Tectonic evolution of the easternmost Piedmont, North Carolina

Several epigenetic mineral deposits in the Ca1rolina slate belt are intimately related to meteoric-hydrothermal systems of late Precambrian and early Paleozoic age. At Pilot Mountain, low 18 O rocks correlate well with zones of strong silicic alteration and alkali leaching accompanied by high alumina minerals (sericite, pyrophyllite, andalusite + or - topaz) and anomalous concentrations of Cu, Mo, Sn, B, and Au. The alteration occurs within andesitic volcanic and volcaniclastic rocks and is associated with a subvolcanic(?) dacite porphyry stock on the southeastern slope of the mountain. Tilting and erosion have exposed an oblique section through the original system, interpreted to expose shallower rocks to the northwest. A 4-km 2 central zone of slight 18 O depletion (delta 18 O (sub whole rock) = 4.3-6.1ppm) occurs on the broad and resistant (silicifled) western flank of Pilot Mountain, predominantly within quartz-sericite schist and quartz granofels containing pods of high A1 minerals. A magmatic source for much of the sulfur and metal is likely, and a subordinate magmatic water component in the fluid of the central zone is possible. This central zone is surrounded by a >30-km 2 peripheral zone of low 18 O sericite schists, chlorite-sericite schists, and andesitic volcanic rocks (delta 18 O (sub whole rock) < 3.8ppm), with the lowest values (1.4ppm) occurring in intensely sericitized rocks on the eastern flank of Pilot Mountain, near the apex of the dacite porphyry stock. Rhyolites of the Uwharrie Formation (delta 18 O = 3.8-6.3ppm) are not as strongly altered as nearby andesites and may postdate the hydrothermal alteration. The fluid calculated to be in equilibrium with the lowest 18 O quartz veins and country rocks at 300 degrees + or - 50 degrees C would have delta 18 O approximately -4.5 + or - 2.0 per mil, whereas analyses of radiating pyrophyllite indicate equilibrium with a fluid having delta D approximately -30 per mil, consistent with a slightly 18 O-shifted, low-latitude meteoric water. Subsequent greenschist metamorphism caused intermineral isotopic reequilibration in several samples and may have modified preexisting alteration assemblages, but it did not destroy the large delta 18 O anomaly produced by meteoric-hydrothermal activity at Pilot Mountain. Reconnaissance studies of other alteration zones in the Carolina slate belt have so far disclosed the involvement of meteoric-hydrothermal fluids at the Snow Camp pyrophyllite deposit, at the Hoover Hill and Sawyer Au mines, and probably at the Haile and Brewer Au mines.

The Carolina slate belt (CSB) is located in the southeastern Appalachian Piedmont, cropping out as a narrow continuous zone extending from central Virginia southwestward to central Georgia. Geologic investigations of the CSB began in the 1820s, shortly after discovery of gold in Cabarrus County, North Carolina. Early workers established the general distribution and character of the CSB relative to adjacent belts, and more recently, mappable units have been delineated. Present interest in the CSB is in part due to recognition of similarities between slate-belt rocks and those associated with sulfide deposits in New Brunswick, and in part to the recent recognition of sedimentary features in the relatively underformed slate-belt rocks. End_Page 1437------------------------------ Early workers in the CSB recognized the volcanic origin of slate-belt rocks, as well as subsequent metamorphic alteration. More recently, the sedimentologic-stratigraphic aspects of the CSB have been investigated. Interpretations of tectono-sedimentary environments have been made, based on petrologic, geochemical, and stratigraphic relationships, in light of the articulation of the concepts of plate tectonics and accreted terranes. Age interpretations of the CSB have been based on degree of metamorphism, radiochronology, and sparse fossil evidence. Age interpretations in the late 1800s and early 1900s suggested a Precambrian age for the CSB. This was modified in the 1960s by the discovery of a purported Middle Cambrian trilobite and a lead-alpha date of 440 to 470 ± 60 Ma. Post-1960s radiometric dates for the CSB range from 705 ± 15 Ma to 511 ± 14 Ma, representing various postdepositional intrusion and cooling events. The discovery of a mid-Cambrian Atlantic province trilobite fauna and upper Precambrian Ediacarian fossils not only unequivocally date the southern part of the CSB, but also support the accreted terrane concept and Euro-African origin of sedimentary units of CSB. End_of_Article - Last_Page 1438------------

Boggs, Johnny, Ge Sun, David Jones, and Steven G. McNulty, 2012. Effect of Soils on Water Quantity and Quality in Piedmont Forested Headwater Watersheds of North Carolina. Journal of the American Water Resources Association (JAWRA) 1‐19. DOI: 10.1111/jawr.12001Abstract: Water quantity and quality data were compared from six headwater watersheds on two distinct soil formations, Carolina Slate Belt (CSB) and Triassic Basins (TB). CSB soils are generally thicker, less erodible, and contain less clay content than soils found in TB. TB generated significantly more discharge/precipitation ratio than CSB (0.33 vs. 0.24) in the 2009 dormant season. In the 2009 growing season, TB generated significantly less discharge/precipitation ratio than CSB (0.02 vs. 0.07). Over the entire monitoring period, differences in discharge/precipitation ratios between CSB and TB were not significantly different (0.17 vs. 0.20, respectively). Storm‐flow rates were significantly higher in TB than CSB in both dormant and growing season. Benthic macroinvertebrate biotic index scores were excellent for all streams. Nutrient concentrations and exports in CSB and TB were within background levels for forests. Low‐stream nitrate and ammonium concentrations and exports suggested that both CSB and TB were nitrogen limited. Soils appear to have had a significant influence on seasonal and storm‐flow generation, but not on long‐term total water yield and water quality under forested conditions. This study indicated that watersheds on TB soils might be more prone to storm‐flow generation than on CSB soils when converted from forest to urban. Future urban growth in the area should consider differences in baseline hydrology and effects of landuse change on water quantity and quality.

A comparison of high-alumina mineral assemblages spatially associated with the Haile and Brewer gold deposits in the Paleozoic Carolina slate belt (CSB) of the southeast United States and the Sons of Gwalia and Mount Celia gold deposits in the Archean Norseman–Wiluna greenstone belt (NWGB) in Western Australia suggests a similar hydrothermal origin and subsequent metamorphic and deformational history. A common hydrothermal origin is supported by the striking similarity in whole-rock chemistry, even though there were probably significant variations in original unaltered protoliths. An analysis of rocks from each of the deposits that contain high-alumina minerals demonstrates that the protoliths were leached of alkalis with respect to aluminum and have a ratio of Al2O3/Na2O + CaO + K2O greater than three. Although the rocks contain abundant high-alumina minerals, the aluminum content in these rocks is not unusually high, and it does not appear that there has been any significant transport of aluminum either into or out of the rocks that were altered.The most common high-alumina minerals found in rocks affected by the feldspar destructive alteration event include andalusite, kyanite, pyrophyllite, kaolinite, and sericite. Other minerals present in variable amounts include diaspore, chloritoid, alunite, natroalunite, paragonite, and topaz. It is possible that some of these minerals formed during the early hydrothermal alteration event and were recrystallized during metamorphism. Regardless of when the high-alumina minerals formed, textural relations suggest that the rocks had been hydrothermally altered by the time the metamorphic minerals formed. A comparison of alteration from the deposits studied in the CSB and the NWGB suggests there are many similarities to acid-sulfate alteration associated with geothermal areas, such as Yellowstone Park, Wyoming, and with acid-sulfate gold deposits, such as Goldfield, Nevada. Thus, it is possible that the protolith of the metamorphosed rocks in the CSB and NWGB contained an alteration assemblage that included alunite, pyrophyllite, and kaolinite.A generalized paragenetic sequence determined from petrographic and field observations, beginning with regional metamorphism, follows: (i) formation of andalusite, kyanite, chloritoid, and topaz during prograde metamorphism, depending on whole rock chemistry, (ii) formation of pyrophyllite and quartz-rich pods during silicification of aluminosilicate-bearing rocks, (iii) bedding parallel schistosity and fracturing produced by a deformational event, (iv) fractures filled by quartz, sericite, pyrophyllite, or calcite, (v) folding of early layering in the rocks to form a crenulation cleavage accompanied by introduction of quartz veins at high angles to foliation; and (vi) retrograde metamorphism of andalusite–kyanite-pyrophyllite to produce an assemblage of kaolinite ± diaspore.The spatial association of the acid-sulfate alteration with gold mineralization, together with comparison of analogous alteration associated with younger unmetamorphosed acid-sulfate gold deposits, suggests that at least some of the gold was introduced during the early premetamorphic alteration event. The present location of gold in each deposit is a result of local changes brought about by later metamorphic and deformational events.

A nearly concordant U-Pb zircon age of 550 ± 4 Ma is interpreted to closely date crystallization of the epizonal Little Mountain metatonalite in the southeastern part of the Charlotte belt in South Carolina. This confirms field studies which indicate that the Charlotte belt contains a plutonic metaigneous complex that developed as a sub-volcanic-arc infrastructure, contemporaneous with vulcanism manifested in the Carolina slate belt. Both paleontological and geochronological controls indicate that the South Carolina slate belt is mostly younger than 570 Ma (Cambrian?), whereas the slate belt in North Carolina and Virginia is mostly of late Proterozoic age. A regionally significant mid-Paleozoic (ca. 340–360 Ma) thermal event is suggested by discordant 40Ar/39Ar whole-rock age spectra of slate/phyllite in the northwestern Carolina slate belt and from hornblende in the southeastern Charlotte belt. It is uncertain if this event was associated with deformation in the eastern Piedmont; however, mid-Paleozoic deformation has been previously documented elsewhere in the western Piedmont. A slightly disconcordant U-Pb zircon age of 317 ± 4 Ma is interpreted to closely date initial crystallization of the deformed Edge-field granite and confirms a record of late Paleozoic penetrative deformation in the Kiokee belt of South Carolina. U-Pb isotope data for the Lake Murray orthogneiss and Clouds Creek granite are discordant and suggest that the magmas of these plutons were derived by partial melting of a sialic Precam-brian source and then emplaced in the eastern Piedmont at ca. 315 Ma (prior to or during the early stages of the Alleghanian orogeny). The thermal maximum of Alleghanian regional metamorphism (amphibolite facies in the Kiokee belt; greenschist facies in the southeastern part of the Carolina slate belt) occurred during ca. 295–315 Ma. During the late Carboniferous and Early Permian, the eastern Piedmont experienced differential uplift, erosion, and relatively rapid postmeta-morphic cooling. Isothermal surfaces were folded into an antiform-synform-antiform configuration corresponding to the Kiokee, Carolina slate, and Charlotte belts, respectively. The geochronological data provide the following calibration for the late Paleozoic deformational chronology recorded in the Kiokee and Carolina slate belts: D2 (Lake Murray deformation), ca. 295–315 Ma; D3 (Clarks Hill deformation), ca. 285–295 Ma; and D4 (Irmo deformation), ca. 268–290 Ma.

Discovery of oil and gas in the western overthrust belt has spurred renewed efforts in the southwestern and eastern overthrust belts. Reinterpretations of existing data and acquisition of new data, both geologic and geophysical, have led to several interpretations of the sedimentary history and overthrust geometry of these belts. Although the Carolina Slate belt (CSB) is not a prime petroleum exploration target, the documentation of metazoan elements belonging to the late Precambrian Ediacaran fauna in the CSB is new data pertinent to interpretations of sedimentary history and accretion geometry of an exotic terrane that by some interpretations may be involved in overthrusting and is thus concealing potentially petroleum-bearing strata. The presence of Pteridinium in the CSB provides correlation with late Precambrian strata of the Russian platform, South West Africa, and South Australia, and is thus very significant in paleogeographic reconstructions. Pteridinium in the CSB is represented by 4 specimens that are impressions of petal-like metazoans. These metazoans are approximately bilaterally symmetrical, crudely ovoid-shaped, and composed of curved segments that join across a medial zig-zag groove created by the proximal End_Page 479------------------------------ ends of alternating left and right segments. The segments curve toward one end of the organism, terminating distally in spines. Individual segments exhibit longitudinal ornamentation, and grooves separating adjacent segments indicate articulation. Data from the USSR, Africa, and South Australia suggest that Pteridinium lived in a shallow water, near-shore, high-energy environment. However, the CSB examples are preserved in an essentially bedding-parallel position in deep-water flysch, suggesting transportation from nearshore into deep water. End_of_Article - Last_Page 480------------

Felsic volcaniclastic rocks and massive pyrite of a part of the Carolina slate belt in South Carolina referred to as the “Haile-Brewer block” seem to have remained closed systems with respect to U, Th, and Pb since ∼465 Ma. U-Pb and Th-Pb whole-rock isochrons indicate ages of 466 ± 40 (2σ) and 462 + 53 Ma, respectively. The Pb-Pb secondary isochron age of the volcaniclastic rocks is ∼455 Ma. Because of the divergent ways in which U, Th, and Pb have behaved during the various alteration events that have affected the Haile-Brewer block (metamorphism, post-tectonic intrusion, weathering), the isochronous relationships most likely represent the emplacement age of the rocks. The preservation of U-Pb and Th-Pb isochrons is thought to be due to the originally glassy nature of the volcaniclastic rocks and to the relatively impermeable character of the rocks, which may have been aided by the sealing of pore space by infiltration of penecon-temporaneous, silica-rich hydrothermal fluids. The U-Pb and Th-Pb whole-rock ages are considerably younger than the ⩾550-Ma age inferred from U-Pb zircon ages and Ediacaran fossil assemblages for the slate belt in North Carolina. The younger ages agree, however, with the presence of sponge spicules no older than Middle Cambrian in the Haile-Brewer block. The younger age of the Haile-Brewer block with respect to other parts of the Carolina slate belt indicates that the belt is more complex than has been thought.

Research Article| July 01, 1984 Ediacarian fossils from the Carolina slate belt, Stanly County, North Carolina Gail G. Gibson; Gail G. Gibson 1Department of Geography and Earth Sciences, University of North Carolina, Charlotte, North Carolina 28223 Search for other works by this author on: GSW Google Scholar Steven A. Teeter; Steven A. Teeter 1Department of Geography and Earth Sciences, University of North Carolina, Charlotte, North Carolina 28223 Search for other works by this author on: GSW Google Scholar M. A. Fedonkin M. A. Fedonkin 2Paleontological Institute, Academy of Sciences, Profsoyuznaye 113, Moscow B-321, Union of Soviet Socialist Republics 117868 Search for other works by this author on: GSW Google Scholar Author and Article Information Gail G. Gibson 1Department of Geography and Earth Sciences, University of North Carolina, Charlotte, North Carolina 28223 Steven A. Teeter 1Department of Geography and Earth Sciences, University of North Carolina, Charlotte, North Carolina 28223 M. A. Fedonkin 2Paleontological Institute, Academy of Sciences, Profsoyuznaye 113, Moscow B-321, Union of Soviet Socialist Republics 117868 Publisher: Geological Society of America First Online: 01 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1984) 12 (7): 387–390. https://doi.org/10.1130/0091-7613(1984)12<387:EFFTCS>2.0.CO;2 Article history First Online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Gail G. Gibson, Steven A. Teeter, M. A. Fedonkin; Ediacarian fossils from the Carolina slate belt, Stanly County, North Carolina. Geology 1984;; 12 (7): 387–390. doi: https://doi.org/10.1130/0091-7613(1984)12<387:EFFTCS>2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract Discovery of metazoan fossils, comparable to those of the late Precambrian Ediacarian fauna, in the Carolina slate belt, Stanly County, North Carolina, extends the paleobiogeographic range of the Ediacarian fauna into the southern Piedmont of the southeastern United States. These fossils provide paleontologic correlation with parts of the Precambrian Valdai Series of the Vendian System of the Soviet Union, the Nama Group of South-West Africa, and the Pound Quartzite of South Australia. In light of the recent discoveries, North Carolina fossil material previously described as the Middle Cambrian trilobite ?Paradoxides carolinaensis St. Jean, 1973, was re-examined and identified as an element of the late Precambrian Ediacarian fauna. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Volcanic rocks of the Persimmon Fork Formation host the largest known gold mines of the Carolina slate belt. U-Pb (SHRIMP) zircon ages have been obtained from rocks closely associated with pyrite-enargite-gold deposits at Brewer (quartz-topaz rhyolite breccia from the argillic alteration zone in the Brewer pit and felsic ash-flow tuff from the quartz sericite alteration zone), from the disseminated and semimassive pyrite-gold deposits at Haile (crystal lithic rhyolitic ash-flow tuffs from the Champion pit), and from the Ridgeway deposit (felsic ash-flow tuff from the stratigraphic host of the North pit gold deposit). Generally, the zircons are fine grained, fractured, and contain crystal imperfections (corrosion, inclusions, and pits). 206 Pb/ 238 U zircon spot ages for all deposits span a wide range, mostly from 400 to 760 Ma. Inclusions and cores indicative of inherited domains in the zircons were not found, and only a few analyses range from 1.1 to 1.8 Ga. A distinct xenocrystic zircon population was not identified. The 206 Pb/ 238 U weighted age averages of zircon indicate the following crystallization dates for the volcanic and volcaniclastic rocks closely associated with the gold deposits: 550 ± 3 Ma for Brewer, 553 ± 2 Ma for Haile, and 556 ± 2 Ma for the Ridgeway deposit. These zircon crystallization ages represent close estimates of the age of the original gold mineralizing events. Younger zircon spot ages can be attributed to the effects of Paleozoic regional metamorphism. Pb isotope compositions of sulfide minerals (galena, pyrite, enargite, sphalerite, chalcopyrite, and molybdenite) and silicate minerals (K-feldspar, and sericite) in the gold deposits help to constrain the sources of fluids and metals during the mineralizing events. The deposits are pyrite rich, containing multiple generations of pyrite, including early-crystallized pyrite that is closely associated with the original gold mineralizing event, as well as recrystallized pyrite formed in response to Paleozoic metamorphism. Pb isotope compositions of pyrite span a wide range, including the most radiogenic values for the sulfides. Galena and K-feldspar are not abundant but where present they are typically the least radiogenic minerals. Galena has a limited range of Pb isotope compositions that are representative of the gold deposits as a group ( 206 Pb/ 204 Pb = 18.020–18.326, 207 Pb/ 204 Pb = 15.550–15.639, 208 Pb/ 204 Pb = 37.605–38.286). Values of 207 Pb/ 204 Pb straddle the average crustal Pb growth curve, consistent with contributions involving the mantle and continental crust. Whole-rock Pb isotope compositions of volcanic and volcaniclastic rocks of the Persimmon Fork Formation nearly match the range for sulfides in the gold deposits. Subtle regional contrasts in Pb isotope compositions exist among the deposits. Sulfide minerals from Barite Hill (e.g., galena 206 Pb/ 204 Pb 206 Pb/ 204 Pb > 18.169), Haile ( 206 Pb/ 204 Pb > 18.233), and Brewer ( 206 Pb/ 204 Pb > 18.311) in northern South Carolina. Because Pb isotope compositions of basement rocks from Grenville massifs in the southern Appalachians and sulfide minerals from the gold deposits do not match, a direct genetic connection cannot be established. Diversity in values of 206 Pb/ 204 Pb and the relatively high values of 207 Pb/ 204 Pb suggest that the deposits evolved adjacent to or closely related to continental blocks, perhaps linked to a back-arc tectonic setting. Among potential younger analogues of the slate belt gold deposits are the sulfide deposits of the Okinawa trough in the western Pacific. Mantle-derived isotopic contributions were more important at Barite Hill in southern South Carolina, the least radiogenic among the deposits where oceanic crust had developed, than at Brewer, Haile, and Ridgeway in northern South Carolina where rifting thinned the continental crust.

Research Article| August 01, 1971 Nappe Formation in Part of the Southern Appalachian Piedmont OTHMAR T TOBISCH; OTHMAR T TOBISCH Division of Natural Sciences, University of California, Santa Cruz, California 95060 Search for other works by this author on: GSW Google Scholar LYNN GLOVER, III LYNN GLOVER, III Department of Geology, Virginia Polytechnic Institute, Blacksburg, Virginia 24060 Search for other works by this author on: GSW Google Scholar Author and Article Information OTHMAR T TOBISCH Division of Natural Sciences, University of California, Santa Cruz, California 95060 LYNN GLOVER, III Department of Geology, Virginia Polytechnic Institute, Blacksburg, Virginia 24060 Publisher: Geological Society of America Received: 06 Nov 1970 Revision Received: 09 Mar 1971 First Online: 02 Mar 2017 Online ISSN: 1943-2674 Print ISSN: 0016-7606 Copyright © 1971, The Geological Society of America, Inc. Copyright is not claimed on any material prepared by U.S. government employees within the scope of their employment. GSA Bulletin (1971) 82 (8): 2209–2230. https://doi.org/10.1130/0016-7606(1971)82[2209:NFIPOT]2.0.CO;2 Article history Received: 06 Nov 1970 Revision Received: 09 Mar 1971 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn Email Permissions Search Site Citation OTHMAR T TOBISCH, LYNN GLOVER; Nappe Formation in Part of the Southern Appalachian Piedmont. GSA Bulletin 1971;; 82 (8): 2209–2230. doi: https://doi.org/10.1130/0016-7606(1971)82[2209:NFIPOT]2.0.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Structural studies of rocks along the Carolina slate belt – Charlotte belt boundary reveal two generations of folding, the earlier of which is represented by a large-scale antiformal nappe. As shown by field relations and quantitative analysis of the fold geometry, this early folding began prior to metamorphism, the mechanism being largely buckling. With the onset of metamorphism and cleavage-forming process, new folds were formed and the pre-existing buckle folds were modified by compressive strain. During this time, a metamorphic gradient developed along the boundary of the two belts; as the rocks became more ductile, the large antiformal nappe was emplaced in the Charlotte belt, with its root located close to the boundary between the belts. Sillimanite-grade metamorphism in the Charlotte belt outlasted the early deformation, and some upwelling of material in this hot zone may have gently arched the nappe. Late, post-metamorphism deformation produced two sets of folds with different orientation, which appear to have a conjugate relationship, and which probably formed contemporaneously.The relation between the Charlotte and Carolina slate belts may be analogous to the infrastructure/superstructure relation commonly found in other intensely deformed mountain belts of the world. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Ririe states that the purpose of his comparison of the mineralogy and chemistry of gold deposits from Western Australia (Sons of Gwalia and Mount Celia) and the Carolina slate belt (Haile and Brewer) is illustrate that alteration in these two terranes is the result of similar processes that were also responsible for the introduction of gold into the altered (p. 1561). The alteration assemblages contain highalumina minerals such as andalusite, kyanite, pyrophyllite, kaolinite, and sericite, plus local alunite. Ririe interprets these rocks as having ... been altered by acid hydrothermal solutions prior to regional (p. 1561) based upon relations [that] indicate that the rocks had their alteration composition by the time the suite of aluminosilicate minerals was forming (p. 1574) and the absence of documented low-pH regional metamorphic fluids capable of producing alunite plus a suite of high-alumina minerals such as andalusite-pyrophyllite (p. 1574). He concludes that the best analogs for these gold deposits are acid-sulphate epigenetic gold deposits such as Goldfield, Nevada, and modern geothermal systems. The important question to be asked is, Does the presented evidence convincingly support the interpretation? In this writer's opinion, the presented evidence does not positively answer this question. ~easons why the two principal arguments proposed above by Ririe inadequately support his interpretation follow below. The textural evidence consists of photomicrographs of randomly oriented andalusite porphyroblasts, fractured and rotated andalusite crystals, and folded quartz-pyrophyllite + pyrite banding in the Western Australia deposits (Fig. 3, p. 1564), randomly oriented andalusite porphyroblasts at Brewer, and deformed and altered argillite at Haile (Fig. 7, p. 1568). It is reasonable to suggest that the high-alumina assemblages reflect metamorphism of a previously altered and 1 aluminous rock. But that is all that it proves; the products of hydrothermal alteration have been metamorphosed! However, I the critical questions is the timing of hydrothermal alteration relative to metamorphism and regional deformation? and What is the metamorphic and deformation history of the surrounding country rocks? are not addressed. ree ens chi st facies regional metamorphism is implied for Western Australia or stated (Carolina slate belt, p. 1563) with only one period of deformation and metamomhism imolied. ow ever. more than one period of deformationkd metahorphism occurred in both the Norsemen-Wiluna greenstone belt (Archibald et al. 1978; Bickle and Archibald 1984) and the Carolina slate belt (Williams and Hatcher 1983).

Near the South Carolina and Georgia border, the southeastern parts of the Charlotte belt and Carolina slate belt near the Coastal Plain overlap are coincident with the northwestern edge of an isolated negative Bouguer gravity anomaly. This anomaly is interpreted as evidence for a detached fragment of continental crust. The pattern of the magnetic and gravity anomaly contours for the northwestern edge of this fragment is similar to the pattern of magnetic anomaly contours and the Piedmont gravity gradient in central Georgia. This geometric similarity suggests that the fragment may have been separated from a larger continental block by a rift zone nearly 160 km wide. The Carolina slate belt in Georgia and South Carolina may delineate the axis of this continental rift or rift system and may represent remnants of rift-derived volcanic and sedimentary rocks. Gravity profiles across the edges of the hypothesized rift indicate the existence of anomalous high-density rocks in the upper 5 km of the crust in the proposed rift and low-density rocks at the base of the adjacent continental crust. Seismic data in Georgia indicate a typical rift-zone velocity structure that consists of a high-velocity (6.3 km/s) discontinuous surface layer 0.0 to 5.0 km thick over a low-velocity (6.0 km/s) crustal layer which extends to depths of at least 30 km. Magnetic lineations provide evidence for the faults and/or depositional layering of the rift and outline the structures and margins of the rift. The rift developed from late Precambrian through Cambrian time (650 to 520 m.y. B.P.), as determined from radiometric dating of Carolina slate belt rocks. In North Carolina the rift was reactivated during the Triassic, but in Georgia and South Carolina, Triassic extension was restricted to the southeastern edges of the detached crustal fragment.

The volcanosedimentary sequence of the Carolina slate belt in south-central North Carolina was long thought to be unfossiliferous; however, the 5,484–7,315 meters of dominantly evenly bedded siltstones and mudstones have recently yielded body fossils of the late Precambrian Ediacarian fauna and a Middle Cambrian trilobite assemblage. Ongoing stratigraphic studies in the Carolina slate belt of southern North Carolina have now revealed trace fossils representing the ichnotaxa Gordia arcuata?, ?Helminthopsis sp., Monocraterion sp., Neonerites biserialis, N. uniserialis, ?Neonerites sp., Planolites beverlyensis, P. montanus, ?Planolites sp., Syringomorpha nilssoni?,? Tomaculum sp., Torrowangea sp., and three additional indeterminate ichnogenera. These trace fossils, lacking ornamentation and complex patterns, compare favorably with ichnofossil assemblages from Late Proterozoic stratigraphic sequences (Ichnofossil Zone I) elsewhere and support the late Precambrian age interpretation for the Carolina slate belt in south-central North Carolina.

Thick zones of mylonitic rock are exposed in or between a number of the suspect crystalline terranes in the Transverse Ranges and eastern Peninsular Ranges of southern California. After palinspastic reconstruction of strike‐slip displacements along Neogene faults in the region the mylonite zones appear in a semicontinuous belt several hundred kilometers long. Mylonitic deformation in these areas is of a similar style and age. Lineation trends in the mylonitic rocks are closely aligned when palinspastic reconstruction takes into account the block rotations in the region, and the sense of shear is consistently west directed. The mylonite zones appear to have formed concurrently in a major midcrustal thrust system that juxtaposed the basement terranes during the Late Cretaceous. A kinematic model is proposed in which a west directed ductile thrust zone along the eastern side of the Peninsular Ranges is offset by a sinistral tear fault or lateral thrust ramp along the southern margin of the San Gabriel Mountains from a ductile thrust underlying crystalline basement terranes to the north. This model requires the suspect basement rocks of the Peninsular and Transverse Ranges to be linked tectonically by the latest Cretaceous. This Late Cretaceous thrust system also appears to continue directly into autochthonous basement rocks in the San Bernardino Mountains. The Late Cretaceous westward displacement of basement rocks in the Transverse Ranges relative to the northern end of the Peninsular Ranges batholith is mirrored by similar tectonic movement around the southern end of the Sierra Nevada batholith. It is argued here that a formerly continuous batholithic belt was breached by ductile west directed thrusting during the Late Cretaceous between the two still recognizable batholiths. The Salinia terrane represents the westernmost portion of this westward escaping arc segment and would have been established as a crustal salient by the latest Cretaceous. This model implies that the basement terranes involved in this thrusting episode are parautochthonous fragments of a Cretaceous continental arc and refutes suggestions that they have been accreted in the Cenozoic.

Ophiolites and ocean plate stratigraphy (OPS) preserved across the Central Mongolian Microcontinent: A new mega-archive of data for the tectonic evolution of the Paleo-Asian Ocean