August GEOLOGY and GSA TODAY Media Highlights

Queen Maud block: A newly recognized Paleoproterozoic (2.4–2.5 Ga) terrane in northwest Laurentia
Michael E.J. Schultz et al., University of Alberta, Department of Earth and Atmospheric Sciences, 1-26 Earth Sciences Building, Edmonton, Alberta T6G 2E3, Canada. Pages 707-710.

Schultz et al. describe a large, remote, and understudied bedrock terrane in Arctic Canada. The sedimentary basins found within the terrane, and the age and timing of high-temperature metamorphism of the rocks found there, challenge previous models and offer new insight into how the different continental fragments of North America assembled billions of years ago. Specifically, Shultz et al. contend that the development of this area likely occurred 500 million years earlier than previously thought and involved the incipient break-up and reassembly of an ancient continent.

Kinematics and geometry of active detachment faulting beneath the Trans-Atlantic Geotraverse (TAG) hydrothermal field on the Mid-Atlantic Ridge
Brian J. deMartin et al., Brown University, Geological Sciences, 324 Brook Street, Box 1846, Providence, RI 02912, USA. Pages 711-714.

The Trans-Atlantic Geotraverse (TAG) hydrothermal field on the Mid-Atlantic Ridge is one of the largest, longest-lived regions of focused, high-temperature fluid flow on the seafloor. Encompassing an area of roughly six square miles, the hydrothermal field includes relict mounds containing vast stores of precious metals and sulfide ores, and at least one active mound that vents fluids in excess of 360 ºC (680 ºF) and hosts a flourishing deep-sea ecosystem. The TAG hydrothermal field lies above an active oceanic detachment fault, a long-lived zone of weakness in Earth’s crust where extension has been focused for the past 175,000–350,000 years. Although numerous inactive detachment faults have been identified on the seafloor, the subsurface morphology of an active detachment fault and the relationship between detachment faulting and fluid flow has remained speculative. deMartin et al. report results from an eight-month ocean bottom seismometer experiment that provide important new perspectives on the nature of fluid circulation at the TAG hydrothermal field and show a detailed image of the subsurface structure of an active oceanic detachment fault for the first time. Their results also indicate that entrained seawater extracts the energy necessary for hydrothermal circulation near the crust/mantle interface at least 7 kilometers (4.3 miles) below the seafloor. This finding dramatically effects the geologic understanding of hydrothermal flow, because it has been widely supposed that hydrothermal convection within the seafloor is driven by much shallower, crustal heat sources. These results suggest high-temperature hydrothermal circulation may be a natural consequence of the detachment faulting process, and may indicate that significant numbers of hydrothermal fields await discovery along the slowly diverging plate boundaries in the Atlantic, Indian, and Arctic oceans.