FT4: CHUBUT DIATREMES

Organizers and leaders: Dr. Miguel J. Haller, Argentina, haller@cenpat.edu.ar and Dr. Karoly Nemeth, New Zealand, K.Nemeth@massey.ac.nz

Purpose: In Patagonia, Argentina, newly discovered diatremes stand about 100 m above the surrounding plain at the southern border of the Cenozoic Somuncura mafic lava plateau, documenting phreatomagmatic episodes associated with the formation of these volcanic fields. The identified pyroclastic and intrusive rocks are exposed in lower diatremes of former phreatomagmatic volcanoes and their feeding dyke systems.

Participants in this excursion will observe the features of mafic dykes intruding pyroclastic successions.

Timing and Logistics: This excursion is post-conference and is planned for 5 days/4 nights. The excursion begins in Malargüe, on Saturday morning, 18 April, 2009, and ends in Buenos Aires on 22 April in the late evening. Participants will depart from Microtel Inn Malargüe on 18 April at 07:00. A bus transfer will transport them to Mendoza airport (3 hs. drive).

Climate: Weather in Chubut is subject to much variation in a single day. The average temperature during April nears 8°C, similar to November conditions in continental Europe, and is comfortable for field work. Temperature can reach up to 15°-16°C but the weather could suddenly become rainy with strong winds. Night frost is present, and snow could occur.

Clothing and field conditions: Clothing must be appropriate for all weather and should include layered clothing with a warm rainproof overcoat, sweater, gloves, warm underwear, T-shirt, walking boots, sun-glass, hat, and sun cream. Most stops require a relatively easy walk, occasionally up to 1.5 km per outcrop, but one or two may include more difficult conditions with climbing on rocky slopes up to 100 m height. If it rains, the slopes could be slippery. Cameras are recommended, and compasses and hammers are optional.

Accommodation, Transport, Meals: The first night is in a three-star hotel in Buenos Aires. Other overnight accommodations are rustic at the mine camp of the Argentine Atomic Energy Commission in Los Adobes. Therefore participants are required to bring their own sleeping bags, pads, and towels.  There is hot water and showers at the camp.

Group transportation to the Mendoza airport will be by bus. During the excursion, four-wheel-drive vehicles will be used. Most roads in Patagonia are gravel roads. All outcrops to be visited can be reached by vehicle and then by reasonable walking.

Meals during the excursion include breakfast, lunch and dinner. Further details for accommodation, transport and meals are listed below, along with the fee for the excursion. Please inform the organizers of any special food requirements (e.g. vegetarian, religious, or allergies).

Excursion fee: The price for the excursion is € 855 based on double room in Buenos Aires and shared rooms in the mine camp. A minimum of 8 participants is required. The maximum number of participants is 12 due to transport constraints. The excursion fee covers the following:

Add €100 for single-room accommodation in Buenos Aires. Sorry, no single accommodation is possible in the mine camp.

The excursion fee does not include:

Booking, Payment and cancellation: The participants must register and book the excursion through the Conference main registration system. Payments will be collected during registration by Conference 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 advertised in February 2009.

Day-by-day stops: The following is a brief outline of the excursion in Chubut province. This is still provisional and may have to be adapted to correspond with updated flight timetables.

Day 1: Malargüe-Buenos Aires. Participants will be transported by bus from Malargüe to Mendoza airport. After arrival at the Buenos Aires domestic airport, participants will then be transferred by bus to their overnight accommodation to relax and have dinner.

Day 2: Buenos Aires-Trelew-Los Adobes mine camp. Participants will be transferred from the Hotel to Buenos Aires domestic airport. After arrival to Trelew airport, a welcome and a brief introduction to the excursion are planned. Once on the road to the camp, participants will be taken to the outcrops of Jurassic volcanic rocks and will have lunch in the field. The trip will follow the Chubut river valley where the transition from siliceous to calc-alkaline mesosiliceous Jurassic volcanic rocks, and the overlying Cretaceous sedimentary rocks, can be observed. After arriving and accommodation in the Los Adobes mine camp, dinner will be served at the camp canteen.

Day 3: Los Adobes-Los Chivos-Los Adobes with lunch in the field. The plan for the day is to observe the dykes and pipe-like features standing 100 m above the desert floor. Close ups will give insights into the diatreme geometry, intruded diatreme-filling pyroclastic units and the rare bituminous amygdules in the volcanic rocks. Participants will observe and analyze the relations of these features with the surrounding volcanic surface.

Day 4: Los Adobes-El Escorial-Cerro Gorro Frigio-Los Adobes with lunch in the field. Arrival This day will involve a drive of 350 km. On the way, the late Oligocene basaltic plateau remnants and numerous volcanic pipes can be seen. A brief stop at El Escorial will show the oldest rocks in northern Patagonia, of Early Paleozoic age. Gorro Frigio neck stands 180 m above the surrounding surface. At the contact with the sedimentary host rock, participants will observe peperitic dykes intruding diatreme-filling pyroclastic units. The intrusion of hot magma in water-saturated diatreme-filling pyroclastic sediments will be discussed on the basis of the shape and dimension of dykes, size of pyroclastic sediments and shape, distribution and composition of accidental lithic fragments.

Day 5: Los Adobes-Bajada Moreno-Trelew-Buenos Aires with lunch on the road. The trip is a reconnaissance of the geology of Somuncura basalt plateau.  The Somuncura volcanic sequence will be studied, with stops at relevant points. After the last outcrop, participants will be driven to Trelew airport in early evening.

The excursion ends upon our arrival at Buenos Aires domestic airport (“Aeroparque”) and from there on, participants are on their own. The transfers to the hotel as well as extended stays (booking and payments of hotels, meals, etc.) are at participants' costs.  Any transfer to the international airport of Buenos Aires (“Ezeiza”) should allow at least two hours for the transfer, plus a reasonable amount of time for check-in and arrival at the gate.

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 shall 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.

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