uses · 2011. 1. 8. · uses science for a changing world Apatite Fission-track Analysis of Twelve Outcrop Samples from the Chandler Lake and Killik River l:250,000-scale Quadrangles,

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Apatite Fission-track Analysis of Twelve Outcrop Samples from the Chandler Lake and Killik River l:250,000-scale Quadrangles, South-central North Slope, Alaskaby Thomas E. Moore 1 , David W. Houseknecht2, and Christopher J. Potter3 ,

Open-File Report 00-220

2000

This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government.

U.S. DEPARTMENT OF THE INTERIOR U.S. GEOLOGICAL SURVEY

'Menlo Park, California 2Reston, Virginia 3Denver, Colorado

Moore, Houseknecht, and Potter: Apatite Fission-Track Analysis of Twelve Samples OF 00-220

INTRODUCTION

This Open-File report releases to the public the results of apatite fission-track analysis (AFTA) of twelve rock samples from the south-central North Slope of Alaska. These samples were collected by geologists of the U.S. Geological Survey from rock outcrops of Early Cretaceous age in the Killik River and Chandler Lake l:250,000-scale quadrangles during July, 1999 as part of a petroleum resource investigation of the National Petroleum

Reserve, Alaska (NPRA). The fission-track investigation was undertaken for the purpose

of determining the thermal-chronologic history of the subsurface section in NPRA.

Laboratory analysis of the samples was completed by GeoTrack Inernational on contract to

the U.S. Geological Survey. This report contains the raw data results of GeoTrack's apatite fission-track analysis without interpretation. Interpretations of the raw data released

here will be made and presented elsewhere at a later date.

The locations, the stratigraphic age, rock formation assignment, and apatite yields from

the twelve samples are present in Table 1. The analytical results of the apatite fission-track analysis are presented in Table 2 and a summary of the length distribution data is presented in Table 3. Following a discussion provided by GeoTrack of the sample preparation techniques used for the analysis, background information about the methods of determining apatite fission-track ages, and methods of reporting fission-track data, the results of the analysis are presented in individual data sheets by sample number. The data sheets include

both tabular and graphical presentations of the fission-track results. The results include fission-track ages (both individual grains and mean age), confined length measurements, and the chlorine content of each age grain.

The quality of the AFTA results reported here is excellent. Apatite yields in all samples were excellent, with all samples providing twenty or more grains for fission track age determination. The apatite grains are detrital grains of very good quality. In most samples,

the apatite grains are euhedral with a small number of rounded and angular grains observed

in all samples. Overall, the samples provided age and length data of excellent quality.

SAMPLE PREPARATION

Core and outcrop samples are crushed in a jaw crusher and then ground to sand grade in a rotary disc mill. Cuttings samples are washed and dried before grinding to sand grade.


The ground material is then washed to remove dust, dried and processed by conventional heavy liquid and magnetic separation techniques to recover heavy minerals. Apatite grains are mounted in epoxy resin on glass slides, polished and etched for 20 sec in 5M HNOa at

20°C to reveal the fossil fission tracks.After etching, all mounts are cut down to 1.5 X 1 cm, and cleaned in detergent, alcohol

and distilled water. The mounts are then sealed in intimate contact with low-uranium

muscovite detectors within heat shrink plastic film. Each batch of mounts is stacked between two pieces of uranium standard glass which has been prepared in similar fashion. The stack is then inserted into an aluminium can for irradiation.

After irradiation, the mica detectors are removed from the grain mounts and standard glasses and etched in hydrofluoric acid to reveal the fission tracks produced by induced

fission of 235U in the apatite and standard glass.

FISSION-TRACK AGES

Fission-track ages are calculated using the standard fission track age equation using the zeta calibration method (equation 5 of Hurford and Green, 1983), viz:

F.T. AGE = f in [ 1 + ( U° Ps g PD ) ] equation 1 AD pi

where: XD = total decay constant of 238U (= 1.55125 x 1CH0)

£ = Zeta calibration factorps = Spontaneous track densitypi = Induced track density

pD = Track density from uranium standard glass

g = A geometry factor (= 0.5)Fission track ages are determined by the external detector method or EDM (Gleadow,

1981). The EDM has the advantage of allowing fission track ages to be determined on single grains. In apatite, tracks are counted in 20 grains from each mount wherever possible. In those samples where the desired number is not present, all available grains are counted, the actual number depending on the availability of suitably etched and oriented

grains. Only grains oriented with surfaces parallel to the crystallographic c-axis are analysed. Such grains can be identified on the basis of the etching characteristics, as well as from morphological evidence in euhedral grains. The grain mount is scanned sequentially, and the first 20 suitably oriented grains identified are analysed.


Tracks are counted within an eyepiece graticule divided into 100 grid squares. In each grain, the number of spontaneous tracks, Ns, within a certain number of grid squares, Na,

is recorded. The number of induced tracks, NI, in the corresponding location within the mica external detector is then counted. Spontaneous and induced track densities, ps and pi, respectively, are calculated by dividing the track counts by the total area counted, given by

the product of Na and the area or each grid square (determined by calibration against a ruled stage graticule or diffraction grating). Fission track ages may be calculated by substituting track counts, Ns and Nj, for track densities ps and pi in equation 1, since the areas cancel

in the ratio.Translation between apatite grains in the grain mount and external detector locations

corresponding to each grain is carried out using Autoscan microcomputer-controlled

automatic stages (Smith and Leigh Jones, 1985). This system allows repeated movement

between grain and detector, and all grain locations are stored for later reference if required.

Neutron irradiations are carried out in a well thermalised flux (X-7 facility; Cd ratio for Au -98) in the Australian Atomic Energy Commission's HIFAR research reactor. Total neutron fluence is monitored by counting tracks in mica external detectors attached to two pieces of NBS standard glass SRM612 included in the irradiation canister at each end of the sample stack. In determining track densities in external detectors irradiated adjacent to

uranium standard glasses, 25 fields are normally counted in each detector, and the total

track count ND is divided by the total area counted to obtain the track density po- The

positions of the counted fields are arranged in a 5 X 5 grid covering the whole area of the

detector. For typical track densities of between ~5 X 105 and 5 X 106 this is a convenient arrangement to sample across the detector while gathering sufficient counts to achieve a precision of ~±2% in a reasonable time.

A small flux gradient is often present in the irradiation facility over the length of the sample package (note that this developed only in late 1991, after extended refurbishment of the reactor, before which no detectable flux gradient was present). If a detectable gradient

is present, the track count in the external detector adjacent to each standard glass is converted to a track density po and a value for each mount in the stack is calculated by linear interpolation. When no detectable gradient is present, the track counts in the two

external detectors are pooled to give a single value of po which is used to calculate fission

track ages for each sample.A Zeta calibration factor, £, has been determined empirically for each observer by

analysing a set of carefully chosen age standards with independently known K-Ar ages, following the methods outlined by Hurford and Green (1983) and Green (1985).


All track counting is carried out using ZeissW Axioplan microscopes, with an overall linear magnification of 1068 x using dry objectives.

For further details and background information on practical aspects of fission track age determination, see e.g. Fleischer, Price and Walker (1975), Naeser (1979) and Hurford (1986).

TRACK-LENGTH MEASUREMENTS

For track length studies in apatite, the full lengths of 'confined' fission tracks are measured. Confined tracks are those which do not intersect the polished surface but have been etched from other tracks or fractures, so that the whole length of the track is etched. Confined track lengths are measured using a digitising tablet connected to a microcomputer, superimposed on the microscope field of view via a projection tube. With this system, calibrated against a stage graticule ruled in 2 [im divisions, individual tracks can be measured to a precision of ± 0.2 um. Tracks are measured only in prismatic grains, characterised by sharp polishing scratches with well etched tracks of narrow cone angle in all orientations, because of the anisotropy of annealing of fission tracks in apatite (as discussed by Green and others, 1986). Tracks are also measured following the recommendations of Laslett and others (1982), the most important of which is that only horizontal tracks should be measured. One hundred tracks are measured whenever possible. In apatite samples with low track density, or in those samples in which only a small number of apatite grains are obtained, fewer confined tracks may be available, and in such cases, the whole mount is scanned to measure as many confined tracks as possible.

INTEGRATED FISSION-TRACK AGE AND LENGTH MEASUREMENTS

Fission track age determination and length measurement are now made in a single pass of the grain mount, in an integrated approach. The location of each grain in which tracks are either counted or measured is recorded for future reference. Thus track length measurements can be tied to age determination in individual grains. As a routine procedure we do not measure the age of every grain in which lengths are determined, as this would be much too time consuming. Likewise we do not only measure ages in grain in which lengths are measured, as this would bias the age data against low track density grains. Nevertheless, the ability to determine the fission track age of certain grains from which


length data originate can be a particularly useful aid to interpretation in some cases. Grain location data are not provided in this report, but are available on request.

PRESENTATION OF FISSION-TRACK AGE DATA

Data sheets summarising the apatite fission track age data, including full details of fission track age data for individual apatite grains in each sample, together with the primary counting results and statistical data, are given in the following pages. Individual grain fission track ages are calculated from the ratio of spontaneous to induced fission track counts for each grain using equation 1, and errors in the single grain ages are calculated using Poissonian statistics, as explained in more detail by Galbraith (1981) and Green (1981). All errors are quoted as ±lc throughout this report, unless otherwise stated.

The variability of fission track ages between individual apatite grains within each sample can be assessed using a chi-squared (%2) statistic (Galbraith, 1981), the results of which are summarised for each sample in the data sheets. If all the grains counted belong to a single age population, then the probability of obtaining the observed %2 value, for v degrees of freedom (where v = number of crystals -1), is listed in the data sheets as P(%2) or P(chi squared).

A P(%2) value greater than 5% can be taken as evidence that all grains are consistent with a single population of fission track age. In this case, the best estimate of the fission track age of the sample is given by the "pooled age", calculated from the ratio of the total spontaneous and induced track counts in all grains analysed. Errors for the pooled age are calculated using the 'conventional' technique outlined by Green (1981), based on the total number of tracks counted for each track density measurement (see also Galbraith, 1981).

A P(5C2) value of less than 5% denotes a significant spread of single grain ages, and suggests that real differences exist between the fission track ages of individual apatite grains. A significant spread in grain ages can result either from inheritance of detrital grains from mixed source areas (in sedimentary rocks), or from differential annealing in apatite grains of different composition, within a narrow range of temperature.

Calculation of the pooled age inherently assumes that only a single population of ages is present, and is thus not appropriate to samples containing a significant spread of fission track ages. In such cases Galbraith has recently devised a means of estimating the modal age of a distribution of single grain fission track ages which is referred to as the "central age". Calculation of the central age assumes that all single grain ages belong to a Normal distribution of ages with a standard deviation, a, known as the "age dispersion". An iterative algorithm (Galbraith and Laslett, 1993) is used to provide estimates of the central


age with its associated error, and the age dispersion, which are all quoted in the data sheets.

Note that this treatment replaces use of the "mean age" which has used been in the past for

those samples in which P(x2)<5%. For samples in which P(x2)>5%, the central age and the pooled age should be equal, and the age dispersion should be less than ~10%.

Table 2 summarises the fission track age data in apatite from each sample analysed.

CONSTRUCTION OF RADIAL PLOTS OF SINGLE GRAIN AGE DATA

Single grain age data are best represented in the form of radial plot diagrams (Galbraith,

1988,1990). As illustrated in Figure 1, these plots display the variation of individual grain

ages in a plot of y against x, where:y = (zj - z0) /Oi x = 1/Oj equation 2

and; Zj = fission track age of grain j z0 = a reference age Oj = error in age for grain j

In this plot, all points on a straight line from the origin define a single value of fission

track age, and at any point the value of x is a measure of the precision of each individual

grain age. Therefore, precise individual grain ages fall to the right of the plot (small error, high x), which is useful, for example, in enabling precise, young grains to be identified. The age scale is shown radially around the perimeter of the plot (in Ma). If all grains belong to a single age population, all data should scatter between y = +2 and y = -2,

equivalent to scatter within ±2o. Scatter outside these boundaries shows a significant spread of individual grain ages, as also reflected in the values of P(X2) and age dispersion.

In detail, rather than using the fission track age for each grain as in equation 2, we use:Nsi

Zj = j^r GJ ={ l/Nsj+ l/Ny} equation 3

as we are interested in displaying the scatter within the data from each sample in

comparison with that allowed by the Poissonian uncertainty in track counts, without the

additional terms which are involved in determination of the fission track age (pD, £, etc).

Zero ages cannot be displayed in such a plot. This can be achieved using a modified plot, (Galbraith, 1990) with:______ _________

/ f Nsj+3/8 l 1 If I f z\=arcsin\l 1 vr . , vj.. j. *IA I <Ji = T v 1 vr . _,_ xr . i eq. 4


Note that the numerical terms in the equation for Zj are standard terms, introduced for statistical reasons. Using this arc-sin transformation, zero ages plot on a diagonal line which slopes from upper left to lower right. Note that this line does not go through the origin. Figure 2 illustrates this difference between conventional and arc-sin radial plots, and also provides a simple guide to the structure of radial plots.

Use of arc-sin radial plots is particularly useful in assessing the relative importance of zero ages. For instance, grains with Ns = 0, NI = 1 are compatible with ages up to ~900 Ma (at the 95% confidence level), while grains with Ns = 0, NI = 50 are only compatible with ages up to ~14 Ma. The two data would readily be distinguishable on the radial plot as the 0,50 datum would plot well to the right (high x) compared to the 0,1 datum.

In this report the value of z corresponding to the fission track age of each sample is adopted as the reference value, z0 .

Note that the x axis of the radial plot is normally not labelled, as this would obscure the age scale around the plot. In general labelling is not considered necessary, as we are concerned only with relative variation within the data, rather than absolute values of precision.

Radial plots of the single grain age data in apatite from each sample analysed in this report are shown on the fission track age data summary sheets at the end of this report.

HISTOGRAMS OF TRACK-LENGTH DATA

Distributions of confined track lengths in apatite from each sample are shown as simple histograms on the fission track age data summary sheets at the end of this report. For every track length measurement, the length is recorded to the nearest 0.1 urn, but the measurements have been grouped into 1 um intervals for construction of these histograms. Each distribution has been normalised to 100 tracks for each sample to facilitate comparison. A summary of the length distribution in each sample is presented in Table 3, which also shows the mean track length in each sample and its associated error, the standard deviation of each distribution and the number of tracks (N) measured in each sample. The angle which each confined track makes with the crystallographic c-axis is also routinely recorded, as is the width of each fracture within which tracks are revealed. These data are not provided in this report.

BREAKDOWN OF DATA INTO COMPOSITIONAL GROUPS


Apatite fission-track data are grouped into compositional intervals of 0.1 wt% Cl width. Parameters for each interval represent the data from all grains with Cl contents within each interval. Also shown are the parameters for each compositional interval predicted from the Default Thermal History. These data form the basis of interpretation of the AFTA data,

which takes full account of the influence of Cl content on annealing kinetics. Distributions

of Cl contents in all apatites analysed from each sample (i.e. for both age and length determinations) are shown on the fission-track age data summary sheets at the end of this

report.

PLOTS OF FISSION-TRACK AGE AGAINST Cl CONTENT FOR INDIVIDUAL APATITE GRAINS

Fission-track ages of single apatite grains within individual samples are plotted against the Cl content of each grain on the fission-track age data summary sheets at the end of this report. These plots are useful in assessing the degree of annealing, as expressed by the fission-track age data. For example, if grains with a range of Cl contents from zero to

some upper limit all give similar fission-track ages which are significantly less than the

stratigraphic age, then grains with these compositions must have been totally annealed.

Alternatively, if fission-track age falls rapidly with decreasing Cl content, the sample displays a high degree of partial annealing.

A NOTE ON TERMINOLOGY

Note that throughout this report, the term "fission-track age" is understood to denote the

parameter calculated from the fission-track age equation, using the observed spontaneous

and induced track counts (either pooled for all grains or for individual grains). The resulting number (with units of Ma) should not be taken as possessing any significance in

terms of events taking place at the time indicated by the measured fission-track age, but should rather be regarded as a measure of the integrated thermal history of the sample, and should be interpreted in that light. Use of the term "apparent age" is not considered to be

useful in this regard, as almost every fission-track age should be regarded as an apparent age, in the classic sense, and repeated use becomes cumbersome.

Moore, Houseknecht, and Potter: Apatite Fission-Track Analysis of Twelve Samples

Estimates z.

Standard errors G;Reference value zoStandardised estimates y. = (

Precision x. = 1

OF 00-220

PLOT y. against x-

y:

+2 +1

0-1-2

Z;

z -

X.

Slope of line from origin through data point

= 7-71 O

Key Points;Radial lines emanating from the origin correspond to fixed values of z Data points with higher values of Xj have greater precision. Error bars on all points are the same size in this plot.

Figure 1. Basic construction of a radial plot. In AFTA, the estimates z[ correspond to the fission-track age values for individual apatite grains. Any convenient value of age can be chosen as the reference value corresponding to the horizontal in the radial plot. Radial lines emanating from the origin with positive slopes correspond to fission-track ages greater than the reference value. Lines with negative slopes correspond to fission- track ages less than the reference value.


Normal radial plot (equations 2 and 3)

OF 00- 220

^

Allowed 'range for a single population '

+210 i

r -2

\"

L LtSb ____ _ MORE

>. PRECISE"* ̂ PRECISE

°\ / YOUNGER ~~/

*

^ _ Reference age

0

Arc-sin radial plot (equations 2 and 4)

Allowed ' range for a single population <

, +2

0

r -2

^

\.DER

Is Lbbb ^ __ ___ ̂MORE s s PRECISE"* ̂PRECISE

\ /S yr

S ^ s y/ YOUNGER

%

^ _ Reference age

Figure 2 Simplified structure of Normal and Arc-sin radial plots.

10

Moore, Houseknecht, and Potter: Apatite Fission-Track Analysis of Twelve Samples OF 00- 220

Table 1. Fission-track sample numbers, locations, stratigraphic assignment, age, and apatite yields for analyzed samples. Stratigraphic ages from Micropaleo Consultants, Inc._______________

Sample USGS field Location and number Number Elevation (ft)

Stratigraphic Subdivision

Stratigraphic Raw Washed Apatiteage weight weight yield *l

(Ma) (g) (g)

Outcrop samplesGC763-36 99TM-503B

GC763-37 99TM-515B

GC763-38 99TM-538

GC763-39 99TM-551B

GC763-40 99TM-564B

GC763-41 99TM-568A

GC763-42 99TM-576B

GC763-43 99TM-578B

GC763-44 99DH-52

GC763-45 99DH-54

GC763-46 99DH-65B

GC763-47 99CP-A13

Okokmilaga at Akmaktaksrak Bluff 68°37.513'N 153°13.650'W 1640'

Siksikpuk Rv at Tiglukpuk Ck 68031.911'N 152002.981'W 1500'

Gunsight Mtn 68°42.820' N 151°52.092'W 450'

Okpikruak Rv at Sivogakruak Bluff 68.66894° N 153.45382° W 1542'

Kiruktagiak Rv 68°37.666' N 152°39.349'W 1500'

Tiglukpuk Ck 68°25.943' N 151°54.091'W 200'

Pediment Ck 68°42.347' N 153°13.854'W 1345'

junction of Killik - Okokmilaga Rvs 68°55.728' N 153°26.058'W 869'

trib. To E fork, Oolamnagavik Rv 68.78355°N 153.96614°W 1200'

Killik bend, Colville Rv 68.97000°N 153.94053° W 600'

Okpikruak Rv at Sivogakruak Bluff 68°40.452' N 153°25.987'W 1476'

Siksikpuk Rv near Confusion Ck 68°28.060' N 152°05.216'W 2000'

Fortress Mtn Fm

Fortress Mtn Fm

Tuktu Fm

Torok Fm

Fortress Mtn Fm

Okpikruak

Torok Fm

Chandler Fm

Torok Fm

Chandler Fm

Torok Fm

Okpikruak Fm

115-105 4580 660 excellent

115-105 5000 640 excellent

110-100 6750 550 excellent

112-105 6070 790 excellent

115-105 6530 590 excellent

141-136 5760 800 excellent

112-105 4210 990 excellent

90-84 5450 540 excellent

112-105 9040 1790 excellent

90-84 5670 1580 excellent

112-105 5240 1390 excellent

141-136 2870 880 excellent

Yield based on quantity of mineral suitable for age determination. Excellent: >20 grains; Good: 15-19 grains; Fair: 10-14 grains; Poor: 5-9 grains; Very Poor: <5 grains. 11


Table 2. Apatite fission-track analytical results.

OF 00- 220

Sample number

Outcrop samplesGC763-36

GC763-37

GC763-38

GC763-39

GC763-40

GC763-41

GC763-42

GC763-43

GC763-44

GC763-45

GC763-46

GC763-47

Number of

grains

27

25

34

25

29

31

23

26

25

20

25

29

PD(ND)

x!06 /cm2

1.397(2253)1.403

(2253)

1.409(2253)

1.415(2253)

1.420(2253)1.426

(2253)

1.432(2253)

1.438(2253)1.444

(2253)

1.450(2253)1.455

(2253)

1.461(2253)

PS(Ns)

x!06 /cm2

0.569(383)0.459(513)

0.497(439)

0.437(355)0.553(580)0.397(389)

0.621(244)

0.395(331)0.711(408)0.061(36)0.656(409)0.336(328)

P'(Ni)

x!06 /cm2

2.367(1594)2.104(2350)

1.955(1727)

1.764(1434)1.736

(1821)1.776

(1742)

2.592(1018)

1.059(888)2.539(1457)0.402(239)2.433(1517)1.527

(1491)

Uranium content

(ppm)

19

17

16

14

14

14

21

8

20

3

19

12

P(%2 )

(%)

90

<1

1

5

<1

<1

65

<1

<1

1

<1

3

Age dispersion

(%)

<1

36

30

18

27

31

2

46

36

124

40

26

Fission track age

(Ma)

63.9 ±4.0

58.3 ±3.258. 9 ±5.9*68.1 ±4.064.8 ±6.1*66.6 ±4.369. 1 ±5.6*85.9 ±4.686. 1 ±7.6*60.6 ± 3.764.2 ±6.1*65.3 ±4.9

101.7 ±7.089.8 ±13.6*76.8 ±4.775.9 ±8.1*41.6 ±7.5

33.2 ±12.9*74.6 ±4.6

97.2 ±10.4*61.2 ±4.060.2 ±'5.3*

p s = spontaneous track density; P i = induced track density; P D = track density in glass standard external detector. Brackets show number of tracks counted. P D and P i measured in mica external detectors; p s measured in internal surfaces. *CentraI age, used where sample contains a significant spread of single grain ages (P(^)<5%). Errors quoted at 10. Ages calculated using dosimeter glass CN5, with a zeta of 382.4 ± 5.5 (Analyst: S. Marshallsea) for samples; 36 - 47

12


Table 3. Length distribution summary data.

OF 00- 220

Sample number

Mean track length

(urn)

Outcrop samplesGC763-36 13.59 ±0.18GC763-37GC763-38GC763-39GC763-40GC763-41GC763-42GC763-43GC763-44 GC763-45 GC763-46GC763-47

13.36 ±0.2212.78 ± 1.9313.70 ±0.2614.37 ±0.2113.88 ±0.1813.50 + 0.2413.21+0.4013.80 ±0.21 No confined 13.39 ±0.2214.26 ±0.19

Standard deviation

1.692.161.931.991.461.84

2.212.252.08

tracks 2.031.67

Number of tracks

(N)

851002258481088532101

8477

Number of tracks in Length Intervals (urn) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

------- 2 2 3 7

- - - - 1 1 - 2 - 4 1........ 1 . 1-------- 1 2 3--..-..... 1-------- 1 6 2

- - 1 1 ----- 1 2......... 4 4

- - - - 1 - - 1 3 2 1

... 1 ... 1 . 2 7

.......... 2

12735287-

6

49

181737611

946

117

2231512112124

622

199

17168109

2825635

2522

211-

11132210616

1217

17 18 19 20

6 3 - -1 ...7 ...6 ...9 ...

5 - - -2 - - -7 1 - -

1 1 - -11 ...

Track length measurements by: S. Marshallsea for samples; 36 - 47

13


EXPLANATION FOR FISSION-TRACK DATA SHEETS

Ns = Number of spontaneous tracks in Na grid squaresNi = Number of induced tracks in Na grid squaresNa = Number of grid squares counted in each grainRATIO = Ns/NiU (ppm) = Uranium content of each grain (= U content of standard glass *

pi/PD) Cl (wt%) = Weight percent chlorine content of each grain

RHOs = Spontaneous track density (ps) = Ns/ (Na*area of basic unit)

RHOi = Induced track density (pi) = Ni/(Na*area of basic unit) F.T. AGE = Fission-track age, calculated using equation 1 Area of basic unit = Area of one microscope eyepiece grid square

Chi squared = %2 parameter, used to assess variation of single grain ages within the sample

P(chi squared) = Probability of obtaining observed %2 value for the relevant number of degrees of freedom, if all grains belong to a single population

Age Dispersion = % variation in single grain ages - see discussion in text re "Central age"

Ns/Ni = Pooled ratio, total spontaneous tracks divided by total induced tracks for all grains

Mean ratio = Mean of (Ns/Ni) for individual grainsZeta = Calibration constant, determined empirically for each observer

RhoD = Track density (p£>) from uranium standard glass (interpolated from values at each end of stack)

ND = Total number of tracks counted for determining pj) POOLED AGE = Fission-track age calculated from pooled ratio Ns/Ni. Valid only

when %2 > 5%

CENTRAL AGE = Alternative to pooled age when %2 < 5%

14


Organization and captions for graphical plots shown in data sheets:

Plot A: Radial plot of single grain ages for analyzed sample.(See Figures 1 and 2 for details of radial plot construction)

Plot B: Distribution of Cl contents in apatite grains for analyzed sample.

Plot C: Single grain age vs weight % Cl for individual apatite grains in analyzed sample

Plot D: Distribution of confined track lengths in analyzed sample.

15

Moore, Houseknecht, and Potter: Apadte Fission-Track Analysis of Twelve Samples GC763-36 APATITE IRRADIATION G820 TTOr'O c« i~ (uvrnv/r cniSLIDE NUMBER i USlrS Sample 99TM-503COUNTED-BY: SJM

OF 00-220 99TM-503B

Current grain no.

3412131518212225293031323334373941434448495253627379

Ns

12132

3218104261429

266817311541

25232862166

Ni

6658168971841196

27621038893854871297385

11269982708124

Na

422442204420602824162032324819505040705030404880306348

RHOs

4.540E4058.607E4057.567E+042.542E+063.612E+046.356E4052.648E4052.270E4051.324E4055.959E4051.112E+069.932E+044.469E4058.607E4055.018E4052.542E4055.403E4051.232E+063.405E4051.271E4055.297E+049.932E+057.614E4055.562E4053.284E+064.036E4051.986E405

RHOi

2.497E+063.840E+066.054E+057.071E+062.528E4051.430E+061.086E+061.078E4063.973E4052.682E+064.926E+064.966E4051.887E+062.946E+063.178E+061.716E+062.765E+065.125E+061.657E+062.542E4052.648E+054.449E+062.284E+061.947E+061.430E+072.043E+067.945E+05

RATIO

0.1820.2240.1250.3600.1430.4440.2440.2110.3330.2220.2260.2000.2370.2920.1580.1480.1950.2400.2050.5000.2000.2230.3330.2860.2300.1980.250

U (ppm)

20.431.34.9

57.72.1

11.78.98.83.2

21.940.24.1

15.424.025.914.022.641.813.52.12.2

36.318.615.9

116.716.76.5

a(wt%)

0.000.060.050.060.510.210.440.020.020.020.130.350.720.000.230.000.070.050.000.490.650.570.040.200.270.010.01

F.T. AGE (Ma)

48.4 ± 15.259.6 ± 18.433.3 ± 25.095.3 ± 19.838.1 ± 40.7

117.7± 50.164.8 ± 22.956.0 ± 30.888.4 ± 72.259.1 ± 26.760.0 ± 17.853.2 ± 41.263.0 ± 23.477.6 ± 17.442.0 ± 18.539.5 ± 15.052.0 ± 13.863.9 ± 12.954.7 ± 15.6

132.2± 81.053.2 ± 58.359.4 ± 13.288.4 ± 21.475.9 ± 16.461. 1± 8.752.6 ± 14.466.4 ± 30.4

383 1594 5.688E+05 2.367E+06 19.3

Area of basic unit = 6.293E-07 cm-2

Chi Squared = 17.322 with 26 degrees of freedomP(chi squared) = 89.9 %Age Dispersion = 0.295 % (did not converge)Ns/Ni= 0.240 ± 0.014Mean Ratio = 0.245 ± 0.017

Ages calculated using a zeta of 382.4 ± 5.5 for CN5 glass Rho D = 1.397E+06cm-2; ND = 2253Rho D interpolated between top of can; Rho D = 1.397E+06cro-2, ND = 1099

bottom of can; Rho D= 1.467E+06cm-2, ND = 1154

POOLED AGE = 63.9 ± 4.0 MaCENTRAL AGE = 63.9 ± 4.0 Ma

A:

+2+1

0-1

-2

53

20

15

10

5

0.5 1.0 1.5 2.0 2.5 3.0 Wt % Chlorine

C: D:

300

stratigraphic age range

40

30

20

10

0.4 0.6 0.8 1 Weight % Chlorine

1.2 1.4 5 10 15 20 TRACKLB4GTH (microns)

16

Moore, Houseknecht, and Potter: Apatite Fission-Track Analysis of Twelve Samples GC763-37 APATITE

OF 00-22099TM-515B

IRRADIATION G820 SLIDE NUMBER 2 COUNTED BY: SJM

USGS Sample 99TM-515B

Current grain no.

45689101112131415161719212223

2831364448545758

Ns

144351

483

214612346

212562

665

84511851851

Ni

266185113

2092561157594651389136439

32159

369207593673

278

Na

100509039566470427074677010049848080901005070100804060

RHOs

2.225E-K)51.271E-K)55.297E+042.037E-K)52.838E+041.192E+066.810E+047.945E-K)59.080E+041.288E+052.846E+057.718E-K)59.534E+046.810E+054.729E-K)51.192E-K)53.973E+041.165E+067.945E+042.670E+061.158E+062.860E-K)59.932E+047.151E-K)51.351E+06

RHOi

4.132E-K)51.907E+053.178E-K)52.078E+063.689E-K)55.189E+065.675E+052.308E+063.405E-K)51.611E+062.229E+061.476E+062.066E-K)52.886E+062.573E+068.541E+051.788E-K)55.668E+069.375E+051.173E+074.699E+069.375E-K)57.151E-K)52.900E+067.363E+06

RATIO

0.5380.6670.1670.0980.0770.2300.1200.3440.2670.0800.1280.5230.4620.2360.1840.1400.2220.2060.0850.2280.2460.3050.1390.2470.183

U (ppm)

3.41.52.6

16.93.0

42.24.6

18.82.8

13.118.112.01.7

23.520.96.91.5

46.17.6

95.338.27.65.8

23.659.8

a(wt%)

1.051.240.280.010.000.030.260.000.020.000.141.040.500.030.060.500.670.060.060.770.090.570.050.070.30

FT. AGE (Ma)

142.9± 47.5176.4 ±114.044.6 ± 27.826.2 ± 12.320.6 ± 21.461.3 ± 9.932.1 ± 19.691.7± 23.371. 1± 40.121.4± 9.134.2 ± 10.5

138.8± 29.6122.6± 60.663.0 ± 15.449.1 ± 10.837.3 ± 16.359.3 ± 46.454.9 ± 7.622.7 ± 10.660.8 ± 7.565.8 ± 10.481.3± 22.037.2 ± 17.865.8 ± 17.449.0 ± 7.6

513 2350 4.593E-K)5 2.104E+06 17.1


Chi Squared = 61.083 with 24 degrees of freedom P(chi squared) = 0.0 % Age Dispersion = 35.928 %

Ns/Ni= 0.218 ± 0.011 Mean Ratio = 0.245 ± 0.031

Ages calculated using a zeta of 382.4 ± 5.5 for CN5 glass RhoD= 1.403E+06cm-2; ND= 2253Rho D interpolated between top of can; Rho D = 1.397E+06cm-2. ND = 1099

bottom of can; Rho D = 1.467E+06cm-2, ND = 1154

POOLED AGE = 58.3 ± 3.2 Ma CENTRAL AGE = 58.9 ± 5.9 Ma

A:

+2+10

-1

-2

176

20

OURANQO 20 APATITE

0.5 1 .0 1.5 2.0 2.5 3.0 Wt % Chlorine

C: D:

300

<'

. stratigraphic age range _

40

30

20

10

0.2 0.4 0.6 0.8 1 1.2 1.4 Weight % Chlorine

5 10 15 20 TRACKLB4GTH (microns)

17


USGS Sample 99TM-538

OF 00- 220

GC763-38 APATITE


99TM-538

Current grain no.

4579101112131417182021222529303132353738394041425153434647485058

Ns

2020006710010735408

366

7425841002038243

294

319

Ni

5313232172034333

27920312

4311626

337117207139

1591228912794411056

Na

315624301550142040707010080181834802424287071282880722428253642252128

RHOs

1.025E+05O.OOOE-fOO1.324E+05O.OOOE-fOOO.OOOE-fOOO.OOOE-fOO6.810E+055.562E+053.973E404O.OOOE+OOO.OOOE-fOO1.589E404O.OOOE-fOO6.180E+052.648E+052.337E+057.945E404O.OOOE-fOO5.297E4052.043E4061.362E4051.656E4061.419E+064.767E+061.986E+05O.OOOE-fOO1.324E+062.157E+061.526E+061.324E+051.097E+062.542E+052.346E4065.108E405

RHOi

2.563E+058.513E+048.607E+051.059E+053.178E4056.356E+041.930E+061.589E+061.192E4059.080E4046.810E+044.767E4045.959E+042.384E+067.945E4059.347E4056.158E+051.324E4052.847E+066.583E+065.902E4057.542E+066.640E+061.175E+072.761E+062.207E+043.906E+066.924E+065.657E+065.297E+052.989E+062.797E+068.324E+063.178E+06

RATIO

0.4000.0000.1540.0000.0000.0000.3530.3500.3330.0000.0000.3330.0000.2590.3330.2500.1290.0000.1860.3100.2310.2200.2140.4060.0720.0000.3390.3110.2700.2500.3670.0910.2820.161

U (ppm)

2.10.77.00.92.60.5

15.612.91.00.70.60.40.5

19.36.47.65.01.1

23.053.34.8

61.053.795.122.30.2

31.656.045.84.3

24.222.667.425.7

a(wt%)

0.000.000.070.000.000.000.020.030.000.000.000.000.000.120.300.020.320.000.030.150.410.010.070.250.010.000.030.170.120.320.120.140.070.13

FT. AGE (Ma)

106.9 ± 89.40.0 ± 0.0

41.3 ± 31.40.0 ± 0.00.0 ± 0.00.0 ± 0.0

94.4 ± 44.993.6 ± 41.289.2 ± 103.0

0.0 ± 0.00.0 ± 0.0

89.2 ± 103.00.0 ± 0.0

69.5 ± 29.589.2 ± 59.567.0 ± 33.534.7 ± 18.40.0 ± 0.0

49.9 ± 19.383.1 ± 16.061.9 ± 28.158.9 ± 7.757.3 ± 12.7

108.4 ± 14.319.4 ± 6.40.0 ± 0.0

90.7 ± 23.683.4 ± 15.672.2 ± 16.767.0 ± 43.398.1 ± 21.524.4 ± 12.875.5 ± 15.543.1 ± 15.5

439 1727

Area of basic unit = 6.293E-07 cra-2

4.969E405 1.955E+06 15.8


Ns/Ni= 0.254 ± 0.014 Mean Ratio = 0.194± 0.024

Ages calculated using a zeta of 382.4 ± 5.5 for CN5 glass RhoD= 1.409E+06cm-2; ND= 2253RhoD interpolated between top of can; RhoD= 1.397E+06cm-2, ND = 1099

bottom of can; RhoD= 1.467E+06cm-2, ND = 1154


18

Moore, Houseknecht, and Potter: Apatite Fission-Track Analysis of Twelve Samples OF 00- 220

USGS Sample 99TM-538 (continued)

GC763-38 APATITE CONTINUED 99TM-538

A:

42

+10

1-2

C:

300

OJ

S

0200< j*

S

§ 1 °°:COw

u_

0 i

C

l\

f

i 1 1

)

*bm

s«

f*1

0.2

90

1 i

0

*~D

^

"^ -

D

\1 22

r ... stratigraphic age range

I

1 1 I 1 I ! I I I

4 0.6 0.8 1 1.2 Weioht % Chlorine

11

88

66

44

1

0

4

B:

20""'D:

40

N

30

20

10

APATITE

1

11

1

1

1

ll0.5 1.0 1.5 20 2.5 3.0

Wt '/.Chlorine

-

- Jill, nr! n ,5 10 15 20

TRACK LB4GTH (microns)

19

Moore, Houseknecht, and Potter: Apatite Fission-Track Analysis of Twelve Samples OF 00- 220 GC763-39 APATITE 99TM-55IB


USGS Sample 99TM-551B

Current grain no.

356791011121314161719202122232527283135633738

Ns

12211503165

, 249301138132324181127653410

Ni

818102864154985

24911220151671101116

655118722910842

Na

42164920425056502080803680804990842420543280564260

RHOs

3.783E4041.986E+056.486E4048.740E+051.892E+05O.OOOE-fOO8.513E4045.085E+053.973E+053.973E4049.733E+051.324E+062.185E+055.959E4042.594E+052.295E+054.351E+051.324E+053.178E+055.297E4055.462E+055.363E+051.844E+061.286E+062.648E405

RHOi

3.027E+051.788E+063.243E+052.225E+062.270E+051.271E+054.256E+051.557E+066.356E+059.932E4044.946E+064.944E+063.973E+052.980E+055.189E+051.254E+061.911E+067.283E+054.767E+051.913E+062.533E+063.714E+066.498E+064.086E+061.112E+06

RATIO

0.1250.1110.2000.3930.8330.0000.2000.3270.6250.4000.1970.2680.5500.2000.5000.1830.2280.1820.6670.2770.2160.1440.2840.3150.238

U (ppm)

2.414.42.6

17.91.81.03.4

12.55.10.8

39.939.83.22.44.2

10.115.45.93.8

15.420.429.952.432.99.0

a(wt%)

0.000.000.340.010.340.000.360.180.110.110.080.071.190.010.000.090.050.100.700.120.040.010.040.150.48

FT. AGE (Ma)

33.7 ± 35.830.0 ± 22.453.9 ± 41.8

105.4 ± 37.6221.6 ±134.3

0.0 ± 0.053.9 ± 34.187.7 ± 25.4

166.9 ± 95.2107.3 ± 89.853.0 ± 8.472.0 ± 14.9

147. 1± 55.353.9 ± 34.1

133.8 ± 58.149.3 ± 14.961.3 ± 14.249.0 ± 37.7

177.9 ±114.974.5 ± 19.958.1 ± 19.438.9 ± 8.176.3 ± 10.984.6 ± 16.864. 1± 22.6

355 1434 4.366E+05 1.764E+06 14.2



Ns/Ni= 0.248 ± 0.015 Mean Ratio = 0.306 ± 0.039

Ages calculated using a zeta of 382.4 ± 5.5 for CN5 glass RhoD= 1.415E+06cm-2; ND= 2253Rho D interpolated between top of can; Rho D = 1.397E+06cm-2, ND = 1099



A:

+2+1

0-1

-2

221 177

\

132

88

44

0.5 1.0 1.5 2.0 2.5 3.0 Wt % Chlorine

D:

300


40

30

20

10

0 0.2 0.4 0.6 0.8 1 Weight % Chlorine

1.2 1.4 5 10 15 20 TRACKLB4GTH (microns)

20


USGS Sample 99TM-564BGC763-40 APATITE IRRADIATION G820 SLIDE NUMBER 5 COUNTED BY: SJM

OF 00- 220 99TM-564B

Current grain no.

Ns Ni Na RHOs RHOi RATIO U (ppm)

a(wt%)

F.T. AGE (Ma)

345678910111415171820232627282933384143455153556162

925471323

\4152648577107231334233955880

119152114115121091415681018323171526361277219174108417214238

49709084785640806040563620606435608149602645325856100608042

2.919E+054.540E4048.828E4047.567E+041.426E+052.838E4041.192E+053.973E+047.945E4047.945E+048.513E4041.766E+051.192E+065.297E4041.490E+051.816E+052.119E+059.809E4042.270E+051.854E+056.112E+052.472E+051.142E+063.644E+061.192E+065.244E+052.516E+061.152E+063.027E+06

3.567E4052.043E4052.648E4053.973E4052.852E4053.121E4051.986E4052.384E4052.648E4053.575E4053.973E4056.621E+055.403E+062.648E+054.469E+051.362E4056.091E4053.335E+054.864E4056.886E4052.200E+064.238E4053.824E-H)66.000E+064.937E+061.716E+061.104E+074.251E+069.005E+06

0.8180.2220.3330.1900.5000.0910.6000.1670.3000.2220.2140.2670.2210.2000.3331.3330.3480.2940.4670.2690.2780.5830.2990.6070.2410.3060.2280.2710.336

2.91.62.13.22.32.51.61.92.12.93.25.343.42.13.61.14.92.73.95.517.73.430.748.239.613.888.634.172.3

0.81 '0.410.240.710.380.330.340.360.330.720.450.160.000.330.300.350.260.620.250.050.150.200.001.040.030.510.100.630.24

218.5 ± 98.460.1 ± 47.089.9 ± 46.551.5 ± 28.1134.4± 62.324.6 ± 25.7160.9 ±117.645.1 ± 34.581.0± 53.360.1 ± 47.057.9 ± 36,972.0 ± 40.659.6 ± 17.154.1 ± 41.989.9 ± 42.4

352.3 ± 269.393.8 ± 38.679.4 ± 40.4125.5± 57.572.7 ± 31.075.0 ± 26.9156.51 74.580.6 ± 19.3162.9± 18.465.2 ± 11.382.5 ± 16.561.6 ± 7.273.2 ± 11.090.7 ± 11.9

580 1821 Area of basic unit = 6.293E-07 cm-2

5.529E405

Chi Squared = 68.223 with 28 degrees of freedom P(chi squared) = 0.0 % Age Dispersion = 26.695 % Ns/Ni= 0.318 ± 0.015 Mean Ratio = 0.3631 0.045

1.736E+06 13.9 Ages calculated using a zeta of 382.4 ± 5.5 for CN5 glass Rho D = 1.420E+06cm-2; ND = 2253Rho D interpolated between top of can; Rho D= 1.397E+06cm-2, ND = 1099



A:

+2+10

-1-2

352 286 221

155

90

1.0 1.5 2.0 2.5 Wt % Chlorine

3.0

C: D:

400

i. 300

200

100stratlgraphtc age range

40

30

20

10

0.2 0.4 0.6 0.8 1 1.2 1.4 Weight % Chlorine

5 10 15 20 TRACK LBJGTH (microns)

21


USGS Sample 99TM-568A

GC763-41 APATITE


389 1742


3.965E405 1.776E+06 14.2

OF 00- 220

99TM-568A

Current grain no.

5678101112131718212228293031343539464752545758677375858692

Ns

3675232222'

06216

10141318

1275103

2961114228

2318

Ni

168371294

298108026204

511862115336

6364

38161152535525816

10387

Na

60282436244080648042703516702015607021100804010042304220703010050

RHOs

7.945E4043.405E+054.635E+052.207E+051.324E+051.192E+053.973E4044.966E4044.370E+05O.OOOE-fOO1.362E+059.080E4041.589E4062.270E404O.OOOE+001.059E+051.059E+052.951E+05I.362E4062.018E4069.932E+043.973E+054.767E4041.097E4063.178E+054.162E+051.112E+064.994E+054.238E+053.655E+055.721E+05

RHOi

4.238E+054.710E+064.701E+061.280E+062.648E+051.152E+06I.589E+052.483E+051.589E+069.837E+054.540E+051.816E+055.065E+064.086E+054.767E+052.119E+052.913E+051.203E+062.724E+061.011E+077.945E+041.510E+062.542E+054.351E+061.324E+061.324E+064.132E+061.317E+068.475E+051.637E+062.765E+06

RATIO

0.1880.0720.0990.1720.5000.1030.2500.2000.2750.0000.3000.5000.3140.0560.0000.5000.3640.2450.5000.2001.2500.2630.1880.2520.2400.3140.2690.3790.5000.2230.207

U (ppm)

3.437.637.610.22.19.21.32.0

12.77.93.61.5

40.53.3-3.81.72.39.6

21.880.80.6

12.12.0

34.810.610.633.010.56.8

13.122.1

a(wt%)

0.340.010.190.100.700.040.270.251.070.011.180.410.240.790.530.350.331.060.300.110.351.160.490.041.021.260.341.161.151.061.35

F.T. AGE (Ma)

50.9 ± 32.119.7± 8.3

26.8 ± 10.746.9 ± 22.7

134.9 ±116.928.2 ± 17.167.8 ± 53.654.3 ± 42.174.6 ± 18.0

0.0 ± 0.081.3± 37.9

134.9 ±116.985.0 ± 24.515.1 ± 15.60.0 ± 0.0

134.9 ±165.398.4 ± 57.566.6 + 20.7134.9± 39.154.2 ± 5.4

332.2 ± 223.071.4± 25.450.9 ± 32.168.4 ± 14.365.1 ± 29.785.1 ± 29.573.0 ± 22.1

102.6 ± 25.8134.9 ± 58.560.6 ± 14.156.2 ± 14.6


Ns/Ni= 0.223 ± 0.013 Mean Ratio = 0.288 ± 0.041

Ages calculated using a zeta of 382.4 ± 5.5 for CN5 glass Rho D = 1.426E406cm-2; ND = 2253Rho D interpolated between top of can; Rho D = I.397E+06cm-2, ND = 1099



22


USGS Sample 99TM-568A (continued)

OF 00- 220

GC763-41 APATITE CONTINUED 99TM-568A

+2 +1 0

-2

332 265

\

199

132

66

B:DURA NO 0

20 _ APATITE

0.5 1.0 1.5 2.0 2.5 3.0 Wt % Chlorine

C:

400

2300o> 01< g 200

100

stratigraphic age range "0.2 0.4 0.6 0.8 1 1.2 1.4

Weight % Chlorine

D:

40

30

20

10

5 10 15 20 TRACKLB4GTH (microns)

23

Moore, Houseknecht, and Potter: Apatite Fission-Track Analysis of Twelve Samples GC763-42 APATITE,RRAD,ATION0820 USGS Sa«»Ple WTM-576BSLIDE NUMBER 7 COUNTED BY: SJM

OF 00- 220 99TM-576B

Current grain no.

910111213141516192021222629303637384348535568

Ns

2061

26015112*

6046108013206310391127

Ni

58381193583104127391856377

66771610391806173

Na

4012363030206015322428302021243028281830252815

RHOs

7.945E+057.945E+054.414E+041.377E+06O.OOOE-fOO1.192E+062.648E4041.271E+062.980E+05O.OOOE+002.270E+053.178E+057.945E+056.054E+05O.OOOE+006.886E+051.135E+063.405E+052.648E+055.297E+052.479E+066.243E+052.860E+06

RHOi

2.304E+065.032E+064.855E+054.926E+062.648E+056.595E+062.648E+054.343E+061.341E+061.986E+055.108E+059.534E+054.449E+062.800E+064.635E+053.496E+064.370E+069.080E+058.828E+052.066E+061.144E+073.462E+067.733E+06

RATIO

0.3450.1580.0910.2800.0000.1810.1000.2930.2220.0000.4440.3330.1790.2160.0000.1970.2600.3750.3000.2560.2170.1800.370

U (ppm)

18.340.13.9

39.22.1

52.52.1

34.610.71.64.17.6

35.422.33.7

27.834.87.27.0

16.491.127.661.6

a(wt%)

0.030.370.060.220.000.050.000.010.030.090.020.350.010.060.000.000.170.000.230.000.180.050.51

F.T. AGE (Ma)

93.7 ± 24.443.1 ± 19.024.8 ± 26.076.1 ± 17.00.0 ± 0.0

49.3 ± 13.927.3 ± 28.779.7 ± 26.260.6 ± 27.4

0.0 ± 0.0120.6± 72.590.6 ± 42.848.7 ± 16.858.9 ± 23.0

0.0 ± 0.053.7 ± 16.470.7 ± 17.8

101.9 ± 48.881.6 ± 53.869.8 ± 24.859.1 ± 10.549.2 ± 16.2

100.5 ± 22.8

244 1018 6.214E+05 2.592E+06 20.6


Chi Squared = 18.886 with 22 degrees of freedomP(chi squared) = 65.2%Age Dispersion = 2.250 % (did not converge)

Ns/Ni= 0.240 ± 0.017 Mean Ratio = 0217 ± 0.025

Ages calculated using a zeta of 382.4 ± 5.5 for CN5 glass RhoD= 1.432E+06cm-2; ND= 2253Rho D interpolated between top of can; RhoD= 1.397E+06cm-2, ND = 1099


POOLED AGE = 65.3 ± 4.9 MaCENTRAL AGE = 65.3 ± 5.0 Ma

A:

+2

+1

0-1

-2

H

a " *

a " _n n

a B a

n -» D

\ ^

1 24

120

96

72

48

C: snn

Track Age (Ma)

' ro (

> o > o

c luu i oa ;IT

0 , ._ ....

1

1

0 0.2

I. 1stratigraphic age range

i i i i i i i i

0.4 0.6 0.8 1 1.2 1.4 Weight % Chlorine

B:

20.

15

,.

D:

40

N

30

20

10

1 DURANQO APATITE

L , , , , ,0.5 1.0 1.5 2.0 2.5 3.0

Wt % Chlorine

_r

_. A.5 10 15 20

TRACK LBIGTH (microns)

24

loore, Houseknecht, and Potter: Apatite Fission-Track Analysis of Twelve Samples GC763-43 APATITE IRRADIATION G820 TTCr'C C«mnl 0 OOTlV/f ff'TCHSLIDE NUMBER 8 USCrS Sample 99TM-578B

OF 00- 220 99TM-578B

COUNTED BY: SJM

Currentgrain no.

7891112131517181920212324273440414243444649505253

Ns

003

76010085,00000

96258

3301

3130248

Ni

212

151371287812111

19013131851

16

931484441

Na

24498060100803070498035364056603625484048703650803020

RHOs

O.OOOE+00O.OOOE+005.959E+042.013E+06O.OOOE+001.986E+04O.OOOE+00O.OOOE+002.594E+059.932E+04O.OOOE+00O.OOOE+00O.OOOE+00O.OOOE+00O.OOOE+004.238E+061.271E+051.655E+053.178E+051.092E+06O.OOOE+004.414E+049.852E+055.959E+051.271E+066.356E+05

RHOi

1.324E+053.243E+043.973E+043.999E+064.767E+041.390E+055.297E+044.540E+042.821E+061.589E+054.540E+048.828E+043.973E+042.838E+042.648E+048.387E+068.263E+054.304E+057.151E+051.688E+062.270E+042.648E+052.956E+062.940E+062.331E+063.258E+06

RATIO

0.0000.0001.5000.5030.0000.1430.0000.0000.0920.6250.0000.0000.0000.0000.0000.5050.1540.3850.4440.6470.0000.1670.3330.2030.5450.195

U(ppm)

1.00.30.3

31.70.41.10.40.4

22.41.30.40.70.30.20.2

66.56.63.45.7

13.40.22.1

23.423.318.525.8

a(wt%)

0.000.000.330.610.000.330.000.000.032.800.000.000.000.000.000.080.160.420.000.660.000.410.670.690.650.64

F.T. AGE(Ma)

0.0 ± 0.00.0 ± 0.0

399.8 ±365.1136.9± 19.6

0.0 ± 0.039.2 ± 41.90.0 ± 0.00.0 ± 0.0

25.2 ± 9.3169.6 ± 96.8

0.0 ± 0.00.0 ± 0.00.0 ± 0.00.0 ± 0.00.0 ± 0.0

137.4± 17.642.2 ± 32.0

104.9 ± 55.3121. 1± 51.5175.5 ± 39.5

0.0 ± 0.045.7 ± 49.391.0± 19.055.5 ± 11.2

148.3 ± 37.853.4 ± 20.7

331 888 3.949E+05 1.059E+06 8.4


Chi Squared = 61.272 with 25 degrees of freedom P(chi squared) = 0.0% Age Dispersion = 46.002 %

Ns/Ni = 0.373 ± 0.024 Mean Ratio = 0.248 ± 0.067

Ages calculated using a zeta of 382.4 ± 5.5 for CN5 glass RhoD= 1.438E+06cm-2; ND = 2253Rho D interpolated between top of can; Rho D = 1.397E+06cm-2, ND = 1099

bottom of can; RhoD= 1.467E+06cm-2, ND = 1154

POOLED AGE =101.7 ± 7.0 Ma CENTRAL AGE = 89,8 ± 13.6 Ma

A:

+2

+1 0

1

-2

C:

500

J 400

f 300 ^e

£ 200

8 % 100

LL.

0

(

'Hi «

-

inrD C

' .

:.\i

.4

399319 239X ' ' **

'

i

~~"

\1

1 i

stratkjraphic age range

! t t i i i i i i i i0.8 1.2 1.6 2 2.4 2.

Weight % Chlorine

15<

79

8

}

B:

20

15

10

5

D:

40

N

30

20

10

APATITE

I

I

I

I

I

I

1

HI, , , , ,0.5 1.0 1.5 2.0 2.5 3.0

Wt % Chlorine

-

rJ~

. I. .1 .5 10 15 20

TRACK LBJGTTH (microns)

25

Moore, Houseknecht, and Potter: Apatite Fission-Track Analysis of Twelve Samples GC763-44 APATITEIRRADIATION 0820 USGS Sample 99DH-52SLIDE NUMBER 9 COUNTED BY: SJM

408 1457


7.109E405 2.539E+06 20.0

OF 00- 220 99DH-52

Current grain no.

111213141519212223242527282930313536394041467699110

Ns

5282913787210610126

2336142714313297

Ni

36901368371835

286924281467

24461125741615446069

402

Na

3570484036163530163035326028354015144245 -3824363676

RHOs

2.270E4056.356E4056.621E+043.575E4054.414E+042.980E4053.178E4054.608E+061.986E4055.297E+052.724E4054.966E4052.648E+041.135E4052.724E4059.137E+053.178E4056.810E4055.297E+05

J 7.063E+042.927E4059.270E4051368E4061.412E+062.028E+06

RHOi

1.634E+062.043E+064.304E4052.701E+061.633E+061.788E+061.589E+061.515E+078.938E4051.271E+061.271E+066.952E4051.589E4053.973E+051.090E+061.827E+061.165E+062.838E+062.800E+065.650E4056.273E4052.913E+062.648E+063.046E+068.405E+06

RATIO

0.1390.3110.1540.1320.0270.1670.2000.3040.2220.4170.2140.7140.1670.2860.2500.5000.2730.2400.1890.1250.4670.3180.5170.4640.241

U (ppm)

12.916.13.4

21.312.914.112.5

119.67.1

10.010.05.51.33.18.6

14.49.2

22.422.14.55.0

23.020.924.066.4

a(wt%)

0.090.250.060.190.000.060.770.110.750.050.000.120.050.000.000.590.010.040.100.270.620.071350.910.01

F.T. AGE (Ma)

38.2 ± 18.385.3 ± 18.642.3 ± 32.236.4 ± 13.07.5 ± 7.6

45.8 ± 28.655.0 ± 22.883.4 ± 10.461.1 ± 47.8114.0± 43.058.9 ± 26.5

194.2± 80.645.8 ± 49.578.4 ± 62.968.6 ± 31.4136.6± 35.174.9 ± 48.865.9 ± 30.052.0 ± 15.234.4 ± 25.8

127.6± 58.587.2 ± 26.9

141.1 ± 31.4126.81 27.366.3 ± 7.7


Ns/Ni= 0.280 ± 0.016 Mean Ratio = 0281 ± 0.031

Ages calculated using a zeta of 382.4 ± 5.5 for CN5 glass RhoD= 1.444E+06cm-2; ND=2253RhoD interpolated between top of can; RhoD= 1.397E+06cm-2, ND = 1099



A:

+2+1

0-1-2

194 156

119

82

0.5 1.0 1.5 2.0 2.5 3.0 Wt % Chlorine

C: D:

300

§,200 <

100 stratigraphic age range 1

40

30

20

10

0.2 0.4 0.6 0.8 1 Weight % Chlorine

1.2 1.4 5 10 15 20 TRACK LBIGTH (microns)

26


USGS Sample 99DH-54GC763-45 APATITE


OF 00- 220

99DH-54

Currentgrain no.

3457891011121314151617182021272829

Ns

800000630000060002011

36

Area of basic unit

Ni

175431957532213

61834183

66

239

Na

8034357042603221506056406040406035356035

RHOs

1.589E+05O.OOOE+00O.OOOE+00O.OOOE+00O.OOOE+00O.OOOE+002.980E+052.270E+05O.OOOE+00O.OOOE+00O.OOOE+00O.OOOE+00O.OOOE+002.384E+05O.OOOE+00O.OOOE+00O.OOOE+009.080E+04O.OOOE+004.994E+05

6.054E+04

RHOi

3.377E+052.337E+051.816E+056.810E+047.189E+051.324E+053.476E+053.783E+059.534E+045.297E+045.675E+043.973E+047.945E+042.423E+063.178E+057.945E+041.816E+058.172E+057.945E+042.997E+06

4.019E+05

RATIO

0.4710.0000.0000.0000.0000.0000.8570.6000.0000.0000.0000.0000.0000.0980.0000.0000.0000.1110.0000.167

= 6.293E-07 cm-2 Ages calculated using a zeta o

U(ppm)

2.71.81.40.55.71.02.73.00.70.40.40.30.6

19.12.50.61.46.40.6

23.6

3.2

f 382.4 ± 5.51

a(wt%)

0.510.000.000.000.430.000.450.020.000.000.000.010.000.020.000.000.0 10.470.000.02

ror CN5 glas

FT. AGE(Ma)

129.1± 55.50.0 ± 0.00.0 ± 0.00.0 ± 0.00.0 ± 0.00.0 ± 0.0

233.3 ± 129.9164.2 ±120.0

0.0 ± 0.00.0 ± 0.00.0 ± 0.00.0 ± 0.00.0 ± 0.0

27.2 ± 11.70.0 ± 0.00.0 ± 0.00.0 ± 0.0

30.7 ± 22.90.0 ± 0.0

46.0 ± 15.0

;s


Ns/Ni= 0.151 ± 0.027 Mean Ratio = 0.115± 0.054

Rho D = 1.450E+06cm-2; ND = 2253Rho D interpolated between top of can; Rho D = 1.397E+06cm-2, ND = 1099

bottom of can; Rho D= 1.467E+06cm-2, ND= 1154


A:

+2

233

B:DO RAN 00

20 APATITE

15

10

0.5 1.0 1.5 2.0 2.5 3.0 Wt % Chlorine

C: D: No confined tracks

300

200

100

(

(III.( >

slratigraphic age range

t i i t i i i i

0.2 0.4 0.6 0.8 1 Weight % Chlorine

1.2 1.4

27

Moore, Houseknecht, and Potter: Apatite Fission-Track Analysis of Twelve SamplesGC763-46 APATITE

IRRADIATION G820 USGS Sample 99DH-65BSLIDE NUMBER 11 COUNTED BY: SJM

OF 00-220 99DH-65B

Current grain no.

4568101112131415161920232426273031466163727374

Ns

2642312321

50196

204111515683

27397241461

Ni

351952

83433

2658810465

84211736

247

9912810

10828198

Na

38644070252525405035323030403070644035502135243048

RHOs

1.087E+061.043E+061.192E+052.724E+051.907E-K)51.271E+056.356E4041.986E+066.038E+052.724E+059.932E+052.119E+055.827E+053.973E4042.648E+053.405E+051.490E+053.178E+051.362E+058.581E+052.951E+063.178E+051.589E+067.416E+052.019E+06

RHOi

1.464E+064.842E+067.945E+041.884E+062.542E+051.907E+051.907E+051.053E+072.797E+064.540E+052.284E+062.648E+054.449E+067.945E4045.827E+051.657E+061.490E+059.534E+053.178E+053.146E+069.686E+064.540E+057.151E+061.483E+066.555E+06

RATIO

0.7430.2151.5000.1450.7500.6670.3330.1890.2160.6000.4350.8000.1310.5000.4550.2051.0000.3330.4290.2730.3050.7000.2220.5000.308

U (ppm)

11.537.90.6

14.82.01.51.5

82.521.93.6

17.92.1

34.90.64.613.01.27.52.5

24.675.93.6

56.011.651.3

a(wt%)

O.II0.420.760.061.050.380.310.050.630.760.500.620.140.541.110.202.190.910.350.570.020.780.161.220.40

F.T. AGE (Ma)

203.51 52.959.7 ± 10.3

404.5 ± 369.440.1 ± 12.4

205.41157.01 82.9 ±167.092.1 ±106.452.3 ± 8.259.8 ± 15.2

164.9 ± 85.2119.9± 32.3

2 18.9 ±146.936.3 ± 11.7

137.7 ±168.6125.3± 67.656.9 ± 16.2

272.5 ±157.592.1 ± 37.7

1 18.2 ± 81.675.5 ± 16.584.2 ± 15.6

191.91 94.761.5 1 14.0

137.7± 45.285.2 ± 12.7

409 1517 6.558E+05


Chi Squared = 68.877 with 24 degrees of freedom P(chi squared) = 0.0% Age Dispersion = 39.843 %

Ns/Ni= 0.2701 0.015 Mean Ratio = 0.478 ± 0.063

2.432E+06 19.1

Ages calculated using a zeta of 382.4 ± 5.5 for CN5 glass Rho D = 1.455E+06cm-2; ND = 2253Rho D interpolated between top of can; Rho D = 1.397E+06cm-2, ND = 1099

bottom of can; Rho D= I.467E+06cm-2, ND= 1154

POOLED AGE = 74.6 1 4.6 Ma CENTRAL AGE = 91.2 ± 10.4 Ma

A:

+2+ 1

0-1-2

404 300 200

36

125

75

B:DO RAN 00

20 - APATITE

0.5 1.0 1.5 2.0 2.5 3.0 Wt %Chlorine

C:

500

^ 400

If 300

,? 200

g'8 100 il

0

D:


40

30

20

10

0.4 0.8 1.2 1.6 Weight % Chlorine

2.4 5 10 15 20 TRACK LENGTH (microns)

28


USGS Sample 99CP-A13

OF 00- 220

GC763-47 APATITE


99CP-A13

Current grain no.

347910111417182021222326272829313233343962664448515471

Ns

362110210001070114601043347143071217412121413

Ni

1071157899

117

572428211111821819192043381611657982237567139

Na

7270563542703550304960563270402010010048351002870702856505624

RHOs

7.945E+054.767E+052.838E+059.534E+05O.OOOE+00O.OOOE+00O.OOOE+003.178E+053.708E+05O.OOOE+002.913E+051.305E+06O.OOOE+002.270E+051.589E+052.384E+054.767E+046.356E+042.317E+056.356E+054.767E+053.973E+052.724E+053.859E+052.270E+053.405E+053.814E+053.973E+058.607E+05

RHOi

2.362E+062.611E+062.213E+064.495E+063.783E+042.270E+043.178E+051.812E+061.271E+066.486E+042.172E+063.150E+065.462E+051.861E+067.151E+051.510E+063.019E+053.178E+051.424E+061.725E+062.558E+069.080E+051.294E+062.225E+061.249E+061.050E+061.780E+062.015E+062.582E+06

RATIO

0.3360.1830.1280.2120.0000.0000.0000.1750.2920.0000.1340.4140.0000.1220.2220.1580.1580.2000.1630.3680.1860.4380.2110.1730.1820.3240.2140.1970.333

U (ppm)

18.420.417.335.10.30.22.5

14.19.90.5

16.924.64.3

14.55.6

11.82.42.5

11.113.520.07.1

10.117.49.78.2

13.915.720.1

a(wt%)

0.200.690.400.000.000.000.980.400.700.000.831.120.380.410.760.410.300.330.410.500.670.870.281.020.831.670.430.781.10

F.T. AGE (Ma)

93.3 ± 18.150.8 ± 12.135.7 ± 12.059.0 ± 14.30.0 ± 0.00.0 ± 0.00.0 ± 0.0

48.8 ± 16.881.0± 34.80.0 ± 0.0

37.4 ± 12.0114.8± 20.3

0.0 ± 0.034.0 ± 11.461. 8 ± 34.244.0 ± 27.344.0 ± 27.355.6 ± 30.545.3 ± 18.5

102. 1± 32.051. 9 ± 10.4

121. 1± 55.058.6 ± 18.748.3 ± 12.750.6 ± 27.590.0 ± 30.059.6 ± 19.054.9 ± 16.192.5 ± 29.7

328 1491


3.358E+05 1.S27E+06 11.9


Ns/Ni= 0.220 ± 0.013 Mean Ratio = 0.191 ± 0.023

Ages calculated using a zeta of 382.4 ± 5.5 for CN5 glass RhoD= 1.461E+06cm-2; ND= 2253Rho D interpolated between top of can; Rho D = 1.397E+06cm-2, ND = 1099


POOLED AGE = 61.2 ± 4.0 Ma CENTRAL AGE = 60.2 ± 5 J Ma

29


USGS Sample 99CP-A13 (continued)

OF 00- 220

GC763-47 APATITE CONTINUED 99CP-A13

A:

+2

+10

-1 2

fc"

28

B:

0.5 1.0 1.5 2.0 2.5 3.0 Wt % Chlorine

C:

300

g.200

100


0.4 0.8 1.2 1.6 Weight % Chlorine

2.4

D:

40

30

20

10

fl

S 10 15 20 TRACK LBJCTH (microns)

30


REFERENCES

Fleischer, R.L., Price, P.B., and Walker, R.M., 1975, Nuclear tracks in solids, University of California Press, Berkeley.

Galbraith, R.F. 1981, On statistical models for fission-track counts. Mathematical Geology, 13, 471-488.

Galbraith, R.F. 1988, Graphical display of estimates having differing standard errors. Technometrics, 30, 271-281.

Galbraith, R.F., 1990, The radial plot: graphical assessment of spread in ages. Nuclear tracks, 17, 207-214.

Galbraith, R.F. & Laslett, G.M. 1993. Statistical methods for mixed fission track ages. Nuclear Tracks 21, 459-470.

Gleadow, A.J.W. 1981, Fission track dating methods; what are the real alternatives? Nuclear Tracks, 5, 3-14.

Green, P.P. 1981. A new look at statistics in fission track dating. Nuclear Tracks 5, 77- 86.

Green, P.P. 1985. A comparison of zeta calibration baselines in zircon, sphene and apatite. Chem. Geol. (Isot. Geol Sect), 58, 1-22.

Green, P.P., Duddy, I.R., Gleadow, A.J.W., Tingate, P.R. and Laslett, G.M. 1986. Thermal annealing of fission tracks in apatite 1. A qualitative description. Chem. Geol (Isot Geosci. Sect), 59, 237-253.

Hurford, A.J., 1986. Application of the fission track dating method to younf sediments: Principles, methodology and Examples. In: Hurford, A.J., Jager, E. and Ten Cate, J.A.M., Dating young sediments, CCOP Technical Publication 16, CCOP Technical Secretariat, Bangkok, Thailand.

Hurford, A.J. and Green, P.P. 1982. A user's guide to fission track dating calibration. Earth. Planet. Sci Lett. 59, 343-354.

Hurford, AJ. and Green, P.P. 1983. The zeta age calibration of fission track dating. Isotope Geoscience 1, 285-317.

Laslett, G.M., Kendall, W.S., Gleadow, A.J.W. and Duddy, I.R. 1982. Bias in measurement of fission track length distributions. Nuclear Tracks, 6,79-85.

Naeser, C.W., 1979. Fission track dating and geologic annealing of fission tracks. In: Jager, E. and Hunziker, J.C. (eds), Lectures in Isotope Geology, Springer Verlag, Berlin.

Smith, M.J. and Leigh-Jones, P. 1985. An automated microscope scanning stage for fission-track dating. Nuclear Tracks, 10, 395-400.

31

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