Red River Fault Research Articles

CRUSTAL MAGNETIC ANOMALIES AND GEOLOGICAL STRUCTURE IN THE YUNNAN REGION

AbstractBased on the geomagnetic field model (NGDC‐720) established by the U.S. National Geophysical Data Center, the spatial variations of crustal magnetic anomalies in the Yunnan region were studied, including the distribution of magnetic anomalies and their gradients, attenuation of magnetic anomalies with altitude, and the contributions of components with different wavelengths to overall magnetic anomalies. The magnetic anomalies were compared with other geophysical data such as gravity anomalies, terrestrial heat flow, and seismic activities to reveal similarities and differences, and the relationship between crustal magnetic anomalies and geological structure was studied. The research results show that the magnetic anomalies are relatively weak in the Sanjiang (Three Rivers) and western Yunnan orogenic belts to the west of the Lijiang‐Xiaojinhe and Red River fault zones, and relatively strong in the rhombic block. The crustal magnetic anomalies in the study region were mainly generated by the shallow magnetic bodies superposed on the background of weak magnetism basement. The satellite magnetic anomalies show that the middle Yunnan depression area has clear dipole field characteristics. The positive and negative magnetic anomaly zones distributed along the Red River fault zone have consistent strikes with that of the faults. The Lijiang‐Xiaojinhe fault, the Red River fault, the Kangding‐Yiliang‐Shuicheng fault and the Mile‐Shizong‐Shuicheng fault zones surrounding the rhombic block are transition belts between strong and weak magnetic anomalies. The places with active seismicity and the areas with high terrestrial heat flow values have negative or relatively weak crustal magnetic anomalies.

Development Characteristics and Formation Mechanism of Nanoparticles in the Ductile Shear Zone of the Red River Fault

Nanoparticles in the ductile shear zones of faults are thought to be closely related to fault activity and the seismogenic mechanism. Using scanning electron microscopy (SEM), nanoparticles with a variety of morphological characteristics were found in mylonite, gneiss, and schist from the ductile shear zones of the Red River Fault. The nanoparticle morphology is dominated by rods, spherulites, massive forms, lamellae and film-like shapes. Energy spectrum analysis showed that the nanoparticles were mainly composed of silicate minerals, while a few contained carbonate minerals. Nanoparticles follow certain spatial distribution rules in ductile shear zones. Near the main fault plane of the Red River Fault Zone, the nanoparticles are dispersed, brittle and spherulitic, with a small particle diameter. Those far from the main fault plane are agglomerated and plastic, with rod-like, massive, lamellar and film-like shapes, and a relatively large particle diameter. According to nanoparticle development characteristics and the theory of microscopic deformation, a study on the formation mechanism of nanoparticles in the ductile shear zones of the Red River Fault was carried out. The rock minerals are the first to experience granulation, through intergranular movement under strong strain, generating brittle spherulitic particles, which eventually loosen and disperse. In the later stages, through recrystallization, nanoparticle crystals may become large or develop various morphologies.

The relation between fault movement potential and seismic activity of major faults in Northwestern Vietnam

The relation between fault movement potential and seismic activity of major faults in Northwestern Vietnam

Surface uplift of the Central Yunnan Plateau since the Pliocene

The Central Yunnan Plateau (CYP) is located in the southeastern end of the Sichuan‐Yunnan rhombic block. CYP is surrounded by the South China Block to the east and the Indo‐China Block to the southwest. Stratigraphy and topography research shows the relative surface uplift of the CYP since the Pliocene. However, the widely accepted model of lower crustal flow is very difficult to fully explain the surface uplift of CYP, with faults and fold structures in the brittle shallow crust. The lower crust thickening led by the lower crustal flow only contributes 34–54% (600–950 m) of the total surface uplift. The wide‐angle seismic profiles and topography analysis show that the CYP surface uplift is predominately a consequence of isostatic compensation due to surface erosion, upper‐middle crustal shortening, and lower crustal thickening. The average isostatic adjustment caused by surface erosion of CYP is about 500 m, which is about 29% of the total surface uplift (1750 m). The GPS station velocities, focal mechanisms, and seismic anisotropy show the strong decoupling relationship between upper‐middle crust and lower crust. In detail, there is a movement with southeast‐directed and clockwise rotation around the Eastern Himalayan syntaxis in the upper‐middle crust, although south‐directed flow in the lower crust. The southeast motion of the upper‐middle crust could be resolved into two portions. The eastward component of upper‐middle crust motion is obstructed by the South China Block in the east. The result is the W‐E direction shortening of upper‐middle crust, shown by the S‐N trending CYP anticlinorium. The W‐E direction shortening of upper‐middle crust contributes 17–37% (300–650 m) of the total surface uplift. In contrast, the southward component of upper‐middle crust motion, shown by the sinistral strike‐slip displacement of the Xiaojiang fault zone, could pass through the Red River fault zone into the Indo‐China Block, where the left‐lateral Dien Bien Phu Fault would be the counterpart. The contribution of upper‐middle crustal shortening in a S‐N direction is very limited. The lower crustal flow could have been playing a prominent role in the growth of the whole southeast margin of the Tibetan Plateau, and the contribution from upper‐middle crustal shortening cannot be ignored in some local areas.

Assessment of earthquake-induced ground liquefaction susceptibility for Hanoi city using geological and geomorphologic characteristics

Assessment of earthquake-induced ground liquefaction susceptibility for Hanoi city using geological and geomorphologic characteristics

Study on active tectonic faults using soil radon gas method in Viet Nam

Study on active tectonic faults using soil radon gas method in Viet Nam

Reappraisal of the Jianchuan Cenozoic basin stratigraphy and its implications on the SE Tibetan plateau evolution

We present a new stratigraphy of the Jianchuan basin, one of the largest Cenozoic sedimentary basins in southeastern Tibet. This basin was regarded as recording sedimentation from the Eocene up to the Pliocene, and as such has been the focus of several studies aiming at constraining the environmental, tectonic and topographic evolution of the area. Within the Shuanghe and Jianchuan formations thirteen new zircon U/Pb ages and one biotite 40Ar/39Ar age of interbedded and cross-cutting ultrapotassic magmatic rocks show that a brief magmatic event occurred from ~35.7 to ~34.5Ma (35.2±0.4Ma on average). The uppermost formation (Jianchuan Fm), supposedly Pliocene in age, is related to this magmatic event and is 35.4±0.8Ma old. All sedimentary formations are thus Eocene in age, with neither Oligocene nor Miocene sediments. The coal-bearing Shuanghe Formation yields a fossil of a large amynodontid typical of the Upper Eocene Ergilian interval (37.2 to 33.9Ma). Sedimentation of the Shuanghe Formation took place in a short time interval at ~35.9±0.9Ma, after a large-scale drainage reorganization that induced the abandonment of a large braided-river system. This reorganization was possibly linked with the initiation of the left-lateral Ailao-Shan Red River fault and/or to widespread magmatism in the Jianchuan basin. Previous high paleoaltitude estimates for the Jianchuan basin are thoroughly re-evaluated and yield a value of 1200±1200m.a.s.l. for the Upper Eocene.

Upper mantle discontinuity structure beneath eastern and southeastern Tibet: New constraints on the Tengchong intraplate volcano and signatures of detached lithosphere under the western Yangtze Craton

AbstractWe present new constraints on the upper mantle transition zone structure beneath eastern and southeastern Tibet based on P wave receiver functions for a large broadband data set from two very dense seismic arrays. A clear depression of both the 410 km and 660 km discontinuities is detected west of the Red River fault relative to the east. The correlated topographic variations across the Red River fault are indicative of temperature changes in the upper mantle above the transition zone, which suggests that the fault is a deep‐rooted structure that penetrates into the upper mantle and separates Indochina from South China. West of the Red River fault, the transition zone thickness under the Tengchong volcano is found to be normal compared to the global average. This strongly suggests that the intraplate volcano may originate from slab tearing of the eastward subducting Indian plate at shallow depths in the upper mantle rather than from dehydration of a flattened plate within the transition zone. Our results further show that the 660 km discontinuity is significantly depressed under the western Yangtze Craton and that the transition zone therefore thickens by up to 20 km. This thickening is suggestive of lowered temperatures associated with a remnant of detached lithosphere in response to overlying asthenospheric escape flow in and around the western Yangtze Craton. In addition, we find that the transition zone thickness beneath much of the Sichuan Basin is similar to the global average.

The July 11, 1995 Myanmar–China earthquake: A representative event in the bookshelf faulting system of southeastern Asia observed from JERS-1 SAR images

On July 11, 1995, an Mw 6.8 earthquake struck eastern Myanmar near the Chinese border; hereafter referred to as the 1995 Myanmar–China earthquake. Coseismic surface displacements associated with this event are identified from JERS-1 (Japanese Earth Resources Satellite-1) SAR (Synthetic Aperture Radar) images. The largest relative displacement reached 60cm in the line-of-sight direction. We speculate that a previously unrecognized dextral strike-slip subvertical fault striking NW–SE was responsible for this event. The coseismic slip distribution on the fault planes is inverted based on the InSAR-derived deformation. The results indicate that the fault slip was confined to two lobes. The maximum slip reached approximately 2.5m at a depth of 5km in the northwestern part of the focal region. The inverted geodetic moment was approximately Mw=6.69, which is consistent with seismological results. The 1995 Myanmar–China earthquake is one of the largest recorded earthquakes that has occurred around the “bookshelf faulting” system between the Sagaing fault in Myanmar and the Red River fault in southwestern China.

Source and sink characteristics of the continental slope-parallel Central Canyon in the Qiongdongnan Basin on the northern margin of the South China Sea

The “source-conduit-sink” model is crucial for studying deep-water sedimentary systems along a continental margin. Using seismic data, bulk rare earth element compositions of sediments and zircon U-Pb age data, we examined the supply and deposition (i.e., the source and sink) of the sediments in the Central Canyon of the South China Sea. Five phases of secondary canyon fill are present in the Central Canyon. The natural levees developed at the head of phase 1 of the secondary canyon deposits indicate that the Central Canyon initially developed at 10.5Ma. The sediments in the Central Canyon were supplied by the Ledong submarine fan, and the provenance of the material in the Ledong submarine fan and Central Canyon was eastern Vietnam. Large amounts of sediments were transported through the Central Canyon to the Shuangfeng Basin and deposited during four phases of submarine fan development. Phases 1–3 of the Shuangfeng submarine fans are composed of deep-water branching channel and inter-channel sediments. Phase 4 of the Shuangfeng submarine fan consists of deep-water channel and lobe sediments. Tectonic events, including the broad uplift of the Tibetan Plateau and central-southern Vietnam during the late Miocene, reversal of the strike-slip Red River Fault, and rapid subsidence in the Qiongdongnan Basin at approximately 5.5Ma, provided favourable conditions for the growth of the Ledong submarine fan, Central Canyon and Shuangfeng submarine fan system.

Structure of the Upper Mantle and Transition Zone Beneath the South China Block Imaged by Finite Frequency Tomography

AbstractWe applied the finite frequency tomography method to S wave data recorded by 350 broadband stations beneath the South China Block (SCB) and its surroundings from earthquakes occurring between July 2007 and July 2010, to better understand upper mantle deformation. Differential travel‐times in the pair of stations with appropriate weighting for each station are used in the inversion. Our results are consistent with previous tomography that show a high velocity anomaly beneath the Sichuan basin and a high velocity anomaly in the transition zone beneath the Yangtze Craton. However, the resolution of mantle heterogeneity provides new insight into the tectonic framework of subduction of Burmese lithosphere in the west part of the study region and subduction of oceanic lithosphere in the east. In the subduction realm, west of 107°E, a significant fast S‐wave anomaly is located on the southeast of Sichuan Basin. East of 107°E, and two narrow and discontinuous fast S‐wave anomalies occur at a depth of 400–600 km beneath the middle of the South China block overlain by the pronounced low S‐wave anomalies at a depth of 100 and 400 km. If the fast anomalies located in the mantle transition zone represent stagnant slabs, their fragmented nature may suggest that they could be produced by different episodes of subduction beneath western Pacific island and the above slow velocity anomaly may associated with the back‐arc regions of ongoing subduction. In addition, tomography also reveals an anomalously high S‐wave velocity continental root extends eastward to a depth 400 km beneath the eastern Sichuan Basin. This anomaly may be related to eastern extrusion of Indian lithosphere associated with the collision of India and Eurasia. Moreover, our results also show large slow anomalies beneath the Red River fault region connected to deeper anomalies beneath the South China Fold Belt and South China Sea. All these observations are consistent with the scenario that the South China block has been built by both of subduction of Paleo‐pacific plate and eastward subduction of Burma microplate.

K‐Ar Dating of Fault Gouges from the Red River Fault Zone of Vietnam

AbstractConstraining the timing of fault zone formation is fundamentally important in terms of geotectonics to understand structural evolution and brittle fault processes. This paper presents the first authigenic illite K‐Ar age data from fault gouge samples collected from the Red River Shear Zone at Lao Cai province, Vietnam. The fault gouge samples were separated into three grain‐size fractions (<0.1 µm, 0.1–0.4 µm and 0.4–1.0 µm). The results show that the K‐Ar age values decrease from coarser to finer grain fractions (24.1 to 19.2 Ma), suggesting enrichment in finer fraction of more‐recently grown authigenic illites. The timing of the fault movement are the lower intercept ages at 0% detrital illite (19.2 ± 0.92 Ma and 19.4 ± 0.49 Ma). In combination with previous geochronological data, this result indicates that the metamorphism of the Day Nui Con Voi (DNCV) metamorphic complex took place before ca. 26.8 Ma. At about 26.8 Ma‐25 Ma, the fault strongly acted to cause the rapid exhumation of the rocks along the Red River‐Ailoa Shan Fault Zone (RR‐ASFZ). During brittle deformation, the DNCV slowly uplifted, implying weak movement of the fault. This brittle deformation might have lasted for ca. 5 Ma.

Cenozoic tectonic subsidence in the Qiongdongnan Basin, northern South China Sea

AbstractA number of major controversies exist in the South China Sea, including the timing and pattern of seafloor spreading, the anomalous alternating strike‐slip movement on the Red River Fault, the existence of anomalous post‐rift subsidence and how major submarine canyons have developed. The Qiongdongnan Basin is located in the intersection of the northern South China Sea margin and the strike‐slip Red River fault zone. Analysing the subsidence of the Qiongdongnan Basin is critical in understanding these controversies. The basin‐wide unloaded tectonic subsidence is computed through 1D backstripping constrained by the reconstruction of palaeo‐water depths and the interpretation of dense seismic profiles and wells. Results show that discrete subsidence sags began to form in the central depression during the middle and late Eocene (45–31.5 Ma). Subsequently in the Oligocene (31.5–23 Ma), more faults with intense activity formed, leading to rapid extension with high subsidence (40–90 m Myr−1). This extension is also inferred to be affected by the sinistral movement of the offshore Red River Fault as new subsidence sags progressively formed adjacent to this structure. Evidence from faults, subsidence, magmatic intrusions and strata erosion suggests that the breakup unconformity formed at ca. 23 Ma, coeval with the initial seafloor spreading in the southwestern subbasin of the South China Sea, demonstrating that the breakup unconformity in the Qiongdongnan Basin is younger than that observed in the Pearl River Mouth Basin (ca. 32–28 Ma) and Taiwan region (ca. 39–33 Ma), which implies that the seafloor spreading in the South China Sea began diachronously from east to west. The post‐rift subsidence was extremely slow during the early and middle Miocene (16 m Myr−1, 23–11.6 Ma), probably caused by the transient dynamic support induced by mantle convection during seafloor spreading. Subsequently, rapid post‐rift subsidence occurred during the late Miocene (144 m Myr−1, 11.6–5.5 Ma) possibly as the dynamic support disappeared. The post‐rift subsidence slowed again from the Pliocene to the Quaternary (24 m Myr−1, 5.5–0 Ma), but a subsidence centre formed in the west with the maximum subsidence of ca. 450 m, which coincided with a basin with the sediment thickness exceeding 5500 m and is inferred to be caused by sediment‐induced ductile crust flow. Anomalous post‐rift subsidence in the Qiongdongnan Basin increased from ca. 300 m in the northwest to ca. 1200 m in the southeast, and the post‐rift vertical movement of the basement was probably the most important factor to facilitate the development of the central submarine canyon.

Tectonic and climatic impacts on the biota within the Red River Fault, evidence from phylogeography of Cycas dolichophylla (Cycadaceae).

Dramatic crustal deformation and river incision in Southwest China induced by the Indo-Asian collision have long been argued to contribute to the complicated landscapes, heterogeneous environment and abundant biodiversity in this region. However, biological impacts in promoting intraspecific phylogeographical subdivision and divergence along the Red River Fault zone (RRF) remain poorly understood. To investigate the possible biological effects of tectonic movements and environment variations within the RRF, the phylogeography of Cycas dolichophylla-an endemic but widely distributed Cycas in Southwest China and North Vietnam along the RRF were carried out based on four chloroplast DNA intergenic spacers (cpDNA), three nuclear DNA sequences (nDNA) and 16 simple sequence repeat variations (SSR). Two different phylogeographical patterns were detected: a Southwest-Northeast break across the RRF disclosed by chlorotypes and a China-Vietnam separation revealed by SSR. A Bayesian skyline plot from cpDNA data demonstrated a historical increasing, but a recent declining, dynamic in population size during the Pleistocene. Consequently, we infer it is the local environmental variation during Cenozoic that contributed to the complex landscape and microclimate mosaics, facilitating speciation and divergence of C. dolichophylla. Subsequently, the Quaternary climatic fluctuations coupled with human activities profoundly influenced the genetic structure and demographic history of this species.

Submarine slide evidence for late Miocene strike-slip reversal of the Red River Fault

During the late Miocene (~5.5 Ma), a large-scale submarine slide with an area of approximately 18000 km2 and a maximum thickness of 930 m formed in the deep-water region of the Qiongdongnan Basin. The large-scale submarine slide has obvious features in seismic profile, with normal faults in the proximal region, escarpments at the lateral boundary, and a pronounced shear surface at the base. The internal seismic reflections are chaotic and enclosed by parallel and sub-parallel seismic events. The main direction of sediment transport was from south to north and the main sediment source was the southern region of the Qiongdongnan Basin, which is located in the east of the Indo-China Peninsula and the north of the Guangle uplift. In this region, late Miocene strike-slip reversal of the Red River Fault, uplift and increased erosion of the Indo-China Peninsula, and an abrupt rise in the rate of deposition in the western part of the South China Sea provided the basic conditions and triggering mechanism for the large-scale submarine slide. The discovery of the large-scale submarine slide provides sedimentological evidence for the tectonic event of late Miocene strike-slip reversal of the Red River Fault. It can also be inferred that the greatest tectonic activity during the process of the Red River Fault reversal occurred at ~5.5 Ma from the age of top surface of the submarine slide.

USING THE ANALYTIC SIGNAL METHOD OF GRAVITY GRADIENT TENSOR (GGT) TO DETERMINE THE LOCATION AND DEPTH OF THE FAULTS IN THE PRE-CENOZOIC BASEMENT ROCKS OF THE RED RIVER TROUGH

USING THE ANALYTIC SIGNAL METHOD OF GRAVITY GRADIENT TENSOR (GGT) TO DETERMINE THE LOCATION AND DEPTH OF THE FAULTS IN THE PRE-CENOZOIC BASEMENT ROCKS OF THE RED RIVER TROUGH

In situ stress analysis in the Yinggehai Basin, northwestern South China Sea: Implication for the pore pressure-stress coupling process

The Yinggehai Basin is located in the triangle between the Sunda block, South China block, and the South China Sea and is an interesting target for in situ stress investigation, not only because of its specific tectonic position but also due to its abnormally high pore pressures. Magnitudes and orientations of in situ stress were directly constrained by measurements operated in the vertical boreholes that were drilled in the Yinggehai Basin. Gradients and magnitudes of the least horizontal stress remarkably increase with overpressure enhancement, indicating that the least principal stress and pore pressure are in fact coupled. The ratios of pore pressure/stress coupling (ΔƠh/ΔPp) are similar in the north and south central Yinggehai Basin, despite the burial depths of overpressure top are different. However, a deeply buried strike-slip faulting regime under WNW-ESE oriented horizontal compression was identified in the central Yinggehai Basin, where the ΔƠh/ΔPp ratios have intermediate values, ranging from that for an idealized normal faulting stress regime to that for the southeastern South China (a strong strike-slip or even reverse faulting stress regime). Additionally, the WNW-ESE orientations of maximum horizontal stress determined from drilling-induced tensile fractures in the Yinggehai Basin are inappropriate for the present maximum horizontal stress derived from earthquake focal mechanism solutions in the northern segment of the Red River Faults, suggesting that the dextral movement of Red River Faults has slightly influenced the present stress state in the Yinggehai Basin. The present stress state of the Yinggehai Basin was primarily generated by the ESE absolute horizontal motion of the Sunda and South China blocks.

Nuclear genetic variation of Rosa odorata var. gigantea (Rosaceae): population structure and conservation implications

Rosa odorata var. gigantea is one of the most important ancestors of modern roses, which owns many merit traits including large flower, early flowering, and tea scent. Due to habitat loss and fragmentation, it has been listed as a rare and endangered species in China. In this study, a total of 424 accessions from 27 locations across its major distribution range were sampled. Its genetic diversity and population structure were assessed using a combination of seven nuclear microsatellite markers and one single-copy nuclear gene. Moderate to high within-population genetic diversity and moderate differentiation among populations were revealed despite its narrow distribution. The sampled 27 populations were resolved into two genetic clusters with limited contemporary and historical gene flows. The Red River Fault Zone was inferred to be a physical or geographical barrier to gene flow between these two genetic clusters. Genetic distances were significantly associated with geographic distances, indicating the isolation-by-distance model. Our ecological niche modeling indicated that R. odorata var. gigantea had high current potential areas in the central Yunnan province and substantial losses of high potential distribution areas in the western Yunnan in the future. Two detected clusters showed significant genetic differentiation and represented two separate evolutionary lineages, which should be recognized as two evolutionary significant units (ESUs) for conservation concerns. These results could be applied for the decision-making and conservation planning for this important species.

Triassic tectonics of the Ailaoshan Belt (SW China): Early Triassic collision between the South China and Indochina Blocks, and Middle Triassic intracontinental shearing

In SE Yunnan, the Ailaoshan Belt has been extensively studied for the ductile shearing coeval with the left-lateral Cenozoic activity of the Red River fault. However, the Late Triassic unconformity of the continental red beds upon metamorphic and ductilely deformed rocks demonstrates that the Ailaoshan Belt was already built up by Early Mesozoic tectonics. From West to East, the belt is subdivided into Western, Central, Eastern Ailaoshan, and Jinping zones. The Western Ailaoshan and Central Ailaoshan zones correspond to a Carboniferous–Permian magmatic arc, and an ophiolitic mélange, respectively. The Eastern Ailaoshan, and the Jinping zones consist of deformed Proterozoic basement and Paleozoic to Early Triassic sedimentary cover series both belonging to the South China Block. This litho-tectonic zonation indicates that the Ailaoshan Belt developed through a SW-directed subduction followed by the collision between Indochina and South China blocks. Crustal thickening triggered per-aluminous magmatism dated at ca 247–240Ma. Field and microscope-scale top-to-the-NE ductile shearing observed only in the pre-Late Triassic formations, but never in Late Triassic or younger formations, complies with this geodynamic polarity. Furthermore, the late collisional two-mica granitoids and felsic per-aluminous volcanites record a ductile deformation that argues for a continuing crustal shearing deformation after the Early Triassic collision up to the Middle Triassic. Therefore, a two-stage tectonic evolution accounts well for the documented structural and magmatic features. The Triassic architecture of the Ailaoshan Belt, and its geodynamic evolution, correlate well to the South and North with the North Vietnam orogens and the Jinshajiang Belt, respectively.

Zircon U–Pb ages, Hf isotope data, and tectonic implications of Early–Middle Triassic granitoids in the Ailaoshan high-grade metamorphic belt of Southeast Tibet

The Ailaoshan tectonic belt, where the effects of the Paleo-Tethyan ocean evolution and Indian–Eurasian plate collision are superimposed, is one of the most significant geological discontinuities in western Yunnan province of southeast Tibet. An Ailaoshan micro-block within the belt is bounded by the Ailaoshan suture zone to the west and the Red River Fault to the east, and consists of low- and high-grade metamorphic belts. Late Permian–Middle Triassic granitoids that are widely distributed to the west of the Ailaoshan suture zone and within the Ailaoshan micro-block may yield significant information on the Tethyan tectonic evolution of the Ailaoshan tectonic belt. This study reports new LA–ICP–MS zircon U–Pb geochronology and Hf isotope data of four granitoids from the Ailaoshan high-grade metamorphic belt. Zircon grains from the Yinjie granitoid do not have inherited cores and yield a weighted mean U–Pb age of 247.1 ± 2.0 Ma. The zircon e Hf(t) values range from 7.8 to 12.1, and Hf model ages from 775 to 546 Ma, indicating that the granitoid was derived from juvenile crust. The rims of zircons from the Majie and Yuanjiang granitoids yield weighted mean U–Pb ages of 239.5 ± 1.8 and 237.9 ± 2.6 Ma, respectively, whereas the cores yield ages of 1608–352 Ma. The e Hf(t) values of zircon rims range from −20.4 to −5.3, yielding Hf model ages from 2557 to 1606 Ma and suggesting that the source magma of the Majie and Yuanjiang granitoids was derived from ancient crust. An additional granitoid located near the Majie Village yields a zircon U–Pb age of 241.2 ± 1.0 Ma. Based on our geochronological and geochemical data, combined with geological observations, we propose that the Ailaoshan micro-block was derived from the western margin of the Yangtze block, and is comparable to the Zhongzan and Nam Co micro-blocks. The presence of late Permian mafic rocks with rift-related geochemical characteristics within the Ailaoshan micro-block, together with granitoids derived from partial melting of ancient/juvenile crust, indicates the presence of an Ailaoshan rift. This possible rift may correspond to the Ganzi–Litang Ocean to the northwest and the Jinping–Song Da rift to the southeast. It is suggested that westward subduction of the Jinshajiang–Ailaoshan–Song Ma oceanic lithosphere triggered the separation of the Zhongzan, Ailaoshan, and Nam Co micro-blocks from the western passive continental margin of the Yangtze block through the opening of the Ganzi–Litang–Ailaoshan–Jinping–Song Da ocean/rift. This ocean/rift may represent a subsidiary branch of the Paleo-Tethyan Ocean along the western margin of the Yangtze block.