Abstract Many archaeological sites with jadeitite artefacts are known in the Caribbean region, but defining the source of the raw material is a major problem because of great mineralogical heterogeneity both in potential sources and in artefacts. The archaeological settlement site of Playa Grande on the northern coast of the Dominican Republic is particularly significant because it yielded evidence of on-site axe manufacture, and lies only 20–30 km NE of a recently discovered potential source area of serpentinite mélanges in the nearby Río San Juan Complex (RSJC). A suite of nine artefacts was chosen from a collection of over 100 excavated woodworking tools rich in jadeite, as well as two blueschist artefacts. Permission to perform destructive analysis allowed data on petrography, mineral chemistry and bulk-rock chemistry to be obtained. Seven of the nine artefacts are jadeitite sensu stricto (>90 vol% jadeite), which are identical to material known from the RSJC. Two artefacts are jadeite–lawsonite rocks. These and the two blueschists show only minor differences from corresponding rocks of the RSJC source. With this direct linking of source and site material, it is now possible to better define source discriminators for the Caribbean and to assess sampling bias.

Detailed stratal tilt information for radioisotopically dated Tertiary rocks in the Lemitar Mountains of the central Rio Grande rift allows discrimination of two episodes of extension in the late Oligocene (largely 28.6 to 27.4 Ma) and middle to late Miocene (16 to 10 Ma). Rapid deformation in the late Oligocene (at least 25% extension) produced narrow, wedge-shaped accumulations of ash-flow tuffs and mafic lavas within half grabens defined by closely spaced (2 to 5 km) planar-rotational normal faults. Volcanic accumulation rates during this episode were sufficient to bury the developing fault-block topography, resulting in preservation of only minor amounts of intercalated sedimentary rocks. Following a period of weak extension in the early Miocene, rates of extensional strain again began to increase in the early middle Miocene (about 16 Ma) and continued to increase until about 10 Ma, when a more moderate rate ensued. During the time interval of 16 to 10 Ma, the Lemitar Mountains area was extended about 30% along widely spaced (5 to 15 km) planar-normal faults. Increased stratal-tilt rates in the middle Miocene caused the development of accommodation space to locally exceed sediment supply on the down-thrown side of a major intrabasinal fault (Silver Creek fault), resulting in topographic closure and the development of playa deposits within the lower Santa Fe Group (Popotosa Formation). As stratal-tilt rates further increased in the late Miocene, fluvial-lacustrine sedimentation offlapped toward narrow zones of maximum subsidence along active faults, causing the carving of widespread unconformities on older sediments on hanging-wall dip slopes. As tectonism waned in the latest Miocene-early Pliocene, sediment supply exceeded the development of accommodation space, resulting in onlap and aggradation of the upper Santa Fe Group (Sierra Ladrones Formation) that enabled the eventual integration of an axial-fluvial system (ancestral Rio Grande) between the longitudinally arrayed half grabens to the north and south of the Socorro Basin. The late Oligocene episode of rapid extension appears to be related to strain focusing by local thermal weakening due to voluminous concurrent magmatism in the area. In contrast, the late Miocene extensional event may be of regional scale, as shown by evidence for contemporaneous tectonism in other areas and the development of widespread unconformities between Miocene and Pliocene deposits of the Santa Fe Group in many basins of the Rio Grande rift.

Abstract 0.0 Exit to eastbound Interstate Highway 40 toward Flagstaff from Andy Devine Avenue in Kingman. 0.1 Behind and to the left in the foothills of the Cerbat Mountains is the Kingman Feldspar mine, a 1700 Ma zoned pegmatite (Heinrich, 1960; Wasserburg and Lanphere, 1965) that intrudes Early Proterozoic granitic rocks. Minerals of principal economic interest are microcline and allanite. 0.9 Prominent strata at the top of the Grand Wash Cliffs (fig. 26) in the far distance at 9:00 are Cambrian through Mississippian limestone and associated sedimentary rocks. Rocks beneath the Paleozoic section are mainly Early Proterozoic foliated to gneissic granite to granodiorite. Most of the Proterozoic rocks of the Grand Wash Cliffs are unmapped; only the Garnet Mountain area (Blacet, 1975; Theodore and others, 1982) has been mapped in any detail. 2.6 To the left and north is Hualapai Valley, which drains to the north into the playa of Red Lake at the northern end of the Cerbat Mountains. One of the thickest accumulations of halite in Arizona (minimum of 4,000 ft; possibly as thick as 10,000 ft) underlies Red Lake and the Hualapai Valley south of Red Lake (Peirce, 1973; 1976). 3.8 Crossing Rattlesnake Wash. Hills to our right are composed of mildly flow foliated, 1400 Ma coarse-grained porphyritic granite of Rattlesnake Hill 1400 (Kesler, 1976). 5.1 Outcrops on the right that weather into large bouldery piles are the granite of Rattlesnake Hill (fig. 24). 6.2 Exit 59, DW Ranch Road, provides access into the northern Hualapai Mountains. Roadcuts