Appendix 1: Petrographical Descriptions

Appendix 1: Petrographical descriptions

Sample YT1-1 and YT1-2 are picrites. They are recovered from 5558m and 5557m deep in borehole YT1 respectively. They all have porphyritic texture (Fig 1).

The dominant phenocryst is Ol (~20 modal%) with minor Cpx (~5 modal%), with length of mainly 1-5mm. All the Ol are altered to serpentine, rimming by red-brown iddinsite, whereas the crystal shape of Ol is well preserved (Fig 1). Cpx is euhedral and fresh (Fig 2), with Mg# of ~90.

The matrix is composed of altered glass, minor amount of microcrystalline Cpx and minor altered Pl. The glass is mainly replaced by chlorite. Most Cpx in the matrix are fresh. Patches of secondary carbonate are present in the matrix.

Observed opaque phases include titanomagnetite and minor chromite.

Fig. 1 Petrography of picrite YT1-1, with phenocrysts of Ol and Cpx.

(plain-polarized, picture width=2.5mm). Note the porphyritic texture and Ol pseudomorph.

Fig. 2 Euhedral and fresh clinopyroxene phenocryst of sample YT1-1 (cross-polarized light).

Note some fresh Cpx grains are present in the matrix. The Ol phenocrysts are in dark color with a little red-brown. The small round object on the surface of the Cpx is a glue bubble.

Sample YH5-1 is an aphyric picrite. It is sampled at the depth of 5922m in borehole YH5. Hand specimen shows aphyric texture. Only one altered Ol grain is observed (<1 modal%), no Cpx phenocryst.

Under microscope, its texture is coarser than the matrix of YT1 picrites, similar to subophitic texture (Fig. 3). Pl is subhedral to euhedral, and partially enclosed by clinopyroxene.

Microcrystalline Ol (<0.1mm) is abundant (>15 modal%) in some area. All the Ol are altered to serpentine, rimming by iddinsite.

Most Cpx are fresh while Pl commonly altered .

Opaque phases include titanomagnetite and magnetite.

Fig. 3 Petrography of picrite YH5-1 (cross-polarized, picture width=0.5mm).

Note the replacement of Ol by iddinsite.

Sample YM5-1 is an Ol-basalt. It is sampled at the depth of 5428m in borehole YM5.

Fig. 4 shows the porphyritic texture of YM5-1.

Phenocrysts are Cpx (~7 modal%) and Pl (~8 modal%) with minor Ol (not shown in Fig. 4).

The matrix is composed of altered glass (~50 modal%), labradorite laths (~25 modal%), Cpx (~25 modal%) and minor opaque minerals.

Fig. 4 Petrography of basalt YM5-1 (cross-polarized, picture width=2mm), with phenocrysts of Cpx and Pl in a matrix of glass, labradorite laths and clinopyroxene grains.

Sample YM5-4 is an Ol-basalt. It is sampled at the depth of 5434m in borehole YM5.

Fig. 5 shows the porphyritic texture of YM5-4.

The phenocrysts are mainly Cpx (shown in Fig. 5) and Pl, no Ol observed (but Ol-normative).

The matrix is composed of labradorite laths, clinopyroxene grains and minor glass.

Opaque phases include titanomagnetite and magnetite.

Alteration is weak.

Fig. 5 Petrography of basalt YM5-4 (cross-polarized, picture width=2mm).

With phenocrysts of Cpx and Pl (not shown) in a matrix of labradorite laths and clinopyroxene grains with minor glass.

Sample YM5-5 and YM5-6 are Ol-basalts (Ol-normative). They are sampled at the depth of 5439m and 5440m in borehole YM5 and show similar petrography characteristics.

Fig. 6 shows the porphyritic texture of YM5-5. YM5-6 is similar (not shown).

The phenocrysts are Cpx and Pl, Ol not observed.

The matrix is composed of labradorite laths, clinopyroxene grains and minor chlorite (possibly altered glass).

Opaque phases include titanomagnetite and magnetite.

Cpx is partly altered to chlorite and carbonate(?). Pl is partly altered to sericite. Glass is not observed, may be completely replace by chlorite.

Fig. 6 Petrography of basalt YM5-5 (cross-polarized, picture width=2mm).

With phenocrysts of Cpx and Pl (not shown) in a matrix of labradorite laths and clinopyroxene grains with minor glass. Black objects on the upper right and lower left are later holes.

Sample YM5-8 is a dacite and is difficult to be identified from other rhyolites by only hand specimen examination. This sample is recovered at the depth of 5484m in borehole YM5.

Fig. 7 shows the porphyro-aphanitic texture of YM5-9.

The phenocrysts are alkali feldspar (Afs) (~14 modal%) and minor altered Ol.

The matrix is composed of Afs, Q, minor Cpx, Bitite (not shown in Fig. 7).

Opaque phases are magnetite with minor titanomagnetite.

Ol is altered to chlorite and serpentine, and leave a Fe-rich rim or iddingsite-like rim.

Fig. 7 Petrography of dacite YM5-8 (cross-polarized, picture width=1mm).

With phenocrysts of Afs (upper left) and altered Ol (lower right) in a matrix of mainly Afs and Q.

Sample YM5-9 is an Ol-basalts. It is sampled at the depth of 5531m.

Fig. 8 shows the vitrophyric texture of YM5-9.

The phenocrysts are Cpx (~6 modal%), Pl (~7 modal%) and altered Ol (~2%).

The matrix is dominantly glass, with minor labradorite laths and small Cpx grains.

Opaque phases include titanomagnetite and magnetite.

Ol is altered to serpentine and chlorite. Pl is slight altered to sericite on the surface. Glass is also sight altered to little green color.

Fig. 8 Petrography of basalt YM5-9 (cross-polarized, picture width=2mm).

With phenocrysts of Cpx, Pl and altered Ol (mid right).

Sample DH12-1 and DH12-2 are Ol-dolerite. They are sampled at the depth of 5780m and 5784m in borehole YM5 and show similar petrographical characteristics.

Fig. 9 shows the subophitic texture of DH12-1. DH12-2 is similar (not shown).

Pl is subhedral to euhedral, and partially enclosed by clinopyroxene.

Altered Ol (>0.2mm) is common. Opaque phases include titanomagnetite and magnetite.

Ol is replaced by serpentine with iddingsite in the rim. Cpx is partly altered to chlorite and clay mineral. Pl is partly altered to clay mineral.

Fig. 9 Petrography of olivine dolerite DH12-1 (cross-polarized, picture width=2mm).

Sample YM8-4 is a vesicular basalt. It is sampled at the depth of 5785m in borehole YM8.

Fig. 10 shows the vesicular and porphyritic texture of YM8-4.

The phenocrysts are mainly Cpx (~8 modal%) and Pl (~4 modal%), minor altered Ol (possible) is replaced by chlorite.

The matrix is composed of labradorite laths, clinopyroxene grains and glass.

Opaque phases include titanomagnetite and magnetite.

Alteration is weak. Only minor Ol is replaced by chlorite. No vesicular has been filled by amygdules.

Fig. 10 Petrography of basalt YM8-4 (cross-polarized, picture width=2mm).

With phenocrysts of Cpx and Pl in a matrix of labradorite laths and clinopyroxene grains with glass. Vesicular is common.

Sample YT6-1 is a basalt from a lava flow. It is sampled at the depth of 5788m in borehole YT6.

Fig. 11 shows the porphyritic and “trachyte-like” texture of YT6-1.

The phenocrysts are mainly Pl (~6 modal%) and Cpx (~4 modal%), with no Ol.

The matrix is composed of mainly Pl, glass and minor Cpx grains. Pl grains show a preferred orientation due to flowage, and the interstices between plagioclase grains are glass and cryptocrystalline Cpx.

Different from normal trachyte, the matrix Pl is labradorite. The “trachyte-like” texture only implies a rapid cooling of a flowing basaltic lava.

Opaque phases include titanomagnetite and magnetite.

Alteration is weak. Only Pl is partly altered to clay minerals on the surface.

Fig. 11 Petrography of basalt YT6-1 (cross-polarized, picture width=2mm).

With phenocrysts of Pl in a matrix of labradorite laths and clinopyroxene grains with glass. Note the

Sample YT6-2 is a basalt. It is sampled at the depth of 5786m in borehole YT6.

Fig. 12 shows the porphyritic texture of YT6-1.

The phenocrysts are mainly Cpx (~8 modal%) and Pl (~4 modal%), no Ol.

The matrix is composed of labradorite laths, clinopyroxene grains and glass.

Opaque phases include titanomagnetite and magnetite.

Pl and Cpx are partly altered to clay minerals. Glass is altered to chlorite. Some vesiculars are filled by amygdules.

Fig. 12 Petrography of basalt YT6-2 (cross-polarized, picture width=2mm).

With phenocrysts of Cpx and Pl in a matrix of labradorite laths and clinopyroxene grains with glass. Vesicular is present. Note the phenocrysts of Cpx and Pl at upper right are destroyed during thin section cutting, a glue bubble is present in the hole.

Sample YM201-1 is a dolerite. It is sampled at the depth of 5813m in borehole YM201.

Fig. 13 shows the subophitic texture of YM201-1.

Pl and Cpx are major minerals, no Ol. Pl is subhedral to euhedral, and partially enclosed by clinopyroxene. Some Pl and Cpx grains are bigger than others, similar to phenocrysts, implying they are possibly earlier stage crystals.

Opaque phases include titanomagnetite and magnetite.

This sample is quite fresh.

Fig. 13 Petrography subophitic texture of dolerite YM201-1 with plagioclase partially enclosed by clinopyroxene (cross-polarized, picture width=2mm).

Sample SL1-2 is a basalt. It is sampled at the depth of 5545m in borehole SL1.

Fig. 14 shows the porphyritic texture of SL1-2. Vesiculars is present (not shown in Fig. 14).

The phenocrysts are mainly Cpx (~4 modal%) and Pl (~6 modal%), no Ol.

The matrix is composed of labradorite laths, clinopyroxene grains and minor glass.

Opaque phases include titanomagnetite and magnetite.

Matrix Cpx is altered to clay minerals and chlorite. Some vesiculars are filled by amygdules.

Fig. 14 Petrography of basalt SL1-2 (cross-polarized, picture width=2mm).

With phenocrysts of Cpx and Pl in a matrix of labradorite laths and clinopyroxene grains with glass. Vesicular is present. Note the phenocrysts of Cpx and Pl at upper right are destroyed during thin section cutting, a glue bubble is present in the hole.

Sample SL1-3 is a basalt. It is sampled at the depth of 5542m in borehole SL1.

Fig. 15 shows the porphyritic texture of SL1-3. Amygdules.are present, ulfilled vesiculars are also present (not shown in Fig. 15).

The phenocrysts are mainly Cpx (~3 modal%) and Pl (~7 modal%), no Ol.

The matrix is composed of labradorite laths, altered clinopyroxene grains and some secondary clay mineral and chlorite.

Opaque phases include titanomagnetite and magnetite.

Cpx is altered to clay minerals. Some clay mineral and chlorite are possibly altered glass.

Fig. 15 Petrography of basalt SL1-3 (cross-polarized, picture width=2mm).

With phenocrysts of Cpx and Pl in a matrix of labradorite laths, altered clinopyroxene grains and altered glass(?).Amygdules.are present

Sample SL1-4 is a vesicular basalt. It is sampled at the depth of 5248m in borehole SL1.

Fig. 16 shows the porphyritic texture of SL1-4. Vesiculars are common.

The phenocrysts are mainly Cpx (~6 mode ) and Pl (~4 modal%), no Ol.

The matrix is composed of labradorite laths, clinopyroxene grains and minor glass.

Opaque phases include titanomagnetite and magnetite.

Alteration is weak. No vesicular is filled by amygdule.

Fig. 16 Petrography of basalt SL1-4 (cross-polarized, picture width=2mm).

With phenocrysts of Cpx and Pl (not shown) in a matrix of labradorite laths and clinopyroxene grains with glass. Vesicular is common. Note twinning of the Cpx phenocryst at lower right.

Sample MN1-1 and MN1-2 are rhyolites. They are recovered at the depth of 5166 and 5168m in borehole MN1 and have similar petrographical characteristics.

Fig. 17 shows the porphyric texture of MN1-1.

The phenocrysts are Q (~12 modal%).

The matrix is composed of Afs, Q, minor Cpx (not shown in Fig. 17).

Opaque phases are magnetite.

The samples are fresh.

Fig. 17 Petrography of rhyolite MN1-1 (cross-polarized, picture width=2mm).

With phenocrysts of Q in a matrix of mainly Q and Afs.

Sample YM16-1 and YM16-2 are rhyolites. They are recovered at the depth of 5195 and 5204m in borehole YM16 and have similar petrographical characteristics.

Fig. 18 shows the porphyric texture of YM16-1.

The phenocrysts are Q (~12 modal% for YM16-1 and ~15modal% for YM16-2).

The matrix is composed of Afs, Q, and minor biotite (not shown in Fig. 18).

Opaque phases are magnetite.

The samples are fresh.

Fig. 18 Petrography of rhyolite YM16-1 (cross-polarized, picture width=2mm).

With phenocrysts of Q in a matrix of mainly Q and Afs.

Sample NK1-1 is a rhyolite recovered at the depth of 5270m in borehole NK1.

Fig. 19 shows the porphyric texture of NK1-1. Some are possibly vitric fragments, implying it is possibly related to ignimbrite.

The phenocrysts are Q (~15 modal%).

The matrix is composed of Afs, Q and minor biotite.

Opaque phases are magnetite.

No alteration.

Fig. 19 Petrography of rhyolite NK1-1 (cross-polarized, picture width=2mm).

With phenocrysts of Q in a matrix of mainly Q and Afs.

Some are lithic fragments (?), see dark objects.

Sample YM30-1 and YM30-2 are rhyolites. They are recovered at the depth of 6330 and 6333m in borehole YM30 and have similar petrographical characteristics.

Fig. 20 shows the porphyric texture of YM30-1.

The phenocrysts are Q (~15 modal% for YM30-1).

The matrix is composed of Afs, Q and minor Bi.

Opaque phases are magnetite.

The samples are fresh.

Fig. 20 Petrography of rhyolite YM30-1 (cross-polarized, picture width=2mm).

With phenocrysts of Q in a matrix of mainly Q and Afs.

Sample YT8-1 and YT8-2 are rhyolites. They are recovered at the depth of 5771 and 5773m in borehole YT8.

Fig. 20 shows the porphyric texture of YT8-1. Some Q phenocrysts are remelted (Fig. 21).

The phenocrysts are Q (~15 modal% for YM30-1).

The matrix is composed of Afs, Q and minor Bi.

Opaque phases are magnetite.

The samples are fresh.

Fig. 21 Petrography of rhyolite YT8-1 (cross-polarized, picture width=2mm).

With phenocrysts of Q in a matrix of mainly Q and Afs. Not Q phenos. are remelted.