The carbonate-dominated supracrustal sequences of the western Grenville Province formed between similar to 1200 and similar to 1300 Ma and are well-known for high-grade metamorphosed SEDEX and VMS deposits. However, there is limited information on base metal mineralization hosted in the clastic-dominated supracrustal sequences in the Allochthonous Medium to Low Pressure Belt of the central Grenville Province. The Moucou zinc occurrence (>1.3 wt.% Zn), located 50 km NW of Lac Saint-Jean, Quebec, provides an example of such mineralization. This zinc occurrence is hosted in metavolcanic rocks interbedded with quartzite layers of the Barrois Complex, a clastic-dominated supracrustal sequence, and metamorphosed under granulite facies. We present geochemical data, titanite geochronology, and petrographic observations for the Moncou zinc occurrence. The metavolcanic rocks have a transitional signature, Nb and Ta negative anomalies, and Ba and Th enrichments suggesting a back-arc setting comparable to the well-mineralized carbonate-dominated supracrustal sequences of the western Grenville Province. Zinc mineralization consists of (i) a first sphalerite generation (Sp1) systematically surrounded by a thin layer of plagioclase+quartz (Pl+Qz); (ii) deformed Zn-rich biotite crosscut by the titanite grains dated at similar to 1000 Ma, indicating the minimum age for the first zinc remobilization; and (iii) Zn-rich chlorite spatially associated with a second sphalerite generation (Sp2). These observations suggest that Zn mineralization occurred following this sequence: a pre-metamorphic event crystallizing Sp1 as it is surrounded by anatectic melt (Pl+Qz) and shows typical high-temperature crystallization textures, then a syn- to post-metamorphic event characterized by the Zn-rich biotite, and finally a low-temperature hydrothermal event crystallizing the Zn-rich chlorite and the second sphalerite generation. This study reveals the potential for Zn mineralization of the clastic-dominated supracrustal sequences of the Medium to Low Pressure Belt such as the Barrois Complex.

Chloritization of biotite by fluids is common in low-temperature tectonic regimes. Using three metapelites from the Tatric Superunit in the Western Carpathians (northern Slovakia), we demonstrated that in situ Rb/Sr geochronology of partially chloritized biotite can be used to date chloritization. The Superunit records high-temperature Variscan tectonics overprinted by low-temperature Alpine tectonics. Petrographic and chemical characteristics demonstrate that muscovite did not react with fluids and have uniform Rb/Sr geochronology, broadly reflecting Variscan metamorphism. In contrast, biotite grains are partially chloritized and yield dispersed 87Rb/86Sr and 87Sr/86Sr values, plotting as wedge-shaped arrays in a Nicolaysen isochron diagram. The arrays are consistent with re-equilibration of the Variscan Rb/Sr records in the remaining biotite. The youngest isochrons extracted for the three metapelites overlap at ca. 55−50 Ma, coeval with Alpine tectonism. Therefore, biotite Rb/Sr systematics can be reset by low-temperature hydrothermal fluid circulation, which has important implications for dating shallow-crustal tectonics and hydrothermal ore deposits that are otherwise difficult to date.

This study examines the potential influence of deformation on the systematics of Rb-Sr geochronology in mica phases under different conditions. Biotite and muscovite porphyroclasts in deformed specimens were characterized using electron backscattered diffraction, electron probe microanalysis and laser ablation inductively coupled plasma mass spectrometry to quantify spatial variations in crystal lattice orientations, element concentrations and in situ Rb-Sr geochronology. S29, a specimen subjected to deformation at greenschist facies conditions, is characterized by a spread in in situ Rb-Sr two-point isochron spot dates, which exhibit a strong inverse correlation with lattice deformation. As such, these Rb-Sr dates are interpreted to record partial re-equilibration controlled by deformation. Rb-Sr data from white mica in a specimen (NP17-58), which was deformed at lower amphibolite facies conditions, define a single population isochron. No correlation between lattice distortion and Rb-Sr spot dates is noted. Finally, two biotite porphyroclasts and matrix grains in a specimen (AC4), deformed at upper amphibolite facies conditions, define unique, single population Rb-Sr isochrons. The Rb-Sr systematics of the older porphyroclast are interpreted to be mainly temperature-controlled. In contrast, the Rb-Sr systematics for the younger porphyroclast and matrix grains are interpreted to reflect fluid-mediated resetting. The results of this study demonstrate that the multi-faceted influences on Rb-Sr systematics make isolating the effect of deformation difficult. Due to the complexity of the Rb-Sr systematics in deformed specimens, careful consideration of the mica phase analysed, as well as the temperatures, fluids and deformation experienced throughout the rock's history, needs to be accounted for.

The processes involved during subduction initiation (SI) remain poorly constrained, in part due to the rarity of geological archives. Ophiolites and their underlying metamorphic soles are thought to form during subduction zone infancy and may thus provide critical constraints. Metamorphic soles are derived from oceanic crust of the lower plate accreted to the base of the upper plate following SI and are exhumed during upper plate extension and ophiolitic crust generation. Their metamorphic evolution therefore provides insights into the thermal conditions at the nascent subduction plate interface and the trajectory of the lower plate during subduction infancy. In this study, we revisit the Bay of Islands complex (BOIC) metamorphic sole in the Newfoundland Appalachian Orogen and constrain P-T-t paths using phase equilibria modelling, melt reintegration and in situ U-Pb titanite geochronology. Our findings reveal generic SI and early subduction processes that align with geochronologic and metamorphic constraints reported for other soles as well as with the proposed early development of some modern subduction zones. The BOIC sole exhibits an inverted metamorphic gradient, with granulite and amphibolite facies metabasites at upper and middle structural levels, and greenschist facies metasedimentary and meta-igneous rocks in the lowest level. Our results are consistent with burial of garnet-clinopyroxene-amphibolite sole rocks to peak pressure conditions of similar to 14 kbar and 750 degrees C-850 degrees C, followed by decompression to peak temperature conditions of 880 degrees C-940 degrees C and 10.5-12 kbar. The immediately underlying plagioclase-hornblende amphibolites equilibrated at similar to 740 degrees C and similar to 8.5 kbar. Sole metamorphism produced melts and fluids that may have contributed to arc magmatism during early subduction. Titanite geochronology of granulite facies samples yields dates of 512 +/- 11 Ma and 501 +/- 11 Ma, interpreted to constrain prograde metamorphism. Our results indicate that the sole formed along a clockwise P-T-t path, with initial burial occurring along a relatively cold 18 degrees C/km metamorphic gradient, followed by heating of the subduction interface during decompression and eventually exhumation to a 26 degrees C-27 degrees C/km gradient. Peak temperature conditions in the sole were coeval with c. 484-488 Ma ophiolitic crust formation. We propose that subduction initiated from far-field forces and evolved to a self-sustained state as the slab pull force increased. Upwelling of hot asthenospheric mantle during rollback can explain decompressional heating and ensuing exhumation along an increasing thermal gradient, coeval with upper plate extension.

Porphyry deposits are major sources of copper, gold, molybdenum, and silver globally. However, the potential for critical raw materials (CRM) to be mined as by-products (e.g., antimony, bismuth, platinum group elements, and tellurium) at these deposits is poorly understood. Herein we present results from a lithogeochemical survey (n = 331), detailed mineralogy, and trace element mapping to characterize the concentrations of CRM and their deportment within the Golden Triangle, northwest British Columbia, Canada. We demonstrate that the host rocks to porphyry copper-gold (i.e., Galore Creek, Copper Canyon, KSM, Dok, Yeti, and Burgundy) and epithermal gold-silver (i.e., Brucejack) deposits were derived from oxidized and water-rich parental melts that suppressed sulphide crystallization, resulting in the pre-enrichment of CRM relative to other arc rocks globally. The structural juxtaposition, local thickening, and preservation of these prospective source rocks is likely one of the factors contributing to the mineral district's exceptional gold and CRM endowment. Multiple analytical methods (e.g., aqua-regia, four-acid, fusion) for the same samples further demonstrate that the highest Bi (39 ppm), Pd (460 ppb), Sb (375 ppm), and Te (15 ppm) concentrations are associated with sulphide and/or other non-resistate minerals within the most hydrothermally altered samples. Detailed mineralogy and trace element mapping by laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) reveals that CRM within the Golden Triangle are hosted by at least 58 different minerals. We apply these results to estimate the contained CRM at the Galore Creek and KSM deposits and to discuss their potential to be recovered as by-products. Lithogeochemical results are also applied to predict the mineral potential of different igneous suites within the Golden Triangle based on their CRM concentrations.

This study examines the microstructural and geochronological record in specimens collected along transects away from the Shannon fault and d'Abbadie fault, in the northern Canadian Cordillera. Microstructural analysis for both shear zones indicate dextral shear and an increase in paleostress and inferred strain magnitude toward each fault. In situ mica Rb–Sr geochronology from across a strain gradient developed by a single phase of deformation within the Shannon pluton, adjacent to the Shannon fault, dominantly records syn-emplacement deformation and/or rapid cooling at ca. 100 Ma with sparse analyses ranging to as young as ca. 63 Ma. U–Pb geochronology in apatite from the same specimens returns three ca. 100 Ma dates and two ca. 85 Ma dates. In contrast, lithologically heterogenous specimens that have experienced multiple deformational events, collected in proximity to the d'Abbadie fault, exhibit more variation in Rb–Sr dates, ranging from presumed regional cooling at ca. 195 Ma, a possible thermo-tectonic event at ca. 150 Ma, syn-pluton emplacement deformation and/or rapid cooling at ca. 100 Ma, and local partial resetting of Rb–Sr in mica most likely by brittle fault movement at ca. 80 Ma. U–Pb in apatite geochronology in the same specimens also records the ca. 100 Ma event. The results of this study demonstrate that lithological differences and multi-phase deformational histories create complexity in patterns of in situ Rb–Sr geochronology, and require interpretation within thermal and structural contexts, to quantify the timing of deformation in ductile high-strain shear zones.

Mica crystals have a highly asymmetric structure, arranged in sheets of two tetrahedral layers bonded to a single octahedral layer. The individual sheets are only weakly bonded, leading to perfect basal cleavage. The recent proliferation of in situ laser ablation-based Rb-Sr geochronology of mica makes it critical to understand if orientation of the crystal lattice relative to the laser beam may impart a differential 'matrix' effect on Rb-Sr ratios during ablation. Analyses of mica crystals from eight different samples, including biotite, muscovite and phlogopite, mounted with their c-axes approximately parallel (flat-mounted) and perpendicular (vertically mounted) to the incident laser beam, result in dates that are statistically indistinguishable. Moreover, and consistent with previous work, analysis of vertically mounted crystals generally resulted in less within-spot variation in 87Rb/86Sr, and is, therefore, the recommended orientation for Rb-Sr geochronology measurements, where practical.

The Late Triassic Burgundy porphyry system in the Golden Triangle of northwest British Columbia, Canada hosts Cu-Au mineralization in multiple prospective centers. Preliminary geologic mapping of the surface expression of the prospect and a cross section through the southern extension at The Ridge provide a preliminary structural understanding of the system with respect to the surrounding host rocks. The porphyries that make up the Burgundy prospect are emplaced into Upper Stikine Assemblage to Lower Stuhini Group strata with discrete episodes of texturally and geochemically distinct porphyry emplacement and igneous/hydrothermal brecciation. Lithogeochemical data indicate the prospect is a silica-undersaturated alkalic porphyry system consistent with the ubiquitous absence of quartz. A complex history of potassic, calc-potassic, phyllic, and propylitic alteration events overprint the porphyries, breccias, and wallrocks. The age of alteration was determined using in situ U-Pb and Rb-Sr geochronology. Titanite U-Pb (212.8 [+2.6] to 208.6 [+1.9] Ma), apatite U-Pb (216.7 [+2.9] to 208.2 [+4.1] Ma), garnet U-Pb (215.1 [+1.3] to 211.4 [+0.95] Ma), and biotite Rb-Sr (218.9 [+5.4] to 200.5 [+0.5] Ma) ages are interpreted alongside trace and major element geochemistry to reflect the timing of hydrothermal precipitation and/or equilibration of the dated phases during infiltration of hydrothermal fluids. The geochronology results define a minimum emplacement age for the porphyry suite and outline a protracted period (>10 Myr) of localized, likely episodic, post-emplacement hydrothermal alteration/equilibration. The oldest ages from apatite (216.7 + 2.9 Ma), garnet (215.1 + 1.3 Ma), and biotite (218.9 + 5.4 Ma) indicate emplacement of Burgundy porphyries began before emplacement of the neighboring Galore Creek alkalic suite (212-205 Ma). In addition, the youngest biotite date (200.5 + 0.5 Ma) indicates Burgundy experienced localized high-T hydrothermal fluid infiltration associated with either a long-lived hydrothermal system related to cooling of structurally deeper Burgundy melts and/or externally derived fluids during the onset of local Tatogga/Texas Creek suite magmatism. The new age data from Burgundy indicate alkalic magmatism in the Golden Triangle began earlier than is currently recognized within the working regional framework model and that Burgundy was a conduit for protracted hydrothermal activity during this critical metallogenic epoch near the Triassic-Jurassic boundary.

Subvertical glaucophane + quartz ± phengite veins exposed in the footwall of a major extensional detachment on southern Evia (NW Cyclades, Greece) record mode-I brittle fracturing with variable principal stress orientations. The dense network of veins displays systematic cross-cutting relationships with a prominent youngest vein set spaced 5-10 cm apart transecting all other veins. Interlayered jadeite-rich metabasalt and quartzite host the veins and promote a pronounced rheological control on fracturing, with veins preferentially hosted in metabasalt layers and terminating abruptly as pressure solution seams or shear bands at contacts with the ductily deformed quartzite. Vein-hosted ferromagnesian minerals do not exhibit recrystallization or dissolution-reprecipitation microstructures. Jadeite in the metabasalt forms both i) 'fuzzy' euhedral crystals overgrown by hematite and ii) symplectitic intergrowths with quartz and albite. Vein-hosted glaucophane and phengite grew at fixed angles (normal and oblique) to vein walls. Phengite is compositionally homogeneous with elevated Si content (3.41–3.52 apfu). Glaucophane from all veins shows a homologous concentric compositional zoning with core chemistry intermediate between glaucophane and magnesioriebeckite, glaucophane-rich mantles, and rims of magnesioriebeckite or winchite. Phengite yields consistent single-grain total-fusion 40Ar/39Ar dates with a weighted mean of 22 ± 1 Ma (n: 22), whereas the low-K glaucophane produced equivocal and dispersed dates. Phengite (n: 44, 20) and glaucophane (n: 8, 42) in-situ 87Rb/87Sr isochrons from two samples yield mutually indistinguishable dates of 21 ± 5 Ma and 25 ± 4 Ma, within uncertainty of the 40Ar/39Ar dates. The uniform mineral chemistry, compositional zoning, and geochronology indicate that the veins formed over a short time without major shifts in ambient pressure-temperature conditions. Contrary to the apparent mineralogically-defined high pressure-low temperature paragenesis of the veins, dates obtained from pristine high-Si phengite support crystallization in the latest Oligocene to earliest Miocene, coincident with regional extension and widespread greenschist-facies retrogradation in the Aegean. Abundant hematite and the predominance of Fe3+-rich sodic amphibole and clinopyroxene species implicates a highly oxidizing fluid in the stabilization of these nominally ‘high-pressure’ minerals under conditions widely responsible for producing retrogradational greenschist-facies assemblages throughout the Cyclades.

The Shuswap Metamorphic Complex in southeastern British Columbia, Canada, exposes penetratively deformed rocks exhumed from deep crustal levels (similar to 25-30 km depth) of the Canadian Cordillera. Existing models describing its tectonometamorphic evolution are not directly linked to absolute age constraints acquired through modern petrochronological methods and, therefore, remain ambiguous. To differentiate between proposed models, here we apply U-Th-Pb monazite petrochronology, petrological modeling, and microstructural analysis to quantify conditions and timing of deformation across a transect of the Shuswap Metamorphic Complex. Our results demonstrate that metamorphism decreases in age with increased structural depth associated with progressive localization of NE-directed shearing toward the base of the Shuswap Metamorphic Complex. Monazite U-Th-Pb age data from the structural level exposed in the study area are consistent with protracted northeast-directed compression from ca. 167 Ma to ca. 59 Ma, after which west-directed ductile extension continued until at least ca. 49 Ma and was progressively localized along the Okanagan Valley fault system. New data presented are consistent with a model of basal accretion in front of a foreland-propagating ductile thrust system, followed by exhumation of the Shuswap Metamorphic Complex facilitated in large part by crustal-scale extension.

General shear, wherein deformation incorporates elements of both coaxial and non-coaxial strain, is a prevalent strain regime in natural high-strain zones. In extensional tectonic settings, three-dimensional forms of general shear may enhance exhumation via additional crustal thinning (i.e., via pure shear or flattening strain components) or counteract it by inducing crustal thickening (i.e., via a constrictive strain component), without necessarily producing a conspicuous crustal-scale shear zone or fault. Schists and phyllonites demarcating a major tectonic boundary between thrust sheets on Evia in the NW Cyclades record structural evidence for general shear with a NE-directed non-coaxial component and contemporaneous flattening. The package of rock accommodating this strain is lithologically heterogeneous, comprising intercalations of carbonate-, quartz-, and phyllosilicate-dominated schist, as well as dispersed m- to hm-scale olistoliths and blocks of marble and metabasite. Flattening in these rocks is exemplified by foliation-oblique quartz ± calcite veins exhibiting pinch-and-swell or boudinage structure alongside dominant bidirectional dips perpendicular to the regional NE-SW stretching lineation. We combine in-situ 40Ar/39Ar and 87Rb/87Sr dating of white mica with quartz c-axis petrofabric analysis of the deformed quartz veins to elucidate the timing and styles of deformation recorded by these rocks. White mica provides mainly late Oligocene 40Ar/39Ar dates in samples with a single dominant foliation, whereas mica defining composite or crenulated foliations records late Eocene-early Oligocene dates, or age populations spanning the Oligocene. Some samples record dispersed Paleocene-Eocene dates older than the earliest proposed timing of metamorphism, although white mica from these rocks provides more geologically plausible early Oligocene 87Rb/87Sr dates. Vein quartz c-axis fabrics consist primarily of c-axis maxima or small-circle girdles centered about the Z-axis, with subordinate fabrics defining top-to-NE asymmetric type-I cross girdles or Y-axis maxima. Considered together with vein macro- and micro-structure, our data indicate that the deformed schists accommodated top-to-NE general shear at temperatures only slightly above 300°C, resulting in an oblate finite strain ellipsoid. Deformation over this interval produced differential transposition of earlier tectonic fabrics and structures into a sub-horizontal penetrative cleavage in the rheologically weak mica schists, whereas sections dominated by more quartzose- and carbonate-rich lithotypes display comparatively well-preserved older foliations and structures and a spaced secondary cleavage. The prevalence of late Oligocene 40Ar/39Ar dates in samples exhibiting a single, shallowly-dipping micaceous foliation implies that flattening general shear coincided with, and likely helped facilitate, exhumation. Our data indicate that unroofing may be partly facilitated by inconspicuous zones accommodating distributed inhomogeneous strain, a potentially important observation for exhumed subduction zones featuring prevalent block-in-matrix mélanges.

Regional and detailed mapping at Gordon Lake has closely outlined the structural timing of a km-scale refold and linked this event to the formation gold-bearing quartz–breccia zones. Early (F1) isoclinal folds, that were refolded (F2) during a secondary (D2) deformation event coeval with peak regional metamorphism, lead to the development of a pervasive (S2) regional cleavage and sub-vertical (L2) stretching lineation. Tightening and increased strain within the east limb of the Gordon Lake refold structure occurred during D3 along with the development of a localized (S3) crenulation cleavage and an episode of quartz–breccia mineralization. The nearby Spud Lake pluton intruded the region post-peak metamorphism. New in situ Rb–Sr geochronology on white mica from the pluton defined an overdispersed regression date of 2573 ± 17 Ma, which overlaps an existing 40Ar/39Ar date of 2592 ± 14 Ma and other U–Pb zircon ages for nearby granitic plutons of the Prosperous Suite. Rb–Sr geochronology of biotite from a sample of quartz–breccia mineralization yielded a single population regression at 2480 ± 53 Ma. This date is significantly younger than a previous 40Ar/39Ar date of 2564 + 14 Ma, perhaps indicating the incorporation of excess 40Ar available during the mineralization event. The Rb–Sr date from the quartz–breccia is consistent with field relationships that indicate the mineralization post-dates peak metamorphism.

Extensive debate has focussed on the nature and location of the Snowbird Tectonic Zone (STZ), the suture between the Rae and Hearne cratons. Geological mapping in the Baker Lake area revealed a similar to 7 km wide deformation zone associated with the Chesterfield Fault Zone (CFZ), a south-dipping, dextral strike-slip structure previously interpreted to represent the northern segment of the STZ. New geochronology across the CFZ indicates both the footwall and hangingwall are dominated by ca. 2.72 Ga tonalite gneisses and ca. 2.6 Ga porphyritic monzogranite, effectively ruling out the CFZ as the northern segment of the STZ. Geochronology, thermobarometry, and thermodynamic modelling from the hangingwall indicate three Paleoproterozoic metamorphic events (M1-M3) that outline a clockwise P-T-t path. Prograde metamorphism (M1) reaching peak conditions of 0.75 GPa and 700 degrees C is dated by early titanite growth at ca. 1.92 Ga, consistent with burial during southeast-verging folding and thrusting associated with collision of the Rae-Chesterfield and Hearne cratons. Peak conditions of similar to 1.0 GPa and 740 degrees C at ca. 1.87 Ga (M2; garnet Lu-Hf) are coeval with northwest-vergent folding and thrusting during early, intra-oceanic accretionary episodes associated with the Trans-Hudson Orogeny. Dextral strike-slip kinematics argue against the CFZ as the structure responsible for exhumation of ca. 1.9 Ga high-pressure rocks to the south. Instead, exhumation may have been accommodated along discrete, reverse-sense shear zones associated with the CFZ, or an alternate structure to the south. Together, these data highlight that crustal-scale shear zones can preserve tectonometamorphic information, critical for tectonic reconstructions and understanding orogenic processes, that is not recorded in the surrounding lithotectonic blocks.

Advances in analytical instrumentation over the past decade have facilitated the development of new geochronological methods. In particular, the triple quadrupole inductively coupled plasma mass spectrometers with in-line reaction cells have made it possible to investigate beta decay geochronological systems, including Lu-Hf in garnet, in situ via laser ablation. While these new methods allow different kinds of studies to be carried out, their utility relative to well-established methods has not been investigated in detail. Herein we present the results of in situ garnet Lu-Hf and monazite U(-Th)-Pb geochronological analyses of two adjacent Archean meta-pelitic rocks from the Northwest Territories, Canada. Whereas the garnet Lu-Hf analyses define single population isochrons of ca. 2570 Ma, monazite U(-Th)-Pb analyses define two chemically distinct populations. An older ca. 2570 Ma monazite population has low Y concentrations, while a younger, ca. 2530 Ma monazite population has high Y concentrations. The change in Y concentrations in the monazite is consistent with coeveal growth with garnet during prograde metamorphism whereas the younger high Y monazite is interpreted to reflect growth during garnet breakdown during decompression. The results presented herein demonstrate that incorporating both in situ garnet and monazite geochronological data takes advantage of each method (i.e. the spatial precision, variable (re)crystalization under different conditions, and the ability to determine a date without relying on an isochron for monazite U-Pb, and the ability to date a primary metamorphic phase for garnet Lu-Hf) to build a more robust geochronological history.

The Triassic collision between the Yangtze and North China blocks resulted in the formation of ultrahigh-pressure metamorphic rocks along the Dabie-Sulu orogenic belt, the development of the Tan-Lu fault zone, and the establishment of a crustal-scale décollement within the Lower Yangtze foreland fold-thrust zone. The ductile fabrics exposed in the Zhangbaling–Feidong Complex of the southern Tan-Lu fault zone record the strain that accumulated during that collision. Herein, field observations and structural analysis of high-strain rocks (i.e. microstructures and quartz crystallographic preferred orientations) from the eastern Feidong Complex are combined with estimates of deformation P-T conditions to reveal that top-to-SSW subhorizontal, amphibolite-facies (600 and 700℃, 4.0–6.6 Kbar) ductile fabrics overprint the Paleo-Proterozoic Feidong Complex. U–Pb geochronology on zircon rims and syntectonic titanite indicates that the overprinting deformation occurred in the Middle Triassic (ca. 246–242 Ma). Reinterpretation of reflection seismic profiles across the Tan-Lu fault zone and Lower Yangtze foreland fold-and-thrust zone identifies a large, subhorizontal décollement beneath the sedimentary cover that appears to have influenced the formation of fold-thrust structures in the Lower Yangtze foreland. These new observations and geochronological results are consistent with a transpressional tectonic model wherein the Early-Middle Triassic northward indentation of the Yangtze block into the North China block drove deformation within the southern Tan-Lu fault zone.

New in situ apatite U-Pb and mica Rb-Sr and Ar-40/Ar-39 geochronology outline a break in geochronology within the Mount Everest massif at an elevation of c. 8000 m. Above the break, most chronometers record dates from the Eocene epoch, whereas below, most dates are from the Middle Miocene epoch. Raman spectroscopy of carbonaceous material and Ti-in-biotite-based thermometry results outline a break in temperatures at the same elevation. From the summit downwards, temperatures increase to a maximum of c. 500 degrees C at c. 8500 m before decreasing to c. 400 degrees C at c. 7900 m. The coinciding breaks in the independent datasets are interpreted to reflect movement along a previously unrecognized structure, here termed the Adrishya thrust that was active c. 18 Ma. The Adrishya thrust may reflect re-equilibration of the evolving orogenic wedge, perhaps further influenced by cooling and strain localization structurally away from the exhuming orogenic core.

Re-examination of sediment samples collected from the Bay of Bengal via laser-ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) Rb-Sr geochronology demonstrates the viability of the Rb-Sr system for use as a detrital chronometer. The age population defined by the Rb-Sr dates essentially reproduces that previously published for detrital 40Ar/39Ar dates. The assumed initial 87Sr/86Sr on the calculated population has some influence on the age of the final population, but that influence can be ameliorated by filtering for higher 87Rb/86Sr ratios. The 87Rb/86Sr ratio cut-off used for such filters to minimize the effect of initial 87Sr/86Sr on the final population is strongly dependant on the age of the material being analysed (i.e. ~> 87Rb/86Sr = 500 @ 250 Ma and ~>87Rb/86Sr = 50 @ 2500 Ma). Finally, Ti-in-biotite temperatures calculated based on data collected during LA-ICP-MS overlap with those calculated for the same material based on electron probe microanalyzer data demonstrating the potential for petrochronolgy based on the Rb-Sr system.