The structural, metamorphic and magmatic evolution of Mesoproterozoic orogens

The Mesoproterozoic (1600–1000 Ma) is an Era of Earth history that has been defined in the literature as being quiescent in terms of both tectonics and the evolution of the biosphere and atmosphere (Holland, 2006; Piper, 2013b; Young, 2013). The ‘boring billion’ is an informal term that is given to a time period overlapping the Meso- proterozoic period, extending from 1.85 to 0.85 Ga (Holland, 2006). Orogenesis was not absent from this period however, with vari- ous continents featuring active accretionary orogenesis along their margins for the entire Mesoproterozoic (see Condie, 2013; Roberts, 2013), and others featuring major continental collisional oroge- nesis that relates to the formation of the supercontinent Rodinia towards the end of the Mesoproterozoic. Looking at it another way, this period followed the formation of perhaps the first long-lived supercontinent, Columbia (a.k.a. Nuna), and then it prepared the ground for the momentous geological and biological events in the Neoproterozoic that paved the way for the Cambrian explosion of life. As such it is a very important period of Earth history to under- stand better. Do orogens formed in the Mesoproterozoic differ from those formed in the recent past, or those formed in early Earth history, and if so in what way? Do orogens in the Mesoproterozoic have dis- tinct structural, metamorphic or magmatic characteristics? How are Mesoproterozoic orogens related geodynamically and kine- matically? These are overarching questions that this collection of sixteen research papers aims to address. This introduction presents a brief discussion of the contribution of these papers to these ques- tions and topics.