Evaluating the paleomagnetic potential of single zircon crystals using the Bishop Tuff
Evaluating the paleomagnetic potential of single zircon crystals using the Bishop Tuff
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使用 Bishop Tuff 评估单锆石晶体的古地磁潜力
DOI：
10.1016/j.epsl.2016.09.038
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发表时间：
2017
影响因子：
5.3
通讯作者：
Harrison, Richard J.
中科院分区：
文献类型：
--
作者：
Fu, Roger R.;Weiss, Benjamin P.;Lima, Eduardo A.;Kehayias, Pauli;Araujo, Jefferson F.D.F.;Glenn, David R.;Gelb, Jeff;Einsle, Joshua F.;Bauer, Ann M.;Harrison, Richard J.
锆石晶体提供了适合高精度辐射测年和高抗蚀变性能的独特组合。对古老的锆石进行的古地磁实验可能会限制最早的地球发电机的历史，这将对早期地球内部和大气产生广泛的影响。然而，锆石准确记录地磁场的能力还没有得到证实。在这里，我们对加利福尼亚州毕晓普凝灰岩中767.1年前的锆石进行了热和交变磁场(AF)古强度实验。这些锆石在特征良好的磁场中的快速就位为锆石固有的古地磁记录精度提供了高保真测试。利用超导量子干涉仪(SQUID)对11块锆石进行了成功的双重加热实验，获得的平均古强度为54.1±6.8μT(1σ；排除可能含磁赤铁矿的锆石后为42.6±5.3μT)，这与毕晓普凝灰岩全岩的高精度结果(43.0±3.2μT)一致。高分辨率量子金刚石磁(QDM)图、电子显微镜和X射线层析成像表明，毕晓普凝灰石锆石中的大部分剩余磁化强度是由与磷灰石包裹体共生的铁氧化物携带的，在较老的锆石中，这种氧化物可能容易通过变质作用和水蚀变而破坏。因此，虽然锆石可以可靠地记录地磁场，但从锆石获得的可靠的古地磁结果需要仔细描述铁磁载体并证明它们在原生包裹体中的存在。我们进一步得出结论，量子钻石磁测量和高分辨率成像的结合可以提供地质样品的铁磁矿物学的详细、直接的表征。
Zircon crystals offer a unique combination of suitability for high-precision radiometric dating and high resistance to alteration. Paleomagnetic experiments on ancient zircons may potentially constrain the history of the earliest geodynamo, which would hold broad implications for the early Earth's interior and atmosphere. However, the ability of zircons to record accurately the geomagnetic field has not been demonstrated. Here we conduct thermal and alternating field (AF) paleointensity experiments on 767.1 thousand year old (ka) zircons from the Bishop Tuff, California. The rapid emplacement of these zircons in a well-characterized magnetic field provides a high-fidelity test of the zircons' intrinsic paleomagnetic recording accuracy. Successful dual heating experiments on eleven zircons measured using a superconducting quantum interference device (SQUID) microscope yield a mean paleointensity of 54.1±6.8 μT (1σ; 42.6±5.3 μT after excluding possible maghemite-bearing zircons), which is consistent with high-precision results from Bishop Tuff whole rock (43.0±3.2 μT). High-resolution quantum diamond magnetic (QDM) mapping, electron microscopy, and X-ray tomography indicate that the bulk of the remanent magnetization in Bishop Tuff zircons is carried by Fe oxides associated with apatite inclusions, which may be susceptible to destruction via metamorphism and aqueous alteration in older zircons. As such, while zircons can reliably record the geomagnetic field, robust zircon-derived paleomagnetic results require careful characterization of the ferromagnetic carrier and demonstration of their occurrence in primary inclusions. We further conclude that a combination of quantum diamond magnetometry and high-resolution imaging can provide detailed, direct characterization of the ferromagnetic mineralogy of geological samples.