Ken Rubin/SOEST Isotope Lab Research

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----____Dating Very Young Submarine Basalts____----
210Po-210Pb ages of lavas from 9°50'N EPR
From: Rubin, K.H., Macdougall, J.D. and Perfit, M.R. (1994) 210Po-210Pb dating of recent volcanic eruptions on the sea floor, Nature, 368, 841-844.


    This page describes results of the inaugural application of the 210Po-210Pb dating technique to dating mid-ocean ridge eruptions using basalts from 9º50'N on the East Pacific Rise (Rubin et al., Nature 1994). The method itself is described on the 210Po-210Pb dating. page. Basically, one monitors the rate of change of 210Po with time in a lava once it is sampled, to determine the date of eruption, when the Po in the lava was degassed. This dating technique was used to determine the dates of very recent eruptive activity at 9º50'N on the East Pacific Rise (EPR), where it can be argued that the first observations of a deep submarine eruption were made by humans. The dates are depicted on the calendar diagram below. Eruption ages resulted in the following interpretations:
Recent eruption chronology at 9 deg 50 min N EPR

    Figure 1 (above) Colored bars plotted versus calendar time represent our best-estimate of the time of the eruption for the various EPR basaltsamples we analyzed. The smaller bars show the error in the estimation of the maximum ages for this particular sample set. The inset at the top of the figure gives relevant details of these time bars. The sample data used to calculate these ages is given further below.

 

 

    Figure 2 (right) 4 year time series of a site on the new lava flow and associated vent fauna (1991-1994). The first year shows baterial floc in the water above the flow, the second year shows a young flow largely devoid of life, and the two subsequent years show increased tube worm colonization/growth. Figure courtesy of Mike Perfit, U. Florida

  • Changes in biological community distribution between remote-sensing surveys using “ARGO” in 1988 (Haymon et al. 1991) and ALVIN dives in 1991 (Haymon et al. 1993), as well as rapid changes observed to occur over the course of 1991 and early 1992, were better understood in terms of the timing of eruptions, providing a baseline for the rebound time scale of sea floor communities following an e ruption that decimated entire hydrothermal vent field populations.
  • Rapid changes in vent water chemistry, including an apparent "reset" of the system in early 1992, were interpreted as chemical evolution following eruption (Von Damm et al. 1995).
  • Lavas erupted over 8 to 10 months of 1991 from an area known as the area the "Barbecue Pit" were essentially constant in composition, implying that magmatic processes had been constant in overall effect over this time interval.
  • A lava of different composition collected in 1992 from a suspected newly formed rift just north of the "Barbecue Pit" was dated to be younger than the rest, confirming that eruptive activity had shifted northward over the course of 1991 into a region that had not been active during the April-May 1991 ALVIN dives (Macdonald et al. 1992; Haymon et al. 1993).

    time

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9°50'N EPR - 210Po Data and Eruption Ages

Sample

Collection Date

Location

Aliquot Number

Analysis Date

Total Mass

Aliquot Mass

210Po

210Pb

Eruption Window

 

 

Lat N

Long W

 

 

(g)

(g)

(dpm/g)

(dpm/g)

 

2392-9-G

5/27/91

9°50.6'

104°17.5'

1

8/15/91

8.056

2.094

0.081 ± 0.008

0.117 ± 0.006

30 Dec 1990 to

25 Feb 1991

 

 

2

11/3/91

 

1.609

0.092 ± 0.010

 

3

1/27/92

 

1.270

0.102 ± 0.013

4

5/31/92

 

1.268

0.107 ± 0.019

5

1/15/93

 

1.772

0.114 ± 0.011

2392-9-WR

5/27/91

9°50.6'

104°17.5'

1

9/12/91

10.238

3.409

0.107 ± 0.009

0.115 ± 0.006

---

 

2

11/7/91

 

1.905

0.108 ± 0.012

 

3

5/31/92

 

0.993

0.111 ± 0.018

4

6/21/93

 

1.468

0.115 ± 0.011

2372-1-G

4/23/91

9°50.6'

104°17.5'

1

9/23/91

4.397

1.574

0.082 ± 0.008

0.119 ± 0.006

25 Feb to

23 April 1991

 

2

11/18/91

 

0.765

0.088 ± 0.015

 

3

5/29/92

 

0.672

0.109 ± 0.025

4

1/22/93

 

1.473

0.115 ± 0.014

2363-7-G

4/14/91

9°50.6'

104°17.6'

1

1/3/92

3.191

1.227

0.082 ± 0.011

0.097 ± 0.005

24 Jan to

22 Mar 1991

 

2

5/29/92

 

0.951

0.090 ± 0.012

 

3

2/15/93

 

1.008

0.095 ± 0.013

2504-1-G

3/12/92

9°50.3'

104°17.5'

1

6/11/92

3.032

1.240

0.077 ± 0.011

0.114 ± 0.005

2 Nov to

29 Dec 1991

 

2

3/12/93

 

0.975

0.105 ± 0.019

 

2497-1b-G

3/5/92

9°53.3'

104°17.9'

1

6/11/92

2.146

0.834

0.079 ± 0.012

0.145 ± 0.007

7 Jan to

5 Mar 1992

 

2

6/21/93

 

1.302

0.135 ± 0.015

 

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