Half Dome Research Articles

Slowly positively drifting bursts generated by large-scale magnetic reconnection

Context. The slowly positively drifting bursts (SPDBs) are rarely observed in radio emission of solar flares. Aims. To understand how the SPDBs are generated, we studied the radio observations at 600–5000 MHz together with the imaging observations made in ultraviolet (UV) and extreme ultraviolet (EUV) during the SPDB-rich C8.7 flare of 2014 May 10 (SOL2014-05-10T0702). Methods. Because the SPDBs propagate towards locations of higher plasma density, we studied their associations with individual flare kernels, located either within the flare core itself, or distributed at longer distances, but connected to the flaring region by large-scale hot loops. For each kernel we constructed light curves using 1600 Å and 304 Å observations and compared these light curves with the temporal evolution of radio flux at 1190 MHz, representing all observed groups of SPDBs. We also analysed the UV/EUV observations to understand the evolution of magnetic connectivity during the flare. Results. The flare starts with a growing hot sigmoid observed in 131 Å. As the sigmoid evolves, it extends to and interacts with a half dome present within the active region. The evolving sigmoid reconnects at the respective hyperbolic flux tube, producing large-scale magnetic connections and an EUV swirl. Three groups of SPDBs are observed during this large-scale magnetic reconnection, along with a group of narrow-band type III bursts. The light curves of a kernel corresponding to the footpoint of spine line analogue show good agreement with the radio flux at 1190 MHz, indicating that the SPDBs are produced by the large-scale magnetic reconnection at the half dome. In addition, one of the kernels appeared in the neighbouring active region and also showed a similar evolution to the radio flux, implying that beams of accelerated particles can synchronize radio and UV/EUV light curves across relatively large distances.

A Complex Interplay Between Pluton Emplacement, Tectonic Deformation, and Plate Kinematics in the Cretaceous Sierra Nevada Magmatic Arc, California

AbstractThe relation of plate kinematics to the structural record of arc plutons and their host rocks is complex and still not fully understood. We address this issue through a combination of field mapping, structural analysis, anisotropy of magnetic susceptibility analysis, and fabric modeling in the Late Cretaceous Tuolumne Intrusive Complex, Sierra Nevada, California. A pattern of anti‐clockwise rotation from ∼NNW–SSE to WNW–ESE steep foliations and change in fabric ellipsoid shape from oblate to prolate was revealed in successively emplaced Kuna Crest (∼95–92 Ma), Half Dome (∼92–89 Ma), and Cathedral Peak (∼89–84 Ma) granodiorites. The numerical model indicates that the Kuna Crest was emplaced in a transpressional setting with an angle of convergence α = 60–40°, whereas the Half Dome and Cathedral Peak required simultaneous vertical constriction overprinted by transpression with α = 35–15°. This transition, which occurred at ∼92 Ma, is accompanied by a shallowing of the lineation plunge observed also in other ∼88–84 Ma central Sierra Nevada plutons. Provided that the Cretaceous Sierra Nevada arc was constructed during overall dextral transpression, these transitions reflect significant changes in kinematics, where ∼107–92 Ma plutons were emplaced during pure shear‐dominated transpression, which was followed by a transition to wrench‐dominated transpression recorded in ∼92–84 Ma plutons. Such a transition in kinematics is explained as a result of progressively increasing obliquity of the relative convergence of the Farallon plate subducting beneath the North American continental margin, in agreement with most paleogeographic reconstructions.

Absolute doubly differential angular sputtering yields for 20 keV Kr+ on polycrystalline Cu

We have measured the absolute doubly differential angular sputtering yield for 20 keV Kr+ impacting a polycrystalline Cu slab at an incidence angle of θi = 45° relative to the surface normal. Sputtered Cu atoms were captured using collectors mounted on a half dome above the sample, and the sputtering distribution was measured as a function of the sputtering polar, θs, and azimuthal, ϕs, angles. Absolute results of the sputtering yield were determined from the mass gain of each collector, the ion dose, and the solid angle subtended, after irradiation to a total fluence of ∼1 × 1018 ions/cm2. Our approach overcomes shortcomings of commonly used methods that only provide relative yields as a function of θs in the incidence plane (defined by the ion velocity and the surface normal). Our experimental results display an azimuthal variation that increases with increasing θs and is clearly discrepant with simulations using binary collision theory. We attribute the observed azimuthal anisotropy to ion-induced formation of micro- and nano-scale surface features that suppress the sputtering yield through shadowing and redeposition effects, neither of which are accounted for in the simulations. Our experimental results demonstrate the importance of doubly differential angular sputtering studies to probe ion sputtering processes at a fundamental level and to explore the effect of ion-beam-generated surface roughness.

Artwork Analysis of Anastasis Fresco at Khora South Chapel and Its Interaction with the Architectural Program

Bu makalede Kariye Manastırı güney şapelinde yer alan Anastasis freskinin ikonografik olarak çözümlenmesi ve bu yapıtın yapının mimari programıyla kurduğu ilişkinin irdelenmesi hedeflenmiştir. İlk olarak eserin yer aldığı Kariye (Khora) Manastırı mimari nitelikleri bakımından incelenmiştir. Eserin sanatçısı ve hamisi hakkında bilgi verilmesinin ardından, esere konu olan Anastasis temasının mitolojik kökeni irdelenmiştir. Anastasis freskinin yapımında kullanılan tekniğin özgün tarafları ortaya konmuştur. Yapıtın ikonografik çözümlemesi yapılırken Erwin Panofsky’nin geliştirdiği yöntemden faydalanılmıştır. Bu kapsamda Anastasis freski incelenirken ilk olarak biçimsel analizi yapılarak kompozisyonda yer alan figürlerin birbirleriyle ilişkileri irdelenmiş; ikinci aşamada teolojik ve alegorik bilgiler ışığında figürlerin temsil ettiği karakterler ve aktarılan kavramlar ortaya çıkarılmaya çalışılmıştır. Üçüncü aşamada ise yapıtın, dönemin koşulları içerisinde sahip olduğu anlamlar irdelenirken; yakın döneminde üretilen, benzer temaya sahip eserlerle de karşılaştırılmıştır. Son olarak yapının mimari ve ikonografik programları arasındaki etkileşim ele alınmıştır.Kariye Manastırı, mimari programla ikonografinin iç içe geçtiği, hatta ikonografiyle anlatılan hikaye dizisinin mimari elemanları belirlediği bir düzene sahiptir. Bu nedenle Rönesans’a öncülük yapan Bizans Sanatı ikonografisinin incelenebileceği özgün örnekler arasında sayılabilir. Kariye güney şapeli apsis yarım kubbesi üzerinde yer alan Anastasis freski, Hristiyan literatüründe önemli bir yeri olan diriliş temasını işlemektedir. Şapeldeki ikonografik programın bütünü düşüldüğünde diriliş sahnesi ana temayı oluşturmaktadır. Anastasis freskinin parekklesionda yer alması, mezarı burada bulunan Kariye Kilisesi’nin hamisi Metokhites’in ölümsüzlük / diriliş beklentisini de simgelemektedir.

Coupled magmatic and host rock processes during the initiation of the Tuolumne Intrusive Complex, Sierra Nevada, California, USA: A transition from ephemeral sheets to long-lived, active magma mushes

Abstract The initiation of pluton formation is rarely preserved as the rock record is typically overprinted by younger intruding pulses. An exception is the 80 km2 Kuna Crest lobe, which marks the initiation of the 95–85 Ma, 1100 km2 Tuolumne Intrusive Complex in the Sierra Nevada, California, USA. We present a detailed map of the lithologies and structure of the Kuna Crest lobe, associated sheeted complex and satellite plutons, and their host rocks, using chemical abrasion–isotope dilution–thermal ionization mass spectrometry and laser ablation–inductively coupled plasma–mass spectrometry U-Pb zircon geochronology, element and isotope geochemistry, and Al-in-hornblende thermobarometry to conclude the following: (a) The 94.91 ± 0.53 Ma to 92.75 ± 0.11 Ma Kuna Crest lobe and its marginal sheeted complex preserved the oldest intrusive pulses and most mantle-like compositions of the entire Tuolumne Intrusive Complex. (b) Emplacement began with magma wedging of low volume magma pulses resulting in a sheeted complex that is compositionally heterogeneous at outcrop scales, but isotopically homogeneous. (c) These early magmas established a pre-heated pathway within just a few hundreds of thousands of years that gave way to the formation of the ~1.5 million-year-long active, compositionally more homogeneous but isotopically more heterogeneous magma mush across the Kuna Crest lobe. The host rocks and previously intruded magma were displaced largely vertically through downward flow. (d) The melt-interconnected mush zone in the lobe allowed for magma mixing and crystal-liquid separation at the emplacement level. We interpret this lobe to represent an upper- to mid-crustal, vertical magma transfer zone that likely fed shallower plutons and potentially volcanic eruptions. We propose a filter pressing mechanism driven by vertical magma transport through the lobe resulting in margin-parallel fabrics, plagioclase-rich crystal cumulates, inward draining and upward loss (of up to 40%) of interstitial melts. Some inward drained melts hybridized with later intruding Half Dome magmas at the transition to the main Tuolumne Intrusive Complex. Some of the lobe magmas, including fractionated melts, drained laterally into the strain shadow of the lobe to form the satellite plutons, further contributing to cumulate formation in the lobe. This study documents that within only a few hundreds of thousands of years, arc magma plumbing systems are capable of establishing a focused magma pathway to build up to increasingly larger magma bodies that are capable of undergoing magma differentiation and feeding shallower plutons and volcanic eruptions.

A tale of five enclaves: Mineral perspectives on origins of mafic enclaves in the Tuolumne Intrusive Complex

AbstractThe widespread occurrence of mafic magmatic enclaves (mme) in arc volcanic rocks attests to hybridization of mafic-intermediate magmas with felsic ones. Typically, mme and their hosts differ in mineral assemblage and the compositions of phenocrysts and matrix glass. In contrast, in many arc plutons, the mineral assemblages in mme are the same as in their host granitic rocks, and major-element mineral compositions are similar or identical. These similarities lead to difficulties in identifying mixing end members except through the use of bulk-rock compositions, which themselves may reflect various degrees of hybridization and potentially melt loss. This work describes the variety of enclave types and occurrences in the equigranular Half Dome unit (eHD) of the Tuolumne Intrusive Complex and then focuses on textural and mineral composition data on five porphyritic mme from the eHD. Specifically, major- and trace-element compositions and zoning patterns of plagioclase and hornblende were measured in the mme and their adjacent host granitic rocks. In each case, the majority of plagioclase phenocrysts in the mme (i.e., large crystals) were derived from a rhyolitic end member. The trace-element compositions and zoning patterns in these plagioclase phenocrysts indicate that each mme formed by hybridization with a distinct rhyolitic magma. In some cases, hybridization involved a single mixing event, whereas in others, evidence for at least two mixing events is preserved. In contrast, some hornblende phenocrysts grew from the enclave magma, and others were derived from the rhyolitic end member. Moreover, the composition of hornblende in the immediately adjacent host rock is distinct from hornblende typically observed in the eHD. Although primary basaltic magmas are thought to be parental to the mme, little or no evidence of such parents is preserved in the enclaves. Instead, the data indicate that hybridization of already hybrid andesitic enclave magmas with rhyolitic magmas in the eHD involved multiple andesitic and rhyolitic end members, which in turn is consistent with the eHD representing an amalgamation of numerous, compositionally distinct magma reservoirs. This conclusion applies to enclaves sampled <30 m from one another. Moreover, during amalgamation of various rhyolitic reservoirs, some mme were evidently disrupted from a surrounding mush and thus carried remnants of that mush as their immediately adjacent host. We suggest that detailed study of mineral compositions and zoning in plutonic mme provides a means to identify magmatic processes that cannot be deciphered from bulk-rock analysis.

Feldspar recycling across magma mush bodies during the voluminous Half Dome and Cathedral Peak stages of the Tuolumne intrusive complex, Yosemite National Park, California, USA

Abstract Incremental pluton growth can produce sheeted complexes with no magma-magma interaction or large, dynamic magma bodies communicating via crystal and melt exchanges, depending on pulse size and frequency of intrusions. Determining the degree and spatial extent of crystal-melt exchange along and away from plutonic contacts at or near the emplacement level, such as in the large, long-lived Tuolumne intrusive complex (TIC) in California, sheds light onto the process and evolution of incremental growth. This study used field mapping and petrographic and geochemical analysis of plagioclase and K-feldspar populations in the equigranular Half Dome (eHD), porphyritic Half Dome (pHD), and Cathedral Peak (CP) Granodiorites of the southeastern section of the TIC to determine the presence and/or extent of feldspar recycling at interunit contacts. Our results suggest that contacts between major units are predominantly ∼400-m- to 3-km-thick gradational zones. K-feldspar is compositionally distinct in eHD and neighboring gradational zones and shows no evidence of mixing. K-feldspar in a gradational zone between pHD and CP shows evidence of mixing between the two. Plagioclase in eHD and CP display distinct ranges of anorthite content, Sr, and light rare earth element abundances; both populations are observed in pHD. Major oxide and trace element calculations of melts in equilibrium with plagioclase cores indicate that the melts were more silicic, less calcic, and lower in Sr and Rb than corresponding analyzed whole-rock samples. These results suggest that the magmas also underwent plagioclase and biotite accumulation. The presence of two plagioclase populations in pHD is consistent with eHD and CP hybridizing to form pHD in an increasingly maturing and exchanging TIC magmatic system during the eHD-pHD-CP stages but before groundmass and small K-feldspar phenocrysts crystallized.

Enhancement of Edge Crack Predictability for Automotive High-Strength Thick Steel Sheets Considering the Pressure Effect

This paper deals with the prediction accuracy of edge crack of automotive high-strength thick steel sheets according to the numerical simulation method. The mechanical tests under tension, tension/compression and loading-unloading conditions were performed to evaluate anisotropy, hardening behaviour and elastic modulus change, respectively. Edge stretchability was evaluated by the HER(hole expansion ratio) test according to the hole processing method. Based on the measured data, three simulation methods were constructed with respect to the material model and the element type. The half dome test was selected for verifying edge crack predictability according to the simulation method. The simulation results show that the pressure effect along the thickness direction has significant effect on prediction accuracy of edge crack for high-strength thick steel sheets used for automotive chassis parts.

Shape and size of large-scale vortices: A generic fluid pattern in geophysical fluid dynamics

Planetary rotation organizes fluid motions into coherent, long-lived swirls, known as large-scale vortices (LSVs), which play an important role in the dynamics and long-term evolution of geophysical and astrophysical fluids. Here, using direct numerical simulations, we show that LSVs in rapidly rotating mixed convective and stably stratified fluids, which approximates the two-layer, turbulent-stratified dynamics of many geophysical and astrophysical fluids, have a generic shape and that their size can be predicted. We show that LSVs emerge in the convection zone from upscale energy transfers and can penetrate into the stratified layer. At the convective-stratified interface, the LSV cores have a positive buoyancy anomaly. Due to the thermal wind constraint, this buoyancy anomaly leads to winds in the stratified layer that decay over a characteristic vertical length scale. Thus LSVs take the shape of a depth-invariant cylinder with a finite-size radius in the turbulent layer and of a penetrating half dome in the stratified layer. Importantly, we demonstrate that when LSVs penetrate all the way through the stratified layer and reach a boundary that is no-slip, they saturate by boundary friction. We provide a prediction for the penetration depth and maximum radius of LSVs as a function of the LSV vorticity, the stratified layer depth, and the stratification. Our results, which apply for cyclonic LSVs, suggest that LSVs in slowly rotating stars and Earth's liquid core are confined to the convective layer, while in Earth's atmosphere and oceans they can penetrate far into the stratified layer.

Aplite diking and infiltration: a differentiation mechanism restricted to plutonic rocks

The Half Dome Granodiorite in Yosemite National Park, California, contains multiple crosscutting generations of high-silica dikes that vary in texture but share the distinctive trace element characteristics of fine-grained aplite dikes of the region (e.g., low Y and middle REE). Dikes of the youngest generation are typical fine-grained, sugary aplites with sharp planar contacts, whereas progressively older dikes are increasingly coarse-grained. The oldest ghostly forms recognizable as dikes are similar in grain size to the host granodiorite and their contacts are irregular at the grain scale, making them easy to overlook in the field. Mineral compositions and microstructures of felsic dikes indicate that all dikes, including fine-grained aplite, have undergone significant recrystallization. We propose that older dikes were originally fine-grained aplites that, after emplacement, recrystallized together with the host to a typical granitic texture. Extraction, transport, and redistribution of aplitic melt by various mechanisms explains major and trace element variation in the pluton and likely was the dominant differentiation mechanism at the level of emplacement. This late-stage differentiation process can only occur in a largely crystallized host capable of sustaining tensile cracks, and therefore cannot play a role in the differentiation of volcanic rocks. Predicted geochemical effects of aplite redistribution are evident in trace-element geochemical patterns of Circum-Pacific plutonic rocks but are absent from corresponding volcanic rocks. This indicates that aplite infiltration may be an important and widespread late-stage process of pluton differentiation.

Half a million years of magmatic history recorded in a K-feldspar megacryst of the Tuolumne Intrusive Complex, California, USA

Abstract K-feldspars reach megacrystic size (>3 cm) relative to their groundmass in many granitoid plutons and some volcanic rocks. However, the nature of the growth environment and the time scales for megacrystic growth remain poorly constrained. Chemical abrasion–isotope dilution–thermal ionization mass spectrometry with trace-element analysis (CA-ID-TIMS-TEA) U-Pb geochronology was carried out on zircon inclusions from the core and rim of one K-feldspar megacryst sampled from the interior of the Tuolumne Intrusive Complex (TIC), California, USA. Combined with new zircon ages from the groundmass, these data can test if K-feldspar megacrysts are igneous and capable of recycling and transport in the magmatic system or whether they formed by textural coarsening in low-melt-fraction or subsolidus conditions. The zircon ages reveal that the megacryst core is 0.5 m.y. older than the rim, which itself is older than the groundmass. Core ages match zircon dates from the TIC’s porphyritic Half Dome unit, and rim and groundmass ages overlap with the younger Cathedral Peak unit. Trace elements of the zircons from the megacryst core and rim are similar and less evolved than the groundmass zircons. The core-to-rim age progression of zircon inclusions is inconsistent with subsolidus K-feldspar coarsening, but instead indicates that megacrysts in the TIC grew in an igneous environment over at least 0.5 m.y., and that growth likely occurred spanning two or more intrusive episodes. This supports models of an increasingly maturing magmatic system, where crystal recycling from older into younger magma batches is common.

Printgrammetry—3-D Model Acquisition Methodology From Google Earth Imagery Data

This article proposes a technique named Printgrammetry, a structured workflow that allows the extraction of 3-D models from Google Earth platform through the combination of image captures from the screen monitor with structure from motion algorithms. This technique was developed to help geologists and other geoscientists in acquiring 3-D photo-realistic models of outcrops and natural landscapes of big proportions without the need of field mapping and expensive equipment. The methodology is detailed aiming to permit easy reproducibility and focused on achieving the highest resolution possible by working with the best images that the platform can provide. The results have shown that it is possible to obtain visually high-quality models from natural landscapes from Google Earth by acquiring images at high level of detail regions of the software, using a 4K monitor, multidirectional screenshots, and by marking homogeneously spaced targets for georeferencing and scaling. The geometric quality assessment performed using light detection and ranging ground truth data as comparison shows that the Printgrammetry dense point clouds have reached 98.1% of the total covered area under 5 m of distance for the Half Dome case study and 96.7% for the Raplee Ridge case study. The generated 3-D models were then visualized and interacted through an immersive virtual reality software that allowed geologists to manipulate this virtual field environment in different scales. This technique is considered by the authors to have a promising potential for research, industrial, and educational projects that do not require high-precision models.

Permits were supposed to make climbing Yosemite’s Half Dome safer. They made things worse

Permits were supposed to make climbing Yosemite’s Half Dome safer. They made things worse

Impact of a Half Dome Cable Permitting Process on Search and Rescue Activity, Hiker Mortality Rates, and Operational Costs Above Little Yosemite Valley

The summit of Yosemite's Half Dome is reached using cable handrails for the final 146 m (480 ft). Access to these cables was restricted to users with permits in 2010. The authors aim to describe the impact of permitting on search and rescue (SAR) in the region of the park most affected by permitting. An observational study from 2005 to 2009 and 2011 to 2015 comparing the number of incidents, major incidents (exceeding $500), victims, and fatalities before and after permitting the use of cable handrails on Half Dome in the area above Little Yosemite Valley (LYV) and parkwide. Each year was analyzed separately with t tests and Mann-Whitney U tests. Data are presented as mean±SD. The number of hikers in the study area was reduced by up to 66% by permitting. Above LYV from 2005 to 2009, there were 85 SAR incidents, 134 victims, 8 fatalities, 38 major incidents, and annual SAR costs of $44,582±28,972. From 2011 to 2015, the same area saw 54 SAR incidents, 156 victims, 4 fatalities, 35 major incidents, and annual SAR costs of $27,027±19,586. No parameter showed statistical significance. Parkwide SAR incidents decreased from 232 to 198 annual incidents (P=0.013) during the same time period, with parkwide mortality increasing from 8 to 12 deaths annually (P=0.045). SAR incidents, victims, fatalities, or costs above LYV did not decrease after cable handrail permitting. Parkwide SAR activity decreased during the same intervals. This strongly suggests that overcrowding is not the key factor influencing safety on Half Dome. This discordant trend warrants close observation over 5 to 10 y.

Death on the Dome: Epidemiology of Recreational Deaths on Half Dome in Yosemite National Park

One of the most popular destinations in Yosemite National Park is Half Dome. Overcrowding at the turn of the 21st century prompted a restriction of hiker access to cable handrails to the summit without technical rock climbing equipment. Prior epidemiological study of Half Dome deaths is not known to the authors. Our goal was to identify trends among all Half Dome-related fatalities in Yosemite National Park. Multimedia sources were searched for deaths involving the cable handrails, subdome, summit, technical climbing, or base jumping. Results are reported as mean±SD (range). Twenty-nine confirmed deaths occurred on Half Dome, with 2 additional deaths likely on Half Dome. Age was 32±14 (16-86) y; 4 were female. Activity at time of death included technical climbing (36%), suicide (26%), utilizing cable handrails (16%), hiking (16%), and base jumping (6%). Of the cable handrail-related fatalities, only 2 were due to weather. There were 3 medically related deaths due to cardiac disease and altitude. We identified 31 Half Dome deaths over 85 y. A minority were attributable to unfavorable weather or unskilled hiking participants. Climber registration could provide dependable denominators for accident incidence statistics. A renewed focus on suicide prevention is warranted.

Dike intrusion and deformation during growth of the Half Dome pluton, Yosemite National Park, California

Dike intrusion and deformation during growth of the Half Dome pluton, Yosemite National Park, California

Dike intrusion and deformation during growth of the Half Dome pluton, Yosemite National Park, California

Dike intrusion and deformation during growth of the Half Dome pluton, Yosemite National Park, California

Death on the Dome: Epidemiology of Recreational Deaths on Half Dome in Yosemite National Park

Half Dome is a popular destination in Yosemite with inconsistent public reporting of recreational mortality. The highest number of deaths in a single source is 20. Multimedia sources describing deaths involving the cables, summit, climbing, or base jumping were included. Deaths occurring on trails were excluded. Twenty-nine deaths occurred on Half Dome, with 2 additional deaths likely. The earliest was in 1930. The rate of 1 to 2 deaths per decade ended in the 1980s, which saw 8 fatalities. The 2000s had 9 fatalities. This decade has 4 deaths currently. The typical profile is a 32-year-old hiking man (only 4 women were reported); the median age is 27 years (range 16–86). Hikers (12; 39%) predominated, followed by 9 climbers (29%). The most common mechanism was climbing incidents related to lost anchors (5), free climber falls (3), and head injury from rock fall (1). Fatal hiker falls from the cables (7) were occasionally weather related (3), and 71% (5) occurred on descent. Lightning caused 3 summit deaths and a cable-related death. Medical mortality, in 3 hikers, was attributed to cardiac causes (2) and altitude illness (1). There were 8 suicides (29%). Base jumping fatalities (2) resulted from chute malfunction and wind slamming a jumper into Half Dome’s face. We identified 31 Half Dome deaths, the highest published. A minority of deaths were attributable to unfavorable weather or unskilled hikers, despite this being a popular assertion. Climber accidents, often unpublicized, challenge the assumption that this increasingly popular sport is safe. These findings urge a particular educational focus on accidents during descent of the cables, a renewed focus on suicide prevention, and prompt consideration of permitting climber access to reduce mortality on Half Dome.

Igneous or metamorphic? Hornblende phenocrysts as greenschist facies reaction cells in the Half Dome Granodiorite, California

The Half Dome Granodiorite, Yosemite National Park, California, is recognized in the field by euhedral, fresh-looking, black hornblende phenocrysts up to 2 cm in length. This variety of granodiorite typifies intermediate-age hornblende-phyric units of Cretaceous nested plutonic suites in the Sierra Nevada batholith. Although only inclusions of feldspar are evident in hand samples, the phenocrysts are riddled with up to 50% inclusions of every major mineral found in the host granodiorite plus metamorphic minerals formed during cooling. Amphibole compositions within single phenocrysts vary from actinolite with less than 1 wt% Al 2 O 3 to magnesiohornblende with over 8 wt%. Elemental zoning within the amphibole is highly irregular on the micrometer scale, showing patches and polygonal zones with dramatically different compositions separated by sharp to gradual transitions. The chemical compositions of entire phenocrysts are equivalent to hornblende plus a small proportion of biotite, suggesting that the non-biotite inclusions are the result of metamorphism of the phenocrysts. Backscattered electron imaging shows evidence of brecciation that may have been the result of volume changes as hornblende was converted to actinolite. Pressure calculations using the Al-in-hornblende barometer show unreasonably wide variations on the micrometer scale that cannot have been produced by temperature or pressure variations during crystallization. These hornblende phenocrysts would thus be unsuitable for geobarometry, and caution must be used to avoid similarly zoned phenocrysts in the application of the Al-in-hornblende geobarometer.

Specificity of Testing in a Cardiac Rehabilitation Setting Resulting in a Patient's Return to High-Intensity Outdoor Activity Following Aortic Dissection Repair

A 66-year-old man who had undergone aortic dissection repair a year earlier sought to assess the feasibility of returning to the high-intensity outdoor activities he had long enjoyed. In response to his inquiry, the cardiac rehabilitation staff at Baylor Hamilton Heart and Vascular Hospital designed a comprehensive testing plan that simulated the specific movements and anticipated cardiac requirements associated with his goal activities. The activities included 1) lifting and manipulating a 50-pound suitcase, 2) hiking to the top of Half Dome in California's Yosemite National Park, and 3) scuba diving. To illustrate our approach, we describe some of the tests that were performed and report the results. After analyzing the detailed physiological data collected during testing, we provided the patient with an exercise prescription and specific guidelines that he could use to gauge his level of physical exertion during his outdoor adventures. Within approximately 6 months of testing, he successfully performed the goal activities without adverse symptoms.