Deep structure of the Baikal rift zone revealed by joint inversion of gravity and seismology

Abstract

[1] The question of plate boundary forces and deep versus shallow asthenospheric uplift has long been debated in intracontinental rift areas, particularly in the Baikal rift zone, Asia, which is colder than other continental rifts. As previous gravity and teleseismic studies support the dominance of opposing mechanisms in the Baikal rift, we reconsidered both data sets and jointly inverted them. This more effective approach brings insight into location of the perturbing bodies related to the extension in this region. Our new joint inversion method allows for inverting the velocity-density relationship with independent model parametrization. We obtain velocity and density models that consistently show (1) crustal heterogeneities that coincide with the main tectonic features at the surface, (2) a faster and denser cratonic mantle NW of Lake Baikal that we relate to the thermal contrast between old and depleted Archean (Siberian platform) and Paleozoic orogenic belt (Sayan-Baikal belt), (3) three-dimensional topographic variations of the crust-mantle boundary with well-located upwarpings, and (4) the lithosphere-asthenosphere boundary uplift up to 70 km depth with a NW dip. Our resulting velocity and density models support the idea of a combined influence of lithospheric extension and inherited lithospheric heterogeneities for the origin of the Baikal rift zone.INDEX TERMS: 1234 Geodesy and Gravity: Regional and global gravity anomalies and Earth structure; 7218 Seismology: Lithosphere and upper mantle; 8122 Tectonophysics: Dynamics, gravity and tectonics; 8180 Tectonophysics: Evolution of the Earth: Tomography; KEYWORDS: joint inversion, gravity, seismology, intracontinental rift, lithospheric structures, Baikal rift zone Citation: Tiberi, C., M. Diament, J. Déverchère, C. Petit-Mariani, V. Mikhailov, S. Tikhotsky, and U. Achauer, Deep structure of the Baikal rift zone revealed by joint inversion of gravity and seismology,

Mantle transition zone discontinuities beneath the Baikal rift and adjacent areas

“…The observed variation of the MTZ thickness is consistent with seismic tomography results. Although most seismic tomography studies [e.g., Achauer and Masson , 2002; Gao et al , 1994b, 2003; Tiberi et al , 2003] revealed low‐velocity regions in the upper mantle beneath the rift, there still lacks strong evidence for such anomalies extending to the MTZ. On the contrary, a recent seismic tomography study [ Zhao et al , 2006] suggested a high‐velocity region with a magnitude of 1–2% in the MTZ beneath the rift.…”

“…Thus the use of a standard earth model in calculating the moveout times and the location of the ray‐piercing points has insignificant effects on the main conclusions of the study, i.e., the BRZ is underlain by a thickened MTZ, as most clearly suggested by the uplift of the d 410. In addition, the currently available velocity models for the study area [e.g., Zhao et al , 2006; Gao et al , 2003; Tiberi et al , 2003; Achauer and Masson , 2002; Petit et al , 1998] show considerable inconsistencies with each other. This will make it difficult technically to use any one of them for the correction.…”

“…While most other continental rifts such as the Rio Grande and East African rifts were found to be underlain by a low‐velocity zone in the upper mantle and even the mantle transition zone (MTZ, 410–660 km depth range) [e.g., Davis , 1991; Slack et al , 1996; Achauer and Masson , 2002; Wilson et al , 2005a], contradictory seismic tomography results were obtained beneath the BRZ. Most studies suggested low seismic velocities in the upper mantle beneath the rift [e.g., Gao et al , 1994b, 2003; Achauer and Masson , 2002; Friederich , 2003; Brazier and Nyblade , 2003; Tiberi et al , 2003; Zhao et al , 2006], and others did not find such anomalies [e.g., Petit et al , 1998]. The depth extent of the low‐velocity anomaly differs greatly among the studies, from less than 100 km to as deep as 600 km.…”

The Digital Map of the Pliocene–quaternary Crustal Faults in the Southern East Siberia and the Adjacent Northern Mongolia

“…Краевой шов Сибирской платформы блокирует распространение рифтогенных процес-сов к западу, а его изогнутая геометрия влияет на кинематические параметры существующих раз-рывных нарушений, активизированных в позднем кайнозое под воздействием СЗ-ЮВ растяжения. Независимо от механизма формирования Байкаль-ской рифтовой зоны, который объясняют подъ-емом аномальной мантии и/или воздействием на подошву литосферы астеносферного потока в ЮВ направлении, а также сжатием в СВ направлении, связанным с Индо-Евразийской коллизией [Molnar, Tapponnier, 1975;Zorin, 1981;Petit et al, 1998;Logachev et al, 2000;Zorin et al, 2003;Tiberi et al, 2003;Lebedev et al, 2006;Kulakov, 2008;Petit, Déverchère, 2006;San'kov et al, 2011;Sankov et al, 2015;и мн. др.…”

2D joint inversion of geophysical data using petrophysical clustering and facies deformation

“…To reduce this nonuniqueness, recent approaches have been developed in using multiple geophysical data sets especially when their sensitivity maps are complementary to each other (e.g., Gallardo-Delgado et al, 2003;Tiberi et al, 2003;Buland and Kolbjømsen, 2012). Various structural approaches have been developed for the joint inversion of geophysical data (e.g., Haber and Oldenburg, 1997;Zhang and Morgan, 1997).…”