Abstract The Farallon Resources, Ltd., Campo Morado precious metal-rich, massive sulfide deposits occur in a Lower Cretaceous, bimodal, calc-alkaline volcanic sequence that forms a major, north-trending belt in the Guerrero terrane in northeastern Guerrero state, Mexico. During Upper Cretaceous to lower Tertiary greenschist facies regional metamorphism, the rocks were deformed strongly into a northeast-verging fold and thrust belt. Three stages of later, weak deformation were dominated by kink folds, broad warps, and extensional faults, respectively. Most deposits occur at the stratigraphic contact of a sequence of felsic flows and het-erolithic volcaniclastic rocks with overlying chert and argillite-sandstone. The Reforma and El Rey deposits are on the overturned limb of a major thrusted anticline, and the Naranjo, South Naranjo, and El Largo deposits are on the upright limb of the same fold to the south. The La Lucha and San Rafael showings are in a thrust plate west-southwest of South Naranjo. In the Reforma and South Naranjo massive sulfide deposits, gold, silver, lead, and zinc are concentrated near the stratigraphic top, and copper is concentrated near the stratigraphic base. Major minerals are pyrite, quartz, ankerite, sphalerite, galena, and chalcopyrite. Gold and silver occur in gold-electrum, ten-nantite, and freibergite. The underlying pyrite-quartz stockworks contain chalcopyrite, sphalerite, and chlorite. In the stratigraphic footwall, hydrothermal alteration minerals are pyrite, quartz, chlorite, and ferroan dolomite/ankerite. In the stratigraphic hanging wall, hydrothermal alteration minerals are sericite, calcite-dolomite, and lesser clays and quartz. The deposits belong to a low-sulfidation, volcanogenic massive sulfide system formed in a subaqueous environment, and are of the bimodal, siliciclastic, massive sulfide type.

Abstract The Adirondack dome of northeastern New York State is located near the eastern edge of the North American craton. As the southeastern extension of the Grenville Province, it constitutes the largest well-exposed Proterozoic crystalline terrain in the United States. COCORP has recorded a series of lines across the dome and the onlapping Paleozoic cover sequence (Brown et al, 1982; see location map Figure 1). In this article, line drawings are presented for lines 1, 7 and 10 (Figure 2) and data from line 7 is reproduced (Figure 3). Despite the extreme degree of deformation and metamorphism of the surface rocks, reflections from throughout the crust were recorded. The most striking result of this survey is a set of layered, gently northwest-dipping reflectors observed to span a depth range of about 17 to 25 km (10.5 to 15.5 mi) beneath the Marcy anorthosite massif. Such an observation is thusfar unique, but the geological interpretation of these data are still ambiguous. The rocks of the Adirondack mountains comprise a multiply-folded stratigraphic sequence of highgrade metasedimentary and metavolcanic rocks which are intruded by syntectonic bodies of metanorthosite and metagabbro (Isachsen and Fisher, 1970). Recent studies (McLelland and Isachsen, 1980) suggest that at least four phases of folding have occurred, and that the complex surface outcrop pattern is produced by the interference of large nappe structures with wavelengths of many kilometers. The Highlands region, which includes most of the Adirondack dome (Figure 1), consists principally of granulite facies rocks which were buried to a depth of 20 to 25 km (12.4 to 15.5 mi) during peak metamorphism (Bohlen, Essene, and Hoffman, 1980), The Highlands are bounded on the northwest by the Carthage-Colton mylonite zone, beyond which are the Lowlands, dominated by metasedimentary rocks equilibrated at somewhat lower pressures (equivalent to 16 to 21 km, or 10 to 13 mi, depth) (Brown, Essene, and Kelly, 1978). The regional exposure of rocks metamorphosed to such high pressures raises the question, how were they brought to the surface? Since the Adirondack crust is now of normal thickness, was it formerly much thicker? If so, was this greater thickness caused by continental collision and subduction, or by some kind of igneous underplating? Several models have been proposed (Baer, 1981; Dewey and Burke, 1973; Seyfert, 1980; Wynne-Edwards, 1976) which represent the Grenville orogeny variously as the product of large-scale continental obduction, crustal thickening by basement reactivation to absorb continental convergence, or drift of a continent over a hot zone or chain of hot spots. A possibly related question concerns the current domical structure of the Adirondack basement. The present surface topography is apparently post-Devonian (Crough, 1981) but the age of uplift is uncertain. Isachsen (1975) has argued from geodetic data that the Adirondack dome is still rising, but this theory has been questioned (Brown and Reilinger, 1980).

Abstract Seismic reflection profiling in northeastern Kansas by COCORP was initiated to investigate several prominent features of the midcontinent, including the Midcontinent Geophysical Anomaly (MGA), which has been associated with a buried extension of the Keweenawan rift, and the Nemaha Uplift, part of a crystalline basement block uplifted in Pennsylvanian time (Figure 1). The MGA is characterized by gravity and aeromagnetic highs extending from the Lake Superior region to near the Kansas-Oklahoma border (Figure 1, 2, 3; see Yarger, 1981). Surface exposures in the north, as well as samples drilled along the trend of the anomalies, indicate that mafic volcanic rock and associated clastic sediments were deposited in a narrow trough formed by continental rifting of Keweenawan age (1.1 b.y. ago; see also King and Zietz, 1971; Chase and Gilmer, 1973). The Nemaha Uplift is a north-south trending feature extending from Omaha, Nebraska to northern Oklahoma (Figure 1). in northeastern Kansas the Nemaha separates the Forest City basin from the Salina basin to the west (Steeples, in press). The origin of the Nemaha Uplift and associated Humboldt border fault (Figure 4) is enigmatic, but their lateral proximity and subparallelism to the MGA suggests that they may represent reactivated rift structures (Yarger, 1981).

Abstract The Consortium for Continental Reflection Profiling (COCORP) recorded deep seismic profiles across the Southern Oklahoma aulacogen. The profiles run from the Hardeman basin, across the Wichita Uplift, and into the northern part of the Anadarko basin. The location of the COCORP lines and major geologic features are shown on Figure 1. The three major findings of the survey include evidence for: (1) an extensive Proterozoic basin lying south of the Wichita Mountains; (2) thrusting of the Wichita Mountains over the Anadarko basin by several kilometers; and (3) anticlinal structures within the Anadarko basin that can be interpreted as cored by blind listric thrust faults. These features are illustrated on the two seismic lines and the generalized geologic cross section. The following summary is abstracted from more detailed description published by Brewer et al (1981, in press). The Southern Oklahoma aulacogen is a major tectonic element of the southern midcontinent. The exact definition of the aulacogen and even the time of the initiation is unclear, with some authors using the term for the deep Paleozoic Anadarko basin (the most obvious manifestation), while others suggest it also includes the Wichita Mountains and Hardeman basin to the south. The Southern Oklahoma aulacogen was placed within a plate tectonic framework by Burke and Dewey (1973) and Hoffman et al (1974), who suggested that the aulacogen may represent a "failed" rift arm which was reactivated by Pennsylvanian deformation associated with closure of an ocean to the southeast. Initially, subsidence was thought to have started in the Late Cambrian with transgression of the basal Reagan sandstone over Precambrian basement. However, extensive studies by Ham et al (1964) showed that thick sequences of pre-Reagan sandstone, rhyolites, basalts, and metagraywackes are also present in this area. Ham et al (1964) suggested that major downwarping of the whole area occurred in the Late Precambrian or Early Cambrian, followed in the middle Cambrian by outpouring of basalts over the graywackes and intrusion by gabbros. Faulting and differential erosion was followed in the middle Cambrian by extrusion of silicic volcanic fields and intrusion of granites, forming what is now the Wichita Mountain block. Paleozoic subsidence and sedimentation was then concentrated in the Anadarko basin with deformation culminating in the Pennsylvanian.