Suprasubduction zone ophiolites are relics of oceanic upper plate forearcs and are typically preserved as discontinuous belts with discrete massifs along suture zones. Ophiolites usually contain an incomplete condensed section compared to average modern oceanic lithosphere. The incompleteness and discontinuity of ophiolites are frequently attributed to dismemberment, but tectonic causes remain poorly constrained. Here we show new paleomagnetic and field geological evidence for the preservation of extensional detachment faults that thinned and dismembered the south Tibetan ophiolite belt during the Early Cretaceous. Similar to those documented in modern slow-and ultraslow-spreading ridges, these detachments exhumed lithospheric mantle, and subophiolitic mélange, to the seafloor, which became unconformably covered by Asia-derived forearc strata. We call this mechanism forearc hyperextension, whereby widespread detachment faults accommodate upper plate extension above a subduction zone. We propose that hyperextension is the key mechanism responsible for dismemberment of the south Tibetan ophiolitic belt shortly after its magmatic accretion.

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Introduction 4 Background 7 Site summaries 40 Preliminary scientific assessment 45 References

The best precaution is to ensure that the operating temperature is constant during measurements, and preferably cool, and that sensor and samples have time to reach an equilibrium temperature. This may be more difficult when operating in the field. Wet ConditionsCaution: These instruments are protected against the ingress of moisture but operation in very wet conditions should be avoided.Note: Some sensors can be operated while submerged in water: see product brochure for further information. Noise and Interference CheckCaution: These instruments should not be operated close to high power radio transmitters, heavy electrical machinery, computers, or other electrical or magnetic equipment. Note:The unit is unlikely to be affected by interference from other equipment in the normal operating environment. However, by their nature the sensors are susceptible to electromagnetic interference and operation close to a radio frequency source with a frequency close to the operating frequency of the sensor should be avoided. It is important to position the sensor to minimise interference and obtain the best performance.Select the normal sensitivity, x1.0 range. With no sample present, first press the 'Z' button and then select continuous measurements on the 'M' toggle switch. If fluctuations of greater than ±1 least significant digit per reading appear on the display then external electrical noise should be suspected. In this case the only solution is to re-site the equipment.Before using the laboratory sensors, first check the selected area for freedom from large ferrous objects by moving the sensor and watching for any changes on the display.