During the mid Cenozoic, the Chocolate Mountains region of southeastern California experienced crustal extension slightly before, during, and after the main pulse of magmatism. This combined with mid-late Cenozoic faulting to locally uplift plutonic rocks interpreted to represent the plumbing system(s) for volcanic units, allowing an examination of both the extrusive and intrusive result of magmatism. Zircon U-Pb ages of from six magmatic units yield late Oligocene to early Miocene ages and correlate better with stratigraphic relationships than previously compiled ages. These units are four silicic volcanic units – Quechan volcanic rocks, tuff of Felipe Pass, ignimbrite of Ferguson Wash, and tuff of Black Hills – and two plutonic units – the granites of Mount Barrow and Peter Kane Mountain. Regarding contemporaneous plutonic systems as baseline comparisons, zircons from the volcanic units commonly record plutonic temperatures; interpreted to be solidus or near solidus temperature. Remobilization may be a common process leading to eruption. Quartz and zircon thermometers reveal the ignimbrite of Ferguson Wash and tuff of Black Hills magmatic systems evolved differently. Quartz yields temperatures of 700°C to ~750°C in both units with no core-rim trends. Cores of zircons from the ignimbrite of Ferguson Wash yield temperatures between 750°C and 890°C. Zircon rim temperatures are between 875°C and 950°C. Tuff of Black Hills zircon cores generally record temperatures of ~850°C and zircon rim temperatures are ~700°C. Rims from tuff of Black Hills zircon record the same temperature range as zircons from coeval granites. The temperature increase from core to rim in zircons from the ignimbrite of Ferguson Wash indicates reheating and that zircon grew later than and at higher temperatures than quartz. The low zircon temperatures from tuff of Black Hills reveals a system that was growing quartz and zircon at the same low, nearly solidus temperatures. Reasons for its eruption are not readily apparent in the thermal history of zircon and quartz. These two systems record different thermal histories than previously studied, younger systems like the Bishop tuff, in which quartz records late reheating just prior to eruption and a system that was growing quartz later and at higher temperatures than zircon.

Call number: LD2668 .T4 1978 K623 / Master of Science

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The Dos Cabezas Mountains lie in the northeastern most part of Arizona, in Cochise county. They area medium-sized range of some 150 square miles area, and are almost wholly surrounded by unconsolidated basin-fill material. Most of the range is composed of a number of Precambrian igneous and metamorphic rock masses. Its core is composed of a large, complex, terrain of Cretaceous intrusive volcanic breccias and magmatic aphanites. A large number of Laramide and mid-Tertiary intrusive plutons and dikes cut the range. The Precambrian rocks consist of eight granitoid plutons and three areas of phyllitic and argillitic metamorphosed sediments and volcanics. The metamorphic rocks display a primary greenschist facies dynamothermal metamorphic fabric and a later superimposed biotite-forming hornfelsic thermal metamorphic fabric. The metasediments are mostly phyllites and argillites, but contain over 10,000 feet of metaconglomerate showing marked primary cross-bedding. Many of the metamorphic units are weakly metamorphosed volcanic flows or tuff-contaminated fluvial clastic sediments. These rocks are all classified as Pinal Schist, although some may be equivalent Mazatzal Quartzite. The plutons consist of a pre-Pinal-metamorphism dacite porphyry stock, one quartz monzonite gneiss synkinematic with the Pinal dynamothermal metamorphism, and four gneissic quartz monzonite plutons which appear to post-date the Pinal metamorphism and imply a mild tectonic event at about 1450 million years ago, and two large post-kinematic quartz monzonite stocks which are of circa 1400 million years age. One of these latter stocks displays prominent rapakivi texture; this is considered to be the result of normal magmatic crystallization. The texture is caused by reaction breakdown of hornblende to form biotite among crystals floating in the magma, thereby extracting potassium from the magma and temporarily halting potash feldspar crystallization while allowing plagioclase crystallization. Rb-Sr dating of the plutons reveals that one of the older post-Pinal gneisses is 1470 ± 30 m.y. old, while the rapakivi is 1380 ± 30 m.y. old and the other large stock is 1425 m.y. old and has undergone a marked Sr redistribution at 1000 m.y., ago; this thermal event has biased all the Precambrian K-Ar ages in the northwestern part of the range toward 1000 m.y., also. A large complex assemblage of Cretaceous welded intrusive volcanic breccias underlies 17 square miles of the core of the range. They are largely composed of small angular fragments torn from foundering large fragments of surficial andesite flows, sinking in a fluidized bed. The gas source was a crystallizing magma at depth; entrained quartz and plagioclase crystals from this magma appear in the breccia ground mass. The breccias are cut by a large number of small mafic magmatic instrusives. Several large diabasic and quartz dioritic plutons of Cretaceous or Paleocene age appear in the range and mark Laramide plutonism. K-Ar data from all but the northwestern most part of the Precambrian rocks in the range display a remarkably uniform Paleocene age which reflects a Paleocene thermal metamorphism. Mid-Tertiary plutonism is recorded by several mafic dike sets, including one of "Turkey Track" andesite porphyry, a granodiorite stock, and numerous quartz veins. Basin and Range block faulting is not obvious in the range, but may account for its present high-standing nature, especially along the northern range margin. Dynamothermal metamorphism is recorded strongly in the Pinal Schist, and dynamic tectonism, at circa 1450 million years. Thermal metamorphism is recorded at 1000 million years, circa 55 million years, and circa 35 million years. Plutonism is recorded before Pinal metamorphism, during Pinal metamorphism, then over the 1470-1380 million year interval, in the Cretaceous-Paleocene Laramide interval, and in the mid-Tertiary Oligocene-Miocene interval.

Thesis (MSc (Botany and Zoology))--University of Stellenbosch, 2005. / The Dwarf Crag Lizard, Pseudocordylus nebulosus, is one of several relict ectotherm species associated with the mistbelt of the Cape folded mountain belt. Prior to this study, it was only known from a single locality in the Hottentots Holland Mountains. In this study, the distribution range and microhabitat preferences of P. nebulosus were determined and resource partitioning among the three melanistic cordylids (C. oelofseni, P. capensis and P. nebulosus), co-occurring in this area, investigated. Using the locality where P. nebulosus was first discovered as centerpoint, surveys were conducted in all directions and the occurrence of all three melanistic species recorded. The previous known range of P. nebulosus, of only 0.04 km2, was extended to 11 km2. Of the three melanistic cordylids, P. nebulosus has by far the smallest range, completely overlapping with the ranges of both the other two melanistic cordylids. Pseudocordylus nebulosus was found to show a distinct affinity for water bodies such as mountain streams and seepage areas. Distinct differences in resource partitioning were found among the three species regarding crevice selection, which will prevent any significant competition during periods of environmental stress. Cordylus oelofseni preferred small crevices at ground level, P. capensis preferred large rock structures high above ground level and P. nebulosus utilized intermediate sized rock structures. Because of its relatively small range and melanistic colour, P. nebulosus could be a key indicator species of environmental change. Although the lack of objective fire management and global warming may be immediate threats to the survival of this species, possible illegal collection due to the easy access via the popular hiking trail in the area, is probably less significant a threat than was previously thought. Although its known range has been extended considerably, it is recommended that the Vulnerable status of P. nebulosus be maintained. This study provides baseline data that could be useful in future monitoring programmes to predict declines and fluctuations. In the second part of this study, the aim is to provide information about sexual dimorphism in P. nebulosus and to discuss the observed variation in sexual size dimorphism among montane cordylids. Data were recorded for all P. nebulosus individuals encountered in the Landdroskop area (Hottentots Holland Mountains), irrespective of size and sex. The total sample of 87 lizards recorded, consisted of 26 adult males, 49 adult females and 12 indeterminates. Size at sexual maturity was determined at 60 mm snout-vent length (SVL) for both sexes. The highly female-biased adult sex ratio recorded for P. nebulosus, is considered to be due to sampling error, gravid females probably basking more than males, making them easier to locate during searches. Generation glands were found to be present in males only and the number present was significantly correlated to body size. Both adult males and adult females possessed active femoral glands, but males had significantly more than females. Females were found to reach larger body sizes than males, but adult males had relatively larger heads than females. No significant difference in scar frequency was found between the male and female samples. Variation in sexual size dimorphism among montane cordylids is discussed and the need for more comprehensive data pointed out. The female-biased sexual size dimorphism in P. nebulosus and its sister species, P. capensis, is tentatively ascribed to fecundity selection for offspring to be large at birth in order to survive in a predictable unfavourable environment at high altitudes. Sexual dimorphism in head size is ascribed to sexual selection, males probably being territorial as in many other cordylids.

No description available.

The Swisshelm Quartz Monsonite covers about two square miles on the western slope of the Swisshelm Mountains, Cochise County, Arizona. Field observation and petrographic study indicate that the quartz monsonite was derived by differentiation and late-stage alkali metasomation of probably a quartz dioritic magma rich in alkali and volatile constituents. The high concentration of the volatiles is believed to be of great importance in the development of the different facies and rock types. Four different facies of the Swisshelm Quartz Monsonite have been distinguished as (1) the normal facies, (2) the altered facies, (3) the fine-grained facies, and (4) the contact facies. Also, several aplite dikes, local beryl-bearing pegmatite patches, and numerous quartz veins are present and attributed to late magmatic differentiation. Inclusions of an early and late magmatic facies are sparcely disseminated through the quartz monsonite. The Swisshelm Quartz Monsonite magma has intruded and metamorphosed the Upper Paleozoic sediments of the Mace Group as well as the Lower Cretaceous sediments of the Bisbee Group. The metamorphism is of a contact metasomatic type to which the mineralogical and textural changes in the country rocks have been attributed.