Silica alteration zones in the Barberton greenstone belt: A window into subseafloor processes 3.5–3.3 Ga ago

Hofmann, Axel; Harris, Chris

doi:10.1016/j.chemgeo.2008.09.015

Cited by 156 publications

(119 citation statements)

References 72 publications

Supporting

Mentioning

107

Contrasting

Order By: Relevance

“…In using these and similar arguments, the assumption has generally been made that chert represents a marine chemical precipitate, and that its isotopic composition directly reflects the composition and temperature of the Archean ocean at the time of deposition. This is, however, unlikely for Paleoarchean cherts within volcano-sedimentary sequences of greenstone belts, because their origin was closely linked to syndepositional, low-temperature hydrothermal processes on the sea floor (Hofmann and Bolhar, 2007;Hofmann and Harris, 2008). Temperature estimates obtained from stable isotope paleothermometry, therefore, reflect the temperature of chert precipitation as a result of mixing of hydrothermal waters with colder seawater.…”

Section: Traditional Light Stable Isotopesmentioning

confidence: 99%

“…Although bedded cherts are relatively common, true iron formations are rare. Cherts are uniformly underlain by zones of low-temperature sea-floor alteration up to several tens of meters thick (Duchac and Hanor, 1987;Hofmann and Wilson, 2007;Hofmann and Harris, 2008). These zones are characterized by silicification and depletion of many elements, including Fe, Mg, and some transition and base metals, which were likely exhaled by hydrothermal systems to the Paleoarchean ocean, providing a source of dissolved iron (Hanor and Duchac, 1990;Hofmann and Harris, 2008).…”

Section: Paleoarchean Bifsmentioning

confidence: 99%

“…The Buck Reef Chert is an unusually thick sequence of predominantly black and white banded chert that contains a unit as much as 100 m thick of banded ferruginous chert, which is composed mainly of microquartz and goethite, although siderite is regarded to be the main iron-bearing mineral at depth (Tice and Lowe, 2004). Whereas most of the Onverwacht Group cherts can be readily linked to hydrothermal activity during their formation (Hofmann and Harris, 2008), hydrothermal influence on the Buck Reef Chert has been debated (Tice and Lowe, 2004;de Vries et al, 2006). Nevertheless, with the evidence for syndepositional volcanism, hydrothermal activity, and extensional deformation in the Buck Reef Chert (Hofmann, 2010), it is difficult to invoke an absence of elevated heat flow during the deposition, making a hydrothermal influence on the deposition of ferruginous cherts probable.…”

Section: Paleoarchean Bifsmentioning

confidence: 99%

See 2 more Smart Citations

Iron Formation: The Sedimentary Product of a Complex Interplay among Mantle, Tectonic, Oceanic, and Biospheric Processes

Bekker¹,

Krapež²,

Slack³

et al. 2010

Economic Geology

826

494

View full text Add to dashboard Cite

Iron formations are economically important sedimentary rocks that are most common in Precambrian sedimentary successions. Although many aspects of their origin remain unresolved, it is widely accepted that secular changes in the style of their deposition are linked to environmental and geochemical evolution of Earth. Two types of Precambrian iron formations have been recognized with respect to their depositional setting. Algoma-type iron formations are interlayered with or stratigraphically linked to submarine-emplaced volcanic rocks in greenstone belts and, in some cases, with volcanogenic massive sulfide (VMS) deposits. In contrast, larger Superior-type iron formations are developed in passive-margin sedimentary rock successions and generally lack direct relationships with volcanic rocks. The early distinction made between these two iron-formation types, although mimimized by later studies, remains a valid first approximation. Texturally, iron formations were also divided into two groups. Banded iron formation (BIF) is dominant in Archean to earliest Paleoproterozoic successions, whereas granular iron formation (GIF) is much more common in Paleoproterozoic successions. Secular changes in the style of iron-formation deposition, identified more than 20 years ago, have been linked to diverse environmental changes. Geochronologic studies emphasize the episodic nature of the deposition of giant iron formations, as they are coeval with, and genetically linked to, time periods when large igneous provinces (LIPs) were emplaced. Superior-type iron formation first appeared at ca. 2.6 Ga, when construction of large continents changed the heat flux at the core-mantle boundary. From ca. 2.6 to ca. 2.4 Ga, global mafic magmatism culminated in the deposition of giant Superior-type BIF in South Africa, Australia, Brazil, Russia, and Ukraine. The younger BIFs in this age range were deposited during the early stage of a shift from reducing to oxidizing conditions in the ocean-atmosphere system. Counterintuitively, enhanced magmatism at 2.50 to 2.45 Ga may have triggered atmospheric oxidation. After the rise of atmospheric oxygen during the GOE at ca. 2.4 Ga, GIF became abundant in the rock record, compared to the predominance of BIF prior to the Great Oxidation Event (GOE). Iron formations generally disappeared at ca. 1.85 Ga, reappearing at the end of the Neoproterozoic, again tied to periods of intense magmatic activity and also, in this case, to global glaciations, the so-called Snowball Earth events. By the Phanerozoic, marine iron deposition was restricted to local areas of closed to semiclosed basins, where volcanic and hydrothermal activity was extensive (e.g., backarc basins), with ironstones additionally being linked to periods of intense magmatic activity and ocean anoxia.Late Paleoproterozoic iron formations and Paleozoic ironstones were deposited at the redoxcline where biological and nonbiological oxidation occurred. In contrast, older iron formations were deposited in anoxic oceans, where ferrous iron oxid...

show abstract

Section: Traditional Light Stable Isotopesmentioning

confidence: 99%

Section: Paleoarchean Bifsmentioning

confidence: 99%

Section: Paleoarchean Bifsmentioning

confidence: 99%

See 1 more Smart Citation

Iron Formation: The Sedimentary Product of a Complex Interplay among Mantle, Tectonic, Oceanic, and Biospheric Processes

Bekker¹,

Krapež²,

Slack³

et al. 2010

Economic Geology

826

494

View full text Add to dashboard Cite

show abstract

“…In this context, the degree of carbonation of greenstones has been considered to qualitatively reflect CO 2 concentrations in ancient seawater (Kitajima et al 2001;Nakamura and Kato 2004;Hofmann and Harris 2008). The 3.5 and 3.2 Ga greenstones in extensional geological settings (mid-ocean ridge or rift basin) underwent strong carbonation caused by intense interaction with ambient CO 2 -rich seawater (Nakamura and Kato 2004;Shibuya et al 2007aShibuya et al , 2012.…”

Section: Introductionmentioning

confidence: 99%

Weak hydrothermal carbonation of the Ongeluk volcanics: evidence for low CO2 concentrations in seawater and atmosphere during the Paleoproterozoic global glaciation

Shibuya

Komiya

Takai

et al. 2017

Prog Earth Planet Sci

View full text Add to dashboard Cite

It was previously revealed that the total CO 2 concentration in seawater decreased during the Late Archean. In this paper, to assess the secular change of total CO 2 concentration in seawater, we focused on the Paleoproterozoic era when the Earth experienced its first recorded global glaciation. The 2.4 Ga Ongeluk Formation outcrops in the Kaapvaal Craton, South Africa. The formation consists mainly of submarine volcanic rocks that have erupted during the global glaciation. The undeformed lavas are mostly carbonate-free but contain rare disseminated calcites. The carbon isotope ratio of the disseminated calcite (δ 13 C cc vs. VPDB) ranges from − 31.9 to − 13.2 ‰. The relatively low δ 13 C cc values clearly indicate that the carbonation was partially contributed by 13 C-depleted CO 2 derived from decomposition of organic matter beneath the seafloor. The absence of δ 13 C cc higher than − 13.2‰ is consistent with the exceptionally 13 C-depleted CO 2 in the Ongeluk seawater during glaciation. The results suggest that carbonation occurred during subseafloor hydrothermal circulation just after the eruption of the lavas. Previously, it was reported that the carbonate content in the uppermost subseafloor crust decreased from 3.2 to 2.6 Ga, indicating a decrease in total CO 2 concentration in seawater during that time. However, the average CO 2 (as carbonate) content in the Ongeluk lavas (< 0.001 wt%) is much lower than those of 2.6 Ga representatives and even of modern equivalents. This finding suggests that the total CO 2 concentration in seawater further decreased during the period between 2.6 and 2.4 Ga. Thus, the very low content of carbonate in the Ongeluk lavas is probable evidence for the extremely low CO 2 concentration in seawater during the global glaciation. Considering that the carbonate content of the subseafloor crusts also shows a good correlation with independently estimated atmospheric pCO 2 levels through the Earth history, it seem highly likely that the low carbonate content in the Ongeluk lavas reflects the low atmospheric pCO 2 at that time. We conclude that the continuous decrease in CO 2 concentration of seawater/atm. from 3.2 Ga was one of the contributing factors to the Paleoproterozoic global glaciation.

show abstract

“…Several trace elements such as rare earth elements (REEs) Y, Th, Zr, Hf, Nb, and Sc are best suited for provenance study, because of their relatively low mobility during sedimentary processes and their short residence times in sea water (Cullers et al, 1979;Young et al, 2013). Numerous studies showed that major and trace elements can be added or subtracted from a rock during seawater-basalt interaction (Verma, 1992;Verma et al, 2005;Hofmann and Harris, 2008). A study carried out by Greenough et al (1990) on geochemical effects of alteration on basalts from the Indian Ocean pointed out that REEs and elements like Zr, Nb, Y, Ti, Al, V, Th, P, and Hf were immobile and Cu, Cr, and Zn were mobile during alteration processes.…”

Section: Introductionmentioning

confidence: 99%

Geochemistry of sands along the San Nicolás and San Carlos beaches, Gulf of California, Mexico: implications for provenance and tectonic setting

Armstrong‐Altrin¹,

Nagarajan²,

Lee³

et al. 2014

Turkish J Earth Sci

112

View full text Add to dashboard Cite

Th, P, and Hf were immobile and Cu, Cr, and Zn were mobile during alteration processes. However, Torres-Alvarado et al. (2007) recently studied the effect of hydrothermal alteration on the chemistry of volcanic rocks from the Los Azufres geothermal field, Mexico, and found that most major elements and a few trace elements, including high field strength elements such as Zr, Ti, and P, were mobilized during hydrothermal alteration. They cautioned against the use of these elements for petrogenetic studies of igneous and metamorphic rocks. Although provenance studies are common (Hossain et al., 2010(Hossain et al., , 2014Armstrong-Altrin and Natalhy-Pineda, 2013), studies focused on the geochemical variation in sediments with respect to grain size are meagre (e.g., Ohta, 2008;Effoudou-Priso, 2014).The study areas of the San Nicolás (SN) and San Carlos (SC) beaches are located along the Gulf of California.

show abstract

Silica alteration zones in the Barberton greenstone belt: A window into subseafloor processes 3.5–3.3 Ga ago

Cited by 156 publications

References 72 publications

Iron Formation: The Sedimentary Product of a Complex Interplay among Mantle, Tectonic, Oceanic, and Biospheric Processes

Iron Formation: The Sedimentary Product of a Complex Interplay among Mantle, Tectonic, Oceanic, and Biospheric Processes

Weak hydrothermal carbonation of the Ongeluk volcanics: evidence for low CO2 concentrations in seawater and atmosphere during the Paleoproterozoic global glaciation

Geochemistry of sands along the San Nicolás and San Carlos beaches, Gulf of California, Mexico: implications for provenance and tectonic setting

Contact Info

Product

Resources

About