# Multi-generation Fluid Inclusions in Ophicarbonates in Oman and Western Alps Ophiolite

Inukai Tomohiro, Kawamoto Tatsuhiko, Godard Marguerite, Christian

Nicollet, Kenneth T. Koga, Estelle F. Rose-Koga, Debret Baptiste, Tasaka

Miki, Kageta Mikiya, Taniuchi Hajime

► To cite this version:

Inukai Tomohiro, Kawamoto Tatsuhiko, Godard Marguerite, Christian Nicollet, Kenneth T. Koga, et al.. Multi-generation Fluid Inclusions in Ophicarbonates in Oman and Western Alps Ophiolite.

Japanese Geoscience Union, May 2024, Makuhari Messe, Chiba, Japan. hal-04760502

HAL Id: hal-04760502

https://hal.science/hal-04760502v1

Submitted on 30 Oct 2024

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<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
# オマーンと西アルプスオフィオライトのオフィカーボネート中の多世代流体包有物
## Multi-generation Fluid Inclusions in Ophicarbonates in Oman and Western Alps Ophiolite

Tomohiro Inukai ¹, Tatsuhiko Kawamoto ¹, *, Marguerite Godard ², Christian Nicollet ³, Kenneth T. Koga ⁴, Estelle F. Rose-Koga ⁴, Baptiste Debret ⁵, Miki Tasaka ¹, Mikiya Kageta ¹, Hajime Taniuchi ¹, ⁶

¹ Shizuoka University Department of Geosciences, Japan, ² CNRS Géosciences Montpellier, France, ³ Université Clermont Auvergne, CNRS, France, ⁴ Institute des Sciences de la Terre à Orléans, CNRS, Université d'Orléans, France, ⁵ Institut de physique du globe de Paris, France, ⁶ GSJ, AIST, Japan

## 1. Mantle Carbonation in Fast and Slow Spreading Ridges

**Carbonation of serpentinite is important because of**
Global carbon cycle (Alt + 2013, Lithos), Slow earthquakes (Okamoto + 2021, Comm Earth Environ, Uno + PNAS 2022), Carbon capture and storage (Kelemen + 2011, Ann Rev Earth Planet Sci).

**Ophicarbonate: Carbonates in serpentinites**
Common in serpentinized mantle in ophiolites and in oceanic core complex, where the mantle is exhumed on the seafloor.

**Our fluid inclusion analysis**
Clarifies fluid compositions and PT conditions recorded in fluid inclusions of carbonates formed in Oman and Western Alps, which are formed at fast and slow spreading ridges, respectively.

## 2. Ophicarbonates in Oman and Western Alps Ophiolites

**Oman ophiolite** represents an oceanic lithosphere originally formed at **fast-spreading ridges** and then exhumed in subduction zone. Serpentinite in Wadi Tayin massif is characterized by type 1 carbonate veins at suboceanic stage and type 2 carbonate veins during exhumation (Noel +, 2018 Lithos).

**Piemont Zone of western Alps** is an oceanic unit containing a paleo oceanic core complex formed at **slow-spreading ridge** (Manatschal + 2010, Lithos). We studied from the lowest metamorphose ophiolites: Chenaillet (free of subduction metamorphism, Lafay + 2017, Lithos) and Lago nero (metamorphosed at green-schist facies).

## 3. Methods

### Raman microscopy

Chemical species in fluid inclusions and crystals.

### Microthermometry

Salinity and homogenization temperature (density) of fluid inclusions.

## 4. Variations of Ophicarbonates

<figure><img src="image_2.png" /><figcaption>**Oman carbonated serpentinite**</figcaption></figure>

Multi-generated carbonate veins are observed as a time sequence. Type 1 (Noel +, 2018 Lithos) is <0.2 mm thick and composed of calcite and formed at suboceanic stage. Type 2 veins are 1-10 mm thick and of large calcite and small calcite and dolomite and formed at exhumation stage. Type 3 is composed of 0.01 mm calcite and dolomite at the last stage.

<figure><img src="image_3.png" /></figure>

<figure><img src="image_4.png" /></figure>

<figure><img src="image_5.png" /></figure>

<figure><img src="image_6.png" /><figcaption>**Chenaillet ophicarbonate in Western Alps**</figcaption></figure>

Serpentinite is veined by primary calcite (PCV, Lafay + 2017, Lithos) and serpentine is locally replaced by calcite cores (CC). Serpentinite breccias are filled with calcite matrix (MxC).

<figure><img src="image_7.png" /><figcaption>**Lago nero ophicarbonate in Western Alps**</figcaption></figure>

Branching calcite veins are developed in the serpentinite (BCV).

<figure><img src="image_8.png" /></figure>

<figure><img src="image_9.png" /></figure>

<figure><img src="image_10.png" /></figure>

## 5. Seawater-like or Slightly Salty Fluids

<figure><img src="image_11.png" /><figcaption>**Oman carbonated serpentinite**</figcaption></figure>

Type 1 has salinity similar to seawater and can be formed in suboceanic mantle.

Type 2 calcite has almost fresh water and can be formed on land.

Type 2 small dolomite have a range of salinity and some of them can be formed in subduction stage.

No inclusion is observed in Type 3 due to its small size (<0.01mm).

Followed classification by Noel + (2018 Lithos)

<figure><img src="image_12.png" /><figcaption>**Chenaillet and Lago nero (Western Alps) ophicarbonate**</figcaption></figure>

No difference in salinity (5%) and homogenization temperature (145°C) among primary calcite vein (PCV), calcite cores (CC), calcite matrix (MxC), and last calcite vein (LCV).

Classification by Lafay + (2017 Lithos)

Lago nero (BCV) show higher salinity (6%), and higher homogenization temperature (220°C), possibly formed in subduction processes.

## 6. Concluding Remarks

Fluid inclusions suggest that ophicarbonates are formed during seawater interaction beneath the oceanic crust (in Oman) and on the seafloor (Chenaillet) and during subduction processes (in Lago nero). Further analysis of ophicarbonates associated with higher-grade metamorphism is in progress.