Publication Date:
2022-12-15
Description:
Most pyroclastic deposits of Popocatépetl volcano were emplaced at high temperatures and have similar mafic to more evolved compositions, suggesting a long‐lived, interconnected magma environment. We performed a magnetic and microscopic study on different eruptive sequences 〈14 ky in age and found that temperature and field dependence of magnetic susceptibility are suited to separate eruption phases. We observed homogeneous titanomagnetite with Curie temperatures (TC) of 50–200°C and 200–400°C, together with different amounts of oxy‐exsolved titanomagnetite with TC ∼ 570°C. Some block‐and‐ash flow deposits show remarkably irreversible TC in heating and cooling branches with a positive ΔTC (TC heating–TC cooling) of up to 130°C in the center. The central part of this sequence is characterized by decreasing magnetic susceptibility and low field dependence of magnetic susceptibility (〈10%), which is atypical for ulvöspinel‐rich titanomagnetite. The nonreversibility of heating and cooling runs measured with rates of around 10 K/min is probably related to vacancy‐enhanced nanoscale chemical clustering, which seems to occur preferentially during rapid quenching, possibly combined with subtle maghemitization. In contrast, pumice layers have the highest field dependence (∼20%) and contain Ti‐rich and intermediate titanomagnetite with TC 〈 100 and ∼300°C, which are in line with mafic and more evolved magma composition. In intermediate phases, irreversibility of TC is more common but with a relatively low ΔTC of ±20°C. We suggest that magneto‐mineralogy in pyroclastic density currents is complex but offers a complementary tool to the paleomagnetic directional analysis for emplacement temperature and contribute information on the volcanic material history and their emplacement conditions.
Description:
Plain Language Summary:
Explosive eruptions of volcanoes are a dangerous threat to human settlements. In this study, we investigated pyroclastic material from the last 14 ky of Popocatépetl volcano using magnetic mineral assemblages, hysteresis properties, and temperature‐ and field‐dependent magnetic susceptibility. The data are suited to separate different eruption phases and provide information on the volcanic material history and emplacement conditions. Magnetic susceptibility analyses are suggested to be a complementary tool to the paleomagnetic directional analysis for the determination of emplacement temperatures.
Description:
Key Points:
Several Curie temperatures were observed in pyroclastic deposits.
Temperature and field dependence of magnetic susceptibility are suited to separate eruption phases.
Irreversible Curie temperatures in heating and cooling curves observed in block‐and‐ash flows may suggest rapid quenching.
Description:
DGAPA‐UNAM
Description:
https://doi.org/10.17632/9g2tszftvr.2
Description:
https://earthref.org/MagIC/19591/206809c5-acfc-41e3-b4cb-411630a7025e
Keywords:
ddc:552.2
;
Popocatépetl volcano
;
pyroclastic deposits
;
magnetic rock studies
;
magnetic mineralogy studies
;
cooling temerature
Language:
English
Type:
doc-type:article
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