FT2: MALACARA TUFF CONE AND CARAPACHO TUFF RING in Llancanelo Volcanic Field, Malargüe-Mendoza.

Organizers and leaders: Dr. Corina Risso , Argentina , corina@gl.fcen.uba.arr, and Dr. Karoly Nemeth , New Zealand , K.Nemeth@massey.ac.nz.

Purpose: The Plio-Pleistocene Llancanello and Payun Matru volcanic fields comprise at least 800 scoria cones along with subordinate tuff rings and cones. The purpose of the field trip is to study several of the volcanoes with evidence of explosive eruptions involving magma-water interaction. The volcanic structures consist of phreatomagmatic tuff rings and tuff cones of olivine basalt composition. This subordinate phreatomagmatism in the Llancanelo Volcanic Field suggests the presence of ground and/or shallow surface water during some of the eruptions. The strong palagonitization at each of the phreatomagmatic cones formed hard beds, resistant to erosion, and therefore the volcanic landforms are well preserved.

Timing and Logistics: This will be a full-day pre-conference excursion on April 13^th . The trip will start at 7 am and returning to Malargüe at approximately 7 pm in order to attend the Icebreaker reception at 8 pm .

Climate: Days will be sunny and moderately warm (17-18 ºC) with fresh nights.

Clothing and field conditions: Clothing must be appropriate for all weather and should include light clothing during the day, such as a T-shirt with walking boots, sunglasses, hat, and sunscreen. A jacket and a sweater or windbreaker is needed if the day is cloudy and windy.

All outcrops to be visited can be reached by vehicle and then by reasonable walking in sandy soils.

Cameras are recommended.

Accommodation, Transport, Meals:

Group transportation will start in the early morning from each hotel and return in the same way. During the excursion, small busses will be used. All roads are gravel.

Meals during the excursion include lunch and 2 coffee snacks. Please inform the organizers of any special food requirements (e.g. vegetarian, religious, or allergies).

Excursion fee: The cost for the full day trip with 1 field lunch and logistical organization and transport is € 60. There are no limitations on the maximum number of participants for this field trip.

The excursion fee covers the following:

• 1 field lunch
• 2 coffee snacks
• Travel Insurance
• All organization and administration costs

Booking, Payment and cancellation: The participants must register and book the excursion through the Congress main registration system. Payments will be collected on registration by Congress support (see 3rd IMC website for more information). The excursion will not take place if the number of participants is less than 8. In this case, notification of cancellation will take place in January 2009. If the excursion is scheduled, any additional conditions for cancellation will be announced in February 2009.

Day-by-day stops: The following is a brief outline of the excursion in Llancanelo Volcanic Field.

Day 1: Departure at 7:00 am from Malargüe to Malacara Volcano.

We will begin by climbing of the NNE sector of the volcano, where most of the initial yellow pyroclastic sequence is exposed. The participants will observe a succession consisting entirely of yellow lapilli tuff of wet and dry fall units dipping away from the crater at 30-32º, with small interbeds of base surges. Many outcrops with deformational structures documenting slump and failure of the water-saturated oversteepened beds will be observed and discussed.

Returning to the valley, the participants can recognize the last pyroclastic deposits generated by sub-Plinian eruptions represented by black pyroclastic fall deposits ending with an effusive event. Wind and water erosional features created fantastic landscapes.

Field lunch in Malacara.

After a one-hour drive, we will arrive at the Carapacho tuff ring, located on the marginal flat floor of the saline Llancanelo Lake . Carapacho has a horseshoe-shaped crater open to the west, with a wide crater with a low crater rim-to-rim. The bedding exhibits quaquaversal dips and is continuous from the crater to the outer flanks

The participants can enjoy beautiful examples of volcanic breccias rich in non-volcanic country rocks and deposits of high-particle-density wet surges and high-temperature ‘dry’ base surges.

Participants will observe and analyze deformed beds with impact sags, slumping textures, asymmetrical ripples, dunes, cross- and planar-lamination, syn-volcanic faulting and accretionary lapilli beds, all of which indicate an eruption scenario dominated by excessive water in the transport and depositional regimes.

Return to Malargüe arriving at approximately 7 pm .

Guide book: The guidebook will follow the standard format required by the Conference. It will be made available in an electronic format to be incorporated on to a CD and a sufficient number will be printed for the needs of the fieldtrip participants.

Note: Information on the route and the stops will be updated regularly to include more details.