Geology,structure and age of the Nahuel Niyeu Formation in the Aguada Cecilio area,North Patagonian Massif,Argentina

The low-grade Nahuel Niyeu Formation in the Aguada Cecilio area (40°50′S–65°53′W) shows ultramafic to felsic metaigneous rocks forming a sill swarm intercalated in the metasedimentary sequence and a polyphase deformation which permit an integrated study of the magmatic and tectonometamorphic evolution of this geological unit.In this paper we present a geological characterization of the Nahuel Niyeu Formation in the Aguada Cecilio area combining mapping, structural and metamorphic analysis with a SHRIMP U–Pb age and geochemical data from the metaigneous rocks.The metasedimentary sequence consists of alternating metagreywackes and phyllites, and minor metasandstones and granule metaconglomerates. The sills are pre-kinematic intrusions and yielded one SHRIMP U–Pb, zircon crystallization age of 513.6 ± 3.3 Ma. Their injection occurred after consolidation of the sedimentary sequence. A syn-sedimentary volcanic activity is interpreted by a metaandesite lava flow interlayered in the metasedimentary sequence. Sedimentary and igneous protoliths of the Nahuel Niyeu Formation would have been formed in a continental margin basin associated with active magmatic arc during the Cambrian Epoch 2. Two main low-grade tectonometamorphic events affected the Nahuel Niyeu Formation, one during the Cambrian Epoch 2–Early Ordovician and the other probably in the late Permian at ∼260 Ma. Local late folds could belong to the final stages of the late Permian deformation or be even younger.In a regional context, the Nahuel Niyeu and El Jagüelito formations and Mina Gonzalito Complex show a comparable Cambrian–Ordovician evolution related to the Terra Australis Orogen in the south Gondwana margin. This evolution is also coeval with the late and early stages of the Pampean and Famatinian orogenies of Central Argentina, respectively. The late Permian event recorded in the Nahuel Niyeu Formation in Aguada Cecilio area is identified by comparable structures affecting the Mina Gonzalito Complex and El Jagüelito Formation and resetting ages from granitoids. This event represents the Gondwanide Orogeny within the same Terra Australis Orogen.     

Lower Pliensbachian caldera volcanism in high-obliquity rift systems in the western North Patagonian Massif,Argentina

In the Cerro Carro Quebrado and Cerro Catri Cura area, located at the border between the Neuquén Basin and the North Patagonian Massif, the Garamilla Formation is composed of four volcanic stages: 1) andesitic lava-flows related to the beginning of the volcanic system; 2) basal massive lithic breccias that represent the caldera collapse; 3) voluminous, coarse-crystal rich massive lava-like ignimbrites related to multiple, steady eruptions that represent the principal infill of the system; and, finally 4) domes, dykes, lava flows, and lava domes of rhyolitic composition indicative of a post-collapse stage.The analysis of the regional and local structures, as well as, the architectures of the volcanic facies, indicates the existence of a highly oblique rift, with its principal extensional strain in an NNE–SSW direction (∼N10°).The analyzed rocks are mainly high-potassium dacites and rhyolites with trace and RE elements contents of an intraplate signature. The age of these rocks (189 ± 0.76 Ma) agree well with other volcanic sequences of the western North Patagonian Massif, as well as, the Neuquén Basin, indicating that Pliensbachian magmatism was widespread in both regions. The age is also coincident with phase 1 of volcanism of the eastern North Patagonia Massif (188–178 Ma) represented by ignimbrites, domes, and pyroclastic rocks of the Marifil Complex, related to intraplate magmatism.     

a revised age for the granites of the central Somuncura Batholith, North Patagonian Massif

The age of the granites of the La Esperanza region of the Somuncura Batholith, North Patagonian Massif has been revised, based in part on Rb---Sr whole-rock data obtained by reanalyzing samples from a previous study. The new ages are 258 ± 15 Ma for the Prieto Granodiorite and 259 ± 16 Ma for the Donosa Granite, both from the older La Esperanza plutonic complex, and 239 ± 4 Ma for the Calvo Granite, from the younger volcano-plutonic Dos Lomas complex. The initial ⁸⁷Sr/⁸⁶Sr ratios are all in the range 0.7070–0.7076. The ages probably correspond stratigraphically to Late Permian and Early Triassic for the two complexes, respectively, consistent with traditional geologic interpretation. Together with recently published Triassic ages from the Batholith of Central Patagonia, it is clear that the acidic volcano-plutonic associations of northern Patagonia are very latest Paleozoic and Mesozoic in age. They are not obviously related to terrane collision but are part of a Permo-Triassic acid magmatic province that extends throughout the central Andes and that preceded, or was associated with, the early rifting of Gondwana.     

Variations in sediment yield over the advance and retreat of a calving glacier, Laguna San Rafael, North Patagonian Icefield

Bathymetric and sub-bottom acoustic data were collected in Laguna San Rafael, Chile, to determine sediment yields during the Little Ice Age advance and subsequent retreat of San Rafael Glacier. The sediment volumes and subaqueous landforms imaged are used to interpret the proglacial dynamics and estimate erosion rates from a temperate tidewater glacier over a complete advance-retreat cycle. Sediment yields from San Rafael Glacier averaged 2.7 × 10⁷ m³/a since the end of the Little Ice Age, circa AD 1898, corresponding to average basin-wide erosion rates of 23 ± 9 mm/a; the highest erosion rates, 68 ± 23 mm/a, occurred at the start of the retreat phase, and have since been steadily decreasing. Erosion rates were much lower during glacial advance, averaging at most 7 mm/a, than during retreat. Such large glacial sediment yields over two centuries of advance and retreat suggest that the contribution of sediments stored subglacially cannot account for much of the sediment being delivered to the terminus today. The detailed sub-bottom information of a proglacial lagoon yields important clues as to the timing of erosion, deposition and transfer of glacigenic sediments from orogens to the continental shelves, and the influence of glacier dynamics on this process.     

东准噶尔北缘乌伦古地区晚二叠世A型花岗质岩墙成因及构造背景

中亚造山带西南缘的东准噶尔地区出露大量晚古生代花岗岩,是揭示该造山带地壳演化的良好对象.在东准噶尔北缘乌伦古西北的阿克吉拉识别出一套走向与区域构造线总体垂直的晚古生代花岗质岩墙,其时代和成因研究对深入理解本区的构造演化具有重要意义.SHRIMP锆石U-Pb测年结果显示其侵位于晚二叠世(266±2 Ma).岩石地球化学组...     

Geochemistry and evolution of the Wolf River Batholith,a late Precambrian Rapakivi Massif in North Wisconsin,U.S.A.

The Wolf River Batholith is an anorogenic rapakivi massif in central and northeastern Wisconsin with an age of 1.5 Ga. The Batholith has alkaline affinities and consists of biotite granite and biotite-hornblende adamellite with minor occurrences of quartz syenite and older monzonite and anorthosite. The batholith is part of a major Late Precambrian (1.4–1.5 Ga) magmatic event of continental proportions, represented by separate intrusions extending from Labrador to southern California (Silver et al., 1977).The major and trace element composition (Li, Rb, Sr, Ba, and REE) of 40 samples from the anorthosite, monzonite, and rapakivi granite and adamellite plutons precludes a comagmatic (although not cogenetic) model between all three rock units. However, the monzonite may be related to the anorthosite alone by fractional crystallization of plagioclase, orthopyroxene, clinopyroxene, and apatite. Alternatively, the monzonite may be a separate parent melt or a hybrid associated with the granite and adamellite plutons. The high REE content of the monzonite precludes it from being related to the rapakivi granite and adamellite plutons as a source material, a residuum, or a cumulate.A major portion of the Batholith is an undifferentiated intrusive sequence ranging from older rapakivi granite to younger adamellite. The compositions of these plutons suggest a crustal fusion origin at intermediate to lower levels of the crust (25–36 km). The trace element data are consistent with partial fusion of tonalitic to granodioritic source material.During crystallization and emplacement into the upper crust (less than 4 km), 55–70% fractionation of two feldspars, biotite and hornblende from one of the granite plutons produced a small volume of differentiated granitic melt high in Si, Fe/Mg, Rb, Li, and REE (except Eu), and low in Ca, Mg, Al, Ca/Na, Sr, Ba, and K/Rb and with a large negative Eu anomaly. Presumed associated cumulate material ranges from silica-poor quartz monzonite and quartz syenite.The chemical and mineralogical similarity between the Wolf River Batholith and younger magmatic analogs associated in continental break-up (Nigerian younger granites, White Mountain magma series, and the peralkaline volcanics of the Red Sea Region) are suggestive but not conclusive of an extensional tectonic setting. A preliminary tectonic model suggests that the 1.4–1.5 Ga event is in response to thermal doming in an extensional regime leading to continental separation in the western Cordillera (pre-Belt) and extensive crustal fusion with no rifting or separation across the North American Craton.     

阿尔泰中蒙边界塔克什肯口岸后造山富碱侵入岩体的形成时代、成因及其地壳生长意义

塔克什肯口岸富碱侵入岩体是阿尔泰造山带典型的后造山岩体。本次锆石U-Pb定年给出~(206)Pb/~(238)U年龄286±1Ma(MSWD=0．05),代表其形成年龄。这为阿尔泰后造山岩浆作用提供了一个可靠的年代学证据。该岩体主要岩石类型为正长岩、石英二长岩、石英碱长正长岩、正长花岗岩,富钾、富钠、准铝,富集轻稀土、大离子亲石元素,亏损高场强元素,与区内相邻的碱性花岗岩(A型花岗岩)在岩石学、地球化学方面不同。该岩体Sr初始值变化于0．7038～0．7040,ε_(Nd)(t)值为正值(+6．2～+6．3),Nd模式年龄T_(DM)为542～546Ma,与中亚造山带典型的高(正)ε_(Nd)(t)值花岗岩类似。而且,其ε_(Nd)(t)值远高于区内同造山花岗岩,也高于造山带内部同时期的Ⅰ-A型后造山花岗岩。依据岩体构造特征、年代学、地球化学和区域地质背景综合分析,该岩体应为后造山岩体,在时空上可与蒙古南部碱性岩带对比,其形成可能与富集高场强元素的亏损地幔岩浆底侵,导致下地壳重熔,并发生岩浆混合有关。这说明,在阿尔泰造山带后造山阶段,除了可能的俯冲下埋的年轻洋壳或岛弧物质外,还有新的幔源物质加入到地壳。这为中亚造山带后造山阶段陆壳垂向生长提供了一个新证据。同时,也为东北北部-蒙古南部碱性岩带向西沿入阿尔泰造山带提供了证据。     

若尔盖地块三叠系泥质岩微量元素地球化学特征与构造背景

研究了若尔盖地区三叠系泥质岩微量元素地球化学特征。三叠系各地层样品中轻稀土显著富集,重稀土变化平缓,稀土总量为173.41×10-6~238.46×10-6,其变化不大。稀土含量与中国东部泥质岩相比差别不大。微量元素地球化学特征表明本区三叠系物源为大陆岛弧。     

The Early Triassic Indosinian orogeny in Vietnam (Truong Son Belt and Kontum Massif); implications for the geodynamic evolution of Indochina

New structural field data at various scale and ⁴⁰Ar–³⁹Ar geochronological results, from the basement rocks in the Truong Son belt and Kontum Massif of Vietnam, confirm that ductile deformation and high-temperature metamorphism were caused by the Early Triassic event of the Indosinian Orogeny in the range of 250–240 Ma. A compilation of isotopic data obtained in other countries along the Sibumasu–Indochina boundary broadly indicates same interval of ages. This tectonothermal event is interpreted as the result of a synchronous oblique collision of Indochina with both Sibumasu and South China, inducing dextral and sinistral shearing along E–W to NW–SE and N–S fault zones, respectively. The collision along Song Ma follows the northwards subduction of Indochina beneath South China and the subsequent development of the Song Da zone which in turn was affected by the Late Triassic Indosinian phase of shortening. Within the Indochina plate, internal collisions occurred coevally in the Early Triassic, as along the Poko suture, at the western border of the Kontum Massif.     

华北南缘古元古代末岩墙群侵位的磁组构证据

华北克拉通南缘的中条山及邻区广泛发育元古宙放射状基性岩墙群,与五台山-恒山和大同地区的北北西向基性岩墙群以及熊耳中条拗拉谷的火山岩在时空分布和地球化学方面均具有密切的相关性。中条山及邻区放射状基性岩墙群的宏观和微观流动构造(包括捕虏体、冲痕构造、矿物线理和定向斑晶)指示岩墙群以一定的仰角向北西侵位。通过该区岩墙群磁化率各向异性(AMS)测量得到磁组构的最大磁化率长轴优势方位分布图和磁组构各向异性特征分析进一步指示华北南缘古元古代末岩墙群从熊耳中条拗拉谷的底部向北西侵位。岩墙群的流动构造和磁组构的统计成果夯实了华北克拉通古元古代末基性岩墙群与熊耳中条拗拉谷的成生联系。     

40Ar/39Ar hornblende dating of a microgranodiorite dyke: implications for early Permian extension in the Moldanubian Zone of the Bohemian Massif

Laser fusion ⁴⁰Ar/³⁹Ar ages of titanian pargasite from a microgranodiorite dyke swarm in the southern Bohemian Massif effectively date the early Permian (late Autunian) emplacement of dykes into a cool Moldanubian crust. This intrusion represents the youngest magmatic phase recorded in this part of the Moldanubian Zone. Strontium and neodymium isotopic ratios of microgranodiorites point to magma derivation from re-melting the lower crustal rocks with a possible component of upper mantle composition. Spatial and temporal association of the dykes with movements on a major N-S (NNE-SSW) tectonic discontinuity (Blanice-Kaplice-Rödl fault zone) suggests that their emplacement corresponds to the maximum age of fault movements associated with the E/W-oriented extension in this part of the Bohemian Massif.     

Geochronology and Geochemistry of Late Triassic Intrusive Rocks in the Xiuyan Area,Liaodong Peninsula,Eastern North China Craton: Petrogenesis and Implications for Lithospheric Thinning

The timing and mechanisms of lithospheric thinning and destruction of the North China Craton (NCC) remain controversial, and the overall geodynamics of the process are poorly understood. This paper documents Late Triassic igneous rocks including monzogranite, gabbro, and diorite from the Xiuyan District on the Liaodong Peninsula in the eastern NCC, which have LA-ICP-MS zircon U-Pb ages of 229.0 ± 0.4 Ma, 216.2 ± 0.9 Ma, and 210.6 ± 2.0 Ma, respectively. Monzogranite shows high-SiO2 adakite affinity, negative εHf(t) values (?20.6 to ?17.9), and old TDM2 ages (3.53–3.29 Ga), suggesting that their parental magma was derived from thickened Paleoarchean mafic lower crust and minor mantle materials that were also involved their generation. Gabbro is ultrapotassic, strongly enriched in LREEs and LILEs, depleted in HFSEs, and has evolved zircon Hf isotopes with negative εHf of ?10.04 to ?5.85 and old TDM2 ages (2.59–2.22 Ga). These are diagnostic signatures of a crustal component, but their high contents of MgO, Cr, Co, Ni indicate that the primary magma originated from enriched mantle. Diorite is enriched in LILEs and LREEs, depleted in HFSEs (with negative Nb, Ta, and Ti anomalies), and contains negative εHf(t) values (?13.64 to ?11.01). Compared with the gabbro, the diorite is relatively enriched in Nb, Ta and HREEs, and also contains younger TDM2 ages (2.11–1.94 Ga), suggesting that the diorite was formed by mixing between ancient lower crust-derived felsic magmas and asthenospheric mantle-derived magmas. Field observations, geochronology, geochemistry, and zircon Lu-Hf isotopes indicate that Late Triassic magmatism and tectonic activity resulted from deep subduction of the Yangtze Craton beneath the NCC in the Xiuyan area. This phase of tectonic activity was completed in the eastern NCC by the Late Triassic (216 Ma), and was subsequently followed by lithospheric thinning that began in the Late Triassic.     

青藏高原北羌塘盆地查涌蛇绿岩的地球化学特征及其构造意义

查涌蛇绿岩为甘孜-理塘缝合带在青藏高原北羌塘盆地治多地区的北延部分,由基性堆晶岩、辉绿岩墙群、基性喷出岩及沉积成因的硅质岩组成,缺乏地幔橄榄岩。受后期构造强烈破坏,岩石变质变形较强,多呈被肢解的构造岩块、岩片产出。堆晶岩包括蚀变橄榄辉石岩、辉长岩,蚀变橄榄辉石岩具有低SiO₂、TiO₂、P₂O₅含量及高MgO含量的特征,Rb、Th、Cr等元素呈强富集型,Sr、Nb、Y等元素具亏损型;辉长岩低SiO₂及K₂O含量,高MgO、TiO₂及Al2O3含量;辉绿岩墙以Rb、Ba、Th等元素的明显富集和Y、Yb的轻微亏损为特征,微量元素蛛网图曲线与洋中脊玄武岩类似;玄武岩具高TiO₂含量、低K₂O含量,属低钾拉斑玄武岩系列,轻重稀土元素分馏程度明显,具有轻稀土富集型,铕不显异常,玄武岩REE模式呈近平坦型曲线,与大洋玄武岩特征相似。由上述蛇绿岩地球化学特征及结合区域地质、构造环境等特征,推测查涌蛇绿岩产于洋盆环境。     

华北太行岩墙群斜锆石生长世代和U-Pb年龄及其对岩浆演化的启示

斜锆石U-Pb定年是基性岩墙时代确定的有效方法。前人对太行岩墙群高分异组岩墙(Ti O2通常1%,Mg O一般6%)进行了较多的定年,但缺少对低分异组岩墙(Ti O2约为1%,Mg O6%)的高精度测年。两者年龄是否一致是讨论两组岩墙是否来源于同一岩浆的基本前提。本研究对华北太行岩墙群丰镇地区低、高分异组代表性岩墙进行了斜锆石离子探针207Pb/206Pb定年。结果表明,低分异组车道沟岩墙207Pb/206Pb平均年龄为1768±4Ma(n=9,MSWD=2.1);而高分异组酸刺湾岩墙斜锆石207Pb/206Pb年龄可以分为两组,加权平均值分别为1780±3Ma(n=8,MSWD=0.65)和1760±3Ma(n=5,MSWD=1.7)。斜锆石成分分析表明,酸刺湾岩墙两组年龄对应的矿物成分存在差异,如晚期斜锆石比早期更富Ti,Zr/Hf比值变化范围相对较小。据此认为,酸刺湾岩墙两组斜锆石可能结晶于岩浆不同阶段:早期(~1780Ma)的斜锆石可能结晶于成分更加原始的岩浆,很可能形成于岩浆房中;晚期(~1760Ma)的斜锆石可能结晶于成分更加演化的岩浆,可能是岩浆通道(岩墙)或岩浆房中。Zr/Hf值与单点年龄的负相关趋势可能记录了单斜辉石的结晶过程。已有的太行岩墙群U-Pb年代学结果集中于1785~1760Ma。我们的研究认为,太行岩墙群岩浆房存在了约20Myr,即岩浆房形成于~1785Ma,岩墙就位于1785~1760Ma。     

Sedimentary record of Triassic intraplate extension in North China: evidence from the nonmarine NW Ordos Basin, Helan Shan and Zhuozi Shan

The Helan Shan and Zhuozi Shan of the NW Ordos basin, China, contain thick (up to 4 km) sequences of nonmarine Triassic strata. These rocks represent a major intraplate sedimentary basin, the paleogeography, tectonic setting and provenance of which are poorly understood and controversial. Studies of the sedimentary geology of the basin, supported by new palinspastic reconstruction of younger deformation, demonstrate that the basin filled from three sides by fluvial, lacustrine-deltaic and alluvial fan depositional systems. The basin forms a westward-thickening wedge that reaches its maximum thickness along the western margin of the Helan Shan and thins to a relatively constant 600–800 m east of the Zhuozi Shan. The stratigraphy of the basin is strongly asymmetric; alluvial fan strata are restricted to the extreme western margin of the basin and interfinger with axial fluvial deposits low in the section and deep lacustrine facies high in the section. Much of the eastern part of the basin is dominated by west-flowing meandering river and deltaic systems. Large structures of Triassic age have not been identified in the Helan Shan or Zhuozi Shan, but small Triassic normal faults have been documented in the western and central Helan Shan. These characteristics most strongly support an extensional origin for the Triassic basin in NW Ordos. The basin is interpreted to have been a north-trending half graben, bound along its western margin by an east-dipping normal fault, presently concealed beneath Quaternary cover west of the Helan Shan. The eastern margin, now found in the Zhuozi Shan, has simple ramp-margin geometry. Driving mechanisms for this extension are not obvious due to limited documentation of Triassic structure throughout the region, but probably relate to far-field stresses from the Qinling or Jinsha active margins interacting with the stable Ordos block.     

Zircon dating of North Bohemian granulites, Czech Republic: further evidence for the Lower Carboniferous high-pressure event in the Bohemian Massif

U-Pb zircon and rutile multigrain ages and ²⁰⁷Pb/²⁰⁶Pb zircon evaporation ages are reported from high-pressure felsic and metapelitic granulites from northern Bohemia, Czech Republic. The granulites, in contrast to those from other occurrences in the Bohemian Massif, do not show evidence of successive HT/MPLP overprints. Multigrain size fractions of nearly spherical, multifaceted, metamorphic zircons from three samples are slightly discordant and yield a U-Pb Concordia intercept age of 348 ± 10 Ma, whereas single zircon evaporation of two samples resulted in ²⁰⁷Pb/²⁰⁶Pb ages of 339 ± 1.5 and 339 ± 1.4 Ma, respectively. A rutile fraction from one sample has a U-Pb Concordia intercept age of 346 ± 14 Ma. All ages are identical, within error, and a mean age of 342 ± 5 Ma was adopted to reflect the peak of HP metamorphism. Because rutile has a lower closing temperature for the U-Pb isotopic system than zircon, the results and the P-T data imply rapid uplift and cooling after peak metamorphism. The above age is identical to ages for high-grade metamorphism reported from the southern Bohemian Massif and the Granulite Massif in Saxony. It can be speculated that all these granulites were part of the same lower crustal unit in early Carboniferous, being separated later due to crustal stacking and subsequent late Variscan orogenic collapse.     

Fluvial Geochemistry through a Short-Duration, Tropical-Cyclone Induced Discharge event in the Burdekin River and Hann Creek, North Queensland, Australia

The chemical composition of river water integrates a number of factors such as weathering, land use, climate, vegetation cover and human activity that individually affect its chemistry. Short term variations may also be significant. The Burdekin River, NE Australia, is an example of a class of tropical streams which experiences two to four orders of magnitude variation in discharge in response to seasonal but erratic monsoonal and cyclonic rainfall. In these systems individual discharge events last for days to weeks. Given the inherent difficulty sampling these events published data on water chemistry (and thus calculated fluxes and global budgets) may tend to be biased to low flow conditions. One such discharge event in February 1996 has been investigated for its impact on the chemistry of the water. Major cations (Na, Mg, K, Ca) all decreased in concentration as the water level rose, as did the minor elements Sr, Ba and U. Some other trace elements, notably Rb, Cr, Pb and REE were enriched in the peak flow waters. The flux of all measured elements increased substantially during the seven days of the discharge event. Such short term but significant events will have a major impact on the annual fluxes of elements delivered to the oceans from the land and global discharge budgets may need to take them into account when refining databases in the future.     

河南南召盆地上三叠统碎屑岩地球化学特征及物源示踪

三叠纪是秦岭造山带全面碰撞造山的关键时期,随着扬子、秦岭和华北板块分别沿勉略、商丹缝合带的汇聚拼合, 秦岭造山带逐渐形成并从板块构造体制向陆内造山体制转化,同时强烈的造山作用控制着周缘盆地的形成与演化。文章通 过研究区的碎屑岩元素地球化学分析,对河南南召盆地上三叠统的物源区及构造背景特征进行探讨。结果表明,上三叠统 源岩成分主要为上地壳长英质火山岩;源岩经历了中等的化学风化强度,校正后CIA值指示其形成于温暖潮湿的气候和相 对较强的构造活动环境;太山庙组源区构造背景主要为大陆岛弧与活动大陆边缘,太子山组源区构造背景主要为大陆岛弧 与被动大陆边缘。根据南召盆地近源沉积特征和秦岭造山带构造演化过程推断,秦岭造山带和华北南缘是南召盆地晚三叠 世的重要物源区,前期太山庙组物源主要由北秦岭隆升基底提供,后期太子山组物源可能来自南秦岭、北秦岭和华北南缘 沉积再循环。南召盆地上三叠统物源区的转变是晚三叠世秦岭造山带逆冲推覆作用逐渐增强的体现,对研究恢复秦岭构造 带造山隆升过程和周缘盆地盆山系统演化具有重要的意义。     

The Puesto Piris Formation: Evidence of basin-development in the North Patagonian Massif during crustal extension associated with Gondwana breakup

The Marifil Volcanic Complex, exposed in the eastern North Patagonian Massif, Argentina, includes up to 550 m of red conglomerates, sandstones, black siltstones, limestones, and reworked tuff of the Puesto Piris Formation. The basal part of this unit, which was deposited in high-gradient topographic relief, is composed of conglomerates and sandstones with thin layers of reworked tuffs. The lithofacies associations of the basal part indicate that the depositional mechanisms were mantled and gravitational flows.The middle part of the unit consists of fine sandstones, limestones, and black siltstones that were deposited in low-energy fluvial and lacustrine environments. The outcrops are located along the NEe SW direction and the major thickest units represented by limestones and siltstones, occur near the southeastern border of this NEeS W depocenter. Since the rhyolitic and trachytic lava flows and tuffs of the Marifil Volcanic Complex are interbedded with the sedimentary sequences of the Puesto Piris Formation,both units are coeval. Zircon Ue Pb age was obtained for a trachytic lava flow(193.4 ±3.1 Ma) suggesting that sedimentation and volcanism are Sinemurian. This extensional episode was recorded in the eastern,western, and southwestern sectors of the North Patagonian Massif, and is possibly associated with the Gondwana supercontinent breakup.