EPICA Dronning Maud Land EDML ice core drilling protocol

We report on the EPICA Dronning Maud Land (East Antarctica) deep drilling operation. Starting with the scientific questions that led to the outline of the EPICA project, we introduce the setting of sister drillings at NorthGRIP and EPICA Dome C within the European ice-coring community. The progress of the drilling operation is described within the context of three parallel, deep-drilling operations, the problems that occurred and the solutions we developed. Modified procedures are described, such as the monitoring of penetration rate via cable weight rather than motor torque, and modifications to the system (e.g. closing the openings at the lower end of the outer barrel to reduce the risk of immersing the drill in highly concentrated chip suspension). Parameters of the drilling (e.g. core-break force, cutter pitch, chips balance, liquid level, core production rate and piece number) are discussed. We also review the operational mode, particularly in the context of achieved core length and piece length, which have to be optimized for drilling efficiency and core quality respectively. We conclude with recommendations addressing the design of the chip-collection openings and strictly limiting the cable-load drop with respect to the load at the start of the run

The EPICA Dronning Maud Land deep drilling operation

We report on the EPICA Dronning Maud Land (East Antarctica) deep drilling operation. Starting with the scientific questions that led to the outline of the EPICA project, we introduce the setting of sister drillings at NorthGRIP and EPICA Dome C within the European ice-coring community. The progress of the drilling operation is described within the context of three parallel, deep-drilling operations, the problems that occurred and the solutions we developed. Modified procedures are described, such as the monitoring of penetration rate via cable weight rather than motor torque, and modifications to the system (e.g. closing the openings at the lower end of the outer barrel to reduce the risk of immersing the drill in highly concentrated chip suspension). Parameters of the drilling (e.g. core-break force, cutter pitch, chips balance, liquid level, core production rate and piece number) are discussed. We also review the operational mode, particularly in the context of achieved core length and piece length, which have to be optimized for drilling efficiency and core quality respectively. We conclude with recommendations addressing the design of the chip-collection openings and strictly limiting the cable-load drop with respect to the load at the start of the run

Surface heat flow, crustal temperatures and mantle heat flow in the Proterozoic Trans-Hudson Orogen, Canadian Shield

International audienceThe Paleo-Proterozoic (1.8 Ga) Trans-Hudson Orogen (THO), of intermediate age between the Superior (2.7 Ga) and Grenville (1.0 Ga) provinces, is located near the center of the Canadian Shield. We report on new measurements of heat flow and radiogenic heat production in 30 boreholes at 17 locations in this province. With these data, reliable values of heat flow and heat production are available at 45 sites in the THO. The mean and standard deviation of heat flow values are 42 ± 9 mW m-2. In this province, distinctive geological domains are associated with specific heat flow distributions. The heat flow pattern follows the surface geology with a central area of low values over an ancient back arc basin (Kisseynew) and an ancient island arc (Lynn Lake Belt) made of depleted juvenile rocks. Higher heat flow values found in peripheral belts are associated with recycled Archean crust. Within the Canadian Shield, there is no significant variation in heat flow as a function of age between provinces spanning about 2 Gyr. There is no geographic trend in heat flow across the Canadian Shield from the THO to the Labrador Sea. Low heat flow areas where the crustal structure is well-known are used to determine an upper bound of 16 mW m-2 for the mantle heat flow. Present and paleogeotherms are calculated for a high heat flow area in the Thompson metasedimentary belt. The condition that melting temperatures were not reached in Proterozoic times yields a lower bound of 11-12 mW m-2 for the mantle heat flow