Modification of the magnetic mineralogy in basalts due to fluid-rock interactions in a high-temperature geothermal system (Krafla, Iceland)

Oliva‐Urcia, Belén; Kontny, Agnes; Vahle, C.; Schleicher, Anja M.

doi:10.1111/j.1365-246x.2011.05029.x

Cited by 26 publications

(24 citation statements)

References 72 publications

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“…The lack of correlation between the applied field and AMS in the Lonar basalt is primarily due to the low-temperature hydrothermal alteration of titanomagnetite into titanomaghemite (cf. Oliva-Urcia et al, 2011). Variations in the magnetic domain size, as observed in the Lonar basalts, lead to differences in their magnetic hardness (Fig.…”

Section: Magnetic Mineralogy and The Origin Of Magnetic Properties Inmentioning

confidence: 83%

Shock pressure estimates in target basalts of a pristine crater: A case study in the Lonar crater, India

Agarwal

Kontny

Srivastava

et al. 2015

Geological Society of America Bulletin

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The study of shock pressure indicators can provide important clues for understanding the cratering process, though the estimation of shock pressures in weakly shocked rocks is commonly difficult. In this study, we selected a very young and well-preserved impact structure, the Lonar crater in India. The crater, devoid of any tectonic overprint, can be assumed as pristine. We used a combination of rock magnetic and microfracture studies to estimate shock pressure in the crater rim. On the basis of present results, the magnetic fabrics are interpreted to be of magmatic origin related to the Deccan basalt emplacement. The high-coercivity component of the natural remnant magnetization in the crater rim basalt is similar to that in the unshocked basalt. The lack of any shock-related magnetic overprint on the crater rim basalt is, therefore, evident in the Lonar crater.In contrast, radial and concentric microfractures observed in basalts at the crater rim and farther away show symmetric distribution with respect to the crater. The concentric microfractures consistently overprint the radial microfractures. We infer that the radial and concentric microfractures were developed during propagation of the early compressional and the late decompressional shock wave components, respectively. The results of our rock magnetic and microfracture studies, when interpreted in light of published experimental and numerical simulation studies on the Lonar basalt, reveal that the shock pressure in the Lonar crater rim was less than 0.5 GPa but greater than 0.2 GPa. This shock pressure was high enough to produce fractures but too low to affect the magnetic fabrics. These results give new information on the relationship between shock pressure and resulting microfractures.

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Section: Magnetic Mineralogy and The Origin Of Magnetic Properties Inmentioning

confidence: 83%

Shock pressure estimates in target basalts of a pristine crater: A case study in the Lonar crater, India

Agarwal

Kontny

Srivastava

et al. 2015

Geological Society of America Bulletin

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“…3b). To our knowledge, most other studies of maghemitized titanomagnetite show much more distinct substructures in the ferrimagnetic grains (e.g., Akimoto et al 1984;Dunlop and Özdemir 1997;Oliva-Urcia et al 2011).…”

Section: Samplementioning

confidence: 88%

Cooling rates of pyroclastic deposits inferred from mineral magnetic investigations: a case study from the Pleistocene Mýtina Maar (Czech Republic)

Lied

Kontny

Nowaczyk

et al. 2020

Int J Earth Sci (Geol Rundsch)

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Tephra layers of the Mýtina Maar, Czech Republic, contain ferrimagnetic Mg-Al-rich titanomagnetite, which is suggested to originate from a fractionated alkaline CO 2-rich lithospheric mantle melt. We investigated the magnetic mineralogy and Curie temperature (T C) from tephra deposits of two drill cores (< 9 m depth). T C calculated (208 ± 14 °C) from chemical composition (Fe 2+ 0.8 Mg 0.5 Fe 3+ 1.1 Al 0.3 Ti 0.3 O 4) is in accordance with T C retrieved from cooling curves of temperature-dependent magnetic susceptibility measurements (195-232 °C). However, thermomagnetic curves are irreversible either with lower (type I) or higher (type II) T C in the heating curve. All curves show transition temperatures above ca. 390 °C, indicating maghemitization. We interpret the irreversibility of T C (∆T C) in terms of different degrees of cation ordering, overprinted or masked by different degrees of maghemitization, which is a low-temperature phenomenon. Negative ∆T C indicates that original deposited titanomagnetite has cooled faster and, therefore, has stored a lower degree of cation ordering compared to heating/cooling rate of 11 °C/min in the Kappabridge. Type II with positive ∆T C indicates higher degree of cation ordering, and, therefore, slower cooling rate. The central part of this deposit shows most severe maghemitization, indicating rather wet emplacement. We, therefore, suggest different eruption styles for deposition of type I pyroclastics with more phreatomagmatic and type II pyroclastics with more phreato-Strombolian eruption styles. Our study is a new approach to discriminate different cooling histories in maar deposits using the Curie temperature of titanomagnetite. We suggest that this method has the potential to discriminate different emplacement modes resulting from different eruption styles.

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“…Evidence of how hydrothermal alteration modifies magnetic mineralogy mainly comes from terrestrial geothermal regions (e.g., Ade‐Hall et al, 1971; Hochstein & Soengkono, 1997; Oliva‐Urcia et al, 2011) and ophiolites (e.g., Hall, 1992), where primary magnetic minerals, typically titanomagnetites or magnetite, are altered to less magnetic phases, resulting in pronounced decreases in natural remanent magnetization (NRM). There are uncertainties whether such on‐land knowledge is directly applicable to the seafloor hydrothermal systems.…”

Section: Introductionmentioning

confidence: 99%

Progressive Dissolution of Titanomagnetite in High‐Temperature Hydrothermal Vents Dramatically Reduces Magnetization of Basaltic Ocean Crust

Wang

Chang

et al. 2020

Geophysical Research Letters

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Hydrothermal alteration at high-temperature vents near mid-ocean ridge is thought to produce pervasive magnetization lows on basaltic ocean crust, but the detailed alteration process is insufficiently documented. Here, we performed microscopic and magnetic analyses on a large set of hydrothermal-related basaltic samples from the Southwest Indian Ridge. Fresh basalts were chloritized and brecciated during hydrothermal alteration, where titanomagnetite nanoparticle clusters hosted in interstitial glasses were dissolved in the first order, followed by large micron-scale dendritic particles. Natural remanent magnetization was reduced from 10 0 -10 1 A/m for fresh basalts to 10 −3 A/m for fully altered basalts. Hydrothermal deposits acquired a chemical remanent magnetization of 10 −2 A/m. Our results link direct magneto-mineralogical observations to geophysical interpretations, which is important in understanding seafloor hydrothermal circulation and mid-ocean ridge geodynamics.Plain Language Summary Seafloor hydrothermal vents, also known as black chimneys, produce valuable mineral resources through fluid-rock reactions beneath the seafloor-a process called hydrothermal alteration. On basaltic ocean crust, hydrothermally altered regions are generally found to be less magnetic, which provides a way to detect seafloor hydrothermal vents. To understand the cause of this phenomenon, we studied how fluid-rock reactions modify magnetic minerals on basaltic ocean crust in the Southwest Indian Ridge. We have established a detailed alteration pathway that the primary magnetic minerals were progressively replaced by nonmagnetic minerals with increasing alteration degree and the strongly magnetized nanoparticles were preferentially consumed at the very beginning of the reaction. This finding directly contributes to magnetic surveying the seafloor hydrothermal vents and establishes the value of rock magnetic proxies for quantifying the alteration degree to trace fluid-rock reactions.

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Modification of the magnetic mineralogy in basalts due to fluid-rock interactions in a high-temperature geothermal system (Krafla, Iceland)

Cited by 26 publications

References 72 publications

Shock pressure estimates in target basalts of a pristine crater: A case study in the Lonar crater, India

Shock pressure estimates in target basalts of a pristine crater: A case study in the Lonar crater, India

Cooling rates of pyroclastic deposits inferred from mineral magnetic investigations: a case study from the Pleistocene Mýtina Maar (Czech Republic)

Progressive Dissolution of Titanomagnetite in High‐Temperature Hydrothermal Vents Dramatically Reduces Magnetization of Basaltic Ocean Crust

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