The evolution of many modern intra-oceanic and continental arc systems is exemplified by cycles of arc construction, rifting, and separation of remnant and active arcs by a backarc basin floored by oceanic crust. Rifted arc complexes and backarc basins are inherently subductable, and hence only a fragmentary record of rifting and arc construction is preserved in the ancient record. In this contribution, we synthesize available geochronological, geochemical, isotopic, and stratigraphic data in order to discuss the evolution of the Cambrian to Ordovician Penobscot-Victoria Arc, which developed on the leading edge of Ganderia, a peri-Gondwanan microcontinent. Although the Penobscot and Victoria stages of arc-backarc development occurred in a predominantly extensional suprasubduction-zone setting, they each display a distinctly different character of magmatism and sedimentation. These stages are separated by an orogenic episode marked by the obduction of backarc ophiolites onto the Ganderian passive margin. The Cambrian to Lower Ordovician Penobscot Arc is characterized by the continuous migration of the magmatic front and development of multiple volcanically active rift zones. The rift basins display a variety of characteristics, including bimodal calc-alkaline magmatism, felsic-dominated incipient rift magmatism, and formation of rifts floored by tholeiitic to boninitic suprasubduction-zone ophiolite. Comparison to modern analogues suggests that part of the Penobscot Arc area developed in a similar setting to the volcanically active Havre Trough and Taupo volcanic zone. In contrast, the Victoria Arc phase was dominated by multiple epiclastic rich, volcano-sedimentary basins overlying tectonically modified Penobscot basement. Igneous rocks are sparse, typified by calc-alkaline felsic volcanic and tholeiitic to alkaline backarc basin basalts. The change in character of the backarc volcanic rocks over time is interpreted to reflect multiple tectonic factors, including the variation of slab retreat rate, degree of extension in the arc (Cambrian Penobscot Arc) versus the backarc basin (Ordovician Exploits-Tetagouche backarc), reactivation of inverted Penobscot extensional faults during Middle Ordovician rifting, and/or depletion of fertile components by the Middle Ordovician.

Abstract The Bathurst Mining Camp is made up of several different tectonic blocks and slivers—the Fournier, California Lake, Tetagouche, and Sheephouse Brook blocks and the blueschist and Bamford Brook slivers. These blocks and slivers are characterized by unique Arenig-Caradoc volcanic stratigraphies, indicating they represent widely separated, ensialic to ensimatic portions of the Tetagouche-Exploits back-arc basin. Their structural juxtaposition took place during the Ashgill-Ludlow closure of the Tetagouche-Exploits back-arc basin. The Tetagouche-Exploits back-arc basin formed in response to rifting of the northwest-facing Popelogan arc, although the extension-rifting history was diachronous and involved multiple stages. The rifting responsible for the California Lake block (ca. 472–468 Ma) took place before the rifting of the Tetagouche (ca. 467–465 Ma) and Sheephouse Brook blocks (ca. 466–464 Ma). These three blocks have ensialic to transitional crust and share a similar pre-Arenig basement consisting of Miramichi Group deep-water sandstones and shales. Oceanic to transitional back-arc crust is preserved in the Fournier block and the blueschist and Bamford Brook slivers. The various blocks and slivers were sequentially incorporated into the Brunswick subduction complex during closure of the back-arc basin. Massive sulfide deposits in the Brunswick mining camp mainly occur in the California Lake, Tetagouche, and Sheephouse Brook blocks. Radiometric age dating indicates that massive sulfide deposition took place during a protracted period of ca. 12 m.y., although occurring at different intervals in each block. High heat flow due to extension and/or rifting of the Popelogan arc combined with anoxic bottom conditions in the associated basins seem to be a prerequisite for formation of the large massive sulfide deposits. The oldest known massive sulfides are hosted by early Arenig (ca. 478 Ma) dacites of the Clearwater Stream Formation of the Sheephouse Brook Group, which may represent the earliest stages of extension of the Popelogan arc. The main massive sulfide bodies in the California Lake Group are represented by the middle to upper Arenig (ca. 472–470 Ma) Caribou-type deposits, whose formation coincides with the early stages of rifting of the California Lake block from the Popelogan arc. The large, massive sulfide deposits in the Tetagouche Group (referred to as the Brunswick-type deposits) are typically hosted by, or intimately associated with, the pyroclastic and tuffaceous sedimentary rocks that occur near or at the top of the Nepisiguit Falls Formation (ca. 469–468 Ma). The Brunswick-type deposits formed during extension rather than rifting of the Tetagouche block from the Popelogan arc, because mafic volcanism does not accompany felsic volcanism in the Nepisiguit Falls Formation. Rifting-related mafic volcanism becomes abundant in the overlying Flat Landing Brook Formation (ca. 467–465 Ma), the rhyolites of which host a few small massive sulfide deposits. Some contemporaneous massive sulfide mineralization occurs also in the coeval feldspar-porphyritic rhyolites of the Sheephouse Brook Group.

Abstract A new geologic map of the Bathurst Mining Camp was produced by integrating outcrop data with a large rock geochemical database, geochronology, and high resolution, multiparameter airborne geophysical data. These datasets were manipulated with geographic information systems (GIS) that enabled compiled point data, such as a whole-rock geochemical analyses and field observations for individual outcrops, to be spatially linked with the various geophysical images. The resulting new map outlines the regional distribution of six different complexly deformed, crustal blocks and slivers, each comprising a unique volcanic stratigraphy and associated massive sulfide deposits. The blocks and slivers, which represent widely separated crustal fragments that formed in the Early to Middle ordovician Tetagouche-Exploits back-arc basin, have been amalgamated into a tectonic collage of thrust nappes during their incorporation into the Brunswick subduction complex. The individual lithostratigraphic units of the blocks, comprising five groups of rocks, have been assembled together in the Bathurst Supergroup.

Abstract Massive sulfide deposits of the Bathurst Mining Camp experienced the following M 1 metamorphic conditions in the Ashgillian to Llandoverian ages (442–430 Ma): Caribou = 350°C, 5.5 kbars; Brunswick 12 = 360°C, 5.8 kbars; Heath Steele and Stratmat = 365°C, 5.5 kbars; and Brunswick 6 = 400°C, 5.8 kbars. Some deposits underwent a Late Silurian or Early Devonian M 2 metamorphism at pressures of ˜3 to 4 kbars and temperatures locally reaching 350° to 400°C. Silicate assemblages within, and in the host rocks of, the deposits exhibit metamorphic conditions identical to those of the sulfide assemblages of the deposits, showing that the deposits were emplaced prior to peak M 1 conditions, compatible with a syngenetic origin. Sphalerite barometry provided accurate, consistent pressure estimates when applied to appropriate assemblages (sphalerite-pyrite- hexagonal pyrrhotite). Arsenopyrite and chlorite-phengite thermometry gave useful temperature estimates. The latter assemblage was calibrated by least squares fitting of 51 pairs of analyses of coexisting chlorite and white mica to a formula deduced from thermodynamic reasoning giving where T e is the temperature of equilibration, and where is the mol fraction of j in the k site. x cl , x am , and x da are the proportions of clinochlore, amesite, and daphnite in chlorite analyses reduced to these three end members plus aluminum-free chlorite. Standard deviation between temperatures estimated from chlorite-phengite thermometry and those estimated by other means is 35°C. The narrow range of P-T observed in the Bathurst camp (350°-400°C, 5.5–5.8 kbars) supports structural observations that some of the nappes containing the California Lake and Tetagouche Groups were assembled and internally deformed prior to the recorded M 1 metamorphism.

Abstract The chemical signatures of the sedimentary rocks of the Bathurst Mining Camp of northern New Brunswick define a regionally consistent stratigraphy with the chemical variations reflecting the changes in provenance over time. The Cambro-Ordovician Miramichi Group metasedimentary rocks indicate a derivation from a continental source (relatively low concentrations of Cr, Ni, and V, with high Zr and Y contents). In contrast, those of the Middle Ordovician California Lake, Tetagouche, and Fournier Groups are predominantly the erosional products of obducted ultramafic rocks (relatively depleted in Nb, Ti, Y, and Zr, and enriched in Cr and Ni). However, a transitional sequence of felsic (remnant arc-derived) rocks occurs in the earliest stages of the California Lake and Tetagouche Groups (i.e., Vallée Lourdes Member of the Nepisiguit Falls Formation) prior to the establishment of the mafic provenance that typifies the majority of sedimentary rocks in these groups. Subtle chemical variations have been identified throughout the Miramichi, California Lake, and Tetagouche Groups, such as the higher Mn content of the Chain of Rocks Formation compared to the Knights Brook Formation and the higher nickel content of the Little River Formation compared to the Nepisiguit Falls and Flat Landing Brook Formations. These chemical characteristics have locally enabled the resolution of stratigraphy within allochthonous thrust panels that are devoid of petrographically distinguishable sedimentary rocks, volcanic rocks, and/or fossil locations. The changing sediment provenance closely reflects the tectonic evolution of the region. Most of the Miramichi Group sedimentary rocks are derived from the generally granodioritic Avalonian basement. However, the uppermost part of the Miramichi Group (the Patrick Brook Formation) and the earliest parts of the California Lake and Tetagouche Groups (the Charlotte Brook and Vallée Lourdes Members, respectively) are juvenile products of the eroding remnant arc. In contrast, the great majority of the California Lake and Tetagouche Groups, as well as the coeval to slightly younger Fournier Group, contain clastic sedimentary rocks derived from an ophiolitic source, with the sedimentary rocks becoming progressively more mafic as the obducted sequence is unroofed. The development of indistinguishable clastic sedimentary stratigraphies within several groups that were deposited on potentially widely separated crustal blocks within the Tetagouche-Exploits back-arc basin dictates that the sedimentary rocks were not locally derived. As such, the sedimentary stratigraphy is able to complement the volcanic stratigraphies that are unique to each block in resolving the tectonic evolution of the region. For example, the possible remnant-arc volcanic rocks of the Clearwater Stream Formation are built on the arc-derived Patrick Brook Formation. This indicates that the history of arc development and rifting is diachronous from one block to another.

Abstract The felsic volcanic rocks of the northern Bathurst Mining Camp occur in both the California Lake and Tetagouche Groups. The felsic volcanic rocks of these groups are in part coeval but differences in their chemistry, petrology, stratigraphic relationships, environments of deposition, and associated mafic volcanic rocks indicate that they formed in different regions of the Tetagouche-Exploits back-arc basin. They are both preserved within small fragments of attenuated continental arc crust that rifted away from the Popelogan arc during the Arenig. These crustal blocks became separated by oceanic basins underlain by transitional to oceanic lithosphere. By comparison with modern-day arc-back-arc systems it is apparent that these blocks underwent extension and subsequently rifting at different times. This indicates that the opening of the Tetagouche-Exploits back-arc basin was diachronous along the arc, such that at ca. 470 Ma the California Lake Group was within a rifting environment, while the Tetagouche Group was in the earlier extensional phase of arc break-up. The crustal blocks were later tectonically juxtaposed during the Late Ordovician to Late Silurian closure of the Tetagouche-Exploits basin.

Abstract The approximately coeval California Lake, Fournier, and Tetagouche Groups of the Bathurst Mining Camp formed separately and represent different tectonic settings within the Tetagouche-Exploits back-arc basin. They formed on small fragments of attenuated continental crust that rifted due to the northwestward migration of the Popelogan arc during the Arenig. These crustal fragments were subsequently tectonically juxtaposed by closure of the Tetagouche-Exploits basin in the Late Ordovician to Late Silurian.