Petrology and of the Beemerville -alkalic complex, New Jersey

LAWRENCE R. MAXEY* Department of Geosciences, Rider College, Lawrenceville, New jersey 08648

ABSTRACT Folded miogeosynclinal sedimentary rocks bound the Precam- brian rocks to the west (Fig, 1). The Hardyston Formation of Early The Beemerville carbonatite-alkalic rock complex of Late Or- Cambrian age, about 35 m thick and composed of conglomerate, dovician age consists of two stocklike bodies of nepheline syenite sandstone, and sandy and shaly dolomite, overlies the Precambrian and dikes or sills of phonolite, tinguaite, lamprophyre micromalig- rocks nonconformably. The Kittatinny Formation of Late Cam- nite, lamprophyre micromelteigite, and carbonatite. The complex brian to Early Ordovician age, about 825 m thick, conformably also includes several lamprophyric diatremes with of overlies the Hardyston Formation. The Kittatinny Formation, de- sedimentary rock and gneiss and autoliths of carbonatite, potassic posited in a supratidal to neritic environment, is composed mostly syenite, and lamprophyre micromelteigite. The largest diatreme of bedded to massive dolomite. The Jacksonburg Limestone of also contains a small pluglike body of nepheline syenite; fenite after Middle Ordovician age disconformably overlies the Kittatinny graywacke occurs adjacent to one of the diatremes. Intense hy- Formation and is about 80 m thick. The Jacksonburg Limestone is drothermal alteration is particularly evident in phonolite, lam- composed of calcarinite and calcilutite and was deposited when the prophyre, diatreme autoliths, and diatreme rock. area was changing from a carbonate shelf to a flysch basin. The Field and bulk chemical evidence suggests that parental Upper Ordovician Martinsburg Formation, composed of slate and was of either highly carbonated melteigitic or slightly carbonated shale interlayered with graywacke siltstone and graywacke, con- malignitic composition. A petrogenetic model based on each of formably overlies the Jacksonburg Limestone. The Martinsburg these possibilities is explored. The model that begins with highly Formation, about 3,000 m thick, locally shows evidence of deposi- carbonated melteigite magma involves immiscibility relations be- tion by turbidity currents. The Lower Silurian Shawangunk Con- tween melteigite and carbonatite as well as fractional crys- glomerate, mostly quartzite conglomerate and quartzite, overlies tallization processes. The model that begins with slightly carbon- the Martinsburg Formation and is about 500 m thick. It is sepa- ated malignite magma includes, in addition, immiscibility relations rated from the Martinsburg Formation by an angular uncon- between carbonated melteigite and syenite magmas. formity and records molasse-type sedimentation following the Taconic orogeny. INTRODUCTION More detailed descriptions of the regional geology are by Hague and others (1956), Baker and Buddington (1970), and Smith The Beemerville complex is an isolated occurrence of highly un- (1969) for the Precambrian rocks and Spink (1967), Drake (1969), dersaturated to nearly silica saturated alkalic rocks and carbona- and Epstein and Epstein (1969) for the Cambrian to Silurian rocks. tite. Rock types in addition to carbonatite are nepheline syenite, phonolite, potash syenite, phonolite, tinguaite, lamprophyre micromalignite, lamprophyre micromelteigite, and fenite. It is the ALKALIC ROCKS AND CARBONATITE only alkalic rock complex in the eastern United States in which carbonatite has been recognized. Since the alkalic rocks form Nepheline Syenite Plutons. The major occurrence of nepheline stocklike bodies, diatremes, dikes, and possibly sills in folded and syenite in the complex is as two stocklike bodies at the western faulted country rock, the complex is clearly a posttectonic feature. extremity (Fig. 1). Nepheline syenite also forms two small pluglike Zartman and others (1967) obtained a radiometric age for Beemer- bodies, one in and one immediately adjacent to a diatreme, which ville of 435 ± 20 m.y., which, considered with the observed will be considered in a following section dealing with the dia- intrusive contacts of the alkalic rocks with country rocks ranging in tremes. age from Precambrian to Late Ordovician, indicates that the intru- The nepheline syenite plutons are bounded on the west by the sive activity followed soon after the Taconic orogeny. Shawangunk Conglomerate and on the east by the Martinsburg Formation baked into a hornfels near nepheline syenite contacts COUNTRY ROCKS that are not, however, exposed. Emerson (1882) and Kemp (1892) believed that the nepheline syenite intruded along the The Precambrian rocks in the eastern part of the complex (Fig. 1) Shawangunk—Martinsburg Formation contact and is, con- underlie the Reading Prong, a northeast-trending physiographic sequently, at least as young as Early Silurian. Vogel (1970) believed and geologic province, and consist of a wide variety of high-grade that the nepheline syenite intruded the Martinsburg Formation, quartzofeldspathic orthogneiss and paragneiss, , and which was eroded to a level exposing the nepheline syenite before marble that were plastically deformed and intruded by syntectonic the Shawangunk Conglomerate was deposited. Evidence bearing granite and syenite about 1,150 m.y. ago. The Precambrian rocks on this problem, which is not easily resolved due to the lack of are cut by numerous northeast-trending high-angle faults and lo- exposed nepheline syenite—Shawangunk Conglomerate contacts, is cally contain within them belts of infaulted Cambrian to Silurian an exposure of nepheline syenite southwest of the southernmost sedimentary rocks. pluton. This exposure consists of two blocks of nepheline syenite that are stratigraphically higher than basal Shawangunk (Fig. 1). If " Present address: Direktorat Geologi, Jalan Diponegoro 57, Bandung, Indonesia. in place, they define a offshoot into the Shawangunk Con-

Geological Society of America Bulletin, v. 87, p. 1551-1559, 3 figs., November 1976, Doc. no. 61103.

1551

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Figure 1. (Inset is on facing page.) Geologic map of the Beemerville complex. Precambrian ge- ologic Map of the Franklin Furnace Quadrangle (1908). Alkalic rock locations compiled from the ology generalized from geologic maps by Hague and others (1956) and Baker and Buddington above sources and geologic maps by Wilkerson (1952), Davidson (1948), and Spink (1967). (1970). Sedimentary rock geology taken from the Geologic Map of New lersey (1950) and the Ge-

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Figure 1. (Continued). EXPLANATION

CAMBRIAN-SILURIAN SEDIMENTARY ROCKS

Ssg Shawangunk Conglomerate Omb Martinsburg Formation Ojb Jacksonburg Limestone €0k Kittotinny Formation •eh Hardyston Formation

PRECAMBRI AN IGNEOUS AND METAMORPHIC ROCKS

p-Cm Marble

pCg Silicic rockS) includes various types of quartzo-feldspathic gneisses, amphibolite, and granite

LATE ORDOVICIA N IGNEOUS ROCKS

NS Nepheline syenite

P Highly-altered phonolite dikes/ sills, PA where pronounced albi- tization is evident in

BP Basic phonolite dikes

L Extremely fine-grained and/or highly-altered lamprophyre dikes

LMA Lamprophyre micromalignite dikes

LME Lamprophyre micromelteigite dike

T Tlngualte dikes/sills

C Silicocarbonatite dike/

D Diatremes

to aegerine. The distinction between the latter two in this study is based on optic sign, negative for aegerine and posi- tive for aegerine-augite. Zoned clinopyroxene has cores of -hedenbergite (X-.c = 38°) and rims of aegerine-augite or cores of aegerine-augite and rims of aegerine. Biotite occurs in discrete grains and also replaces . Cancrinite and sodalite partly replace nepheline, and trace fluorite partly replaces pyroxene. Veinlets of sodalite are common; veinlets of albite are extremely rare. Table 1 gives bulk chemical and modal data for 5 nepheline syenite samples from the two plutons. Data for 13 other nepheline syenite samples are in Appendix l.1 The chemical analyses were made by atomic absorption spectroscopy using the fusion method of Medlin and others (1969) for sample preparation. U.S. Geologi- glomerate from the nepheline syenite pluton immediately north- cal Survey rock standards were used for calibration. Acid-soluble east. C02 values were obtained using the method of Kolthoff and others Iddings (1898a) and Wilkerson (1946) gave detailed pétro- (1969, p. 1105). graphie descriptions of the nepheline syenite. The texture is Phonolite Bodies. Phonolite forms dikes in the southernmost medium to coarse grained and ranges from hypautomorphic- nepheline syenite pluton, dikes that crosscut diatreme materials, granular to porphyritic with of either nepheline or and dikes and possibly sills in the Martinsburg Formation. The orthoclase. Other primary minerals are clinopyroxene, biotite, phonolite dikes in nepheline syenite vary in width from a few mil- sphene, melanite, magnetite, , and traces of pyrite and zir- limetres to 25 cm and, in some places, occupy irregularly distrib- con. Refractive indices of orthoclase, only rarely microperthitic, uted fractures. The dikes are uniformly fine grained and show only suggest that it is either sodic orthoclase or orthoclase cryptoper- thite. Vogel (1970) concluded that the orthoclase generally is in- 1 Copies of GSA supplementary material 76-20 may be ordered from Documents termediate between sodic orthoclase and orthoclase cryptoperthite. Secretary, Geological Society of America, 3300 Penrose Place, Boulder, Colorado Clinopyroxene ranges from diopside-hedenbergite to aegerine- 80301.

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minor secondary alteration. Phonolite chemical compositions and albitized. Sample 3, which also has nepheline pseudomorphs, has modes (Table 1) are similar to those of the enclosing nepheline been intensely albitized but only slightly carbonatized and, con- syenite. Data for two other phonolite dikes in nepheline syenite are sequently, is rich in Na20 and poor in K20. Sample 4, in addition in Appendix 1 (see footnote 1). to being intensely albitized, has also been moderately carbonatized. The phonolite bodies in the Martinsburg Formation, previously Twenty-seven other chemical analyses of intensely altered phono- described by Wilkerson (1952), and the Rutan Hill diatreme range lite are in Appendix 1 (see footnote 1). in width from 1 to 50 m. Phonolite of this occurrence is characteris- Tinguaite Bodies. Tinguaite forms dikes in both nepheline syen- tically intensely altered. All of the intrusions have been extensively ite plutons and dikes and possibly sills in the Martinsburg Forma- sericitized and chloritized, and many have also been albitized and tion. The tinguaite dikes in nepheline syenite mostly trend north- (or) carbonatized. Veins of albite or albite with as wide as 1 west, range in width from 0.25 to 0.50 m, and are as long as 15 m. cm are common. In all of the intrusions, sericite and chlorite com- Most are porphyritic and have medium-grained phenocrysts of pletely replace nepheline and pyroxene, respectively. Albite, com- nepheline, orthoclase, pyroxene, and sphene; phenocrystic monly with checkerboard twins, in most cases replaces orthoclase, pseudoleucite is also sporadically present. Phenocrystic pyroxene and in some of the intrusions only trace remnant orthoclase can be has cores of diopside-hedenbergite (X:c = 40°) and narrow rims of detected in thin section. The most intensely albitized phonolite aegerine-augite. The matrix consists of the phenocrystic minerals bodies (Fig. 1) commonly have a sheared appearance and may have and traces of biotite, magnetite, and pyrite. Acicular pyroxene, been partly mobilized during albitization. Calcite with biaxial op- ranging in composition from aegerine-augite to aegerine, is particu- tics shows a patchy distribution and apparently replaced previous larly abundant in the matrix and occurs both as inclusions in minerals indiscriminately. nepheline and orthoclase and as interstitial felty aggregates. Some In spite of the intense alteration, the primary minerals can be samples also contain trace amounts of the secondary minerals can- identified in most cases and original modes roughly estimated. crinite, fluorite, and analcite. Modes were not measured because of Medium-grained phenocrysts of nepheline and orthoclase amount the extremely fine grain size of matrix minerals. Kemp (1892), to about 40 vol percent of the rock in some of the intrusions. Wolff (1902), and Aurousseau and Washington (1922) gave de- Corroded phenocrysts of biotite are also rarely present. Other min- tailed petrographic descriptions of several tinguaite dikes in erals present, except for the rare appearance of melanite, are the nepheline syenite. same as found in the relatively unaltered phonolite dikes in The tinguaite bodies in the Martinsburg Formation range in nepheline syenite. Nepheline and orthoclase together amount to 85 width from 0.4 to 50 m. The tinguaite of this occurrence has an to 95 percent of the rock but vary widely in relative abundance. appearance in thin section very similar to tinguaite from dikes in Several of the intrusions are borderline potassic trachyte, since nepheline syenite. Pseudoleucite has not, however, been noted. nepheline is about 5 percent of the rock. Secondary alteration is slight to moderate with sericite and cancri- Table 2 shows bulk chemical data from four of the intensely nite partly replacing both nepheline and orthoclase. Two of the altered phonolite bodies. Sample 1 has been intensely sericitized intrusions contain considerable epidote and calcite. Veins of albite and chloritized. This intrusion, with nepheline pseudomorphs, con- and albite with calcite also occur but are rare. Wilkerson (1952) tains only a trace of Na20 and is rich in K20, reflecting replace- summarized the petrography of several tinguaite intrusions in the ment of nepheline by sericite. Sample 2, which is intensely se- Martinsburg Formation. ricitized and chloritized, has also been partly carbonatized but not Although tinguaite chemical compositions (Table 2) are similar

TABLE 1. SELECTED CHEMICAL AND MODAL ANALYSES OF MASSIVE NEPHELINE SYENITE AND PHONOLITE DIKES IN NEPHELINE SYENITE

Nepheline syenite Phonolite 1 2 3 4 5 1 2

SiOz 44.76 50.42 55.68 52.84 54.92 53.93 55.92 AI2O3 21.96 21.80 20.93 21.07 20.26 19.89 22.14

Fe2CV 7.38 6.00 5.00 4.63 6.45 5.38 3.59 MgO 1.85 0.90 0.54 0.38 0.33 0.48 0.28 CaO 6.89 2.17 0.82 2.13 1.59 1.70 0.26 Na20 8.67 6.68 5.74 8.17 6.94 6.25 6.46 K2O 6.15 10.06 10.94 9.21 8.76 10.08 11.50 TiO, 2.28 1.79 0.60 0.54 1.08 0.61 0.35 MnO 0.24 0.13 0.20 0.18 0.23 0.19 0.09 co2 0.08 0.13 0.40 0.47 0.37 0.46 0.25 Total 100.26 100.08 100.85 99.62 100.93 98.97 100.84

Modal analysesf Nepheline 64.5 42.3 17.1 28.3 28.1 33.0 40.6 Orthoclase 11.0 39.6 72.0 42.7 58.1 54.8 49.8 Cancrinite 1.3 4.2 2.2 Sodalite 2.3 7.3 1.1 2.0 Pyroxene 12.8 5.2 1.7 15.7 7.4 4.2 6.8 Biotite 5.3 5.8 1.3 0.2 2.0 2.0 1.4 Sphene 3.8 3.6 0.5 1.2 tr. 0.8 0.6 Melanite 0.5 Opaque minerals 1.6 3.3 3.8 0.4 1.1 3.2 0.8 Apatite 0.5 0.2 tr. tr. tr. tr. tr. Zircon tr. tr. tr. tr. tr.

Note: Nepheline syenite analyses 1 to 3 are of samples from the southernmost nepheline syenite pluton, and 4 and 5 are of samples from the northern- most nepheline syenite pluton. 1 Total Fe as Fe203. t Modal analyses in volume percent, 500 points.

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to those of nepheline syenite (phonolite), tinguaite for a given Si02 Mafic Phonolite. Mafic phonolite forms two dikes in the Mar- content tends to be richer in total iron as Fe203, CaO, Na20, and tinsburg Formation (Fig. 1). One of the dikes is about 30 m wide MnO, and poorer in A1203 and KaO (Fig. 2). This difference is due and the other is 10 m wide. Mafic phonolite is porphyritic and has at least in part to the greater abundance of -rich pyroxene in phenocrysts of diopside-hedenbergite (X:c = 52°), corroded bio- tinguaite. Appendix 1 (see footnote 1) includes 10 additional tite, melanite, magnetite, nepheline, and orthoclase. The fine- analyses of tinguaite. grained matrix consists of the phenocrystic minerals with apatite, Lamprophyre Dikes. Lamprophyre dikes, which occur sphene, and traces of pyrite and zircon. Cancrinite after nepheline throughout the complex, mostly trend northwest and vary in width is abundant. Diopside-hedenbergite and biotite grains have rims of from about 10 cm to 7 m. Most of the 13 lamprophyre dikes aegerine-augite. Melanite is euhedral and poikilitic, and inclusions examined (Fig. 1) were found in thin section to be so intensely of most of the other minerals are present. Ocelli do not occur. altered that original is in part problematical. Relatively Mafic phonolite chemical compositions and modes (Table 3), al- unaltered samples were, however, collected from three of the dikes. lowing for cancrinite replacement of nepheline, roughly fall be- Two are lamprophyre micromalignite, and the third is lam- tween lamprophyre micromalignite and more pyroxene-rich prophyre micromelteigite. nepheline syenite. The lamprophyre micromalignite dikes, which occur in Pre- SiO, cambrian rocks (Fig. 1), consist of medium-grained phenocrysts of unzoned diopside-hedenbergite (X:c = 47°) and biotite in a fine- grained matrix that also contains nepheline, orthoclase, sphene, melanite, magnetite, apatite, and traces of pyrite. In samples from the center of one of these dikes, both nepheline and orthoclase have been almost completely replaced by analcite, and there has been accompanying chloritization of pyroxene. The single known micromelteigite dike, about 30 cm wide, cuts fractured Martinsburg Formation rocks immediately adjacent to a small diatreme between the nepheline syenite plutons (Fig. 1). Lamprophyre micromelteigite contains medium-grained pheno- crysts of diopside-hedenbergite (X :c = 38°) with rims of aegerine- augite. The fine-grained matrix consists of aegerine-augite, biotite, nepheline, sphene, calcite, magnetite, apatite, and traces of pyrite. Much of the biotite present replaces pyroxene. Chemical compo- sitions and modes of lamprophyre micromalignite and lam- prophyre micromelteigite are listed in Table 3. The remaining lamprophyre dikes of the complex are probably either micromalignite or micromelteigite. Secondary analcite is the only felsic present in several of the dikes; others contain only secondary albite or albite with calcite. The lamprophyre dike at Franklin, New Jersey, is crossed by veins composed of albite, Total Ft at Ft^+MnO Al2°3+° epidote, and calcite. In this dike, away from the veins, albite and + CaO + NazO calcite partly replace analcite, and epidote partly replaces pyroxene. In all of the dikes, pyroxene is partly replaced by chlorite Figure 2. Bulk chemistry plot (oxides, weight percentages) showing that and ferric green biotite. Kemp (1893), Iddings (1898b), and Wolff tinguaite and nepheline syenite (phonolite) are chemically distinguishable; (1908) described two of the intensely altered dikes. Appendix 1 (see dots are nepheline syenite and phonolite dikes in nepheline syenite; crosses footnote 1) includes 10 chemical analyses of intensely altered lam- are tinguaite. prophyre. Diatremes. The complex includes several diatremes in the Mar- Ocelli up to several millimetres wide are a characteristic feature tinsburg Formation (Fig. 1); the largest diatreme is known locally of Beemerville lamprophyre. The ocelli in the known micromalig- as Rutan Hill. The diatremes consist of a variety of angular to nite dikes consist of about 75 vol percent orthoclase and 25 percent subangular xenoliths and autoliths in a dark, dense matrix rock nepheline and are usually rimmed by tangential biotite. The ocelli considered by Kemp (1889) to be ouachitite-type lamprophyre. in the known micromelteigite dike consist entirely of slightly bi- The inclusions range in size from microscopic in dimension to as axial calcite and have rims of cancrinite where they are in contact much as 1 m wide. with nepheline. Martinsburg Formation fragments are by far the most common

TABLE 2. SELECTED CHEMICAL ANALYSES OF INTENSELY ALTERED PHONOLITE AND SLIGHTLY ALTERED TINGUAITE

Phonolite Tinguaite 1 2 3 4 1 2 3 4

Si02 49.45 45.20 57.70 55.54 52.29 54.62 47.62 54.21 AI2O3 23.65 17.19 20.53 18.35 20.01 19.19 20.68 19.35 Fe203* 6.79 6.73 3.59 3.27 5.98 7.10 6.18 4.81 MgO 1.59 1.38 0.27 0.44 0.56 0.41 1.20 0.37 CaO 1.24 8.58 1.22 4.61 2.03 1.88 4.79 2.24 Na20 0.10 0.38 9.25 8.33 9.40 8.49 7.47 8.18 K2O 12.02 9.75 1.28 1.16 8.36 7.17 6.97 6.68 Ti02 0.62 1.26 0.29 0.30 0.98 0.46 1.65 0.46 MnO 0.08 0.36 0.06 0.36 0.27 0.26 0.23 0.35 co2 1.10 6.47 1.08 4.05 0.80 0.28 0.97 1.60 Total 96.64 97.30 95.27 96.41 100.68 99.86 97.76 98.25 Note: Tinguaite analyses 1 and 2 are of dikes in nepheline syenite, 3 and 4 are of intrusions in the Martinsburg Formation. * Total Fe as Fe203.

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type of in the diatremes. Also common, particularly at very similar in appearance to those found in the lamprophyre mi- Rutan Hill, are xenoliths of fine-grained pale-blue dolomite, prob- cromelteigite inclusions and, consequently, are also probably xeno- ably from the Kittatinny Formation, and xenoliths of cream- crystic. The groundmass of the diatreme matrix rock consists of colored fine-grained limestone, probably from the Jacksonburg calcite, magnetite, biotite (both brown and ferric green varieties), Limestone. Gneiss xenoliths occur in all the diatremes but are par- chlorite, albite, and apatite. The groundmass rock from one of the ticulary abundant at Rutan Hill. The types of gneiss noted, which smaller diatremes also contains considerable melanite. All of these are similar to those found in the Reading Prong to the east, are minerals are extremely fine grained and usually anhedral. Veins of -oligoclase gneiss, quartz-oligoclase-microcline gneiss, and calcite or calcite with albite are common. Although the ground- biotite-quartz-oligoclase gneiss. Sedimentary rock xenoliths have mass of the matrix rock has been so intensely altered that iden- narrow reaction rims but are otherwise unaltered. Most gneiss tification of the minerals originally present is precluded, chemical xenoliths are unaltered; some contain secondary albite after oligo- compositions of two relatively inclusion-free matrix rocks (Table clase, and others contain a few veinlets filled with aegerine and 4) are similar to those of lamprophyre micromelteigite. sodic . The Rutan Hill diatreme contains a small body of nepheline The Rutan Hill diatreme also contains autolithic inclusions of syenite, and another occurs in the Martinsburg Formation im- potassic syenite, lamprophyre micromelteigite, and carbonatite. mediately adjacent to one of the small diatremes (Fig. 1). At Rutan The syenite inclusions are medium to coarse grained and consist of Hill nepheline syenite exposure suggests the presence of an oval tabular interlocking orthoclase grains with minor interstitial body about 30 m wide. Although contacts are not exposed, this nepheline, aegerine, biotite, and traces of apatite and magnetite. body is surrounded by diatreme breccia, which suggests that it was Original nepheline has been completely replaced by sericite. Or- emplaced after the diatremes formed. The other body, no wider thoclase is dusty, probably owing to finely disseminated hematite. than 3 m, is in contact with fenitized and fractured Martinsburg Orthoclase is commonly partly replaced by fine-grained calcite and Formation rocks. The nepheline syenite of both of the small bodies albite that form oval areas that may include parts of several ortho- is very similar to the nepheline syenite of the larger plutons. Table 4 clase grains. Veinlets filled with calcite and albite also occur. The includes the chemical composition and mode of the Rutan Hill chemical composition and mode of the least altered of the potassic nepheline syenite. syenite autoliths examined is included in Table 4. The Martinsburg Formation is partly fenitized in the fracture Lamprophyre micromelteigite autoliths consist of medium- zone immediately adjacent to the small diatremes between the grained phenocrysts of aegerine-augite (X:c = 35°) that have nar- nepheline syenite plutons. Martinsburg Formation rocks are not row rims of more sodium-rich aegerine-augite set in a fine-grained exposed in the immediate vicinity of the other diatremes. Adjacent matrix composed of aegerine-augite, nepheline, biotite, melanite, to the small diatremes, the Martinsburg Formation consists of in- sphene, magnetite, apatite, calcite, and traces of pyrite. Most of the terlayered shale and graywacke whose individual bed thicknesses inclusions examined are rich in melanite, but others are instead rich range from a few millimetres to 20 cm. The shale layers do not in sphene. Sericite completely replaces nepheline, but the other show much alteration, except for development of grains of biotite minerals are generally unaltered. Calcite forms interstitial grains large enough to be recognized in thin section. Metasomatic altera- and also occurs in ocelli. Some of the inclusions also contain vein- tion of the graywacke layers has, however, been intense. Unaltered lets of calcite with albite. Table 4 includes the chemical composi- graywacke in the Beemerville area consists of angular grains, tion and mode of a melanite-rich inclusion. Additional data on lamprophyre micromelteigite autoliths are in Appendix 1 (see foot- TABLE 3. SELECTED CHEMICAL AND MODAL ANALYSES OF note 1). LAMPROPHYRE AND MAFIC PHONOLITE On the basis of the carbonatite classification of Heinrich (1966, p. 12), the carbonatite autoliths are sovite and silicocarbonatite. Lamprophyre Mafic phonolite Sovite autoliths of rare occurrence consist of about 97 vol percent 1 2 3 4 1 2 calcite and 3 percent apatite; they are medium to coarse grained Si0 45.19 45.74 39.71 42.35 43.71 44.51 and have a marblelike appearance. In the silicocarbonatite au- 2 AI O 15.32 15.50 13.62 13.81 16.14 16.13 toliths, coarse-grained calcite, usually of dusty appearance, makes 2 3 Fe203* 10.98 10.19 12.61 10.47 8.26 8.27 up at least 50 percent of the rock. Biotite is also abundant. Both MgO 3.03 2.78 3.89 3.58 1.71 1.64 biotite and calcite grains usually show much evidence of strain. CaO 10.09 8.90 11.45 11.56 12.32 11.08

Calcite is biaxial even where not obviously strained. Orthoclase of NazO 4.14 5.85 4.96 6.96 6.84 6.50 tabular habit varies in abundance from trace amounts to about 15 K2O 5.25 4.67 4.27 2.70 4.54 6.01 vol percent. The rims of orthoclase grains are invariably replaced Ti02 4.21 3.92 4.47 4.24 1.19 1.32 by fine-grained calcite and albite; calcite and albite also form vein- MnO 0.26 0.29 0.30 0.27 0.41 0.38 lets. All of the silicocarbonatite autoliths examined contain minor co2 0.92 0.64 1.53 4.03 3.00 1.70 magnetite and traces of pyrite. Small amounts of aegerine-augite Total 99.39 98.48 96.81 99.97 98.12 97.54 occur in some of the inclusions but not in others. Silicocarbonatite Modal analysesf autoliths in hand specimen may have a banded appearance due to concentrations of aligned orthoclase tablets as long as 2 cm. Table Nepheline 28.4 23.0 tr. 24.0 5.6 26.8 Orthoclase 13.0 9.6 tr. 11.4 18.0 4 includes the chemical composition of a silicocarbonatite inclu- Cancrinite 0.3 33.2 8.8 sion. Bulk chemical data for two other silicocarbonatite inclusions Analcite 34.4 are in Appendix 1 (see footnote 1). Pyroxene 36.2 49.2 46.8 31.6 33.4 30.4 Diatreme matrix rock consists of a variety of megacryst minerals, Biotite 8.4 10.2 8.8 24.2 4.4 3.4 subhedral to euhedral, in an obscure, extremely fine grained Sphene 4.2 5.8 2.4 7.8 tr. 0.6 groundmass. The fine- to coarse-grained megacryst minerals are, in Melanite 6.2 2.8 9.0 8.8 approximate order of decreasing abundance, biotite, diopside- Opaque minerals 3.0 2.2 4.8 2.0 1.2 0.6 hedenbergite, aegerine-augite, orthoclase, magnetite, apatite, and Apatite 0.6 tr. tr. 3.7 1.8 2.6 Calcite 6.4 nepheline (sericite pseudomorphs only). The two varieties of clinopyroxene megacrysts only rarely are zoned. Tabular ortho- Note: Lamprophyre analyses 1 and 2 are of slightly altered micro- clase megacrysts have rims of fine-grained calcite and albite; calcite malignite; analysis 3 is of intensely altered micromalignite from same dike also partly replaces pyroxene megacrysts. Orthoclase and as analysis 2; analysis 4 is of slightly altered micromelteigite. nepheline megacrysts are probably from disrupted potassic syenite * Total Fe as Fe203. and possibly carbonatite inclusions. The aegerine-augite grains are t Modal analyses in volume percent, 500 points.

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mostly of quartz but also of considerable microcline, orthoclase, angular to subangular and at most show only narrow reaction and sodic embedded in a fine-grained matrix that con- rims. tains, in addition to the framework minerals, considerable calcite The high Fe/Mg ratios of all the alkalic rocks including carbona- and chlorite. Fenitized graywacke consists of albite, aegerine, and tite apparently rule out significant assimilation of sedimentary sodic amphibole with traces of biotite and biaxial calcite. Albite in rocks, since dolomite is abundant in the sedimentary rock section. part preserves the original shape of replaced . In one place The possibility that the carbonatite magma formed by syntexis of fenitized graywacke has been mobilized and forms a 0.5-m-wide basement Precambrian marble cannot be excluded from considera- dike that crosscuts Martinsburg Formation layering. The chemical tion on this basis, however, since marble, only locally dolomitic, analysis and mode of the fenite are included in Table 4. occurs at the surface a few kilometres east of the known occurrence Carbonatite Intrusion. The only known occurrence of carbona- of carbonatite. There are, however, many strong arguments, based tite in the complex other than as diatreme inclusions is a 2-m-wide on thermodynamic principles, experimental evidence, and isotope by 8-m-long body, probably a dike, in the Martinsburg Formation data, as summarized by Carmichael and others (1974, p. 517-522) adjacent to the zone of small diatremes between the nepheline syen- and Wyllie (1974), that speak against the possibility that carbona- ite plutons (Fig. 1). The carbonatite contains angular Martinsburg tite magma may arise through syntexis of crustal carbonate rocks. Formation inclusions and is cut by a 15-cm-wide lamprophyre dike Although fenitization is an important process in many carbona- of questionable type. Intrusive carbonatite consists of irregularly tite complexes, there is no evidence of widespread fenitization in shaped areas of fine- to medium-grained calcite, biotite, and apatite the Beemerville complex. Sedimentary rock and gneiss xenoliths in that are separated by smaller oval areas of extremely fine grained the diatremes at most show only minor fenitization. Fenite after calcite, biotite, magnetite, pyrite, and albite. The chemical compo- graywacke has a restricted occurrence and, in addition, has a bulk sition and roughly estimated mode of the carbonatite is included in composition unlike that of any other alkalic rock of the complex. Table 4. It is interpreted to be intensely altered biotite sovite. Lamprophyre ocelli are considered to be evidence on a small scale of immiscibility relations between carbonatite-melteigite and PETROGENESIS malignité—leucocratic nepheline syenite magmas. Both experimental evidence (Koster van Groos and Wyllie, 1966; Massion and Koster Carbonatite is considered to be dominantly of igneous origin van Groos, 1973; Ferguson and Currie, 1971; Philpotts, 1971, owing to the intrusive nature of the small carbonatite body and the 1972) and field evidence for other occurrences of lamprophyre igneous-appearing texture of carbonatite autoliths. Since experi- ocelli (Ferguson and Currie, 1971; Philpotts, 1972) support this mental evidence (Wyllie, 1966, p. 350) does not indicate that it is conclusion. possible for orthoclase to precipitate with calcite from a lime-rich Field evidence suggests a relative age sequence for the Beemer- carbonatite magma, the orthoclase in silicocarbonatite is regarded ville rocks of, from oldest to youngest, potassic syenite, carbona- as xenocrystic and probably derived from partial assimilation of tite, lamprophyre, nepheline syenite, and phonolite/tinguaite. potassic syenite by carbonatite magma. Silicocarbonatite inclusions contain orthoclase interpreted Evidence is lacking that country rock assimilation at depth to be xenocrysts from partly assimilated syenite. The single car- played an important role in the evolution of the complex. Both bonatite intrusion is crossed by a lamprophyre dike. Syenite, car- sedimentary and metamorphic rock xenoliths in the diatremes are bonatite, and lamprophyre micromelteigite occur as inclusions in

TABLE 4. SELECTED CHEMICAL AND MODAL ANALYSES OF CARBONATITE INTRUSION AND DIATREME ROCKS

1 2 3 4 5 6 7 8

Si02 21.77 21.98 39.74 41.10 34.63 55.34 54.61 61.80

AI2O3 7.96 6.62 9.48 9.60 10.21 18.92 19.89 12.35 Fe203* 14.71 11.64 16.36 15.05 12.56 7.92 3.80 7.01 MgO 5.30 2.74 6.00 5.67 3.50 1.54 0.36 2.57 CaO 24.68 30.25 18.80 18.28 17.96 0.08 2.82 3.40 Na20 1.80 0.85 0.68 0.51 2.88 3.31 7.42 9.69 K2O 2.42 2.49 1.69 2.49 3.06 8.95 7.55 0.51 Ti02 1.70 1.89 3.99 3.10 2.87 0.94 0.50 1.03 MnO 0.51 0.40 0.35 0.33 0.33 0.04 0.15 0.12

C02 18.41 20.47 1.73 1.67 10.83 0.39 2.00 0.44 Total 99.26 99.33 98.82 97.80 98.83 97.43 99.10 98.92

Modal analyses~\ Nepheline 24.9 Cancrinite 10.3 Orthoclase 1.2 95.3 55.4 Albite (2) 0.5 49.0 Pyroxene 56.8 1.2 7.0 39.2 Alkali amphibole 11.8 Biotite (25) 28.9 9.6 2.3 tr. Sericite 11.6 1.2 Sphene tr. tr. Melanite 10.2 Opaque minerais (11) 5.8 4.6 tr. 2.4 Apatite (2) 3.4 6.2 tr. tr. Calcite (60) 60.2 1.0 tr.

Note: Modal values in parentheses are estimated. Key: Analysis 1 = carbonatite intrusion; 2 = silicocarbonatite inclusion; 3 = altered melteigite inclu- sion; 4 and 5 = matrix rock from two diatremes; 6 = potassic syenite inclusion; 7 = nepheline syenite intrusion in diatreme; 8 = fenite after graywacke.

* Total Fe as Fe203. f Modal analyses in volume percent, 500 points.

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the Rutan Hill diatreme with lamprophyric matrix rock. Nepheline magma; the average agpaitic index of Beemerville syenite is 1.04. syenite intrudes the Rutan Hill diatreme. Both phonolite and tin- Enrichment of Fe, Ca, and Na and impoverishment of A1 and K in guaite form dikes in nepheline syenite and, in addition, a phonolite tinguaite residua may have arisen through temporary suppression dike cuts a small lamprophyre dike immediately southeast of the of clinopyroxene crystallization — the agpaitic fractionation se- southernmost nepheline syenite pluton. Where mafic phonolite fits quence. Enrichment of Na in the residua may have also been aided into the possible sequence or whether phonolite and tinguaite are by the "orthoclase effect" of Bailey and Shairer (1964). Experimen- essentially contemporaneous cannot be established from known tal work on the crystallization of peralkalic liquids as summarized field evidence. by Macdonald (1974) and Edgar (1974) is consistent with this Variation diagrams (Fig. 3) suggest a sequence for the silicate interpretation of tinguaite origin. The model as stated, however, rocks of lamprophyre micromelteigite, lamprophyre micromalig- does not account for potassic syenite that field evidence indicates is nite, mafic phonolite, nepheline syenite-phonolite-tinguaite, and generally contemporaneous with carbonatite. Leucocratic potassic syenite. Tinguaite and intensely altered phonolite plot orthoclase-rich rocks are closely associated with carbonatite in points are not shown in Figure 3. Tinguaite plots with nepheline other complexes (Heinrich and Moore, 1970). These rocks have syenite (phonolite) on both the AFM and K20-Na20-Ca0 dia- been interpreted to be in-place fenites, rheomorphically intruded grams. Intensely altered phonolite plots with nepheline syenite on fenites, or anatectites after feldspar fenite (Heinrich and the AFM diagram but blankets the K20-Na20-Ca0 diagram in a Moore, 1970; Sutherland, 1965, 1967). An anatectic origin after random pattern. Carbonatite and fenite plot points are included in fenite may explain the Beemerville potassic syenite, although, ad- Figure 3. Carbonatite plots with lamprophyre on both diagrams, mittedly, there is no textural evidence of potassium feldspar but fenite plots off the trend established for the other rock types on metasomatism in the complex. the K20-Na20-Ca0 diagram, which is not surprising in view of its The second model, in which parental magma is slightly carbon- known metasomatic origin. Except for potassic syenite, the varia- ated malignite, involves a more complicated sequence of postulated tion trend evidence for the rock sequence is in accord with field events. Parental malignite magma came to occupy two poorly con- evidence. nected chambers — a smaller, higher level chamber under the west- No single completely satisfactory petrogenetic model can at ern part of the complex and a deeper chamber that underlay the present be proposed for the Beemerville rocks. It seems evident that entire complex. In the shallower chamber, under lower confining immiscibility as well as fractional crystallization played a role in pressure, slightly carbonated malignite magma separated into de- the evolution of the complex. I conclude that the immediate paren- carbonated potassic syenite and moderately carbonated melteigite tal magma was of either highly carbonated melteigitic or slightly magmas. Following loss of equilibrium between the two magmas, carbonated malignitic composition. Speculative models based on moderately carbonated melteigite magma upon cooling separated each of these possibilities warrant brief consideration. into carbonatite and decarbonated melteigite magmas. Subsequent If highly carbonated melteigite magma was the parental magma, fractional crystallization of the decarbonated melteigite magma it may have separated at an early stage into carbonatite and decar- may have led directly to residua of tinguaitic composition, which bonated melteigite magmas. Following loss of equilibrium between would explain the high Fe and Na content of tinguaite compared it and carbonatite magma, decarbonated melteigite magma then with nepheline syenite. Parental malignite magma in the deeper evolved by fractional crystallization with gravity settling through chamber, which was under higher confining pressure, did not sepa- malignitic to nepheline syenitic composition. Tinguaite with an rate into immiscible fractions but instead through fractional crys- average agpaitic index of 1.14 in the complex may have formed tallization processes evolved to nepheline syenitic (phonolitic) from more strongly peralkalic residua of the nepheline syenite composition. With this model both tinguaite and phonolite may

Figure 3. Variation diagrams (oxides, weight percentages) for the Beemerville rocks: crosses are altered lamprophyre micromelteigite autoliths, altered diatreme matrix rock, and altered lamprophyre dikes of questionable type; open triangles are silicocarbonatite autoliths and carbonatite intrusion; open squares are lamprophyre micromelteigite, lamprophyre micromalignite, and mafic phonolite dikes; dots are massive nepheline syenite, phonolite dikes in nepheline syenite, and nepheline syenite intrusion in diatreme; open circles are potassic syenite autolith; and open are fenite after Martinsburg Formation graywacke.

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have multiple origins. Orthoclase-rich phonolite intrusions in the Geology and structure of the Franklin-Sterling area, New Jersey: Geol. Martinsburg Formation may in part be the offspring of early- Soc. America Bull., v. 67, p. 435-474. formed potassic syenite magma in the upper chamber. Tinguaite Heinrich, E. W., 1966, The geology of : New York, John Wiley could also be in part derived from late-stage peralkalic residua of 8c Sons, Inc., 535 p. Heinrich, E. W., and Moore, D. G., Jr., 1970, Metasomatic potash feldspar nepheline syenite magma in the deeper chamber. rocks associated with igneous alkalic complexes: Canadian Of the two models considered, the second is most open to criti- Mineralogist, v. 10, p. 571-598. cism, because, first, it postulates a more complex and, con- Iddings, J. P., 1898a, Nephelite-syenite from Beemerville, Sussex County, sequently, perhaps less likely series of events, and second, it runs New Jersey: U.S. Geol. Survey Bull., v. 150, p. 209-211. counter to the commonly held view that silicate-silicate liquid im- 1898b, Minette from Franklin Furnace, Sussex County, New Jersey: miscibility is not a petrologically important process. The second U.S. Geol. Survey Bull., v. 150, p. 236-239. model does, however, have many points in common with the model Kemp, J. F., 1889, On certain porphyritic bosses in northwestern New proposed by Ferguson and Currie (1971) for the Callander Bay, Jersey: Am. Jour. Sci., 3rd ser., v. 38, p. 130-134. Ontario, carbonatite complex. 1892, The elaeolite syenite near Beemerville, Sussex Co., N.J.: New York Acad. Sci. Trans., v. 11, p. 60-71. My tentative preference is for the first and simpler model 1893, A basic dike near Hamburg, Sussex Co., New Jersey, which has presented, regardless of the difficulty in the model in accounting for been thought to contain leucite: Am. Jour. Sci., 3rd ser., v. 45, the potassic syenite autoliths in the Rutan Hill diatreme. Although p. 298-305. the petrogenesis of the complex remains problematical, I do not Kolthoff, I. M., Sandell, E. B., Meehan, E. J., and Bruckenstein, S., 1969, think the situation is now as bad as it was in 1892, when Kemp Quantitative chemical analysis: London, MacMillan, 1199 p. concluded, "there is some underlying genetic connection between Koster van Groos, A. F., and Wyllie, P. J., 1966, Liquid immiscibility in the the elaeolite [nepheline]-syenite and these other basic rocks, but system Na20-Al203-Si02-C02 at pressures to 1 kilobar: Am. Jour. what it is I feel at a loss to say." Sci., v. 264, p. 234-255. Macdonald, R., 1974, The role of fractional crystallization in the formation ACKNOWLEDGMENTS of the alkaline rocks, in Sarensen, H., ed., The alkaline rocks: New York, John Wiley & Sons, Inc., p. 442-459. Massion, P. J., and Koster van Groos, A. F., 1973, Liquid immiscibility in A Rider College faculty research grant is gratefully acknowl- silicates: Nature Phys. Sci., v. 245, p. 60-63. edged. I thank Peter Michael, Leslie Kihn, and Victor D'Angiulillo Medlin, J. H., Suhr, N.' H., and Bodkin, J. B., 1969, Atomic absorption

for their help in the field and in the preparation of samples for analysis of silicates employing LiB02 fusion: Atomic Absorption chemical analyses. Newsletter, v. 8, no. 2, p. 25-29. Philpotts, A. R., 1971, Immiscibility between feldspathic and gabbroic REFERENCES CITED magmas: Nature, v. 229, p. 107-109. 1972, Density, surface tension and viscosity of the immiscible phase in a basic, alkaline magma: Lithos, v. 5, p. 1-18. Aurousseau, M., and Washington, H. S., 1922, The nephelite syenite and Smith, B. L., 1969, The Precambrian geology of the central and northeast- nephelite of Beemerville, New Jersey: Jour. Geology, v. 30, ern part of the New Jersey Highlands, in Subitzky, S., ed., Geology of p. 571-586. selected areas in New Jersey and eastern Pennsylvania and guidebook Bailey, D. K., and Schairer, J. F., 1964, Feldspar-liquid equilibria in peral- of excursions: New Brunswick, N.J., Rutgers Univ. Press, p. 35-47. kaline liquids — The orthoclase effect: Am. Jour. Sci., v. 262, Spink, W. J., 1967, Stratigraphy and structure of the Paleozoic rocks of p. 1198-1206. northwestern New Jersey [Ph.D. thesis]: New Brunswick, N.J., Rut- Baker, D. R., and Buddington, A. F., 1970, Geology and magnetite deposits gers Univ., 311 p. of the Franklin quadrangle and part of the Hamburg quadrangle, New Sutherland, D. S., 1965, Potash-trachytes and ultrapotassic rocks as- Jersey: U.S. Geol. Survey Prof. Paper 638, 73 p. sociated with the carbonatite complex of the Toror Hills, Uganda: Carmichael, I.S.E., Turner, F. J., and Verhoogen, J., 1974, Igneous petrol- Mineralog. Mag., v. 35, p. 363-378. ogy: New York, McGraw-Hill Book Co., 739 p. Davidson, E. S., 1948, The geological relationship and petrography of a 1967, A note on the occurrence of potassium-rich trachytes in the nepheline syenite near Beemerville, Sussex County, New Jersey [M.S. Kaiserstuhl carbonatite complex, West Germany: Mineralog. Mag., v. thesis]: New Brunswick, N.J., Rutgers Univ., 140 p. 36, p. 334-341. Drake, A. A., Jr., 1969, Precambrian and lower Paleozoic geology of the Vogel, T. A., 1970, Albite-rich domains in potash feldspar: Contr. Delaware Valley, New Jersey-Pennsylvania, in Subitzky, S., ed., Mineralogy and Petrology, v. 25, p. 138-143. Geology of selected areas in New Jersey and eastern Pennsylvania and Wilkerson, A. S., 1946, Nepheline syenite from Beemerville, Sussex guidebook of excursions: New Brunswick, N.J., Rutgers Univ. Press, County, New Jersey: Am. Mineralogist, v. 31, p. 284-287. p. 51-131. 1952, Tinguaite and in northwestern New Jersey: Am. Mineralogist, v. 37, p. 120-125. Edgar, A. D., 1974, Experimental studies, in S0rensen, H., ed., The alkaline rocks: New York, John Wiley & Sons, Inc., p. 355-389. Wolff, J. E., 1902, Leucite-tinguaite from Beemerville, New Jersey: Har- Emerson, B. K., 1882, On a great dike of foyaite or elaeolite-syenite cutting vard Univ. Mus. Comp. Zoology Bull., v. 38, p. 273—277. the Hudson River shales in northwestern New Jersey: Am. Jour. Sci., 1908, Post-Ordovician rocks, in Spencer, A. C., and others, Descrip- 3rd ser., v. 23, p. 302-308. tion of Franklin Furnace quadrangle: U.S. Geol. Survey Folio 161, Epstein, J. B., and Epstein, A. G., 1969, Geology of the Valley and Ridge p. 12-13. province between Delaware Water Gap and Lehigh Gap, Pennsyl- Wyllie, P. J., 1966, Experimental studies of carbonatite problems: The vania, in Subitzky, S., ed., Geology of selected areas in New Jersey and origin and differentiation of carbonatite magmas, in Tuttle, O. F. and eastern Pennsylvania and guidebook of excursions: New Brunswick, Gittins, J., eds., Carbonatites: New York, Interscience Pubs., N.J., Rutgers Univ. Press, p. 132-205. p. 311-352. Ferguson, J., and Currie, K. L., 1971, Evidence of liquid immiscibility in 1974, Limestone assimilation, in Serensen, H., ed., The alkaline rocks: alkaline ultrabasic dikes at Callander Bay, Ontario: Jour. Petrology, New York, John Wiley & Sons, Inc., p. 459-474. v. 12, p. 561-585. Zartman, R. E., Brock, M. R., Heyl, A. V., and Thomas, H. H., 1967, K-Ar Geologic Map of New Jersey, 1950, Trenton, N.J., New Jersey Geol. Sur- and Rb-Sr ages of some alkalic intrusive rocks from central and east- vey. ern United States: Am. Jour. Sci., v. 265, p. 848-870. Geologic Map of the Franklin Furnace Quadrangle, 1908, Spencer, A. C., and others, Description of Franklin Furnace quadrangle: U.S. Geol. MANUSCRIPT RECEIVED BY THE SOCIETY APRIL 7, 1975 Survey Folio 161, p. 12—13. REVISED MANUSCRIPT RECEIVED DECEMBER 29, 1975 Hague, J. M., Baum, J. L., Herrmann, L. A., and Pickering, R. J., 1956, MANUSCRIPT ACCEPTED MARCH 3, 1976

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