Apatite

The oxygen isotope results for apatites are presented in detail in Chapter 1, and are plotted

in Figure 4 - 12, the data table is provided in Appendix table A1 – 1. As most apatite

samples are homogenous for δ

_{O but show BSE zoning (Figure 4 - 16), the δ}

_{O data are}

described in light of chemical zoning in the apatites identified by BSE and LA-ICP-MS

analysis. The complete apatite REE dataset is plotted in the Appendix figure A4 – 10.

Figure 4 - 16. BSE images of Halilbağı apatites, with CL when available. δ18_{O in ‰ is presented with} the analysis spots, around 25x25 µm in size. Scale bar is 200µm.

Two types of zoning can be seen in Halilbağı apatites. First, in some samples, both magmatic, mixed and sedimentary, REE-rich BSE- and CL-bright cores can be seen (Figure 4 - 16), usually rounded and outlined by small fluid and mineral inclusions. In metsediments SIB50B, SIS52 and SIS53, the cores are LREE-enriched (1000 chondrite) and are overgrown by LREE-poor rims (0.1-1 chondrite in SIS52, ca 10 chondrite in SIS53 and SIB50B, Appendix table A4 – 1 and figure A4 - 10), the latter show a pronounced positive anomaly in Ce in SIS52. Rim analyses are depleted in HREE compared to MREE in SIB50B and SIS53. Cores are also seen in samples of magmatic

origin, although they sometimes have less rounded shapes than in the previously described metasedimentary samples. Magmatic samples SHB44A, SHB44B and SHB05 contain BSE and CL-bright cores that are enriched in REE and yield a pronounced negative anomaly, even if none is present in the whole rock (Figure 4 - 17). They are surrounded by a mantle that is poorer in REE, and more specifically in LREE and HREE, with a Eu anomaly that is comparable to the WR.

Second, some apatites display less BSE contrast, but sometimes faint core and rim can be detected. In this case, the cores make up most of the apatite volume, and yield a much lesser amount of REE. This contrast can also be present in the mantles and rims of the previously described samples. The more faint core-rim contrast is best seen in quartzite SHS03, where rims are systematically depleted in most REE and spectacularly so in HREE compared to the cores (Figure 4 - 18). Eclogite SHB45 shows LREE and MREE depletion in the rims compared to the cores, in addition to a dip in HREE.

Core-rim REE relationships are less systematic in blueschist SHB08, eclogite SHB12B and SHB53, calcsilicate SHM23B and marble SGM21. In blueschist SHB08 and eclogites SHB12B and SHB53, apatites are variably depleted in LREE, down to 0.1 -1 chondrite (see SHB12B in Figure 4 - 18). In other samples such as calcsilicates SHS27, and SHM23B and marble SGM21, the BSE and REE zoning are restricted, but some grains analyses are enriched in MREE (up to 1000 chondrite in SHM23B) compared to other REE (ca 100 chondrite, slightly more in SHM23B). SGM21 and SHM23B display complex zoning in CL, which potentially correlates with MREE abundance.

Figure 4 - 18. Chondrite-normalised REE profiles for δ18_{O-zoned apatites samples, with WR profile in} black. Thick lines in shades of grey are non-determined zones (e.g. no BSE contrast or fragmental grain).

In contrast with this rich trace element zoning, most apatite samples and grains are homogenous for oxygen isotopes, as shown in Chapter 1. Particularly, the δ18_{O composition of small bright}

cores, in both metasedimentary and magmatic samples, is systematically identical to the mantles surrounding them (Figure 4 - 16, Appendix table A1 – 1). Some variation in δ18_{O is observed}

along the rims of apatite crystals in SHB03 and SHB12B. In SHB12B, in two grains, the cores yield lower δ18_{O of ca. 10 ‰ and the rims have a higher δ}18_{O of ca. 15 ‰ (pictured in Figure 4 -}

16). In SHB03, the variation is smaller and inverse, with cores at ca. 19.5 ‰ and rims at ca. 17 ‰. In SHB12B, LREE depletion does not correlate with δ18_{O, only in that the two most LREE-}

depleted profiles yield the two highest δ18_{O. Particularly, in the two grains that show 5 ‰ core-}

rim zoning in δ18_{O, core and rim REE composition are identical, but grain to grain variation in}

seen in REE. In SHS03, no good correlation is found between oxygen isotopes and REE with grain to grain variations occulting core-rim variations in δ18_{O. Nevertheless, the 3 most HREE}

depleted rim spectra are the lowest δ18_{O. In SHB45, despite large variations in LREE, no}

variations in δ18_{O are observed in the apatite rims. Some co-variation is observed between δ}18_O

and Fe and is most spectatular in SHS03, where BSE-dark rims yield less Fe and a lower δ18_O

compared to BSE-bright cores (Figure 4 - 25c). Apatite δ18_{O changes show a weak co-variation}

Figure 4 - 19. Systematics of Sr and Pb concentration in apatite and lawsonite, and their correlation with δ18_{O. In c. and d., arrows point to core-rim evolution in single grains.}

The analysed apatite samples have significant variations in Sr-Pb systematics (Figure 4 - 19a). Apatite in metasedimentary samples yields low Sr contents (up to ca 1000 ppm). A few analyses above this concentration correspond to the LREE-rich cores, and might be affected by small inclusions. Pb contents are variable, from 0.1 ppm for SIS52 apatite to up to 60 ppm in metasediment SHS3. In the impure marble SGM21, contents in Sr and Pb are among the lowest and are constant across the analysed zones. Samples SIS52 and SHS27 produce Sr-Pb arrays that spread in Sr and Pb respectively, along an array of similar Sr/Pb. A similar behaviour is seen in apatite from intermediate samples SIB32 and SIB50B, which also has low Sr contents. Apatite in

Sample SHS03, SHM27 and SHM23B yields more scattered analyses. In metabasites, apatite is much richer in Sr compared to Pb (up to 5000 ppm Sr and 40 ppm Pb). Samples SHS44A and SHB44B form arrays of constant Sr/Pb, which is also observed in SHB53ep. A couple of apatite analyses in SHS44A deviate to higher Pb concentrations, a few analyses of SHB53ep deviate to higher Sr concentrations, with SHB53ecl at similar Pb but much higher Sr (up to 0.15 wt%). Some samples have homogenous Sr and Pb compositions such as SHB08 and SHB05. Apatite in two of the metabasites show significant scatter in Sr and Pb content: SHB45 yields high and variable Sr contents, with no particular systematics between analyses. SHB12B sows some small-scale variation for moderate amounts of both Sr and Pb. Sr/Pb and δ18_{O are compared in Figure 4 - 19c.}

In most samples, Sr/Pb varies without changes in δ18_{O. Typically, Sr/Pb decreases from core to}

rim, as is most seen in SHB45 with a change from 600 to 80. In SHB12B, higher δ18_{O rim values}

correspond to lower Sr/Pb ratios. A reverse trend is seen in SHS03 where the lowest δ18_{O rims}

yield higher Sr/Pb ratios.