Age,geochemistry, and emplacement of the ~40-Ma Baneh granite–appinite complex in a transpressional tectonic regime,Zagros suture zone,northwest Iran

The Baneh plutonic complex is situated in the Zagros suture zone of northwest Iran between the Arabian and Eurasian plates. This complex is divided into granite and appinite groups. Zircon U–Pb dating shows that granites crystallized 41–38 million years ago but appinites experience more protracted magmatic evolution, from at 52 to 38 Ma. Whole-rock chemical compositions show significant major and trace element variations between the two lithologies. Granitic rocks are more evolved, with high contents of SiO₂ (62.4–77.0 wt%), low contents of TiO₂ (0.25 wt%), MgO (0.05–1.57 wt%), and Fe₂O₃ (0.40–4.06 wt%) and high contents of Na₂O + K₂O (≈10 wt%). In contrast, appinites have low contents of SiO₂ (51.0–57.0 wt%) and K₂O (<2.1 wt%) and high Fe₂O₃ (6.4–9.35 wt%), MgO (2.0–9.9 wt%), and Mg number (Mg# = 35–76). The concentration of rare earth elements in the appinites is higher than in granitic rocks, making it difficult to form granites solely by fractionation of appinite magma. (⁸⁷Sr/⁸⁶Sr)_i and ε_Nd(40 Ma) in both groups are similar, from 0.7045 to 0.7061 and ?1.2 to +2.6, except for a primitive gabbroic dike with ε_Nd(40 Ma) = +9.9. Appinites show mainly typical I-type characteristics, but granites have some S-type characteristics. The sigmoidal shape of the Baneh pluton and its emplacement into deformed Cretaceous shales and limestone showing kink bands, asymmetric and recumbent folds in a broad contact zone, with pervasive ductile to brittle structures in both host rocks and intrusion, indicate that magma emplacement was controlled by a transpressional tectonic regime, perhaps developed during early stages in the collision of Arabia and Eurasian plates.     

Transpressive Structures in the Ghadir Shear Belt,Eastern Desert,Egypt: Evidence for Partitioning of Oblique Convergence in the Arabian‐Nubian Shield during Gondwana Agglutination

Transpressional deformation has played an important role in the late Neoproterozoic evolution of the ArabianNubian Shield including the Central Eastern Desert of Egypt. The Ghadir Shear Belt is a 35 km-long, NW-oriented brittleductile shear zone that underwent overall sinistral transpression during the Late Neoproterozoic. Within this shear belt, strain is highly partitioned into shortening, oblique, extensional and strike-slip structures at multiple scales. Moreover, strain partitioning is heterogeneous along-strike giving rise to three distinct structural domains. In the East Ghadir and Ambaut shear belts, the strain is pure-shear dominated whereas the narrow sectors parallel to the shear walls in the West Ghadir Shear Zone are simple-shear dominated. These domains are comparable to splay-dominated and thrust-dominated strike-slip shear zones. The kinematic transition along the Ghadir shear belt is consistent with separate strike-slip and thrustsense shear zones. The earlier fabric(S1), is locally recognized in low strain areas and SW-ward thrusts. S2 is associated with a shallowly plunging stretching lineation(L2), and defines ～NW-SE major upright macroscopic folds in the East Ghadir shear belt. F2 folds are superimposed by ～NNW–SSE tight-minor and major F3 folds that are kinematically compatible with sinistral transpressional deformation along the West Ghadir Shear Zone and may represent strain partitioning during deformation. F2 and F3 folds are superimposed by ENE–WSW gentle F4 folds in the Ambaut shear belt. The sub-parallelism of F3 and F4 fold axes with the shear zones may have resulted from strain partitioning associated with simple shear deformation along narrow mylonite zones and pure shear-dominant deformation in fold zones. Dextral ENEstriking shear zones were subsequently active at ca. 595 Ma, coeval with sinistral shearing along NW-to NNW-striking shear zones. The occurrence of upright folds and folds with vertical axes suggests that transpression plays a significant role in the tectonic evolution of the Ghadir shear belt. Oblique convergence may have been provoked by the buckling of the Hafafit gneiss-cored domes and relative rotations between its segments. Upright folds, fold with vertical axes and sinistral strike-slip shear zones developed in response to strain partitioning. The West Ghadir Shear Zone contains thrusts and strikeslip shear zones that resulted from lateral escape tectonics associated with lateral imbrication and transpression in response to oblique squeezing of the Arabian-Nubian Shield during agglutination of East and West Gondwana.     

Transpressional deformation in northwestern Sardinia (Italy): insights on the tectonic evolution of the Variscan BeltDéformation transpressive dans le Nord-Ouest de la Sardaigne (Italie) : considérations sur l'évolution tectonique de la chaı̂ne Varisque

Structural investigations in northwestern Sardinia highlight the occurrence of a regional D2 transpressional deformation related both to NNE–SSW direction of compression and to a NW–SE shear displacement. The deformation is continuous and heterogeneous, showing a northward strain increase, indicated by progressively tighter folds and occurrence of F2 sheath folds. D2 transpression is characterised by the presence of a crustal-scale shear deformation overprinting previous D1 structures, related to nappe stacking and top-to-the-south and southwest thrusting. The L2 prominent stretching lineation points to an orogen-parallel extension and to a change in the tectonic transport from D1 to D2. It is attributed to the position of Sardinia close to the northeastern part of the Cantabrian indenter during the progressive evolution of the Ibero-Armorican Arc. D1 phase developed during initial frontal collision, whereas D2 deformation characterised the progressive effect of horizontal displacement during the increasing curvature of the arc. To cite this article: R. Carosi, G. Oggiano, C. R. Geoscience 334 (2002) 287–294.     

东昆仑中部构造混杂岩带右行走滑韧性剪切变形特征

东昆仑中部构造混杂岩带是经历了新元古代、加里东末期和晚海西期3次碰撞事件而形成的多旋回复合的碰撞缝合带。通过对东昆中构造混杂岩带晚海西期右行走滑韧性剪切变形的几何学、运动学及流变学特征的研究，探讨了其形成的动力学背景，指出东昆中晚海西期的碰撞缝合带是不同陆块间斜向碰撞形成的转换挤压带。     

Late Cenozoic polyphase deformation and basin development,Kütahya region,western Turkey

The Neogene–Quaternary succession in the Kütahya region is of importance in the neotectonic evolution of western Anatolia because the strata contain clear evidence of compression and extension. During the early-middle Miocene, N–S compression/transpression as well as NE–SW- and NW–SE-oriented oblique conjugate faults formed. NE–SW-oriented horsts and grabens developed, controlled by the dominant NE–SW faults. The Seyitömer and Sabuncup?nar grabens were filled primarily by terrestrial clastic sedimentary and volcanic rocks. At the end of the middle Miocene, the graben fill was locally folded and reverse faulted, reflecting reactivation of compression. Between the late Miocene and the middle Pliocene, the region underwent erosion and lacustrine sediments accumulated in topographic lows. Between the middle and late Pliocene, compression in the region was again reactivated and basal units were thrust over the pre-upper Pliocene units. The late Plio-Quaternary marked the onset of N–S extension and development of the NW–SE-oriented Kütahya Graben, co-genetic equivalents of which are common throughout western Anatolia. This study indicates that tectonic evolution of western Anatolia involved multiple stages of contraction and extension.     

A Quantitative structural study of late pan-african compressional deformation in the central eastern desert (Egypt) during Gondwana assembly

The Arabian-Nubian-Shield (ANS) is composed of a number of island arcs together with fragments of oceanic lithospere and minor continental terranes. The terranes collided with each other until c. 600 Ma ago. Subsequently, they were accreted onto West Gondwana, west of the present River Nile. Apart from widespread ophiolite nappe emplacement, collisional deformation and related lithospheric thickening appear to be relatively weak. Early post-collisional structures comprise not only extensional features such as fault-bounded (molasse) basins and metamorphic core complexes, but also major wrench fault systems, and thrusts and folds. The Hammamat Group was deposited in fault-bounded basins, which formed due to N-S to NW-SE directed extension. Hammamat Group sediments were intruded by late orogenic granites, dated as c. 595 Ma old. A NNW-SSE-oriented compression prevailed after the deposition of the Hammamat Sediments. This is documented by the presence of NW-verging folds and SE-dipping thrusts that were refolded and thrusted in the same direction. Restoration of a NNW-SSE- oriented balanced section across Wadi Queih indicates more than 25% of shortening. Transpressional wrenching related to the Najd Fault System followed this stage. The wrenching produced NW-SE sinistral faults associated with positive flower structures that comprise NE-verging folds and SW-dipping thrusts. Section restoration across these late structures indicates 15 17% shortening in the NE-SW direction. At a regional scale, the two post-Hammamat compressional phases produced an interference pattern with domes and basins. It can be shown that the Najd Fault System splays into a horsetail structure in the Wadi Queih area and loses displacement towards N and NW. The present study shows a distinct space and time relationship between deposition of Hammamat Group/late-Pan-African clastic sediments and late stages of Najd Fault wrench faulting: Hammamat deposition is followed by two episodes of compression, with the second episode being related to Najd Fault transpression. Therefore, the Hammamat sediments do not represent the latest tectonic feature of the Pan-African orogeny in the ANS. The latest orogenic episodes were the two successive phases of compression and transpression, respectively. It is speculated that extension during (Hammamat) basin formation was sufficiently effective to reduce the thickness of the orogenic lithosphere until it became gravitationally stable, and incapable of further gravitational deformation.     

南中国海成因:右行拉分作用与左行转换挤压作用交替

总结分析了南中国海各次级盆地及其周缘有关盆地的裂谷作用序列 ,认为它们的裂谷作用序列是相似的 ,虽然存在局部差异。古近纪 (—早中新世 )和新近纪分别为一级裂谷阶段和后裂谷阶段 ,并可进一步划分次一级裂谷和后裂谷阶段。南中国海总体几何学特征及其次级盆地和周缘盆地的几何学特征表明 ,它们的裂谷作用是以近南北向主断裂为主剪切的右行拉分作用。在右行拉分过程中 ,东越南断裂的南延 (翼他陆架部分 )可能没有发生巨大脆性平移而表现为巨大的右行韧性牵引 ;印支—苏门答腊地块是被东越南断裂、东安达曼海断裂、红河断裂和苏门答腊断裂等四条断裂围限的呈菱形的右行走滑双重构造。深海盆的洋壳在许多方面与概念化大洋洋壳不同 ,相互矛盾的各种磁异常条带年龄并不可信。它的洋壳是右行拉分作用形成的洋壳。它们的后裂谷作用是以近南北向主断裂为主剪切的左行转换挤压反转变形为特征。联系到裂谷作用序列 ,南中国海成因具有右行拉分作用、裂谷作用和左行转换挤压作用交替出现的特征 ,表现了具有转换性质的“开”与“合”的更迭     

A synthesis: Late Cenozoic stress field distribution at northeastern corner of the Eastern Mediterranean,SE Turkey

Fault kinematic analysis and inversion of focal mechanisms of shallow earthquakes reveal significant evolution of the regional stress regime in the northeastern most corner of the Eastern Mediterranean region since the Mio-Pliocene to the present time. This study was carried out in the interaction area between the Arabian/African plates and the Anatolian block. The evolution of stress regimes consists of a change from older transpression to younger transtension. Both strike-slip stress regimes having a NNW- to northwest-trending σ_Hmax (σ₁) and ENE- to northeast-trending σ_Hmin (σ₃) axes induce a sinistral component of displacement on the major intra-continental Karatas–Osmaniye and Misis–Ceyhan faults elongated with the northeast-trending Misis Range between Adana and Osmaniye provinces (sub-area i) and by a NNE-trending plate boundary Amanos fault running along Amanos Range between Antakya and Kahramanmaras provinces (sub-area ii). The inversion results show that the transtensional stress regime is dominantly strike-slip to extension, with an ENE- to northeast-trending σ_Hmin (σ₃) axis for sub-areas (i) and (ii), respectively. The inversions of earthquake focal mechanisms indicate that the transtensional stress regime is still active in the whole study area since probably recent Quaternary time. To cite this article: S. Over et al., C. R. Geoscience 336 (2004).     

南大巴山冲断构造及其剪切挤压动力学机制

南大巴山是一个形成于T3－K1，滑脱深度小于8－10km 的扬于板块北缘薄皮冲断锲它主要由发育在显生宙地层中台阶状逆断层及断层相关褶皱构成的逆冲岩席、双重推覆体和冲起构造等组成。变形扩展以前列式为主。经平衡地质剖面制作，因冲断南大巴山地壳缩短率平均达49.3％。并以每年约1.28mm 的速率总体缩短约64km，它的成因受控于秦岭碰撞造山过程中扬于板块北缘A型俯冲所提供挤压应力，在向南扩展时，由于古大陆边缘形态不一所诱发的右旋剪切挤压动力学机制。     

GEOLOGICAL EVOLUTION AND OROGENY OF EAST KUNLUN TERRAIN ON THE NORTHERN QINGHAI—TIBET PLATEAU

GEOLOGICAL EVOLUTION AND OROGENY OF EAST KUNLUN TERRAIN ON THE NORTHERN QINGHAI—TIBET PLATEAU1　XuZQ ,YangJS ,ZhangJX ,etal.AcomparisonbetweenthetectonicunitsonthesidesoftheAltunsinistralstrike slipfaultandthemechanismoflithosphericshearing[J] :ActaGeologicaSinica,1999,73:193～ 2 0 5(inChinesewithEnglishabstract) . 2　YangJS ,XuZQ ,LiHB ,Wu ,etal.DiscoveryofeclogiteatthenorthernmarginofQaidambasin,NWChina[J] .Chi neseScienceBulletin,1998,4 3…