Aquatic Heteroptera in New Guinea 327 Assembling New Guinea: 40 million years of island arc accretion as indicated by the distributions of aquatic Heteroptera (Insecta) Dan A Polhemus1 and John T Polhemus2 1Department of Entomology, MRC 105, National Museum of Natural History, Smithsonian Institution, Washington, D% C%, USA 20560 2Colorado Entomological Museum, 3115 S% York St%, Englewood, CO, USA 80110 Key words: New Guinea, island arcs, geology, biogeography, aquatic Heteroptera Abstract tory have revealed that at least two major epi- sodes of collision and terrane accretion have The island of New Guinea consists of the northern margin occurred in the northern half of the island of the Australian continental craton that has collided over (Pigram and Davies, 1987; Davies, 1990; Smith, the past 40 million years with a series of migrating island arcs Each of these arcs has had a separate tectonic history 1990; Pigram and Symonds, 1991), and each of and carried a correspondingly different biota Recent faunal these has in turn left a biological signature The surveys and phylogenetic analyses, coupled with evolving current challenge for regional biogeographers tectonic knowledge, are now allowing us to identify ele- lies in deciphering these signatures, and deter- ments within the New Guinea aquatic Heteroptera biota that may be correlated with particular accreted arc systems mining, if possible, which plant and animal It appears that many Asian-derived groups arrived via a groups aggregated to the present faunal mixture Papuan arc that collided obliquely with the northern margin via which arcs of Australia between the Late Eocene and Early Oligocene, In a previous paper, Polhemus (1996) re- while other distinctively Melanesian groups evolved on an viewed the history of biogeographic concepts isolated Solomons arc that was initiated in the Oligocene and accreted terranes to northeastern New Guinea from the relating to New Guinea, in particular the devel- Miocene into the Pliocene This gradually improving under- opment of the Inner arc versus Outer arc para- standing of the islands interrelated tectonic and biotic his- digm that has dominated most modern analyses tory is permitting a better comprehension of the complex of the islands biogeography The underlying patterns of faunal fusion and disjunction currently present geological concepts upon which this hypothesis within the Melanesian region was based were shown to be correct in the broad sense, but flawed in many other aspects Introduction In particular, the concept of a single Outer arc extending from New Guinea to Tonga was A long standing goal of zoogeographers and his- shown to be simplistic, since the arcs grouped torical geologists has been to integrate biologi- under this concept represented at least four cal information and Earth history models No- separate systems with dissimilar ages, origins, where is this better pursued than in the young and subduction polarities (those readers unfa- and tectonically complex region surrounding miliar with the nomenclature, geological struc- New Guinea The island represents the northern ture, and mobilistic nature of island arcs are also margin of the Australian continental craton, referred to the paper cited above, which con- which has been uplifted through a series of col- tains a review of these subjects) In this paper lisions with southward-migrating island arcs that we seek to correlate particular groups of aquatic have formed along the boundary between the and semi-aquatic true bugs (referred to hereafter Australian and Pacific tectonic plates (Hamilton, as aquatic Heteroptera) with particular arc sys- 1979, 1988; Kroenke, 1984) Recent advances in tems and terranes, assessing their probable time our understanding of the islands geological his- of arrival in New Guinea, and their subsequent Biogeography and Geological Evolution of SE Asia, pp 327-340 Edited by Robert Hall and Jeremy D Holloway © 1998 Backhuys Publishers, Leiden, The Netherlands 328 D% A% Polhemus and J% T% Polhemus speciation or dispersal within the island east of New Guinea appear to have been formed In the analysis below, brief synopses of cur- during alternating episodes of volcanism along rent geological hypotheses for the assembly of two distinct zones of crustal weakness in the New Guinea are presented, noting also areas of Solomons and northern New Guinea According current uncertainty One difficulty in providing to Kroenkes (1984) model, each time that sub- such a discussion lies in the confusing number duction along one of these zones became inacti- of different names that have been given by vari- vated, it would reactivate along the other The ous authors to the Tertiary arc systems that sequence below has been postulated (terminol- formed north of New Guinea In the present pa- ogy for trenches and arc systems follows per we follow the terminology of Kroenke Kroenke, 1984) (1984), recognizing both his Papuan and Northern New Guinea subduction episodes Solomons arcs The former is equivalent to the and corresponding trench systems: Salumei System of Davies (1990), while the lat- 1 Early Eocene to Early Oligocene: Aure- ter corresponds to the Melanesian arc of Smith Moresby-Pocklington trenches (1990) and Weiland and Cloos (1996) 2 Early Miocene to Late Miocene: Wewak- The known distributions of aquatic Heter- Trobriand trenches (= the New Guinea trench of optera are compared to these geological mod- Davies, 1990) els, and the degree of congruence discussed Solomons subduction episodes and corre- The analysis of such patterns is far from com- sponding trench systems: plete Several of the most potentially informative 1 Early Oligocene to Early Miocene: North Solo- groups, such as Rhagovelia (Veliidae) and mon trench Ptilomera (Gerridae) have not yet been taxo- 2 Late Miocene to Holocene: South Solomon nomically revised, much less cladistically trench analyzed, and as a result this paper relies heavily These alternating episodes of subduction ac- on currently unpublished data (i%e , undescribed tivity in eastern New Guinea are correlated with species in the collections of the authors) The the following tectonic events (for a CD ROM analysis should thus be seen as a preliminary video of the hypothesized plate and arc motions evaluation of biogeographic hypotheses based consult Yan and Kroenke, 1993): on work in progress, rather than a validation of Cretaceous Rifting and basin formation oc- such hypotheses; the latter can only be based on curred along the passive northern Australian phylogenetic analyses of the insect groups in- margin This rifting, which took place in several volved Many such analyses are in the process of phases, isolated small slivers of continental crust being completed, however, and in the near fu- outboard of marginal basins These slivers have ture it should be possible to provide more rigor- been referred to as the Inner Melanesian arc by ous tests of the hypotheses presented below many previous biogeographers While there may have been some arc related activity and back-arc spreading in the marginal basins dur- Geological setting ing the final phases of this process, it was for the most part a rifting event, similar to the process The northern half of New Guinea is a composite seen in current day East Africa of island arcs that have accreted to the northern Middle Eocene Eastward subduction below margin of Australia at various times over the last the Pacific plate along the Aure-Moresby- 40 million years Kroenke (1984), in a synthesis Pocklington trenches, lying well north and east of covering the eastern half of the island, recog- the rifted Australian margin, produced a south- nized three such arc systems, the Papuan, ward migrating Papuan arc in an oceanic setting Trobriand, and Solomons arcs, that had already Early Oligocene The eastward subduction collided with New Guinea, and a fourth, the Bis- below the Papuan arc ceased as the arc collided marck arc, that was in the process of doing so with the Australian margin, causing overthrust- In the west, Hamilton (1979, 1988) discussed the ing of arc terranes onto the Australian craton incipient collision of a fifth system, the Banda New westward subduction was initiated below arc, that is approaching New Guinea from the the Australian plate in the Solomons zone along southwest the North Solomon trench, forming the eastward The Banda arc system in the west is formed migrating Solomons arc in an isolated oceanic along the boundary of the Australian and Eura- setting Western extensions of this arc, linked by sian plates above the well defined Sunda sub- transforms, appear to have extended to the area duction zone By contrast, the arcs lying to the north of Irian Jaya Aquatic Heteroptera in New Guinea 329 Fig1 Map of New Guinea showing geological provinces discussed in the text Unstippled areas = Australian craton and Vogelkop craton fragment; black areas = Papuan arc terranes, accreted in the Eocene and Oligocene; dark stippled areas = Solomons arc terranes, accreted in the Miocene; light stippled areas = Banda arc terranes and associated uplifts, currently in the process of accretion; very finely shaded areas = mountainous regions at elevations above 2000 metres Areas in the Bird's Neck are of uncertain geological affinity; although assigned to the Australian craton in this figure, they are also likely to contain accreted terranes from other sources Early Miocene The Ontong Java plateau ward over the Solomon Sea In the west, the jammed the North Solomons trench, ending this accreted