- Van Kranendonk, Martin Prof.
The North Pole Dome in Western Australia is a small feature within the ancient Pilbara Complex, which represents a remarkable raft of virtually unaltered crust from Earth’s Archean Eon. It is a roughly circular ring of hills, approximately 12 kilometers in diameter, surrounding a relatively flat depression that represents a “caldera”—the collapsed center of a 3.5 billion-year-old volcano. Following the collapse, the caldera gradually filled with layers of sediments, some of which contain pristine microbial fossil mounds called “stromatolites,” as well as other features that point to a dynamic shallow water environment.
The North Pole Dome holds Earth’s oldest unambiguous fossils, as well as extensive carbon-bearing rocks and hints regarding Earth’s early geochemical environment. This study will include detailed mapping of North Pole Dome hydrothermal systems and will investigate distributions of organic carbon, the geochemistry of carbonate minerals, and the nature and extent of diagnostic detrital minerals in these ancient rocks.
Geological Context: Life may have arisen in a hydrothermal environment, in an alkaline, low-temperature (<100°C) system. Indeed, the oldest convincing evidence for life occurs in just such a system, within the exceptionally well-preserved volcanic caldera and associated hydrothermal vein system of the ~3.5 Ga North Pole Dome, Pilbara Craton, Western Australia. Previous work documented a variety of early life signatures in this area, but it remains unclear whether early life was exclusively linked to hydrothermal systems, or if it occupied a variety of niches that reflect diverse microbial environments.
This field study will entail detailed mapping of carbon-bearing zones of the North Pole Dome hydrothermal system. We will also leverage ongoing detailed geological mapping and laboratory analysis of the North Pole Dome to explore three topics tied to DCO Decadal Goals related to Deep Life, Reservoirs and Fluxes, and Deep Energy. First, we will characterize the composition and distribution of carbonaceous materials within the North Pole hydrothermal system, to search for co-variation with changes in fluid temperature, system chemistry, and depth. These studies will assist with discriminating between a biogenic vs. abiogenic origin for the stromatolites, microfossils, and carbonaceous materials preserved in hydrothermal veins, in footwall basalts, in bedded sedimentary rocks, and perhaps in sulfide minerals. Second, we will characterize trace elements in carbonate minerals, including stromatolites. We will test hypotheses on redox-sensitive element distributions and will include these geochemical data as part of the DCO-sponsored Mineral Evolution Database project to develop an open access data infrastructure to probe Earth’s changing C cycle through deep time. Third, we will collect and analyze heavy detrital grains. The study of ancient detrital zircon (and to a lesser extent monazite) grains has opened a new window on early Earth. However, other potentially revealing ancient detrital heavy minerals, such as ilmenite, rutile, cassiterite, and uraninite, have not received comparable attention. We propose to acquire and analyze suites of these heavy mineral separates from the most ancient sedimentary terrains of Western Australia. These studies will complement and amplify decades of field and analytical research, representing millions of dollars in grants for investigations of North Pole Dome geology.