Major element compositions of the minerals were obtained on polished thin sections using a

Transcription

1 DR846 APPENDIX A: ANALYTICAL METHODS Mineral chemistry Major element compositions of the minerals were obtained on polished thin sections using a Cameca SX electron microprobe fitted with five spectrometers at the Service commun microsonde (Université de Montpellier). The standard analytical procedure uses an accelerating voltage of kv, a beam current of na, a µm spot size, and integrated counting times ranging from to 3 s. Alkalis were determined first to minimize Na loss during measurements. Detection limits are ca..% for major elements. The analytical error is between and 5% for concentrations higher than % and between 5 and % for concentrations lower than %. 4Ar/39Ar geochronology Minerals and rocks samples were pretreated and concentrated by standard laboratory techniques and later selected by handpicking under a binocular microscope from fractions that ranged in size from (4 6-8-) mesh at the mineral separation laboratory at Centro de Geociencias-UNAM, Campus Juriquilla, Querétaro, Qro. Mineral separates were loaded into Alfoil packets and irradiated together with MAC-83 (4. Ma) biotite as a neutron-fluence monitor at the McMaster Nuclear Reactor (Hamilton, Ontario). 4Ar/39Ar analyses were performed by standard laser step-heating techniques, described in detail by Clark et al. (998), at the Geochronology Research Laboratory of Queen s University, Kingston, Ontario, Canada. All data have been corrected for blanks, mass discrimination, and neutron-induced interferences. Geochemistry Rock samples were ground first in a steel jaw crusher and then finely powdered in an agate grinder. Major and compatible trace elements were analyzed by inductively coupled plasmaatomic emission spectrometry (ICP-AES) at CEREGE (Université Aix-Marseille 3) using a 6

2 DR846 Jobin-Yvon system. Na, K and Rb were determined by flame atomic absorption spectrophotometry, and Fe+ by titration. Rare earth elements (REE) and additional trace elements were obtained for a subset of samples by inductively coupled plasma-mass spectrometry (ICP-MS) at ALS Chemex laboratory. Analytical errors are 3% for major elements and about 3% for trace elements. Sr (static acquisition) and Nd (dynamic acquisition) isotopic ratios were measured at the Laboratoire de Géochimie isotopique de l Université Paul Sabatier de Toulouse on a Finnigan MAT6 multicollector mass spectrometer using the analytical procedures of Lapierre et al. (997). Results on La Jolla Nd standard yielded 43Nd/44Nd =.585 ± 8 (mean on 39 runs), corresponding to an external reproducibility of.. Results on NBS 987 Sr standard yielded 87Sr/86Sr =.75 (mean on runs). The within-run precision (σ absolute) for 87 Sr/ 86 Sr was.8-.5 and.7-. for 43 Nd/ 44 Nd. For lead separation, powdered samples were weighed to obtain approximately to ng of lead. The chemical separation of Pb was carried out following the procedure modified from Manhès et al. (98). Total Pb blanks are less than 65 pg, for a mg sample. Lead isotope analyses were made on a VG model Plasma 54 multicollector-inductively coupled plasma-mass spectrometer (MC-ICP-MS) at the Ecole Normale Supérieure de Lyon. Lead isotope compositions were measured using the Tl normalization method described by White et al. (). For Pb isotope analysis, samples were bracketed between NIST 98 standards and calculated with respect to the value reported for this standard by Todt et al. (996). This technique yields internal precision of ca. 5 ppm (σ) and an external reproducibility of ca. 5 ppm (σ) for 6Pb/4Pb ratios determined on NIST standards. 7

3 DR846 AOR-7: 9-3 Plg 4/6 Run date: 4/5/6 Printed: 6/4/8 Can/Pos: 9/8 Mass: 33. mg J Value:.356 ±.6 Volume 39K:.66 x E- cm3 NTP Integrated Age: 3.93 ± 7.44 Ma Initial 4/36: 98.9 ± 58.7 (MSWD =.3, isochron between -.4 and 3.83) Correlation Age: 9.87 ±.45 Ma (.% of 39Ar, steps marked by >) Plateau Age:.7 ±.7 Ma ( 47.% of 39Ar, steps marked by <) Approx. MSWD Mod. err..33% K % Ca < 8. 36Ar/4Ar 39Ar/4Ar r Ca/K %4Atm %39Ar 4Ar*/39K Age.3385±.35.4± ± ± < 8. 4Ar 39Ar 38Ar 37Ar 36Ar Blank 4Ar Atmos 4/ ±.87.±.4.5±.3 4.7±.6.59± Measured volumes are x E- cm3 NTP. All errors are x standard error. Intrim3 8-Mar-

4 DR846 AOR-7: 9-3 Plg 4/ Ar/4Ar.5. Age (Ma) Ar/4Ar Cumulative Volume 39Ar Volume 39Ar / mw Ca/K Cl/K %4 Atmos (W)... Measured volumes are x E- cm3 NTP. All errors are x standard error. Intrim3 8-Mar-

5 DR846 AOR-R73: JR98- Plg 4/6 Run date: 4/5/6 Printed: 5/6/8 Can/Pos: 9/9 Mass: 66. mg J Value:.357 ±.6 Volume 39K:.6 x E- cm3 NTP Integrated Age: 6.3 ±.7 Ma Approx..65% K 4.39% Ca Initial 4/36: Correlation Age: Linear regression has positive slope. MSWD Plateau Age: 9. ±.86 Ma ( 4.7% of 39Ar, steps marked by <) Mod. err < Ar/4Ar 39Ar/4Ar r Ca/K %4Atm %39Ar 4Ar*/39K Age.895±.7.495± ±.49.5± < 7.5 4Ar 39Ar 38Ar 37Ar 36Ar Blank 4Ar Atmos 4/36.34±.9.66±.7.9±..44±.5.39± Measured volumes are x E- cm3 NTP. All errors are x standard error. Intrim3 8-Mar-

6 DR846 AOR-R73: JR98- Plg 4/ Ar/4Ar.7.6 Age (Ma) Ar/4Ar Cumulative Volume 39Ar Volume 39Ar / mw Ca/K Cl/K %4 Atmos (W)... Measured volumes are x E- cm3 NTP. All errors are x standard error. Intrim3 8-Mar-

7 DR846 AOR-R7: JR97-3 Plg 4/6 Run date: 4/5/6 Printed: 5/6/8 Can/Pos: 9/7 Mass: 33. mg J Value:.355 ±.6 Volume 39K:.9 x E- cm3 NTP Integrated Age: 6.8 ±.59 Ma Initial 4/36: 99.6 ± 4. (MSWD =.69, isochron between -.4 and 3.83) Correlation Age: 9.89 ± 9.3 Ma ( 43.3% of 39Ar, steps marked by >) Plateau Age:.64 ±.7 Ma ( 56.7% of 39Ar, steps marked by <).77 ±.9 Ma ( 43.3% of 39Ar, steps marked by {) Approx. MSWD Mod. err..45% K.35% Ca { 3.> { 5.> { 6.> < 7. 36Ar/4Ar 39Ar/4Ar r Ca/K %4Atm %39Ar 4Ar*/39K Age.39±.8.76± ±.99.6± { 3.> { 5.> { 6.> < 7. 4Ar 39Ar 38Ar 37Ar 36Ar Blank 4Ar Atmos 4/ ±.57.88±.3.9±..378±.9.3± Measured volumes are x E- cm3 NTP. All errors are x standard error. Intrim3 8-Mar-

8 DR846 AOR-R7: JR97-3 Plg 4/ Ar/4Ar.6.4 Age (Ma) Ar/4Ar.. Cumulative Volume 39Ar Volume 39Ar / mw Ca/K Cl/K %4 Atmos (W)... Measured volumes are x E- cm3 NTP. All errors are x standard error. Intrim3 8-Mar-

9 DR846 AOR-L75: JR98- Plg 4/6 Run date: 4/5/6 Printed: 4/7/ Can/Pos: 9/ Mass: 55. mg J Value:.366 ±.8 Volume 39K:.79 x E- cm3 NTP Integrated Age:.7 ±. Ma Initial 4/36: 67.6 ±. (MSWD =.8, isochron between. and 3.) Correlation Age: 4.93 ± 6.67 Ma ( 66.5% of 39Ar, steps marked by >) Approx. MSWD.53% K.78% Ca.745 Plateau Age: 3.53 ±.4 Ma ( 54.% of 39Ar, steps marked by <) Mod. err..4 3.> 5.> < 6.5> < 7.> < 7. 36Ar/4Ar 39Ar/4Ar r Ca/K %4Atm %39Ar 4Ar*/39K Age.34± ± ± ± > 5.> < 6.5> < 7.> < 7. 4Ar 39Ar 38Ar 37Ar 36Ar Blank 4Ar Atmos 4/36 3.7±.73.46±.5.77±..7±.7.45± Measured volumes are x E- cm3 NTP. All errors are x standard error. Intrim3 8-Mar-

10 DR846 AOR-L75: JR98- Plg 4/ Ar/4Ar.3. Age (Ma) Ar/4Ar Cumulative Volume 39Ar Volume 39Ar / mw Ca/K Cl/K %4 Atmos (W)... Measured volumes are x E- cm3 NTP. All errors are x standard error. Intrim3 8-Mar-

11 DR846 AOR-R74: JR99-83 Hb 4/6 Run date: 4/5/6 Printed: 5/6/8 Can/Pos: 9/ Mass: 3. mg J Value:.358 ±.6 Volume 39K:.93 x E- cm3 NTP Integrated Age:.34 ±. Ma Initial 4/36: ± 9.93 (MSWD =.77, isochron between.37 and.6) Correlation Age:. ±.48 Ma (.% of 39Ar, steps marked by >) Plateau Age:.4 ±.37 Ma ( 63.9% of 39Ar, steps marked by <) Approx. MSWD Mod. err..6% K 5.4% Ca < 6. < 7. < 7.5 < 8. 36Ar/4Ar 39Ar/4Ar r Ca/K %4Atm %39Ar 4Ar*/39K Age.34± ± ±.97.95± < 6. < 7. < 7.5 < 8. 4Ar 39Ar 38Ar 37Ar 36Ar Blank 4Ar Atmos 4/ ±.37.93±.3.38±..57±.3.6± Measured volumes are x E- cm3 NTP. All errors are x standard error. Intrim3 8-Mar-

12 DR846 AOR-R74: JR99-83 Hb 4/ Ar/4Ar.3. Age (Ma) Ar/4Ar.. Cumulative Volume 39Ar.5.5 Volume 39Ar / mw Ca/K Cl/K %4 Atmos (W)... Measured volumes are x E- cm3 NTP. All errors are x standard error. Intrim3 8-Mar-

13 DR846 AOR-R76: PO3-7 Obs 4/6 Run date: 4/5/7 Printed: 5/6/8 Can/Pos: 9/ Mass: 3. mg J Value:.34 ±.8 Volume 39K: x E- cm3 NTP Integrated Age: 4.7 ±.5 Ma Initial 4/36: ± (MSWD =.6, isochron between -.4 and 3.83) Correlation Age: 4.6 ±.8 Ma (.% of 39Ar, steps marked by >) Plateau Age: 5.3 ±.6 Ma ( 58.4% of 39Ar, steps marked by <) Approx. MSWD Mod. err. 7.74% K.4% Ca.76.3.>.> 3.> < 6. < 7. < 7. < Ar/4Ar 39Ar/4Ar r Ca/K %4Atm %39Ar 4Ar*/39K Age.388± ± ±.46.6± >.> 3.> < 6. < 7. < 7. < 7.5 4Ar 39Ar 38Ar 37Ar 36Ar Blank 4Ar Atmos 4/ ± ±.9.79±.4.5±..57± Measured volumes are x E- cm3 NTP. All errors are x standard error. Intrim3 8-Mar-

14 DR846 AOR-R76: PO3-7 Obs 4/ Ar/4Ar..5 Age (Ma) Ar/4Ar Cumulative Volume 39Ar Volume 39Ar / mw Ca/K Cl/K %4 Atmos (W)... Measured volumes are x E- cm3 NTP. All errors are x standard error. Intrim3 8-Mar-

15 DR846 AOR-R75: JR98-3 Wr 4/6 Run date: 4/5/6 Printed: 5/6/8 Can/Pos: 9/ Mass: 77. mg J Value:.359 ±.6 Volume 39K:.9 x E- cm3 NTP Integrated Age: 3.94 ±.4 Ma Plateau Age: 4.3 ±.5 Ma ( 9.7% of 39Ar, steps marked by <) Approx. MSWD Mod. err. 4.7% K.33% Ca. < 7. 36Ar/4Ar 39Ar/4Ar r Ca/K %4Atm %39Ar 4Ar*/39K Age.37± ± ±.464.± < 7. 4Ar 39Ar 38Ar 37Ar 36Ar Blank 4Ar Atmos 4/ ±.37.89±.8.55±.4.544±.8.± Measured volumes are x E- cm3 NTP. All errors are x standard error. Intrim3 8-Mar-

16 DR846 AOR-R75: JR98-3 Wr 4/ Ar/4Ar.5 Age (Ma) Ar/4Ar Cumulative Volume 39Ar Volume 39Ar / mw Ca/K Cl/K %4 Atmos (W)... Measured volumes are x E- cm3 NTP. All errors are x standard error. Intrim3 8-Mar-

17 DR846 AOR-R77: PO3--OBS Obs 4/6 Run date: 4/5/8 Printed: 5/6/8 Can/Pos: 9/5 Mass: 56. mg J Value:.348 ±.8 Volume 39K: 9.34 x E- cm3 NTP Integrated Age: 3.5 ±.58 Ma Initial 4/36: 9.6 ± (MSWD =.7, isochron between. and 3.) Correlation Age: 3.7 ± 7.3 Ma ( 5.% of 39Ar, steps marked by >) Plateau Age: 4.7 ±.87 Ma ( 48.8% of 39Ar, steps marked by <).8 ±.6 Ma ( 5.% of 39Ar, steps marked by {) Approx. MSWD Mod. err. 8.6% K.49% Ca {.> { 4.> { 6.> { 7.> < Ar/4Ar 39Ar/4Ar r Ca/K %4Atm %39Ar 4Ar*/39K Age.375± ± ± ± {.> { 4.> { 6.> { 7.> < 7.5 4Ar 39Ar 38Ar 37Ar 36Ar Blank 4Ar Atmos 4/36 4.9±.3.45±.9.535±.5.3±..34± Measured volumes are x E- cm3 NTP. All errors are x standard error. Intrim3 8-Mar-

18 DR846 AOR-R77: PO3--OBS Obs 4/ Ar/4Ar..5. Age (Ma) Ar/4Ar Cumulative Volume 39Ar Volume 39Ar / mw Ca/K Cl/K %4 Atmos (W)... Measured volumes are x E- cm3 NTP. All errors are x standard error. Intrim3 8-Mar-

19 DR846 AOR-R756: PO3--OBS-HCL Obs 4/6 Run date: 4/5/3 Printed: 5/6/8 Can/Pos: 9/6 Mass: 44. mg J Value:.35 ±.6 Volume 39K:. x E- cm3 NTP Integrated Age:.77 ±.6 Ma Approx. 8.5% K.45% Ca Initial 4/36: Correlation Age: Linear regression has positive slope. MSWD Plateau Age: 4.5 ±.5 Ma ( 36.6% of 39Ar, steps marked by <).98 ±.6 Ma ( 63.4% of 39Ar, steps marked by {) Mod. err. {. { 4. { 6. { 7. < 7. 36Ar/4Ar 39Ar/4Ar r Ca/K %4Atm %39Ar 4Ar*/39K Age.958± ± ±.5.9± {. { 4. { 6. { 7. < 7. 4Ar 39Ar 38Ar 37Ar 36Ar Blank 4Ar Atmos 4/ ± ±.8.56±.5.3±..8± Measured volumes are x E- cm3 NTP. All errors are x standard error. Intrim3 8-Mar-

20 DR846 AOR-R756: PO3--OBS-HCL Obs 4/ Ar/4Ar.4.4 Age (Ma) Ar/4Ar Cumulative Volume 39Ar Volume 39Ar / mw Ca/K Cl/K %4 Atmos (W)... Measured volumes are x E- cm3 NTP. All errors are x standard error. Intrim3 8-Mar-

21 DR846 AOR-R73: PO-8 Lag-Obs 4/6 Run date: 4/5/8 Printed: 5/6/8 Can/Pos: 9/3 Mass: 55. mg J Value:.345 ±.8 Volume 39K: 7.34 x E- cm3 NTP Integrated Age:.75 ±. Ma Initial 4/36: 7.5 ± 38.7 (MSWD =.4, isochron between. and 3.) Correlation Age:.6 ±.8 Ma ( 95.5% of 39Ar, steps marked by >) Plateau Age:.6 ±.7 Ma ( 93.% of 39Ar, steps marked by <) Approx. MSWD Mod. err. 8.8% K.6% Ca.59.4.> 4. < 6.> < 7.> < 7.5> 36Ar/4Ar 39Ar/4Ar r Ca/K %4Atm %39Ar 4Ar*/39K Age.63± ± ±.47.39± > 4. < 6.> < 7.> < 7.5> 4Ar 39Ar 38Ar 37Ar 36Ar Blank 4Ar Atmos 4/ ±.3.677±.5.5±..7±..5± Measured volumes are x E- cm3 NTP. All errors are x standard error. Intrim3 8-Mar-

22 DR846 AOR-R73: PO-8 Lag-Obs 4/ Ar/4Ar. Age (Ma) Ar/4Ar Cumulative Volume 39Ar Volume 39Ar / mw Ca/K Cl/K %4 Atmos (W)... Measured volumes are x E- cm3 NTP. All errors are x standard error. Intrim3 8-Mar-

23 DR846 AOR-R743: PO-8-HCL-OBS Lag-Obs 4/6 Run date: 4/5/9 Printed: 5/6/8 Can/Pos: 9/4 Mass: 37. mg J Value:.346 ±.8 Volume 39K: 8.7 x E- cm3 NTP Integrated Age:. ±. Ma Initial 4/36: ± 9.34 (MSWD = 4.45, isochron between.8 and.63) Correlation Age:.3 ±.38 Ma (.% of 39Ar, steps marked by >) Plateau Age:. ±. Ma ( 97.% of 39Ar, steps marked by <) Approx. MSWD Mod. err. 8.% K.5% Ca < 4. < 6. < 7. < 7. 36Ar/4Ar 39Ar/4Ar r Ca/K %4Atm %39Ar 4Ar*/39K Age.6±.89.97± ±.7.48± < 4. < 6. < 7. < 7. 4Ar 39Ar 38Ar 37Ar 36Ar Blank 4Ar Atmos 4/36.75± ±.4.±..±..5± Measured volumes are x E- cm3 NTP. All errors are x standard error. Intrim3 8-Mar-

24 DR846 AOR-R743: PO-8-HCL-OBS Lag-Obs 4/ Ar/4Ar. Age (Ma) Ar/4Ar.. 3 Cumulative Volume 39Ar 5 5 Volume 39Ar / mw Ca/K Cl/K %4 Atmos (W)... Measured volumes are x E- cm3 NTP. All errors are x standard error. Intrim3 8-Mar-

25 DR846 AOR-R76: PO-8 Wr 4/6 Run date: 4/5/6 Printed: 5/6/8 Can/Pos: 9/3 Mass: 34. mg J Value:.36 ±.6 Volume 39K: 9.53 x E- cm3 NTP Integrated Age:.4 ±.8 Ma Initial 4/36: ±99. (MSWD = 5., isochron between -.4 and 3.83) Correlation Age:.93 ±.7 Ma ( 4.% of 39Ar, steps marked by >) Plateau Age:.5 ±.7 Ma ( 9.3% of 39Ar, steps marked by <) Approx. MSWD Mod. err. 9.39% K.44% Ca >.5> < 4.> < 6. < 7. 36Ar/4Ar 39Ar/4Ar r Ca/K %4Atm %39Ar 4Ar*/39K Age.9± ± ±.53.65± >.5> < 4.> < 6. < 7. 4Ar 39Ar 38Ar 37Ar 36Ar Blank 4Ar Atmos 4/ ±.8.79±.6.4±..5±..4± Measured volumes are x E- cm3 NTP. All errors are x standard error. Intrim3 8-Mar-

26 DR846 AOR-R76: PO-8 Wr 4/ Ar/4Ar.3. Age (Ma) Ar/4Ar.. Cumulative Volume 39Ar Volume 39Ar / mw Ca/K Cl/K %4 Atmos (W)... Measured volumes are x E- cm3 NTP. All errors are x standard error. Intrim3 8-Mar-

27 DR846 REFERENCES: Clark, A.H., Archibald, D.A., Lee, A.W., Farrar, E., and Hodgson, C.J., 998, Laser Probe 4 Ar/ 39 Ar agers of early- and late-stage alteration assemblages, Rosario porphyry copper molybdenum deposit, Collahuasi District, I Region, Chili: Economic Geology and the Bulletin of the Society of Economic Geologists, v. 93, p Lapierre, H., Dupuis, V., Mercier de Lepinay, B., Tardy, M., Ruiz, J., Maury, R.C., Hernandez, J., and Loubet, M., 997, Is the Lower Duarte igneous complex (Hispaniola) a remnant of the Caribbean plume-generated oceanic plateau?: The Journal of Geology, v. 5, p.. Manhès, G., Allègre, C.J., Dupré, B., and Hamelin, B., 98, Lead isotope study of basicultrabasic layered complex: Speculations about the ages of the Earth and primitive mantle characteristics: Earth and Planetary Science Letters, v. 47, p , doi:.6/-8x(8)94-. Todt, W., Cliff, R.A., Hanser, A., and Hoffmann, A.W., 996, Evaluation of a Pb/ 5 Pb double spike for high-precision lead isotope analysis, in Basu, A., and Hart, S., eds., Earth processes: Reading the isotopic code: American Geophysical Union, Geophysical Monograph, v. 95, p White, M.W., Albarède, F., and Telouk, F.,, High-precision analysis of Pb isotopic ratios by multi-collector ICP-MS: Chemical Geology, v. 67, p. 57 7, doi:.6/s9-54(99)8-5.