کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
6430377 1634793 2012 12 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Long-term low latitude cosmogenic 3He production rate determined from a 126 ka basalt from Fogo, Cape Verdes
موضوعات مرتبط
مهندسی و علوم پایه علوم زمین و سیارات علوم زمین و سیاره ای (عمومی)
پیش نمایش صفحه اول مقاله
Long-term low latitude cosmogenic 3He production rate determined from a 126 ka basalt from Fogo, Cape Verdes
چکیده انگلیسی

An ankaramite lava from Fogo, Cape Verdes, has been used to determine the long-term cosmogenic 3He (3Hecos) production rate at low latitude (14.9°N). 40Ar/39Ar incremental heating yield an eruption age of 125.8±7 ka. Cosmogenic 3He abundances yield local production rates of 75.6±7.0 atoms/g/year in olivine (1σ, n=10) and 70.1±2.9 atoms/g/yr in pyroxene (1σ, n=11). The lower 3Hecos production rate in pyroxene is consistent with compositional control on production. When scaled to sea level high latitude using available algorithms, the olivine 3Hecos production rate ranges from 86-109 atoms/g/yr. These values overlap the long-term production rate determined at the Canary Islands (99 atoms/g/yr). They are, however, lower than previously reported long-term production rates from Hawaii and southern South America (129-152 atoms/g/yr), and the range of <20 ka calibration sites (110-130 atoms/g/yr). Erosion-burial and high atmospheric pressure appear to be of negligible importance. The likeliest explanation is that the geomagnetic field strength was higher in the past. The agreement between the Fogo geomagnetic field strength-corrected production rate scaled using various published scaling algorithms suggests that differences in incorporation of the non-dipole component of the Earth magnetic field in the scaling algorithms are negligible for long-term production rate determinations at low elevation and low latitude. Longitudinal variation in long-term cosmogenic nuclide production rates between the central Atlantic Ocean and the Americas (Hawaii and Patagonia) may exist. This has implications for exposure dating of old surfaces. It will require that locally determined production rates should be used where available, and that scaling schemes incorporating longitudinal variations should be used if nearby calibration sites are not available. Furthermore, if long-term longitudinal production rate variations exist, it implies that variation in the geomagnetic field may not average out after around 20 ka, but may require significantly longer periods (up to 100 ka).

► New olivine and pyroxene cosmogenic 3He production rates (P3) from Fogo, Cape Verde. ► Data obtained on a 125 ka flow, and from the lowest yet reported latitude (15°N). ► P3 data are determined by fluctuations in Earth magnetic field. ► Comparison to other long-term P3 studies, suggest for latitudinal variations.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Earth and Planetary Science Letters - Volumes 359–360, 15 December 2012, Pages 14-25
نویسندگان
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