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Whole-rock weigh-percent H 2 O determined by combustion analysis of whole-rock powders versus depth of OH band (where band depth is given as 1 minus value at reflectance minimum) near 1.4 μm for 19 samples from Teakettle Junction aureole. Inset shows examples of spectra with band depths of 0.04, 0.13, 0.28, and 0.64 in continuum-removed spectrum between 1.2 and 1.6 μm. Fields of characteristic hydrous minerals detected with visiblenear infrared (Vis-NIR) are labeled. Mineral abbreviations: Brc-brucite; Chu-clinohumite; Ilt-illite; Phl-phlogopite; Srp-serpentine; Tlc-talc; Tr-tremolite.
Source publication
Mineral distribution in a previously undescribed contact aureole in siliceous dolomite at Teakettle Junction, Death Valley National Park (California, USA), was mapped with a handheld visible and near-infrared (Vis-NIR, 0.35–2.5 μm) spectrometer. With increasing distance from a small Jurassic(?) pluton, the following mineral zones occur: periclase (...
Contexts in source publication
Context 1
... the value of the continuum is 1, the band depth is given as 1 minus the value at the reflectance minimum. The inset in Figure 8 illustrates examples of spectra with band depths of 0.04, 0.13, 0.28, and 0.64 calculated in this fashion. The main part of Figure 8 shows the relationship between OH band depth and whole-rock H 2 O content. ...
Context 2
... inset in Figure 8 illustrates examples of spectra with band depths of 0.04, 0.13, 0.28, and 0.64 calculated in this fashion. The main part of Figure 8 shows the relationship between OH band depth and whole-rock H 2 O content. Fields of characteristic hydrous minerals detected with Vis-NIR are labeled. ...
Context 3
... H 2 O content for these phases ranges from roughly 2 wt% to 4 wt%, and modal abundances for these phases rarely exceed 3 vol%, especially in the unmetamorphosed rocks. Figure 8 (main figure) shows five such samples, and these have the lowest OH band depth values and whole-rock H 2 O content of 0.01-0.34 wt%. ...
Context 4
... H 2 O content for these phases ranges from ~2 wt% for clinohumite (depending on OH/F) to 12 wt% for serpentine, and modal abundances for each are generally >5 vol%, and in cases exceed 20 vol%. Figure 8 shows twelve such samples, and these have OH band depth values of 0.1-0.7 and whole-rock H 2 O content of 0.12-5.37 wt%. ...
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... Two brucite-bearing samples are shown in Figure 8. Stoichiometric H 2 O content for brucite is 31 wt%, and brucite modal abundance in the samples is estimated at 10-15 vol% along with ~8 vol% serpentine and traces of phlogopite. ...
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... The lowermost spectrum in the inset in Figure 8 shows the brucite-bearing sample with OH band depth of 0.64 (also shown in the SEM image in Fig. 4A). ...
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... relationship between OH band depth and whole-rock H 2 O content (Fig. 8) provides overall support for the contention that OH band depth is an indicator of the degree of hydration of the rocks in this study. There is, however, significant scatter in the data. Several factors may contribute to the observed scatter. Band depth is easily computed from the spectra, but the integrated area of the OH absorption ...
Context 8
... data from a subset of 19 samples presented above and shown in Figure 8 establish overall correlations among OH band depth, whole-rock H 2 O content, and occurrence of hydrous minerals in the aureole. In order to place these relationships in a spatial context, Figure 9 illustrates the variation in OH band depth at all 145 sites in the aureole. ...
Context 9
... OH band depth for the site. As an example of variation at a site, one site with five samples has OH band depths that range from 0.04 in a sample that contains only calcite and dolomite to 0.64 in a sample that contains brucite, serpentine, and phlogopite in addition to calcite and dolomite (the latter is one of the brucite-bearing samples in Fig. ...
Context 10
... OH band depth of 0.2 is used to discriminate low and high levels of hydration following the results shown in Figure 8. With one exception, samples with band depth <0.2 have whole-rock H 2 O content <0.5 wt% (>82% of the 946 samples have band depth <0.2). ...
Context 11
... one exception, samples with band depth <0.2 have whole-rock H 2 O content <0.5 wt% (>82% of the 946 samples have band depth <0.2). Samples with band depth >0.2 in Figure 8 generally have whole-rock H 2 O content >0.5 wt% (<18% of total samples). Sites with OH band depth values >0.2 are restricted to distances within ~300 m from the contact in the central part of the aureole where the contact is well exposed (Fig. 9). ...
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... outer limit of these values is effectively the same as the serpentine (forsterite) isograd. This observation follows directly from the previous discussion of the correlation between band depth and mineral occurrence in connection with Figure 8. ...
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... should be noted that one site with brucite is projected on to profile B-B′ (Fig. 10), and a possible brucite (periclase) zone is indicated. However, the OH band depth for this sample is only slightly above 0.2, which is unexpectedly low for a brucite-bearing sample (compare brucite samples in Fig. 8 with band depth of >0.6). The Vis-NIR identification of brucite at the site near profile B-B′ was highly questionable, and a thin section is not available. It is therefore possible that brucite is absent or occurs at very low abundance, and this might explain the low OH band depth value for this sample in Figure ...
Context 14
... the value of the continuum is 1, the band depth is given as 1 minus the value at the reflectance minimum. The inset in Figure 8 illustrates examples of spectra with band depths of 0.04, 0.13, 0.28, and 0.64 calculated in this fashion. The main part of Figure 8 shows the relationship between OH band depth and whole-rock H 2 O content. ...
Context 15
... inset in Figure 8 illustrates examples of spectra with band depths of 0.04, 0.13, 0.28, and 0.64 calculated in this fashion. The main part of Figure 8 shows the relationship between OH band depth and whole-rock H 2 O content. Fields of characteristic hydrous minerals detected with Vis-NIR are labeled. ...
Context 16
... H 2 O content for these phases ranges from roughly 2 wt% to 4 wt%, and modal abundances for these phases rarely exceed 3 vol%, especially in the unmetamorphosed rocks. Figure 8 (main figure) shows five such samples, and these have the lowest OH band depth values and whole-rock H 2 O content of 0.01-0.34 wt%. ...
Context 17
... H 2 O content for these phases ranges from ~2 wt% for clinohumite (depending on OH/F) to 12 wt% for serpentine, and modal abundances for each are generally >5 vol%, and in cases exceed 20 vol%. Figure 8 shows twelve such samples, and these have OH band depth values of 0.1-0.7 and whole-rock H 2 O content of 0.12-5.37 wt%. ...
Context 18
... Two brucite-bearing samples are shown in Figure 8. Stoichiometric H 2 O content for brucite is 31 wt%, and brucite modal abundance in the samples is estimated at 10-15 vol% along with ~8 vol% serpentine and traces of phlogopite. ...
Context 19
... The lowermost spectrum in the inset in Figure 8 shows the brucite-bearing sample with OH band depth of 0.64 (also shown in the SEM image in Fig. 4A). ...
Context 20
... relationship between OH band depth and whole-rock H 2 O content (Fig. 8) provides overall support for the contention that OH band depth is an indicator of the degree of hydration of the rocks in this study. There is, however, significant scatter in the data. Several factors may contribute to the observed scatter. Band depth is easily computed from the spectra, but the integrated area of the OH absorption ...
Context 21
... data from a subset of 19 samples presented above and shown in Figure 8 establish overall correlations among OH band depth, whole-rock H 2 O content, and occurrence of hydrous minerals in the aureole. In order to place these relationships in a spatial context, Figure 9 illustrates the variation in OH band depth at all 145 sites in the aureole. ...
Context 22
... OH band depth for the site. As an example of variation at a site, one site with five samples has OH band depths that range from 0.04 in a sample that contains only calcite and dolomite to 0.64 in a sample that contains brucite, serpentine, and phlogopite in addition to calcite and dolomite (the latter is one of the brucite-bearing samples in Fig. ...
Context 23
... OH band depth of 0.2 is used to discriminate low and high levels of hydration following the results shown in Figure 8. With one exception, samples with band depth <0.2 have whole-rock H 2 O content <0.5 wt% (>82% of the 946 samples have band depth <0.2). ...
Context 24
... one exception, samples with band depth <0.2 have whole-rock H 2 O content <0.5 wt% (>82% of the 946 samples have band depth <0.2). Samples with band depth >0.2 in Figure 8 generally have whole-rock H 2 O content >0.5 wt% (<18% of total samples). Sites with OH band depth values >0.2 are restricted to distances within ~300 m from the contact in the central part of the aureole where the contact is well exposed (Fig. 9). ...
Context 25
... outer limit of these values is effectively the same as the serpentine (forsterite) isograd. This observation follows directly from the previous discussion of the correlation between band depth and mineral occurrence in connection with Figure 8. ...
Context 26
... should be noted that one site with brucite is projected on to profile B-B′ (Fig. 10), and a possible brucite (periclase) zone is indicated. However, the OH band depth for this sample is only slightly above 0.2, which is unexpectedly low for a brucite-bearing sample (compare brucite samples in Fig. 8 with band depth of >0.6). The Vis-NIR identification of brucite at the site near profile B-B′ was highly questionable, and a thin section is not available. It is therefore possible that brucite is absent or occurs at very low abundance, and this might explain the low OH band depth value for this sample in Figure ...
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