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Excerpt from Cruz et al., 2007 introduction...

Speleothems have become an important archive for studying climate change in the Late Pleistocene and Holocene. Most commonly, the oxygen isotope ratios of speleothem calcite have been used as a proxy for changes in the isotopic composition of rainfall of a particular region. Then, depending on the specific local relationships between climate and the d18O of rainfall, d18O of the speleothem may be interpreted in terms of mean temperature (Linge et al., 2001) or of rainfall source (Cruz et al., 2005a) or amount (Burns et al., 2000; Fleitmann et al., 2003). But speleothems contain a number of other, less-frequently utilized, chemical proxies for climate. For one, trace element ratios such as Mg/Ca and Sr/Ca have the potential to reveal changes in karst-water processes that may be climate related. For example, studies utilizing drip water modern monitoring programs performed in karst systems in different environments around the world (Fairchild et al., 2000; Tooth and Fairchild, 2003; Musgrove and Banner, 2004; McDonald et al., 2004) suggest that Mg/Ca and Sr/ Ca ratios reflect the meteoric water infiltration rate in the vadose zone of caves, and that they, therefore, can be used to estimate relative variations in amount of rainfall. The relationships between climate parameters and trace element ratios obtained from studies such as these have been used to infer past hydrological changes from speleothems on decadal to subannual (Huang et al., 2001; Fairchild et al., 2001; Baldini et al., 2002; Treble et al., 2003; Johnson et al., 2006) to long-term time scales (Verheyden et al., 2000; Li et al., 2005).

 

Upper right: Trace element ratios in stalagmite from Botuvera´ cave, Southern Brazil, 116 ky record. BP Mg/Ca and Sr/Ca ratios are positively correlated with one another, and vary with variations of d18O in the same speleothem during the last glacial period. Prior calcite precipitation in the vadose zone of the cave system is the main factor affecting the incorporation of Mg and Sr into calcite of the stalagmite. Higher Mg/Ca and Sr/Ca values are associated with lower levels of recharge into the karstic aquifer, as such conditions lead to an increase in the volume of calcite precipitated in the unsaturated zone above the cave during dry periods. Trace element variations point to generally dryer conditions during lower phases of summer insolation in the southern hemisphere. These periods coincide with decreased activity of the South American summer monsoon, as revealed by d18O stalagmite records. In addition trace element variations show that rather wet conditions persisted throughout most of the last glacial period from approximately 70 to 17 ky BP. Glacial boundary conditions, especially ice volume buildup in the northern hemisphere, played an important role for monsoon rainfall intensification in the region. For details see Cruz et al. (2007).
1.7 cm section of annually laminated speleothem, southern Oman (Fleitman et al., 2004). SHRIMP and Ultrachron S and Sr analysis follows yellow line, with S concentrations shown above.. Top (youngest) to right. This section records a general increase in S since the late 1950's, reflecting increasing sulfur emissions on the Arabian Peninsula and Indian subcontinent. High amplitude S peaks coincide with volcanic eruptions in some cases.
CaKb counts with beam exposure time. 200nA, 15kV, 15um beam diameter (LPET). Vertical dashed lines are at 0 and 300 sec. Absorbed current is shown in red for comparison. Characteristic x-ray intensity vs. time is not a simple (e.g., exponential or 2nd order polynomial) function. Error on the total cps relative to the initial (time-zero) intensity is -1.8% after 300 seconds, but is +2.8% error if counted during the first 30 seconds of beam exposure. Similar tests for sulfur at 400nA indicate about -2.3% error integrating 300 seconds of counting.
High intensity monochromators permit lowering of beam intensity or exposure time to limit beam damage effects and/or oount times. Some examples of precision and sensitivity are given in the table to right.
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Dumond, G., Goncalves, P., Williams, M.L., and Jercinovic, M.J. (2010) Subhorizontal fabric in exhumed continental lower crust and implications for lower crustal flow: Athabasca granulite terrane, western Canadian Shield. Tectonics, 29, doi:10.1029/2009TC002514. PDF

Mahan, K.H., Wernicke, B.P., and Jercinovic, M.J. (2010) Th-U-total Pb geochronology of authigenic monazite in the Adelaide rift complex, South Autstralia, and implications for the age of the type Sturtian and Marinoan glacial deposits. Earth and Plantetary Science Letters, 289, 76-86. PDF

Jercinovic, M.J., Williams, M.L., and Lane, E.D. (2008) In-situ trace element analysis of monazite and other fine-grained accessory minerals by EPMA. Chemical Geology 254, 197-215. PDF

Dumond, G., McLean, N., Williams, M.L., Jercinovic, M.J., and Bowring, S.A. (2008) High-resolution dating of granite petrogenesis and deformation in a lower crustal shear zone, Athabasca granulite terrane, western Canadian Shield. Chemical Geology 254, 175-196. PDF

Hetherington, C.J., Williams, M.L., Jercinovic, M.J., and Mahan, K. (2008) Application of electron-probe microanalysis to composition, chronology, and occurrence of xenotime for understanding geologic processes. Chemical Geology 254, 123-147. PDF

Budzyn, B., Hetherington, C.J., Williams, M.L., Jercinovic, M.J., Dumond, G., and Michalik, M. (2008) Application of electron probe micro-analysis total Th-U-Pb geochronology to provenance studies of sedimentary rocks: An example from the Carpathian Flysch. Chemical Geology 254, 148-163. PDF

Williams, M.L., Jercinovic, M.J., and Hetherington (2007), C.J. Microprobe Monazite Geochronology: understanding geologic processes through integration of composition and chronology. Annual Review of Earth and Planetary Sciences 37, 137-175. PDF

Heumann, M.J., Bickford, M.E., Hill, B.M., McLelland, J.M., Selleck, B.W., and Jercinovic, M.J. (2007) Timing of anatexis in metapelites from the Adirondack lowlands and southern highlands, a manifestation of the Shawinigan Orogeny and subsequent AMCG magmatism. Geological Society of America Bulletin 118, 1283-1298.

Cruz, Francisco, W., Burns, S.J., Jercinovic, M.J., Karmann, I., Sharp, W.D., and Vuille, M. (2007) Evidence of rainfall variations in southern Brazil from trace element ratios (Mg/Ca and Sr/Ca) in a Late Pleistocene stalagmite. Geochimica et Cosmochimica Acta 71, 2250-2263. PDF

Mahan, K.H., Williams, M.L., Flowers, R.M., Jercinovic, M.J., Baldwin, J.A., and Bowring, S.A. (2006) Geochronological constraints on the Legs Lake shear zone with implications for regional exhumation of lower continental crust, western Churchill Province, Canadian Shield. Contributions to Mineralogy and Petrology 152, 223-242. PDF

Mahan, K.H., Goncalves, P., Williams, M.L., and Jercinovic, M.J. (2006) Dating metamorphic reactions and fluid flow: Application to exhumation of high-P granulites in a crustal-scale shear zone, western Canadian Shield. Journal of Metamorphic Geology 24, 193-217. PDF

Boyce, J. W., K. V. Hodges, W. J. Olszewski, M. J. Jercinovic, Carpenter, B.D., and Reiners, P.W. (2006), Laser microprobe (U-Th)/He geochronology, Geochem. Cosmochim Acta,70, 3031-3039. PDF

Baldwin, J.A., Bowring, S.A., Williams, M.L., & Mahan, K.H., (2006) Geochronological constraints on the evolution of high-pressure felsic granulites from an integrated electron microprobe and ID-TIMS geochemical study. Lithos 88, 173-200.

Williams, M.L., Jercinovic, M.J., Goncalves, P., and Mahan, K. (2006) Format and philosophy for collecting, compiling, and reporting microprobe monazite ages. Chemical Geology225 , 1-15. PDF

 

 

Jercinovic, M.J., and Williams, M.L. (2005) Analytical perils (and progress) in electron microprobe trace element analysis applied to geochronology: Background acquisition, interferences, and beam irradiation effects. American Mineralogist90 , 526-546. PDF

Dahl, P.S., Terry, M.P., Jercinovic, M.J., Williams, M.L., Hamilton, M.A., Foland, K.A., Clement, S.M., and Friberg, L.M. (2005) Electron probe (Ultrachron) microchronometry of metamorphic monazite: Unraveling the timing of polyphase thermotectonism in the easternmost Wyoming Craton (Black Hills, South Dakota). American Mineralogist90 , 1712-1728. PDF

Dahl, P.S., Hamilton, M.A.., Jercinovic, M.J., Terry, M.P., Williams, M.L., and Frei, R. (2005) Comparative isotopic and chemical geochronometry of monazite in metamorphic rocks from the eastern Wyoming province (USA), with implications for U-Th-Pb dating by electron microprobe. American Mineralogist 90 , 619-638. PDF

Goncalves, P., Williams, M.L., and Jercinovic, M.J. (2005) Electron microprobe age mapping. American Mineralogist 90 , 578-585. PDF

Williams, M.L., and Jercinovic, M.J. (2002) Microprobe monazite geochronology: Putting absolute time into microstructural analysis. Journal of Structural Geology24 , 1013-1028.

Shaw, C.A., Karlstrom, K.E., Williams, M.L., Jercinovic, M.J., and McCoy, A.M. (2001) Electron microprobe monazite dating of ca. 1.71 – 1.63 Ga and ca. 1.45-1.38 deformation in the Homestake shear zone, Colorado: Origin and early evolution of a persistent intracontinental tectonic zone. Geology29 , 739-742.

Terry, M.T., Robinson, P., Hamilton, M.A., and Jercinovic, M.J. (2000) Monazite geochronology of UHP and HP metamorphism, deformation, and exhumation, Nordoyane, Western Gneiss Region, Norway. American Mineralogist 85, 1651-1664.

Williams, M.L., Jercinovic, M.J., and Terry, M.P. (1999) Age mapping and dating of monazite on the electron microprobe: Deconvoluting multistage tectonic histories. Geology27, 1023-1026.

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