We review Phanerozoic sea-level changes [543 million years ago (Ma) to the present] on various time scales and present a new sea-level record for the past 100 million years (My). Long-term sea level peaked at 100 ± 50 meters during the Cretaceous, implying that ocean-crust production rates were much lower than previously inferred. Sea level mirrors oxygen isotope variations, reflecting ice-volume change on the 10 4 - to 10 6 -year scale, but a link between oxygen isotope and sea level on the 10 7 -year scale must be due to temperature changes that we attribute to tectonically controlled carbon dioxide variations. Sea-level change has influenced phytoplankton evolution, ocean chemistry, and the loci of carbonate, organic carbon, and siliciclastic sediment burial. Over the past 100 My, sea-level changes reflect global climate evolution from a time of ephemeral Antarctic ice sheets (100 to 33 Ma), through a time of large ice sheets primarily in Antarctica (33 to 2.5 Ma), to a world with large Antarctic and large, variable Northern Hemisphere ice sheets (2.5 Ma to the present).

/pdf/the-phanerozoic-record-of-global-sea-level-change-14696qrujw.pdf

The Phanerozoic Record of Global Sea-Level Change

The Mars Orbiter Laser Altimeter (MOLA), an instrument on the Mars Global Surveyor spacecraft, has measured the topography, surface roughness, and 1.064-μm reflectivity of Mars and the heights of volatile and dust clouds. This paper discusses the function of the MOLA instrument and the acquisition, processing, and correction of observations to produce global data sets. The altimeter measurements have been converted to both gridded and spherical harmonic models for the topography and shape of Mars that have vertical and radial accuracies of ~1 m with respect to the planet's center of mass. The current global topographic grid has a resolution of 1/64° in latitude × 1/32° in longitude (1 × 2 km^2 at the equator). Reconstruction of the locations of incident laser pulses on the Martian surface appears to be at the 100-m spatial accuracy level and results in 2 orders of magnitude improvement in the global geodetic grid of Mars. Global maps of optical pulse width indicative of 100-m-scale surface roughness and 1.064-μm reflectivity with an accuracy of 5% have also been obtained.

/pdf/mars-orbiter-laser-altimeter-experiment-summary-after-the-3w1byzpn90.pdf

Mars Orbiter Laser Altimeter: Experiment summary after the first year of global mapping of Mars

The geological evolution of the Tibetan plateau is best viewed in a context broader than the India-Eurasia collision zone. After collision about 50 million years ago, crust was shortened in western and central Tibet, while large fragments of lithosphere moved from the collision zone toward areas of trench rollback in the western Pacific and Indonesia. Cessation of rapid Pacific trench migration (∼15 to 20 million years ago) coincided with a slowing of fragment extrusion beyond the plateau and probably contributed to the onset of rapid surface uplift and crustal thickening in eastern Tibet. The latter appear to result from rapid eastward flow of the deep crust, probably within crustal channels imaged seismically beneath eastern Tibet. These events mark a transition to the modern structural system that currently accommodates deformation within Tibet.

http://science.sciencemag.org/content/sci/321/5892/1054.full.pdf

The Geological Evolution of the Tibetan Plateau

[1] We present here a new InSAR persistent scatterer (PS) method for analyzing episodic crustal deformation in non-urban environments, with application to volcanic settings. Our method for identifying PS pixels in a series of interferograms is based primarily on phase characteristics and finds low-amplitude pixels with phase stability that are not identified by the existing amplitude-based algorithm. Our method also uses the spatial correlation of the phases rather than a well-defined phase history so that we can observe temporally-variable processes, e.g., volcanic deformation. The algorithm involves removing the residual topographic component of flattened interferogram phase for each PS, then unwrapping the PS phases both spatially and temporally. Our method finds scatterers with stable phase characteristics independent of amplitudes associated with man-made objects, and is applicable to areas where conventional InSAR fails due to complete decorrelation of the majority of scatterers, yet a few stable scatterers are present.

/pdf/a-new-method-for-measuring-deformation-on-volcanoes-and-3x99a7e12s.pdf

A new method for measuring deformation on volcanoes and other natural terrains using InSAR persistent scatterers

Granitic plutonism is the principal agent of crustal differentiation, but linking granite emplacement to crust formation requires knowledge of the magmatic evolution, which is notoriously difficult to reconstruct from bulk rock compositions. We unlocked the plutonic archive through hafnium (Hf) and oxygen (O) isotope analysis of zoned zircon crystals from the classic hornblende-bearing (I-type) granites of eastern Australia. This granite type forms by the reworking of sedimentary materials by mantle-like magmas instead of by remelting ancient metamorphosed igneous rocks as widely believed. I-type magmatism thus drives the coupled growth and differentiation of continental crust.

https://science.sciencemag.org/content/sci/315/5814/980.full.pdf

Magmatic and Crustal Differentiation History of Granitic Rocks from Hf-O Isotopes in Zircon

High-resolutlon radar images from the M_ellan spacocral't have revealed the Fwst deta;isthe morphology of the Lavinia Planhia region of Venus. A number of gbologic units can bedistinguished, including volcanic plains units with • range of ages. Transecting these phdr_ overp_s,umu wnn_e nages ana exzenslonal grooves. The dormnant tectonic features of Laviniaare broad elevated belts of intense deformation that transect the plains with complex geometry.They are many tens to • few hundred kilometers wide, as much as 1000 km long, and elevatedhundreds of mctecs above the am'rounding plains. Two classes of deformation belts axe seen inthe Lavin[a region. "Ridge belts" are composed of parallel ridges, each • few hundred metersin elevation, that we interpret to he folds. Typical fold spacings are 5-10 kin. "l_racture belts"are dominated instead by intense faulting, with faults in some instances paired to form narrowgrabens. There is also some evidence for modest amounts of horizontal shear distributed a_ssboth ridge and fracture belts. Crosscutting relationships among the belts show there to be •range in belt ages. In western I_vL, ds in particular, many ridge and fracture belts appear to bear• relationship to the much smaller wrinkle ridges and _oves ma the surrounding plains: Ridgemorphology tends to d0_dnate belts that lie more nearly Wage] to local plains wrinkle ridges,and fracture morphology tends to dominate belts th_ l;e more Dmu-]y parallel to local plainsgrooves. We use simple models to explore the formation of ridge and fracttwe belts. We showthat convective motions in the mantle can couple to the crust to cause horizontal stresses of •magnitude sul_cient to induce the formation of deformation belts llke those observed in Lavinia.We _ use the sin•U-scale wavelengths of deformation observed within individual ridge belts toplace an approximate lowe_ limit on the ve_nsian thermal _t in the LsvinLs region at thetime o_"deformstion.

DcPartmest of EsrtA, Atmo#pherlc, ,lid PI, set,rl .qciesce#, M_,escAueffa I_,Nf_te of TecA_ololl , CsmbriqIIe

The thickness of the outer ice shell plays an important role in several geodynamical processes at ocean worlds. Here, we show that observations of tidally driven diurnal surface displacements can constrain the mean ice shell thickness, d∼ice ${\tilde{d}}_{\mathit{ice}}$ . Such estimates are sensitive to any significant structural features that break spherical symmetry such as faults and lateral variation in ice shell thickness and structure. We develop a finite‐element model of Enceladus to calculate diurnal tidal displacements for a range of d∼ice ${\tilde{d}}_{\mathit{ice}}$ values in the presence of such structural heterogeneities. Consistent with results from prior studies, we find that the presence of variations in ice shell thickness can significantly amplify deformation in thinned regions. If major faults are also activated by tidal forcing—such as Tiger Stripes on Enceladus—their characteristic surface displacement patterns could easily be measured using modern geodetic methods. Within the family of Enceladus models explored, estimates of d∼ice ${\tilde{d}}_{\mathit{ice}}$ that assume spherical symmetry a priori can deviate from the true value by as much as ∼41% when structural heterogeneities are present. Additionally, we show that crustal heterogeneities near the South Pole produce differences of up to 35% between Love numbers evaluated at different spherical harmonic orders. A ∼41% range in estimates of d∼ice ${\tilde{d}}_{\mathit{ice}}$ from Love numbers is smaller than that found with approaches relying on static gravity and topography (∼250%) or analyzing diurnal libration amplitudes (∼85%) to infer d∼ice ${\tilde{d}}_{\mathit{ice}}$ at Enceladus. As such, we find that analysis of diurnal tidal deformation is a relatively robust approach to inferring mean crustal thickness.

Inferring the Mean Thickness of the Outer Ice Shell of Enceladus From Diurnal Crustal Deformation

A secondary zone of surface uplift (SZU), located from 200 to 400 km landward of the trench, has been measured after several megathrust earthquakes. The SZU reached a few centimeters hours to days after the 2011 Mw 9.1 Tohoku (Japan) and 2010 Mw 8.8 Maule (Chile) earthquakes. Published coseismic finite‐fault models for these events do not reproduce the measured SZU. One interpretation is that this SZU is universal, driven by volume deformation around the slab interface (van Dinther et al., 2019, https://doi.org/10.1007/s00024-019-02250-z). In contrast, we demonstrate the SZU may instead result from slip on the slab interface, and suggest it might be caused by rapid afterslip. We can reproduce the SZU with fault slip if elastic heterogeneities associated with the subducting slab are accounted for, as opposed to assuming homogeneous or layered elastic lithospheric structures.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1029/2022GL101510

A Secondary Zone of Uplift Measured After Megathrust Earthquakes: Caused by Early Downdip Afterslip?

We study the distribution of slip on faults during earthquakes with integrated analysis of geodetic imaging and seismic data to learn about parameters that control how faults slip and potentially how damaging future earthquakes may be. We mapped complex fault ruptures for a number of large earthquakes in 2015–2020 using analysis of synthetic aperture radar (SAR) data from the Copernicus Sentinel-1A and Sentinel-1B satellites operated by the European Space Agency and the Advanced Land Observation Satellite-2 (ALOS-2) satellite operated by the Japan Aerospace Exploration Agency (JAXA). We used regular SAR interferometry, along-track or multiple-aperture interferometry, and pixel offset tracking to measure surface displacements and combined this with other geodetic and seismic data to infer slip on faults at depth.

Imaging Complex Fault Slip of Large Earthquakes with Sentinel-1 and ALOS-2 SAR Analysis and Other Geodetic and Seismic Data*

Antarctic ice shelves play a key role in regulating the rate of ice flow in tributary ice streams. Temporal variations in the associated ice‐shelf buttressing stress are observed to impact ice flow in glaciers and ice streams. Ephemeral grounding induced by tides is an important mechanism for modulating the buttressing stress. Here, we develop an approach to inferring variations in 3‐D surface displacements at an ice‐shelf‐stream system that explicitly accounts for ephemeral grounding. Using a temporally dense nine‐month‐long synthetic‐aperture radar image acquisition campaign collected over Rutford Ice Stream, West Antarctica, by the 4‐satellite COSMO‐SkyMed constellation, we infer the ephemeral grounding zones and the spatiotemporal variation of the fortnightly ice‐flow variability. We find ephemeral grounding zones along the western ice‐shelf margin as well as a few prominent ephemeral grounding points in the central trunk and in the vicinity of the grounding zone. Our observations provide evidence for tide‐modulated buttressing stress and the temporally asymmetric response of ice‐shelf flow to tidal forcing. Long‐term oceanic warming and ice‐shelf thinning will cause the loss of ephemeral grounding and decrease in ice‐shelf buttressing stress.

Mark Simons

Papers

DcPartmest of EsrtA, Atmo#pherlc, ,lid PI, set,rl .qciesce#, M_,escAueffa I_,Nf_te of TecA_ololl , CsmbriqIIe

Inferring the Mean Thickness of the Outer Ice Shell of Enceladus From Diurnal Crustal Deformation

A Secondary Zone of Uplift Measured After Megathrust Earthquakes: Caused by Early Downdip Afterslip?

Imaging Complex Fault Slip of Large Earthquakes with Sentinel-1 and ALOS-2 SAR Analysis and Other Geodetic and Seismic Data*

Inferring Tide‐Induced Ephemeral Grounding in an Ice‐Shelf‐Stream System: Rutford Ice Stream, West Antarctica