Statistics – Applications
Scientific paper
Dec 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994gecoa..58.5299e&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 58, Issue 23, pp.5299-5306
Statistics
Applications
8
Scientific paper
The isotopic composition of lead released by chemical weathering of granitoids was investigated in order to evaluate the sensitivity of this natural tracer as a tool for monitoring mineral weathering and soil development. The isotopic composition of lead was found to change systematically with the relative degree (or maturity) of weathering in both Cretaceous granitoids from the Sierra Nevada batholith (SN) and Precambrian granitoids from the Wind River Range, Wyoming (WRR). In the SN, lead released from crushed bedrock by dilute acid leaching (to simulate the initial stages of weathering) has a composition more radiogenic than observed in soils (average 206 Pb / 207 Pb = 1.335). Lead released by leaching from soils developed on a relatively young terrain (~10 kyr old) is less radiogenic (average 206 Pb / 207 Pb = 1.270) than crushed bedrock and lead released by leaching from soil developed on older surfaces (~ 100 kyr) is even less radiogenic (average 206 Pb / 207 Pb = 1.255). Lead released from the total digestion of the rock has the least radiogenic composition (average 206 Pb / 207 Pb = 1.240). In the WRR, systematic changes in the isotopic composition of lead released by leaching were observed in soils developed on glacial moraines of variable ages. Lead released from soil developed on a 21 kyr old moraine was the most radiogenic ( 208 Pb / 207 Pb = 3.257). Lead released from soil developed on a 130 kyr old moraine was less radiogenic ( 208 Pb / 207 Pb = 2.780) and lead released from soil developed on 350 kyr old moraine was the least radiogenic ( 208 Pb / 207 Pb = 2.532). The observed systematic changes in the isotopic composition of lead with time in both field areas demonstrates the potential of lead isotopes to ascertain the degree (or maturity) of chemical weathering of granitoids and may have applications in determinations of the relative ages of some glacial deposits.
Blum Joel D.
Erel Yigal
Harlavan Yehudit
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