کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
4677172 1634792 2013 12 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Mechanisms of magma degassing at mid-oceanic ridges and the local volatile composition (4He–40Ar⁎–CO2) of the mantle by laser ablation analysis of individual MORB vesicles
موضوعات مرتبط
مهندسی و علوم پایه علوم زمین و سیارات علوم زمین و سیاره ای (عمومی)
پیش نمایش صفحه اول مقاله
Mechanisms of magma degassing at mid-oceanic ridges and the local volatile composition (4He–40Ar⁎–CO2) of the mantle by laser ablation analysis of individual MORB vesicles
چکیده انگلیسی

Individual vesicles in <1 cm3 samples of MORB glasses commonly preserve significantly different volatile (He, Ar, CO2) compositions. Five separate MORB glass samples from different ridges were investigated, selectively opening targeted vesicles using a 193 nm excimer laser. One sample shows evidence of syn-emplacement selective helium loss from the vesicles in the glass rim close to the crystallised zone of the pillow lava, proving that He contents and low He/Ar ratios do not always reflect mantle and/or magmatic processes. However the composition of the different vesicles of three of these samples covers large ranges in He/Ar and Ar/CO2 with linear variations in plots of ln(He/Ar) vs. ln(Ar/CO2) which are consistent with a Rayleigh distillation at equilibrium and allow the relative abundances of the volatiles in the MORB mantle source to be estimated by correcting for degassing processes on a sample-by-sample basis. This technique presents a new tool for characterising and correcting for volatile fractionation processes that have modified the initial mantle source composition. The results confirm a heterogeneous CO2/3He ratio in the MORB source regions with the Azores mantle source enriched in C/3He compared to that of N-MORBs. The considerable heterogeneity in vesicle compositions within such a small volume (<1 cm3) requires injection of less degassed magma at shallow level before eruption. The maximum time interval between magma mixing and quenching on the seafloor is of the order of a few hours.


► Vesicles in MORB glasses have heterogeneous compositions at the cm scale.
► Variations are consistent with solubility controlled Rayleigh distillation.
► The heterogeneity can be explained by magma mixing prior to eruption.
► He loss during magma cooling affects bubbles close to the crystallised margin.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Earth and Planetary Science Letters - Volume 361, 1 January 2013, Pages 183–194
نویسندگان
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