The Tan-Lu fault zone (TLF) is a major strike-slip fault with a long and complex history in East Asia, whose evolution provides a new perspective on the formation of large-scale faults (> 1000 km long). Fault displacement analysis, geological mapping and U-Pb LA-ICP-MS dating have been performed to understand the evolution of the TLF. Along-strike displacement variation reveals that the TLF consists of two kinematically independent segments, the northern and southern TLF, with opposite long-term propagation directions. Structural and geochronological studies in the eastern Yanshan belt, located around the linkage area of the southern and northern TLF, indicate that NNE-trending sinistral strike-slip faults initiated at 167-164 Ma and were reactivated at 124-121 Ma. Structural analysis suggests that these early NNE-trending strike-slip faults transferred sinistral motion along the northern TLF into southward thrusting along the Yanshan belt, representing the Middle Jurassic southern termination of the northern TLF. Our studies suggest that the through-going TLF formed when the younger southward-propagating northern TLF merged with the older northward-propagating southern TLF in the Late Jurassic. A new model is thus proposed for the Mesozoic evolution of the TLF. The initiation and southward propagation of the northern TLF is interpreted to have resulted from the southward indentation of the Siberian craton into the amalgamated Central Asian Orogenic Belt and North China block. The divergent mega-splays of the northern TLF likely resulted from westward-younging formation during the clockwise rotation of northeast Asia. Coalescence of two genetically unrelated faults could be an alternative mode for large-scale fault formation.

Detrital zircons from northeast China record cyclic magmatism along the northern and eastern margins of the North China block during late Paleozoic time and Mesozoic time, respectively. The late Paleozoic zircons record three magmatic flare-ups with a period of ∼60 m.y. that occurred within a magmatic arc constructed along the Paleoasian (northern) margin of North China, and are accompanied by negative εHf(t) excursions representing shortening and increased crustal melting over the duration of each flare-up. The intervening magmatic lulls are accompanied by rapid positive εHf(t) excursions signifying influxes of juvenile magma into the arc, probably during extension and foundering of underlying melt residua. The lack of similar isotopic patterns in zircons derived from contemporaneous intrusions into older continental settings inboard of the arc indicate that this process was restricted to the arc itself. Mesozoic magmatism in North China occurred along the Paleo-Pacific margin following closure of the Paleoasian Ocean, and exhibits a ∼50 m.y. periodicity that is out-of-phase with that of the Paleozoic arc. Although the tectonic setting of North China during Mesozoic time is complex and still controversial, it is possible that this younger periodicity is governed by similar processes as those that dominated the Paleozoic arc. This is a testable hypothesis that warrants further attention. Crustal shortening was widespread in North China during Mesozoic time, and documented lithosphere removal events in eastern North China occurred during the Mesozoic magmatic lulls. Lithospheric thickening/foundering cyclicity, well-documented in Cordilleran arc systems, may be a common process in continental arcs through space and time.

The EW trending Yanshan belt, an intraplate fold-thrust belt located in the northern North China Craton that has experienced several episodes of deformation widely separated in time, is characterized by out-of-sequence thrusts. According to detailed mapping in the central Yanshan belt, five geometric and stratigraphic criteria used to aid in determining whether a thrust has an out-of-sequence geometry or not can be recognized. They are (1) unconformable relationships, (2) inclination of fault surfaces, (3) irregular changes in apparent offset along strike, (4) short fault length relative to apparent offset, and (5) in-sequence geometry. With the help of these criteria, two generations of out-of-sequence thrusts that postdate the original in-sequence thrusting in the central Yanshan belt are recognized. The ancestral southward verging fold-and-thrust belt that formed prior to 180Ma was deformed and cut by two younger generations of faults that are probably more deeply rooted and are constrained to between 172-165Ma and 152-135Ma. A series of thrusts with opposite vergence formed during the last period, resulting in abundant abnormal field relationships such as younger-on-older thrust relations, fold truncation, and cutting down-section. The nature and occurrence of faults in the Yanshan belt implies that superimposed deformation, a common feature in polycyclic orogenic belts, is a mechanism for the generation of out-of-sequence thrusting. This adds to mechanisms already described in the literature, such as maintaining constant critical taper at an orogenic scale, inhibition of the deformation front, and lateral changes in the nature of the decollement horizons.

A transformation in the tectonic regime affected the continental crust of eastern China during the Middle-Late Jurassic period by changing tectonic trends from E-W to NE and then NNE. The Mesozoic Yanshan tectonic belt in northern China has a distinctive three-segment geometry. This includes a segment south and west of Beijing with a NE trend, a central E-W segment near and east of Beijing, and a NNE-trending segment farther to the east. Field investigations of Mesozoic thrust faults and folds, granitic intrusions and dikes, combined with zircon sensitive high-resolution ion microprobe (SHRIMP) and laser-ablation-inductively coupled plasma-mass spectrometry (LAICP-MS) dating, constrain the age of the NE-SW-trending tectonic belts that occurred during ca. 170-150 Ma. Melting of the lower crust and crust-mantle interaction resulted in volcanic eruptions and granitic intrusions (ca. 165-155 Ma), and widespread NW-SE to NNW-SSE shortening and transpression in the Yanshan tectonic belt were associated with the movement of the upper part of intracontinental crust (ca. 170-150 Ma) upon a basal decollement located between crystalline basement and overlying rocks (layered crustal rotation). After this transformation, deformation, basin sedimentation, and magmatism occurred in NNE-trending tectonic belts that paralleled the eastern Asian continental margin. This tectonic transformation was temporally and spatially linked to the rapid formation of the Pacific plate at 180-160 Ma.

A major rift province, comparable in extent to the Cenozoic Basin and Range province of North America, developed in east Asia during late Mesozoic time. Like the Basin and Range, the east Asian province features numerous extensional basins that developed in both low-strain and high-strain settings within heterogeneous crust that had experienced prior shortening. The low-strain basins comprise isolated or linked half-grabens that are characterized by fluvial-lacustrine facies assemblages and internal drainage. In northeastern China, normal faults that bound numerous Lower Cretaceous half-graben basins sole into Jurassic thrust faults at depth, demonstrating that the geometry of low-strain extension was strongly influenced by the pre-rift basement structure. In southeastern Mongolia, the petroliferous East Gobi basin coalesced from several Upper Jurassic-Lower Cretaceous synrift depocenters as a consequence of fault linkage. An Upper Cretaceous post-rift megasequence was deposited following an episode of mid−Cretaceous transpression that inverted the basin. The high-strain basins associated with the Hohhot metamorphic core complex in northern China constitute a supradetachment basin system that was filled with thin (<1.5 km) successions of dominantly coarse-grained alluvial strata derived from the footwalls of successive detachment splays. It is likely that the late Mesozoic extension in east Asia was related in some manner to the collapse of overthickened crust that developed during the numerous late Paleozoic−early Mesozoic orogenic events responsible for the early assembly of Asia.

ABSTRACTLuanping basin is one of many small rift basins that developed in northeast China during mid‐Cretaceous time. It is filled by alluvial, fan‐deltaic and lacustrine strata of the Lower Cretaceous (post 130 Ma) Xiguayuan Formation. Distribution of facies and stacking patterns are controlled by position within the basin with respect to fault‐bounded basin margins. Luanping basin is bounded by a normal fault consisting of two segments that are perpendicular to each other in map view; one or both of these faults probably accommodates a component of strike‐slip. This geometry gave rise to three distinct depozones within the basin: (1) a region of maximum sediment thickness located near the intersection of these two basin‐bounding fault segments; (2) a shallower part of the basin, located near the tip of the normal fault segment bounding the basin to the north; and (3) a low‐gradient, north‐dipping ramp. The facies found in each of these settings are different. Coarse sublacustrine sediment gravity flows interfinger with profundal black shale near the basin depocentre at the intersection of the two basin‐bounding fault segments. Fan delta and shallow lacustrine sedimentation dominated in the shallower part of the basin near the northeastern tip of the master‐bounding fault. Fine‐grained shallow lacustrine sedimentation predominated along the low‐gradient ramp. The facies in Luanping basin are different from those found in basins of similar size elsewhere in the northeastern China extensional tract. Specifically, profundal, organic‐rich black shales are found in Luanping basin but are largely lacking in neighbouring basins. We suggest that this is due to higher rates of subsidence along more steeply dipping normal faults in Luanping basin, as opposed to the other basins.

ABSTRACTThe Yanshan fold‐thrust belt is an exposed portion of a major Mesozoic orogenic system that lies north of Beijing in northeast China. Structures and strata within the Yanshan record a complex history of thrust faulting characterized by multiple deformational events. Initially, Triassic thrusting led to the erosion of a thick sequence of Proterozoic and Palaeozoic sedimentary strata from northern reaches of the thrust belt; Triassic–Lower Jurassic strata that record this episode are deposited in a thin belt south of this zone of erosion. This was followed by postulated Late Jurassic emplacement of a major allochthon (the Chengde thrust plate), which is thought to have overridden structures and strata associated with the Triassic event and is cut by two younger thrusts (the Gubeikou and Chengde County thrusts). The Chengde allochthon is now expressed as a major east–west trending, thrust‐bounded synform (the Chengde synform), which has been interpreted as a folded klippe 20 km wide underlain by a single, north‐vergent thrust fault. Two sedimentary basins, defined on the basis of provenance, geochronology and palaeodispersal trends, developed within the Yanshan belt during Late Jurassic–Early Cretaceous time and are closely associated with the Chengde thrust and allied structures. Shouwangfen basin developed in the footwall of the Gubeikou thrust and records syntectonic unroofing of the hanging wall of that fault. Chengde basin developed in part atop Proterozoic strata interpreted as the upper plate of the Chengde allochthon and records unroofing of the adjacent Chengde County thrust. Both the Chengde County thrust and the Gubeikou thrust are younger than emplacement of the postulated Chengde allochthon, and structurally underlie it, yet neither Shouwangfen basin nor Chengde basin contain a detrital record of the erosion of this overlying structure. In addition, facies, palaeodispersal patterns and geochronology of Upper Jurassic strata that are cut by the Chengde thrust suggest only limited (ca. 5 km) displacement along this fault. We suggest that the units forming the Chengde synform are autochthonous, and that the synform is bounded by two limited‐displacement faults of opposing north and south vergence, rather than a single large north‐directed thrust. This conclusion implies that the Yanshan belt experienced far less Late Jurassic shortening than was previously thought, and has major implications for the Mesozoic evolution of the region. Specifically, we argue that the bulk of shortening and uplift in the Yanshan belt was accomplished during Triassic–Early Jurassic time, and that Late Jurassic structures modified and locally ponded sediments from a well‐developed southward drainage system developed atop this older orogen. Although Upper Jurassic strata are widespread throughout the Yanshan belt, it is clear that these strata developed within several discrete intermontane basins that are not correlable across the belt as a single entity. Thus, the Yanshan has no obvious associated foreland basin, and determining where the Mesozoic erosional products of this orogen ultimately lie is one of the more intriguing unresolved questions surrounding the palaeogeography of North China.

A widespread and well-documented episode of Late Jurassic-Early Cretaceous rifting followed multiple events of mid- to late Mesozoic crustal contraction in NE China. This extensional deformation was closely associated with widespread Mesozoic magmatism, thought to be related to lithospheric delamination and destabilization of the previously stable North China craton. Early Cretaceous rift-related sedimentary basins in the western Liaoning region of NE China comprise numerous discrete, largely lacustrine half-graben basins bounded by NW-rooting low-angle normal faults that sole into older thrusts or mid-crustal shear zones. These basins characteristically lack post-rift thermal subsidence and significantly postdate most of the Mesozoic volcanism in the region. Instead, magmatism that has been attributed to lower crustal foundering, and hence lithospheric delamination (perhaps as old as 160 Ma) accompanied continuing crustal thickening in eastern North China. Thus, although widespread magmatism plausibly played a role in thermally weakening the crust prior to extension, there is little upper crustal evidence that wholesale removal of the lithosphere and lower crust occur-red during Mesozoic time. The expansive Cenozoic rift basins of Eastern China, which do contain thick post-rift sequences, constitute a more viable response to lithospheric delamination.

Abstract The Tres Pasos Formation, Magallanes Basin, Chile, represents the deposit of a submarine slope depositional system. The formation is approximately 1500 m thick where exposed in the Ultima Esperanza district of southernmost Chile. It is characterized by a basal turbiditic sandstone unit up to 200 m thick that shows a north-to-south, proximal-to-distal facies evolution from turbidite channel-fill complexes to sheet-like sandstone units. This unit is interpreted as having been deposited at or near the base of slope. Overlying the basal sandstone unit is approximately 500 m of amalgamated mass transport complexes, fine-grained strata, and channelized and non-channelized turbidity current deposits, collectively comprising the middle part of the formation. Mass transport complexes exert a primary control on the character and grain size of turbidite sandstone bodies in the basal and middle part of the formation. In the southern part of the study area, a 300 m thick coarse-grained unit interpreted as a turbidite channel-fill complex partially replaces the middle part. The upper part of the formation is approximately 500 m thick and consists primarily of fine-grained strata. Failure scarps and thin turbidite channel-fill units are present in this upper part, interpreted as upper slope deposits.

The Late Paleozoic collision between the North China continental block and the Altaid arc terranes of Mongolia represents one of the earliest and most fundamental tectonic events in the ongoing construction of Asia. New detrital zircon provenance data from Carboniferous-Permian nonmarine strata on the northern margin of North China imply that the northern margin of the North China block constituted a continental margin arc prior to this collision (~400-275 Ma) and that collision took place via south-directed subduction beneath North China. A significant and widespread climate change took place in North China in mid-Permian time, and is recorded by a change from Carboniferous and Lower Permian humid-climate, coal-bearing sedimentary facies to Upper Permian and Lower Triassic arid-climate redbeds. In northern North China, this climate change is accompanied by a paleocurrent reversal, which indicates the onset of uplift on the northern margin of the North China block. The temporal association of climate change and uplift suggests that aridification of North China may have been caused by a rainshadow effect from topography related to the convergence and ultimate collision between the North China block and the Altaid arc terranes of Mongolia. Alternatively, climate change may have occurred as a result of northward drift of the North China block through arid subtropical latitudes.

The ideas and concepts regarding to the analysis of syntectonic sedimentation are briefly introduced together with the investigation approaches and its potential implications to the research of regional tectonic deformation processes. It was studied that the tectonic deformations together with the conglomerate composition variation within the Late Jurassic Tuchengzi Formation in south of Lingyuan City, western Liaoning Province, the following conclusions are reached. (1) The syntectonic/synkinematic sedimentation in the research area was commenced after the volcanism of the Tiaojishan Formation. The provenance area was located to the west of the synkinematic sedimentary basin—Dengzhangzi Basin, instead of the east side of the basin. Dengzhangzi Basin was not a foredeep sedimentary basin of the westward thrusting as it was thought to be by previous investigators. Variations of the conglomerates within the Tuchengzi Formation indicate an erosion and unroofing sequence of the tilted normal sequence of the provenance strata. The erosion reached the upper part of the Wumishan Formation of the Mesoproterozoic Jixian Group. (2) The contacts between the relic slices of Mesoproterozoic Changcheng Group, lying between the Niuyingzi-Guojiadian Basin and the Dengzhangzi Bansin, and the Beipiao group to the east is a major east southeast-ward thrust fault. To the northwest side, however, the Tuchengzi Formation lies unconformably on top of the relics of Changcheng Group. In the area SE of Laohugou where the Changcheng Group disappeared, the Tuchengzi Formation lies directly on top of the Beipiao Formation. The relics of Changcheng Group between the two basins aforementioned is interpreted to be a klippe formed during an extensive east-south-east thrusting events of prior to the volcanic activity of Tiaojishan formation. (3) The thrusting deformation sequence in the south of Lingyuan City, western Liaoning Province, could be identified as follows: starting from a southward thrusting prior to the Early Jurassic Beipiao Formation (the Indosinian), then to the east-south-east ward thrusting before Tiaojishan Formation followed by a thrusting and associated folding with vergence to the southeast after Tiaojishan Formation, finally to the ending of contraction deformation with local thrusting deformation within the Early Cretaceous Jiufotang Formation. About 35% shortening within the covering sequence was achieved during the east-south-east thrusting and folding in the study area.

New sensitive high-resolution ion microprobe-reverse geometry U-Pb detrital zircon data establish the timing of onset of foreland basin subsidence in the Magallanes basin and the age of the Patagonian Andes in southernmost Chile. Initiation of the Magallanes foreland basin is signaled by the abrupt occurrence of sandstone of the Punta Barrosa Formation, loosely dated as upper Albian-Cenomanian from biofacies assemblages. Detrital zircon analyses demonstrate that the Punta Barrosa Formation is not older than 92 +/- 1 Ma and that the linked Andean belt started forming in the Turonian.

Structural and stratigraphic studies of the western Daqing Shan segment of the Yinshan belt have recognized an Early Jurassic extensional episode supported by several lines of evidence. First, normal faults cut the lowermost Jurassic sequence and are overlapped by younger Lower Jurassic rocks. Second, Lower Jurassic rocks include growth strata in small-scale graben at the base of the Jurassic basin. Third, rapid lateral facies changes are mapped from boulder conglomerates along the basin-bounding faults to lacustrine and meandering fluvial rocks in the basin center. Fourth, paleodrainage systems provided sediment input from three sides of the basin, two transverse and one axial. Finally, there is a strongly asymmetric distribution of coarse proximal and fine distal facies within the basin. The Early Jurassic extensional episode was responsible for formation of an east-trending half-graben basin in the western Daqing Shan in which at least 1800 m of syn-extensional nonmarine sediments accumulated and are preserved.Previous studies in the Triassic and Jurassic of other parts of northwest and north-central China have concluded that the early Mesozoic was a time of continental amalgamation and contractile deformation. The recognition of an Early Jurassic extensional episode along the northern mar.-in of the North China Block is problematic in this context, at least superficially. We propose two possible explanations for the Early Jurassic extension: transtension associated with strike-slip tectonics, or gravitational collapse of a pre-existing Late Paleozoic-Early Mesozoic contractile orogenic belt. The first possibility, transtensional deformation, is problematic because specific strike-slip faults have not been identified that could control extension in the western Daqing Shan. However, several lines of evidence allow the possibility of such a driving mechanism, including: documented Early Jurassic transtensional systems in the southwestern North China Block, several candidate strike-slip faults along the China-Mongolia border region, structural discontinuity between the Daqing Shan and southern Mongolia, and along strike-changes in structural style within the Yinshan belt. The second possibility, orogenic collapse, is similarly difficult to establish because of the limited amount of data concerning the regional distribution and orientation of pre-Jurassic contractile structures and Early Jurassic extensional structures. However, documented Late Paleozoic-Triassic contractile deformation, as well as the close temporal and spatial association, and parallelism between Early Jurassic extensional structures and older contractile structures in the western Daqing Shan requires consideration of gravitational collapse as a driving mechanism for Early Jurassic extension in the Yinshan belt. (C) 2001 Elsevier Science B.V. All rights reserved.