EPMA data, monazite U-Pb data and P-T estimates using conventional geothermometers and geobarometers for felsic granulite, Chencai Complex, West Cathaysia terrane, South China
This map synthesizes the field observations and initial interpretations for the Terra Nivea area following five weeks of regional and targeted bedrock mapping on the eastern Meta Incognita Peninsula, Baffin Island, Nunavut. Under the Geo-mapping for Energy and Minerals (GEM) Program, this area was targeted in 2014 to upgrade the geoscience knowledge and document the economic potential of the greater Iqaluit area south of Frobisher Bay. Field observations have constrained the distribution of metasedimentary units comprising quartzite, marble, psammite, pelite, and semipelite, all of which can be correlated with the contiguous middle Paleoproterozoic Lake Harbour Group in the type area north of Kimmirut. The full range of siliciclastic and minor carbonate rock types can be traced to the easternmost tip of Meta Incognita Peninsula. The distribution and eastern limit of high-grade felsic and mafic plutonic rocks, tentatively interpreted as part of the middle Paleoproterozoic Cumberland Batholith, were delineated. Three distinct phases of deformation and one metamorphic episode were recognized. The deformation and metamorphic events can be correlated with similar features and assemblages previously documented both on Baffin Island and on the Ungava Peninsula of northern Quebec, and will be utilized to compare, and improve on, existing regional tectonic models.
Granitoid plutonism, a significant contributor to orogenic evolution, is a commonly overlooked vector in exploration targeting. Using the Flin Flon-Glennie Complex of the Trans-Hudson orogen as a template, we show that the geochemistry of granitoid rocks can be a useful parameter in differentiating prospective and nonprospective areas for volcanic-hosted massive sulfide (VHMS) deposits. The Flin Flon-Glennie Complex includes 1910 to 1860 Ma plutonic rocks that can be subdivided into three suites: (1) juvenile arc-related rocks of ferroan and magnesian subtypes, (2) contaminated arc-related rocks, and (3) successor arc-related rocks of both low and high Sr/Y ratio. Petrogenesis of ferroan juvenile and low Sr/Y successor arc plutons indicates they formed in regions of thinner crust and hence would have been associated with higher heat flow and arc rifting—conditions that favor VHMS endowment. Regions of the orogen with both ferroan and low Sr/Y plutonic subtypes were long-lived zones of thin crust and preserve VHMS mineralization related to both juvenile and successor arc magmatism. In contrast, volcanic belts dominated by contaminated arc or high Sr/Y successor arc plutons formed on thicker substrates, with contaminated arc rocks built on Archean-Paleoproterozoic pericratonic slivers and high Sr/Y successor arc rocks associated with submarine to subaerial arc systems. These regions of thicker crust demonstrably lack VHMS deposits and were also the locus for late unroofing. Our results suggest that pluton geochemistry regionally correlates with mineral occurrence and could represent a useful regional exploration tool in buried or poorly exposed parts of the Flin Flon-Glennie Complex and other Paleoproterozoic orogens.
Three strongly foliated or recrystallized samples were identified in the field as potential Archean basement and were collected for geochronology in order to compare their crystallization ages with the ages of known basement in the Superior Craton and Core Zone. A porphyritic monzonite from the thrust-bound Boullé Complex within the Rachel-Laporte Zone yields a crystallization age of 2690 ± 4 Ma. A 2696 ± 4 Ma magnetite granite of the Saffray Suite is similar in age and composition to large potassic suites of the Superior Craton. These ages stand in contrast to a younger 2668 ± 5 Ma crystallization age for a tonalite of the Wheeler Complex from a separate structural dome within the Rachel-Laporte Zone. The ages of the Champdoré and Lhande plutonic suites are 1839 ± 6 Ma and 1835 ± 4 Ma, respectively. As these units are metamorphosed and strongly foliated, they also provide a maximum age constraint on peak Paleoproterozoic tectonothermal overprint. The post-tectonic pegmatite of the Dancelou Suite provides a 1793 ± 4 Ma constraint on the cessation of deformation in that area.
Abstract The Danba Structural Culmination is a tectonic window into the late Triassic to early Jurassic Songpan‐Garzê Fold Belt of eastern Tibet, which exposes an oblique section through a complete Barrovian‐type metamorphic sequence. Systematic analysis of a suite of metapelites from this locality has enabled a general study of Barrovian metamorphism, and provided new insights into the early thermotectonic history of the Tibetan plateau. The suite was used to create a detailed petrographic framework, from which four samples ranging from staurolite to sillimanite grade were selected for thermobarometry and geochronology. Pseudosection analysis was applied to calculate P – T path segments and determine peak conditions between staurolite grade at ∼5.2 kbar and 580 °C and sillimanite grade at ∼6.0 kbar and 670 °C. In situ U–Pb monazite geochronology reveals that staurolite‐grade conditions were reached at 191.5 ± 2.4 Ma, kyanite‐grade conditions were attained at 184.2 ± 1.5 Ma, and sillimanite‐grade conditions continued until 179.4 ± 1.6 Ma. Integration of the results has provided constraints on the evolution of metamorphism in the region, including a partial reconstruction of the regional metamorphic field gradient. Several key features of Barrovian metamorphism are documented, including nested P – T paths and a polychronic field gradient. In addition, several atypical features are noted, such as P – T path segments having similar slopes to the metamorphic field gradient, and T max and P max being reached simultaneously in some samples. These features are attributed to the effects of slow tectonic burial, which allows for thermal relaxation during compression. While nested, clockwise P – T – t loops provide a useful framework for Barrovian metamorphism, this study shows that the effects of slow burial can telescope this model in P – T space. Finally, the study demonstrates that eastern Tibet experienced a significant phase of crustal thickening during the Mesozoic, reinforcing the notion that the plateau may have a long history of uplift and growth.
Abstract The High Arctic Large Igneous Province (HALIP) represents extensive Cretaceous magmatism throughout the circum-Arctic borderlands and within the Arctic Ocean (e.g., the Alpha-Mendeleev Ridge). Recent aeromagnetic data shows anomalies that extend from the Alpha Ridge onto the northern coast of Ellesmere Island, Nunavut, Canada. To test this linkage we present new bulk rock major and trace element geochemistry, and mineral compositions for clinopyroxene, plagioclase, and olivine of basaltic dykes and sheets and rhyolitic lavas for the stratotype section at Hansen Point, which coincides geographically with the magnetic anomaly at northern Ellesmere Island. New U-Pb chronology is also presented. The basaltic and basaltic-andesite dykes and sheets at Hansen Point are all evolved with 5.5–2.5 wt% MgO, 48.3–57.0 wt% SiO2, and have light rare-earth element enriched patterns. They classify as tholeiites and in Th/Yb vs. Nb/Yb space they define a trend extending from the mantle array toward upper continental crust. This trend, also including a rhyolite lava, can be modeled successfully by assimilation and fractional crystallization. The U-Pb data for a dacite sample, that is cut by basaltic dykes at Hansen Point, yields a crystallization age of 95.5 ± 1.0 Ma, and also shows crustal inheritance. The chronology and the geochemistry of the Hansen Point samples are correlative with the basaltic lavas, sills, and dykes of the Strand Fiord Formation on Axel Heiberg Island, Nunavut, Canada. In contrast, a new U-Pb age for an alkaline syenite at Audhild Bay is significantly younger at 79.5 ± 0.5 Ma, and correlative to alkaline basalts and rhyolites from other locations of northern Ellesmere Island (Audhild Bay, Philips Inlet, and Yelverton Bay West; 83–73 Ma). We propose these volcanic occurrences be referred to collectively as the Audhild Bay alkaline suite (ABAS). In this revised nomenclature, the rocks of Hansen Point stratotype and other tholeiitic rocks are ascribed to the Hansen Point tholeiitic suite (HPTS) that was emplaced at 97–93 Ma. We suggest this subdivision into suites replace the collective term Hansen Point volcanic complex. The few dredge samples of alkali basalt available from the top of the Alpha Ridge are akin to ABAS in terms of geochemistry. Our revised dates also suggest that the HPTS and Strand Fiord Formation volcanic rocks may be the hypothesized subaerial large igneous province eruption that drove the Cretaceous Ocean Anoxic Event 2.
This map summarizes the field observations for the Clearwater Fiord (south) map area following eight weeks of regional and targeted bedrock mapping on western Hall Peninsula. The 2015 field campaign completes a two-decade mission to update map coverage for the whole of Baffin Island south of latitude 70°N. The bedrock is dominated by a Paleoproterozoic metaplutonic suite, ranging in composition from gabbro to syenogranite, with crosscutting relations indicating a progression from mafic to silicic magmatism. Prevailing upper amphibolite to lower granulite facies metamorphic conditions overlap the stability limits of magnetite and orthopyroxene, which is consistent with equilibrium phase diagrams and regional aeromagnetic data. Metasedimentary rocks, including quartzite, pelite, marble, and metagreywacke, are present as screens and enclaves between and within plutonic bodies. An examination of the 'ghost' stratigraphy suggests that the metasedimentary rocks can be correlated with the middle Paleoproterozoic Lake Harbour Group in the south and Piling Group in the north. Two basaltic dyke swarms and shallowly dipping Ordovician limestone respectively crosscut and overly the Paleoproterozoic units.
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