Tan Lu Research Articles

Strain partitioning dominated growth of strike-slip fault: Insight from the Tan-Lu fault in Eastern China

The dynamic variations of the strain field and associated tectonic deformation during fault evolution can provide useful insights into the fault growth mechanisms. As one of the longest strike-slip fault system in the world, the ∼3000-km length Tan–Lu fault zone (TLFZ) in eastern China, is ideal for studying the mechanisms of fault propagation and linkage. This study investigated the Cenozoic Liaodong Bay subbasin, which hosts main structures of four faults in the central TLFZ, using structural analysis and strain calculations based on abundant seismic data. Our new results reveal three stages of fault growth (D1, D2, and D3) during the Cenozoic. Strain partitioning occurred during D1, with non-coaxial deformation within the high-strain regions leading to the growth of individual fault segments. D2 involved the redistribution of strain partitioning, with localized strain overlapping along fault tips to produce both left- and right-stepping fault sets. The locally increased simple-shear component favored the development of right-stepping fault arrays. Fault linkage appears to be achieved in two ways: 1) left-stepping, dextral faults were linked by folds dominated by pure shear along overlapping fault tips, and 2) fault segments were linked via fractures developed in simple-shear-dominated right-stepping overlap zones. D3 was characterized by the continued accumulation of simple shear, which resulted in fault linkage through fractures and formed continuous faults with high strain. Therefore, we propose a tectonic model in which strain partitioning results in linkage of segmented faults along fault tips. This model takes into account the spatial and temporal variations in fault geometry and strain type during the growth of the strike-slip fault, provides theoretical support for the structural patterns observed in natural faults worldwide.

Composition and Sources of Clastic Material of Terrigenous Rocks of the Khabarovsk Accretionary Complex (Sikhote-Alin)

Abstract ––The results of comprehensive studies of terrigenous rocks of the Khabarovsk Sikhote-Alin accretionary complex are presented. It is established that the fragments of Jurassic and Permian–Triassic sandstones are dominated by poorly rounded and poorly separated material mainly from local provenance areas. The detrital part of the rocks is mainly represented by quartz, in a smaller amount by feldspar and rock fragments. Sandstones are characterized by high silica content, moderate alumina content, low concentrations of femic elements and calcium, moderate alkali content with significant variations in the K/Na ratio. Both Jurassic and Permian–Triassic rocks are typically characterized by reduced contents of LILE, REE, to a lesser extent HFSE and negative values of the ɛNd(T) parameter – compared to PAAS. The model Nd age of Jurassic sandstones varies from 1.36 to 1.71 Ga, Permian–Triassic – from 1.14 to 1.35 Ga. Most of the detrital zircon population is of late Paleozoic–early Mesozoic age, approximately 25% are older (pre-Paleoproterozoic). The studied sandstones are mainly rocks of the first cycle of weathering (petrogenic), formed during the erosion of igneous rocks of felsic composition. The synthesis of the obtained data suggests that the main source of the cluster material for the Mesozoic sedimentary rocks was the geological formations of the northern part of the Bureya–Khanka superterrane (Bureya and Malokhingan blocks), as well as, possibly, the eastern part of the Mongol–Okhotsk belt. The Khabarovsk terrane has not drifted significantly along the Tan Lu stike-slip system and is an “autochthonous” block in the present-day structure of Sikhote-Alin.

Intracontinental deformation around the fixed tip of the continental-scale, strike-slip Tan–Lu fault zone in eastern China

It remains unclear whether large-scale polyphase displacement along strike-slip faults is associated with tip propagation, and how the tip-damage zones of these faults respond to intracontinental block movements. Damage structures around the southern tip of the 2400 km long Tan–Lu fault zone (TLFZ) in eastern China provide an ideal opportunity to investigate deformation mechanisms at the tip of an intracontinental strike-slip fault. Structural and geochronological data from the southern Zhangbaling uplift within the TLFZ show that following the Triassic initiation of the fault, two phases of sinistral faulting occurred: an earlier phase at the beginning of the Early Cretaceous and later phase between the Early and Late Cretaceous. The early sinistral structures are expressed by ductile shear zones in the southern Zhangbaling uplift, whereas the younger sinistral structures are expressed as shear zones in the north and brittle faults in the south. Zircon U–Pb dating results for felsic gneiss of the TLFZ suggest that c. 200 km of cumulative displacement occurred during the Cretaceous and was restricted to wall rocks on the western side of the fault. The southern tip of the TLFZ remained fixed during the displacement, and the dilational quadrant associated with the fault is interpreted to have been stationary. The current c. 400 km of sinistral offset of the Dabie and Sulu orogens represents the original offset caused by the Triassic collision of the North China Craton and South China Block. The two phases of sinistral motion were induced by two phases of compression along the c. 460 km long contractional quadrant, which was dominated by thrusting along pre-existing faults as well as fault-related folding and uplift. Damage structures at the southern tip of the TLFZ show that large-scale polyphase strike-slip motion may be associated with a fixed fault tip, hundreds of kilometres of displacement can be restricted to one side of a major fault, and displacement can be accommodated by thrusting along pre-existing faults in the contractional quadrants. Supplementary material : LA-ICP-MS zircon U–Pb data for the felsic gneiss sample FD30 are available at https://doi.org/10.6084/m9.figshare.c.6368850

Строение разломных зон юго-западной части Среднеамурского осадочного бассейна (Приамурье) по данным микросейсмических зондирования

The first results of microseismic sounding the deep structure of the Earth's crust in the western part of the Middle Amur sedimentary basin are presented. Based on the measurement data at 70 points, we produced sections of the relative velocities of S waves along two transversely crossing profiles, total length 90 km. The profiles cross the Itun-Yilan fault zone and other large regional faults zones as well as the Bashmaksky, Preobrazhenovsky, and Samaro-Ditursky grabens. The sections at depths of 4-10 km do not contain velocity anomalies. This may explain the lower seismicity of the studied zone compared to neighboring areas of the Tan Lu fault system.

Sinistral displacement along the Tan–Lu Fault during the Cretaceous induced by Paleo-Pacific subduction: Constraints from new paleomagnetic and U–Pb geochronological data

The Jiaodong Peninsula in eastern China is separated from the main mass of the North China Craton by the Tancheng–Lujiang (Tan–Lu) Fault, the largest fault system in eastern Asia. Although accumulating lines of evidence have suggested that the Tan–Lu Fault underwent strike-slip movement in the Mesozoic, there is still debate about the timing and magnitude of the displacement. To decipher this problem, we conducted paleomagnetic and U–Pb geochronological studies of the Lower Cretaceous volcanic rocks of the Qingshan Group on the Jiaodong Peninsula, to the east of the Tan–Lu Fault on the southeastern edge of the North China Craton. LA–ICP–MS U–Pb dating of zircons from five samples yielded consistent ages of ca. 120 Ma. Stepwise thermal demagnetization conducted on 308 samples (40 sites) from two sections revealed stable characteristic remanent magnetization directions. After paleomagnetic tests and rejecting inappropriate data, the mean direction from 288 samples (31 independent units) is 200.3°/–51.4° (α95 = 4.1°), with a corresponding pole at 215.1°/73.0° (A95 = 4.8°). The paleolatitude calculated for the Jiaodong Peninsula is lower than that of the main block of the North China Craton, which indicates that latitudinal offset occurred between these two parts, and this offset can be ascribed to strike-slip movement along the Tan–Lu Fault. Our data provide new constraints on regional tectonic movement and Paleo-Pacific subduction processes during the late Mesozoic.

Deformation history of the Feidong Segment of the Tan–Lu Fault zone in the Early Cretaceous: Implications for the tectonic evolution in eastern China

The Tan–Lu Fault zone (TLFZ) is the largest fault zone in eastern China and a typical and representative structure of the Circum–Pacific tectonic domain. The Late Mesozoic tectonic evolution of the TLFZ is greatly significant, since it revealed the Jurassic–Cretaceous tectonic evolution of eastern China and the subduction history of the Palaeo–Pacific Plate. However, its tectonic evolution in the Early Cretaceous remains controversial. Based on geological mapping, microstructural analysis, and LA–ICP–MS zircon U–Pb dating, we constrained the deformation history of the Feidong Segment of the TLFZ in the Early Cretaceous. Results showed that the Feidong Segment of the TLFZ experienced a strong sinistral strike–slip movement at the beginning of the Early Cretaceous (~143 Ma); it was subsequently subjected to normal faulting during the Early Cretaceous (135–102 Ma), which controlled the strong magmatic activities within the Feidong area. At the end of the Early Cretaceous (~100 Ma), a weak sinistral strike–slip movement occurred again along the TLFZ. The deformation temperatures of the two sinistral strike–slip shearing stages were 500–550°C and 400–450°C, respectively. The regional comparison indicated that the Early Cretaceous tectonic evolution of the TLFZ was actually the epitome of the contemporaneous tectonic evolution of eastern China and was the result of strain localization in the Cretaceous tectonic framework of eastern China.

Superposition of two orthogonal transpressions: An example from the oblique convergent margin adjoining the Tan–Lu Fault Zone, eastern China

Deformation in oblique convergent margins, especially non-plane deformation in décollement belts within such a margin, is not fully understood. The northern Zhangbaling tectonic belt represents an oblique convergent margin to the east of the NNE–SSW-striking Tan–Lu Fault Zone that separates the Yangtze Block to the east from the North China Craton to the west, and it provides a good opportunity to understand deformation in the margin. The tectonic belt consists of a fold-and-thrust belt in the east and a low-angle ductile décollement belt in the west. The fold-and-thrust belt in the marginal cover rocks indicates a pure shear-dominated deformation, and the fold axes rotated with the long axis of the horizontal finite strain ellipse. The underlying décollement belt was involved in a non-plane deformation owing to the superposition of wrenching along the Tan–Lu Fault Zone and horizontal décollement shearing. The horizontal décollement shearing dominated in the development of the flat-lying foliation, whereas the wrenching mostly dominated in the development of stretching lineations. Top-to-the-SSW sense of shear dominates in the central to southern parts of the décollement belt, whereas top-to-the-SSE sense of shear is widely present in the northern part of the belt and locally in other parts. Partitioning of the non-plane deformation is shown by kinematic partitioning within the originally flat-lying décollement belt, and it is different from the strain partitioning in a transpressional zone involved in plane deformation. The structural and geochronological data for the oblique convergent margin are consistent with sinistral faulting of the initial Tan–Lu Fault Zone during the Triassic.

Kinematic history of the Tan-Lu fault zone constrained by the Late Mesozoic–Cenozoic tectono-sedimentary evolution of basins in the Luxi Block, eastern North China Craton

• The development of basins in the Luxi Block are closely related to the Tan–Lu Fault Zone. • The basins in the Luxi Block were involved in NE–SW compression (150–145 Ma), NE–SW extension (145–122 Ma) and N–S extension (63–32 Ma). • The Tan–Lu Fault Zone experienced sinistral strike-slip, normal faulting and dextral strike-slip in Late Jurassic–Paleogene. • The change from compression to extension at ∼145 Ma in the Luxi Block represents the initiation of craton destruction. The Tan–Lu fault zone (TLFZ), a lithosphere-scale fault in the eastern North China Craton (NCC), experienced multi-stage evolution characterized by alternating extension and strike-slip faulting in different tectonic setting. A series of Meso-Cenozoic sedimentary basins striking NW–SE to nearly E–W are distributed in the Luxi Block (LXB) to the west of the TLFZ. Recently, based on detailed fieldwork focusing on the sedimentary features and the boundary faults of these basins, the genetic relationship between basins and the TLFZ is disclosed in this study. The basins in the LXB were formed in the Late Jurassic–Paleogene, which were controlled by E–W and NW-SE-trending boundary faults. They were filled by the Late Jurassic fluvial coarse clastic rocks, the Early Cretaceous volcanic-clastic rocks, and the Paleogene fluvio-lacustrine sediments. Combined with the fault geochronology and paleo-stress restoration, three evolutionary stages are proposed: NE–SW compression in the Late Jurassic (150–145 Ma), NE–SW extension in the Early Cretaceous (145–122 Ma), and the N–S extension in the Paleogene (63–32 Ma), which were associated with the sinistral strike-slip faulting, extensional rifting, and dextral strike-slip faulting of the TLFZ, respectively. The basin evolution implies that the kinematic transition of the TLFZ occurred at the Earliest Cretaceous (∼145 Ma) and Early Paleogene (∼63 Ma). The tectono-transition from compression to extension in the LXB at ∼145 Ma might indicate the initiation of destruction of the NCC due to the adjustment from continental collision between the NCC and the South China Block (SCB) to back-arc extension of the Paleo-Pacific plate. The variation of extensional stress orientation in the Paleogene is interpreted to be related to the change of subduction direction of the Paleo-Pacific plate.

Geometric Distribution and Earthquake Rupture Characteristics of the Northern Anqiu–Juxian Fault in the Tan–Lu Fault Zone, Eastern China

The Northern Anqiu–Juxian Fault (NAJF) is one of the most active faults in the Tan-Lu Fault Zone (TLFZ), which produced the Anqiu M 7 earthquake in 70 BC. However, there is no clear understanding of the surface rupture caused by this historical earthquake. In this study, we determined the earthquake rupture characteristics of the NAJF based on high-precision surveying, geophysical exploration and drilling profiles. Based on an analysis of 87 horizontal offsets of gullies, we estimated a characteristic offset of ∼ 5 m along the NAJF for a rupture length about 130 km. Geophysical exploration results revealed a shallow geometric distribution of stepovers in the NAJF. We concluded that the ∼ 5 m offset and the rupture length of about 130 km are both in agreement with an empirical relationship among the magnitude, offset, and rupture length and imply that the ∼ 1 km wide stepover could not have terminated ruptures in the Anqiu M 7 earthquake. The relationship among the coseismic offset, magnitude, and surface rupture length of a strike-slip fault show that the 70 BC Anqiu earthquake was more likely to have had a magnitude of M ∼ 7.5.

Superposition of Two Orthogonal Transpressions: An Example from the Oblique Convergent Margin Adjoining the Tan–Lu Fault Zone, Eastern China

Superposition of Two Orthogonal Transpressions: An Example from the Oblique Convergent Margin Adjoining the Tan–Lu Fault Zone, Eastern China

Interactions between large-scale strike-slip intersecting faults: Implication from the Tan–Lu and Xiangfan–Guangji fault zones in eastern China

ABSTRACT The large-scale strike-slip Tan–Lu Fault Zone (TLFZ) and Xiangfan–Guangji Fault Zone (XGFZ) both terminate in the southeastern corner of the Dabie Orogen at an angle of almost 90°, and this corner therefore provides a very good natural laboratory for understanding the mechanism by which large-scale strike-slip faults terminate. We present new geochronological and structural data for the southeastern tip of the XGFZ and the southwestern tip of the TLFZ. The NW–SE-striking XGFZ records ductile shearing in its northwestern segment, characterized by discrete dextral shear zones that formed at temperatures of 350–400°C, as indicated by quartz c-axes fabrics and microstructures. In the southeastern segment of the XGFZ, WNW–ESE-trending thrusts are displayed. The NE–SW-striking TLFZ is characterized by discrete NE–SW-trending sinistral ductile shear zones in the Qianshan–Tongcheng segment, brittle left-lateral strike-slip faults in the Taihu–Qianshan segment, and thrusts to the south of Taihu. The trends of these thrusts change progressively southward from NE–SW to ENE–WSW and E–W. New zircon U–Pb dating results and previous cooling biotite 40Ar/39Ar ages constrain the timing of shearing in the XGFZ to 112–102 Ma (late Early Cretaceous), which is the same as the age of faulting in the TLFZ (110–102 Ma). The large-scale strike-slip TLFZ and XGFZ both terminate at their tips as thrusts. We suggest that interactions between the two faults led to the kinematic changing from strike-slip to thrusting, with this playing an important role in controlling the termination of these two large-scale intersecting strike-slip faults. The dextral shearing of the NW–SE-trending XGFZ, the sinistral shearing of the NE–SW-trending TLFZ, and the nearly E–W-trending thrust faults all indicate continental-scale N–S compression in eastern China during the late Early Cretaceous. This compression resulted from rapid NNW-ward oblique subduction of the Paleo-Pacific Plate.

Bimodal volcanic rocks in the northeastern margin of the Yangtze Block: Response to breakup of Rodinia supercontinent

Mid-Neoproterozoic protoliths of high–ultrahigh-pressure metamorphic rocks in the northeastern margin of the Yangtze Block preserve one of the best examples of 18O-depleted magmatic provinces worldwide, which is the significant record for lithospheric extension associated with continental rifting. In this contribution, we report the depleted 18O signature of felsic meta-volcanic rocks from the Zhangbaling Uplift (ZBLU), a segment of the Tan–Lu fault zone, which is located between the Dabie and Sulu orogenic belts. The low-δ18O signature of these rocks provides crucial information for understanding their origin and tectonic setting. Zircons yield UPb protolith ages of 771 ± 5 Ma to 761 ± 5 Ma and show a narrow range in δ18O values of 1.97‰ to 3.11‰. The typical syn-magmatic characteristics of these zircons indicate that they record inheritance from low-δ18O magmas during the mid-Neoproterozoic, which suggests the occurrence of high-temperature surface-water–rock interaction in a continental rift setting. Quartz keratophyres in the ZBLU exhibit A-type granite geochemical compositions with high contents of high-field-strength elements (Zr + Nb + Ce + Y > 350 ppm) and a zircon saturation temperature of 829 °C. The zircon grains have slightly depleted εHf(t) values of −3.4 to +1.9, which suggest Mesoproterozoic juvenile crustal formation in response to the amalgamation of the Yangtze Block with the Rodinia supercontinent. A few coeval spilites (758 Ma) crop out sporadically in the ZBLU. Their geochemical characteristics include high SiO2 contents (51.06–57.03 wt%), low Mg# values (42–53), and arc-like trace-element distribution patterns. The variable zircon εHf(t) values for the spilite samples can be divided into two groups: negative εHf(761 Ma) values of −16.4 to −11.1, and positive εHf(744 Ma) values of +5.9 to +8.5, which supports source mixing between enriched mantle and residual oceanic crustal material. In conclusion, the ZBLU spilite–keratophyre sequence is composed of a typical bimodal rock association, providing new petrological evidence for the origin of low-δ18O magmas and for a continental rift setting related to the separation of the Yangtze Block from the Rodinia supercontinent at ca. 771 Ma.

Determination of Paleocurrent Directions Based on Well Logging Technology Aiming at the Lower Third Member of the Shahejie Formation in the Chezhen Depression and Its Implications

The Bohai Bay basin, mainly formed in the Cenozoic, is an important storehouse of groundwater in the North China Plain. The sedimentary deposits transported by paleocurrents often provided favorable conditions for the enrichment of modern liquid reservoirs. However, due to limited seismic and well logging data, studies focused on the macroscopic directions of paleocurrents are scarce. In this study, we obtained a series of well logging data for the sedimentary layers of Es3L Formation in the Chezhen depression. The results indicate the sources of paleocurrents from the northeast, northwest, and west to a center of subsidence in the northern Chezhen depression at that time. Based on the well testing data, the physical properties of the layers from Es3L Formation in this region were generally poor, but two abnormal overpressure zones were found at 3700–3800 m and 4100–4300 m deep intervals, suggesting potential high-quality underground liquid reservoirs. By combining with other geological evidence, we suggest that the Pacific Plate was retreating and changing its direction from NE–SE to W–E and the Bohai–Luxi block was suffering an extrusion from NE induced by the Lan–Liao and Tan–Lu strike-slip faults in the early Paleogene.

Geochronology and Petrogenesis of Granitoid Intrusions in the Feidong District, Southern Tan–Lu Fault Zone, China

AbstractThe Feidong district is located in the southern segment of the Tan–Lu fault zone that separates the South China Block (NCB) from the North China Craton (NCC). We report zircon U‐Pb geochronology and Hf isotope data, as well as whole‐rock geochemistry for Xishanyi granodiorite and Jianshan granite in the Feidong district. Zircon U‐Pb dating results show that the emplacement ages of the Xishanyi and Jianshan intrusions are 124 ± 3 Ma and 130 ± 1 Ma respectively, coeval with magmatic events linked to large‐scale lithospheric thinning in eastern China. The whole‐rock geochemistry of the Xishanyi and Jianshan intrusions demonstrate that they are peraluminous, high potassium calc‐alkaline I‐type granites with adakitic characteristics. Both intrusions underwent weak crustal assimilation during emplacement. The in situ zircon ∊Hf(t) values of the Xishanyi granodiorites range from –26.4 to –21.8, with TDM2 model ages of 2552 to 2841 Ma. The in situ zircon ∊Hf(t) values of the Jianshan granite are from –27.5 to –23.0 with TDM2 model ages of 2632 to 2904 Ma. The peak age of inherited zircon grains from the Xishanyi granodiorite and the Jianshan granite were ∼2.07 Ga and ∼1.94 Ga, respectively. After compared with the regional magmatism, we suggest that both the Xishanyi and Jianshan granitoid intrusions were derived from partial melting of the NCC lower crust.

Neoproterozoic Crustal Reworking and Growth in the Zhangbaling Uplift, Tan–Lu Fault Zone: Evidence from the Feidong Complex and Zhangbaling Group

AbstractIntensive mid‐Neoproterozoic magmatism is the salient feature of the Yangtze Block, preserving abundant information about crustal reworking and growth. Zircon U–Pb–Lu–Hf isotope analysis was performed on material from the Feidong Complex (FDC) and Zhangbaling Group (ZBLG) of the Zhangbaling Uplift, in order to determine the age and magmatic source of the Neoproterozoic igneous rocks as well as the detrital provenance for the sedimentary rocks, to further provide important data for understanding the mid‐Neoproterozoic crustal evolution of the Northeast Yangtze Block. The amphibolite and gneissic granites in the Feidong Complex (FDC) gave similar protolith ages of 782–776 Ma. The synmagmatic zircons exhibited variable negative ∊Hf(t) values of –26.9 to –8.3. Early (ca. 2.4 Ga) to late Paleoproterozoic (ca. 2.0–1.9 Ga) inherited zircons were found in the gneissic monzogranite, with negative ∊Hf(t) values of –11.2 to –7.2, indicating strong reworking of the ancient crustal materials of the Northeast Yangtze Block. Whereas the amphibolites represent minor crustal growth through emplacement of continental rifting‐related mafic magmas. The quartz–keratophyres in the Xileng Formation of the ZBLG in contrast systematically yield young protolith crystallization ages of 754–727 Ma with high ∊Hf(t) values of –2.0 to +5.6, indicating their derivation from the reworking of juvenile crustal materials. The detrital zircons from the metasiltstone in the Beijiangjun Formation yield variable 206Pb/238U ages (871–644 Ma) with a peak age at 741 ± 11 Ma and ∊Hf(t) values of –4.3 to +5.3, which is consistent with those of the Xileng Formation, but distinct from the FDC, indicating that the provenance of the metasiltstone is primarily the underlying Xileng Formation. The mid‐Neoproterozoic igneous and sedimentary rocks of the Zhangbaling Uplift were products from continental rifting zones along the northern margin of the Yangtze Block, situated in different positions from the Susong Complex and the Haizhou Group. The transition from ancient to juvenile crustal sources for felsic magmatic rocks is attributed to gradually increased crustal extension during continental rifting.

Deep-shallow coupling response of the Cenozoic Bohai Bay Basin to plate interactions around the Eurasian Plate

The Bohai Bay Basin (BBB) is a Meso–Cenozoic intracontinental petroliferous basin, where four pre-existing continental-scale fault zones intersect, in East China. The BBB has experienced complex deformational and evolutionary history that records significant information about how the lithosphere there has responded to the coeval plate interactions around the Eurasian Plate and/or their resulting deep crust-mantle processes in the Cenozoic. Now both deep and shallow deformational and evolutionary processes of the BBB have been well-studied, but many geodynamic mechanisms previously proposed for those processes are too general to explain them well. Based on various data and principles, we first summarized both deep and shallow responses and processes of the BBB in the Cenozoic and then matched reasonable geodynamic mechanisms for each of them. The results show as follows: the Cenozoic differential reactivation of pre-existing continental-scale weak zones controlled the coeval deep-shallow differential coupling evolution of the BBB. The Paleogene extension in the BBB was mainly caused by crust-mantle processes triggered by the stagnant Izanagi slab. The Cenozoic strike-slip faulting was influenced by various plate interactions, in which the oblique subduction and anticlockwise rotation of young Pacific Plate resulted in the complex pre-Oligocene strike-slip history of the Tan–Lu Fault Zone to the south of the Zhang–Peng Fault Zone, while the India-Eurasia collision has caused the intense and synchronous strike-slip faulting of various faults there since ~35 Ma, which was then weakened by the oblique subduction and clockwise rotation of young Philippine Sea Plate in the Neogene. The compression resulting from both the India-Eurasia collision and the Philippine Sea Plate's subduction contributed to the latest Paleogene tectonic inversion in the BBB. The arrival of mantle flow triggered by both the India-Eurasia collision and the stagnant slab of the Pacific Plate resulted in the tectonic reactivation there in the late Neogene.

Continental response to mid-Cretaceous global plate reorganization: Evidence from the Tan–Lu Fault Zone, eastern China

Investigation of the ~2400-km-long Tan–Lu Fault Zone (TLFZ) in eastern China is the key to understanding how the Izanagi Plate in the western Pacific Basin and the East Asian continental margin responded to global plate reorganization during the mid-Cretaceous. We present new structural and geochronological data to show that the central segment of the NNE–SSW-striking TLFZ underwent a phase of sinistral transpression after the Early Cretaceous rifting. The resultant strike-slip structures are ductile shear belts in the south of the segment and brittle faults in the north. Quartz c-axis fabrics and other microstructures indicate deformation temperatures of 350–500 °C in different parts of the shear belts. The brittle faults were associated with the formation of NE–SW-trending folds and an angular unconformity between Lower and Upper Cretaceous volcanic or sedimentary rocks. Fault-slip data indicate that sinistral faulting was the result of NS compression. UPb dating constrains the timing of sinistral faulting between 97 and 82 Ma (early Late Cretaceous). Integration of these and existing data demonstrates that the entire TLFZ underwent sinistral displacement at the beginning of the Late Cretaceous, consistent with continental-scale NS compression in eastern China. Such compression in the overriding plate was caused by rapid oblique subduction of the Izanagi Plate and reflected global plate reorganization at this time. Both the changes in the kinematics of the Izanagi Plate and the resultant variation of stress states in the continental margin around the mid-Cretaceous are ascribed to this plate reorganization.

Refertilization of lithospheric mantle beneath the North China Craton in Mesozoic: Evidence from in situ Sr isotopes of Fuxin peridotite

The Mesozoic was a critical period for the evolution of the North China Craton (NCC). We present the petrological observations and in situ mineral major and trace elements and Sr isotopic data for spinel harzburgite and lherzolite xenoliths in Late Cretaceous Fuxin basalts from the northern margin of the NCC. These data are used to investigate the nature and evolution of the subcontinental lithospheric mantle (SCLM) beneath the NCC during the Mesozoic. The peridotite xenoliths commonly have porphyroclastic and granoblastic textures, and can be divided into high-Mg# and low-Mg# peridotites. Compared with the low-Mg# peridotites, the high-Mg# peridotites have higher olivine Fo (>91) and spinel Cr# values (>35), and their clinopyroxenes are light REE-enriched with uniform 87Sr/86Sr ratios (ca. 0.7042). These observations suggest that the high-Mg# peridotites could be relics of old SCLM and were metasomatized by melts derived from subducted Paleo-Asian oceanic slab. The low-Mg# peridotites are characterized by minerals with sieve textures and melt pockets. The olivine Fo of the low-Mg# peridotites are low and variable (81.2–90.4), and decrease from core to rim in some crystals. Thus, the low-Mg# peridotites underwent extensive peridotite–melt interactions. Their clinopyroxenes are enriched in LREE and show large variations in the 87Sr/86Sr ratios (0.7039–0.7052). Moreover, 87Sr/86Sr ratios positively correlate with MgO and negatively correlate with Al2O3, Eu and Dy contents. These observations suggest that the low-Mg# peridotites experienced multiple stages of mantle metasomatism, involving high-87Sr/86Sr melts derived from the subducted Paleo-Asian oceanic crust in early stage and low-87Sr/86Sr melts derived from more recent asthenospheric upwelling. Therefore, the low-Mg# peridotites are representative of SCLM fragments that were strongly modified beneath the Fuxin region during the Late Cretaceous. Combined with previous studies, our findings suggest that refertilization of the SCLM by asthenospheric melts beneath the northern margin of the NCC commenced before eruption of the Fuxin basalts (ca. 100 Ma), which is much earlier than previously thought. This process resulted in a highly heterogeneous SCLM. In addition, the Tan–Lu Fault contributed substantially to the evolution of the SCLM beneath the NCC during the Mesozoic.

Petrogenesis of late Mesozoic granitoids from the southern segment of the Tan–Lu Fault, eastern China: implications for the tectonic affinity of the Zhangbaling Uplift

ABSTRACT Late Mesozoic magmatic rocks of the Zhangbaling Uplift (ZBU) in eastern China, which comprises the northern Zhangbaling area and the southern Feidong area, can provide insights into the deep crustal processes and tectonic affinity of the massif. These rocks are dominated by granitoids with formation ages of 132–120 Ma and a peak at 129 Ma. The Shankouling dyke (120.4 ± 1.1 Ma) and the Zhuyuanzhang quartz monzodiorite (129.0 ± 2.2 Ma) crop out sporadically in the Feidong area. These rocks show adakitic signatures of high Al2O3 and Sr contents, high Sr/Y, (La/Yb)N, and (Dy/Yb)N ratios, and low Y and YbN contents. They have enriched (87Sr/86Sr)i ratios, negative εNd(t) and εHf(t) values, and unradiogenic Pb isotopic compositions that resemble those of coeval high Sr/Y granitoids in the Dabie Orogen. These ZBU rocks can be divided into two groups: low-Mg granitoids with more enriched Sr–Nd isotopic signatures and low Mg# values (<50), and high-Mg granitoids with weakly enriched Sr–Nd isotopic signatures and high Mg# values (mostly >50). Combining their geochemical features with previous results of experimental melts, we conclude that the low-Mg granitoids were derived from fluid-absent partial melting of in situ thickened lower continental crust, resulted from Triassic continental subduction and collision in this area, whereas the high-Mg granitoids were derived from delaminated eclogitic lower crust followed by interaction with mantle peridotites during magma ascent. Isotopic compositions show that these granitoids could have been derived from ancient crust of the Yangtze Block via re-melting of Neoarchean and Paleoproterozoic lower continental crust. The great depth of the Tan–Lu Fault Zone enabled delamination of the thickened eclogitic mountain root beneath the ZBU, which resulted in the formation and emplacement of the high-Mg rocks, followed by uplift of the Zhangbaling massif associated with rollback of the subducting Paleo-Pacific (Izanagi) Plate.

Structural architecture and tectonic evolution of the Cenozoic Zhanhua Sag along the Tan–Lu Fault Zone in the eastern North China: Reconciliation of tectonic models on the origin of the Bohai Bay Basin

The Zhanhua Sag, a major depocenter within the larger Bohai Bay Basin (BBB) along the Tan–Lu Fault Zone (TLFZ) in the eastern North China, developed through two successive phases with different stress regimes during the Paleogene. The kinematics and the slip history of the NW–SE– and N–S–striking normal fault systems strongly controlled the internal structure and stratigraphy of the Paleocene–Lower Eocene strata in the Zhanhua Sag during Phase 1. Isopach maps of the Paleocene–Lower Eocene stratigraphy show ~4000–m–thick clastic rock sequences in these structurally controlled depocenters. The average dip–slip rates of the NW–SE– and N–S–striking faults were 78.96 and 50.82 m/m.y. (respectively) in the Paleocene–Early Eocene, but decreased to 45.87 and 35.81 m/m.y. in the Middle–Late Oligocene. The NE–SW–striking fault systems and their slip history controlled the development of the Middle Eocene–Oligocene depocenters and their strata during Phase 2. The average dip–slip rate of the NE–SW–striking faults was 10.47 m/m.y. in the Paleocene–Early Eocene but increased to 93.49 m/m.y. in the Middle–Late Oligocene. The NE–SW–oriented faults cut across and displace the NW–SE–striking faults, indicating their relatively younger ages. These fault patterns and kinematics recorded in the Zhanhua Sag reflect an abrupt change in extension directions from ENE–WSW to NW–SE before and after the Middle Eocene that was related to a reversal in the slip direction from sinistral to dextral along the TLFZ. This slip reversal was, in turn, a result of a major change in the subduction direction of the Pacific Plate beneath eastern Asia and in the mode of strain partitioning across the TLFZ in the continental upper plate.