@article {Ludwig2011,
	title = {{U-Th systematics and ages of carbonate chimneys at the Lost City Hydrothermal Field}},
	journal = {Geochimica et Cosmochimica Acta},
	volume = {75},
	number = {7},
	year = {2011},
	pages = {1869{\textendash}1888},
	abstract = {The Lost City Hydrothermal Field (LCHF) is a serpentinite-hosted vent field located 15~km west of the spreading axis of the Mid-Atlantic Ridge. In this study, uranium{\textendash}thorium (U{\textendash}Th) geochronological techniques have been used to examine the U{\textendash}Th systematics of hydrothermal fluids and the 230Th ages of hydrothermally-precipitated carbonate chimneys at the LCHF. Fluid sample analyses indicate that endmember fluids likely contain only 0.0073~ng/g U or less compared to 3.28~{\textpm}~0.03~ng/g of U in ambient seawater. For fluid samples containing only 2{\textendash}21{\%} ambient seawater (1.1{\textendash}11~mmol/kg~Mg), Th concentration is 0.11{\textendash}0.13~pg/g and surrounding seawater concentrations average 0.133~{\textpm}~0.016~pg/g. The 230Th/232Th atomic ratios of the vent fluids range from 1 ({\textpm}10)~{\texttimes}~10-6 to 11 ({\textpm}5)~{\texttimes}~10-6, are less than those of seawater, and indicate that the vent fluids may contribute a minor amount of non-radiogenic 230Th to the LCHF carbonate chimney deposits. Chimney 238U concentrations range from 1 to 10~$μ$g/g and the average chimney corrected initial $δ$234U is 147.2~{\textpm}~0.8, which is not significantly different from the ambient seawater value of 146.5~{\textpm}~0.6. Carbonate 232Th concentrations range broadly from 0.0038~{\textpm}~0.0003 to 125~{\textpm}~16~ng/g and 230Th/232Th atomic ratios vary from near seawater values of 43 ({\textpm}8)~{\texttimes}~10-6 up to 530 ({\textpm}25)~{\texttimes}~10-3. Chimney ages, corrected for initial 230Th, range from 17~{\textpm}~6~yrs to 120~{\textpm}~13~kyrs. The youngest chimneys are at the intersection of two active, steeply-dipping normal faults that cut the Atlantis Massif; the oldest chimneys are located in the southwest portion of the field. Vent deposits on a steep, fault-bounded wall on the east side of the field are all Th, range from 17~{\textpm}~6~yrs to 120~{\textpm}~13~kyrs. The youngest chimneys are at the intersection of two active, steeply-dipping normal faults that cut the Atlantis Massif; the oldest chimneys are located in the southwest portion of the field. Vent deposits on a steep, fault-bounded wall on the east side of the field are all},
	keywords = {HOV Alvin (Human Occupied Vehicle)},
	issn = {0016-7037},
	doi = {10.1016/j.gca.2011.01.008},
	url = {http://dx.doi.org/10.1016/j.gca.2011.01.008},
	author = {Ludwig, K A and Shen, C C and Kelley, D S and Cheng, H and Edwards, R L}
}
