#1EGU European Geosciences Union UNIVERSIDAD NACIONAL AUTONOMA B MEXICO POR MI บ "Resistivity model for the Colima Volcanic Complex from magnetotelluric observations" Héctor Manuel Romo Lozano1, Jorge Arturo Arzate Flores¹ 1 Centro de Geociencias, Universidad Nacional Autónoma de México, Querétaro, México [email protected] Motivation No resistivity models are available for the Colima Volcanic Complex which could complement previous geophysical models about its volcanic magmatic system. Key question How is magma transported to the surface? Is there a magmatic chamber beneath CVC? CC BY#2Study area and its dynamic context 32°0'N -114°0'W -108°0'W -102°0'W -96°0'W -90°0'W N Michoacán Block CVC Colima Rift Jalisco Block 24°0'N GULF OF CALIFORNIA PACIFIC OCEAN Rivera Microplate Guadalajara City- MVB Mexico City 16°0'N GULF OF MEXICO N A. Mantle Flow Cocos Plate Figure 2 Mesoamerican Trench Rivera Plate A. Mantle Toroidal Mantle Flow 500 1000 km COCOS PLATE Figure 1 Transform Fault - Oceanic dorsal Mexican Volcanic Belt Main Cities Colima Volcanic Complex Mesoamerican Trench The Colima Volcanic Complex (CVC) is located in the occidental part of Mexico, within the westernmost side of the so called Trans-Mexican Volcanic Belt (TMVB). The CVC structure is 120 km far from the Mesoamerican Trench, 80 km from the Pacific Coast and 100 km south of Guadalajara City. Two oceanic plates; Rivera and Cocos, converge obliquely and with different slab angles to the North American continental plate. From seismic tomography (Yang et al. 2009) has been inferred that a slab window ocurrs at 150 km depth, just beneath north and central Colima Rift, that allows a flow of asthenospheric mantle to the mantle wedge enabling the crust to melt. This coincides with the volcanism in the CVC, which is north-south migrating/old- young aging. CC BY 2#339.000'- 30.000'' 21.000' BY -103°57.000' -103°48.000' -103°39.000' -103°30.000' + SM JB Tamazula Fault CCG SCG VF NV NCG 0 5 MB 10 km Quaternary Sediments Cantaro Volcano Deposits Colima Volcano Deposits Tertiary Intrusives Nevado Volcano Deposits Alkaline Lavas Paleofuego Debris, Avalanche Deposits Pumice And Ash Fall (Unkown Origin) Collapse Escarpments Fault Escarpments Nevado and Volcan Colima Cretaceous Sandstones, Limestones And Volcanics Geology The CVC lies in the westernmost part of the TMVB which is the largest neogene volcanic arc in North America with an area of 160,000 km2 (Ferrari et al. 2017) and a basement composed mainly volcanic deposits and marine sedimentary rocks. Particularly for the CVC, the basement consists of carbonated rocks and volcanic intrusives which are overlain by Colima rift's sedimentary infill sequences and the volcanic products of the Volcan Cántaro, Nevado de Colima and Volcan de Fuego, which form the CVC. Two main structural features can be evidenced; a north-south normal faulting that delineates the north part of the rift, which continuation along the central and south parts it is not so clear, and an almost east- west structure called Alseseca graben, inferred to be constructed by the active Tamazula fault, which played an important role in the gravitational collapses of the CVC to the south (Norini et al. 2010). Figure 3. Geologic map taken and edited from the recapitulation made by Crummy (2013) after the works of Rodríguez-Elizarrarás (1995), Cortés (2002,2005 and 2010) and Ferrari et al. (2017). NCG: North Colima Graben, CCG: Central Colima Graben, SCG: South Colima Graben, RA: Armería River, NR: Naranjo River, SM: Manantlan Mountain Range, JB: Jalisco Block, MB: Michoacán Block, VF: Volcan de Fuego, NC: Nevado de Colima,³ Blue dots are MT soundings and thin blue lines are MT profiles.#4DEPTH (M) 19°45.000' -104°0.000' Resistivity models From resistivity models we conclude a good correlation with superficial geology and with the normal faults that delineate the northern and central part of the Colima rift. A homogenous basament goes along all the structure where no avidence for shallow or medium crust depth reservoirs are present. Anomaly C2 and C3 are of interest because of the agreement with the subsurface prolongation of the main faults. From this, we can hyphotesize a tectonic-structural control for magma ascend, along fault planes. WWE PROFILE AA' 19°30.000' 19°15.000' SSE 10000- NV1 20000- R2 30000- 40000 CC ↑ BY O 20000 R1 NV2 CVC9 _L_ NORTH COLIMA GRABEN T-AN. C3 R2 40000 DISTANCE (M) NV4 C3 60000 80000 RESISTIVITY IN OHM-M -103°45.000' A 20 km W -103°30.000' Figure 4 -103°15.000 B PROFILE BB' 5000 3391 2299 1559 C2 1057 717 10000 R2 486 330 224 152 20000 103 70 47 32 22 30000 15 10 40000 10000 DISTANCE (M) 4 CVC6 A 25000 E#5DEPTH (M) WWE PROFILE CC' 10000- 20000- 30000- R2 40000 R3 SV1 SOUTH COLIMA GRABEN C1 SV3: R2 SV4 30000 60000 DISTANCE (M) C2 SV5 SSE S PROFILE DD' CVC5 CVC2 10000- R2 R1 20000 C3 C4 30000- MAGMA ASCEND AND SILL EMPLACEMENT 40000 CC Seismic models correlation with resistivity models Profile DD' resistivity model show a conductive anomaly vertically extensive parallel to Tamazula fault plane and an horizontal extensive sill complex around 20 km depth. Velocity model from Sychev et al. (2019) elucidates an anomaly. Low velocity zones correlate with our conductive body. ↑ BY Below, seismic models from Sychev et al. (2019) showing in the first and second row velocity anomalies and the third row the Vp/Vs ratio. Above, north-south MT resistivity model 20- 40- 20- -40- V1 TAMAZULA FAULT CVC9 ΕΛΝ R2 20000 DISTANCE (M) 40000 Figure 5 IS FC NC CCG CAN N NC NW SE SW NE 40 Section 1, Section 2, Section 3, P-wave anomalies P-waves anomalies -80-f~ P-wave sales -80- 60- 20 40 60 BO 80 100 20 40 60 100 IS FC NC CAN CCG N INW SE SW NE 0 0- 40- Section 1, Section 2, S-wave anomalies 60- 20 40 60 S FC NO CAN CCG N NW S-wave anomalies 40 NC TF °- Section 1, Vp/Vs ratio 60 20 40 60 distance, km -20- Section 2, Vp/Vs ratio -40- Section 3, 1.85 60-S-wave anomalies 100 20 40 80 100 1.8 SE SW NC NE 1.75 Section 3, 00- Vp/Vs ratio 20 1.0 80 100 0 20 BO 100 distance, im distance, km 1.65 1,7 -10 velocity anomalies N#6Gravity (mGa) Magnetics (nT) Depth (km) 0 CVC LO SW -100 -200 0 -20 -40 -60 -Observed -Calculated =Observed =Calculated -3 0 3 6 12 L4L3 L2 LI D-2.55 D-2.45 D-2.6 D-2.36 D-2.75 -23 D=2.78 D=2.36 D-3.1 D-2.8 15 10 20 30 40 50 Distance (km) Figure 6 NE depth, km Volcán de Colima debris NW TF avalanche deposits Figure 7 SE 1.85 magma shallow conduit magma reservoir -10- Upper crust 1.8 -20- silicic. magma. -30- Lower crust -40- mafic magma Mantle -50- Mantle diapir -60+ 0 10 20 20 8- 30 40 50 50 60 -0 70 distance, km -80 1.6 90 90 100 CC Gravimetric and magnetic model from Alvarez & Yutsis (2015) show several magmatic chambers interconnected with dykes. Low magnetic and gravimetric anomalies correlate with our profile DD' anomaly. No resistivity model evidence stands for the magma chambers south the CVC. ↑ BY Our results support Sychev et al. (2019) schematic model for the CVC magmatic system, where a mafic magma intrudes and then evolves to a more silisic magma during its ascend through weakness planes. 6 1.75 1.7 1.65 Vp/Vs ratio#7CC • . . Conclusions Resistivity models obtained from magnetotelluric data inversion depicts a good correlation with actual structural and geological information for the Central Colima Graben but new insights for new structures can be established from resistivity models. No shallow magma chamber seems to be south the CVC as inferred in seismic models. Apparently conductive anomalies west of Profile BB', vertical conductive body west of Profile CC' and the evidence of Tamazula fault in the NS profile show a main tectonic-structural control for magma or hydrothermal fluids ascend. Further work must consider a denser MT soundings array to constrain geological structures smaller than 5 km and the comparison of 3D models resistivity models (in process). BY 7