气候变化领域集成服务门户(CCPortal): Magnetic Cr-Rich Spinel in Serpentinized Ultramafic Complexes

CCPortal

DOI	10.1029/2020JB020443
	Magnetic Cr-Rich Spinel in Serpentinized Ultramafic Complexes
	Yu Y.; Tikoff B.
发表日期	2020
ISSN	21699313
卷号	125 期号:11
英文摘要	In comparison to the six spinel end-members in the spinel prism, magnetic information on the intermediate spinel compositions is relatively poorly established. To investigate magnetic properties of intermediate compositions of Cr-rich spinel, we collected 12 samples that might contain potentially magnetic Cr-rich spinel. On the basis of chemical composition analysis and physical magnetic behavior, magnetic Group A Fe-rich spinel (i.e., magnetite), magnetic Group B Cr-rich spinel, and paramagnetic Group C Cr-Al-rich spinel were identified. Magnetite is solely responsible for the natural remanent magnetization (NRM) in severely serpentinized samples from intraoceanic island arcs, orogenic exposures of ultramafics, and back-arc continental lithosphere settings. Magnetic Group B Cr-rich spinel shows maximum unblocking temperatures of 200–280°C. Such temperatures permit Cr-rich spinel to contribute to magnetic anomalies up to about 8–12 km in terrestrial lithosphere settings, given a normal geothermal gradient of 25 K/km. The existence of magnetic Cr-rich spinel requires certain compositional conditions including a cation ratio of [Cr]/[Fe2+ + Fe3+] from 1.33 to 1.56 as well as a low oxide ratio of (Al2O3 + MgO)/(Cr2O3 + FeO + Fe2O3) less than 10%. It is evident that compositions of spinels are related with the degree of serpentinization as Group A spinel is observed along the fractures between/among olivine grains in heavily serpentinized rocks. Spinels in Groups B and C seem to experience less severe metasomatic or hydrothermal alteration during serpentinization. Distribution of magnetic Cr-rich spinel along the fractures of silicates (mostly olivine) may support a chemical origin of the NRM. Thus, Cr-rich spinel is a potential NRM carrier and a source of magnetic anomalies in ultramafic complexes. ©2020. The Authors.
英文关键词	Cr-rich spinel; magnetite; serpentinization; spinel; ultramafic complexes
语种	英语
来源期刊	Journal of Geophysical Research: Solid Earth
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/187497
作者单位	Department of Geological Sciences, Chungnam National University, Daejeon, South Korea; Department of Geology and Geophysics, University of Wisconsin-Madison, Madison, WI, United States
推荐引用方式 GB/T 7714	Yu Y.,Tikoff B.. Magnetic Cr-Rich Spinel in Serpentinized Ultramafic Complexes[J],2020,125(11).
APA	Yu Y.,&Tikoff B..(2020).Magnetic Cr-Rich Spinel in Serpentinized Ultramafic Complexes.Journal of Geophysical Research: Solid Earth,125(11).
MLA	Yu Y.,et al."Magnetic Cr-Rich Spinel in Serpentinized Ultramafic Complexes".Journal of Geophysical Research: Solid Earth 125.11(2020).