RESULTADOS OBTENIDOS

In the following section, we discuss our new data along with published Kaua‘i, Ni‘ihau, and North Arch isotope data from Lassiter et al. (2000), Mukhopadhyay et al. (2003), Frey et al., 2000, Frey et al., 2005, Dixon et al. (2008), Garcia et al. (2010), and Cousens and Clague (2015) to provide a comprehensive overview of the full available dataset for these volcanic centers. Data are presented in Figures 3.2 (shield, post-shield) and 3.3 (rejuvenated).

3.3.1 Kaua‘i and Ni‘ihau shield lavas

Ni‘ihau shield tholeiites and late-shield transitional basalts are virtually identical in all isotope diagrams, therefore they are discussed as a single group, referred to as Ni‘ihau

shield lavas. In a εNd − εHf plot, shield lavas from Kaua‘i and Ni‘ihau form two overlapping

arrays with identical slopes of 0.7 ± 0.2 and 0.7 ± 0.1, and intercepts of 6.1 ± 0.9 and 6.0 ± 0.8, respectively (R2 _{= 0.8 for both). Kaua‘i shield lavas span from ε}

Nd = 4.9 to 7.8, εHf =

9.4–11.1 (Fig. 3.2a) and 87_Sr/86_{Sr = 0.70345–0.70383, whereas Ni‘ihau shield lavas are}

slightly more radiogenic in Nd, Hf and less radiogenic in Sr, with εNd = 6.3 to 8.2, εHf =

10.5–12.0, and 87_Sr/86_{Sr = 0.70347–0.70365.}

In a 206_Pb/204_Pb–208_Pb/204_{Pb plot, Kaua‘i and Ni‘ihau shield lavas define a single}

broad trend with a slope of 0.9 ± 0.3 and range from 206_Pb/204_{Pb = 18.0 to 18.4 (Fig. 3.2b).}

3.3.2 Kaua‘i and Ni‘ihau post-shield lavas

Kaua‘i post-shield lavas range from εNd = 6.0 to 8.6, εHf = 10.1–14.3 (Fig. 3.2a) and 87_Sr/86_{Sr = 0.70317–0.70372, partially overlapping shield lavas but extending to}

significantly more radiogenic Nd and Hf and less radiogenic Sr isotope compositions. In a

206_Pb/204_Pb–208_Pb/204_{Pb plot, Kaua‘i late-shield tholeiites overlap with Kaua‘i shield lavas}

(Fig. 3.2b).

Ni‘ihau submarine samples T320-R8 and T320-R12 were tentatively classified as post-shield in Cousens and Clague (2015), since they could not be dated. These two lavas have significantly more radiogenic εHf values than shield lavas (εHf > 13) and overlap

Ni‘ihau rejuvenated lavas in all isotope diagrams. We therefore reclassify these two samples as part of the rejuvenated stage of Ni‘ihau, based on their isotope composition. Two samples (T319-R12 and T321-R2) classified as post-shield in Cousens and Clague (2015) overlap Ni‘ihau shield lavas in all isotope diagrams. We therefore maintain their

classification as post-shield, again based on isotope values, in the absence of clear stratigraphic information.

3.3.3 Kaua‘i rejuvenated lavas (Kōloa volcanics)

In εNd–εHf–87Sr/86Sr plots, Kaua‘i rejuvenated lavas extend from εNd = 9.1, εHf =

14.2, 87_Sr/86_{Sr = 0.7030 to (1) ε}

Nd = 7.0, εHf = 11.9, 87Sr/86Sr = 0.7034, and (2) εNd = 7.5,

εHf = 10.5, 87Sr/86Sr = 0.7031, below the εNd–εHf mantle array (Chauvel et al., 2008), with

a lower εHf for a given εNd–87Sr/86Sr compared to shield lavas (Fig. 3.3a, c). All Kaua‘i

rejuvenated lavas plot either along or below the mantle array in εNd–εHf.

These lavas range from 206_Pb/204_{Pb = 18.06 to 18.40 and show a single trend in a} 206_Pb/204_Pb–208_Pb/204_{Pb plot with a slope of 1.34 ± 0.04 and R}2 _{= 0.99, in accord with older}

values from Lassiter et al. (2000) and Garcia et al. (2010). This trend is significantly steeper than the Kaua‘i–Ni‘ihau shield trend (Fig. 3.3d).

This linear trend is also seen in 206_Pb/204_{Pb–εNd and} 206_Pb/204_{Pb–εHf isotope plots,}

(Fig. 3.3b) and is orthogonal to- and crosses beyond the less defined trend described by Kaua‘i and Ni‘ihau shield lavas.

3.3.4 Ni‘ihau rejuvenated lavas (Ki‘eki‘e lavas)

Ni‘ihau rejuvenated lavas have a significantly higher εHf for a given εNd–87Sr/86Sr

compared to all Kaua‘i lavas and Ni‘ihau shield to post-shield lavas (Fig. 3.3a, c). They do not form distinct trends in εNd–εHf and εNd–87Sr/86Sr plots but rather cluster at εNd = 7.2 to

8.1, εHf = 12.5–14.2 and 87Sr/86Sr = 0.7033–0.7035. These lavas plot above the mantle array

ratios similar to the least radiogenic Kaua‘i rejuvenated lavas with 206_Pb/204_{Pb = 18.02 to}

18.15, and distinctly lower than Kaua‘i and Ni‘ihau shield and post-shield lavas (Fig. 3.3d). They form a linear trend in a 206_Pb/204_Pb–208_Pb/204_{Pb plot with a slope of 1.00 ± 0.09 (R}2 ₌

0.88), shallower than the Kaua‘i rejuvenated trend, but steeper than the shield trend.

3.3.5 North Arch lavas

Lavas from the North Arch volcanic field generally overlap isotopically with Hawaiian rejuvenated lavas, as well as for trace and major elements. In εNd–εHf–87Sr/86Sr

plots, North Arch samples lie at the isotopically depleted end of the entire dataset of Hawaiian lavas at εNd = 8.4 to 9.2, εHf = 12.8–15.2 and 87Sr/86Sr = 0.7030–0.7032 (Fig.

3.3a, c). They plot slightly below the mantle array in εNd–εHf overlapping with the most

depleted Kaua‘i rejuvenated lavas, and distinct from Ni‘ihau rejuvenated lavas.

In a 206_Pb/204_Pb–208_Pb/204_{Pb plot, North Arch lavas range from} 206_Pb/204_{Pb = 18.13}

to 18.24, similar to Ni‘ihau, Ka‘ula and the most depleted Kaua‘i rejuvenated lavas, and form a trend with a slope of 1.3 ± 0.2 (R2 _{= 0.84) offset from Kaua‘i, Ni‘ihau and Ka‘ula}

rejuvenated trends to higher 206_Pb/204_{Pb for a given} 208_Pb/204_{Pb (Fig. 3.3d).}