کد مقاله کد نشریه سال انتشار مقاله انگلیسی نسخه تمام متن
4698490 1637564 2015 11 صفحه PDF دانلود رایگان
عنوان انگلیسی مقاله ISI
Carbonate composition and its impact on fluvial geochemistry in the NE Tibetan Plateau region
ترجمه فارسی عنوان
ترکیب کربنات و تاثیر آن در ژئو شیمیایی رشته ای در منطقه پلاتو تبت
موضوعات مرتبط
مهندسی و علوم پایه علوم زمین و سیارات ژئوشیمی و پترولوژی
چکیده انگلیسی


• Carbonate composition and its variability in bedrock and sediments are examined.
• The disseminated carbonates are widely found in silicate rocks.
• Carbonate precipitation processes control the authigenic carbonate chemistry.
• Carbonate weathering in surface sediments not bedrock controls fluvial chemistry.

Using co-variations of Sr/Ca and Mg/Ca, we examined the carbonate compositions of various bedrocks (silicate and carbonate rocks) and sediments (eolian and fluvial sediments, sand, and topsoil) found in the NE Tibetan Plateau (TP) region. A combined carbonate composition dataset based on our results and other reported data shows that bedrock carbonate composition on the NE TP displays a much broader range of Sr/Ca and Mg/Ca ratios than restricted source carbonate endmembers reported upon in previous studies. This has clear implications for modern weathering studies in addition to paleo-reconstructions in this tectonically active and climatically variable area during the Late Cenozoic. Bedrock carbonate compositions are characterized by disseminated carbonates with higher Sr/Ca and Mg/Ca ratios, and sedimentary carbonates (mostly marine) with lower Sr/Ca, but variable Mg/Ca, ratios. The mostly authigenic carbonates found in sediments show similar trends, with a gradient ~ 0.97–1.00 in a plot of log (Sr/Ca) versus log (Mg/Ca), suggesting that ‘calcite precipitation’ processes – i.e. the sources of the dissolved cations in the water – control their chemistry. Based on observations and modeling, we conclude that the mixing of authigenic and bedrock carbonate endmembers, plus the incongruent dissolution of bedrock carbonates, accounts for the bulk carbonate composition of sediments (e.g. loess, sand and topsoil). A comparison of bedrock and sedimentary carbonate composition with reported fluvial water data in the NE TP suggests that weathering of carbonates in terrigenous sediments, rather than in bedrock, is mostly responsible for the changes in fluvial Sr, Mg and Ca compositions. Our study suggests that interactions between carbonates and water occur widely during the exposure, transport and deposition of sediments, significantly modifying regional carbonate compositions and fluvial geochemistry.

ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Chemical Geology - Volume 410, 2 September 2015, Pages 138–148
نویسندگان
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