Reconstructions of the early thermal history of the H-chondrite parent body have focused on two competing hypotheses. The first posits an undisturbed thermal evolution in which the degree of metamorphism increases with depth, yielding an “onion-shell” structure. The second posits an early fragmentation–reassembly event that interrupted this orderly cooling process. Here, we test these hypothese...

The Ross orogen of Antarctica is one of Earth’s great Phanerozoic mountain belts. It is thought from igneous geochemistry, deformation patterns, and sedimentation history to be the result of late Neoproterozoic and early Paleozoic plate-margin convergence between paleo-Pacifi c oceanic lithosphere and continental lithosphere represented by the composite East Antarctic shield. Convergence along ...

Highly cracked and isomerized archaeal lipids and bacterial lipids, structurally changed by thermal stress, are present in solvent extracts of 2,707- to 2,685-million-year-old (Ma) metasedimentary rocks from Timmins, ON, Canada. These lipids appear in conventional gas chromatograms as unresolved complex mixtures and include cyclic and acyclic biphytanes, C36-C39 derivatives of the biphytanes, a...

The identification and confirmation of bona fide Archean-Paleoproterozoic microfossils can prove to be a challenging task, further compounded by diagenetic and metamorphic histories. While structures of likely biological origin are not uncommon in Precambrian rocks, the search for early fossil life has been disproportionately focused on lesser thermally altered rocks, typically greenschist or l...

The microstructure of a dry alpine snowpack is a dynamic environment where microstructural evolution is driven by seasonal density profiles and weather conditions. Notably, temperature gradients on the order of 10–20 K m, or larger, are known to produce a faceted snow microstructure exhibiting little strength. However, while strong temperature gradients are widely accepted as the primary driver...

3 INTRODUCTION 4 Aim and approach 4 Structural domains in the Swedish part of the Baltic Shield defined by deformation zones and formline patterns 4 Age and character of high-T deformation zones in the Baltic Shield 6 GEOLOGY OF EAST CENTRAL SWEDEN 7 Rocks and ages 7 Metamorphism 8 Typical features of low pressure-high temperature metamorphism 9