Dating recent lava flows
9), the K-Ar method cannot be used to date samples that are much younger than 6,000 years old (Dalrymple, 1991, p.
93)Cambridge, Massachusetts, USA, performed the K-Ar dating for Austin et al. However, when they did, their website clearly stated in a footnote that their equipment could not accurately date rocks that are younger than about 2 million years old ("We cannot analyze samples expected to be younger than 2 M.
Popular Dating Methods Both the K-Ar and Rb-Sr methods make use of radioactive decay of a parent isotope to a stable daughter isotope. Leeman, "Late Cenozoic Alkali-Rich Basalt from the Western Grand Canyon Area, Utah and Arizona: Isotopic Composition of Strontium," Geological Society of America Bulletin, 85 (Nov. Six analyses of Uinkaret Plateau basalts (U-33, U-35, U-59, U-24, U-43, U-58) were used.
Potassium-40 (Rb has occurred since the rock cooled from the lava flow.
While we have some good estimates and hypotheses, the frequency and size of these eruptions, which are occurring under the oceans globally, is basically unproven,” said Dr. However, using a new method developed at GEOMAR the scientists have been able to simultaneously survey and date young lava flows on a segment of the Mid-Atlantic Ridge north of Iceland and show that large volume, episodic eruptions must be occurring.
The new method, developed using the Autonomous Underwater Vehicle (AUV) ABYSS at GEOMAR utilizes acoustic data of the seafloor collected by the robot alongside records from sediment cores collected in the vicinity.
Two lava flows from the Ceboruco volcano in west-central Mexico were sampled for palaeomagnetic dating.
The younger one was emitted in 1870 and used to validate the method, while the older one known as Ceboruco flow is of unknown age but probably younger than ∼1005 AD and older than 1528 AD.
For the 1870 flow, between site differences were notable and additionally post-cooling block movements were important; therefore, two sites had to be rejected.The Rb-Sr ratios in various rock samples from the same lava flow might differ, but all should plot as a straight line on the graph if the lava was isotopically homogeneous (each rock sample had the same initial Sr ratio) and each rock remained closed to gain or loss of rubidium and strontium since crystallization. In the ideal case, multiple samples from the same lava flow should plot perfectly along a line with slope e Ar give lines whose slopes supposedly reflect the ages of lava flows. The analytical equipment used to determine the abundances of isotopes is more accurate in determining ratios of isotopes than their absolute abundances. Therefore, Sr as the y-axis would allow the isotope ratios of all rocks in a lava flow to be plotted. Damon, "K-Ar Age of Lava Dam in the Grand Canyon," Geological Society of America Bulletin, 79 (Jan.