Insights Into the Structure of the Mongol-Okhotsk Suture Zone, Adaatsag Ophiolite, and Tectonic Boundaries of the Central Asian Orogenic Belt (Mongolia) From Electrical Resistivity Imaging and Seismic Velocity Models

The Mongol-Okhotsk suture and the Adaatsag ophiolite belt are associated with the closure of the Mongol-Okhotsk paleo-ocean and are located within the Central Asian Orogenic Belt (CAOB) and Mongolia. The suture zone is flanked by volcanic-plutonic belts that host significant metallogenic zones, containing deposits of copper and gold. The tectonic evolution of this region is not fully understood and the lithospheric structure has been poorly studied. We analyze magnetotelluric data and generate a model of the electrical resistivity distribution across this region. Whereas the northern segment has a sharp transition from a high-resistivity upper crust to a low-resistivity lower crust, as observed beneath the Hangai Dome, the southern segment does not show this transition. A wide, low-resistivity zone (1-100 Omega m) imaged in the crust and lithospheric mantle is coincident with the Mongol-Okhotsk suture and ophiolite, revealing a clear and significant lithospheric-scale feature. Across the profile, numerous narrow, vertically oriented, low-resistivity features (1-100 Omega m) are spatially associated remarkably well with the proposed boundaries of tectonic domains. These results confirm ideas about the development of the CAOB. Some of these low-resistivity features are beneath the surface locations of large mineral zones, and likely represent fossil fluid pathways. We show congruent seismic velocity models for comparison and the results show a large-scale low-velocity anomaly (decrease of 2%-3%) that correlates with the location of the low-resistivity anomaly below the Mongol-Okhotsk suture. The geophysical results, combined with geological and geochemical data, provide insights into the structure of this region and help shed light on unanswered questions. When the ancient Mongol-Okhotsk ocean closed, due to subduction from tectonic re-arrangement, it left the Mongol-Okhotsk suture zone and the Adaatsag ophiolite as a trace of its location. Similarly, other tectonic boundaries are hypothesized to exist from terrane accretion across the Central Asian Orogenic Belt (CAOB) and Central and Southern Mongolia, which is located between the Siberian and North China cratons. This region is also rich in economically significant copper and gold deposits. The tectonic evolution of this region and especially the lithospheric structure is not fully understood and has been poorly studied. We analyze magnetotelluric data and generate a model of the electrical resistivity distribution. Additionally, we show models of the seismic velocity for comparison. Examining multiple complementary geophysical models helps to reduce interpretation uncertainty. Anomalies are observed in both models (e.g., low resistivity and low velocity). The suture zone is proven to be a strong lithospheric-scale boundary. The proposed boundaries of tectonic domains are also imaged, confirming ideas about the development of the CAOB, and solving some controversies. Lithospheric-scale, wide, low-resistivity zone revealed below the ophiolite belt associated with the closure of the Mongol-Okhotsk ocean Vertical, narrow low-resistivity features aligned with proposed tectonic boundaries and locations of large mineral zones (copper and gold) The northern part of central Mongolia has a sharp mid-crustal transition from high to low resistivity, whereas the southern part does not