Mazzini 2011

Simposium Internasional Ilmiah Lusi

25-26 Mei 2011, di Lusi dan Surabaya

Dilaksanakan oleh BPLS-HSH

Field observations and key findings in eastern Java:

a) Numerous mud volcanoes and seeps  Lusi not the only mud eruption site;

b) Lusi is aligned along a major fault zone  External trigger plausible;

c) Proximity to the volcanic arc Influence of deep volcanic system?

Key findings: mud volcanism is common

Mud volcanism is a very common phenomenon in Indonesia.

The geological setting of Java: text book example for mud volcano formation.

Has there ever been a Lusi in the past? Likely,

based on geological and historical data.

Key findings:

Seismics show pre-existing piercement

Seismic profiles from 1980’s show presence of growing piercement structure at Lusi site.

Typical of gelogical features that will manifest to the surface Lusi would have erupted sooner or later.

Key findings: Origin of erupted solid/fluids

(based on observations made in 2006)

Key points: The LUSI system formed in a geological setting prone to mud volcanism

•Main gas CO2+CH4+acqueous vapour

• Illitization throughout clayey unit

• Source water-gas-mud 1100-1850

Main for water gas 1100 m

Large amount of water available

• Possible deeper water/source of gas NOT

obvious from sample analyses.

What is Lusi?

MUD VOLCANISM

“Geological phenomena made manifest through the sudden eruption or quiescent extrusion of sediment, rock, and fluids from deeper strata of an hydrocarbon bearing basin”

Is Lusi really a mud volcano?

TYPICAL FOR MUD VOLCANO

• Setting

• Morphology

• Presence of mud breccia

• Water from illitization of clay minerals

• ATYPICAL FOR MUD VOLCANO

• High geothermal gradient (shallow geochemical reactions)

• Longlasting eruption

• Pulsating behavious (geyser-like?)

• CO2-dominated gas

Methane zonation diagrams

Diagrams indicate that

•Lusi 2006: the early sampling made in 2006 shows

contributions of microbial CH4 component (Kalibeng Fm.+ alluvial)

•Lusi after 2006: Thermogenic signature

•Wunut: Thermogenic signature (although very shallow)

•Other MVs in east Java: mixed gas

• Maturity plots indicate a deep origin of Lusi gas.

• Lusi plumbing system is much deeper than

previously expected

• Lusi gas was generated at high temperatures

• Wunut gas is more fractionated compared to Lusi

CO2 and helium origin

• CO2 gas isotopic composition indicates that high temperature reactions generated the erupted gas

• Helium isotopic values and CO2/CH4 also indicate high equilibrium temperatures as well as presence of mantle origin fluids

• Hot fluids are involved in the ongoing

geochemicalreactions

A new scenario for the lusi eruption

Arjuno-Welirang volcanic complex explains the

observations indicating that it is responsible for:

• High geothermal gradient

• Significant CO2 production

• High temperature generation of CO2 and CH4

• Presence of mantle gas

The intrusion scenario

Possible intrusion from the neighbouring volcanic complex already suggested in 1999

The Arjuno-Welirang volcanic complex

• Growth of the complex evolving towards the NE

• Watukosek fault system follows the same NE direction hosting other mud volcanoes

• Evidence of hot fluids interaction along the escarpment

Seismicity?

Is the frequent seismicity affecting the system:

Lusi Fault Volcanic system?

Increased activity of other mud volcanoes along

fault after May 2006 earthquake

Coincidentially other mud volcanoes along Watukosek fault were more active after earthquake when activity started around Lusi.

Semeru + Merapi stronger activity after earth quake

Predictions about Lusi longevity

• Combined effect of:

– Seismicity

– Alterations of magmatic chamber

– Reactivation of Watukosek fault

– Effect on rheology of sediments and critical overpressure

Summary

Lusi is part of a larger sediment-hosted hydrothermal system connected to the Arjuno-Welirang volcanic complex

A deeper sited magmatic intrusion or migration of hot fluids explains the geochemical signature observed Lusi cannot be a representative example of a mud volcano