Miocene‐Pliocene half‐graben evolution, detachment faulting and late‐stage core complex uplift from reflection seismic data in south‐east Arizona

Abstract

A B S T R A C TReflection seismic data show that the late Cenozoic Safford Basin in the Basin and Range of south-eastern Arizona, is a 4.5-km-deep, NW-trending, SW-dipping half graben composed of middle Miocene to upper Pliocene sediments, separated by a late Miocene sequence boundary into lower and upper basin-fill sequences. Extension during lower basin-fill deposition was accommodated along an E-dipping range-bounding fault comprising a secondary breakaway zone along the north-east flank of the Pinaleiio Mountains core complex. This fault was a listric detachment fault, active throughout the mid-Tertiary and late Cenozoic, or a younger fault splay that cut or merged with the detachment fault. Most extension in the basin was accommodated by slip on the range-bounding fault, although episodic movement along antithetic faults temporarily created a symmetric graben. Upper-plate movement over bends in the range-bounding fault created rollover structures in the basin fill and affected deposition within the half graben. Rapid periods of subsidence relative to sedimentation during lower basin-fill deposition created thick, laterally extensive lacustrine or alluvial plain deposits, and restricted proximal alluvian-fan deposits to the basin margins. A period of rapid extension and subsidence relative to sediment influx, or steepening of the upper segment of the range-bounding fault at the start of upper basin-fill deposition resulted in a large downwarp over a major fault bend. Sedimentation was restricted to this downwarp until filled. Episodic subsidence during upper basin-fill deposition caused widespread interbedding of lacustrine and fluvial deposits. Northeastward tilting along the south-western flank of the basin and north-eastward migration of the depocentre during later periods of upper basin-fill deposition suggest decreased extension rates relative to late-stage core complex uplift.Reflection seismic data were acquired by industry and processed using a typical processing flow. The Amoco data, which include lines 1, 3A, 3B and 4 (Figs 1 and 3 -9 , were acquired using a split spread configuration with a 96-channel system. T h e station interval was 33.5m (1lOft) with a far offset of 1.6km (1 mile). Vibration points were at every other station (67x11 (220 ft)) using a 12-s up-sweep from 14 to 80 Hz. These data were reprocessed at the University of Arizona using the SierraseisrM processing package in order to preserve relative true amplitudes for seismic facies interpretation. 132 0 (1986) The relationship between the geometry of normal faults and that of the sedimentary layers in their hanging walls. 3. struct. Geol., 8, 897-909. WYNN, J. C. (1981) Complete Bouguer gravity anomaly map of the Silver City I" X 2" quadrangle, New Mexico-Arizona.

Neogene supradetachment basin development on Crete (Greece) during exhumation of the South Aegean core complex

“…Associated with extension and core complex exhumation, subsidence will lead to the formation of supradetachment basins (Dinter & Royden, 1993; Friedmann & Burbank, 1995; Kruger et al , 1995; Janecke et al , 1999; Kocygit et al , 1999; Sánchez‐Gómez et al , 2002; Sözbilir, 2002). These basins have frequently been described in 2D cross‐section based on seismic analysis (e.g.…”

“…These basins have frequently been described in 2D cross‐section based on seismic analysis (e.g. Kruger et al , 1995) or based on field analysis (e.g. Dorsey & Becker, 1995; Sözbilir, 2002).…”

Oligocene‐Miocene Exhumation of the Pinaleño Metamorphic Core Complex, Southeastern Arizona: Support for Magmatism and Plate Margin Reorganization as Controls on Regional Exhumation Trends

“…(1995) based on the age of nearby volcanic rocks that show a transition from intermediate, calc‐alkaline compositions to more mafic, alkaline compositions. Seismic images from the Safford Basin show that the Pinaleño detachment fault is cross‐cut by a high‐angle normal fault located at the range front, which helped accommodate uplift of the Pinaleño Mountains and subsidence of the Safford Basin in Miocene time (Kruger & Johnson, 1994; Kruger et al., 1995). Scoggin, Reiners, et al.…”

“…The transition from core complex style extension to Basin and Range style extension is recorded by reflection seismic data from the Safford Basin, located in the hangingwall of the Pinaleño detachment fault, that shows (a) a high-angle normal fault cross-cutting a low-angle detachment fault and (b) a major unconformity in the subsurface separating faulted, rotated and eroded sediments below relatively flat-lying sediments (Kruger & Johnson, 1994). The age of this unconformity is not well constrained, but was estimated to be 12-13 Ma by Eberly and Stanley (1978) based on regional correlation to basins located further west and ∼17 Ma by Kruger et al (1995) based on the age of nearby volcanic rocks that show a transition from intermediate, calc-alkaline compositions to more mafic, alkaline compositions. Seismic images from the Safford Basin show that the Pinaleño detachment fault is crosscut by a high-angle normal fault located at the range front, which helped accommodate uplift of the Pinaleño Mountains and subsidence of the Safford Basin in Miocene time (Kruger & Johnson, 1994;Kruger et al, 1995).…”

Seismic reflection evidence for detachment polarity beneath a major accommodation zone, west-central Arizona

“…The overall listric geometry of the White Tank detachment fault northeast of the core complex (Fig. 4) is similar to that of other core complexes that contain an inferred secondary breakaway zone (e.g., Spencer, 1984;Spencer and Reynolds, 1989;Kruger, 1991;Kruger and Johnson, 1994;Kruger et al, 1995;Dorsey and Becker, 1995).…”