Table T1. Summary of thermochronological results, Leg 180.

Table T1. Summary of thermochronological results, Leg 180.

Hole,
core

Rock type

Mineral

Analysis

Age
(Ma)

Comments

180-1109D-

45R Diabase Plagioclase ⁴⁰Ar/³⁹Ar-TF 161.1 ± 35.1 No K alteration

45R Diabase Plagioclase ⁴⁰Ar/³⁹Ar-SH 58.9 ± 5.8 Unaltered, plagioclase cooling age

180-1117A-

11R Gabbro Zircon ²³⁸U/²⁰⁶Pb 66.4 ± 1.5 Thin section, crystallization age

11R Gabbro Plagioclase ⁴⁰Ar/³⁹Ar-TF 51.4 ± 22.6 Moderate K alteration

11R Gabbro Plagioclase ⁴⁰Ar/³⁹Ar-SH 43.6 ± 2.5 Moderate K alteration

alt Gabbro Plagioclase ⁴⁰Ar/³⁹Ar-TF 54.7 ± 3.7 More altered 1117 separate

alt Gabbro Plagioclase ⁴⁰Ar/³⁹Ar-SH 35.4 ± 1.0 More altered 1117 separate

180-1118A-

70R Diabase Plagioclase ⁴⁰Ar/³⁹Ar-TF 32.7 ± 5.8 Pervasive K alteration, K alteration age

70R Diabase Plagioclase ⁴⁰Ar/³⁹Ar-SH 31.0 ± 0.9 Pervasive K alteration, K alteration age

180-1110B-

3X Rhyolite K-feldspar ⁴⁰Ar/³⁹Ar-TF 12.5 ± 0.2 K-feldspar altered to sericite

3X Rhyolite K-feldspar ⁴⁰Ar/³⁹Ar-SH 11.9 ± 0.2 K-feldspar altered to sericite, hydrothermal alteration 10-11 Ma

3X Rhyolite Zircon ²³⁸U/²⁰⁶Pb 15.7 ± 0.3 Mineral separate, crystallization age of arc-related volcanics

180-1111A-

16R Rhyolite K-feldspar ⁴⁰Ar/³⁹Ar-TF 14.4 ± 0.6 K-feldspar altered to sericite

16R Rhyolite K-feldspar ⁴⁰Ar/³⁹Ar-SH 14.1 ± 0.3 K-feldspar altered to sericite, hydrothermal alteration 10-11 Ma

16R Rhyolite Zircon ²³⁸U/²⁰⁶Pb 15.7 ± 0.3 Mineral separate, crystallization age of arc-related volcanics

180-1108B-

6R Microgranite Biotite ⁴⁰Ar/³⁹Ar-TF 2.6 ± 0.2 Some chlorite contamination, biotite cooling age

6R Microgranite Feldspar ⁴⁰Ar/³⁹Ar-TF 2.1 ± 0.3 Unaltered, mixture of albite and microcline, feldspar cooling age

6R Microgranite Zircon ²³⁸U/²⁰⁶Pb 3.1 ± 0.1
550± 12
Two generations of zircon, 3 Ma zircon represents crystallization age

6R Microgranite Apatite Fission Track 2.7 ± 1.2 Apatite rapid cooling age

Hole, core	Rock type	Mineral	Analysis	Age (Ma)	Comments
180-1109D-
45R	Diabase	Plagioclase	⁴⁰Ar/³⁹Ar-TF	161.1 ± 35.1	No K alteration
45R	Diabase	Plagioclase	⁴⁰Ar/³⁹Ar-SH	58.9 ± 5.8	Unaltered, plagioclase cooling age
180-1117A-
11R	Gabbro	Zircon	²³⁸U/²⁰⁶Pb	66.4 ± 1.5	Thin section, crystallization age
11R	Gabbro	Plagioclase	⁴⁰Ar/³⁹Ar-TF	51.4 ± 22.6	Moderate K alteration
11R	Gabbro	Plagioclase	⁴⁰Ar/³⁹Ar-SH	43.6 ± 2.5	Moderate K alteration
alt	Gabbro	Plagioclase	⁴⁰Ar/³⁹Ar-TF	54.7 ± 3.7	More altered 1117 separate
alt	Gabbro	Plagioclase	⁴⁰Ar/³⁹Ar-SH	35.4 ± 1.0	More altered 1117 separate
180-1118A-
70R	Diabase	Plagioclase	⁴⁰Ar/³⁹Ar-TF	32.7 ± 5.8	Pervasive K alteration, K alteration age
70R	Diabase	Plagioclase	⁴⁰Ar/³⁹Ar-SH	31.0 ± 0.9	Pervasive K alteration, K alteration age
180-1110B-
3X	Rhyolite	K-feldspar	⁴⁰Ar/³⁹Ar-TF	12.5 ± 0.2	K-feldspar altered to sericite
3X	Rhyolite	K-feldspar	⁴⁰Ar/³⁹Ar-SH	11.9 ± 0.2	K-feldspar altered to sericite, hydrothermal alteration 10-11 Ma
3X	Rhyolite	Zircon	²³⁸U/²⁰⁶Pb	15.7 ± 0.3	Mineral separate, crystallization age of arc-related volcanics
180-1111A-
16R	Rhyolite	K-feldspar	⁴⁰Ar/³⁹Ar-TF	14.4 ± 0.6	K-feldspar altered to sericite
16R	Rhyolite	K-feldspar	⁴⁰Ar/³⁹Ar-SH	14.1 ± 0.3	K-feldspar altered to sericite, hydrothermal alteration 10-11 Ma
16R	Rhyolite	Zircon	²³⁸U/²⁰⁶Pb	15.7 ± 0.3	Mineral separate, crystallization age of arc-related volcanics
180-1108B-
6R	Microgranite	Biotite	⁴⁰Ar/³⁹Ar-TF	2.6 ± 0.2	Some chlorite contamination, biotite cooling age
6R	Microgranite	Feldspar	⁴⁰Ar/³⁹Ar-TF	2.1 ± 0.3	Unaltered, mixture of albite and microcline, feldspar cooling age
6R	Microgranite	Zircon	²³⁸U/²⁰⁶Pb	3.1 ± 0.1 550± 12	Two generations of zircon, 3 Ma zircon represents crystallization age
6R	Microgranite	Apatite	Fission Track	2.7 ± 1.2	Apatite rapid cooling age

Note: TF = total fusion, SH = step heat.