Evidence of ongoing crustal deformation related to magmatic activity near Socorro, New Mexico

Abstract

Recent leveling conducted by the National Geodetic Survey in central New Mexico provides new evidence of ongoing tectonic deformation associated with the Rio Grande rift. A 1980-1981 resurvey over suspected midcrustal and shallow magma bodies near Socorro, New Mexico, indicates continued uplift averaging 0.18 cm/yr between 1951 and 1980. Although this rate is somewhat smaller than that reported previously (0.34 cm/yr between 1912 and 1951), the new observations suggest possible systematic errors in the earlier surveys. Reanalysis of the earlier data gives an average rate of 0.23 cm/yr from 1912 to 1951, consistent not only with the new releveling observations but also with geomorphic evidence which indicates an average uplift rate of 0.18 cm/yr over the past 20,000 years. Thus the rate of uplift may be relatively constant. The new releveling measurements also confirm prominent zones of subsidence flanking the central uplift. Modeling the deformation, together with other geophysical observations, suggests that the movements in the Socorro area are likely associated with the 19-km-deep Socorro magma body. Although the details of magma movements are not well constrained, plausible models include flow of magma from the periphery toward the central magma chamber and flow from sources in the lower crust into the midcrust. Horizontal strain calculated for these models is generally consistent with the small strain reported from repeated trilateration surveys in the Socorro area. The Rio Grande rift is clearly an important site for future monitoring of crustral deformation. INTRODUCTION AND GEOLOGIC SETTING Geophysical and geological observations indicate the existence of magma at intermediate and shallow depths in the crust beneath the Rio Grande rift in the vicinity of Socorro, New Mexico [Sanford et al., 1973, 1977a, b; Sanford, 1983; Brown et al., 1979; Shuleski, 1976; Johnston, 1978; Roach, 1982]. The most prominent magma body lies at a depth of 19-20 km and has the shape of a thin sill with a minimum areal extent of 1700 km 2 [Rinehart et al., 1979]. In addition, shallow magma intrusions predominantly between 5 and 10 km below the surface have been inferred from m,•croearthquake seismograms [e.g., Sanford, 1983]. Evidence that the magma bodies are currently active includes (1) anomalously high earthquake activity (including swarms) in the Albuquerque to Socorro section of the rift, as compared to other parts of the rift [Sanford et al., 1979, 1981], (2) geomorphic and other geologic evidence for post-Pliocene activity in the Socorro area [Sanford et al., 1972; Chapin and Seager, 1975; Bachman and Mehnert, 1978; Ouchi, 1983-1, and (3) geodetic evidence for historic crustal deformation above the magma body [Reilinger and Oliver, 1976; Reilinger et al., 1980]. This paper reports and interprets new leveling measure-ments conducted in 1980 and 1981 by the National Geodetic Survey (NGS) in the Socorro area of the Rio Grande rift. The new observations confirm previously published results of crustal uplift apparently relate...

Sombrero Uplift Above the Altiplano-Puna Magma Body: Evidence of a Ballooning Mid-Crustal Diapir

“…S2). The monotonic uplift in the center of the APULVZ contrasts with episodic inflation typical of shallow magma bodies in the upper crust (7,11,20) but is similar to deformation associated with another large mid-crustal magma body in the Rio Grande Rift in New Mexico (21,22).…”

“…In both cases, the modeled source of inflation is smaller than the seismically imaged magma body (22). There is indication of subsidence around the central uplift due to the SMB (10,21,22), although the rates of both uplift and subsidence due to the SMB are smaller than those due to the Altiplano-Puna Magma Body and therefore subject to greater uncertainties (Fig. 3).…”

Denudation, vertical crustal movements and sedimentary basin infill

“…Since soil may form from saprolite, defined as ,>soft, friable, isovolumetrically weathered bedrock that retains the fabric and structure of the Yellowstone (Pelton & Smith 1982) Socorro (Reilinger & Oliver 1976;Larsen et al 1985) Iwo Jima (Kaizuka et al 1983) Taiwan (Li 1976) Huon (Chappell 1974) Mean, South Island, New Zealand (Wellman 1979) Maximum, South Island (ibid) Mean, Central Japan (Yoshikawa 1974) Japan, Boso (Matsuda et al 1978) Japan, Holocene (Ota, 1985) Japan, Pleistocene (ibid) Mean uplift rates for 100Ka terraces from U-Th dating studies (Muhs et al 1990) 0 E1 Asnam, Algeria (Meghraoui 0.47 et al 1988) 0.2-0.9 Ventura, California (Rockwell et al 1988 (Okaya & Thompson 1985) Megara basin footwall to Skinos-Psatha fault, Central Greece for 100 Ky (Leeder et al 1991) Gulf of Suez for 10 My (Jackson et al 1988) Tibet, last 2Ma…”

Evidence for on‐going inflation of the Socorro Magma Body, New Mexico, from interferometric synthetic aperture radar imaging

“…Three leveling surveys conducted in the Socorro area in 1911, 1951, and 1980-1981 have measured average uplift rates of a few millimeters per year [Larsen et al, 1986]. …”