期刊
CHEMICAL GEOLOGY
卷 450, 期 -, 页码 145-153出版社
ELSEVIER SCIENCE BV
DOI: 10.1016/j.chemgeo.2016.12.026
关键词
Calcite; Uranium; Partition coefficient; Growth rate; SIMS; Disequilibrium
资金
- NSF, EAR, Instrumentation and Facilities Program [1029193]
- ETH [4443869-AL-20600]
- ERC grant [NEWLOG 267931]
- European Atomic Energy Community's Seventh Framework Programme (FP7) [269688]
- Division Of Earth Sciences
- Directorate For Geosciences [1029193] Funding Source: National Science Foundation
Elemental to calcium ratios in calcium carbonate minerals are used to study environmental conditions. In particular, uranium to calcium ratio (U/Ca) has been proposed as a proxy for seawater carbonate ion concentration (CO32-) and seawater pH. This work is focused on the evaluation of growth rate and its effect on uranium partitioning between calcite and fluid. We grew inorganic calcite (by diffusion of CO2) isothermally from NH4Cl-CaCl2 doped with uranium. The growth rate of calcite (crystal extension rate, V) was monitored by sequentially spiking calcite-precipitating fluids with rare earth element (REE) dopants. The REE was analyzed with secondary ion mass spectrometry (SIMS) at spots matching those where U/Ca was determined. Partition coefficient K-U = (U/Ca)(calcite) / (U/Ca)(fluid) increases with increasing growth rate (V). Specifically, K-U increases from 0.02 to 0.06 when V increases from 0.01 to 0.14 nm/s and remains nearly constant at faster rates. Numerical simulations using the growth entrapment model (GEM) and unified uptake kinetics model (UUKM) were undertaken to explain K-U-V relationship in the recent data on calcite. (C) 2016 Elsevier B.V. All rights reserved.
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