Late Cretaceous Paleocene Time Research Articles

Океаническая кора, трансрегиональные зоны сдвига и Амеразийская микроплита в мел-кайнозойской геодинамике формирования океана в Арктике

The author has reconstructed the structural-tectonic setting of the Late Cretaceous-Early Cenozoic stage of the geodynamic evolution of the Arctic Ocean. It is shown that the oceanic crust in the Eurasian and Canadian basins occupies a much smaller area than previously thought and was formed in both on blocks of the continental basement strongly stretched by Cretaceous rifting. Due to the processes, large and extended transregional shear zones were set in motion: the Chukchi-Canadian during the opening of the Canadian basin in the Early Cretaceous, and the continental marginal ones — Khatanga-Lomonosov and Northern Greenland-Canadian, the activation of shear movements in which is associated with the Late Cretaceous-Paleocene time, when the consistent formation of the Makarov and Eurasian basins took place. As a result new composite Amerasian microplate was detached and set in motion, which combined the blocks of Arctic Alaska, the Canadian Basin, the Chukchi Rise, the Alpha–Mendeleev Rise, the Podvodnikov and Makarov Basins, and the Lomonosov Ridge. The movement of the microplate along approximately parallel large shear zones at the edges of the Canadian Arctic and Siberian-Chukotka shelves was directed towards the Pacific subduction zone. The movement of the Amerasian microplate was accompanied by rifting and detachment of the Lomonosov Ridge from the Barents-Kara margin, opening of the Eurasian Basin in the rear of the ridge, and transform displacements — right-sided along the Khatanga-Lomonosov zone and left-sided along the North Greenland-Canadian fault zone. At the same time, as a result of the movement of the Amerasian microplate, the previously unified area of Cretaceous plateau basalts (HALIP) was broken, and the Central Arctic province of magmatism was separated and moved away from the Barents Sea province.

Late extension of a passive margin coeval with subduction of the adjacent slab: The Western Alps and Maghrebides files

The evolution of the Alpine Tethys margins during the beginning of the African-Eurasian convergence was little studied compared to their evolution during the post-Pangea rifting and oceanic expansion,i.e., from the Early Jurassic to the early Late Cretaceous. The present work firstly aims to make up for this shortcoming in the case of the distal European margin of the Alpine Tethys, namely the Briançonnais domain of the Western Alps. We show that this margin was affected by strong post-rifting extension mainly in Late Cretaceous-Paleocene times and propose to make it the type of the (rare) “Late Extension Passive Margins”. Remarkably, this extension shortly preceded Lutetian times, when Briançonnais margin encroached the SE-dipping subduction zone under the Adria microplate. Secondly, we assess the post-rifting evolution of the north-Tethyan paleomargin in the Maghrebides transects,i.e., south-west of the Briançonnais transect along the same European-Iberian paleomargin. For this purpose, we consider the Triassic-Eocene series of the “Dorsale Calcaire” in the Alkapeca Blocks located along southeastern Iberia until the Eocene then transported onto the North African margin. Examination of the literature shows that the Tethyan margin of the Alboran block was strongly affected by normal faulting as early as Late Jurassic-Early Cretaceous times whereas post-rifting extension of the Kabylian blocks mainly occurred in the Late Cretaceous-Paleocene like in the Briançonnais. We propose that post-rifting extension of the Alboran block southern margin resulted from the sinistral movement of Africa relative to Iberia while the later extension of the Kabylian blocks can be related to the further convergence kinematics. Subduction of the Ligurian-Maghrebian slab under the North African margin would have occurred at that time in the southward continuation of the Alpine subduction. The overriding Adria and North African margins did not experience significant compression at that time. During the Eocene, a subduction polarity reversal occurred, which was associated with the relocation of the subduction zone along the Alkapeca block. This was the beginning of the Apenninic subduction, which triggered the back-arc opening of the Mediterranean basins.

The western Durkan Complex (Makran Accretionary Prism, SE Iran): A Late Cretaceous tectonically disrupted seamounts chain and its role in controlling deformation style

The Durkan Complex is a key tectonic element of the Makran accretionary prism (SE Iran) and it has been interpreted as representing a continental margin succession. We present here a multidisciplinary study of the western Durkan Complex, which is based on new geological, stratigraphic, biostratigraphic data, as well as geochemical data of the volcanic and meta-volcanic rocks forming this complex. Our data show that this complex consists of distinct tectonic slices showing both non-metamorphic and very low-grade metamorphic deformed successions. Stratigraphic and biostratigraphic data allow us to recognize three types of successions. Type-I is composed by a Coniacian – early Campanian pelagic succession with intercalation of pillow lavas and minor volcaniclastic rocks. Type-II succession includes a volcanic sequence passing to a volcano-sedimentary sequence with Cenomanian pelagic limestones, followed by a hemipelagic sequence. This succession is characterized by abundant mass-transport deposits. Type-III succession includes volcanic and volcano-sedimentary sequences, which are stratigraphically covered by a Cenomanian platform succession. The latter is locally followed by a hemipelagic sequence. The volcanic rocks in the different successions show alkaline geochemical affinity, suggesting an origin from an oceanic within-plate setting. Our new results indicate that the western Durkan Complex represents fragments of seamounts tectonically incorporated in the Makran accretionary wedge during the latest Late Cretaceous–Paleocene. We propose that incorporation of seamounts in the frontal prism caused a shortening of the whole convergent margin and possibly contributed to controlling the deformation style in the Makran Accretionary Wedge during Late Cretaceous–Paleocene times.

ROLE OF THE CRUSTAL DETACHEMENTS DURING RIFTING, INSIGHTS FROM LABRADOR SEA

The Labrador Sea is part of the Atlantic rift system which opens during Early Cretaceous times in the intracontinental domain. The rifting stage continues and generates an expansion center, with the establishments of an oceanic ridge during Late Cretaceous-Paleocene times. The rifting was asymmetric with a gradual propagation northward. The Cretaceous stretching and thinning of the continental crust led to the development of the transitional domain, with a controversial origin either thinned continental or oceanic. With this study, we bring new evidences for the presence of exhumed upper mantle in the transition domain based on geometry of the detachment faults, typical “S” shape, and we emphasize the role of thedetachments in the rifting of continental crust and its ultimate break-up. We observed the lateral change, from South to North, of the continental to oceanic crust transition, from a step-up to a step-down. Based on, we suggest that it might reflect the changes in the upper versus lower plate position of the Labrador Sea, a change accommodated across the Snorri Fracture Zone.

Evolution of the Chos Malal and Agrio fold and thrust belts, Andes of Neuquén: Insights from structural analysis and apatite fission track dating

The Chos Malal and Agrio fold and thrust belts are located in the western part of the Neuquén basin, an Andean retroarc basin of central-western Argentina. Both belts show evidence of tectonic inversion at the western part during Late Cretaceous times. The eastern part is dominated by late Miocene deformation which also partially reactivated the western structures. This work focuses on the study of the regional structure and the deformational event that shaped the relief of this part of the Andes. Based on new field work and structural data and previously published works a detailed map of the central part of the Neuquén basin is presented. Three regional structural cross sections were surveyed and balanced using the 2d Move™ software. In order to define a more accurate uplift history, new apatite fission track analyses were carried on selected structures. These data was used for new thermal history modeling of the inner part of the Agrio and Chos Malal fold and thrust belts. The results of the fission track analyses improve the knowledge of how these fold and thrust belts have grown trough time. Two main deformational events are defined in Late Cretaceous to Paleocene and Late Miocene times. Based on this regional structural analysis and the fission track data the precise location of the orogenic front for the Late Cretaceous-Paleocene times is reconstructed and it is proposed a structural evolution of this segment of the Andes. This new exhumation data show how the Late Cretaceous to Paleocene event was a continuous and uninterrupted deformational event.

Olistostromes of the Pieniny Klippen Belt, Northern Carpathians

AbstractThe olistostromes form two belts within the Pieniny Klippen Belt (PKB) in the Northern Carpathians. They mark an early stage of the development of the accretionary prism. The first belt was formed during Late Cretaceous time as a result of subduction of the southern part of the Alpine Tethys. The fore-arc basin originated along this subduction zone, with synorogenic flysch deposits. Huge olistoliths deposited within the Cretaceous–Palaeogene flysch of the Złatne Basin, presently located in the vicinity of the Haligovce village (eastern Slovakia), provide a good example of the fore-arc olistostrome setting. The second belt is related to the movement of the accretionary prism, which overrode the Czorsztyn Ridge during Late Cretaceous–Paleocene time. The destruction of this ridge led to the formation of submarine slumps and olistoliths along the southern margin of the Magura Basin. The Upper Cretaceous – Paleocene flysch sequences of the Magura Basin constitute the matrix of olistostromes. The large Homole block in the Jaworki village represents the best example of the Magura Basin olistolith. Numerous examples of olistoliths were documented in western Slovakia, Poland, eastern Slovakia and Ukraine. The olistostromes formed within the Złatne and Magura basins orginated during the tectonic process, forming the olistostrome belts along the strike of the PKB structure.

Mesozoic and Cenozoic evolution of salt structures within the Polish basin: An overview

Abstract The Permian–Cretaceous Polish Basin belonged to the system of epicontinental depositional basins of Western and central Europe and was filled with several kilometres of siliciclastics, carbonates, and also thick Zechstein (approximately Upper Permian) evaporites. Its axial part (the so-called Mid-Polish Trough) characterized by the thickest Permo-Mesozoic sedimentary cover, developed above the Teisseyre–Tornquist Zone, lithospheric-scale boundary separating the East European Craton and the Palaeozoic Platform. The Polish Basin was inverted in Late Cretaceous–Paleocene times. A synthesis of studies based on seismic reflection data allowed some general rules regarding salt tectonics of the Polish Basin to be formulated. Two general classes of structures genetically related to the presence of the Zechstein evaporites have been described: peripheral structures located within NE and SW flanks of the Polish Basin, outside its axial part and structures located within its axial part. The first class of structures includes grabens bounded by listric faults detached above salt or salt pillows that developed where Zechstein evaporites were of relatively smaller thickness and where sub-Zechstein fault tectonics played a relatively smaller role. The second class of structures includes more mature salt structures such as salt pillows and salt diapirs and is related to the more axial part of the basin, characterized by relatively thicker Zechstein evaporites and by more intense basement tectonics. First salt movements (salt pillowing) took place in the Early Triassic that in certain cases was followed by the Late Triassic salt diapirism and extrusion. In Jurassic–Early Cretaceous times, no significant growth of salt structures took place. Most of the salt diapirs have been finally shaped by the Late Cretaceous inversion tectonics. Some salt diapirs also underwent Cenozoic reactivation, associated with localized Oligocene or Miocene subsidence that in some cases was followed by younger (Pliocene–Quaternary) inversion and uplift.

The Late Cenozoic evolution of the Aksu basin (Isparta Angle; SW Turkey). New insights

Abstract The Mio-Pliocene basins around the Antalya gulf in SW Turkey developed above the Tauric Mesozoic platforms on which the Antalya nappes had been thrusted (in Late Cretaceous-Paleocene times). The closure of the initial Isparta Angle during these events (E-W compression) initiated the N-S orientation of the main structural lines, which persisted later and explains the orientation of the Aksu basin in contrast with the E-W orientation of the eastern Neo-gene Mediterranean basins. The area, and all southwestern Turkey, became emergent at the end of the Oligocene and were the site of shallow-marine carbonate deposits in the Chattian-Aquitanian, giving way to the wide Lycian basin in Burdigalian-Langhian times. The progressive emplacement of the Lycian nappes from the north over this basin provoked first its subsidence and then its emersion when the nappes attained their final position over the Bey Daglari platform in Langhian times. Coinciding, or in response to the Lycian nappes emplacement, the Aksu basin was initiated as an elongated N-S graben which was filled by thick accumulations of terrestrial and marine deposits(including coral reefs), which derived from the erosion of the Lycian allochton and its basement (Langhian?, Serravallian and Tortonian times). The syn-sedimentary tectonics : reactivation of the normal faults along the west margin of the basin, the continuous uplift of the neighbouring continental areas (beginning of the Aksu thrust), governed the geometry of the basin. As a result and due to the uplift of its northern margin, the Aksu basin migrated towards the south and in Messinian times it was reduced to a narrow gulf along the eastern margin of which the Gebiz limestones were deposited as fringing coral reefs. The age of these limestones has been debated. Our new data allow us to attribute them to the Messinian. The drastic retreat of the sea at the end of this period, provoked the erosion of large parts of the Messinian deposits and the formation of deep canyons on land and under the sea down to the Antalya abyssal plain, in which evaporites were deposited. During the Zanclean transgression, the Eskiköy-Kargi canyon was filled by coarse clastics of a Gilbert delta derived from the northern continental area following a model well known elsewhere in the Mediterranean basins. Southward, shallow-marine sands and marls unconformably cover the remnants of the Messinian deposits and the emergent areas of the southern Antalya gulf. After Zanclean times (end of Pliocene?), the Aksu basin was deformed, due to the west-directed Aksu compressional event (end of the Aksu thrust). Quaternary terraces of the Aksu river at various altitudes, as well as the terraces of the Antalya tufa can be related to sea level fluctuations.

A late Cretaceous contamination episode of the European–Mediterranean mantle

One of the most challenging issues about the Tertiary–Quaternary alkaline magmatism spreading across the Euro-Mediterranean region is the assessment of both the nature of its mantle source and the mechanism responsible for the common HIMU-like (High μ=high 238U/204Pb) character of erupted lavas, enduring over about 100 million years in diverse tectonic environments. In this paper we try to reconcile geochemical and geophysical data through a multidisciplinary investigation on geochemistry, timing and locations of the main Na-rich alkaline volcanic centers, seismic tomographic images and plate kinematics. We propose that the common component of the Euro-Mediterranean mantle derives from a contamination episode triggered by the rise of the Central Atlantic Plume (CAP) head. Plate reconstruction shows that at late Cretaceous-Paleocene time the oldest magmatic centers of the Euro-Mediterranean region were located more than 2000 km SW of their present day position, in proximity of the CAP hot spot location, where seismic tomography detects a broad low seismic velocity region in the lower mantle. The north-eastward migration of the Eurasian and African plates could have involved also part of the CAP contaminated mantle, which moved in the same direction being coupled to the lithospheric plates, thus explaining the presence of geochemically-uniform material spread in the sub-lithospheric Euro-Mediterranean mantle. During the Tertiary, regional-scale convection and related processes such as rifting, back-arc spreading, slab detachment/windows, may have favored upwelling and partial melting of the frayed plume head material via adiabatic decompression, shaping the spatial and temporal distribution of HIMU-like volcanics. The growing supply of subducted lithosphere may explain as well the increase of crustal isotopic signatures of alkaline magmas with time. In our opinion, the Euro-Mediterranean upper mantle contamination can be eventually related to a global event occurred during the Cretaceous as a consequence of a mantle avalanche caused by the Tethys closure.

PETROLOGY AND ORIGIN OF PLAGIOGRANITES FROM THE DAĞKÜPLÜ (ESKİŞEHİR) OPHIOLITE ALONG THE İZMİR-ANKARA-ERZİNCAN SUTURE ZONE, TURKEY

The Izmir-Ankara-Erzincan Suture Zone (IAESZ) formed through the closure of the northern branch of the Neotethyan Ocean that once separated the Sakarya Continent and the Anatolide-Tauride Platform and the subsequent collision of these two continental blocks during Late Cretaceous-Paleocene time. Mafic-ultramafic rocks representing oceanic lithosphere, metamorphic sole rocks, and ophiolitic melange comprising oceanic and continental fragments and continental margin metamorphic and sedimentary rocks are preserved along the IAESZ. A northward dipping subduction zone developed within the Izmir-Ankara-Erzincan Ocean, a northern branch of Neotethyan Ocean, in the Early Cretaceous. The suprasubduction zone (SSZ) ophiolites formed in this intra-oceanic setting. The Dagkuplu Ophiolite was, like other ophiolite nappes in the region, thrust over the southern Anatolide-Tauride Platform. The Dagkuplu Ophiolite, exhibiting an incomplete and inverted ophiolite suite, consists mostly of refractory peridotites (harzburgite and dunite) representing mantle unit and lesser dunite and wehrlite cumulates, pyroxenites, and massive-layered gabbros. The plagiogranite volumetrically constitutes about 10% of the entire ophiolitic rocks. Petrographic and geochemical data suggest that plagiogranites were generated from TiO2-poor cumulate gabbros by fractional crystallization at a suprasubduction zone spreading center.

Petrotectonic significance of the chemistry of chromite in the ultramafic–mafic complexes of Pakistan

The suture zones, which border the Indian craton in Pakistan are characterized by several large mafic–ultramafic complexes. From south to north these include: (1) Bela, (2) Muslimbagh-Zhob valley, (3) Waziristan, (4) Dargai (Skhakot-Qila), (5) Shangla-Mingora, (6) Jijal, and (7) Sapat. Besides these, there is the huge (300x≤40 km) Chilas mafic–ultramafic complex in the Cretaceous Kohistan magmatic arc. The Sapat, Jijal, Shangla, and Dargai (Skhakot-Qila) complexes are distributed along the Indus suture. The Waziristan, Zhob valley and Bela complexes lie along the suture on the western margin of the Indian plate. All these complexes were emplaced during late Cretaceous–Paleocene time at ca. ∼65 Ma. These complexes largely consist of ultramafic and mafic plutonic rocks (ranging from dunite and peridotite to gabbro). The mafic–ultramafic rocks of the Sapat, Chilas and Jijal complexes are generally well layered and appear to be mainly cumulates. In addition to cumulate plutonic rocks, the remaining five complexes also contain abundant residual peridotites, sheeted dykes, a variety of lava flows (locally pillowed), and associated pelagic sediments. Disseminated and segregated chromite occurs in all the complexes. On the basis of the chromium number [ Cr # = 100 × Cr / ( Cr + Al ) ] of their chromite, the complexes can be divided into three groups: (1) the Sapat and Jijal complexes contain chromites with Cr#>60; (2) the Shangla-Mingora, Dargai (Skhakot-Qila), Waziristan, Muslimbagh-Zhob and Bela rocks contain chromites that display a wide range of composition with Cr# varying from 15 to 90; and (3) rocks of the Chilas complex are characterized by low-Cr chromites (Cr# mostly <60). The chromite compositions appear to indicate different tectonic settings for the origin of the complexes under consideration. Those with high Cr chromite belong to an island arc type tectonic setting. Opinion differs on the origin of the group (2) chromite-bearing complexes; they may well be of complex origin with components, which originated in different tectonic settings. The Chilas complex of group (3) contains low Cr chromite similar to oceanic rocks supporting the idea that it is related to rifting within an island arc setting.

Late Jurassic to Eocene evolution of the Cordilleran thrust belt and foreland basin system, western U.S.A.

Geochronological, structural, and sedimentological data provide the basis for a regional synthesis of the evolution of the Cordilleran retroarc thrust belt and foreland basin system in the western U.S.A. In this region, the Cordilleran orogenic belt became tectonically consolidated during Late Jurassic time (∼155 Ma) with the closure of marginal oceanic basins and accretion of fringing arcs along the western edge of the North American plate. Over the ensuing 100 Myr, contractile deformation propagated approximately 1000 kilometers eastward, culminating in the formation of the Laramide Rocky Mountain ranges. At the peak of its development, the retroarc side of the Cordillera was divided into five tectonomorphic zones, including from west to east the Luning-Fencemaker thrust belt; the central Nevada (or Eureka) thrust belt; a high-elevation plateau (the “Nevadaplano”); the topographically rugged Sevier fold-thrust belt; and the Laramide zone of intraforeland basement uplifts and basins. Mid-crustal rocks beneath the Nevadaplano experienced high-grade metamorphism and shortening during Late Jurassic and mid- to Late Cretaceous time, and the locus of major, upper crustal thrust faulting migrated sporadically eastward. By Late Cretaceous time, the middle crust beneath the Nevadaplano was experiencing decompression and cooling, perhaps in response to large-magnitude ductile extension and isostatic exhumation, concurrent with ongoing thrusting in the frontal Sevier belt. The tectonic history of the Sevier belt was remarkably consistent along strike of the orogenic belt, with emplacement of regional-scale Proterozoic and Paleozoic megathrust sheets during Early Cretaceous time and multiple, more closely spaced, Paleozoic and Mesozoic thrust sheets during Late Cretaceous–Paleocene time. Coeval with emplacement of the frontal thrust sheets, large structural culminations in Archean-Proterozoic crystalline basement developed along the basement step formed by Neoproterozoic rifting. A complex foreland basin system evolved in concert with the orogenic wedge. During its early and late history (∼155 - 110 Ma and ∼70 - 55 Ma) the basin was dominated by nonmarine deposition, whereas marine waters inundated the basin during its midlife (∼110 - 70 Ma). Late Jurassic basin development was controlled by both flexural and dynamic subsidence. From Early Cretaceous through early Late Cretaceous time the basin was dominated by flexural subsidence. From Late Cretaceous to mid-Cenozoic time the basin was increasingly partitioned by basement-involved Laramide structures. Linkages between Late Jurassic and Late Cretaceous Cordilleran arc-magmatism and westward underthrusting of North American continental lithosphere beneath the arc are not plainly demonstrable from the geological record in the Cordilleran thrust belt. A significant lag-time (∼20 Myr) between shortening and coeval underthrusting, on the one hand, and generation of arc melts, on the other, is required for any linkage to exist. However, inferred Late Jurassic lithospheric delamination may have provided a necessary precondition to allow relatively rapid Early Cretaceous continental underthrusting, which in turn could have catalyzed the Late Cretaceous arc flare-up.

Magmatism in western Indonesia, the trapping of the Sumba Block and the gateways to the east of Sundaland

The western Sulawesi magmatic belt and the Sunda–Banda arc define the eastern and south-eastern margins of Sundaland, which is part of the relatively stable Eurasian plate. The eastern margin is bounded by the Makassar Strait which separates western Sulawesi from Kalimantan. The initial opening of the Makassar Strait took place in the late Cretaceous–Early Tertiary leading to the opening of the Pacific–Indian Ocean gateway during Neogene time. Recent studies indicate similarities in the late Cretaceous–Paleogene stratigraphic sequence and calc-alkali magmatism between Sumba, south Sulawesi and south-east Kalimantan, suggesting a Sundaland origin for all of these areas. The southward migration of Sumba to the present frontal arc position of the Sunda–Banda arc has occurred since Late Cretaceous–Paleocene time.

Late Cretaceous-Paleocene Extensional Collapse and Disaggregation of the Southernmost Sierra Nevada Batholith

Geobarometric studies have documented that most of the metasedimentary wall rocks and plutons presently exposed in the southernmost Sierra Nevada batholith south of the Lake Isabella area were metamorphosed and emplaced at crustal levels significantly deeper (∼15 to 30 km) than the batholithic rocks exposed to the north (depths of ∼3 to 15 km). Field and geophysical studies have suggested that much of the southernmost part of the batholith is underlain along low-angle faults by the Rand Schist. The schist is composed mostly of metagraywacke that has been metamorphosed at relatively high pressures and moderate temperatures. NNW-trending compositional, age, and isotopic boundaries in the plutonic rocks of the central Sierra Nevada appear to be deflected westward in the southernmost part of the batholith. Based on these observations, in conjunction with the implicit assumption that the Sierra Nevada batholith formerly continued unbroken south of the Garlock fault, previous studies have inferred that the batholith was tectonically disrupted following its emplacement during the Cretaceous. Hypotheses to account for this disruption include intraplate oroctinal bending, W-vergent overthrusting, and gravitational collapse of overthickened crust. In this paper, new geologic data from the eastern Tehachapi Mountains, located adjacent to and north of the Garlock fault in the southernmost Sierra Nevada, are integrated with data from previous geologic studies in the region into a new view of the Late Cretaceous-Paleocene tectonic evolution of the region. The thesis of this paper is that part of the southernmost Sierra Nevada batholith was unroofed by extensional faulting in Late Cretaceous-Paleocene time. Unroofing occurred along a regional system of low-angle detachment faults. Remnants of the upper-plate rocks today are scattered across the southern Sierra Nevada region, from the Rand Mountains west to the San Emigdio Mountains, and across the San Andreas fault to the northern Salinian block. Batholithic rocks in the upper plates of the Blackburn Canyon fault of the eastern Tehachapi Mountains, low-angle faults in the Rand Mountains and southeastern Sierra Nevada, and the Pastoria fault of the western Tehachapi Mountains are inferred to have been removed from a position structurally above rocks exposed in the southeastern Sierra Nevada and transported to their present locations along low-angle detachment faults. Some of the granitic and metamorphic rocks in the northern part of the Salinian block are suggested to have originated from a position structurally above deep-level rocks of the southwestern Sierra Nevada. The Paleocene-lower Eocene Goler Formation of the El Paso Mountains and the post-Late Cretaceous to pre-lower Miocene Witnet Formation in the southernmost Sierra Nevada are hypothesized to have been deposited in supradetachment basins that formed adjacent to some of the detachment faults. Regional age constraints for this inferred tectonic unroofing and disaggregation of the southern Sierra Nevada batholith suggest that it occurred between ∼90 to 85 Ma and ∼55 to 50 Ma. Upper-plate rocks of the detachment system appear to have been rotated clockwise by as much as 90° based on differences in the orientation of foliation and contacts between inferred correlative hanging-wall and footwall rocks. Transport of the upper-plate rocks is proposed to have occurred in two stages. First, the upper crust in the southern Sierra Nevada extended in a south to southeast direction, and second, the allochthonous rocks were carried westward at the latitude of the Mojave Desert by a mechanism that may include W-vergent faulting and/or oroclinal bending. The Late Cretaceous NNW extension of the upper crust in the southernmost Sierra Nevada postulated in this study is similar to Late Cretaceous, generally NW-directed, crustal extension that has been recognized to the northeast in the Funeral, Panamint, and Inyo mountains by others. Extensional collapse of the upper crust in the southern Sierra Nevada batholith may be closely linked to the emplacement of Rand Schist beneath the batholith during Late Cretaceous time, as has been suggested in previous studies.

Paleogeographic and paleotectonic evolution of the Himalayan Range as reflected by detrital modes of Tertiary sandstones and modern sands (Indus transect, India and Pakistan)

Detrital modes of sandstones derived from the Himalayan suture belt record the history of the mountain range since initial collision between India and Asia, which began in latest Paleocene time. Tertiary clastic wedges deposited in fore-arc, foreland, and remnant-ocean basins, and exposed along the Indus transect from northernmost India to the Arabian Sea, represent the best opportunity to study sedimentary responses to successive tectonic events during continental collision. Quartzose “continental-block” and feldspatholithic “magmatic-arc” sandstones were deposited, respectively, on the passive Indian (Tethys Himalayan succession) and active Asian (Indus Group) continental margins during Late Cretaceous–Paleocene time. Closure of the Neotethys was marked by sudden arrival of volcanic and ophiolitic detritus on the passive continental margin of the Indian plate during deposition of sediments dated at foraminiferal zones P6 (Pakistan) to P8 (India). Starting in early Eocene time (deposition of Chulung La Formation and Murree Supergroup), volcanic and ophiolitic to metasedimentary detritus was accumulated in rapidly subsiding “piggy-back” and foreland basins. Homogeneous petrographic composition within the Eocene–lower Miocene Murree Supergroup, with only slight progressive increase of detrital feldspars, suggests erosion of largely supracrustal rocks involved in thrusting in the north. In middle Miocene time, marked enrichment in medium- to high-grade metamorphic detritus in foreland sandstones (Siwalik Group) reflects rapid uplift of a warm wedge of Indian crust, which was carried southward along the Main Central thrust. This major paleogeographic change was recorded also by quartzolithic remnant-ocean turbidites, which were fed great distances along transverse fracture zones and later accreted in the coastal Makran subduction complex (Panjgur association and Makran Group). Recycled-orogen detritus derived from the elevated Himalayan chain is still accumulating today in the Indus fan. Enrichment in feldspars with respect to ancient sandstones reflects deep erosion levels into mid-crustal rocks along the core of the growing orogen.