Early life history of the red drum,Sciaenops ocellatus (Pisces: Sciaenidae), in Tampa Bay,Florida

The distribution, hatching dates, growth, and food habits of larval and juvenile red drum (Sciaenops ocellatus) in Tampa Bay, Florida, are described. From September 1981 through November 1983, 800 larvae and 7,536 juveniles (98%<100 mm SL) were collected, primarily with plankton nets and bag seines. Analysis of otoliths and length-frequency distributions indicate that spawning took place from mid-August through late November with a major peak during October in 1981 and 1982. Larvae became less abundant, but increased in size, from the mouth to the upper bay, indicating that spawning took place in the bay mouth or nearshore waters. At about 8 mm SL (17 days old) larvae settled out along the bay shore before migrating toward low salinity backwater areas. Juveniles grew to about 55 mm SL by the end of December and 303 mm SL by the end of their first year. Young red drum gradually moved back into the bay with increased size and age. Eighty-five percent of larval stomachs, examined were empty; those with food contained copepods almost exclusively. Fewer than 7% of juvenile stomachs were empty. Small juveniles fed primarily on mysids, amphipods, and shrimp, whereas larger juveniles fed more on crabs and fish. Changes in diet were noted with growth, but few differences were seen among areas or habitat types.     

A comparison of mercury in estuarine fish between Florida Bay and the Indian River Lagoon, Florida, USA

Concentrations of mercury (Hg) in fish were compared between two Florida estuaries, the Indian River Lagoon and Florida Bay. The objective was to determine if differences in Hg concentration exist and to attempt to relate those differences to sources of Hg. Five hundred and thirteen estuarine fish were collected and analyzed for Hg concentration. Fish species collected were black drum, bluefish, bonnethead shark, common snook, crevalle jack, gafftopsail catfish, gray snapper, Mayan cichlid, pompano, red drum, sheepshead, southern flounder, spadefish, and spotted seatrout. Analysis of variance of species-specific Hg data among the three defined regions of eastern and western Florida Bay and the Indian River Lagoon substantiated regional differences. Proximity to known anthropogenic sources of Hg appeared to be a significant factor in the distribution of Hg concentration among the fish collected. Sufficient numbers of crevalle jack, gray snapper, and spotted seatrout were collected to permit statistical analysis among regions. Hg concentrations in all three of these species from eastern Florida Bay were higher than those collected in the other two areas. A major fraction of the estuarine fish collected in eastern Florida Bay exceeded one or more State of Florida or U.S. Food and Drug Administration fish consumption health advisory criteria. In general, fish from western Florida Bay contained less Hg than those from the Indian River Lagoon, and fish from the Indian River contained less Hg than those from eastern Florida Bay. Crevalle jack from all areas and spotted seatrout from Florida Bay were placed on a consumption advisory in Florida. Detailed study of Florida Bay food web dynamics and Hg biogeochemical cycling is recommended to better understand the processes underlying the elevated Hg levels in fish from eastern Florida Bay. This information may be vital in the formulation of appropriate strategies in the ongoing South Florida restoration process.     

The demise and recovery of seagrass in the northern Indian River Lagoon,Florida

Seagrass both disappeared and recovered within 4 yr in one region of northern Indian River Lagoon (IRL). For the specific area referred to as Turnbull Bay, a relatively pristine area of the IRL, over 100 ha of seagrass completely disappeared from 1996 to 1997 and then recovered by 2000. Based on lagoon-wide mapping from aerial photographs taken every 2–3 years since 1986, coverage of seagrass in Turnbull Bay declined from 124 ha in 1989 to 34 ha by 1999 and increased to 58 ha in 2003. Bi-annual monitoring of fixed seagrass transects tells a more detailed story. Species composition along the Turnbull transect shifted fromHalodule wrightii toRuppia maritima beginning in 1995, and macroalgal abundance increased. By the summer of 1997, seagrass completely disappeared along the transect, as well as in most of the surrounding areas in Turnbull Bay; macroalgae covered much of the sediment surface. No significant water quality changes were detected. Light attenuation and suspended solid values did increase after the seagrass disappeared. Porewater sulfide concentrations, taken after all the grass was gone in 1997, were high (2,000 μM), but did improve by 1998 (1,200 μM). Seagrass recovery was rapid and occurred in the reverse sequence of species loss. Seedlings ofR. maritima were the first colonizers, then patches ofH. wrightii appeared. In 2000,Halophila engelmannii returned in the deeper water (>0.6m). By the summer of 2000, the beds had completely recovered. We conclude that this demise was a natural event caused by a long-term buildup of seagrass biomass and a thick (10–15 cm) layer of organic detritus and ooze. We surmise that such a crash and subsequent recovery may be a natural cycle of decline and recovery within this semirestricted, poorly-flushed area. The frequency of this cycle remains uncertain.     

Setting seagrass depth, coverage, and light targets for the Indian River Lagoon system, Florida

Seagrass protection and restoration in Florida’s Indian River Lagoon system (IRLS) is a mutual goal of state and federal programs. These programs require, the establishment of management targets indicative of seagrass recovery and health. We used three metrics related to seagrass distribution: areal coverage, depth limit, and light requirement. In order to account for the IRLS’s spatial heterogeneity and temporal variability, we developed coverage and depth limit targets for each of its 19 segments. Our method consisted of two steps: mapping the union of seagrass coverages from all availabe mapping years (1943, 1986, 1989, 1992, 1994, 1996, and 1999) to delineate wherever seagrass had been mapped and determining the distribution of depth limits based on 5,615 depth measurements collected on or very near the deep-edge boundary of the union coverage. The frequency distribution of depth limits derived from the union coverage, along with the median (50th percentile) and maximum (95th percentile) depth limits, serve as the seagrass depth targets for each segment. The median and maximum depth targets for the IRLS vary among segments from 0.8 to 1.8 and 1.2 to 2.8 m, respectively.Halodule wrightii is typically the dominant seagrass species at the deep-edge of IRLS grass beds. We set light requirement targets by using a 10-yr record of light data (1990–1999) and the union coverage depth limit distributions from the most temporally stable seagrass segments. The average annual light requirement, based on the medians of the depth limit distributions, is 33 ± 17% of the subsurface light. The minimum annual light requirement, based on of the 95th percentile of the depth distributions, is 20 ± 14%; the minimum growing season light requirement (March to mid September) is essentially the same (20 ± 13%). Variation in depth limits and light requirements, is probably due to factors other than light that influence the depth limit of seagrasses (e.g., competition, physical disturbance). The methods used in this study are robust when applied to large or long-term data sets and can be applied to other estuaries where grass beds are routinely monitored and mapped.     

The disruption and recovery of fish communities in the Indian River Lagoon, Florida, following two hurricanes in 2004

During the summer of 2004, four hurricanes (Charley, Frances, Ivan, and Jeanne) affected Florida between August 13 and September 27. Two storms (Frances: category 2 and Jeanne: category 3) made landfall in the southern portion of the Indian River Lagoon (IRL) on the east-central coast of Florida. The presence of Florida Fish and Wildlife Conservation Commission's long-term fisheries monitoring program in the IRL provided a unique opportunity to examine the effects of large tropical events on estuarine fish communities. Increased sampling efforts to monitor the effects of tropical disturbances on the fish community within the IRL and one of its major tributaries (St. Sebastian River) were initiated within days after the passing of the last hurricane (Jeanne). The objectives of the study were to characterize changes to the composition of the fish community within the lagoon and river immediately after the passage of two hurricanes, and to examine the recovery of the fish communities. Analyses indicated that immediately after the last hurricane passed, community diversity within the estuary decreased following these storms due to the absence of many marine species, whereas the fish community within the St. Sebastian River shifted to one containing a greater percentage of freshwater species. Recovery of the community structure to pre-hurricane conditions was evident within several weeks following the last hurricane, and by mid December 2004 (ca. 3 mo after the last storm), there was little difference between the pre-hurricane and post-hurricane fish communities.     

The impacts of the 2004 hurricanes on hydrology, water quality, and seagrass in the Central Indian River Lagoon, Florida

Between August 14 and September 26, 2004, four tropical weather systems (Charley, Frances, Ivan, and Jeanne) affected the central Indian River Lagoon (IRL). The central IRL received a prodigious amount of rainfall for the 2 mo, between 72 and 83 cm, which is a once-in-50-yr rainfall event. High stream discharges were generated that, combined with wind-suspended sediments, significantly reduced salinities and water transparency. In September, salinities among central IRL segments dropped from 30 psu or more to ≤15 psu, color increased from a low of 10 pcu to ≥100 pcu, and turbidity increased from ≤3 NTU up to 14 NTU. Evidence of the hurricanes' physical effects on seagrasses (burial, no scour) was limited to just one of the more than 25 sites inspected. Within 2 to 3 mo following the hurricane period, most parameters related to water transparency returned to or showed improvement over their prehurricane (February–July 2004) levels. Unseasonably low salinities (<20 psu) and moderately high color (>20 pcu) were observed through spring 2005, largely attributable to a relatively long residence time and a wetter-than-average spring season in 2005. By the end of the study period (July 2006), the central IRL generally showed a continuation of two opposite seagrass trends—an increase in depthlimit coverage but a decline in coverage density—that began before 2004. Also, within a limited reach of the central IRL, there was a temporary shift in species composition in summer 2005 (Ruppia maritima increased asHalodule wrightü decreased). It is likely that the persistently low salinities (not color) in 2004–2005 affected the species composition and coverage density. This study reveals that seagrasses are resilient to the acute effects of hurricanes and underscores the need to reduce chronic, an thropogenic effects on seagrasses.     

Climatic Trends and Temporal Patterns of Phytoplankton Composition, Abundance, and Succession in the Indian River Lagoon, Florida, USA

This paper describes the results of 10 years of water quality monitoring in the Indian River Lagoon Florida, with special emphasis on the relationships between trends in climatic conditions and the distribution, composition, and abundance of the phytoplankton community. The Indian River Lagoon, which spans 220 km of Florida’s east coast, is a region of particular concern because of the rapid rate of human development throughout the region and the hydrologically restricted character of the lagoon, which heightens the potential for algal bloom. Water sampling was carried out on a monthly to twice-monthly basis at six sites located in the northern and central lagoon. The 10-year study included both extended periods of below and above average rainfall. A number of ecologically distinct regions exist within the lagoon, which differ considerably in water exchange properties and watershed inputs. The northern lagoon is characterized by longer water residence times, lower phosphorus concentrations, higher nitrogen concentrations, and more stable salinity conditions than the central lagoon. Mean phytoplankton biovolumes were substantially higher at the sites in the northern lagoon than at the sites in the central lagoon, and algal blooms were more common and intense in the former region. Inter-annual patterns of phytoplankton biovolume were also different in the northern and central lagoon. In the northern lagoon, phytoplankton biovolumes were lowest during the drought period, from the autumn of 1998 to the spring of 2001. By contrast, algal bloom events in the central lagoon were not only less frequent but were not tied to periods of high rainfall. The most widespread and common bloom formers were the potentially toxic dinoflagellate Pyrodinium bahamense var. bahamense and two centric diatoms, Dactyliosolen fragilissimus and Cerataulina pelagica. Many of the biovolume peaks observed over the study period were attributable to these three species. The results of time series modeling of phytoplankton dynamics further highlighted the disparities between the two regions of the lagoon in terms of the suite of parameters that best predict the observed trends in the biomass of phytoplankton. Overall, the outcome of this initial modeling effort in the Indian River Lagoon suggests that time series approaches can help define the factors that influence phytoplankton dynamics.     

Tidal and nontidal flushing of Florida’s Indian River Lagoon

The flushing of Florida’s Indian River Lagoon is investigated as a response to tidal and low-frequency lagoon-shelf exchanges in the presence of freshwater gains and losses. A one-dimensional computer model uses the continuity equation to convert water-level variations into both advective transport within the lagoon and lagoon-shelf exchanges. The model also incorporates transport by longitudinal diffusion. Flushing is quantified by calculating the 50% renewal time, R₅₀, for each of 16 segments. R₅₀ is calculated for tidal exchanges enhanced by 0–30 cm nontidal fluctuations in coastal sea level, then for a range of rainfall rates. In both series of simulations, results suggest that in the northern sub-basin, R₅₀ increases dramatically with distance from the inlet due to relatively weak tidal and nontidal exchanges. A 50% renewal occurs in about one tidal cycle just inside Sebastian Inlet; at the northern end of the northern sub-basin, R₅₀ is over 230 d, and only coastal sea-level variations on the order of 30 cm and/or dry season rainfall rates decrease R₅₀ to less than 1 yr. R₅₀ is 1 wk or less throughout the central and southern sub-basins, where lagoon-shelf exchanges occur through two inlets. Simulations involving seasonal variations in precipitation and evaporation indicate that maximum and minimum rates of freshwater input lead minimum and maximum salinities by time periods on the order of 2–3 wk for the lagoon as a whole and in the northern sub-basin. The central and southern sub-basins respond in 1–2 wk.     

Production and nutrient dynamics of aSyringodium filiforme Kütz. Seagrass bed in Indian River Lagoon,Florida

A year-long analysis of the characteristics of the seagrassSyringodium filiforme and the associated dynamics of the nutrient pool in the sediment pore water was done to assess co-variation. Changes in seagrass growth rate and standing stock throughout the year were accompanied by seasonal changes in the nutrient pools. The link between plant production and morphometrics and the sediment nutrient pool was found to be predominantly physiological, with the plant balancing the ability to photosynthesize with the nutrients needed for maintaining production. Measurements of whole plant growth for this seagrass, rather than the more typical leaf growth measurements, show that the production of new shoots and rhizome elongation for these plants represents as substantial amount of growth that usually goes unmeasured. Further, these whole plant growth measures demonstrate the rapid lateral rhizome spread of this species, exceeding one meter per plant per year. The primary cause of seasonal variation in the yearly seagrass cycle was investigated. Correlation analysis supported the hypothesis that the major factor controlling seasonal variation in this seagrass was light. During the peak growing season, however, growth was not regulated by light but by nitrogen. Depletion of the sediment ammonium pool and reduction in pore water ammonium relative to adsorbed ammonium, as well as changes in N content of seagrass leaves, support our hypothesis of peak growing season nitrogen limitation. Our results forSyringodium filiforme in terrigenous sediments are in contrast to our recent findings of phosphorus limitation in this same species occurring in carbonate sediments.     

A comparison of early juvenile red drum densities among various habitat types in Galveston Bay, Texas

Seagrass meadows are often cited as important nursery areas for newly settled red drum even though many estuaries, such as Galveston Bay, Texas, support large numbers of red drum and have limited seagrass cover, suggesting the use of alternate nursery areas. We examined patterns of habitat use for newly settled red drum at six sampling areas in Galveston Bay; two areas had seagrass beds and four areas had no seagrass. We measured densities in different habitat types using epibenthic sleds and enclosure samplers. Peak recruitment of young red drum to the estuary occurred during September through December. Highest densities of new settlers were found in seagrass meadows (primarilyHalodule wrightii), but when seagrass was absent, the highest densities of red drum occurred along theSpartina alterniflora marsh edge interface. Densities were relatively low on nonvegetated bottom away from the marsh edge. We also examined density patterns in other habitat types at selected sampling areas and found no red drum within marsh vegetation away from the marsh edge interface (5 and 10 m into the marsh interior). Oyster reefCrassostrea virginica was sampled using lift nets, and we found no red drum using this habitat, although adjacent seagrass and marsh interface habitats were used. Even though red drum densities in marsh edge were low relative to seagrass, the large areal extent of marshes in the bay complex probably makes marsh edge the most important nursery habitat for red drum in Galveston Bay.     

Food habits of red drum and spotted seatrout in a restored mangrove impoundment

Benthic resource utilization by, red drum (Sciaenops ocellatus) and spotted seatrout (Cynoscion nebulosus) was studied in a restored, mangrove-rimmed impoundment (Cabbagehead Bayou) of Upper Tampa Bay, Florida, and in a nearby, natural site of unaltered tidal regime (Double Branch Bay). Diets of fish captured from August 1990 to May 1992 were determined from stomach content analysis. Simultaneously, food availability was evaluated by sampling benthic macroinvertebrates, mobile decapods, and small fish. Red drum and spotted seatrout utilized the restored habitat 1 yr after it was opened to tidal influence. Both species also were collected in the natural mangrove. Although there were noted differences in benthic assemblages between the two sites, red drum and spotted seatrout exhibited flexibility in diet, feeding on abundant and accessible prey. The high abundance of microcrustacea, such as amphipods, on detritus accumulated in the restored habitat constituted a main food resource for both fish species. Major food items in the diet of small (<200 mm) red drum were amphipods, mysids, and nereid and arenicolid polychaetes. Large (200–590 mm) red drum fed on polychaetes, xanthid crabs, palaemonid shrimp, and small fishes. Spotted seatrout preyed primarily upon mysids, shrimp, and small fishes, and to a lesser extent, upon a nereid polychaete. Our findings on fish feeding in a restored mangrove impoundment indicated that the detrital-associated benthic community is utilized by reinvading fish within a short time period, suggesting that not only habitat but food resources were augmented by the reopening of this wetland.     

Submarine groundwater discharge is an important net source of light and middle REEs to coastal waters of the Indian River Lagoon, Florida, USA

Porewater (i.e., groundwater) samples were collected from multi-level piezometers across the freshwater-saltwater seepage face within the Indian River Lagoon subterranean estuary along Florida’s (USA) Atlantic coast for analysis of the rare earth elements (REE). Surface water samples for REE analysis were also collected from the water column of the Indian River Lagoon as well as two local rivers (Eau Gallie River, Crane Creek) that flow into the lagoon within the study area. Concentrations of REEs in porewaters from the subterranean estuary are 10-100 times higher than typical seawater values (e.g., Nd ranges from 217 to 2409 pmol kg⁻¹), with submarine groundwater discharge (SGD) at the freshwater-saltwater seepage face exhibiting the highest REE concentrations. The elevated REE concentrations for SGD at the seepage face are too high to be the result of simple, binary mixing between a seawater end-member and local terrestrial SGD. Instead, the high REE concentrations indicate that geochemical reactions occurring within the subterranean estuary contribute substantially to the REE cycle. A simple mass balance model is used to investigate the cycling of REEs in the Indian River Lagoon and its underlying subterranean estuary. Mass balance modeling reveals that the Indian River Lagoon is approximately at steady-state with respect to the REE fluxes into and out of the lagoon. However, the subterranean estuary is not at steady-state with respect to the REE fluxes. Specifically, the model suggests that the SGD Nd flux, for example, exported from the subterranean estuary to the overlying lagoon waters exceeds the combined input to the subterranean estuary from terrestrial SGD and recirculating marine SGD by, on average, ∼100 mmol day⁻¹. The mass balance model also reveals that the subterranean estuary is a net source of light REEs (LREE) and middle REEs (MREE) to the overlying lagoon waters, but acts as a sink for the heavy REEs (HREE). Geochemical modeling and statistical analysis further suggests that this fractionation occurs, in part, due to the coupling between REE cycling and iron redox cycling within the Indian River Lagoon subterranean estuary. The net SGD flux of Nd to the Indian River Lagoon is ∼7-fold larger than the local effective river flux to these coastal waters. This previously unrecognized source of Nd to the coastal ocean could conceivably be important to the global oceanic Nd budget, and help to resolve the oceanic “Nd paradox” by accounting for a substantial fraction of the hypothesized missing Nd flux to the ocean.     

Spawning of major carps in the lower Halda River,Bangladesh

Spawning biology and spawn fishery of three valuable species of Indian major carps,Catla catla, Labeo rohita andCirrhinus mrigala, in the lower Halda River, Bangladesh, were studied in 1978. The major carps spawned only in the Sonairchar oxbow-bend from April to June on or near the dates of the full moon and the new moon. The tide was then at its highest level, and there was heavy flood water runoff from the hill region with sharp increases in water level, turbidity and current velocity, as well as decreases in water temperature, dissolved oxygen, and hydrogen ion concentration. These three heterogeneric species, as a result of parallelism or convergence in evolution, overlap in their environmental requirements for spawning. The nursery ground of the major carp fry spawned in the Halda River was found to be in the Bay of Bengal. The brood stock origin is suspected to be at the Shankha River, 40 miles south of the Karnafuli River. The spawn fishery in the Halda River was intensive but inefficient. Engineering works and water management schemes are threatening the spawning habitat.     

Macroalgae,nutrient cycles,and pollutants in the Lagoon of Venice

The Lagoon of Venice is a wide, shallow coastal basin that extends for about 50 km along the northwest coast of the Adriatic Sea. The lagoon has been substantially modified through the actions of man over the last century through the artificial control of the hydraulic dynamics of the laggon including the construction of channels to facilitate navigation. The lagoon is subjected to considerable pollutant loading through the drainage of land under cultivation, municipal sewage, and industrial effluents. In this paper are reported the results of observations designed to document recent changes in macroalgal species composition, seasonal cycles of primary producers and nutrient levels, and the effects of the macroalgal community on concentrations of organic and inorganic pollutants. The dominant macroalgae in the lagoon wasUlva rigida, and the levels of plant nutrients and pollutants were influenced by the seasonal cycles of the macroalgal community.     

Temporal Variation in the Trophic Levels of Secondary Consumers in a Mediterranean Coastal Lagoon (Cabras Lagoon,Italy)

Trophic levels (TLs) of fish were estimated on three sampling dates (March, May, and August 2006) for different fish sizes in the Cabras Lagoon (Sardinia, Italy). A temporal TL variation for Atherina boyeri, Gobius niger, and Engraulis encrasicolus was observed. In March and May, the TL ranged from 3.3 to 3.4, characterizing these species as secondary consumers, while in August, this range moved to between 3.7 and 3.8, indicating a TL shift towards tertiary consumers. For Liza ramada, TL was consistently lower in small individuals (mean TL 2.5) than in larger individuals (mean TL 3.0). Increased TL of the fish species A. boyeri, G. niger, and E. encrasicolus in August was consistent with the seasonal changes in the macrobenthic assemblage in this system, with a dominance of primary consumers (benthic deposit feeders) in winter–spring and a dominance of secondary consumers (the nereidids Alitta succinea and Hediste diversicolor) in summer. These fish species took advantage of the high availability of nereidids leading to a rise in their TL values. Furthermore, the increase of TL with size of L. ramada, the most economically valuable fish species in the Cabras Lagoon, indicated an ontogenetic diet shift, the juveniles being omnivorous, while the adults being secondary consumers. We conclude that variability in the trophic levels of fish due to species traits, ontogenetic diet shifts, and variation in prey availability should be taken into account to further understand the food web structure of coastal lagoons.     

伊拉克M油田白垩系Mishrif组潟湖环境碳酸盐岩储集层成因机理

为深化潟湖相碳酸盐岩储集层非均质性认识,以伊拉克M油田白垩系Mishrif组为例,基于岩心观察、物性分析数据、铸体薄片及压汞实验,对潟湖相储集层特征及成因机理开展研究.结果显示:研究区潟湖环境岩石类型复杂,生物碎屑具有多样性,储集层以低渗、特低渗为主,孔隙度分布范围宽,发育大量的基质微孔、铸模孔和晶间孔.储集层强非均质...     

Geology of the Blue Lagoon

The geology of the Blue Lagoon, Abereiddy Bay, South Wales, has been studied for over a hundred years, and is the type locality for the Abereiddian sub‐stage of the Darriwilian (Ordovician), due to its outstanding fossil assemblages. Despite the work done on the Blue Lagoon, its geological significance has not yet been examined. Strata preserved at the Blue Lagoon comprises Avalonian volcanics and marine sediments. This feature examines Avalonia's palaeogeography, the structure and stratigraphy of Abereiddy Bay and the global significance of the geology at these classic localities.     

Late Quaternary Floodplain History of the Brazos River in East-Central Texas

The floodplain along a 75-km segment of the Brazos River, traversing the Gulf Coastal Plain of Texas, has a complex late Quaternary history. From 18,000 to 8500 yr B.P., the Brazos River was a competent meandering stream that migrated from one side of the floodplain to the other, creating a thick layer of coarse-grained lateral accretion deposits. After 8500 yr B.P., the hydrologic regime of the Brazos River changed. The river became an underfit meandering stream that repeatedly became confined within narrow and unstable meander belts that would occasionally avulse. Avulsion occurred four times; first at 8100 yr B.P., then at 2500 yr B.P., again around 500 yr B.P., and finally around 300 yr B.P. The depositional regime on the floodplain also changed after 8500 yr B.P., with floodplain construction dominated by vertical accretion. Most vertical accretion occurred from 8100 to 4200 yr B.P. and from 2500 to 1250 yr B.P. Two major and three minor periods of soil formation are documented in the floodplain sequence. The two most developed soils formed from 4200 to 2500 yr B.P. and from around 1250 to 500 yr B.P. These changes on the floodplain appear to be the result not of a single factor, but of the complex interplay among changes in climate, sediment yield, and intrinsic floodplain variables over time.     

大别-苏鲁超高压和高压变质带构造演化

大别—苏鲁是世界上超高压 (UHP) ( >2 .7GPa)和高压 (HP)变质岩石出露最为广泛的地区。通过区域研究 ,尤其是在选择的 30多个关键位置上不同尺度构造记录的深入观察 ,结合已有的可利用的变质、热事件及同位素年代学资料分析 ,揭示出它们曾遭受过一个复杂的从深俯冲到折返构造演化历程 ,识别出 5个主要的构造变质事件 :( 1)由块状榴辉岩中发育的微弱面理和线理所代表的第 1期变形变质事件 (D1) ;( 2 )面状榴辉岩中发育的含拉伸线理的透入性主面理、中小型鞘状褶皱及网络状韧性剪切带 ,代表第 2期构造变质事件 (D2 ) ;( 3)第 3期变形事件主体发生于麻粒岩 /角闪岩相后成合晶形成之后 ,主要构造记录是区域性陡倾斜面理及不均一置换的成分层、榴辉岩透镜体及布丁群、面理内褶皱、网状韧性剪切带系统以及减压部分熔融作用形成的混合岩和含榴花岗质岩石组构 ;( 4)区域性的碰撞期后地壳韧性薄化及剪张作用 (D4)形成缓倾斜角闪岩相主面理及线理、穹状及弧形构造和多层韧性拆离带 ,它们主导了现今观察到的大别—苏鲁超高压和高压变质带的区域构造几何图像 ;( 5 )第 5期构造热事件 (D5)表现为不均一断块抬升、红色沉积盆地发育及大规模的岩体和岩脉就位 ,代表造山晚期的构造揭顶及坍陷作用 ,该期构造控制着造山带