopod reference material "Ecnomiosa gerda" (linear drift and accuracy correction) using a value established by Thermal Ionization Mass Spectrometry (TIMS) of 0.709168 (2sd 0.000004, [69]).…”

Section: Methodsmentioning

confidence: 99%

Using 87Sr/86Sr LA-MC-ICP-MS Transects within Modern and Ancient Calcite Crystals to Determine Fluid Flow Events in Deep Granite Fractures

2020

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The strontium isotope signature (87Sr/86Sr) of calcite precipitated in rock fractures and faults is a frequently used tool to trace paleofluid flow. However, bedrock fracture networks, such as in Precambrian cratons, have often undergone multiple fracture reactivations resulting in complex sequences of fracture mineral infillings. This includes numerous discrete calcite crystal overgrowths. Conventional 87Sr/86Sr analysis of dissolved bulk samples of such crystals is not feasible as they will result in mixed signatures of several growth zonations. In addition, the zonations are too fine-grained for sub-sampling using micro-drilling. Here, we apply high spatial resolution 87Sr/86Sr spot analysis (80 µm) in transects through zoned calcite crystals in deep Paleoproterozoic granitoid fractures using laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) to trace discrete signs of paleofluid flow events. We compare the outermost calcite growth zone with 87Sr/86Sr values of the present-day groundwater sampled in the same boreholes to distinguish potential modern precipitates. We then connect our results to previously reported radiometric dating and C and O isotope signatures to understand the temporal history and physicochemical evolution of fluid flow within the fractures. Comparisons of modern calcite precipitated in a borehole over a period of 17 years with modern waters prove the concept of using 87Sr/86Sr as a marker for fluid origin in this environment and for how 87Sr/86Sr changed during marine water infiltration. Intermittent calcite precipitation over very long time spans is indicated in calcite of the currently open fractures, showing an evolution of 87Sr/86Sr from ~0.705–0.707—a population dated to ~1.43 billion years—to crystal overgrowth values at ~0.715–0.717 that overlap with the present-day groundwater values. This shows that high spatial resolution Sr isotope analysis of fine-scaled growth zonation within single calcite crystals is applicable for tracing episodic fluid flow in fracture networks.

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Section: Methodsmentioning

confidence: 99%

Using 87Sr/86Sr LA-MC-ICP-MS Transects within Modern and Ancient Calcite Crystals to Determine Fluid Flow Events in Deep Granite Fractures

2020

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“…9). This means that host-zircons satisfactorily isolated apatite inclusions from external fluids possibly bringing common Pb, which accounts for both the resetting of U-Pb ages, the existence of reversely discordant U-Pb data and the fact that Sr isotope data for apatite inclusions from Emo et al (2018) are less radiogenic than those in the matrix despite zircons showing advanced radiation damage in CL images. If external fluids were to penetrate within zircon, apatite Sr isotope composition should be influenced by the fluids, which are more radiogenic.…”

Section: Apatite Inclusionsmentioning

confidence: 89%

“…The earliest magmatic events that occurred in the AGC had been dated between 3962 ± 3 (Bowring et al, 1989) and 4031 ± 3 Ma (Bowring and Williams, 1999), and recently revised to 4019.6 ± 1.8 Ma by (Reimink et al, 2016b) The AGC, therefore, hosts Earth's oldest rocks but also exhibits evidence for a crustal pre-history as argued by the presence of a 4200 Ma inherited zircon core (Iizuka et al, 2006) and by signatures of both short-and long-lived isotope systematics (e.g., Bowring and Housh 1995;Iizuka and Hirata 2005;Iizuka et al, 2009;Guitreau et al, 2014;Mojzsis et al, 2014;Roth et al, 2014;Bauer et al, 2017;Emo et al, 2018;Reimink et al, 2018);…”

Section: Geological Background and Sample Descriptionmentioning

confidence: 99%

“…One way to overcome this limitation is to study apatite inclusions armored within zircon and, thus, combine the potential of apatite in retrieving magmatic information with the resilience of zircon to metamorphic processes. Previous workers have shown that zircon-hosted apatite inclusions can indeed retain important information about its host-rock (Jennings et al, 2011;Bruand et al, 2016;Emo et al, 2018). For instance, Bruand et al (2016) have studied an unmetamorphosed suite of granitoids and showed that zirconhosted inclusions shared the same trace element signatures as cogenetic apatite crystals within the matrix.…”

Section: Introductionmentioning

confidence: 99%

“…Very recently, Emo et al (2018) demonstrated that zircon-hosted and matrix apatite crystals in two 3.6-3.7 Ga orthogneisses from the Acasta Gneiss Complex (AGC, Canada) exhibit a general discrepancy in their Sr isotope signatures. The authors interpreted the Sr isotopic signature in apatite inclusions as the first direct estimate of initial 87 Sr/ 86 Sr for these ancient rocks whereas Sr isotope signatures in matrix apatite were reset during later metamorphic event.…”

Section: Introductionmentioning

confidence: 99%

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Understanding preservation of primary signatures in apatite by comparing matrix and zircon-hosted crystals from the Eoarchean Acasta Gneiss Complex (Canada)

Bruand¹,

Antoine²,

Guitreau³

et al. 2020

Preprint

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<p>A novel way to investigate the petrogenesis of ancient poly-metamorphosed terranes is to use zircon as a vessel and study protected mineral inclusions which are sensitive to melt evolution such as apatite. Recent contributions have shown that zircon-hosted apatite inclusions of unmetamorphosed granitoids can provide valuable petrogenetic information about a given pluton and, in turn, represent a way to circumvent effects of metamorphism. Yet, the impact of metamorphism on apatite inclusion has never been studied in detail. To address the issue of chemical and isotopic preservation of primary signals in apatite crystals both in the matrix and armored within zircons, we have studied apatite crystals from four 3.6-4.0 Ga orthogneisses of TTG affinity from the Acasta Gneiss Complex (Canada). Our results demonstrate that U-Th-Pb isotope systematics in matrix apatite crystals are reset at the time of the Wopmay orogen (1.8-1.7 Ga) whereas primary REE signatures were preserved in many crystals. On the contrary, zircon-hosted apatite inclusions all preserved primary REE signatures despite U-Th-Pb isotope systematics giving ages between 1.7 and 4.0 Ga. We interpret the variable resetting of these ages as a consequence of radiation damage accumulation in zircon lattice. Only the most pristine zircon has an apatite inclusion with a concordant age consistent with the magmatic age of the zircon (4.0 Ga). In addition, our results show that apatite crystals from TTG have distinct REE composition from post-Archean granitoids apatites, and that even apatites with reset ages preserved some of the chemical signatures characterizing TTG compositions (e.g. HREE). This capacity to retain primary information together with its discriminating power for granitoids makes apatite a very valuable tool for reconstructing the nature and evolution of ancient crustal rocks through the use of either detrital minerals or detrital-zircon hosting inclusions.</p>

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Unravelling the processes controlling apatite formation in the Phalaborwa Complex (South Africa) based on combined cathodoluminescence, LA-ICPMS and in-situ O and Sr isotope analyses

Decrée

Cawthorn

Deloule

et al. 2020

Contrib Mineral Petrol

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Evidence for evolved Hadean crust from Sr isotopes in apatite within Eoarchean zircon from the Acasta Gneiss Complex

Cited by 41 publications

References 46 publications

Using 87Sr/86Sr LA-MC-ICP-MS Transects within Modern and Ancient Calcite Crystals to Determine Fluid Flow Events in Deep Granite Fractures

Using 87Sr/86Sr LA-MC-ICP-MS Transects within Modern and Ancient Calcite Crystals to Determine Fluid Flow Events in Deep Granite Fractures

Understanding preservation of primary signatures in apatite by comparing matrix and zircon-hosted crystals from the Eoarchean Acasta Gneiss Complex (Canada)

Unravelling the processes controlling apatite formation in the Phalaborwa Complex (South Africa) based on combined cathodoluminescence, LA-ICPMS and in-situ O and Sr isotope analyses

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