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The late Mesozoic Era was a time of widespread crustal extension in eastern Asia resulting in both rift basin and metamorphic core complex formation. Two of the more recently documented examples of this extensional phase are the Ereendavaa and Buteel metamorphic core complexes (EMCC, BMCC). Both are located in northern Mongolia proximal to the Mongol Okhotsk Suture Zone (MOSZ). The MOSZ is a profound, yet enigmatic structure that formed due to closure of the Mongol-Okhotsk Ocean, a basin that separated the Siberian and North China cratons and intervening terranes of the Central Asian Orogenic Belt. Based on published work by others, the core complexes record NW-SE extension, cooling and deformation from c. 135 to 120 Ma. We present new data as part of a collaborative research project that aims to constrain the evolution of the MOSZ more broadly and its relationship to intracontinental deformation after suturing. Our methods include analysis of satellite imagery and digital elevation models with synthesis of field, (micro)structural, and geochronologic data with published maps and studies. Based on our findings, the EMCC likely extends several 10's of km to the NE. Satellite imagery and DEMs suggest large-scale corrugations along the N-flank consistent with NW-SE extension. To the SW of the EMCC, Early Cretaceous rift basins are associated with strong NE-SW oriented lineaments. We examined the BMCC along its SW mapped extent, an area for which no data were presented in prior publications; we confirmed the presence of a top-to-the-SE detachment fault. The EMCC and BMCC, like the Yagan-Onch Hayrhan MCC in southern Mongolia, have footwall rocks previously mapped as Precambrian that are, in large part, metamorphosed Paleozoic and Mesozoic igneous and sedimentary rocks. All three MCCs exhibit evidence for structural complexity, such as NE-SW trending lineations orthogonal to the NW-SE extension direction. As in S Mongolia, we hypothesize that the NE-SW lineations in the EMCC and BMCC formed during an earlier phase of shortening. The expression of the Early Cretaceous extension (rift basin vs. MCC) appears to be controlled by the inherited structure.
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This content will become publicly available on August 11, 2026
Rotation of crustal extension and narrowing of rift faulting in the southern Rio Grande rift, Trans-Pecos Texas
Rates and directions of crustal extension in a continental rift vary in time and space as the rift evolves, and these geologic records are often preserved along fault planes. Some fault-kinematic studies have been undertaken in the central to northern segments of the Rio Grande rift, but similar studies from the southern part of the Rio Grande rift of western Texas, USA, and northern Mexico are fewer. We present new fault-kinematic data from six locations in the southern Rio Grande rift of Trans-Pecos Texas, combined with U-Pb dating of calcite slickenlines, to constrain the directions and time scales of extension. All locations preserve NE-SW−oriented extension, and locations within the Sunken Block graben preserve a more complex kinematic history of multiple extension directions. Four U-Pb ages range from 30.1 ± 3.1 Ma to 13.7 ± 0.9 Ma. Combined with fault-kinematic data and assuming a constant stress regime between 30 Ma and 14 Ma, these data support the interpretation that earliest extension in the southern rift was oriented NE-SW, and extension rotated clockwise to E-W and NW-SE after 13.7 ± 0.9 Ma. Based on available data, this rotation was broadly coincident with rotation in the extension direction in the southern Española basin and in the Basin and Range Province. These differences suggest that extension in the Rio Grande rift responded to the evolving western boundary of the North American plate but included initial underlying driving forces that were supplanted by lateral forces as the transform margin lengthened. Additionally, geochronologic and kinematic data across the Sunken Block graben of the southern Rio Grande rift indicate that the locus of rifting concentrated with time toward the center of this basin; such structural narrowing has previously been demonstrated in the northern segment of the rift. This study provides a much-needed comparison between the southern and northern segments of the rift but highlights the need for more collection of combined kinematic and geochronologic data.
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- Award ID(s):
- 2228180
- PAR ID:
- 10632223
- Publisher / Repository:
- Geosphere
- Date Published:
- Journal Name:
- Geosphere
- ISSN:
- 1553-040X
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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We interpret the kinematics of the Tangra Yumco (TYC) rift by evaluating spatiotemporal trends in fault displacement, extension onset, and exhumation rates. We present new geologic mapping, U-Pb geochronology, zircon (U-Th)/He (ZHe) thermochronology, and HeFTy thermal modeling results that are critical to testing dynamic models of extension in Tibet. The TYC rift is bounded by two NNE striking (~N10°E-N35°E) high angle (~45-70°) active normal faults that alternate dominance along strike. Footwall granodiorites show foliation, slip lineation, and fault plane striation measurements indicative of northeast directed oblique sinistral-normal slip. In North and South TYC, hanging wall deposits are cut by a series of active high-angle normal faults which likely sole into a master fault at depth, while in central TYC, hanging wall deposits display synthetic graben structures potentially indicative of low-angle faulting. Analysis of ~50 samples collected across key structural relationships in and around TYC yield 14 mean U-Pb dates between ~59-49 Ma and ~190 single-grain ZHe dates between ~60-4 Ma with spatial trends in ZHe data correlating strongly with latitude. Samples from Gangdese latitudes show a concentration of ~28-15 Ma ages, while those north of ~29.8° latitude yield both younger (~9-4 Ma) and older (~59-45 Ma) ages. We interpret (1) Gangdese Range samples reflect exhumation during contraction and uplift along the GCT peaking at ~21-20 Ma, (2) ~9-4 Ma ages reveal extension timing along fault segments experiencing significant rift-related exhumation, and (3) ~59-45 Ma ages represent un-reset or partially-reset samples from fault segments that have experienced lesser magnitudes of rift exhumation. HeFTy thermal models indicate a two-stage cooling history with initial slow cooling followed by accelerated cooling rates in Late Miocene-Pliocene time (~13-4 Ma) consistent with prior results from TYC and other Tibetan rifts. Our data are consistent with a segment linkage fault evolution model for the TYC rift, with underthrusting of Indian lithosphere likely related to the northward acceleration of rifting. Future work will utilize advanced HeFTy modeling including U-Pb and apatite fission track data to further constrain the exhumation history of TYC and test dynamic models of extension for southern Tibet.more » « less
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null (Ed.)The Española Basin is one of a series of interconnected, asymmetrical basins in the Rio Grande rift that includes a number of north- and northeast-striking faults that accom- modated block tilting and basin subsidence. The western margin of the Española Basin, in particular, is characterized by a greater than 17-km wide zone of normal and oblique-slip faults. To clarify the involvement of block rota- tion in the tectonic evolution of the Española Basin, we carried out a paleomagnetic study of mafic intrusions (Rio del Oso dike swarm) that are genetically related to regionally exten- sive basalt flows of the mid-Miocene Lobato Formation. The primary hypothesis tested was that these intrusions experienced some degree of vertical axis rotation associated with mid-Miocene to recent continental rifting. In situ paleomagnetic results from forty-two sites yield a group mean declination (D) of 344.0°, an inclination (I) of 41.1°, α95 of 6.1°, and k of 14.1. The group mean result is discordant to the <10 Ma pole of D=356.0°, I=54.4°, α95 = 3.3° with a statistically significant inferred rotation (R) of -12.0°± 7.2° and flattening of +13.3° ± 5.5° relative to the <10 Ma pole field direction. These discordant results indicate that a modest degree of counter-clockwise vertical axis rotation occurred in this region, which is likely associated with Rio Grande rifting north of the Jemez Mountains. It is possible that oblique motion along the Santa Clara fault and/ or the Cañada del Almagre fault facilitated the vertical axis rotation. The results from this study imply that vertical axis rotation is common to extensional rift systems and should be considered when modeling continental extension.more » « less
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