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The Mesoproterozoic Single-Lid Tectonic

Episode: Prelude to Modern Plate Tectonics

Robert J. Stern, Geosciences Dept., The University of Texas at Dallas, Box 830688, Richardson, Texas 75083-0688, USA

ABSTRACT 1. Active silicate bodies have convecting man- distributed volcanoes are buried and remelted
The hypothesis that the Mesoproterozoic tles. Tectonics is the lithospheric expression a few kilometers below the surface. Venus
(1600–1000 Ma) tectonic regime was a pro- of mantle convection. exhibits vigorous single-lid behavior domi-
tracted single-lid episode is explored. Single- 2. Plate tectonics is lithosphere divided into a nated by mantle plumes and rifts (Ghail,
lid tectonic regimes contrast with plate tec- mosaic of strong plates, which move on and 2015); the upward magma flux is presumably
tonics because the silicate planet or moon is sink into weaker ductile asthenosphere as a matched by drips and delamination. Mars is a
encased in a single lithospheric shell, not a result of subduction. Plates move relative to good example of sluggish single-lid behavior,
global plate mosaic. Single-lid tectonics dom- each other across three types of boundaries: with a few great volcanoes and one great rift.
inate among the Solar System’s active silicate divergent, convergent, and transform (Bird, From studying other active silicate bodies
bodies, and these show a wide range of mag- 2003). The negative buoyancy of old dense of the Solar System we have learned three
matic and tectonic styles, including heat pipe oceanic lithosphere sinking in subduction important things: (1) there are two distinct
(Io), vigorous (Venus), and sluggish (Mars). zones mostly powers plate movements tectonic styles: single lid and plate tectonics;
Both positive and negative evidence is used to (Forsyth and Uyeda, 1975). (2) there are many single-lid tectonic styles;
evaluate the viability of the Mesoproterozoic 3. Single-lid tectonics contrasts with plate tec- and (3) only Earth has plate tectonics. Because
single-lid hypothesis. Four lines of positive tonics by having a single, unfragmented, single-lid tectonics is so common among
evidence are: (1) elevated thermal regime; all-encompassing lithosphere. active silicate bodies, it seems likely that
(2, 3) abundance of unusual dry magmas such 4. There are many types of single-lid behavior Earth experienced single-lid tectonic episodes
as A-type granites and anorthosites; and (4) but only one type of plate tectonics (Fig. 1). in the past.
paucity of new passive continental margins. 5. We are only beginning to explore the range
Negative evidence is the lack of rock and min- of active silicate body single-lid behaviors, THE MESOPROTEROZOIC
eral assemblages formed by plate-tectonic and terminology is confusing. O’Neill and The Mesoproterozoic (1600–1000 Ma) is
processes such as ophiolites, blueschists, and Roberts (2018) refer to stagnant, sluggish, the heart of the “Boring Billion,” a term
ultra high-pressure terranes. Younger plate- plutonic squishy, or heat pipe variants, coined by Holland (2006) for the interval
tectonic–related and Mesoproterozoic miner- whereas Fischer and Gerya (2016) refer to between 1.85 and 0.85 Ga when atmospheric
alization styles contrast greatly. Paleomagnetic plume-lid tectonics. “Sagduction”—the oxygen levels changed little (Fig. 2A). The
evidence is equivocal but is permissive that vertical sinking of weak lithosphere—is term “Boring Billion” is now used to describe
Mesoproterozoic apparent polar wander paths another vigorous non-plate tectonic–style many more aspects about this time period
of continental blocks did not differ signifi- (Nédélec et al., 2017). than Holland (2006) intended. Cawood and
cantly. These tests compel the conclusion that In 2015 we finished taking a first look at all Hawkesworth (2014) called this “Earth’s mid-
the Mesoproterozoic single-lid hypothesis of the large (= semi-spherical) bodies in the dle age” and marshalled evidence that the
is viable. Solar System using a variety of spacecraft Mesoproterozoic was a time of environmen-
(Stern et al., 2018). Four out of five tectoni- tal, evolutionary, and lithospheric stability
INTRODUCTION cally active silicate bodies in the Solar System distinct from the dramatic changes docu-
Earth’s modern plate-tectonic regime show single-lid behavior; that is, they have an mented for other times.
emerged from earlier tectonic regimes (Sleep, all-encompassing lithospheric lid (Stern et al., I have argued elsewhere (Stern, 2005;
2000; Cawood et al., 2018; Stern, 2018; Holder 2018): Venus and Mars and the two Jovian Stern, 2018) that Earth’s modern plate-tec-
et al., 2019). This paper tests the hypothesis inner moons, Io and Europa. We have imaged tonic regime began in Neoproterozoic time.
that the Mesoproterozoic was a protracted the surfaces of Venus, Mars and Io, but not If Earth did not have plate tectonics, it had
single-lid tectonics. Below, I briefly outline Europa because it is encased in an icy shell. some type of single-lid tectonics. Earth has
what single-lid tectonics is before presenting Venus, Mars, and Io show a wide range of always experienced deformation and mag-
positive and negative evidence to test this single-lid tectonic behaviors. Io is subjected to matism, but studying Io, Venus, and Mars
hypothesis and explore some implications. strong tidal forces from Jupiter, which heats shows that this could have been caused by
its interior so that it is very active volcanically single-lid as well as plate tectonics. An
PLATE TECTONICS AND SINGLE-LID and tectonically (McGovern et al., 2016). Io is active silicate body’s tectonic evolution is
TECTONICS characterized by heat pipe volcanism, where likely to be complicated, with multiple
Five concepts are central to this paper: basaltic layers erupted from randomly different episodes. Earth may have ex-

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4 GSA Today | December 2020