Thermal and Barometric Constraints on the Intrusive and Unroofing History of the Black Mountains: Implications for Timing, Initial Dip, and Kinematics of Detachment Faulting in the Death-Valley Region, California

Unroofing of the Black Mountains, Death Valley, California, has resulted in the exposure of 1.7 Ga crystalline basement, late Precambrian amphibolite facies metasedimentary rocks, and a Tertiary magmatic complex. The Ar-40/Ar-39 cooling ages, obtained from samples collected across the entire length of the range (>55 km), combined with geobarometric results from synextensional intrusions, provide time-depth constraints on the Miocene intrusive history and extensional unroofing of the Black Mountains. Data from the southeastern Black Mountains and adjacent Greenwater Range suggest unroofing from shallow depths between 9 and 10 Ma. To the northwest in the crystalline core of the range, biotite plateau ages from approximately 13 to 6.8 Ma from rocks making up the Death Valley turtlebacks indicate a midcrustal residence (with temperatures >300-degrees-C) prior to extensional unroofing. Biotite Ar-40/Ar-39 ages from both Precambrian basement and Tertiary plutons reveal a diachronous cooling pattern of decreasing ages toward the northwest, subparallel to the regional extension direction. Diachronous cooling was accompanied by dike intrusion which also decreases in age toward the northwest. The cooling age pattern and geobarometric constraints in crystalline rocks of the Black Mountains suggest denudation of 10-15 km along a northwest directed detachment system, consistent with regional reconstructions of Tertiary extension and with unroofing of a northwest deepening crustal section. Mica cooling ages that deviate from the northwest younging trend are consistent with northwestward transport of rocks initially at shallower crustal levels onto deeper levels along splays of the detachment. The well-known Amargosa chaos and perhaps the Badwater turtleback are examples of this "splaying" process. Considering the current distance of the structurally deepest samples away from moderately to steeply east tilted Tertiary strata in the southeastern Black Mountains, these data indicate an average initial dip of the detachment system of the order of 20-degrees, similar to that determined for detachment faults in west central Arizona and southeastern California. Beginning with an initially listric geometry, a pattern of footwall unroofing accompanied by dike intrusion progress northwestward. This pattern may be explained by a model where migration of footwall flexures occur below a scoop-shaped banging wall block. One consequence of this model is that gently dipping ductile fabrics developed in the middle crust steepen in the upper crust during unloading. This process resolves the low initial dips obtained here with mapping which suggests transport of the upper plate on moderately to steeply dipping surfaces in the middle and upper crust.

Barry Saltzman and the Theory of Climate

Barry Saltzman was a giant in the fields of meteorology and climate science. A leading figure in the study of weather and climate for over 40 yr, he has frequently been referred to as the "father of modern climate theory." Ahead of his time in many ways, Saltzman made significant contributions to our understanding of the general circulation and spectral energetics budget of the atmosphere, as well as climate change across a wide spectrum of time scales. In his endeavor to develop a unified theory of how the climate system works, lie played a role in the development of energy balance models, statistical dynamical models, and paleoclimate dynamical models. He was a pioneer in developing meteorologically motivated dynamical systems, including the progenitor of Lorenz's famous chaos model. In applying his own dynamical-systems approach to long-term climate change, he recognized the potential for using atmospheric general circulation models in a complimentary way. In 1998, he was awarded the Carl-Gustaf Rossby medal, the highest honor of the American Meteorological Society "for his life-long contributions to the study of the global circulation and the evolution of the earth's climate." In this paper, the authors summarize and place into perspective some of the most significant contributions that Barry Saltzman made during his long and distinguished career. This short review also serves as an introduction to the papers in this special issue of the Journal of Climate dedicated to Barry's memory.