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Evidence for Present Day Volcanism on Venus: A Case Study of Idunn Mons

Idunn Mons in Imdr Regio on Venus is perhaps one of the best studied volcanoes on Venus in part due to having both radar and night-time emissivity data of the region [1-3]. Smrekar et al. [1] first presented night-time emissivity data of Idunn Mons from the VIRTIS instrument on Venus Express, which showed that some lava flows have high emissivity consistent with unweathered basalt. Smrekar et al. [1], based on known weathering rates at that time, suggested that the lava flows were less than 2.5 million years old and possible as young as 250,000 years old. However, recent experimental work has shown that basaltic rocks and associated minerals in contact with the Venusian caustic atmosphere would react quickly to produce rinds of alteration materials coating the surface and obscure emissivity signatures of igneous minerals within a few to ~10,000 years [4-9]. These new experimentally derived weathering and oxidation rates were used to suggest that lava flows at Idunn Mons with unweathered signatures are quite young and Idunn Mons may be volcanically active today [4, 8]. Independent geologic mapping and related stratigraphic reconstruction over the study area is consistent with the experimental results [2, 10]. Considering all the available evidence, we have taken a comprehensive approach combining these recent experimental results with previous orbital night-time emissivity, as well as atmospheric measurements, to constrain the evolution of Idunn Mons [3,10]. Our results suggest that Idunn Mons is both volcanically and tectonically active today, and that volcanism and tectonic activity are likely related [11]. Venus being volcanically active has been suggested at other volcanic centers, as well [e.g. 12-17]. Therefore, we use Idunn Mons specifically as a case study of a potentially active volcano that may be detectable by the upcoming fleet of missions that will be arriving at Venus in the next decade.

Justin Filiberto↗

NASA NTRS1990

Oxygen and hydrogen isotope geochemistry of zeolites

Oxygen and hydrogen isotope ratios for natural samples of the zeolites analcime, chabazite, clinoptilolite, laumontite, mordenite, and natrolite have been obtained. The zeolite samples were classified into sedimentary, hydrothermal, and igneous groups. The ratios for each species of zeolite are reported. The results are used to discuss the origin of channel water, the role of zeolites in water-rock interaction, and the possibility that a calibrated zeolite could be used as a low-temperature geothermometer.

Karlsson, Haraldur R.↗

NASA NTRS1992

Ureilites - A critical review

The paper discusses the current state of understanding of the petrogenesis of ureilites (which are ultramafic rocks considered to be products of a common planetary differentiation process), identifies areas in which basic knowledge is lacking, and suggests directions for future work on these rocks. The petrographic, chemical, and isotopic characteristics of ureilites are summarized, and petrogenetic implications of these characteristics are discussed. Particular attention is given to the apparent contradiction between the igneous and primitive features of ureilites. Several recently proposed models for ureilite petrogenesis are evaluated in terms of how well they satisfy these constraints and how they attempt to resolve the conflict between the igneous and primitive features. It is concluded that none of the proposed models satisfy all constraints satisfactorily.

Goodrich, Cyrena A.↗

NASA NTRS1993

A geochemical study of acapulcoite and lodranite meteorites

Lodranites and acapulcoites (primitive achondrites) are two classes of meteorites with geochemical signatures similar to chondrite meteorites. Lodranites and acapulcoites, however, have few or none of the chondrules characteristic of the chondrites. Texturally the primitive achondrites appear to have been recystallized though planetary igneous or metamorphic processes. A study of five primitive achondrites, two lodranites, two acapulcoites, and one supposedly intermediate acapulcoite/lodranite, were analyzed petrographically and geochemically to determine the igneous and metamorphic processes which have affected them. Acapulcoites show little evidence of melt extraction. The geochemistry of lodranite samples indicates silicate and metal/sulfide melts were removed from the rocks. The mineralogy and geochemistry of the intermediate meteorite suggest the rock is a metal rich acapulcoite and not a lodranite.

Field, Stephen W.↗

NASA NTRS2024

What Are the Olivine-Rich Boulders in the Upper Fan and Margin Unit at Jezero Crater, Mars?

Since February 2021, the Perseverance rover has explored Jezero Crater in the Nili Fossae region of Mars which hosts large outcrops of a regional olivine-carbonate unit. In the crater floor, Perseverance investigated two igneous formations: Máaz, composed of basaltic lava and/or pyroclastic flows, and Séítah, an olivine-rich cumulate] below Máaz. Then, Perseverance explored the western fan composed by diverse sedimentary rocks of variable composition, but often containing olivine On the upper fan and margin unit, Perseverance encountered number of centimetric to metric boulder rocks. Two main types of boulders were identified based on texture and composition: the olivine-rich and pyroxene-bearing boulders. Here, we use SuperCam data to describe the texture, geochemistry and mineralogy of the olivine-rich boulders. Then, we discuss their possible petrological origin and some possible implications for the regional Nili Fossae olivine-carbonate unit.

Mars 2020↗

NASA NTRS2011

The Regolith of 4 Vesta: Perspectives from Howardite Meteorites and Dawn Mission Observations

4 Vesta is the largest asteroid with a basaltic surface, the only surviving differentiated asteroid recording igneous processes from the earliest phase of solar system history. The Dawn spacecraft is in orbit about Vesta pursuing a campaign of high resolution imaging and visible and infrared spectrometry of the surface; compositional mapping by gamma-ray and neutron spectrometry will follow. Vesta is heavily cratered with a surface covered by impact debris, a regolith. One important goal of the Dawn mission is to develop an understanding of regolith processes that are affecting this surface debris. Regolith characteristics are a record of interaction with the environment (e.g., impactors, dust, solar wind, galactic cosmic-rays) and give evidence of surface processes (down-gravity movement, etc.). Regolith mineralogy and composition reflect the local bedrock, with influences from regional and global mixing. Understanding regolith processes will aid in determining the lithology of underlying crust. Vesta is most likely the parent asteroid of the howardite, eucrite and diogenite meteorites. Eucrites are intrusive and extrusive mafic rocks composed mostly of ferroan low-Ca clinopyroxene and calcic plagioclase, while diogenites are cumulate magnesian orthopyroxenites. Magmatism occurred within a few million years of the formation of the solar system and then ceased. Impacts into the igneous crust produced the howardites - polymict breccias composed of mineral and lithic debris derived mostly from eucrites and diogenites. Some howardites are true regolith breccias formed by lithification of extensively impact-gardened surface debris. However, howardites have a number of significant petrologic and compositional differences from mature lunar regolith breccias and soils reflecting the different environment around Vesta compared to that at 1 AU. The most significant differences are the higher impactor flux with a lower mean impact velocity and the lower gravity. As a result, regolith processes on Vesta differ in detail from those on the Moon. Laboratory study of howardites and orbital investigation of Vesta will allow for development of robust models of regolith formation on hand sample to multi-kilometer scales.

Mittlefehldt, David W.↗

NASA NTRS1993

Lunar ferroan anorthosites - Mineralogy, compositional variations, and petrogenesis

Results of a study of 16 samples from the anorthositic ferroan subgroup, or 'typical' ferroan anorthosites, are reported. The presence of heterogeneous, bimodal, and/or trimodal pyroxene compositions suggests that some of the anorthosites are polymict rocks; however, they are composed entirely of ferroan-anorthosite-suite lithologies. It is suggested that complex processes operated during the formation of the ferroan anorthosites. It is argued that original igneous compositional characteristics were altered during and/or after crystallization. Processes operative during anorthosite formation may have included some mixing of different melts, trapping of variable amounts of intercumulus liquid, postcrystallization redistribution of elements, or perturbations both during adcumulus growth and subsequent to crystallization by impact events.

Mcgee, J. J.↗

NASA NTRS2016

Compositions of Normal and Anomalous Eucrite-Type Mafic Achondrites

The most common asteroidal igneous meteorites are eucrite-type mafic achondrites - basalts and gabbros composed of ferroan pigeonite, ferroan augite, calcic plagioclase, silica, ilmenite, troilite, Ca-phosphate, chromite and Fe-metal. These rocks are thought to have formed on a single asteroid along with howardites and diogenites. However, high precision O-isotopic analyses have shown that some mafic achondrites have small, well-resolved, non-mass-dependent differences that have been interpreted as indicating derivation from different asteroids. Some of these O-anomalous mafic achondrites also have anomalous petrologic characteristics, strengthening the case that they hail from distinct parent asteroids. We present the results of bulk compositional studies of a suite of normal and anomalous eucrite-type basalts and cumulate gabbros.

Mittlefehldt, D. W.↗

DOE OSTI2023

Metasomatic alteration of coarse‐grained igneous calcium‐aluminum‐rich inclusions from CK3 carbonaceous chondrites

Abstract We report on the primary and secondary mineralogies of three coarse‐grained igneous calcium‐aluminum‐rich inclusions (CAIs) (Compact Type A [CTA], Type B [B], and forsterite‐bearing type B [FoB]) from the Northwest Africa (NWA) 5343 (CK3.7) and NWA 4964 (CK3.8) carbonaceous chondrites, compare them with the mineralogy of igneous CAIs from the Allende (CV3.6) chondrite, and discuss the nature of the alteration processes that affected the CK and CV CAIs. The primary mineralogy and mineral chemistry of the CK3 CAIs studied are similar to those from Allende; however, primary melilite and anorthite are nearly completely absent. Although the secondary minerals identified in CK CAIs (Al‐diopside, andradite, Cl‐apatite, clintonite, forsterite, ferroan olivine, Fe,Ni‐sulfides, grossular, ilmenite, magnetite, plagioclase, spinel, titanite, and wadalite) occur also in the Allende CAIs, there are several important differences: (i) In addition to melilite and anorthite, which are nearly completely replaced by secondary minerals, the alteration of CK CAIs also affected high‐Ti pyroxenes (fassaite and grossmanite) characterized by high Ti 3+ /Ti 4+ ratio and spinel. These pyroxenes are corroded and crosscut by veins of Fe‐ and Ti‐bearing grossular, Fe‐bearing Al,Ti‐diopside, titanite, and ilmenite. Spinel is corroded by Fe‐bearing Al‐diopside and grossular. (ii) The secondary mineral assemblages of grossular + monticellite and grossular + wollastonite, commonly observed in the Allende CAIs, are absent; the Fe‐bearing grossular + Fe‐bearing Al‐diopside ± Fe,Mg‐spinel, Fe‐bearing grossular + Fe,Mg‐olivine ± Fe,Mg‐spinel, and Ca,Na‐plagioclase + Fe‐bearing Al‐diopside + Fe‐bearing grossular assemblages are present instead. These mineral assemblages are often crosscut by veins of Fe‐bearing Al‐diopside, Fe,Mg‐olivine, Fe,Mg‐spinel, and Ca,Na‐plagioclase. The coarse‐grained secondary grossular and Al‐diopside often show multilayered chemical zoning with distinct compositional boundaries between the layers; the abundances of Fe and Ti typically increase toward the grain edges. (iv) Sodium‐rich secondary minerals, nepheline and sodalite, commonly observed in the peripheral portions of the Allende CAIs, are absent; Ca,Na‐plagioclase is present instead. We conclude that coarse‐grained igneous CAIs from CK3.7–3.8 s and Allende experienced an open‐system multistage metasomatic alteration in the presence of an aqueous solution–infiltration metasomatism. This process resulted in localized mobilization of all major rock‐forming elements: Si, Ca, Al, Ti, Mg, Fe, Mn, Na, K, and Cl. The metasomatic alteration of CK CAIs is more advanced and occurred under higher temperature and higher oxygen fugacity than that of the Allende CAIs.

Geochemistry & Geophysics↗

NASA NTRS1993

Crustal structure and igneous processes in a chondritic Io

Liquid sulfur can form when metal-free C1 or C2 chondrites are heated. It may be obtained either by direct melting of native sulfur in disequilibrated C1 or C2 chondrites or by incongruent melting of pyrite and other sulfides in thermodynamically equilibrated rocks of the same composition. Hence, Lewis considered C2 chondrites to be the best meteoritic analog for Io's bulk composition. Metal-bearing C3 and ordinary chondrites are too chemically reduced to yield liquid sulfur and are not thought to represent plausible analogs of Io's bulk composition. An important aspect of Lewis' work is that CaSO4 and MgSO4 are predicted to be important in Io. Real C1 and C2 chondrites contain averages of, respectively, 11 percent and 3 percent by mass of salts (plus water of hydration). The most abundant chondritic salts are magnesium and calcium sulfates, but other important components include sulfates of sodium, potassium, and nickel and carbonates of magnesium, calcium, and iron. It is widely accepted that chondritic salts are formed by low-temperature aqueous alteration. Even if Io originally did not contain salts, it is likely that aqueous alteration would have yielded several percent sulfates and carbonates. In any event, Io probably contains sulfates and carbonates. This report presents the results of a model of differentiation of a simplified C2 chondrite-like composition that includes 1.92 percent MgSO4, 0.56 percent CaSO4, 0.53 percent CaCO3, and 0.094 percent elemental sulfur. The temperature of the model is gradually increased; ensuing fractional melting results in these components extruding or intruding at gravitationally stable levels in Io's crust. Relevant phase equilibria were reviewed. A deficiency of high-pressure phase equilibria renders the present model qualitative.

Kargel, J. S.↗

NASA NTRS1972

Remanent magnetization of the lunar surface.

Two lines of evidence support each other in suggesting that a large volume of the rocks near the lunar surface possess a uniform remanent magnetization with an intensity of about .000002 emu/g. The first line is the discovery by several groups of investigators of weak but stable remanent magnetizations in igneous samples returned from the first four Apollo missions. Although the mechanism of acquisition of this remanence has not been definitely established, several lines of evidence, including thermal demagnetization, suggest that it is a thermoremanent magnetization (TRM) carried by iron. Many of the breccias are similarly magnetized. The second line is the measurement of significant fields at the Apollo sites and the discovery of large-scale anomalies by the sub-satellite magnetometer experiment.

Pearce, G. W.↗

NASA NTRS1981

Lu-Hf total-rock age for the Amitsoq gneisses, West Greenland

Lu-Hf total-rock data for the Amitsoq gneisses of West Greenland yield an age of 3.55 + or - 0.22 billion years, based on the decay constant for Lu-176 of 1.96 x 10 to the -11th/year, and an initial Hf-176/Hf-177 ratio of 0.280482 + or - 33. The result is in good agreement with Rb-Sr total-rock and U-Pb zircon ages. In spite of severe metamorphism of the area at 2.9 billion years, zircons from two of the samples have remained on the total-rock line, and define points close to the initial Hf ratio. The initial Hf-176/Hf-177 lies close to a chondritic Hf isotopic evolution curve from 4.55 billion years to present. This is consistent with the igneous precursors to the Amitsoq gneisses having been derived from the mantle at or shortly before 3.6 billion years. Anomalous relationships between Hf concentration and the Lu-176/Hf-177 ratio may suggest that trace element abundances in the Amitsoq gneisses are partly controlled by processes related to metamorphism.

Pettingill, H. S.↗

NASA NTRS1980

Mantle convection pattern and subcrustal stress field under South America

The tectonic, igneous and metallogenic features of South America are discussed in terms of the crustal deformation associated with stresses due to mantle convection as inferred from the high degree harmonics in the geopotential field. The application of Runcorn's model for the laminar viscous flows in the upper mantle to satellite and gravity data results in a convection pattern which reveals the ascending flows between the descending Nazca plate and the overlying South American plate as well as segments of the descending Nazca plate beneath South America. The arc volcanism in South America is shown apparently to be related to the upwelling of high-temperature material induced by the subduction of the Nazca plate, with the South American basin systems associated with downwelling mantle flows. The resulting tensional stress fields are shown to be regions of structural kinship characterized by major concentrations of ore deposits and related to the cordillera, shield and igneous systems and the upward Andean movements. It is suggested that the upwelling convection flows in the upper mantle, coupled with crustal tension, have provided an uplift mechanism which has forced the hydrothermal systems in the basement rocks to the surface.

Liu, H.-S.↗

NASA NTRS1988

Crystal fractionation in the SNC meteorites: Implications for sample selection

Almost all rock types in the SNC meteorites are cumulates, products of magma differentiation by crystal fractionation (addition or removal of crystals). If the SNC meteorites are from the surface of Mars or near subsurface, then most of the igneous units on Mars are differentiated. Basaltic units probably experienced minor to moderate differientation, but ultrabasic units probably experienced extreme differentiation. Products of this differentiation may include Fe-rich gabbro, pyroxenite, periodotite (and thus serpentine), and possibly massive sulfides. The SNC meteorites include ten lithologies (three in EETA79001), eight of which are crystal cumulates. The other lithologies, EETA79001 A and B are subophitic basalts.

Treiman, Allan H.↗

DOE OSTI2023

Chronology of alkali anorthosite 14304 clast “b” records basin forming impact at ~3.95 Ga

Alkali-suite rocks constitute one of three major suites of lunar crustal rocks. As such, constraining their formation timescales and petrogenesis is important for understanding the earliest magmatic history of the Moon. However, the magmatic history of alkali-suite rocks is partly obscured by superimposed effects of major basin-forming impact events on the lunar nearside. Consequently, unambiguous crystallization ages of samples from this suite of rocks have not been determined. Here, the aim of this study is to better understand the petrogenetic history of the alkali-suite and the potential superimposed effects of impact metamorphism by determining Sm-Nd, Rb-Sr, and 40 Ar/ 39 Ar ages for an alkali anorthosite clast from Apollo 14 lithic breccia 14304 termed clast “b”. The new chronologic measurements of clast “b” yield concordant Sm-Nd, Rb-Sr, and 40 Ar/ 39 Ar ages of 3947 ± 13 Ma, 3975 ± 34 Ma, and 3937 ± 37 Ma respectively, resulting in a weighted mean age of 3949 ± 11 Ma. This age is not interpreted to date an igneous event related to production of the lunar highlands crust and instead the chronology and petrography of clast “b” are most readily explained by an impact event at ~3.95 Ga that caused near-complete isotopic re-equilibration of the Sm-Nd, Rb-Sr, and 40 Ar/ 39 Ar chronometers. The weighted mean age of 3949 ± 11 Ma of clast “b” is several hundred Ma younger than 4.3–4.4 Ga ages typically determined for samples of other crustal rock suites but in very good agreement with independent estimates for the formation of Imbrium basin ejecta and other marginally older impact events which are thought to have been sampled at the Apollo 14 landing site. Thus, although petrologic and geochemical examination suggest that clast “b” is a pristine igneous clast, its age likely records an impact event at the Apollo 14 landing site. Whereas the various determined ages of clast “b” do not reflect the timescales of alkali-suite magmatism, the relatively low initial Sr and Nd isotopic compositions of clast “b” indicate that its protolith evolved with very low 147 Sm/ 144 Nd and 87 Rb/ 86 Sr that are distinct from estimates for urKREEP but similar to that of lunar plagioclase. This implies that the igneous protolith of clast “b” derived from a plagioclase-dominated KREEP-rich source that must have formed after the formation of the urKREEP source at ~4.35 Ga but well before the impact event recorded by clast “b” at ~3.95 Ga.

58 GEOSCIENCES↗

NASA NTRS1992

A comparison of the chemistry of pseudotachylyte breccias in the Archean Levack Gneisses of the Sudbury structure, Ontario

The Archean Levack Gneisses of the North Range host millimeter-thick veins and centimeter-thick lenses of pseudotachylyte, as well as substantially larger meter-wide, dykelike bodies of pseudotachylytic 'breccia'. The 'breccia' occurs up to several tens of kilometers away from the Sudbury Igneous Complex and is commonly sited within or near joints and other natural weaknesses such as bedding, dyke contacts, and lithological boundaries. The larger 'breccia' dykes comprise a generally dark matrix containing rounded to subrounded and occasionally angular rock fragments derived predominantly from Levack Gneiss. Selected samples of bulk Sudbury Breccia and Sudbury Breccia matrices were chemically analyzed and compared to existing data on the Levack Gneisses and Sudbury Breccia. The matrices are apparently enriched in Fe and, to a lesser extent, Mg, Ti, and Ca compared to the wallrocks and the majority of clasts. This enrichment can be partly explained by the preferential cataclasis and/or frictional melting of hydrous ferromagnesian wallrock minerals, but also appear to require contamination by more basic exotic lithologies. This suggests that certain components of pseudotachylitic Sudbury Breccia have undergone significant transport during their formation.

Thompson, Lucy M.↗

NASA NTRS1992

Impact melt breccias at the Apollo 17 landing site

Impact melt breccias are by far the most common highland rock type collected on the Apollo 17 mission. They tend to be fine grained, with virtually no clast-free impact melt rocks having been identified. All the highland boulders sampled are impact melt breccia, with the possible exception of one South Massif boulder that might have a friable matrix (but nonetheless consists dominantly of impact melt) and a shocked igneous norite boulder from the North Massif. The impact melt breccias were originally described as metaclastic, but their melt origin became apparent as work progressed. Chemical compositions appear to allow natural groupings of the impact melt breccias. Various groupings of the impact melt breccias are discussed.

Ryder, Graham↗

NASA NTRS1987

Crystal fractionation in the SNC meteorites: Implications for surface units on Mars

Almost all rock types in the SNC meteorites are cumulates, products of magma differentiation by crystal fractionation (addition or removal of crystals). If the SNC meteorites are from the surface of Mars or near sub-surface, then most of the igneous units on Mars are differentiated. Basaltic units probably experienced minor to moderate differentiation, but ultrabasic units probably experienced extreme differentiation. Products of this differentiation may include Fe-rich gabbro, pyroxenite, peridotite (and thus serpentine), and possibly massive sulfides. The SNC meteorites include ten lithologies (three in EETA79001), eight of which are crystal cumulates. The other lithologies, EETA79001 A and B are subophitic basalts. The cumulate lithologies ALHA77005 and EETA79001 C were not fully described or discussed.

Treiman, Allan H.↗