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Conference Paper: Mg isotopes of the late permian evaporites, New Mexico, USA
Title | Mg isotopes of the late permian evaporites, New Mexico, USA |
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Authors | |
Keywords | 1009 Geochemical modeling, GEOCHEMISTRY 1030 Geochemical cycles, GEOCHEMISTRY 1039 Alteration and weathering processes, GEOCHEMISTRY 1041 Stable isotope geochemistry, GEOCHEMISTRY |
Issue Date | 2015 |
Citation | The 48th Annual Fall Meeting of the American Geophysical Union (AGU 2015), San Francisco, CA., 14-18 December 2015. How to Cite? |
Abstract | Mg isotope holds promise to decipher the evaporative environment of evaporites. High-precision Mg isotope compositions of the late Permian langbeinites have been measured by using MC-ICPMS. The equilibrium Mg isotope fractionation factor between langbeinite and aqueous Mg2+ solutions has been determined using quantum chemistry calculations. All computations are employed at B3LYP/6-311++G(2d,2p) level and solvation effects are treated by solvent model ('water-droplet' approach), mineral structures are constructed using volume variable cluster models (VVCM). The Mg isotope compositions of the langbeinite samples, whose total formation thickness ranges up to 100 meters, are extremely isotopically lighter than that of modern seawater and relatively homogeneous (delta26MgDSM3 is from -4.12±0.030/00 to -3.81±0.070/00 v.s. -0.830/00 of modern seawater). The computed equilibrium Mg isotope fractionation factors between langbeinite and aqueous Mg2+ solutions are -2.730/00, -2.660/00 and -2.530/00 at 25, 30 and 40 ℃, respectively. These significant equilibrium fractionation factors indicate that a huge equilibrium Mg isotope fractionation between langbeinite and its parent brine can happen during langbeinite depositions, and langbeinites are enriched in isotopically light 24Mg comparing to the brine. Using the computed fractionation factors to simulate a Rayleigh fractionation process of langbeinite Mg precipitation, we find that a significant Mg isotope difference between langbeinite and its growing brine (seawater) is indeed present but the Mg isotope composition of langbeinite merely increase monotonically in a closed system. Because of that, the homogenous Mg isotope compositions of such a thick evaporite sequence suggest a disequlibrium effect rather than an equilibrium Mg isotope fractionation behavior during its formation. Combined with its prevailing Mg-bearing character, the homogenous Mg isotope compositions reveal that this the late Permian langbeinite sequence has experienced a rapid depositional process and a relatively closed hydrological environment. |
Persistent Identifier | http://hdl.handle.net/10722/233277 |
DC Field | Value | Language |
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dc.contributor.author | Feng, C | - |
dc.contributor.author | Gao, CH | - |
dc.contributor.author | Chang, S | - |
dc.date.accessioned | 2016-09-20T05:35:48Z | - |
dc.date.available | 2016-09-20T05:35:48Z | - |
dc.date.issued | 2015 | - |
dc.identifier.citation | The 48th Annual Fall Meeting of the American Geophysical Union (AGU 2015), San Francisco, CA., 14-18 December 2015. | - |
dc.identifier.uri | http://hdl.handle.net/10722/233277 | - |
dc.description.abstract | Mg isotope holds promise to decipher the evaporative environment of evaporites. High-precision Mg isotope compositions of the late Permian langbeinites have been measured by using MC-ICPMS. The equilibrium Mg isotope fractionation factor between langbeinite and aqueous Mg2+ solutions has been determined using quantum chemistry calculations. All computations are employed at B3LYP/6-311++G(2d,2p) level and solvation effects are treated by solvent model ('water-droplet' approach), mineral structures are constructed using volume variable cluster models (VVCM). The Mg isotope compositions of the langbeinite samples, whose total formation thickness ranges up to 100 meters, are extremely isotopically lighter than that of modern seawater and relatively homogeneous (delta26MgDSM3 is from -4.12±0.030/00 to -3.81±0.070/00 v.s. -0.830/00 of modern seawater). The computed equilibrium Mg isotope fractionation factors between langbeinite and aqueous Mg2+ solutions are -2.730/00, -2.660/00 and -2.530/00 at 25, 30 and 40 ℃, respectively. These significant equilibrium fractionation factors indicate that a huge equilibrium Mg isotope fractionation between langbeinite and its parent brine can happen during langbeinite depositions, and langbeinites are enriched in isotopically light 24Mg comparing to the brine. Using the computed fractionation factors to simulate a Rayleigh fractionation process of langbeinite Mg precipitation, we find that a significant Mg isotope difference between langbeinite and its growing brine (seawater) is indeed present but the Mg isotope composition of langbeinite merely increase monotonically in a closed system. Because of that, the homogenous Mg isotope compositions of such a thick evaporite sequence suggest a disequlibrium effect rather than an equilibrium Mg isotope fractionation behavior during its formation. Combined with its prevailing Mg-bearing character, the homogenous Mg isotope compositions reveal that this the late Permian langbeinite sequence has experienced a rapid depositional process and a relatively closed hydrological environment. | - |
dc.language | eng | - |
dc.relation.ispartof | Fall Meeting of the American Geophysical Union, AGU 2015 | - |
dc.subject | 1009 Geochemical modeling, GEOCHEMISTRY | - |
dc.subject | 1030 Geochemical cycles, GEOCHEMISTRY | - |
dc.subject | 1039 Alteration and weathering processes, GEOCHEMISTRY | - |
dc.subject | 1041 Stable isotope geochemistry, GEOCHEMISTRY | - |
dc.title | Mg isotopes of the late permian evaporites, New Mexico, USA | - |
dc.type | Conference_Paper | - |
dc.identifier.email | Chang, S: suchin@hku.hk | - |
dc.identifier.authority | Chang, S=rp01478 | - |
dc.identifier.hkuros | 263973 | - |