Philip C. Goodell

Eastern Asia and the Western Pacific timing and spatial distribution of rifting in China

Abstract A compilation of recognized rifts in China indicates that five distinct episodes of rifting have occurred. These episodes occurred at approximately 2.3 Ga, 1.85−1.7 Ga, 1.0-0.7 Ga, 550−190 Ma, and 175 Ma to present. The timing and location of rifting has largely been a function of tectonic activity along the margins of the various Chinese paleocontinents. Some of the oldest rocks in China are found in the Sino- Korean and Tarim cratons, and most of the identified Precambrian rifts are found within or on the margins of these cratons. These cratons are viewed as the continental nucleus of China, and fold belts and microcontinents have been accreted to this nucleus through time. Much of the locus of rifting has migrated away from this nucleus as has the location of the continental margin—especially in the Paleozoic. Beginning in the Middle Mesozoic, rifting commenced along the entire eastern margin of China. Extension occurred concomitantly with subduction in a backarc setting; this is the dominant Cenozoic extensional regime in China and is still active today. To date, few Cenozoic rifts have been , found in western China where most tectonism is probably a consequence of the collision between India and China, but it seems likely that more rifts will be discovered in this area as it becomes better studied.

A preliminary description of the Gan-Hang failed rift, southeastern China

Abstract The Gan-Hang failed rift, as defined by present-day topography, extends at least 450 km in length and 50 km in width. It is a northeast-southwest trending series of features spanning from Hangzhou Bay in Zhejiang province into Jiangxi province through Fuzhou City. Southwest of Fuzhou, the rift splits into two portions: one continuing along the southwestern trend, and the other diverging westward. The total extent of the rift cannot be defined at this time. The rift is superimposed upon a major suture zone of Caledonian or early Mesozoic age. The suture represents the fusing of the South China (Huanan) and Yangtze cratons. Perhaps in Late Triassic, but for sure by Late-Middle Jurassic time, the rifting was initiated and followed this older suture, in part. This time corresponds roughly to the middle stage of the Yanshanian orogeny and to the subduction of the postulated Pacific- Kula ridge southeast of the continental margin. The total thickness of the sediments and volcanics filling the rift valley reaches more than 10,000 m. Peak intensity of extension was between Late-Middle Jurassic and Middle to Late Cretaceous. Sedimentation within the rift was not continuous and is marked with periodic unconformities. Sediments within the rift include red beds, sandstones, siltstones, mudstones, conglomerates, breccias, tuffs, and ignimbrites. Vertebrate fossils and dinosaur eggs are also found. Contemporaneous volcanics within and flanking the rift include basalts, rhyolites, granites, gabbros, dacites, and andesites. Silicic volcanics are mostly attributed to caldera systems. Early basalts are tholeiitic and later change to alkaline-olivine basalt. Bimodal volcanism is recognized. Peak intensity of volcanism ranges between 135 and 75 Ma. In Early Cenozoic time, the area was a topographic low. Paleocene- Eocene sediments and evaporites are the last rocks to be deposited in the rift. Today the rift is delineated by major, high-angle faults (the Pingxiang-Guangfeng deep fault belt), red beds, and volcanically derived U deposits. Scismic study of P-wave velocities has produced an earth model which shows substantial crustal thinning under the Gan-Hang rift. The region has been included in the southeastern China Mesozoic fault-depression system, and has not generally been recognized as a distinct “failed rift”.

Aerobic Reduction of Hexavalent Chromium in Soil by Indigenous Microorganisms

Surface soil containing 25,100 mg/kg total Cr [12,400 mg/kg Cr(VI)] obtained from a Superfund site was used in laboratory microcosm studies to evaluate the potential for aerobic reduction of Cr(VI) by the indigenous soil microbial community. Hexavalent chromium in soil was reduced by as much as 33% (from 1840 to 1240 mg/L) within 21 days under enrichment conditions. Reduction of Cr(VI) in this system was biologically mediated and depended on the availability of usable energy sources. Mass balance studies suggested that the microbial populations removed Cr(VI) from the soil solutions by reduction. Indigenous microbial soil communities even with no history of Cr(VI) contamination were capable of mediating this process. However, Cr(VI) removal was not observed when microbial populations from a sewage sludge sample were added to the soil microcosms. The results suggest that Cr(VI)-reducing microbial populations are widespread in soil, and thus the potential exists for in situ remediation of environmentally si...

Retrograde reactions involving galena and Ag-sulphosalts in a zoned ore deposit, Julcani, Peru

Abstract The sulphide ores from the Julcani mining district (Peru) display many retrograde reactions that may be attributed to solid-state processes accompanying cooling. Fahlores [~(Cu,Ag)10(Zn,Fe)2(Sb,As)4S13] from the Herminia mine exhibit pronounced downstream enrichments in molar Ag/(Ag+Cu) ratios that are strongly correlated with the abundance of PbS-AgSbS2-AgBiS2 phases. These correlations, discontinuous core to rim Sb/(Sb+As) enrichments in bournonites, and prominent reaction textures involving fahlores, bournonites and galenas provide strong evidence that the fahlores in these ores have been enriched in Ag by the Ag-Cu exchange reaction which occurred during cooling following mineralization of a PbS-AgSbS2-AgBiS2 galena and has been documented elsewhere. Secondary PbS-AgSbS2-AgBiS2 minerals aramayoite, bismuthian diaphorite [Pb2Ag3(Bi,Sb)3S8], and diaphorite were produced from primary galenas with cooling of ores with high Pb/Cu and Bi/Sb; pyrargyrite formed from the breakdown of the Ag10Zn2Sb4S13 component in the most Ag-rich fahlores, as an exsolution product of galena, and from replacement of aramayoite and galena with the evolution of semimetal sulphides. Based on mineral compositions, phase equilibria, a thermochemical database for sulphides and sulphosalts, and the reintegrated composition for primary grains of Ag-rich PbS-AgSbS2-AgBiS2 phases, we estimate that the primary temperature of hydrothermal mineralization was >320±10ºC, that these reactions ceased to affect fahlore Ag/(Ag+Cu) ratios and Bi/(Bi+Sb) ratios of aramayoite and miargyrite after cooling through 220±10ºC. Galenas, however, appear to have continued to adjust their compositions to reflect even lower temperatures by continued exsolution of semimetals and production a diverse suite of sulphosalts that occur in fine intergrowths with galena.

Chromium-Resistant Bacterial Populations from a Site Heavily Contaminated with Hexavalent Chromium

Chromium-containing industrial effluents are primarily responsible for environmental contamination by toxic and highly mobile, hexavalent chromium. The dilution plate-count method, using media amended with Cr(VI) at concentrations ranging from 0 to 1000 mg L-1, was used to compare the sizes of Cr(VI)-resistant bacterial populations from a soil contaminated with 25 100 mg kg-1 total Cr [12 400 mg kg-1 Cr(VI)] to those isolated from a slightly contaminated soil (99.6 mg kg-1 total Cr) and two other soils without any history of Cr contamination. Bacterial populations resistant to 500 mg L-1 Cr(VI) were isolated from all soils except the heavily contaminated soil. To determine whether Cr-resistant bacterial populations were indigenous to both the contaminated and the uncontaminated soils, enrichment cultures containing Cr(VI) at concentrations ranging from 0 to 1000 mg L-1 were employed. Bacterial populations, as high as 105 (colony forming units) CFU g-1 soil, tolerant of 500 mg L-1 Cr(VI) were isolated from all soils within 48 h of enrichment suggesting that the presence of aerobic Cr(VI)-resistant bacterial populations is unrelated to contamination levels or contamination history. However, identification of these resistant bacteria using fatty acid profiles was unsuccessful suggesting that these populations may have unique characteristics. Fungal colonies resistant to 1000 mg L-1 Cr(VI) were routinely isolated from both uncontaminated and contaminated soils. The results suggest that Cr-resistant microorganisms may be present in soils, even those with no history of Cr contamination.

Heavy metal pollution of soils along North Shuna-Aqaba Highway, Jordan

Attention to heavy metal contamination associated with highways or motorways has risen in the last decades because of the associated health hazards and risks. The present study analysed the metal content in soil samples of one of the main highways along the western part of the Jordanian border, the North Shuna-Dead Sea-Aqaba Highway. The metals analysed were Pb, Zn, Cd, Co and Ni. In the samples collected, the recorded average concentrations were as follows: 40 ppm for Ni, 5 ppm for Cd, 79 ppm for Zn, 79 ppm for Pb, and 25 ppm for Co. The average concentrations of Cd, Pb, and Co are higher than the average natural background values of heavy metals. The geo- accumulation index of these metals in the soils under study indicated that they are uncontaminated with Ni, Zn, and Co and moderately contaminated with Cd and Pb. In all of the investigated locations, the study found that concentrations decreased with depth. The cluster statistical analyses and pollution load index were used to relate pollution to land use or highway conditions. Two main trends were identified: (i) higher concentrations were located near intersections close to the urban areas in the Jordan Valley, in association with junctions controlled by traffic lights and check points, and (ii) lower concentrations were found to the southwest in areas of mainly barren landscape close to the Dead Sea and Aqaba.

Stratigraphy of the PB-1 well, nopal I Uranium deposit, Sierra Peña Blanca, Chihuahua, Mexico

The Nopal I site in the Peña Blanca uranium district has a number of geologic and hydrologic similarities to the proposed high-level radioactive waste repository at Yucca Mountain, making it a useful analogue to evaluate process models for radionuclide transport. The PB-1 well was drilled in 2003 at the Nopal I uranium deposit as part of a DOE-sponsored natural analogue study to constrain processes affecting radionuclide transport. The well penetrates through the Tertiary volcanic section down to Cretaceous limestone and intersects the regional aquifer system. The well, drilled along the margin of the Nopal I ore body, was continuously cored to a depth of 250 m, thus providing an opportunity to document the local stratigraphy. Detailed observations of these units were afforded through petrographic description and rockproperty measurements of the core, together with geophysical logs of the well. The uppermost unit encountered in the PB-1 well is the Nopal Formation, a densely welded, crystal-rich, rhyolitic ashflow tuff. This cored section is highly altered and devitrified, with kaolinite, quartz, chlorite, and montmorillonite replacing feldspars and much of the groundmass. Breccia zones within the tuff contain fracture fillings of hematite, limonite, goethite, jarosite, and opal. A zone of intense clay alteration, encountered in the depth interval 17.45-22.30 m, was interpreted to represent the basal vitrophyre of this unit. Underlying the Nopal Formation is the Coloradas Formation, which consists of a welded lithic-rich rhyolitic ash-flow tuff. The cored section of this unit has undergone devitrification and oxidation, and has a similar alteration mineralogy to that observed in the Nopal tuff. A sharp contact between the Coloradas tuff and the underlying Pozos Formation was observed at a depth of 136.38 m. The Pozos Formation consists of poorly sorted conglomerate containing clasts of subangular to subrounded fragments of volcanic rocks, limestone, and chert. Three thin (2-6 m) intervals of intercalated pumiceous tuffs are present within this unit. The contact between the Pozos Formation and the underlying Cretaceous limestone basement was encountered at a depth of 244.40 m. The water table is located at a depth of ~223 m. Several zones with elevated radioactivity in the PB-1 core occur above the current water table. These zones may be associated with changes in redox conditions that could have resulted in the precipitation of uraninite from downward-flowing waters transporting U from the overlying Nopal deposit. All of the intersected units have low (typically submillidarcy) matrix permeability, thus fluid flow in this area is dominated by fracture flow. These stratigraphic and rock-property observations can be used to constrain flow and transport models for the Peña Blanca natural analogue.

Correlates of Arsenic Mobilization into the Groundwater in El Paso, Texas

This paper addresses the contamination of groundwater by arsenic, a naturally occurring phenomenon that has caused serious cases of arsenic poisoning around the world. While a number of chemical processes are known to be capable of mobilizing arsenic, the extent to which different processes are active in actual geological settings is much less clear. In this work, the El Paso, Texas region is analyzed as a case study to better understand the factors associated with high arsenic levels in groundwater. This study includes two basins that supply drinking water to approximately 2.5 million people. The average arsenic was 8.5 ppb, which is below the current American and WHO Maximum Contaminant Level of 10 ppb. However, arsenic concentrations reached approximately 80 ppb in three different locations. Governmental archival information was combined with field water sampling, and with leaching and analysis of solid phase materials from well cuttings (sediments of the aquifers). The study identifies evidence for both competitive desorption and reductive dissolution operating to mobilize arsenic, with the importance of different mechanisms likely varying throughout the aquifers. A mean of 21% of the solid arsenic content was leached out to solution at pH 9, and mean solid phase arsenic concentration was 4.3 ppm, solid phase iron 7000 ppm, and solid carbon 0.6%, consistent with arsenic desorption out of sediments into the aqueous phase. A potential role of geothermal waters was also identified at a southern hot spot. This information is important to better understand the basic science of the arsenic geochemical cycle and may also provide a rough guide as to where low arsenic waters may be found: groundwater with high potentiometric head and short flow paths, groundwater under the influence of surface water, and lower pH groundwater.

LEARNING ACTIVITIES FOR AN UNDERGRADUATE MINERALOGY/PETROLOGY COURSE - “I AM/WE ARE”

Traditional undergraduate curriculum in the geological sciences consists of mineralogy, optical mineralogy, and petrology. In an attempt to better serve student needs, changes to this classical approach are being made at many educational institutions. A new entry-level mineralogy/igneous petrology course has been initiated, and the present report illustrates a series of learning activities that are a part of this course. A concise flow of ideas from chemical elements to minerals to rocks is emphasized, and magmatic evolution as promoted by Bowens Reaction Series is the pedagogical methodology. Individual learning activities alternate sensibly with cooperative ones. Data sources include textbooks, the library, journal articles, and the Web. Data becomes increasingly complex, and must be analyzed and integrated for individual and group presentations. The concise, focused, and related series of ideas and data appear to provide more effective and efficient learning. Student response to the self-identify of the I AM activities is very positive.

Spectroscopy of Salts Common in Saline Soils

Rapid identification and large-scale mapping of salt-affected lands can help improve environmental resource management. Spectroscopy is a potentially effective tool for assessing the distribution of salt crusts and salt-affected soils in barren landscapes of arid regions. This chapter examines high resolution spectral data of the hand-held spectrometer for characterizing properties of various salts commonly present in saline soils. The materials examined include: i) evaporites commonly formed on the soils of arid and semi-arid regions; halite (NaCl), thenardite (Na2SO4); nahcolite (NaHCO3), gypsum (CaSO4.2H2O), and their mixtures; ii) salt crusts formed on the surface of two torrifluvents. Spectral reflectance was measured with a GER 3700 spectroradiometer in the visible and near infrared region (400–2500 nm); and the positions of the dominant absorption features of the tested samples were documented. Crystal size and salt concentrations affected reflectivity, but did not affect the positions of the absorption bands of the salt crusts significantly. Dominant absorption features of spectra of salt crusts and evaporites were slightly different in their positions. Spectroscopy can be used under certain conditions to identify the presence of primary diagnostic spectral features of gypsum, nahcolite, thenardite and halite crusts. Additional research is needed if spectral data are to be used for identifying the types and quantities of salt crusts present on salt-affected lands.