Late local glacial maximum in the Central Altiplano triggered by cold and locally-wet conditions during the paleolake Tauca episode (17–15 ka,Heinrich 1)

The timing and causes of the last deglaciation in the southern tropical Andes is poorly known. In the Central Altiplano, recent studies have focused on whether this tropical highland was deglaciated before, synchronously or after the global last glacial maximum (～21 ka BP). In this study we present a new chronology based on cosmogenic ³He (³He_c) dating of moraines on Cerro Tunupa, a volcano that is located in the centre of the now vanished Lake Tauca (19.9°S, 67.6°W). These new ³He_c ages suggest that the Tunupa glaciers remained close to their maximum extent until 15 ka BP, synchronous with the Lake Tauca highstand (17–15 ka BP). Glacial retreat and the demise of Lake Tauca seem to have occurred rapidly and synchronously, within dating uncertainties, at ～15 ka BP. We took advantage of the synchronism of these events to combine a glacier model with a lake model in order to reconstruct precipitation and temperature during the Lake Tauca highstand. This new approach indicates that, during the Tauca highstand (17–15 ka BP), the centre of the Altiplano was characterized by temperature ～6.5 °C cooler and average precipitation higher by a factor ranging between ×1.6 and ×3 compared to the present. Cold and wet conditions thus persisted in a significant part of the southern tropical Andes during the Heinrich 1 event (17–15 ka BP). This study also demonstrates the extent to which the snowline of glaciers can be affected by local climatic conditions and emphasizes that efforts to draw global climate inferences from glacial extents must also consider local moisture conditions.     

A 11,000 yr palaeotemperature reconstruction from the southern boreal zone in Finland

The ecotone between the boreo-nemoral (hemiboreal) and the southern boreal vegetation zones constitutes the northern distributional limit of a number of thermophilous tree species in northern Europe and is, to a large extent, controlled by climatic conditions. We present a quantitative annual mean temperature reconstruction from a high-resolution pollen stratigraphy in southern boreal Finland, using a pollen-climate calibration model with a cross-validated prediction error of 0.9°C. Our model reconstructs low but steadily rising annual mean temperature from 10,700 to 9000 cal yr BP. At 8000–4500 cal yr BP reconstructed annual mean temperature reaches a period of highest values (Holocene thermal maximum) with particularly high temperatures (2.0–1.5°C higher than at present) at 8000–5800 cal yr BP. From 4500 cal yr BP to the present-day, reconstructed annual mean temperature gradually decreases by ca 1.5°C. Comparison of present results with palaeotemperature records from the Greenland ice cores, notably with the NorthGRIP δ¹⁸O record, shows marked similarities, suggesting parallel large-scale Holocene temperature trends between the North Atlantic and North European regions. The verification of the occurrence, timing, and nature of the short-term temperature fluctuations during the Holocene in the southern boreal zone in Europe requires replicate, high-resolution climate reconstructions from the region.     

Water chemistry in small lakes along a transect from boreal to arid ecoregions in European Russia: Effects of air pollution and climate change

Water chemistry in 280 small lakes in European Russia along a climatic transect from the Kola Peninsula (in the tundra and taiga zones) to the Caspian Lowland (in the arid zone) was investigated from 2000 to 2005. Here the chemical compositions of lake waters in different climatic ecoregions are characterised. Variability in water chemistry within and between ecozones is documented and discussed. The results show that within the humid zone, there was little variability in water chemistry and anthropogenic, geological and morphometric characteristics of lakes and their catchments had a strong effect on the chemical composition of waters compared to lakes in the arid and semi-arid zones. An estimation of the potential effect of climate warming on water chemistry showed that a temperature rise of 0.5–1 °C is likely to have no effect on major ion concentrations, whereas a temperature increase of 2 °C may lead to an increase of approximately 25% in total ion concentrations in the southern regions. Total P may increase approximately 50% in lakes throughout the study area if the average daily temperature were to increase by 0.5 °C. This would have an important effect on the nutrient status of these lakes. In particular, these processes are expected to be most pronounced in the arid zones.     

Persistent sea surface temperature and declined sea surface salinity in the northwestern tropical Pacific over the past 7500 years

To understand Holocene climate evolutions in low-latitude region of the western Pacific, paired δ¹⁸O and Mg/Ca records of planktonic foraminifer Globigerinoides ruber (250–300 μm, sensu stricto, s.s.) from a marine core ORI715-21 (121.5°E, 22.7°N, water depth 760 m) underneath the Kuroshio Current (KC) off eastern Taiwan were analyzed. Over the past 7500 years, the geochemical proxy-inferred sea surface temperature (SST) hovered around 27–28 °C and seawater δ¹⁸O (δ¹⁸O_W) slowly decreased 0.2–0.4‰ for two KC sites at 22.7° and 25.3°N. Comparison with a published high-SST and high-salinity equatorial tropical Pacific record, MD98-2181 located at the Mindanao Current (MC) at 6.3°N, reveals an anomalous time interval at 3.5–1.5 kyr ago (before 1950 AD). SST gradient between the MC site and two KC site decrease from 1.5–2.0 °C to only 0–1 °C, and δ¹⁸O_W from 0.1–0.3‰ to 0‰ for this 2-kyr time window. The high SST and low gradient could result from a northward shift of the North Equatorial Current, which implies a weakened KC. The long-term descending δ¹⁸O_W and increasing precipitation in the entire low-latitude western Pacific and the gradually decreasing East Asian summer monsoonal rainfall during middle-to-late Holocene is likely caused by different land and ocean responses to solar insolation and/or enhanced moisture transportation from the Atlantic to Pacific associated with the southward movement of ITCZ.     

Paleomagnetism of the Middle–Late Jurassic to Cretaceous red beds from the Peninsular Thailand: Implications for collision tectonics

Jurassic to Cretaceous red sandstones were sampled at 33 sites from the Khlong Min and Lam Thap formations of the Trang Syncline (7.6°N, 99.6°E), the Peninsular Thailand. Rock magnetic experiments generally revealed hematite as a carrier of natural remanent magnetization. Stepwise thermal demagnetization isolates remanent components with unblocking temperatures of 620–690 °C. An easterly deflected declination (D = 31.1°, I = 12.2°, α₉₅ = 13.9°, N = 9, in stratigraphic coordinates) is observed as pre-folding remanent magnetization from North Trang Syncline, whereas westerly deflected declination (D = 342.8°, I = 22.3°, α₉₅ = 12.7°, N = 13 in geographic coordinates) appears in the post-folding remanent magnetization from West Trang Syncline. These observations suggest an occurrence of two opposite tectonic rotations in the Trang area, which as a part of Thai–Malay Peninsula received clockwise rotation after Jurassic together with Shan-Thai and Indochina blocks. Between the Late Cretaceous and Middle Miocene, this area as a part of southern Sundaland Block experienced up to 24.5° ± 11.5° counter-clockwise rotation with respect to South China Block. This post-Cretaceous tectonic rotation in Trang area is considered as a part of large scale counter-clockwise rotation experienced by the southern Sundaland Block (including the Peninsular Malaysia, Borneo and south Sulawesi areas) as a result of Australian Plate collision with southeast Asia. Within the framework of Sundaland Block, the northern boundary of counter-clockwise rotated zone lies between the Trang area and the Khorat Basin.     

Palaeozoic polymetamorphism in the North Qinling orogenic belt,Central China: Insights from petrology and in situ titanite and zircon U–Pb geochronology

The Qinling orogenic belt experienced multiple phases of orogenesis during the Palaeozoic. Unraveling the timing and P–T conditions of these events is the key to understanding the convergence processes between the South China and the North China Blocks. The Songshugou Complex, located in the southern part of the North Qinling orogenic belt, has registered multistage metamorphism in Palaeozoic, and thus potentially provides insights into the tectonic evolution of the Qinling orogenic belt. In this study, three metabasic rocks (a garnet pyroxenite, a garnet amphibolite and a gneissic amphibolite) from the Songshugou Complex were selected for petrological study and zircon and titanite U–Pb dating. Our results show that the metabasic rocks experienced three metamorphic events during the Palaeozoic. The first metamorphic event (M1) is characterized by high pressure conditions. Two zircon grains in equilibrium with garnet and in absence of plagioclase were recognized from the garnet pyroxenite sample. They yielded Ti-in-zircon temperatures of 660–851 °C at ∼12.0 kbar and a weighted mean age of 498 ± 15 Ma, providing the constraints on the temperature and timing of prograde or peak metamorphism (M1-1). Zircons that are inequilibrium with garnet from the garnet pyroxenite and the garnet amphibolite gave U–Pb ages of 494 ± 9 Ma and 484 ± 4 Ma, and Ti-in-zircon temperatures of 793 ± 33 °C and 738 ± 18 °C, respectively. Thus, these zircons were formed on the retrograde amphibolite-facies conditions at ∼8.0 kbar (M1-2). Titanite inclusions were found in actinolite cores of zoned amphibole from the garnet amphibolite. They yielded a U–Pb age of ∼470 Ma and Zr-in-titanite temperature of 676 ± 23 °C at pressure of ∼7.0 kbar, suggesting that the amphibolite-facies retrogression perhaps persisted to ∼470 Ma.Weakly zoned zircons from the garnet amphibolite and inclusion-free titanites from the garnet pyroxenite gave consistent U–Pb ages of 418 ± 5 Ma and 423 ± 10 Ma, and Ti-in-zircon temperature of 742 ± 26 °C and Zr-in-titanite temperature of 764 ± 18 °C at ∼7.0 kbar, respectively. It is suggested that a heating event (M2) is registered by a subsequent phase of amphibolite-facies metamorphism. The ilmenite-bearing titanite crystals from the garnet pyroxenite yielded a U–Pb age of 352 ± 4 Ma, recording a late thermal event (M3).On the basis of combined petrological and geochronological results, we propose a revised tectonic model for the North Qinling orogeny in Palaeozoic. The high pressure granulites were formed by the northward subduction of the Shangdan oceanic slab and the arc-continent collision at ca. 500 Ma. Their exhumation happened at ca. 494–484 Ma as a result of slab breakoff. Subsequent amphibolite-facies metamorphism dated at ca. 440–420 Ma are coeval with the widespread magmatism in the North Qinling Terrane, which are likely caused by the reinitiation northward-subducted of Shangdan oceanic slab. At ca. 350 Ma, the North Qinling Terrane was likely affected by another thermal overprinting event.     

Glaciations and paleoclimate of Mount Erciyes,central Turkey,since the Last Glacial Maximum,inferred from 36Cl cosmogenic dating and glacier modeling

Forty-four boulders from moraines in two glacial valleys of Mount Erciyes (38.53°N, 35.45°E, 3917 m), central Turkey, dated with cosmogenic chlorine-36 (³⁶Cl), indicate four periods of glacial activity in the past 22 ka (1 ka = 1000 calendar years). Last Glacial Maximum (LGM) glaciers were the most extensive, reaching 6 km in length and descending to an altitude of 2150 m above sea level. These glaciers started retreating 21.3 ± 0.9 ka (1σ) ago. They readvanced and retreated by 14.6 ± 1.2 ka ago (Lateglacial), and again by 9.3 ± 0.5 ka ago (Early Holocene). The latest advance took place 3.8 ± 0.4 ka ago (Late Holocene). Using glacier modeling together with paleoclimate proxy data from the region, we reconstructed the paleoclimate at these four discrete times. The results show that LGM climate was 8–11 °C colder than today and moisture levels were somewhat similar to modern values, with a range between 20% more and 25% less than today. The analysis of Lateglacial advance suggests that the climate was colder by 4.5–6.4 °C based on up to 1.5 times wetter conditions. The Early Holocene was 2.1–4.9 °C colder and up to twice as wet as today, while the Late Holocene was 2.4–3 °C colder and its precipitation amounts approached to similar conditions as today. Our paleoclimate reconstructions show a general trend of warming for the last 22 ka, and an increase of moisture until Early Holocene, and a decrease after that time. The recent glacier terminates at 3450 m on the northwest side of the mountain. It is a remnant from the last advance (possibly during the Little Ice Age). Repeated measurements of glacier length between 1902 and 2008 reveal a retreat rate of 4.2 m per year, which corresponds to a warming rate of 0.9–1.2 °C per century.     

Phytoliths as quantitative indicators for the reconstruction of past environmental conditions in China II: palaeoenvironmental reconstruction in the Loess Plateau

Quantitative reconstruction of the climatic history of the Chinese Loess Plateau is important for understanding present and past environment and climate changes in the Northern Hemisphere. Here, we reconstructed mean annual temperature (MAT) and mean annual precipitation (MAP) trends during the last 136 ka based on the analysis of phytoliths from the Weinan loess section (34°24′N, 109°30′E) near the southern part of the Loess Plateau in northern China. The reconstructions have been carried out using a Chinese phytolith–climate calibration model based on weighted averaging partial least-squares regression. A series of cold and dry events, as indicated by the reconstructed MAT and MAP, are documented in the loess during the last glacial periods, which can be temporally correlated with the North Atlantic Heinrich events. Our MAT and MAP estimations show that the coldest and/or driest period occurred at the upper part of L2 unit (Late MIS 6), where MAT dropped to ca 4.4 °C and MAP to ca 100 mm. Two other prominent cold-dry periods occurred at lower Ll-5 (ca 77–62 ka) and L1-1 (ca 23–10.5 ka) where the MAT and MAP decreased to about 6.1–6.5 °C and 150–370 mm, respectively, ca 6.6–6.2 °C and 400–200 mm lower than today. However, the highest MAT (average 14.6 °C, max. 18.1 °C) and MAP (average 757 mm, max. 1000 mm) occurred at Sl interval (MIS 5). During the interstadial of L1-4–L1-2 (MIS 3) and during the Holocene warm-wet period, the MAT was about 1–2 °C and MAP 100–150 mm higher than today in the Weinan region. The well-dated MAT and MAP reconstructions from the Chinese Loess Plateau presented in this paper are the first quantitatively reconstructed proxy record of climatic changes at the glacial–interglacial timescale that is based on phytolith data. This study also reveals a causal link between climatic instability in the Atlantic Ocean and climate variability in the Chinese Loess Plateau.     

Fluorite (U–Th)/He thermochronology: Constraints on the low temperature history of Yucca Mountain,Nevada

Fluorite is one of the secondary minerals precipitated in pore spaces at the future nuclear waste repository site at Yucca Mountain, Nevada. The authors have conducted (U–Th)/He dating of this fluorite in an attempt to constrain the temperature and timing of paleo-fluid flux into the site. Repeated analysis of colourless fluorite yielded a weighted average age of 9.7 ± 0.15 Ma (2σ), younger than previously determined sanidine ⁴⁰Ar/³⁹ Ar ages (12.8 Ma) for deposition of the tuff.Laboratory He-diffusion experiments conducted on the Yucca fluorite yield a preliminary He closure temperature (T_c) of 90 ± 10 °C (cooling rate of 10 °C/Ma) and previous studies have determined that the fluorite precipitated from warm fluids (65–80 °C) at depths of <400 m. However, minerals can experience partial He loss at temperatures well below the T_c and therefore the (U–Th)/He age of 9.7 Ma is interpreted to be a cooling age. This result implies that the last period of elevated temperature fluid circulation through the Yucca site was approximately 9.7 Ma ago.It was observed that the purple coloured outer portion of the fluorite nodule yielded non-reproducible and invariably older ages than colourless fluorite. Several possible reasons are suggested.     

Duration of high-pressure metamorphism and cooling during the intraplate Petermann Orogeny

The Ediacaran–Cambrian Petermann Orogeny, central Australia, is an exceptional example of intraplate orogenesis. It involved sub-eclogite facies metamorphism and extreme basin inversion during the exhumation of Musgrave Province basement from beneath the formerly contiguous Centralian Superbasin. Sensitive High Resolution Ion Microprobe (SHRIMP) U–Pb geochronology of zircon, titanite and rutile, along with Ti-in-zircon thermometry from meta-igneous samples, have been used to determine the timing and duration of high-pressure metamorphism and subsequent cooling associated with this orogenic event. Peak metamorphic temperatures of 720–760 °C were attained at 544 ± 7 Ma (U–Pb zircon). Subsequent cooling to 600–660 °C by ~ 521 Ma occurred at a rate of ~ 2.6–7.0 °C Myr^− 1, as recorded by the closure of Pb diffusion in titanite. Further cooling to 585–560 °C by 498–472 Ma occurred at a rate of 0.9–4.8 °C Myr^− 1, as recorded by Pb closure in rutile. The duration of tectonism was long-lived (> 40 Myr) across the central and western parts of the orogenic system, and deformation occurred in a comparatively warm and weak portion of crust, characterised by regional thermal gradients of 17–26 °C km^− 1. This proposed duration of tectonism is much longer than that permitted by a shear heating mechanism, which requires an exceptionally short duration of tectonism, and additionally, an overall cold lithosphere characterised by geothermal gradients of ~ 9 °C km^− 1.     

Evolution of the Mo-rich scheelite skarn mineralization at Kozbudaklar,Western Anatolia,Turkey: Evidence from mineral chemistry and fluid inclusions

The Kozbudaklar scheelite skarn deposit in the Tavşanlı Zone, located approximately 22 km southeast of Bursa, is hosted by the Triassic calcic İnönü Marble and Eocene Topuk Pluton. At least four stages have been recognized through skarn evolution. Scheelite skarn distributed close to the Topuk Pluton occurred during the early (stage 1) and late (stage 2) prograde substages. The early prograde endo and exoskarn are composed of hedenbergite (Hd₉₆Joh₄)–plagioclase (An_55–64) and hedenbergite (Hd_61–94Joh_4–7), accompanied by calcic garnet (Grs_38–94Sps_1–5Alm₀) and scheelite (Pow_1–6). The second stage represents a relatively oxidized mineralogy dominated by diopside (Hd_16–48Joh_0–9), subcalcic garnet (Grs_24–92Sps_0–11Alm_0–31) and scheelite (Pow_7–32). The stage 3 and 4 mineral assemblages are characterized by few hydrous minerals in the retrograde stage and intense fracturing.Fluid inclusions from skarn rocks are indicative of multiple fluid events: (1) low-moderate salinity (5–16 wt.%NaCl equiv.) inclusions homogenized dominantly by a high-temperature (308 °C to > 600 °C) liquid phase in stage 1. Fluid inclusions in an early garnet homogenized over a similar temperature range (440 °C and 459 °C) into both liquid and vapor phases. Eutectic temperatures ranging from − 61.7 °C to − 35.0 °C that indicate the presence of H₂O–NaCl–(± MgCl₂ ± CaCl₂)–CO₂ solutions; (2) coexisting daughter mineral-bearing high salinity (29.5 ≥ 70 wt.%NaCl equiv.) and vapor-rich moderate salinity (11.5–16.7 wt.%NaCl equiv.) inclusions that homogenized in the liquid phase by the disappearance of the vapor phase at a similar temperature range (308 °C to > 600 °C) in stage 2. Eutectic temperatures range from − 67.9°C to − 51.8°C that shows the presence of H₂O–NaCl–CO₂–(± CH₄/N₂) solutions; (3) low-moderate salinity (12.5–7.6 wt.%NaCl equiv.) and temperature (320 °C to 215 °C) inclusions homogenized by the liquid phase in stage 3. Eutectic temperatures range from − 59.5 °C to − 44.2 °C indicating the presence of H₂O–NaCl–(± MgCl₂ ± CaCl₂)–CO₂ solutions; (4) inclusions of low salinity (9.9–0.9 wt.%NaCl equiv.) and homogenization temperature (183 °C to 101 °C) in stage 4.These data show that the Kozbudaklar skarn deposit was formed in a magmatic–hydrothermal system. In this model, carbonaceous fluids may have been exsolved from the plutonic rock during its emplacement and crystallization. Fluid inclusion data indicate that fluid boiling and immiscibility occurred at temperatures between 440 °C and 459 °C and pressures ranging from 50 MPa to 60 MPa based on hydrostatic considerations. Early scheelite was precipitated with relatively reduced mineral compositions. As a result of depressurization, Mo-rich scheelite with oxidized minerals formed via high salinity and vapor-rich inclusions. The second scheelite mineralization occurred in a normal hydrothermal system by an infiltration mechanism at pressures between approximately 40 and 1.5 MPa. At shallow depths (< 1.5 MPa) with increasing permeability, sulfide and oxide minerals were deposited in the retrograde stage, greatly assisted by meteoric water. Finally, as a result of the diminishing of ore-forming fluids, post-depositional barren quartz and calcite veins were formed.     

Magnetostratigraphy across the Triassic-Jurassic boundary in the main Karoo Basin

The end-Triassic mass extinction and the transition and explosive diversification of fauna over the Triassic-Jurassic boundary is poorly understood and poorly represented in the rock record of the Southern Hemisphere. This is despite the rich diversity in both body and trace fossils of Triassic-Jurassic age in southern Africa, which is not found in coeval Northern Hemisphere localities. We report here the first palaeomagnetic polarity zonation of the Upper Triassic-Lower Jurassic continental red bed succession (Elliot Formation; Stormberg Group) in southern Africa. The results from 10 partially overlapping sections, with a composite thickness of ~ 280 m, provide a magnetic polarity chronology of the main Karoo Basin in South Africa and Lesotho. Palaeomagnetic analyses reveal that heating samples to between 150 °C and ~ 300 °C removes the secondary, moderately inclined (~ 48°) normal-polarity component of remanent magnetization. This component overlaps with the present-day field and is comparable to the overprint direction expected from Lower Jurassic Karoo dolerite intrusions. In contrast, a likely primary, high unblocking temperature component, of dual polarity, consistently is of steeper inclination (~ 63°). This characteristic remanence passes the reversals test, except where means are based on small sample populations. There are only two resulting polarity zones for the ~ 200 m thick lower Elliot Formation (LEF) with potential for a thin 3rd magnetozone in the uppermost part. The upper Elliot Formation (UEF), in contrast, which was sampled over a thickness of ~ 80 m, has five polarity zones. The failure of the reversal test for the UEF and combined Elliot Formation (LEF + UEF) indicates that the normal polarity samples may be biased by a younger overprint of either the Jurassic normal polarity of the Karoo Large Igneous Province or present day field. The separate poles calculated for the four sites in the LEF and ten sites in the UEF overlap with the Late Triassic and Early to Middle Jurassic Gondwana poles, respectively. The combined Elliot Formation and UEF pole positions are better constrained than the LEF and therefore considered more reliable. Overall the LEF shows considerable overlap with the Late Triassic Apparent Polar Wander Paths (APWP) poles.     

Paleomagnetism of the Upper Cretaceous red-beds from the eastern edge of the Lhasa Terrane: New constraints on the onset of the India-Eurasia collision and latitudinal crustal shortening in southern Eurasia

The Late Cretaceous location of the Lhasa Terrane is important for constraining the onset of India-Eurasia collision. However, the Late Cretaceous paleolatitude of the Lhasa Terrane is controversial. A primary magnetic component was isolated between 580 °C and 695 °C from Upper Cretaceous Jingzhushan Formation red-beds in the Dingqing area, in the northeastern edge of the Lhasa Terrane, Tibetan Plateau. The tilt-corrected site-mean direction is D_s/I_s = 0.9°/24.3°, k = 46.8, α₉₅ = 5.6°, corresponding to a pole of Plat./Plon. = 71.4°/273.1°, with A₉₅ = 5.2°. The anisotropy-based inclination shallowing test of Hodych and Buchan (1994) demonstrates that inclination bias is not present in the Jingzhushan Formation. The Cretaceous and Paleogene poles of the Lhasa Terrane were filtered strictly based on the inclination shallowing test of red-beds and potential remagnetization of volcanic rocks. The summarized poles show that the Lhasa Terrane was situated at a paleolatitude of 13.2° ± 8.6°N in the Early Cretaceous, 10.8° ± 6.7°N in the Late Cretaceous and 15.2° ± 5.0°N in the Paleogene (reference point: 29.0°N, 87.5°E). The Late Cretaceous paleolatitude of the Lhasa Terrane (10.8° ± 6.7°N) represented the southern margin of Eurasia prior to the collision of India-Eurasia. Comparisons with the Late Cretaceous to Paleogene poles of the Tethyan Himalaya, and the 60 Ma reference pole of East Asia indicate that the initial collision of India-Eurasia occurred at the paleolatitude of 10.8° ± 6.7°N, since 60.5 ± 1.5 Ma (reference point: 29.0°N, 87.5°E), and subsequently ~ 1300 ± 910 km post-collision latitudinal crustal convergence occurred across the Tibet. The vast majority of post-collision crustal convergence was accommodated by the Cenozoic folding and thrust faulting across south Eurasia.     

The exhumation history of collision-related mineralizing systems in Tibet: Insights from thermal studies of the Sharang and Yaguila deposits,central Lhasa

The large, newly discovered Sharang porphyry Mo deposit and nearby Yaguila skarn Pb–Zn–Ag (–Mo) deposit reside in the central Lhasa terrane, northern Gangdese metallogenic belt, Tibet. Multiple mineral chronometers (zircon U–Pb, sericite ⁴⁰Ar–³⁹Ar, and zircon and apatite (U–Th)/He) reveal that ore-forming porphyritic intrusions experienced rapid cooling (> 100 °C/Ma) during a monotonic magmatic–hydrothermal evolution. The magmatic–hydrothermal ore-forming event at Sharang lasted ~ 6.0 Myr (~ 1.8 Myr for cooling from > 900 to 350 °C and ~ 4.0 Myr for cooling from 350 to 200 °C) whereas cooling was more prolonged during ore formation at Yaguila (~ 1.8 Myr from > 900 to 500 °C and a maximum of ~ 16 Myr from > 900 to 350 °C). All porphyritic intrusions in the ore district experienced exhumation at a rate of 0.07–0.09 mm/yr (apatite He ages between ~ 37 and 30 Ma). Combined with previous studies, this work implies that uplift of the eastern section of the Lhasa terrane expanded from central Lhasa (37–30 Ma) to southern Lhasa (15–12 Ma) at an increasing exhumation rate. All available geochronologic data reveal that magmatic–hydrothermal–exhumation activities in the Sharang–Yaguila ore district occurred within four periods of magmatism with related mineralization. Significant porphyry-type Mo mineralization was associated with Late Cretaceous–Eocene felsic porphyritic intrusions in the central Lhasa terrane, resulting from Neotethyan oceanic subduction and India–Asia continental collision.     

The Diavik Waste Rock Project: Measurement of the thermal regime of a waste-rock test pile in a permafrost environment

The interior thermal regime of a field-scale experimental waste rock pile in the Northwest Territories, Canada, was studied. Test pile construction was completed in the summer 2006, and temperature data was collected continuously since that time to February 2009. The temperature data indicates the test pile cooled over the study period, with an average heat energy release of −2.5 × 10⁴ and −2.6 × 10⁴ MJ in 2007 and 2008, respectively. The mean annual air temperature (MAAT) at the site was −8.9 °C during the period between 2006 and 2009, with a permafrost table at a depth of 4 m in bedrock away from the pile. Because of this cold environment, the upward movement rate of the 0 °C isotherm into the test pile at its base was approximately 1.5 m a⁻¹ during 2007 and 2008. Thermistor strings installed immediately below the base of the test pile showed the test-pile basal temperatures remained near and below 0 °C during the study period. Furthermore, due to low rates of sulfide mineral oxidation, elevated temperatures in the interior of the test pile were not observed. The average air velocity in the pore space in July 2007 and 2008 was about one third of that during January of each year based on temperature distributions. Therefore, due to higher air velocity during the winter, it is expected that heat transfer is greater during winter.     

Glacial and deglacial climatic patterns in Australia and surrounding regions from 35 000 to 10 000 years ago reconstructed from terrestrial and near-shore proxy data

This study forms part of a wider investigation of late Quaternary environments in the Southern Hemisphere. We here review the terrestrial and near-shore proxy data from Australia, Indonesia, Papua New Guinea (PNG), New Zealand and surrounding oceans during 35–10 ka, an interval spanning the lead-up to the Last Glacial Maximum (LGM), the LGM proper (21 ± 2 ka), and the ensuing deglaciation. Sites selected for detailed discussion have a continuous or near continuous sedimentary record for this time interval, a stratigraphically consistent chronology, and one or more sources of proxy climatic data. Tropical Australia, Indonesia and PNG had LGM mean annual temperatures 3–7 °C below present values and summer precipitation reduced by at least 30%, consistent with a weaker summer monsoon and a northward displacement of the Intertropical Convergence Zone. The summer monsoon was re-established in northwest Australia by 14 ka. Precipitation in northeast Australia was reduced to less than 50% of present values until warmer and wetter conditions resumed at 17–16 ka, followed by a second warmer, wetter phase at 15–14 ka. LGM temperatures were up to 8 °C lower than today in mainland southeast Australia and up to 4 °C cooler in Tasmania. Winter rainfall was much reduced throughout much of southern Australia although periodic extreme flood events are evident in the fluvial record. Glacial advances in southeast Australia are dated to 32 ± 2.5, 19.1 ± 1.6 and 16.8 ± 1.4 ka, with periglacial activity concentrated towards 23–16 ka. Deglaciation was rapid in the Snowy Mountains, which were ice-free by 15.8 ka. Minimum effective precipitation in southern Australia was from 14 to 12 ka. In New Zealand the glacial advances date to ～28, 21.5 and 19 ka, with the onset of major cooling at ～28 ka, or well before the LGM. There is no convincing evidence for a Younger Dryas cooling event in or around New Zealand, but there are signs of the Antarctic Cold Reversal in and around New Zealand and off southern Australia. There remain unresolved discrepancies between the climates inferred from pollen and those inferred from the beetle and chironomid fauna at a number of New Zealand sites. One explanation may be that pollen provides a generalised regional climatic signal in contrast to the finer local resolution offered by beetles and chironomids. Sea surface temperatures (SSTs) were up to 5 °C cooler during the LGM with rapid warming after 20 ka to attain present values by 15 ka. The increase in summer monsoonal precipitation at or before 15 ka reflects higher insolation, warmer SSTs and steeper thermal gradients between land and sea. The postglacial increase in winter rainfall in southern Australia is probably related to the southward displacement of the westerlies as SSTs around Antarctica became warmer and the winter pack ice and Antarctic Convergence Zone retreated to the south.     

Pressure solution of quartz aggregates under low effective stress (0.42–0.61 MPa) at 25–45 °C

Dissolution rates of pressure solution (PS) for quartz aggregates in 0.002 M NaHCO₃ solution were experimentally determined under low effective stress conditions of 0.42–0.61 MPa, and low temperatures of 25–45 °C. At temperatures of 25 °C, 35 °C, and 45 °C, the resultant silicon dissolution rates are 4.2 ± 1.2 × 10⁻¹⁵, 6.0 ± 1.0 × 10⁻¹⁵ and 7.8 ± 1.9 × 10⁻¹⁵ mol/cm²/s, respectively. Ratios between these dissolution rates and those of quartz sand at zero effective stress are 4.1 ± 1.2 at 25 °C, 3.0 ± 0.5 at 35 °C, and 2.4 ± 0.6 at 45 °C. As the uniaxial pressure was increased, the dissolution rate of PS also increased, though gradually decreased when the effective stress was kept constant. After the removal of stress, the dissolution rate was observed to increase once again. The activation energy of our PS experiments was determined to be approximately 24 kJ/mol, lower than the amount required for quartz sand dissolution to commence at zero effective stress. Our results clearly show that, even at such low temperature and effective stress, Si released into solution as a result of PS can be detected. This implies that experimental compaction of quartz aggregates can be measured even under such condition.     

Combined paleomagnetic and geochronological study on Cretaceous strata of the Qiangtang terrane,central Tibet

A combined paleomagnetic and geochronological investigation has been performed on Cretaceous rocks in southern Qiangtang terrane (32.5°N, 84.3°E), near Gerze, central Tibetan Plateau. A total of 14 sites of volcanic rocks and 22 sites of red beds have been sampled. Our new U–Pb geochronologic study of zircons dates the volcanic rocks at 103.8 ± 0.46 Ma (Early Cretaceous) while the red beds belong to the Late Cretaceous. Rock magnetic experiments suggest that magnetite and hematite are the main magnetic carriers. After removing a low temperature component of viscous magnetic remanence, stable characteristic remanent magnetization (ChRM) was isolated successfully from all the sites by stepwise thermal demagnetization. The tilt-corrected mean direction from the 14 lava sites is D = 348.0°, I = 47.3°, k = 51.0, α₉₅ = 5.6°, corresponding to a paleopole at 79.3°N, 339.8°E, A₉₅ = 5.7° and yielding a paleolatitude of 29.3° ± 5.7°N for the study area. The ChRM directions isolated from the volcanic rocks pass a fold test at 95% confidence, suggesting a primary origin. The volcanic data appear to have effectively averaged out secular variation as indicated by both geological evidence and results from analyzing the virtual geomagnetic pole (VGP) scatter. The mean inclination from the Late Cretaceous red beds, however, is 13.1° shallower than that of the ~ 100 Ma volcanic rocks. After performing an elongation/inclination analysis on 174 samples of the red beds, a mean inclination of 47.9° with 95% confidence limits between 41.9° and 54.3° is obtained, which is consistent with the mean inclination of the volcanic rocks. The site-mean direction of the Late Cretaceous red beds after tilt-correction and inclination shallowing correction is D = 312.6°, I = 47.7°, k = 109.7, α₉₅ = 3.0°, N = 22 sites, corresponding to a paleopole at 49.2°N, 1.9°E, A₉₅ = 3.2° (yielding a paleolatitude of 28.7° ± 3.2°N for the study area). The ChRM of the red beds also passes a fold test at 99% confidence, indicating a primary origin. Comparing the paleolatitude of the Qiangtang terrane with the stable Asia, there is no significant difference between our sampling location in the southern Qiangtang terrane and the stable Asia during ~ 100 Ma and Late Cretaceous. Our results together with the high quality data previously published suggest that an ~ 550 km N–S convergence between the Qiangtang and Lhasa terranes happened after ~ 100 Ma. Comparison of the mean directions with expected directions from the stable Asia indicates that the Gerze area had experienced a significant counterclockwise rotation after ~ 100 Ma, which is most likely caused by the India–Asia collision.     

Late Quaternary paleoenvironmental record from a sedimentary fill in Cucú cave,Almería,SE Spain

Cucú cave is a small cavity, 1600 m above sea level on the southern slope of Sierra de María (Almería Province, SE Spain), where current mean annual precipitation is < 450 mm. Fossils and palynomorphs contained within a sedimentary sequence, up to 9 m in depth, allow us to consider the prevailing climatic conditions, and the timing of cavern development. The lithological sequence is dominated by clast-supported detrital material with no evidence of alluvial transport. These sediments were formed by freeze-cracking during periglacial conditions, causing further cave enlargement after initial solutional development. The clastic sequence formed during cold climates is covered by a flowstone that was deposited during a period of warmer, wetter conditions. This provides a minimum U–Th isochron age of 40.2 ± 4.5 ka for the timing of periglacial action. Micromammal fossil species indicate a chronology between 140 and 80 ka. Paleoecological data based on the structure of the mammal community indicates that cold conditions prevailed at the time of deposit. In the studied sequence the presence of anthropogenic components has not been documented. The pollen assemblages identified are a common feature of Pleistocene cold stages that are in semi-arid regions.     

An improved cubic model for the mutual solubilities of CO2–CH4–H2S–brine systems to high temperature,pressure and salinity

The phase behavior of CO₂–CH₄–H₂S–brine systems is of importance for geological storage of greenhouse gases, sour gas disposal and enhanced oil recovery (EOR). In such projects, reservoir simulations play a major role in assisting decision makings, while modeling the phase behavior of the relevant CO₂–CH₄–H₂S–brine system is a key part of the simulation. There is a need for an equation of state (EOS) for such system which is accurate, with wide application range (pressure, temperature and aqueous salinity), computationally efficient and easy for implementation in a reservoir simulator.In this study, an improved cubic EOS model of the system CO₂–CH₄–H₂S–brine is developed based on the modifications of the binary interaction parameters in Peng–Robinson EOS, which is widely implemented in reservoir simulators. Thus the new model is suited for numerical implementation in reservoir simulators.The available experimental data of pure gas brine equilibrium and gas mixture solubility in water/brine are carefully reviewed and compared with the new model. From the comparison, the new model can accurately reproduce (1) the CO₂–brine mutual solubility data at temperature from 0 °C to 250 °C, pressure from 1 bar to 1000 bar and NaCl molality (mole number in 1 kg water, molal is used for short) from 0 to 6 molal, (2) CH₄–brine mutual solubility data at temperature from 0 °C to 250 °C, pressure from 1 bar to 2000 bar and NaCl molality from 0 to 6 molal, (3) H₂S–brine mutual solubility data at temperature from 0 °C to 250 °C, pressure from 1 bar to 200 bar and NaCl molality from 0 to 6 molal, and (4) has good accuracy for gas mixture solubility in brine.